In the United States, renal cell cancer (RCC) is the ninth most common cancer with very poor five-year survival rates in patients diagnosed with the metastatic stage of the disease. In advanced RCC patients, tyrosine kinase inhibitors (TKIs) remain as the first line of treatment, however development of resistance to TKIs is a major barrier to therapeutics. To circumvent this barrier, novel molecules that can act as actionable targets need to be identified to inhibit renal carcinogenesis. Among other oncogenic proteins that promote RCC development, CDC-like kinases (CLKs) play an important role in renal oncogenesis. However, there is a research gap in this field since the role of CLK inhibitors in targeting renal oncogenesis have not yet been investigated.
In the context of renal cancer, increased CLK1 mRNA levels have been observed in tumors of RCC patients and is associated with poor disease prognosis. Therefore, there is an urgent need to target CLKs by developing small molecules that can potently inhibit RCC oncogenesis. This study has identified novel 3H- pyrazolo[4,3-f]quinoline-scaffold containing compounds, HSD1400 and HSD1995 with potent activity against CLKs. NCI cell line screen revealed that the compounds are highly sensitive to Caki-1 cells. Structure activity relationship study of HSD1400 analogs against Caki-1 revealed that HSD1791, the methyl analog of HSD1400 has greater selectivity towards CLK inhibition. COMET results indicate that HSD1400 promotes DNA damage in Caki-1. Western assay confirmed induction of DNA damage by HSDs1400, 1995 and 1791. Flow cytometry results indicated that the lead compound, HSD1791 induced cell cycle arrest in Caki-1. Moreover, cyclin D1 mRNA expression and pRb protein levels is reduced upon HSD1791 treatment, indicating that cyclin D1-CDK4/6 pathway is inhibited resulting in cell cycle arrest. In conclusion, the study has identified novel CLK inhibitors that can act as potential drug candidates in RCC therapeutics.

Riddhi Chaudhuri

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