Dual Inhibition of CDK4/6 and mTORC1 Establishes a Preclinical Strategy for Translocation Renal Cell Carcinoma

Purpose: Translocation renal cell carcinoma (tRCC) is a rare and aggressive subtype of kidney Cancer driven by an oncogenic fusion involving a transcription factor in the MiT/TFE gene family, most commonly TFE3 . Treatment of tRCC currently lacks a clear standard of care, underscoring the pressing need to nominate new therapeutic targets with mechanistic rationale in this Cancer.

Experimental design: In this study, we applied integrative genomic approaches to identify activation of the cyclin-dependent kinase 4/6 (CDK4/6) and mammalian target of rapamycin complex 1 (mTORC1) pathways in tRCC. We tested the activity of CDK4/6 inhibitors (CDK4/6i), alone or in combination with mTORC1-selective inhibition, using in vitro and in vivo models of tRCC.

Results: tRCC tumors displayed multiple genomic and transcriptional features associated with activation of the CDK4/6 and mTORC1 signaling pathways. Genetic or pharmacologic inhibition of CDK4/6 suppressed tRCC cell growth and induced cell cycle arrest in vitro but was not cytotoxic, with rapid cell regrowth observed after drug withdrawal. The mTORC1-selective inhibitor, RMC-5552, potently reduced translation of Cyclin D1, which complexes with CDK4/6 proteins to regulate G1-S cell cycle progression. Combined treatment with the CDK4/6 inhibitor, palbociclib, and RMC-5552 resulted in synergistic suppression of tRCC cell viability and increased markers of Apoptosis in vitro . The combination of palbociclib and RMC-5552 in a tRCC xenograft model showed greater eOicacy than either single agent while also being well-tolerated.

Conclusions: Our study indicates the therapeutic potential of combined CDK4/6 and mTORC1 inhibition in tRCC, providing the rationale for further clinical evaluation of this strategy.

Translational relevance: Translocation renal cell carcinoma (tRCC) is a rare and aggressive form of kidney Cancer that accounts for 2-5% of all RCCs in adults and around 50% of RCCs in children. tRCC lacks effective therapies and represents a significant unmet clinical need. Therapies approved for clear cell RCC (ccRCC), including VEGF/multikinase inhibitors and immune checkpoint blockade, typically show decreased efficacy in tRCC. Via an integrative genomic analysis, we nominate combined inhibition of the cyclin-dependent kinase 4/6 (CDK4/6) and mammalian target of rapamycin complex 1 (mTORC1) pathways in tRCC. We demonstrate that combining the CDK4/6 inhibitor palbociclib with the mTORC1-selective inhibitor RMC-5552 synergistically inhibits the growth of tRCC cells in vitro and of tRCC xenografts in vivo , where the combination is well-tolerated. This proof-of-concept study provides preclinical evidence supporting CDK4/6 inhibitor-based combination regimens tailored to tRCC biology, offering a foundation for future clinical studies in tRCC, which currently has no clear standard of care.