Interrogation of fibrolamellar cancer to provide clinically relevant insights into therapeutic vulnerabilities.

10041 Background: Fibrolamellar carcinoma (FLC) is a rare disease that primarily afflicts young adults. Systemic therapy with surgery is the only curative intervention for advanced disease with 5-year survivals of 45%. We examined 3-dimensional tissue explants from FLC patients to measure the efficacy of cytotoxics, targeted agents and novel combinations. Methods: Of 41 FLC specimens; 17 female, 24 male, median age 26 (14-60), 36 (88%) were previously treated, 18/36 (50%) Oxaliplatin & Gemcitabine-Lenvatinib (GEMOX-LEN), 11 (31%) 5FU & Interferon and 18 (50%) Nivolumab. Samples were examined by Ex Vivo Analysis of Programmed Cell Death (EVA/PCD) as previously described. Following disaggregation and 72-hour drug exposures, 5-point dose-response curves were interpolated to provide lethal concentration 50% (LC50) for comparison with 10,000 prior human tumor explant analyses. Drug synergy was evaluated by the method of Chou & Talalay (Chou TC. Cancer Res (2010)15;70(2):440-6). Of 24 drugs and combinations selected for testing, FLC yields were sufficient for 18/24 (75%) to be fully analyzed. To explore mechanisms of response/resistance, single agent LC50’s compared drug activity against all solid tumors by Z-score. Results: By rank order the highest activity for single-agents identified Vorinostat (HDAC), followed by Phenformin (Mitochondrial Complex I) and 6-Diazo-5-Oxo-L-norleucine (Glutaminolysis), then Cobimetinib (MEK) Regorafenib (TKI), KAT (Hexokinase) Lenvatinib (TKI) and Irinotecan (TOPO I). The lowest activity was found for Navitoclax (BH3) followed by Celecoxib (NSAID) and Quercetin (Natural product). Z scores for drug combinations favored GEMOX and 5FU & Interferon compared with other solid tumors. Previously treated tumors were more drug resistant. GEMOX combined with LEN proved synergistic in 40% of samples. Despite low single agent activity, Quercetin showed synergy with Lenvatinib. Discussion: We have previously described the ex vivo study of small molecules as probes of human tumor biology. As FLC uniformly expresses the DNAjb1-PRKACA gene-fusion, we used drugs with known mechanisms of action to interrogate operative pathways and vulnerabilities of the FLC phenotype associated with the DNAjB1-PRKACA genotype. We have previously shown that Vorinostat and Phenformin activities correlate with the MYC-directed BRD-inhibitor JQ1 while Protein Kinase A is known to regulate MYC and glutaminolysis is an established hallmark of MYC activation. Conclusions: The results suggest that the DNAjB1-PRKACA reprograms FLC toward a metabolic phenotype that is vulnerable to epigenetic modulation, mitochondrial targeting and glutaminolysis inhibition. The study met its objective to establish a database for the future management of FLC patients. This will allow each patient’s tissue to be used to craft novel therapies predicated upon new insights into the biology of FLC.