Abstract 3241: IC50-Seeding Density Slope (ISDS)-measurement as a standardized methodology for assessing anti-cancer therapeutic activity in vitro

Abstract

Abstract The 50% inhibitory concentration (IC50) is a widely used measure of how effective a given anti-cancer therapeutic is at reducing cancer cell viability in vitro. It is known that IC50 of a given therapeutic agent is dependent on the seeding density of the treated cells (in that more densely-seeded cells tend to be more resistant to therapeutic agents). We performed experiments using the CellTiter Glo cell viability assay to assess the cytotoxicity of various chemotherapeutic drugs towards various cancer cell lines. To elucidate the role the extracellular environment of densely-seeded cells plays in cancer cell chemoresistance, we tested conditioned media from cells cultured at high density on cells seeded at low densities. The resulting impact on the IC50 of the low-density cells was determined. The IC50 of the various therapeutic agents tested was cell density-dependent in each cancer cell line examined. Based on this analysis, we propose the IC50-seeding density slope (ISDS), which relates seeding density to the effectiveness of a drug and that we believe could be a standardized quantitative measurement of how a given cancer cell line responds to a given therapeutic treatment. Our results from the conditioned media experiments consistently indicated that the environment of densely-seeded tumor cells conferred chemoresistance to sparsely-seeded cells, suggesting that extracellular cytokines and growth factors may be involved in density-dependent chemoresistance mechanisms. We are currently exploring the effect of serum deprivation on in vitro chemoresistance, in order to further understand how the presence of extracellular nutrients impacts observed IC50 trends. In addition, we are examining the role that cell-cell contact, integrin and FGF signaling pathways play in giving rise to density-dependent chemoresistance. Moreover, to analyze the manner in which conditioned media gives rise to chemoresistance and how this effect relates to intracellular survival pathways, we are performing cytokine profiling experiments. Overall, we describe density-dependent IC50 variations as a hallmark of cancer cells and propose that ISDS may serve as a standardized method of assessing chemosensitivity. Citation Format: Ujwal Punyamurtula, Shengliang Zhang, Thomas Brown, Arielle De La Cruz, Alexander Raufi, Jillian Strandberg, Lindsey Carlsen, Lanlan Zhou, Wafik El-Deiry. IC50-Seeding Density Slope (ISDS)-measurement as a standardized methodology for assessing anti-cancer therapeutic activity in vitro [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3241.