TS Overexpression in SCLC: Mechanism and Therapeutic Targeting

Small cell lung cancer (SCLC) is a highly lethal malignancy that is not treatable with targeted therapies and that does not respond long-term to treatment with cytotoxic chemotherapy1. One distinguishing molecular characteristic of SCLC is very high expression levels of thymidylate synthase (TS). TS plays an important role in de novo nucleotide biosynthesis and the very high TS levels expressed in SCLC cells indicate that these cells require the de novo nucleotide biosynthetic pathway to proliferate. Thus, complete TS inhibition could result in highly favorable outcomes in SCLC patients. TS inhibitors have been evaluated in SCLC clinical trials and have anti-tumoral activity when combined with a second chemotherapeutic agent. However, treatment with TS inhibitors has not been shown to surpass other combination chemotherapy regimens. An important point regarding these clinical studies is that TS activity levels were not monitored as an endpoint of drug response, thus it is not known whether TS activity was efficiently inhibited.Investigators predict that complete TS inhibition will result in favorable outcomes. With support from Wake Innovations, Investigators are developing a novel fluoropyrimidine polymer, CF10, which strongly inhibits TS. CF10 is a second generation fluoropyrimidine polymer. The first generation polymer, F10, showed excellent anti-cancer activity in animal models of acute myeloid leukemia, glioblastoma, and prostate cancer. CF10 is designed to have improved tumor penetration and better in vivo stability than F10. Investigators hypothesize that CF10 will be highly effective for treating SCLC both as a single agent and in combination with TS inhibitors that target alternative sites of the TS enzyme. After establishing CF10 has activity as a single agent and in combination with folate-based TS inhibitors (e.g. pemetrexed) in SCLC cell lines and xenograft models, Investigators will test CF10 in patient-derived xenograft (PDX) models and in organoids derived from SCLC patient samples. Investigators will develop PDX models of SCLC and SCLC organoids using transbronchial fine needle aspiration (FNA) from SCLC patients at Baptist/WFBCCC collected by co-I's Bellinger, Dotson, and Thomas. Non-malignant cells will be collected using a brush biopsy to enable comparison of malignant and non-malignant tissue from the same patient with regard to mechanistic endpoints.