Abstract A081 Biomarker-driven targeting of NAD metabolism in rhabdomyosarcoma

Abstract Introduction/Background: New treatments are needed to improve survival in rhabdomyosarcoma (RMS). Cells primarily synthesize nicotinamide adenine dinucleotide (NAD+) through the Preiss-Handler and Salvage pathways driven by nicotinic acid phosphoribosyltransferase (NAPRT) and nicotinamide phosphoribosyltransferase (NAMPT), respectively. NAMPT inhibitors (NAMPTi) have been tested in clinical trials, but their efficacy has been limited by lack of appropriate biomarkers for patient selection. Here, we sought to determine if RMS harbors NAPRT silencing that confers a synthetic lethal interaction with NAMPTi. Methods: NAPRT expression was evaluated by immunohistochemistry (IHC) in human tumor samples. In vitro cell viability assays were performed in RMS cell lines using a panel of NAMPT inhibitors. RMS cells isogenic for NAPRT expression were generated via overexpression or CRISPR/Cas9 KO. For in vivo experiments, orthotopic tumor-bearing mice were treated with vehicle control or OT-82 at 25 mg/kg/dose by oral gavage with or without nicotinic acid (NA) at 25 mg/kg/dose once daily for 3 days per week. Results: In vitro, NAPRT negative isogenic RMS cells showed an exquisite sensitivity to a panel of NAMPT inhibitors. When NA was supplemented to model physiologic conditions, NAPRT+ cells were rescuved while cells harboring loss of NAPRT remained sensitive. In vivo, NAMPTi treatment induced significant tumor regression and improved survival in a NAPRT null RMS xenograft model even in the presence of NA, while NAPRT+ tumors did not response to NAMPTi when combined with NA supplementation. IHC staining in a collection of RMS tissue microarrays obtained from the Children’s Oncology Group demonstrated loss of NAPRT protein expression in roughly 25% of tumors.Conclusion: Overall, these data suggest that NAPRT loss may serve as a therapeutic target in RMS by inducing a synthetic lethal interaction with NAD+ depleting agents. Future studies will determine if NA supplementation can mitigate toxicity and widen the therapeutic index, paving the way for the development of biomarker-driven clinical trials in RMS. Citation Format: Juan C. Vasquez, Prateek Bhardwaj, Sophia Zhao, Katelyn Noronha, Karlie Lucas, Ranjini Sundaram, Collin Heer, Raffaella Morotti, Josh Spurrier, Ranjit S Bindra. Biomarker-driven targeting of NAD metabolism in rhabdomyosarcoma abstract. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pediatric Cancer Research; 2024 Sep 5-8; Toronto, Ontario, Canada. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl):Abstract nr A081.