Casein kinase 1 (CK1) has emerged as a promising target for cancer therapy, with growing evidence linking its altered expression and activity to carcinogenesis and cancer progression (1–6). CK1 belongs to a distinct subgroup of the family of Ser/Thr protein kinases, comprising six isoforms in humans: CK1α, γ1, γ2, γ3, δ, and ϵ. It functions as an autonomous monomeric enzyme, independent of cofactors, and its activity can be regulated by the autophosphorylation of carboxyterminal residues (7, 8).

CK1 plays a crucial role in various cellular processes, including the regulation of cell, survival/apoptosis signaling pathways, and cell division (9). Notably, CK1 isoforms have been associated with cell cycle progression (10), chromosome segregation (11), apoptosis (12), DNA repair (13), the circadian rhythm (14), ribosome biogenesis (15), vesicle trafficking (16), and modulation of signaling pathways such as p53 (7), Wnt, Shh (5), and Hippo (17). Recent advances in our understanding of CK1 have shed light on its involvement in protein phosphorylation processes and its impact on signaling pathways mediated by the epidermal growth factor receptor, estrogen receptor, G protein-coupled estrogen receptor (10). Targeting CK1 holds significant promise as a therapeutic strategy for cancer treatment.

The aim of this review is to provide a comprehensive overview of the current strategies employed in targeting CK1 for cancer therapy. It will explore different approaches, including small-molecule inhibitors, RNA interference (RNAi), and immunotherapies. Additionally, it will discuss the challenges associated with the targeting of CK1 and highlight future perspectives in this field. By elucidating the current state of CK1-targeted cancer therapies and outlining potential future directions, this review aims to contribute to the advancement of effective and innovative strategies for cancer treatment.

CK1 isoforms, including CK1α, CK1δ, CK1ϵ, and CK1γ, play diverse roles in cancer development and progression (7) ( Figure 1 ). Dysregulation of these isoforms contributes to various cancer-related processes, including Wnt/β-catenin signaling, disruption of the circadian rhythm, DNA repair, cell cycle progression, and stability of oncogenic proteins. Targeting specific CK1 isoforms represents a promising avenue for the development of novel anti-cancer agents.

RNA interference (RNAi) has emerged as a powerful tool for silencing specific genes, including CSNK1, offering a potential therapeutic avenue for cancer treatment. RNAi-based approaches utilize small RNA molecules, such as small interfering RNAs (siRNAs) or short hairpin RNAs (shRNAs), to specifically target and degrade CSNK1 mRNA, thereby reducing the expression of CK1 protein.

The application of RNAi-based approaches to inhibit CSNK1 has several advantages. First, it enables precise and selective targeting of CSNK1, allowing isoform-specific down-regulation. This isoform specificity is crucial, as different CSNK1 isoforms may have distinct functions and contributions to tumorigenesis in diverse types of cancer ( Figure 2 ). By selectively silencing specific isoforms, RNAi-based strategies can effectively disrupt CK1-mediated signaling pathways implicated in cancer progression (46). Second, RNAi-based approaches offer the potential for systemic administration and broad delivery to various tumor sites. The development of efficient delivery systems, such as nanoparticles or viral vectors, has improved the delivery and stability of RNAi molecules, enabling their effective transport to tumor cells (47, 48). This systemic delivery approach enhances the feasibility and applicability of RNAi-based therapeutics for the inhibition of CSNK1 in cancer treatment (49). Moreover, the combinatory potential of RNAi-based approaches with other treatment modalities holds promise for enhanced therapeutic efficacy. By targeting CSNK1 along with other key signaling molecules or pathways, synergistic effects may be achieved, leading to more profound and sustained anti-tumor responses. Additionally, combining RNAi-based approaches with conventional chemotherapy, radiotherapy, or targeted therapies will potentially overcome drug resistance and improve treatment outcomes.

However, several challenges need to be addressed to fully exploit the potential of RNAi-based approaches for the inhibition of CSNK1 in cancer therapy. Efficient delivery of RNAi molecules to tumor cells while minimizing off-target effects remains a critical hurdle. Further optimization of delivery systems, including improving stability, cellular uptake, and intracellular localization, is necessary. Furthermore, the identification of reliable and predictive biomarkers for patient stratification and monitoring of treatment response is essential for the successful implementation of RNAi-based therapies. Biomarkers that can indicate CK1 expression levels, isoform-specific alterations, or downstream pathway activity will facilitate personalized treatment strategies and improve patient outcomes.

In addition to RNAi-based approaches, the use of genome editing technologies, such as CRISPR/Cas9, holds immense potential for targeted modifications of the CSNK1 gene. The remarkable efficiency and simplicity of CRISPR/Cas9 enable precise DNA cleavage at specific sites within the CSNK1 gene, facilitating the manipulation of CK1 expression and function with high precision. By introducing double-stranded breaks, CRISPR/Cas9 enables targeted gene disruption, knockout, or insertion of specific sequences to modulate CSNK1 expression or function (50). Similarly, zinc finger nucleases (ZFNs), transcription-activator-like effector nucleases (TALENs) (51), Homing Endonucleases (52), and CRISPR-Cpf1 (53) offer alternative platforms for site-specific DNA cleavage and gene editing, allowing precise modifications of the CSNK1 gene.

These genome editing technologies will provide opportunities to investigate the functional consequences of CSNK1 modulation and uncover the intricate roles of CK1 in cancer development and progression. By introducing specific mutations or alterations in CSNK1, researchers will be able to elucidate the impact of these modifications on downstream signaling pathways and cellular processes involved in cancer. In addition, these techniques will enable the exploration of potential therapeutic targets and the development of personalized treatment strategies based on specific genetic alterations of CSNK1.

Although the roles of CK1 in immunology are not yet fully understood, it is increasingly recognized that CK1 plays a significant role in the modulation of immune responses, particularly through its involvement in the Wnt signaling pathway (7, 29, 40, 54, 55). This emerging knowledge presents an exciting opportunity to explore the potential of developing immunotherapeutic approaches targeting CK1.

The Wnt signaling pathway is known to be critical in various aspects of the regulation of immune responses, including T cell development, differentiation, and activation (56–58). CK1, as a key regulator of the Wnt pathway, influences immune cell function and can impact the outcome of immune responses (59). Therefore, investigating the precise role of CK1 in immune regulation and exploring its potential as a target for immunotherapy holds great promise. Immunotherapies targeting CK1 could offer novel strategies to modulate immune responses in the context of cancer and other immune-related diseases (39). By selectively targeting CK1, it may be possible to manipulate the Wnt signaling pathway and enhance immune cell activation or suppress immune tolerance mechanisms, leading to improved anti-tumor or immune modulatory effects.

Immunotherapies targeting CK1 have several advantages. They have high specificity, allowing for selective targeting of CK1 overexpressing tumors while sparing healthy tissues. Immunotherapies can also elicit potent and durable anti-tumor responses, providing long-term control of cancer progression. In addition, they offer the possibility of systemic treatment, enabling the eradication of both primary and metastatic tumors. However, several challenges need to be addressed to optimize immunotherapies targeting CK1. One key challenge is identifying reliable biomarkers that accurately predict CK1 expression or isoform-specific alterations in tumors. These biomarkers will aid in patient selection, treatment stratification, and monitoring of therapy response. Additionally, overcoming the immunosuppressive tumor microenvironment is crucial to achieving successful immunotherapy. Strategies to improve T cell infiltration, modulate immune checkpoints, or reprogram the tumor microenvironment to promote immune responses are actively being explored.

Additional research is needed to elucidate the specific functions of CK1 in immune cells and to understand its intricate involvement in the regulation of the immune response. This knowledge will guide the development of innovative immunotherapeutic approaches, such as CK1 inhibitors or CK1-specific antibodies, which can selectively modulate CK1 activity in immune cells.

One major challenge is the isoform-specific targeting of CK1. As different CK1 isoforms can have distinct functions and contributions to tumorigenesis, it is crucial to develop strategies that selectively inhibit isoforms involved in relevant to specific types of tumors. This requires a deeper understanding of the isoform-specific roles of CK1 in different cancers and the development of selective inhibitors or modulators for each isoform. Another challenge lies in the development of effective delivery systems for CK1-targeted therapies. Efficient delivery to tumor cells while minimizing off-target effects is critical to therapeutic success. Further advancements in delivery technologies, such as the development of nanoparticle-based systems or targeted drug delivery approaches, are necessary to ensure the precise and effective delivery of CK1 inhibitors to tumor tissues.

Combination therapies involving CK1 inhibitors or immunotherapies with other treatment modalities can enhance therapeutic efficacy and overcome resistance mechanisms. Combining CK1-targeted therapies with conventional chemotherapy, radiotherapy, immune checkpoint inhibitors, or other targeted agents can synergistically inhibit multiple signaling pathways and improve anti-tumor immune responses. Rational design and optimization of combination regimens that rely on mechanistic insights and preclinical studies will be crucial to harnessing the full potential of CK1-targeted therapies in the clinic.

The identification of predictive biomarkers is essential for optimal patient selection and treatment monitoring in CK1-targeted therapies. Biomarkers can help stratify patients who are most likely to benefit from CK1 inhibitors or immunotherapies and provide information on response and treatment resistance. Potential biomarkers may include the determination of CK1 expression, isoform-specific signatures, or alterations in downstream signaling molecules. The development of robust and reliable biomarkers through comprehensive genomic profiling, proteomic analyses, or non-invasive imaging techniques will facilitate personalized treatment strategies and improve patient outcomes.

Looking ahead, the future perspectives of targeting CK1 for cancer therapy appear to be promising. Continued research efforts are required to deepen our understanding of the intricate mechanisms underlying CK1 dysregulation in cancer and its crosstalk with other signaling pathways. This will enable the identification of new therapeutic targets and the development of innovative strategies to overcome treatment resistance and improve patient outcomes.

While the pursuit of CK1 as a therapeutic target in cancer therapy holds great promise, it confronts noteworthy challenges. A pivotal obstacle lies in the imperative need for isoform-specific targeting of CK1. Given the divergent functionalities of distinct CK1 isoforms and their variable contributions to tumorigenesis, the development of strategies that can selectively inhibit isoforms relevant to specific tumor types becomes imperative. Moreover, the specter of undesired side effects, off-target repercussions, and the emergence of drug resistance looms as potential impediments in CK1-targeted therapy. In response to these challenges, RNAi-based and genome editing approaches emerge as valuable strategies. These methodologies have demonstrated their utility by enriching our comprehension of the pathological intricacies pervasive across various malignancies, and they have excelled in uncovering novel drug targets and elucidating the molecular underlying the adaptive responses following kinase inhibition. Although it is undeniably formidable, with continued research and development, the potential of CK1-targeted therapies can be harnessed to improve patient outcomes and contribute to the evolving landscape of cancer therapies.

LNH: conceptualization, investigation, and writing – original draft. S-JL: project administration, resources, supervision, and writing – review & editing. All authors contributed to the preparation of the article and have approved the submitted version.