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<front>
<journal-meta>
<journal-id journal-id-type="publisher-id">Front. Oncol.</journal-id>
<journal-title>Frontiers in Oncology</journal-title>
<abbrev-journal-title abbrev-type="pubmed">Front. Oncol.</abbrev-journal-title>
<issn pub-type="epub">2234-943X</issn>
<publisher>
<publisher-name>Frontiers Media S.A.</publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="doi">10.3389/fonc.2021.735447</article-id>
<article-categories>
<subj-group subj-group-type="heading">
<subject>Oncology</subject>
<subj-group>
<subject>Original Research</subject>
</subj-group>
</subj-group>
</article-categories>
<title-group>
<article-title>Hsa-miR-4277 Decelerates the Metabolism or Clearance of Sorafenib in HCC Cells and Enhances the Sensitivity of HCC Cells to Sorafenib by Targeting <italic>cyp3a4</italic>
</article-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<name>
<surname>He</surname>
<given-names>Xi</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Sun</surname>
<given-names>Huiwei</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff3">
<sup>3</sup>
</xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Jiang</surname>
<given-names>Qiyu</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff3">
<sup>3</sup>
</xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Chai</surname>
<given-names>Yantao</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff3">
<sup>3</sup>
</xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Li</surname>
<given-names>Xiaojuan</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff3">
<sup>3</sup>
</xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Wang</surname>
<given-names>Zhijie</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff3">
<sup>3</sup>
</xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Zhu</surname>
<given-names>Bing</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
<uri xlink:href="https://loop.frontiersin.org/people/958582"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname>You</surname>
<given-names>Shaoli</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
</contrib>
<contrib contrib-type="author" corresp="yes">
<name>
<surname>Li</surname>
<given-names>Boan</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff4">
<sup>4</sup>
</xref>
<xref ref-type="author-notes" rid="fn001">
<sup>*</sup>
</xref>
<uri xlink:href="https://loop.frontiersin.org/people/1351719"/>
</contrib>
<contrib contrib-type="author" corresp="yes">
<name>
<surname>Hao</surname>
<given-names>Junfeng</given-names>
</name>
<xref ref-type="aff" rid="aff5">
<sup>5</sup>
</xref>
<xref ref-type="author-notes" rid="fn001">
<sup>*</sup>
</xref>
</contrib>
<contrib contrib-type="author" corresp="yes">
<name>
<surname>Xin</surname>
<given-names>Shaojie</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
<xref ref-type="author-notes" rid="fn001">
<sup>*</sup>
</xref>
<uri xlink:href="https://loop.frontiersin.org/people/1356121"/>
</contrib>
</contrib-group>
<aff id="aff1">
<sup>1</sup>
<institution>Chinese People&#x2019;s Liberation Army (PLA) Medical School</institution>, <addr-line>Beijing</addr-line>, <country>China</country>
</aff>
<aff id="aff2">
<sup>2</sup>
<institution>Department of Liver Disease of Chinese PLA General Hospital, The Fifth Medical Center of Chinese PLA General Hospital</institution>, <addr-line>Beijing</addr-line>, <country>China</country>
</aff>
<aff id="aff3">
<sup>3</sup>
<institution>Institute of Infectious Disease, Department of Infectious Disease, The Fifth Medical Center of Chinese PLA General Hospital</institution>, <addr-line>Beijing</addr-line>, <country>China</country>
</aff>
<aff id="aff4">
<sup>4</sup>
<institution>Department of Clinical Laboratory, The Fifth Medical Center of Chinese PLA General Hospital</institution>, <addr-line>Beijing</addr-line>, <country>China</country>
</aff>
<aff id="aff5">
<sup>5</sup>
<institution>Department of Nephrology, Jin Qiu Hospital of Liaoning Province/Geriatric Hospital of Liaoning Province</institution>, <addr-line>Shenyang</addr-line>, <country>China</country>
</aff>
<author-notes>
<fn fn-type="edited-by">
<p>Edited by: Xiaojie Xu, Beijing Institute of Technology, China</p>
</fn>
<fn fn-type="edited-by">
<p>Reviewed by: Zhiyi Shao, Shaanxi Normal University, China; Hua Yang, Hebei University, China; Kang Cui, Zhengzhou University, China; Zhongyi Fan, Shenzhen Third People&#x2019;s Hospital, China</p>
</fn>
<fn fn-type="corresp" id="fn001">
<p>*Correspondence: Shaojie Xin, <email xlink:href="mailto:xinshaojie302@163.com">xinshaojie302@163.com</email>; Junfeng Hao, <email xlink:href="mailto:ygzhjf85@gmail.com">ygzhjf85@gmail.com</email>; Boan Li, <email xlink:href="mailto:lba_302@126.com">lba_302@126.com</email>
</p>
</fn>
<fn fn-type="other" id="fn002">
<p>This article was submitted to Molecular and Cellular Oncology, a section of the journal Frontiers in Oncology</p>
</fn>
</author-notes>
<pub-date pub-type="epub">
<day>26</day>
<month>07</month>
<year>2021</year>
</pub-date>
<pub-date pub-type="collection">
<year>2021</year>
</pub-date>
<volume>11</volume>
<elocation-id>735447</elocation-id>
<history>
<date date-type="received">
<day>02</day>
<month>07</month>
<year>2021</year>
</date>
<date date-type="accepted">
<day>12</day>
<month>07</month>
<year>2021</year>
</date>
</history>
<permissions>
<copyright-statement>Copyright &#xa9; 2021 He, Sun, Jiang, Chai, Li, Wang, Zhu, You, Li, Hao and Xin</copyright-statement>
<copyright-year>2021</copyright-year>
<copyright-holder>He, Sun, Jiang, Chai, Li, Wang, Zhu, You, Li, Hao and Xin</copyright-holder>
<license xlink:href="http://creativecommons.org/licenses/by/4.0/">
<p>This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.</p>
</license>
</permissions>
<abstract>
<p>Increasing evidence has shown that the metabolism and clearance of molecular targeted agents, such as sorafenib, plays an important role in mediating the resistance of HCC cells to these agents. Metabolism of sorafenib is performed by oxidative metabolism, which is initially mediated by CYP3A4. Thus, targeting CYP3A4 is a promising approach to enhance the sensitivity of HCC cells to chemotherapeutic agents. In the present work, we examined the association between CYP3A4 and the prognosis of HCC patients receiving sorafenib. Using the online tool miRDB, we predicted that has-microRNA-4277 (miR-4277), an online miRNA targets the 3&#x2019;UTR of the transcript of <italic>cyp3a4</italic>. Furthermore, overexpression of miR-4277 in HCC cells repressed the expression of CYP3A4 and reduced the elimination of sorafenib in HCC cells. Moreover, miR-4277 enhanced the sensitivity of HCC cells to sorafenib <italic>in vitro</italic> and <italic>in vivo</italic>. Therefore, our results not only expand our understanding of CYP3A4 regulation in HCC, but also provide evidence for the use of miR-4277 as a potential therapeutic in advanced HCC.</p>
</abstract>
<kwd-group>
<kwd>advanced hepatocellular carcinoma</kwd>
<kwd>cytochrome P450 3A4</kwd>
<kwd>miR-4277</kwd>
<kwd>chemoresistance</kwd>
<kwd>sorafenib</kwd>
<kwd>metabolism or clearance</kwd>
</kwd-group>
<counts>
<fig-count count="7"/>
<table-count count="6"/>
<equation-count count="0"/>
<ref-count count="75"/>
<page-count count="12"/>
<word-count count="5347"/>
</counts>
</article-meta>
</front>
<body>
<sec id="s1" sec-type="intro">
<title>Introduction</title>
<p>Though many advances have been made in the treatment of advanced HCC, it remains a major challenge for China&#x2019;s public health (<xref ref-type="bibr" rid="B1">1</xref>&#x2013;<xref ref-type="bibr" rid="B3">3</xref>). In China, more than 80 million people suffer from viral liver disease or related acute and chronic liver diseases (<xref ref-type="bibr" rid="B1">1</xref>). These patients have a high risk of developing HCC (<xref ref-type="bibr" rid="B1">1</xref>, <xref ref-type="bibr" rid="B4">4</xref>). Furthermore, most HCC patients are diagnosed with advanced disease, so they are not candidates for radical treatment strategies like surgery or liver transplantation (<xref ref-type="bibr" rid="B5">5</xref>&#x2013;<xref ref-type="bibr" rid="B7">7</xref>). At present, drug treatment strategies for advanced HCC are limited, they are mainly based on various molecular targeted therapeutics (<xref ref-type="bibr" rid="B8">8</xref>&#x2013;<xref ref-type="bibr" rid="B10">10</xref>), or immune checkpoint inhibitors targeting PD-1/PD-L1 (programmed cell death-1/programmed cell death ligand-1) (<xref ref-type="bibr" rid="B11">11</xref>&#x2013;<xref ref-type="bibr" rid="B13">13</xref>). Among them, molecular-targeted agents like sorafenib have been used in clinical treatment for many years, though several problems remain: the efficacy of sorafenib varies based on the patient, and resistance is common; sorafenib treatment often induces serious side effects (<xref ref-type="bibr" rid="B14">14</xref>, <xref ref-type="bibr" rid="B15">15</xref>); newer agents such as lenvatinib, regorafenib, and carbozantinib (<xref ref-type="bibr" rid="B8">8</xref>&#x2013;<xref ref-type="bibr" rid="B10">10</xref>), have the same chemical parent ring structure (1-(4- (pyridin-4-yloxy)phenyl) urea) as sorafenib. Therefore, it is important to understand the mechanisms of resistance to sorafenib and other agents, and to study and explore sensitization strategies for HCC cells to molecular targeted agents. This will not only provide more choice for the patient, but it will also help improve the efficacy of combination therapies using targeted agents and/or immune checkpoint inhibitors.</p>
<p>The metabolism and clearance mechanisms of sorafenib and other exogenous agents in HCC cells are crucial factors in the development of HCC chemoresistance (<xref ref-type="bibr" rid="B16">16</xref>, <xref ref-type="bibr" rid="B17">17</xref>). <italic>Via</italic> a systemic analysis, Feng et&#xa0;al. (<xref ref-type="bibr" rid="B18">18</xref>) and Shao et&#xa0;al. (<xref ref-type="bibr" rid="B19">19</xref>) found that sorafenib can act as a ligand/agonist to activate PXR/NR1I2 (pregnane X receptor/nuclear receptor subfamily 1 group I member 2) and induce expression of downstream genes involved in chemoresistance, including <italic>cyp3a4</italic> and <italic>abcb1</italic> (ATP-binding cassette, sub-family B, member 1). Ultimately, this accelerates elimination of the therapeutic and results in drug resistance through negative feedback regulation (<xref ref-type="bibr" rid="B18">18</xref>, <xref ref-type="bibr" rid="B19">19</xref>). Although related studies have expanded our understanding of PXR in HCC, much remains unclear; PXR is not the only metabolism-related nuclear receptor in HCC cells, and the CAR/NR1I3 (constitutive androstane receptor/nuclear receptor subfamily 1 group I member 3) may have similar functions to PXR (<xref ref-type="bibr" rid="B20">20</xref>, <xref ref-type="bibr" rid="B21">21</xref>). By inhibiting the activity of PXR alone, CAR may have a compensatory effect on the function of PXR. Moreover, targeting oxidative metabolism, which is mediated by CYP3A4 in the initial step of sorafenib elimination in HCC cells, represents a promising approach to enhance the sensitivity of these cells to targeted agents (<xref ref-type="bibr" rid="B22">22</xref>, <xref ref-type="bibr" rid="B23">23</xref>). This makes CYP3A4 more advantageous to target compared with PXR or CAR. Both PXR and CAR mediate the expression of CYP3A4 to eliminate sorafenib. By inhibiting CYP3A4, compensatory effects between PXR and CAR can be avoided.</p>
<p>MicroRNA is a type of small non-coding RNA transcribed by RNA polymerase II (<xref ref-type="bibr" rid="B24">24</xref>&#x2013;<xref ref-type="bibr" rid="B27">27</xref>). In mammalian cells, miRNA can directly affect the 3&#x2019;UTR of the target mRNA to degrade it in a sequence-specific manner and silence gene expression (<xref ref-type="bibr" rid="B28">28</xref>&#x2013;<xref ref-type="bibr" rid="B30">30</xref>). Because of this feature, miRNAs are widely used as anti-cancer therapeutics. By predicting miRNAs that target certain sets of oncogenes, one can identify novel anti-cancer miRNAs that can be added to lentiviral particles to reduce expression of the target oncogene and sensitize cells to targeted agents. Our study used the online tool miRDB to identify miR-4277, a potential repressor of CYP3A4 expression. We infected HCC cells with lentiviral particles containing pre-miR-4277 and confirmed the effect of miR-4277 on CYP3A4 and the elimination of sorafenib.</p>
</sec>
<sec id="s2" sec-type="materials|methods">
<title>Materials and Methods</title>
<sec id="s2_1">
<title>Cell Lines and Reagents</title>
<p>The HCC cell lines, MHCC97-H, HepG2, BEL7402 or SMMC7721, were grown in our lab and described previously (<xref ref-type="bibr" rid="B18">18</xref>, <xref ref-type="bibr" rid="B19">19</xref>). The clinical specimens of advanced HCC were also descripted in our previous work (<xref ref-type="bibr" rid="B18">18</xref>, <xref ref-type="bibr" rid="B19">19</xref>). The use of human subjects was approved by the ethics committee of the Fifth Medical Center, General Hospital of Chinese PLA (People&#x2019;s Liberation Army). All assays were carried out in accordance with the Helsinki Declaration. Sorafenib, lenvatinib, cabozantinib, regorafenib, anlotinib, and apatinib were chemically synthesized by Dr. Shuang Cao at the Wuhan Institute of Technology, Wuhan City, Hubei Province of China. The potential cyp3a4&#x2019;s inhibitor, ketoconazole, amprenavir or diltiazem, was also gifts from Dr. Shuang Cao at the Wuhan Institute of Technology, Wuhan City, Hubei Province of China. All agents were initially prepared as powders purified to &gt;99% by using the HPLC (high performance liquid chromatography) (<xref ref-type="supplementary-material" rid="SM1">
<bold>Supplemental Table&#xa0;1</bold>
</xref>). The miR-4277 was a microRNA potentially targeting to <italic>cyp3a4</italic>&#x2019;s 3&#x2019;UTR <italic>via</italic> an online tool, miRDB, and the full-length sequences of has-pre-miR-4277, wild-type <italic>cyp3a4</italic> and <italic>cyp3a4</italic>, and miR-4277 mutated at its targeting sites (two targeting sites of miR-4277 located in the 3&#x2019;UTR of <italic>cyp3a4</italic>: 1<sup>st</sup> site of 496<sup>th</sup> &#x2013; 503th nt [a 8<sup>mer</sup> site]; 2<sup>nd</sup> site of 984<sup>th</sup> &#x2013; 991<sup>st</sup> nt [a 8<sup>mer</sup> site]) for the 3&#x2019;UTR were chemically synthesized and prepared as lentiviral particles: (1) Luc-1 (the luciferase reporter with the wild type of the 1<sup>st</sup> miR-4277 targeting site), (2) Luc-2 (the luciferase reporter with the wild type of the 2<sup>nd</sup> miR-4277 targeting site), (3) Luc-3 (the luciferase reporter with the wild type of the 1<sup>st</sup> and 2<sup>nd</sup> miR-4277 targeting site), (4) Luc-4 (the luciferase reporter with the wild type of the 2<sup>nd</sup> and the mutated 1<sup>st</sup> miR-4277 targeting site), (5) CYP3A4 mutations (CYP3A4<sup>Mut1</sup> [the vector of <italic>cyp3a4</italic> with the mutation of the 1<sup>st</sup> miR-4277 targeting site], CYP3A4<sup>Mut2</sup> [the vector of <italic>cyp3a4</italic> with the mutation of the 2<sup>nd</sup> miR-4277 targeting site], or CYP<sup>Mut</sup> [the vector of <italic>cyp3a4</italic> with the mutation of the 1<sup>st</sup> and 2<sup>nd</sup> miR-4277 targeting site]).</p>
</sec>
<sec id="s2_2">
<title>Quantitative PCR</title>
<p>The endogenous mRNA levels of <italic>cyp3a4</italic> in HCC clinical specimens were identified using quantitative polymerase chain reaction (qPCR) in accordance with methods described by Wang et&#xa0;al. (<xref ref-type="bibr" rid="B20">20</xref>) and Ma et&#xa0;al. (<xref ref-type="bibr" rid="B20">20</xref>, <xref ref-type="bibr" rid="B25">25</xref>). The primers used were: (1) <italic>cyp3a4</italic>, forward sequence 5&#x2019;-CCGAGTGGATTTCCTTCAGCTG-3&#x2019;, reverse sequence 5&#x2019;-TGCTCGTG GTTTCATAGCCAGC-3&#x2019;; (2) <italic>&#x3b2;-actin</italic>, forward sequence 5&#x2019;-CACCATTGGCAATGA GCGGTTC-3&#x2019;, reverse sequence 5-AGGTCTTTGCGGAT GTCCACGT-3&#x2019;; (3) PXR/NR1I2 (<xref ref-type="bibr" rid="B31">31</xref>), forward sequence 5&#x2019;-CCCACCTCAGA AGACAAAGC-3&#x2019;, reverse sequence, 5&#x2019;-GAACCCCAGACCCTACACAA-3&#x2019; (<xref ref-type="bibr" rid="B4">4</xref>); CAR/NR1I3 (<xref ref-type="bibr" rid="B31">31</xref>): forward sequence, 5&#x2019;-TACTGTGCTTCGTGCTCCTG-3&#x2019;, Reverse sequence, 5&#x2019;-CCTGG TCTTCGGGTTCAAG-3&#x2019;. The results (the relative expression level [folds of &#x3b2;-Actin]) of PXR or CAR was shown as heat-map.</p>
</sec>
<sec id="s2_3">
<title>Western Blot</title>
<p>MHCC97-H cells were cultured and TACT transfected with plasmids, such as miR-4277 or <italic>cyp3a4</italic>; the cells were then harvested and proteins were extracted as previously described by Wei et&#xa0;al. (<xref ref-type="bibr" rid="B32">32</xref>) and Jia et&#xa0;al. (<xref ref-type="bibr" rid="B32">32</xref>, <xref ref-type="bibr" rid="B33">33</xref>). Antibodies against CYP3A4 (Cat. No.: ab124921) and &#x3b2;-Actin (Cat. No.: ab8226) were purchased from the Abcam Corporation, Cambridge, UK). The images of western blot was quantitatively analyzed by Image J Software (National Institutes of Health [NIH], Bethesda, Maryland, USA).</p>
</sec>
<sec id="s2_4">
<title>Assessment of Sorafenib Elimination in HCC Cells</title>
<p>HCC cells were used to examine the rate of elimination of sorafenib (<xref ref-type="bibr" rid="B18">18</xref>, <xref ref-type="bibr" rid="B19">19</xref>, <xref ref-type="bibr" rid="B34">34</xref>, <xref ref-type="bibr" rid="B35">35</xref>). For cell-based experiments, HCC cells were treated with 1 &#x3bc;mol/L of sorafenib for 12&#xa0;h. After treatment, the cells were harvested at a series of time-points. For <italic>in vivo</italic> experimentation, HCC cells were cultured and subcutaneously injected into mice to generate tumors. When tumor volume reached 2000 mm<sup>3</sup>, a solution of sorafenib was directly injected into the tumors. After injection, the tumors were excised at a series of time-points. Next, sorafenib was extracted from MHCC97-H cells or tumors using the acetonitrile (ACN). The sustaining amount of sorafenib at each time-point was measured using liquid chromatography&#x2013;mass spectrometry/mass spectrometry (LC-MS/MS) and the <italic>in vitro</italic>/<italic>in vivo</italic> half-life of sorafenib was determined (<xref ref-type="bibr" rid="B18">18</xref>, <xref ref-type="bibr" rid="B19">19</xref>, <xref ref-type="bibr" rid="B34">34</xref>, <xref ref-type="bibr" rid="B35">35</xref>).</p>
</sec>
<sec id="s2_5">
<title>Assessment of Cell Survival</title>
<p>After transfection or treated with potential inhibitor of <italic>cyp3a4</italic>, HCC cells were treated with a series concentrations of sorafenib, lenvatinib, cabozantinib, regorafenib, anlotinib, or apatinib (10&#xa0;&#x3bc;mol/L, 3 &#x3bc;mol/L, 1 &#x3bc;mol/L, 0.3 &#x3bc;mol/L, 0.1 &#x3bc;mol/L, 0.03 &#x3bc;mol/L, or 0.01 &#x3bc;mol/L). After 48&#xa0;h, MTT was performed to measure ell survival, and the IC<sub>50</sub> value of each agent was calculated (<xref ref-type="bibr" rid="B36">36</xref>&#x2013;<xref ref-type="bibr" rid="B38">38</xref>).</p>
</sec>
<sec id="s2_6">
<title>Nude Mouse Tumor Model</title>
<p>All animal experiments were reviewed approved by the Institutional Animal Care and Use Committee, the Fifth Medical Center, Chinese PLA. All animal experiments were performed in accordance with the UK Animals (Scientific Procedures) Act, 1986 and the associated guidelines. Female nude mice were purchased from the Si-Bei-Fu Corporation, Beijing China. Following transfection, MHCC97-H cells were prepared as a single-cell suspension and subcutaneously injected into nude mice (<xref ref-type="bibr" rid="B39">39</xref>, <xref ref-type="bibr" rid="B40">40</xref>). The mice orally received sorafenib once every two days. Tumors from the mice were harvested, and the volumes and weights were measured (<xref ref-type="bibr" rid="B39">39</xref>, <xref ref-type="bibr" rid="B40">40</xref>).</p>
</sec>
<sec id="s2_7">
<title>Statistical Analysis</title>
<p>SPSS 9.0 statistical software (IBM Corporation, Armonk, NY, USA) was used for all statistical analyses. Statistics were calculated using two-way ANOVA with the Bonferroni correction. IC<sub>50</sub> values and the half-lie values (t<sub>1/2</sub> values) were calculated using Origin software (Origin 6.1; OriginLab Corporation, Northampton, MA, USA). The *P &lt; 0.05 being statistically significant between groups. The heat-map of the qPCR results were obtained according to the methods by Zhou et&#xa0;al. (<xref ref-type="bibr" rid="B41">41</xref>) and Yin et&#xa0;al. (<xref ref-type="bibr" rid="B42">42</xref>).</p>
</sec>
</sec>
<sec id="s3" sec-type="results">
<title>Results</title>
<sec id="s3_1">
<title>High Levels of <italic>cyp3a4</italic> mRNA Expression Are Associated With Poor Prognosis in HCC Patients Receiving Sorafenib</title>
<p>Though it has been suggested that <italic>cyp3a4</italic> participates in the resistance of HCC cells to sorafenib, the clinical significance of <italic>cyp3a4</italic> requires further analysis. As shown in <xref ref-type="fig" rid="f1">
<bold>Figure&#xa0;1</bold>
</xref>, the endogenous mRNA levels of <italic>cyp3a4</italic> were examined in 52 clinical specimens from patients with advanced HCC (<xref ref-type="fig" rid="f1">
<bold>Figure&#xa0;1</bold>
</xref> and <xref ref-type="table" rid="T1">
<bold>Table&#xa0;1</bold>
</xref>). According to the median expression level of <italic>cyp3a4</italic> in HCC tissue samples, patients were divided into two groups: a <italic>cyp3a4</italic> high expression group [<italic>cyp3a4</italic>-high] and a <italic>cyp3a4</italic> low expression group [<italic>cyp3a4</italic>-low]) (<xref ref-type="fig" rid="f1">
<bold>Figure&#xa0;1A</bold>
</xref>). We then performed survival analysis (<xref ref-type="fig" rid="f1">
<bold>Figures&#xa0;1B, C</bold>
</xref>). The prognosis of patients in the <italic>cyp3a4</italic> high expression group [<italic>cyp3a4</italic>-high] treated with sorafenib, as measured by TTP (time to progress) and OS (overall survival), was significantly worse than that of the <italic>cyp3a4</italic> low expression group [<italic>cyp3a4</italic>-low]) (<xref ref-type="fig" rid="f1">
<bold>Figures&#xa0;1B, C</bold>
</xref> and <xref ref-type="table" rid="T1">
<bold>Table&#xa0;1</bold>
</xref>). Therefore, high levels of <italic>cyp3a4</italic> appear to be associated with poor prognosis of HCC patients receiving sorafenib.</p>
<fig id="f1" position="float">
<label>Figure&#xa0;1</label>
<caption>
<p>High levels of <italic>cyp3a4</italic> is associated with poor prognosis in advanced HCC. <bold>(A)</bold> The endogenous mRNA levels of <italic>cyp3a4</italic> were assessed in 52 clinical specimens from patients with advanced HCC. According to the median expression level of <italic>cyp3a4</italic> in HCC tissue samples, patients were divided into two groups: a <italic>cyp3a4</italic> high expression group [<italic>cyp3a4</italic>-high] and a <italic>cyp3a4</italic> low expression group [<italic>cyp3a4</italic>-low]) <bold>(B</bold>, <bold>C)</bold>. Survival analysis included analysis of TTP and OS. *P &lt; 0.05.</p>
</caption>
<graphic mimetype="image" mime-subtype="tiff" xlink:href="fonc-11-735447-g001.tif"/>
</fig>
<table-wrap id="T1" position="float">
<label>Table&#xa0;1</label>
<caption>
<p>CYP3A4 expression and clinical outcome of sorafenib treatment.</p>
</caption>
<table frame="hsides">
<thead>
<tr>
<th valign="top" align="left"/>
<th valign="top" colspan="2" align="center">CYP3A4 mRNA expression</th>
<th valign="top" align="center">P</th>
</tr>
<tr>
<th valign="top" align="left"/>
<th valign="top" align="center">High (n = 26)</th>
<th valign="top" align="center">Low (n = 26)</th>
<th valign="top" align="center"/>
</tr>
</thead>
<tbody>
<tr>
<td valign="top" align="left">TTP</td>
<td valign="top" align="center">9.0</td>
<td valign="top" align="center">11.0</td>
<td valign="top" align="center">0.032</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="center">6.1-11.8 (M)</td>
<td valign="top" align="center">9.5-12.9 (M)</td>
<td valign="top" align="center"/>
</tr>
<tr>
<td valign="top" align="left">OS</td>
<td valign="top" align="center">8.0</td>
<td valign="top" align="center">15.0</td>
<td valign="top" align="center">0.023</td>
</tr>
<tr>
<td valign="top" align="left"/>
<td valign="top" align="center">4.8-11.2 (M)</td>
<td valign="top" align="center">6.9-23.1 (M)</td>
<td valign="top" align="center"/>
</tr>
</tbody>
</table>
<table-wrap-foot>
<fn>
<p>TTP, time to progress; OS, overall survival; PR, partial remission; CR, complete remission; SD, stable of disease; M, months.</p>
</fn>
</table-wrap-foot>
</table-wrap>
</sec>
<sec id="s3_2">
<title>miR-4277 Represses the Expression of <italic>cyp3a4</italic> by Targeting its 3&#x2019;UTR</title>
<p>To explore CYP3A4 as a potential anti-cancer target, miR-4277 was identified <italic>via</italic> the online tool miRDB as a microRNA that could potentially target <italic>cyp3a4</italic>. The potential binding sites of miR-4277 in the 3&#x2032;-UTR of <italic>cyp3a4</italic> as well as in wild type <italic>cyp3a4</italic> and <italic>cyp3a4</italic> with mutated miR-4277 binding sites are shown in <xref ref-type="fig" rid="f2">
<bold>Figure&#xa0;2A</bold>
</xref>. To confirm the effects of miR-4277 on <italic>cyp3a4</italic> expression, we used a luciferase reporter construct for <italic>cyp3a4</italic> and transfected cells with miR-4277. As shown in <xref ref-type="fig" rid="f2">
<bold>Figures&#xa0;2B</bold>
</xref> and <xref ref-type="fig" rid="f3">
<bold>3</bold>
</xref>, overexpression of miR-4277 repressed the activation of Luc-1 (the luciferase reporter with the wild type of the 1<sup>st</sup> miR-4277 targeting site), Luc-2 (the luciferase reporter with the wild type of the 2<sup>nd</sup> miR-4277 targeting site), Luc-3 (the luciferase reporter with the wild type of the 1<sup>st</sup> and 2<sup>nd</sup> miR-4277 targeting site), and Luc-4 (the luciferase reporter with the wild type of the 2<sup>nd</sup> and the mutated 1<sup>st</sup> miR-4277 targeting site). Moreover, miR-4277 did not affect the activation of Luc-5 (the luciferase reporter with the wild type of the 2<sup>nd</sup> and the mutated 1<sup>st</sup> miR-4277 targeting site) (<xref ref-type="fig" rid="f3">
<bold>Figure&#xa0;3</bold>
</xref>).</p>
<fig id="f2" position="float">
<label>Figure&#xa0;2</label>
<caption>
<p>miR-4277 is predicted to target the 3&#x2019;UTR of <italic>cyp3a4</italic>. <bold>(A)</bold> The sequences of miR-4277 and <italic>cyp3a4</italic> are shown as schematic diagrams. <bold>(B)</bold> The luciferase reporters containing the 3&#x2019;UTR region of cyp3a4 containing the miR-4277 binding site are shown as a schematic diagram.</p>
</caption>
<graphic mimetype="image" mime-subtype="tiff" xlink:href="fonc-11-735447-g002.tif"/>
</fig>
<fig id="f3" position="float">
<label>Figure&#xa0;3</label>
<caption>
<p>miR-4277 represses the activation of <italic>cyp3a4</italic>&#x2019;s 3&#x2019;UTR luciferase reporters in MHCC97-H cells. The effect of miR-4277 on the activation of Luc-1 (the luciferase reporter with the wild type of the 1<sup>st</sup> miR-4277 targeting site) or Luc-2 (the luciferase reporter with the wild type of the 2<sup>nd</sup> miR-4277 targeting site), Luc-3 (the luciferase reporter with the wild type of the 1<sup>st</sup> and 2<sup>nd</sup> miR-4277 targeting site), Luc-4 (the luciferase reporter with the wild type of the 2<sup>nd</sup> and the mutated 1<sup>st</sup> miR-4277 targeting site), or Luc-5 (the luciferase reporter with the wild type of the 2<sup>nd</sup> and the mutated 1<sup>st</sup> miR-4277 targeting site) was examined. The results are shown as histograms. *P &lt; 0.05.</p>
</caption>
<graphic mimetype="image" mime-subtype="tiff" xlink:href="fonc-11-735447-g003.tif"/>
</fig>
<p>Next, the effect of miR-4277 on the CYP3A4 protein expression was examined <italic>via</italic> western blot. As shown in <xref ref-type="fig" rid="f4">
<bold>Figure&#xa0;4</bold>
</xref>, miR-4277 not only inhibited the protein expression of the endogenous CYP3A4 in MHCC97-H cells, but also the expression of CYP3A4<sup>MUT1</sup> or CYP3A4<sup>Mut2</sup>. Transfection of miR-4277 did not affect the expression of CYP3A4<sup>MUT</sup> (<xref ref-type="fig" rid="f4">
<bold>Figure&#xa0;4</bold>
</xref>). Therefore, these results suggest that miR-4277 targets the 3&#x2019;UTR of <italic>cyp3a4</italic> in a sequence specific manner.</p>
<fig id="f4" position="float">
<label>Figure&#xa0;4</label>
<caption>
<p>miR-4277 represses the expression of CYP3A4 in MHCC97-H cells. The effect of miR-4277 on wild type CYP3A4 or CYP3A4 mutations (CYP3A4Mut1 [the vector of <italic>cyp3a4</italic> with the mutation of the 1<sup>st</sup> miR-4277 targeting site], CYP3A4<sup>Mut2</sup> [the vector of <italic>cyp3a4</italic> with the mutation of the 2<sup>nd</sup> miR-4277 targeting site], or CYP<sup>Mut</sup> [the vector of <italic>cyp3a4</italic> with the mutation of the 1<sup>st</sup> and 2<sup>nd</sup> miR-4277 targeting site]) in MHCC97-H cells was measured by western blot. The results are shown as blots <bold>(A)</bold> or the quantitative results <bold>(B)</bold>. *P &lt; 0.05.</p>
</caption>
<graphic mimetype="image" mime-subtype="tiff" xlink:href="fonc-11-735447-g004.tif"/>
</fig>
</sec>
<sec id="s3_3">
<title>miR-4277 Reduces the Elimination of Sorafenib in HCC Cells</title>
<p>Our results above suggest that miR-4277 represses the expression of CYP3A4 in MHCC97-H cells; therefore, we assessed whether miR-4277 could affect the elimination of sorafenib <italic>via</italic> LC-MS/MS. As shown in <xref ref-type="table" rid="T2">
<bold>Table&#xa0;2</bold>
</xref>, overexpression of miR-4277 reduces elimination of sorafenib in cultured MHCC97-H cells; the half-life (t<sub>1/2</sub>) of sorafenib in MHCC97-H cells was also decreased in the presence of miR-4277 (<xref ref-type="table" rid="T2">
<bold>Table&#xa0;2</bold>
</xref>). Transfection of CYP3A4<sup>Mut</sup> but not CYP3A4<sup>Mut1</sup> or CYP<sup>Mut2</sup> blocked the effect of miR-4277 on the reduction in t<sub>1/2</sub> of sorafenib (<xref ref-type="table" rid="T2">
<bold>Table&#xa0;2</bold>
</xref>). Therefore, miR-4277 blocked elimination of sorafenib in HCC cells by targeting the 3&#x2019;UTR of <italic>cyp3a4</italic>.</p>
<table-wrap id="T2" position="float">
<label>Table&#xa0;2</label>
<caption>
<p>The effect of miR-4277 on Sorafenib in cultured MHCC97-H cells.</p>
</caption>
<table frame="hsides">
<thead>
<tr>
<th valign="top" align="left">Groups</th>
<th valign="top" align="center">
<italic>t<sub>1/2</sub>
</italic> of Sorafenib (hours)</th>
<th valign="top" align="center">
<italic>IC<sub>50</sub>
</italic> of Sorafenib (&#x3bc;mol/L)</th>
</tr>
</thead>
<tbody>
<tr>
<td valign="top" align="left">control miRNA</td>
<td valign="top" align="center">21.60 &#xb1; 1.34</td>
<td valign="top" align="center">0.70 &#xb1; 0.09</td>
</tr>
<tr>
<td valign="top" align="left">miR-4277</td>
<td valign="top" align="center">38.46 &#xb1; 9.97</td>
<td valign="top" align="center">0.15 &#xb1; 0.01</td>
</tr>
<tr>
<td valign="top" align="left">miR-4277 + CYP3A4<sup>Mut-1</sup>
</td>
<td valign="top" align="center">22.11 &#xb1; 6.59</td>
<td valign="top" align="center">0.22 &#xb1; 0.14</td>
</tr>
<tr>
<td valign="top" align="left">miR-4277 + CYP3A4<sup>Mut-2</sup>
</td>
<td valign="top" align="center">24.68 &#xb1; 8.63</td>
<td valign="top" align="center">0.35 &#xb1; 0.05</td>
</tr>
<tr>
<td valign="top" align="left">miR-4277 + CYP3A4<sup>Mut</sup>
</td>
<td valign="top" align="center">19.88 &#xb1; 2.71</td>
<td valign="top" align="center">0.92 &#xb1; 0.20</td>
</tr>
</tbody>
</table>
</table-wrap>
</sec>
<sec id="s3_4">
<title>miR-4277 Enhances the Sensitivity of HCC Cells to Targeted Agents</title>
<p>To further examine the effect of miR-4277 on <italic>cyp3a4</italic> in HCC cells, the effects of other targeted agents were assessed by MTT. As shown in <xref ref-type="table" rid="T2">
<bold>Table&#xa0;2</bold>
</xref>, overexpression of miR-4277 enhanced the sensitivity of MHCC97-H cells to sorafenib, with a decrease in its IC<sub>50</sub> value. Transfection of CYP3A4<sup>Mut</sup> but not CYP3A4<sup>Mut1</sup> or CYP<sup>Mut2</sup> blocked the effect of miR-4277 on the reduction in t<sub>1/2</sub> value for sorafenib. Similar results were obtained for five other targeted agents, including regorafenib, lenvatinib, anlotinib, cabozantinib, and apatinib (<xref ref-type="table" rid="T3">
<bold>Table&#xa0;3</bold>
</xref>). Therefore, miR-4277 appears to enhance the sensitivity of HCC cells to multiple targeted agents by targeting the 3&#x2019;UTR of <italic>cyp3a4</italic>.</p>
<table-wrap id="T3" position="float">
<label>Table&#xa0;3</label>
<caption>
<p>miR-4277 enhanced the sensitivity of MHCC97-H cells to molecular targeted agents, regorafenib, lenvatinib, anlotinib, cabozantinib, or apatinib.</p>
</caption>
<table frame="hsides">
<thead>
<tr>
<th valign="top" align="left">Groups</th>
<th valign="top" align="center">Regorafenib</th>
<th valign="top" align="center">Lenvatinib</th>
<th valign="top" align="center">Anlotinib</th>
<th valign="top" align="center">Cabozantinib</th>
<th valign="top" align="center">Apatinib</th>
</tr>
<tr>
<th valign="top" align="center"/>
<th valign="top" colspan="5" align="center">
<italic>IC<sub>50</sub>
</italic> values of the agents on MHCC97-H cells (&#x3bc;mol/L)</th>
</tr>
</thead>
<tbody>
<tr>
<td valign="top" align="left">
<bold>control miRNA</bold>
</td>
<td valign="top" align="center">0.67 &#xb1; 0.49</td>
<td valign="top" align="center">0.55 &#xb1; 0.20</td>
<td valign="top" align="center">0.75 &#xb1; 0.03</td>
<td valign="top" align="center">0.51 &#xb1; 0.19</td>
<td valign="top" align="center">0.96 &#xb1; 0.33</td>
</tr>
<tr>
<td valign="top" align="left">
<bold>miR-4277</bold>
</td>
<td valign="top" align="center">0.22 &#xb1; 0.04</td>
<td valign="top" align="center">0.12 &#xb1; 0.06</td>
<td valign="top" align="center">0.10 &#xb1; 0.01</td>
<td valign="top" align="center">0.10 &#xb1; 0.04</td>
<td valign="top" align="center">0.26 &#xb1; 0.07</td>
</tr>
<tr>
<td valign="top" align="left">
<bold>miR-4277 + CYP3A4<sup>Mut-1</sup>
</bold>
</td>
<td valign="top" align="center">0.33 &#xb1; 0.32</td>
<td valign="top" align="center">0.41 &#xb1; 0.01</td>
<td valign="top" align="center">0.30 &#xb1; 0.12</td>
<td valign="top" align="center">0.25 &#xb1; 0.06</td>
<td valign="top" align="center">0.52 &#xb1; 0.27</td>
</tr>
<tr>
<td valign="top" align="left">
<bold>miR-4277 + CYP3A4<sup>Mut-2</sup>
</bold>
</td>
<td valign="top" align="center">0.35 &#xb1; 0.09</td>
<td valign="top" align="center">0.28 &#xb1; 0.11</td>
<td valign="top" align="center">0.45 &#xb1; 0.35</td>
<td valign="top" align="center">0.30 &#xb1; 0.21</td>
<td valign="top" align="center">0.46 &#xb1; 0.30</td>
</tr>
<tr>
<td valign="top" align="left">
<bold>miR-4277 + CYP3A4<sup>Mut</sup>
</bold>
</td>
<td valign="top" align="center">0.71 &#xb1; 0.28</td>
<td valign="top" align="center">0.60 &#xb1; 0.20</td>
<td valign="top" align="center">0.78 &#xb1; 0.55</td>
<td valign="top" align="center">0.56 &#xb1; 0.15</td>
<td valign="top" align="center">0.98 &#xb1; 0.37</td>
</tr>
</tbody>
</table>
</table-wrap>
</sec>
<sec id="s3_5">
<title>miR-4277 Inhibits the Growth and Induces Sensitization of HCC Tumors to Sorafenib in Nude Mice</title>
<p>The effect of miR-4277 to induce sensitivity to sorafenib was further confirmed in a nude mice model. As shown in <xref ref-type="fig" rid="f5">
<bold>Figure&#xa0;5</bold>
</xref>, sorafenib inhibited the subcutaneous growth of HCC cells in a dose-dependent manner, and transfected with miR-4277 further enhanced this effect (<xref ref-type="fig" rid="f5">
<bold>Figure&#xa0;5</bold>
</xref>).</p>
<fig id="f5" position="float">
<label>Figure&#xa0;5</label>
<caption>
<p>miR-4277 enhances the antitumor effects of sorafenib in inhibiting the growth of HCC cells in a nude mouse model. MHCC97-H cells were transfected with vectors (control miR or miR-4277) and subcutaneously injected into nude mice. The mice then received the indicated dose of sorafenib <italic>via</italic> oral administration. The results are shown as tumor images <bold>(A)</bold>, tumor volumes <bold>(B)</bold>, or tumor weights <bold>(C)</bold>. *P &lt; 0.05.</p>
</caption>
<graphic mimetype="image" mime-subtype="tiff" xlink:href="fonc-11-735447-g005.tif"/>
</fig>
<p>Moreover, the specificity of miR-4277 for <italic>cyp3a4</italic> was examined in our subcutaneous tumor model. As shown in <xref ref-type="fig" rid="f6">
<bold>Figure&#xa0;6</bold>
</xref>, MHCC97-H cells were transfected with control, miR-4277, or miR-4277 + CYP3A4<sup>Mut</sup> (the expression vectors of <italic>cyp3a4</italic> with the mutated binding sites of miR-4277). Transfection of miR-4277 inhibited the subcutaneous growth of MHCC97-H cells, and a 0.5 mg/kg dose of sorafenib had no effect (<xref ref-type="fig" rid="f6">
<bold>Figure&#xa0;6</bold>
</xref>). Transfection of miR-4277 enhanced the sensitivity of MHCC97-H cells to sorafenib, whereas CYP3A4<sup>Mut</sup> blocked the effect of miR-4277 (<xref ref-type="fig" rid="f6">
<bold>Figure&#xa0;6</bold>
</xref>).</p>
<fig id="f6" position="float">
<label>Figure&#xa0;6</label>
<caption>
<p>miR-4277 enhances the antitumor effect of sorafenib in a nude mouse model. MHCC97-H cells were transfected with vectors (control miR, miR-4277, or miR-4277 + CYP3A4<sup>Mut</sup>) and subcutaneously injected into nude mice. The mice then received the indicated dose of sorafenib <italic>via</italic> oral administration. The results are shown as tumor images <bold>(A)</bold>, tumor volumes <bold>(B)</bold>, or tumor weights <bold>(C)</bold>. *P &lt; 0.05.</p>
</caption>
<graphic mimetype="image" mime-subtype="tiff" xlink:href="fonc-11-735447-g006.tif"/>
</fig>
<p>The elimination of sorafenib in subcutaneous tumors were also examined to further confirm the effect of miR-4277. As shown in <xref ref-type="table" rid="T4">
<bold>Table&#xa0;4</bold>
</xref>, overexpression of miR-4277 reduced the rates of sorafenib elimination in tumor tissues formed by MHCC97-H cells, and the t<sub>1/2</sub> of sorafenib in these tissues was also decreased. Transfection of CYP3A4<sup>Mut</sup> but not CYP3A4<sup>Mut1</sup> or CYP<sup>Mut2</sup> blocked this effect. These results further confirm the effect of miR-4277 on sorafenib elimination.</p>
<table-wrap id="T4" position="float">
<label>Table&#xa0;4</label>
<caption>
<p>Effect of miR-4277 on the clearance of sorafenib in the subcutaneous tumors formed by MHCC97-H cells.</p>
</caption>
<table frame="hsides">
<thead>
<tr>
<th valign="top" align="left">Groups</th>
<th valign="top" align="center">
<italic>t<sub>1/2</sub>
</italic> of Sorafenib (hours)</th>
</tr>
</thead>
<tbody>
<tr>
<td valign="top" align="left">control miRNA</td>
<td valign="top" align="center">45.68 &#xb1; 5.31</td>
</tr>
<tr>
<td valign="top" align="left">miR-4277</td>
<td valign="top" align="center">72.79 &#xb1; 7.52</td>
</tr>
<tr>
<td valign="top" align="left">miR-4277 + CYP3A4<sup>Mut-1</sup>
</td>
<td valign="top" align="center">52.38 &#xb1; 16.19</td>
</tr>
<tr>
<td valign="top" align="left">miR-4277 + CYP3A4<sup>Mut-2</sup>
</td>
<td valign="top" align="center">48.74 &#xb1; 28.50</td>
</tr>
<tr>
<td valign="top" align="left">miR-4277 + CYP3A4<sup>Mut</sup>
</td>
<td valign="top" align="center">36.67 &#xb1; 12.58</td>
</tr>
</tbody>
</table>
</table-wrap>
</sec>
<sec id="s3_6">
<title>The Endogenous mRNA Level of PXR and CAR in Clinical Specimens</title>
<p>The above results mainly focus on the roles of miR-4277/<italic>cyp3a4</italic> in HCC cells. To further confirm the clinical significance of <italic>cyp3a4</italic>, the expression level of PXR and CAR in HCC clinical specimens was examined by qPCR. As shown in <xref ref-type="fig" rid="f7">
<bold>Figure&#xa0;7</bold>
</xref>, the expression of PXR or CAR were detected in the HCC clinical specimens. The expression level of CAR was also higher than that of PXR (<xref ref-type="fig" rid="f7">
<bold>Figure&#xa0;7</bold>
</xref>). Therefore, the endogenous mRNA level of PXR and CAR are positive in HCC clinical specimens and the compensatory effect between PXR and CAR cannot be ignored.</p>
<fig id="f7" position="float">
<label>Figure&#xa0;7</label>
<caption>
<p>The endogenous expression of PXR or CAR in HCC clinical specimens. The endogenous expression of PXR or CAR in HCC clinical specimens was examined by qPCR. The results were shown as heat-map from the relative expression level (folds of &#x3b2;-Actin).</p>
</caption>
<graphic mimetype="image" mime-subtype="tiff" xlink:href="fonc-11-735447-g007.tif"/>
</fig>
</sec>
<sec id="s3_7">
<title>miR-4277 Also Enhances the Sensitivity of Sorafenib in Some Other HCC Cell Lines</title>
<p>Next, the effect of miR-4277 on sorafenib was examined in some other HCC cell lines. As shown in <xref ref-type="table" rid="T5">
<bold>Table&#xa0;5</bold>
</xref>, transfection with miR-4277 decelerated the metabolism or clearance of sorafenib in HepG2, BEL-7402 or SMMC-7721 cells, and the t<sub>1/2</sub> values of sorafenib increased, respectively (<xref ref-type="table" rid="T5">
<bold>Table&#xa0;5</bold>
</xref>). Moreover, transfection of miR-4277 also enhances the sensitivity of these three HCC cell lines to sorafenib (<xref ref-type="table" rid="T5">
<bold>Table&#xa0;5</bold>
</xref>), and the IC<sub>50</sub> values of sorafenib decreased, respectively (<xref ref-type="table" rid="T5">
<bold>Table&#xa0;5</bold>
</xref>). Transfection of CYP3A4<sup>Mut</sup> almost blocked the effect of miR-4277 on sorafenib&#x2019;s metabolism/clearance rates or the antitumor activation on HCC cells. Therefore, miR-4277 also enhances the sensitivity of sorafenib in some other HCC cell lines by targeting <italic>cyp3a4</italic>&#x2019;s 3&#x2019;UTR.</p>
<table-wrap id="T5" position="float">
<label>Table&#xa0;5</label>
<caption>
<p>The effect of miR-4277 on sorafenib in HCC cells.</p>
</caption>
<table frame="hsides">
<thead>
<tr>
<th valign="top" align="left">Sorafenib on HCC cells</th>
<th valign="top" align="center">Groups</th>
<th valign="top" align="center">HepG2</th>
<th valign="top" align="center">BEL-7402</th>
<th valign="top" align="center">SMMC-7721</th>
</tr>
</thead>
<tbody>
<tr>
<td valign="top" rowspan="3" align="left">t<sub>1/2</sub> values (h)</td>
<td valign="top" align="left">control</td>
<td valign="top" align="center">30.30 &#xb1; 3.31</td>
<td valign="top" align="center">28.20 &#xb1; 8.67</td>
<td valign="top" align="center">25.70 &#xb1; 2.43</td>
</tr>
<tr>
<td valign="top" align="left">miR-4277</td>
<td valign="top" align="center">56.43 &#xb1; 1.90</td>
<td valign="top" align="center">42.40 &#xb1; 3.33</td>
<td valign="top" align="center">46.25 &#xb1; 2.88</td>
</tr>
<tr>
<td valign="top" align="left">miR-4277 + CYP3A4<sup>Mut</sup>
</td>
<td valign="top" align="center">25.74 &#xb1; 4.47</td>
<td valign="top" align="center">26.36 &#xb1; 3.79</td>
<td valign="top" align="center">27.39 &#xb1; 6.93</td>
</tr>
<tr>
<td valign="top" rowspan="3" align="left">IC<sub>50</sub> values (&#x3bc;mol/L)</td>
<td valign="top" align="left">control</td>
<td valign="top" align="center">2.78 &#xb1; 0.59</td>
<td valign="top" align="center">1.79 &#xb1; 0.18</td>
<td valign="top" align="center">1.95 &#xb1; 0.54</td>
</tr>
<tr>
<td valign="top" align="left">miR-4277</td>
<td valign="top" align="center">0.41 &#xb1; 0.07</td>
<td valign="top" align="center">0.28 &#xb1; 0.05</td>
<td valign="top" align="center">0.73 &#xb1; 0.33</td>
</tr>
<tr>
<td valign="top" align="left">miR-4277 + CYP3A4<sup>Mut</sup>
</td>
<td valign="top" align="center">3.56 &#xb1; 0.82</td>
<td valign="top" align="center">2.88 &#xb1; 0.35</td>
<td valign="top" align="center">1.92 &#xb1; 0.55</td>
</tr>
</tbody>
</table>
</table-wrap>
</sec>
<sec id="s3_8">
<title>The Potential Inhibitor of CYP3A4 Enhances the Sensitivity of MHCC97-H Cells to Sorafenib</title>
<p>Furthermore, the effect of potential inhibitors of cyp3a4 were used. As shown in <xref ref-type="table" rid="T6">
<bold>Table&#xa0;6</bold>
</xref>, treatment of 1&#x3bc;mol/L concentration of ketoconazole, amprenavir or diltiazem, decelerated the metabolism or clearance of sorafenib in MHCC87-H cells, and the t<sub>1/2</sub> values of sorafenib increased, respectively (<xref ref-type="table" rid="T6">
<bold>Table&#xa0;6</bold>
</xref>). Treatment of these agents also enhances the sensitivity of MHCC97-H cells to sorafenib (<xref ref-type="table" rid="T6">
<bold>Table&#xa0;6</bold>
</xref>), and the IC<sub>50</sub> values of sorafenib decreased, respectively (<xref ref-type="table" rid="T6">
<bold>Table&#xa0;6</bold>
</xref>). The effect of ketoconazole is much greater than amprenavir or diltiazem. Therefore, the inhibited of CYP3A4 both <italic>via</italic> miR-4277 or inhibitors could enhance the sensitivity of HCC cells to sorafenib.</p>
<table-wrap id="T6" position="float">
<label>Table&#xa0;6</label>
<caption>
<p>The effect of potential inhibitors of CYP3A4 on sorafenib in MHCC97-H cells.</p>
</caption>
<table frame="hsides">
<thead>
<tr>
<th valign="top" rowspan="2" align="left">Cell lines</th>
<th valign="top" colspan="2" align="center">Sorafenib on MHCC97-H</th>
</tr>
<tr>
<th valign="top" align="center">t<sub>1/2</sub> values (h)</th>
<th valign="top" align="center">IC<sub>50</sub> values (&#x3bc;mol/L)</th>
</tr>
</thead>
<tbody>
<tr>
<td valign="top" align="left">Solvent control</td>
<td valign="top" align="center">23.63 &#xb1; 0.70</td>
<td valign="top" align="center">0.68 &#xb1; 0.11</td>
</tr>
<tr>
<td valign="top" align="left">ketoconazole</td>
<td valign="top" align="center">44.17 &#xb1; 2.86</td>
<td valign="top" align="center">0.08 &#xb1; 0.01</td>
</tr>
<tr>
<td valign="top" align="left">amprenavir</td>
<td valign="top" align="center">33.85 &#xb1; 3.92</td>
<td valign="top" align="center">0.42 &#xb1; 0.05</td>
</tr>
<tr>
<td valign="top" align="left">diltiazem</td>
<td valign="top" align="center">37.40 &#xb1; 0.43</td>
<td valign="top" align="center">0.34 &#xb1; 0.10</td>
</tr>
</tbody>
</table>
</table-wrap>
</sec>
</sec>
<sec id="s4" sec-type="discussion">
<title>Discussion</title>
<p>Currently, targeted therapy remains a first-line choice for patients with advanced HCC; however, the overall clinical benefit of these therapies are unsatisfactory (<xref ref-type="bibr" rid="B43">43</xref>&#x2013;<xref ref-type="bibr" rid="B45">45</xref>). It is important to block chemoresistance pathways in HCC to improve sensitivity to targeted agents. Zhu et&#xa0;al. (<xref ref-type="bibr" rid="B14">14</xref>) systematically summarized the possible mechanisms of resistance of HCC cells to sorafenib and discerned the compensatory effects of various signal pathways, including the epithelial-mesenchymal transition and signals from the tumor stem cell environment, may increase resistance to sorafenib (<xref ref-type="bibr" rid="B14">14</xref>). Although studies like these are beneficial to expand our understanding of sorafenib resistance in advanced HCC, several issues persist. The liver is the body&#x2019;s regulatory center for exogenous metabolism and clearance (<xref ref-type="bibr" rid="B46">46</xref>, <xref ref-type="bibr" rid="B47">47</xref>). HCC arises from hepatocytes, and the metabolism and clearance of exogenous agents may be specific to the ability of HCC cells to tolerate sorafenib (<xref ref-type="bibr" rid="B18">18</xref>, <xref ref-type="bibr" rid="B19">19</xref>). Feng et&#xa0;al. (<xref ref-type="bibr" rid="B18">18</xref>) showed that sorafenib can function as a ligand/agonist to induce PXR transcription factor activity and accelerate the metabolism and clearance rate of sorafenib. It does this by inducing the expression of drug resistance genes downstream of PXR, such as <italic>cyp3a4</italic> or <italic>abcb1</italic> (ATP-binding cassette, sub-family B, member 1), and through a similar negative feedback mechanism that induces resistance of HCC cells to sorafenib itself. This means that HCC patients with high background expression levels of PXR may not be sensitive to sorafenib (<xref ref-type="bibr" rid="B18">18</xref>). With long-term treatment, sorafenib can also induce the activity of PXR in HCC cells and the expression of drug-resistant genes, which ultimately leads to multidrug resistance (<xref ref-type="bibr" rid="B18">18</xref>). CYP3A4 is an important regulator of sorafenib metabolism and clearance in HCC cells as it can mediate the oxidative metabolism of sorafenib (<xref ref-type="bibr" rid="B48">48</xref>). Our study identified that a microRNA that can act on the 3&#x2019;UTR of <italic>cyp3a4</italic>: miR-4277. We found that it could down-regulate the expression levels of CYP3A4 in HCC cells, reduce elimination of sorafenib, and ultimately enhance the sensitivity of HCC cells to sorafenib. Therefore, miR-4277 and <italic>cyp3a4</italic> represent ideal targets that can be modulated to overcome the resistance of HCC cells to targeted therapy. Our results also showed that the potential inhibitors of CYP3A4 had the similar effect of miR-4277 on sorafenib in HCC cells. The effect of ketoconazole is significantly stronger than amprenavir or diltiazem (<xref ref-type="bibr" rid="B49">49</xref>&#x2013;<xref ref-type="bibr" rid="B55">55</xref>). Since ketoconazole is also considered to be an inhibitor of PXR, this needs to be discussed in depth.</p>
<p>The transcription of <italic>cyp3a4</italic> is mainly mediated by PXR, but it can also regulated by CAR (<xref ref-type="bibr" rid="B56">56</xref>&#x2013;<xref ref-type="bibr" rid="B58">58</xref>). In cancerous cells, particularly in HCC, the activity of PXR may also be compensated by CAR. Using miRNA or PXR antagonists alone to down-regulate the activity of PXR may be an inefficient method of fully blocking the resistance of malignant tumor cells to anti-tumor agents. CAR can also induce the resistance of tumor cells to anti-tumor agents. Wang et&#xa0;al. (<xref ref-type="bibr" rid="B20">20</xref>) previously used miR-4271 to down-regulate the expression levels of CAR, which significantly enhanced the sensitivity of tumor cells to anlotinib (<xref ref-type="bibr" rid="B20">20</xref>). Our results also examined the expression of PXR and CAR in HCC&#x2019;s clinical specimens. Therefore, we selected CYP3A4 in our study to avoid the compensation effects of PXR and CAR in HCC cells.</p>
<p>miRNA is an important type of non-coding RNA that induces the post-transcriptional silencing of target genes&#x2019; expression in a sequence-specific manner by targeting the 3&#x2019;UTR (<xref ref-type="bibr" rid="B26">26</xref>). This feature makes miRNA an ideal strategy for anti-tumor gene therapy; tumors can be treated by cloning the full pre-miRNA sequence into a vector and delivering it in lentiviral particles (<xref ref-type="bibr" rid="B26">26</xref>). Transfection of lentiviral particles into tumor cells or <italic>via</italic> intratumor tissue injection can down-regulate the expression levels of certain oncogenes (<xref ref-type="bibr" rid="B26">26</xref>). Li et&#xa0;al. (<xref ref-type="bibr" rid="B59">59</xref>), Yang et&#xa0;al. (<xref ref-type="bibr" rid="B60">60</xref>), and Li et&#xa0;al. (<xref ref-type="bibr" rid="B61">61</xref>) showed that miR-140-3p, miR-30c, and miR-148a can inhibit the expression of PXR and CYP3A4, respectively, by acting on the 3&#x2019;UTR of PXR and reduce the elimination of anti-cancer agents in tumor cells. Our study used an online tool to identify miR-4277 as a regulator of <italic>cyp3a4</italic> expression. This miRNA had the highest score among all miRNAs tested from the miRDB database. We then constructed mutants to confirm the effect of miR-4277 on <italic>cyp3a4</italic>. Transfecting HCC cells with miR-4277 decreased the expression levels of CYP3A4 and enhanced the sensitivity of HCC cells to targeted agents. Besides miR-4277, there are also some other miRNAs could target to <italic>cyp3a4</italic>. Ekstr&#xf6;m et&#xa0;al. (<xref ref-type="bibr" rid="B62">62</xref>), Tang et&#xa0;al. (<xref ref-type="bibr" rid="B63">63</xref>), Gill et&#xa0;al. (<xref ref-type="bibr" rid="B64">64</xref>), Huang et&#xa0;al. (<xref ref-type="bibr" rid="B65">65</xref>), Li et&#xa0;al. (<xref ref-type="bibr" rid="B66">66</xref>) and Zastrozhin et&#xa0;al. (<xref ref-type="bibr" rid="B67">67</xref>) suggested that the miR-27 family, miR-142, miR-200a, miR-150 or miR-328 could targets to <italic>cyp3a4</italic> (<xref ref-type="bibr" rid="B62">62</xref>&#x2013;<xref ref-type="bibr" rid="B67">67</xref>). Therefore, our results extended the knowledge of miRNAs on <italic>cyp3a4</italic>.</p>
<p>It is worth mentioning that in our study, elimination of sorafenib was measured <italic>via</italic> LC-MS/MS. We observed that miR-4277 could prolong the half-life of sorafenib in HCC cells and tissues and reduce its elimination. Several other targeted agents were tested for their ability to kill HCC cells; however, we failed to detect the presence of these agents in HCC cells, mainly due to the lack of efficient protocols for assessing the levels of the compounds. In the future, LC-MS/MS methodology for these and other targeted agents will likely be established well enough to determine the effect of miR-4277 on their elimination rate in HCC cells.</p>
<p>Furthermore, Drug interactions mediated by CYP3A4 are not only closely related to clinical treatment and drug contraindications, but also an important mechanism of anti-tumor drug resistance (<xref ref-type="bibr" rid="B68">68</xref>, <xref ref-type="bibr" rid="B69">69</xref>). CYP3A4 is not only closely related to the metabolism and drug resistance of cytotoxic chemotherapy agents such as paclitaxel and camptothecin, but also closely related to the metabolism and drug resistance of molecularly targeted agents such as Imatinib, Gefitinib and Pazopanib (<xref ref-type="bibr" rid="B70">70</xref>&#x2013;<xref ref-type="bibr" rid="B75">75</xref>). Therefore, the results of this study can be extended to other types of malignant tumor molecular targeted therapy in the future.</p>
</sec>
<sec id="s5">
<title>Data Availability Statement</title>
<p>The original contributions presented in the study are included in the article/<xref ref-type="supplementary-material" rid="SM1">
<bold>Supplementary Material</bold>
</xref>. Further inquiries can be directed to the corresponding authors.</p>
</sec>
<sec id="s6">
<title>Ethics Statement</title>
<p>The studies involving human participants were reviewed and approved by the ethics committee of the Fifth Medical Center, General Hospital of Chinese PLA. The patients/participants provided their written informed consent to participate in this study. The animal study was reviewed and approved by the Institutional Animal Care and Use Committee, the Fifth Medical Center, Chinese PLA.</p>
</sec>
<sec id="s7">
<title>Author Contributions</title>
<p>SX, JH, and BL conceived the main ideas and wrote the paper. XL, BZ, and ZW supervised the study. XH, HS, QJ, YC, and SY developed major methodologies, databases, reagents, and primary experiments. XH, HS, and QJ analyzed different aspects of the results. All authors contributed to the article and approved the submitted version.</p>
</sec>
<sec id="s8">
<title>Funding</title>
<p>This work is supported by National Science and Technology Major Project of China, Chinese Government, Chinese Government (new techniques and new schemes for clinical treatment of severe hepatitis B [liver failure]; NO 2017ZX10203201004).</p>
</sec>
<sec id="s9" sec-type="COI-statement">
<title>Conflict of Interest</title>
<p>The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.</p>
</sec>
<sec id="s10" sec-type="disclaimer">
<title>Publisher&#x2019;s Note</title>
<p>All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.</p>
</sec>
</body>
<back>
<ack>
<title>Acknowledgments</title>
<p>Authors all deeply thanks Prof. and Dr. Shuang Cao in Wuhan Institute of Technology.</p>
</ack>
<sec id="s11" sec-type="supplementary-material">
<title>Supplementary Material</title>
<p>The Supplementary Material for this article can be found online at: <ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fonc.2021.735447/full#supplementary-material">https://www.frontiersin.org/articles/10.3389/fonc.2021.735447/full#supplementary-material</ext-link>
</p>
<supplementary-material xlink:href="Table_1.doc" id="SM1" mimetype="application/msword"/>
</sec>
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