Abstract 3775: Characterization of intratumoral heterogeneity in drug sensitivity and modeling of drug combination effects using subclonal cell populations derived from a single breast cancer cell line
Authors: Kuiken Hendrik J. , Friend Chandler M. , Corsello Steven M. , Mader Christopher C. , Brugge Joan S. 
Published: August 2019

Abstract
Intratumoral heterogeneity can have profound effects on tumor progression and drug resistance. While tumor cell heterogeneity has been described at many levels, there is a poor understanding of the extent of heterogeneity in drug sensitivity within a single tumor, the dynamics of tumor cell subpopulations during treatment with anti-cancer agents and non-cell autonomous mechanisms of drug resistance. The overall objective of this study is to characterize heterogeneity in drug sensitivity within a model for human breast cancer and to model and evaluate the effect of drug combinations on the dynamics of subpopulations within heterogeneous mixtures.
We have characterized 31 subclonal cell populations (SCPs) that were generated through single cell cloning of the triple-negative breast cancer cell line MDA-MB-468. These SCPs display considerable heterogeneity with respect to morphology, proliferation rate, colony formation in soft agar and tumorigenicity in mice. To examine the extent of heterogeneity in drug sensitivity, we designed and screened a 200-small molecule compound library in 24 SCPs and the parental cell line. We observed considerable heterogeneity in drug sensitivity and selected 36 compounds for validation, including GPX4 inhibitor ML-210 and gemcitabine, to which the SCPs displayed 12-fold and 150-fold differences in the EC50, respectively. The results of these validation experiments were used to identify transcriptional programs and individual genes which expression correlates with drug sensitivity. We have generated and will evaluate predictive models for drug combination using the SCP drug sensitivity profiles. To test the effect of individual drugs and combinations, as well as different treatment schedules on heterogeneous populations, we will examine the dynamics of individual SCPs within mixed cultures. To this end, we have transduced 22 SCPs with CloneTracer lentiviruses, each encoding for a unique DNA barcode. The distribution of these unique barcodes can be determined by next generation sequencing. Previously, we have found that propagation of a 22 SCP mixture results in reproducible changes in the composition of mixed monolayer cultures with approximately half of the SCPs having a relative abundance of 1% each in the mixed population following propagation for four months.
The results of this study show that there is considerable heterogeneity in drug sensitivity among clonal subpopulations derived from a single cancer cell line. Ongoing experiments will provide insight into the effect of drug combinations and unique treatment schedules on distinct tumor cell subpopulations within heterogenous mixtures. Moreover, using this panel of SCPs, we will be able to test for and investigate non-cell autonomous modes of drug resistance, which may guide the development of new drug combinations.
Citation Format: Hendrik J. Kuiken, Chandler M. Friend, Steven M. Corsello, Christopher C. Mader, Joan S. Brugge. Characterization of intratumoral heterogeneity in drug sensitivity and modeling of drug combination effects using subclonal cell populations derived from a single breast cancer cell line [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3775.