Crippling cancer's energy and escape: NAMPT and BCL2 as dual targets in T-ALL

T-cell acute lymphoblastic leukemia (T-ALL) is a highly aggressive hematologic malignancy with limited targeted therapies. While chemotherapy induces remission, relapse remains a major challenge, with long-term event-free survival of only ~30%. Transcriptomic profiling of patient samples (GSE33469, GSE33470) revealed that T-ALL exhibits elevated oxidative phosphorylation (OXPHOS) activity and upregulation of NAMPT, the rate-limiting enzyme of NAD⁺ salvage pathway. The salvage pathway is the main pathway utilized by eukaryotic cells to produce NAD+, a critical energy currency used for biological processes such as glycolysis, oxidative phosphorylation, and the DNA damage response. Previous targeting of NAMPT was unsuccessful because complete inhibition of NAMPT was associated with unacceptable toxicities. Here, we evaluate RPT1G, a novel hyperbolic NAMPT inhibitor designed to avoid toxicities associated with complete inhibition, as a therapeutic candidate for relapsed/refractory (R/R) T-ALL. RPT1G eliminates NAD+ in cancer cells while allowing NAD+ production in healthy tissues. This was linked to cytotoxicity in T-ALL whereas toxicity in normal PBMCs was mitigated sparing these cells. We hypothesized that hyperbolic inhibition of NAMPT with RPT1G would selectively impair T-ALL cell metabolism while sparing normal cells, and that combining RPT1G with agents targeting compensatory survival pathways could enhance therapeutic efficacy. RPT1G was evaluated in a Phase 1 healthy volunteer clinical study and showed a favorable safety and tolerability profile (NCT06667765). In T-ALL, RPT1G rapidly depleted intracellular NAD⁺/NADH and ATP, with Seahorse assays confirming suppression of mitochondrial energy pathways such as glycolysis and OXPHOS compared to vehicle controls. Further, a CRISPR loss-of-function screen identified the antiapoptotic protein BCL2 as a synthetic lethal partner with RPT1G. Consistently, combining RPT1G with venetoclax, a clinically available BCL2 inhibitor, produced enhanced cytotoxicity across T-ALL cell lines and significantly enhanced ATP depletion compared to single agents. BH3 profiling, a functional assay used to determine BCL2 family dependencies, was used on several patient-derived xenograft (PDX) models. Using different concentrations of BH3 mimetics (BIM, BAD, MS1, and XXA1 0.01uM - 100uM) we demonstrated modest BCL2 dependency in these models, further supporting this strategy. In vivo, the RPT1G-venetoclax combination significantly extended survival in PDX-bearing mice compared to vehicle or monotherapy groups. These findings establish NAMPT inhibition with RPT1G plus BCL2 blockade with venetoclax as a promising therapeutic approach for R/R T-ALL, warranting further translational investigation.