Abstract 2679: Combination of CDK 4/6 inhibitor palbociclib with rapamycin synergistically inhibits growth of hepatocellular carcinoma in preclinical models
Authors: Tiwari Ankur , Huerta Araceli , Bouamar Hakim , Das Debodipta , Cigarroa Francisco , Sun LuZhe 
Published: April 2023

Abstract
Introduction: The cell cycle inhibitor palbociclib has been shown to have a cytostatic effect on hepatocellular carcinoma (HCC) cells via the induction of quiescence and senescence, though it has limited cytocidal effect. We hypothesized that arrested HCC cells upregulate mTOR signaling to stay metabolically active and investigated the effect of combining palbociclib with the mTOR inhibitor rapamycin on preclinical models of HCC.
Methods: We identified commonly altered molecular markers in HCC, including cell cycle related genes, using single sample gene set enrichment analysis (ssGSEA) of 13 paired (tumor and adjacent non-tumor) RNA-seq and 15 paired proteomic data sets as well as 50 paired RNA-seq data sets from TCGA. Subsequently, we studied the in-vitro effects of palbociclib and rapamycin by evaluating induction of senescence, inhibition of cell growth with fixed ratio combination treatment as well as Western Blotting to establish mechanistic effects. We tested the in-vivo anti-tumor efficacy of palbociclib plus rapamycin in athymic nude mice with growing xenograft tumors. We then generated immunocompetent murine HCC models using hydrodynamic transfection of oncogenes ΔN90-β-catenin and c-Met, and measured plasma AFP levels as a marker of HCC to assess the efficacy of treatment with palbociclib and/or rapamycin.
Results: ssGSEA revealed significant positive enrichment of several cell cycle related gene sets in all our HCC cases. Palbociclib treatment in vitro showed an increase in senescence associated β-galactosidase staining as well as increased levels of intrinsic CDK inhibitors p16, p15, p21 and p27, indicating senescence. Fixed ratio treatment with palbociclib and rapamycin established a synergistic interaction between the drugs, as indicated by a combination index of less than 1. We also observed an increase in levels of proteins of the mTOR pathway (p-mTOR, p-4eBP1, p-p70 and p-s6) after palbociclib treatment, followed by suppression of the levels on addition of rapamycin. In the xenograft HCC model, combination treatment with palbociclib and rapamycin resulted in slower tumor growth and significantly increased time to critical tumor volume (2000 mm3) (log rank, p &lt;0.001). In the hydrodynamic transfection HCC model, we observed a significantly lower mean AFP level in the combination treatment group, along with lower liver weights which were closer to the liver weights of normal mice.
Conclusion: HCC cells overexpress genes and proteins that drive cell cycle progression. Palbociclib induces senescence in HCC cells along with an associated upregulation in mTOR signaling, and combination with rapamycin has a synergistic effect on inhibition of tumor growth in vitro as well as in vivo, possibly by abrogating both actively growing and quiescent/senescent HCC cells. The combination of the two drugs may have potential as a novel therapy for HCC.
Citation Format: Ankur Tiwari, Araceli Huerta, Hakim Bouamar, Debodipta Das, Francisco Cigarroa, LuZhe Sun. Combination of CDK 4/6 inhibitor palbociclib with rapamycin synergistically inhibits growth of hepatocellular carcinoma in preclinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2679.