NAMPT as a driver of melanoma progression and immune evasion: therapeutic target for novel combination therapies

Background Targeted-therapy and immune checkpoint inhibitors (ICIs) have notably improved the treatment of BRAFmutated metastatic melanoma (MM) patients; however resistance to treatment dramatically impacts on the survival of patients, indicating that omplementary/alternative therapeutic approaches are needed to obtain long-lasting remission. Resistance to conventional therapies is coupled by a set of rewiring processes in both tumor and immune cells, regulated by the BRAF oncogenic signaling and environmental inputs. We demonstrated that BRAF(i)nhibitors-resistant MM requires increased amounts of NAD, an essential redox cofactor and signaling molecule, achieved by selective over-expression of the rate-limiting enzyme nicotinamide phosphoribosyltransferase (NAMPT). NAMPT become a driver of melanoma progression and resistance to targeted-therapy. In addition, is highly released in MM patients' plasma correlating with tumor burden. Furthermore, NAMPT inhibition decreased cell survival and reduced melanoma tumor growth, suggesting that it may be therapeutically targeted. Hypothesis The innovative hypothesis behind this project is that, in addition to promote BRAFi/MEKi resistance, NAMPT may be also a key regulator of response to ICIs in MM, linking NAMPT-dependent metabolic reprogramming and immune regulation. Aims This proposal aims at dissecting the mechanistic basis of NAMPT functions in BRAF-mutated MM addressing i) its intrinsic oncogenic properties modulating cancer metabolic/epigenetic/transcriptional reprogramming, acting in the cytosol but also as nuclear protein bound to chromatin, and regulating melanoma immune escape mechanisms leading to ICIs resistance; ii) its role as soluble factor, acting on melanoma cells themselves, as well as affecting immune responses within the melanoma microenvironment contributing to immune evasion. For these reasons, NAMPT may be druggable at multiple levels [enzymatic activity; extracellular (e)NAMPT functions], opening the way to novel combination therapies to overcome drug resistance. Therefore, the last goal of the project aims at providing preclinical validation of the therapeutic impact of NAMPT-targeting strategies used in combination with ICIs. Experimental Design The project is organized in 6 work-packages (WP). Combining innovative molecular and "omics" techniques and a solid experimental expertise of functional assays in vitro/in vivo, we will plan to deeply examine the regulation of NAMPT expression, as well as its post-transcriptional modifications and of sub-cellular and intra/extra-cellular trafficking mechanism. Then we will address the multiple NAMPT functions as intracellular/nuclear protein but also as soluble factor conditioning tumor-immune cell crosstalk. Lastly, xenograft MM models in mice will be exploited to test the efficacy of NAMPT-targeting in combination with ICIs. Expected Results The ambition of the project is to shed light on i) nuclear NAMPT chromatin-bound fraction role possibly linking metabolism and epigenetics; ii) functional role of NAMPT as soluble factor within melanoma microenvironment; iii) NAMPT-dependent potential immune suppressive functions; and iv) NAMPT-targeting strategies in combinantion with ICIs. Impact On Cancer This project will dissect the multiple faces of NAMPT in MM as well as the impact of its manipulation in regulating intrinsic properties of tumors, but also modulating immune responses. Lastly, the most translational and long-term area of this project concerns the therapeutic potential of NAMPT-targeting in the current landscape of melanoma drugs, with an eye to possible future application also in other tumors.