Abstract 4760: Inhibition of FASN postpones development of resistance to BRAF inhibitors in colorectal cancer
Authors: Geisen Mariah , weber-Tessmann Josiane , Kelson Courtney , He Daheng , Wang Chi , Faisal Abu Saleh Mosa , Kolesar Jill , Zaytseva Yekaterina 
Published: March 2024

Abstract
Introduction: Mutations in proto-oncogene BRAF occur in about 10-15% of CRC patients and BRAFV600E is the most common. For patients who undergo BRAF-targeted therapy, resistance develops 4-6 months after treatment initiation and results in more aggressive disease. We found that development of resistance to BRAF inhibitors (BRAFi) is associated with an increase in lipid metabolism and expression of fatty acid synthase (FASN). FASN is a key enzyme of lipid synthesis overexpressed in CRC. Therefore, our hypothesis is that inhibition lipid metabolism via FASN will postpone development of resistance to BRAFi.
Methods: We established CRC cells resistant to PLX8394, a novel BRAFi. To evaluate differences in parental and resistance cells, CellTiterGlo 2.0, PrestoBlue, CytoSelectTM Invasion Assay, Triglyceride Assay, Seahorse XF, and confocal microscopy were used. Combination of PLX8394 and TVB3664 or C75 (FASN inhibitors) was tested on cell viability, colony formation, and synergy studies in parental and BRAFi resistant cells.
Results: The development of resistance to BRAFi promotes cellular proliferation and increases cyclin D and survivin expression in vitro and in vivo. BRAFi resistance is also associated with an increase in invasive properties and loss of E-cadherin expression. Metabolic changes include an increase in lipid metabolism, oxidative phosphorylation, and triglycerides storage. RNAseq and western blot analysis show significant upregulation of FASN in BRAFi resistant cells. Using cell viability and soft agar colony formation assays, we show that combined PLX8394 and TVB3664 treatment leads to a significantly higher decrease in cell viability and colony formation as compared to each drug alone in parental cells but not in BRAFi resistant cells. The calculation of a Bliss synergy score confirms that combination treatment with C75 and PLX8394 has synergetic effect in BRAFV600E cells. To further confirm that FASN contributes to resistance to BRAFi, we show that HT29 FASN shRNA cells are more susceptible to PLX8394 treatment as compared to control cells. Importantly, our data show that the long-term treatment with PLX8394 in combination with TVB3664 postpones development of resistance to BRAFi as compared to cells treated with PLX8394 alone.
Conclusion: Our study demonstrates that resistance to BRAFi is associated with a significant increase in proliferation, metastasis, and lipid metabolism. We demonstrate that combination of FASN inhibitors and BRAFi postpones development of resistance in BRAFV600E cells. However, FASN inhibition does not sensitize cells to BRAFi in already resistance cells, suggesting that this approach cannot be used to overcome acquired resistance to BRAFi. In summary our data suggest that an addition of TVB3664 at the beginning of BRAF treatment regimen could be an efficacious treatment strategy for BRAFV600E CRC patients.
Citation Format: Mariah Geisen, Josiane weber-Tessmann, Courtney Kelson, Daheng He, Chi Wang, Abu Saleh Mosa Faisal, Jill Kolesar, Yekaterina Zaytseva. Inhibition of FASN postpones development of resistance to BRAF inhibitors in colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4760.