NAD Synthesis Pathway Interference Is a Viable Therapeutic Strategy for Chondrosarcoma

Nicotinamide phosphoribosyltransferase (NAMPT) and nicotinic acid phosphoribosyltransferase (NAPRT) are rate-limiting enzymes in the NAD⁺synthesis pathway. Chondrosarcoma is a malignant cartilage forming bone tumor, in which mutations altering isocitrate dehydrogenase-1 and-2 (IDH1 and IDH2) activity have been identified as potential driver mutations. Vulnerability for NAD+ depletion has been reported for IDH1/ 2-mutant cells. Here, the potency of NAMPT inhibitors as a treatment of chondrosarcoma was explored. Eleven chondrosarcoma cell lines were treated with NAMPT inhibitors, in which the effect on cell viability, colony formation, and 3D collagen invasion was assessed. The expression level of NAMPT and NAPRT transcripts in chondrosarcoma cells was determined by qRT-PCR. Methylation of the NAPRT promoter was evaluated using a previously published dataset of genome-wide methylation. In addition, a methylation dataset was used to determine methylation of the NAPRT promoter in 20 IDH1/2-mutated cartilage tumors. Chondrosarcoma cells showed a dose-dependent decrease in cell viability, 3D collagen invasion, and colony formation upon treatment with NAMPT inhibitors, in which nearly half of the cell lines demonstrated absolute IC⁵⁰s in the low nanomolar range. Increasing IC⁵⁰s correlated to increasing NAPRT expression levels and decreasing NAPRT promoter methylation. No correlation between IDH1/2 mutation status and sensitivity for NAMPT inhibitors was observed. Strikingly, higher methylation of the NAPRT promoter was observed in high-grade versus low-grade chondrosarcomas. In conclusion, this study identified NAMPT as a potential target for treatment of chondrosarcoma. Implications: Chondrosarcoma patients, especially those of high histologic grade with lower expression and hypermethylation of NAPRT, may benefit from inhibition of the NAD synthesis pathway.