Physicochemical and Metabolic Optimization of NAMPT Inhibitors Enables Effective Antibody-Drug Conjugates for Liquid and Solid Tumors.

Antibody drug conjugates (ADCs) enable selective delivery of highly potent small molecules, yet most clinically validated payloads target solely cell-division pathways with several drawbacks such as high off-target toxicity and a lack of efficacy on nondividing tumor cells (e.g., tumor stem cells). Metabolic targets such as nicotinamide phosphoribosyltransferase (NAMPT) offer a complementary mode of action and are predestined as ADC payloads since systemic toxicities have prevented clinical use of NAMPT inhibitors (NAMPTi) as free drugs. Here we show that highly hydrophobic NAMPTi, especially cyanoguanidine-containing inhibitors, are chemically and metabolically suboptimal for ADC deployment due to limited efficacy likely due to lysosomal conversion to inactive guanylureas. Guided by structure-based design, and molecular dynamics simulations, we developed two next-generation NAMPT inhibitors featuring (i) a tertiary alcohol to balance hydrophilicity and (ii) an isoindoline-urea group to improve lysosomal stability in comparison to the cyanoguanidine. The optimized inhibitors retained high affinity to the NAMPT enzyme and showed strong cellular activity upon targeted delivery through ADCs. When conjugated to anti-CD30, anti-HER2, or anti-TROP2 antibodies, the resulting ADCs showed durable responses in hematologic and solid tumor models, including complete regressions in the metabolically stringent NCI-N87 gastric carcinoma xenograft after a single 2 mg/kg dose. These findings highlight physicochemical tuning and lysosomal stability as key design principles for NAMPT-based payloads and support NAMPT inhibition as a very promising mode of action (MoA) for next-generation ADC therapeutics.