Mechanism-Driven Development of CDK2/4/6 Inhibitors to Combat Resistance and Broaden the Clinical Reach of CDK Inhibitors - Project summary This proposal seeks to develop a therapeutic strategy for cancer treatment by simultaneously inhibiting cyclin- dependent kinases (CDKs) 2, 4, and 6. These kinases regulate cell cycle progression, and their dysregulation drives tumor growth and resistance to therapy. CDK4/6 inhibitors are FDA-approved for metastatic breast cancer and prolong progression-free survival; however, about 20% of patients fail to respond to these agents from the outset, and virtually all patients eventually develop resistance. A key mechanism of resistance is compensatory activation of CDK2, which bypasses CDK4/6 inhibition. Conversely, selective CDK2 inhibition alone is insufficient because CDK4/6 can substitute for CDK2 function. Simultaneous inhibition of CDK2 and CDK4/6 therefore represents a rational approach to overcome resistance and extend therapeutic benefit across cancers. Novel thiazolyl-pyrimidine compounds have been discovered and patented that selectively inhibit CDK2/4/6 while sparing essential kinases such as CDK1, CDK7, and CDK9. Unlike current CDK4/6 inhibitors, which leave CDK2 activity intact, this new class directly targets the cooperative functions of CDK2/4/6. Preliminary studies demonstrate that these compounds suppress proliferation of breast cancer and leukemia cells, indicating proof- of-concept activity. Their selectivity profile also suggests reduced toxicity compared to earlier multi-CDK inhibitors. Our central hypothesis is that the thiazolyl-pyrimidine scaffold provides a structural framework that enables selective targeting of CDK2/4/6, and that its rational multiparameter optimization leads to development candidates capable of overcoming resistance to existing CDK4/6- or CDK2-selective inhibitors and expand the therapeutic reach of CDK inhibition to cancers driven by CDK2. To test this hypothesis, aim 1 will define mechanisms of action through kinase profiling, cell viability and apoptosis assays, and resistance modeling in breast and ovarian cancer. Aim 2 will focus on medicinal chemistry to identify analogs with improved potency, selectivity, and drug-likeness and safety. Compounds will undergo in vitro biochemical characterization, cellular efficacy testing, and absorption, distribution, metabolism, and toxicity evaluations. Beyond direct therapeutic impact, this work addresses a significant gap in cancer pharmacology by providing chemical probes to interrogate CDK2/4/6 biology and mechanisms of resistance. Equally important, the research will enhance the research capacity of Idaho State University, the only provider of graduate education in pharmaceutical sciences in the state, where opportunities for biomedical research are limited. The SuRE-First (R16) program will strengthen this under-resourced environment by supporting the development of next-generation CDK inhibitors while directly involving students in experimental design, laboratory assays, and data analysis. Participation in these studies will provide first-generation and rural students with hands-on training, mentorship, and dissemination opportunities at conferences, preparing them for advanced careers in biomedical science.
