Abstract 47: A cell culture model of resistant cells in solid cancers that opportunistically switch between proliferation and quiescence
Authors: Singh Balraj , Sarli Vanessa N. , Lucci Anthony 
Published: April 2023

Abstract
Most cancer therapies inhibit proliferating cancer cells. A small subpopulation of cancer cells that survives by reversibly switching to quiescence, is often responsible for relapse/metastasis. Our goal is to model this resistant phenotype in cell culture, i.e., an ability to opportunistically switch between proliferation and quiescence. Cell culture models are convenient for mechanism-based manipulation and therapeutic evaluation. However, the major drawback is that typical cell culture conditions promote the proliferation of cancer cells irrespective of their fitness to survive in the body. To remedy this drawback, we have developed a strategy that eradicates majority (&gt;99.99%) of cells in aggressive triple-negative breast cancer cell lines under a prolonged metabolic challenge (a lack of glutamine). Importantly, this selection protocol enriches highly adaptable rare cancer cells that survive in reversible quiescence. This function-based approach is good at modeling cell fitness in cell culture. Here we investigated whether the approach is generalizable to other solid cancers by evaluating two aggressive melanoma cell lines- a human melanoma cell line A375SM and a mouse melanoma cell line B16-BL6. We found that, similar to the results obtained with triple-negative breast cancer cell lines, a lack of glutamine in culture medium eradicated majority of cells in both melanoma cell lines. Rare melanoma cells persisted in quiescence and then proliferated indefinitely. To determine whether the surviving melanoma cells have characteristics of resistant cancer, we asked whether they are resistant to paclitaxel. We found that surviving melanoma cells, both A375SM-MA and B16-BL6-MA (MA for metabolic adaptability), are more resistant to paclitaxel than parental unselected cells. Our protocol to test paclitaxel resistance was optimized to assess whether the increased resistance was due to an ability of melanoma cells to survive in quiescence. The protocol involved treatment of melanoma cells with different concentrations of paclitaxel and then following surviving cells under a microscope for several weeks. After prolonged treatment with paclitaxel, we observed rare non-proliferating cells that would yield colonies upon removal of paclitaxel. In this manner, we found that both A375SM-MA and B16-BL6-MA cell lines had an increased ability to survive in quiescence while maintaining a robust ability to proliferate. We conclude that the function-based strategy presented here may be broadly applicable across resistant heterogeneous cancers for modeling a clinically relevant cancer cell phenotype in cell culture, i.e., an opportunistic switching between quiescence and proliferation. This model is suitable for evaluating therapies to overcome deep intrinsic resistance in cancer. Supported by a State of Texas Grant for Rare and Aggressive Cancers.
Citation Format: Balraj Singh, Vanessa N. Sarli, Anthony Lucci. A cell culture model of resistant cells in solid cancers that opportunistically switch between proliferation and quiescence [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 47.