Deciphering mechanisms of resistance to FK866 in cancer cells

Nicotinamide phosphoribosyltransferase (NAMPT) is a key metabolic enzyme in NAD+ synthesis pathways which is found upregulated in several tumors, depicting NAD(H) lowering agents, as the NAMPT inhibitor FK866, an appealing approach for anticancer therapy. Like other anticancer small molecules, FK866 triggers chemoresistance, observed in several cancer cellular models, which can prevent its clinical application. Here, we unravel molecular mechanisms sustaining the acquisition of resistance to FK866 in a model of triple-negative breast cancer – TNBC - (MDA-MB-231 – MDA p.), exposed to increasing concentrations of the small molecule (MDA r.). Acquired resistance to FK866 was not explained by the increased activity of efflux pumps or by compensatory mechanisms of NAD+ production. Additionally, a chemical high-throughput screening approach with FDA-approved drugs failed to identify potentially targetable MDA r. vulnerabilities. Instead, these cells present an increased mitochondrial spare respiratory capacity and a higher mitochondrial mass compared to the FK866-sensitive counterparts, as well as a metabolic dependence on pyruvate and succinate for energy production. To gain deeper insights into metabolic adaptation in NAD(H) deprived conditions, we focused on the Yes-associated protein (YAP), a cotranscriptional regulator involved in metabolic rewiring. We showed that FK866 induces YAP nuclear translocation in FK866-sensitive but not in FK866-resistant models. Moreover, the up- or down-regulation of YAP levels modulates the sensitivity to the NAD(H) depletion agent, as well as the differential expression of PGC1-α, found upregulated in the TNBC FK866-resistant cells. Taken together, these results unravel novel mechanisms of cell plasticity to counteract FK866 toxicity, which rely on mitochondrial rewiring. Moreover, we described a correlation between YAP activation and sensitivity to NAMPT inhibition, which can be further explored for clinical use.