Abstract 6386: Combined PDE4 and VEGFR2 inhibition as a new preclinical rationale in clear cell renal cell carcinoma

Clear cell renal cell carcinoma (ccRCC) is the most lethal form of kidney cancer. Small molecule VEGFR inhibitors are widely used but are not curative and various resistance mechanisms have been described. Previous studies have indicated cross-talk between the cAMP pathway and the MAPK pathway, and the elevation of cAMP levels by inhibition of Phosphodiesterase-4 (PDE4) activities can result in growth arrest and/or cell death. In this study we focused on the effects of PDE4 in ccRCC. We first analyzed the expression of PDE4 in human RCC cell lines and found PDE4D to be dominantly expressed. PDE4D CRISPR Knockout (KO) was then performed on Caki-1 RCC cells and normal renal proximal tubular epithelial cells as control. Cell proliferation, cell cycle cAMP, MAPK plus PI3K/AKT signaling pathways were additionally analyzed to define the effects of PDE4D inhibition. PDE4D KO Caki-1 cells showed decreased cell viability and a higher apoptosis rate compared with wild type controls. Increased intracellular cAMP levels in PDE4D KO resulted in downregulated MAPK but not PI3K/AKT signaling in Caki-1 tumor cells. In addition, PDE4D KO Caki-1 cells demonstrated higher sensitivity to VEGFR inhibitors. To conclude, we provide a new preclinical rationale for dual PDE4/VEGFR2 inhibition in patients with ccRCC. While the MAPK signaling pathway is activated in ccRCC, dual inhibitors may improve the anti-tumor effects in a patient subset with evidence of MAPK involvement. Future work involving in vivo models will be useful to better define efficacy of this dual strategy of anti-tumor activity. Citation Format: Minghua Cao, Karol Nawalaniec, Yueming Luo, Romana Moench, Li-Li Hsiao, Ana Maria Waaga-Gasser. Combined PDE4 and VEGFR2 inhibition as a new preclinical rationale in clear cell renal cell carcinoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6386.