ESTRO 2020 Abstract book

S27 ESTRO 2020

Twelve short tandem repeat (STR)-validated human TC- derived cell lines were used (ATC n=7, poorly differentiated (PDTC) n=1, papillary (PTC) n=4). All cell lines underwent comprehensive genomic characterization prior to drug testing. High-throughput drug screens were performed using the NCI’s Approved Oncology Set V (n=112) and a custom collection of agents (n=145). The effect of drugs on cell growth and survival was measured after 72 hours of drug exposure. To identify the most effective drugs, we selected individual agents with maximal growth inhibition at each dose level relative to wells examined on the day of treatment (top 25th percentile) and subsequently used non-parametric statistics to compare effect size with other drugs and controls. The concentration-response curves from biological replicates of different passage number were fitted using non-linear regression and the AUC was calculated and used for the development of pharmacologic trees. Confirmatory testing was completed for the most effective drug classes. Results The most effective classes of agents against ATC cell lines were: antimetabolites, inducers of reactive of oxygen species (ROS), proteasome and microtubule inhibitors. These agent classes in addition to HDAC inhibitors achieved the highest effectiveness for PTC cell lines at 0.1μM dose level but only proteasome and microtubule inhibitors remained effective at 0.01μM dose level. TP53 mutational status affected drug sensitivity; mutant TP53 cell lines demonstrated enhanced sensitivity to antimetabolites and Vinca alkaloids, while wild-type TP53 cell lines demonstrated preferential sensitivity to HDAC inhibitors. Likewise, BRAF mutational status affected drug sensitivity with higher sensitivity to taxanes and protein kinase inhibitors in V600E mutation compared with preferential sensitivity to proteasome and HDAC inhibitors in wild-type. Confirmatory testing validated initial screening results.

Figure 1. Example of ATC cell line (MDA-T178) used in the high-throughput screen. A) Boxplots of effective drugs in the initial screen at 0.1μM concentration compared with DMSO and other ineffective drugs; B) Drug tree analysis where the size of the colored dots represents relative effectiveness of each individual agent. * indicates statistical significance P<0.0001 for both. Conclusion High-throughput screening identified classes of systemic agents, which demonstrate preferential effectiveness against aggressive TC variants, particularly those with mutant BRAF and TP53. These agents provide a basis for in vivo preclinical validation prior to clinical trial development.