Development of Novel Antibody-Camptothecin Conjugates.

We have developed a highly active and well-tolerated camptothecin (CPT) drug-linker designed for antibody-mediated drug delivery in which the lead molecule consists of a 7-aminomethyl-10,11-methylenedioxy CPT (CPT1) derivative payload attached to a novel hydrophilic protease-cleavable valine-lysine-glycine tripeptide linker. A defined polyethylene glycol stretcher was included to improve the properties of the drug-linker, facilitating high antibody-drug conjugate (ADC) drug loading, while reducing the propensity for aggregation. A CPT1 ADC with 8 drug-linkers/mAb displayed a pharmacokinetic profile coincident with parental unconjugated antibody and had high serum stability. The ADCs were broadly active against cancer cells in vitro and in mouse xenograft models, giving tumor regressions and complete responses at low (≤3 mg/kg, single administration) doses. Pronounced activities were obtained in both solid and hematologic tumor models and in models of bystander killing activity and multidrug resistance. Payload release studies demonstrated that two CPTs, CPT1 and the corresponding glycine analog (CPT2), were released from a cAC10 ADC by tumor cells. An ADC containing this drug-linker was well tolerated in rats at 60 mg/kg, given weekly four times. Thus, ADCs comprised of this valine-lysine-glycine linker with CPT drug payloads have promise in targeted drug delivery.

Targeted Delivery of Cytotoxic NAMPT Inhibitors Using Antibody-Drug Conjugates.

Antibody-drug conjugates (ADCs) are a therapeutic modality that enables the targeted delivery of cytotoxic drugs to cancer cells. Identification of active payloads with unique mechanisms of action is a key aim of research efforts in the field. Herein, we report the development of inhibitors of nicotinamide phosphoribosyltransferase (NAMPT) as a novel payload for ADC technology. NAMPT is a component of a salvage biosynthetic pathway for NAD, and inhibition of this enzyme results in disruption of primary cellular metabolism leading to cell death. Through derivatization of the prototypical NAMPT inhibitor FK-866, we identified potent analogues with chemical functionality that enables the synthesis of hydrophilic enzyme-cleavable drug linkers. The resulting ADCs displayed NAD depletion in both cell-based assays and tumor xenografts. Antitumor efficacy is demonstrated in five mouse xenograft models using ADCs directed to indication-specific antigens. In rat toxicology models, a nonbinding control ADC was tolerated at >10-fold the typical efficacious dose used in xenografts. Moderate, reversible hematologic effects were observed with ADCs in rats, but there was no evidence for the retinal and cardiac toxicities reported for small-molecule inhibitors. These findings introduce NAMPT inhibitors as active and well-tolerated payloads for ADCs with promise to improve the therapeutic window of NAMPT inhibition and enable application in clinical settings.