NAMPT Inhibitor GMX1778 Enhances the Efficacy of 177Lu-DOTATATE Treatment of Neuroendocrine Tumors

Neuroendocrine tumors (NETs) can be treated by peptide receptor radionuclide therapy using radiolabeled somatostatin analogs. However, the efficacy of such treatment is low and needs to be optimized. Our study evaluated the potential radiosensitizing effects of inhibition of nicotineamide phosphoribosyltransferase on Lu-177-DOTATATE treatment in a NET model. Methods: Nude mice xenografted with the human NET cell line GOT1 were treated with semiefficient doses of Lu-177-DOTATATE (7.5 MBq, intravenously) or the nicotineamide phosphoribosyltransferase inhibitor GMX1778 (100 mg/kg/wk, orally). Results: Median time to tumor progression (tumor volume larger than at day 0) was 3 d for controls, 7 d for single-dose GMX1778, 28 d for single-dose Lu-177-DOTATATE, 35 d for 3 weekly doses of GMX1778, and 98 d for combined treatment with Lu-177-DOTATATE and GMX1778 x 1. After Lu-177-DOTATATE and 3 weekly doses of GMX1778, none of the tumors progressed within 120 d. Conclusion: GMX1778 enhances the efficacy of Lu-177-DOTATATE treatment and induces a prolonged antitumor response.