Abstract 99: Phenotypic characterization of knockdown of CDKs in the intestinal epithelial cells

Cyclin-dependent kinases (CDKs) are serine/threonine kinases that bind to cyclins and together act as regulators of cell cycle progression. CDK inhibitors have various therapeutic potentials including cancer (e.g. CDK4/6 inhibitors). Intestinal epithelial cells are highly proliferative; however, the impact of individual CDK inhibition on intestinal cell proliferation has not been well studied. The IEC6 cell line, a non-transformed rat small intestinal epithelial cell line with characteristics of crypt epithelial cells, was utilized in the current study to understand the role of CDKs in the proliferation and survival of intestinal cells. In the initial experiment CDK4/6 inhibitor palbociclib treatment demonstrated a lack of potent toxicity in the IEC6 in comparison with MCF7 (breast cancer cell line), indicating the absence of intestinal cell reliance on CDK4 or CDK6 for cell cycle progression. To further illustrate the role of CDKs in intestinal cells, targeted gene knockdown experiments using CDK1, 2, 4, and 6 siRNA and lipofectamine-mediated transfection were conducted. Surprisingly, only CDK1 knockdown causes profound cell death. CDK2, 4, or 6 knockdowns, whether single, double or triple combinations, did not have significant impact on IEC6 cells, as measured by multiple endpoints including impedance, ATP viability, and caspase activity. To further understand the role of CDK1 in cell cycle, various seeding densities of IEC6 cells were used with CDK1 siRNA. Although the impact of CDK1 knockdown on IEC6 cells decreased at the initial proliferation phase with the higher seeding density, there was still a decrease of viability observed at the later time point (when cells reached proliferation plateau), indicating a non-canonical role of CDK1 that is not related to cell cycle. This research supports the concept that CDK1, but not CDKs 2, 4, or 6, is essential for intestinal cell cycle progression and explains the lack of GI toxicity observed with palbociclib. Citation Format: Shuyan Lu, Wenyue Hu, Tae Sung, Brad Hirakawa, Marina Amaro, Bart Jessen. Phenotypic characterization of knockdown of CDKs in the intestinal epithelial cells [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 99.