Unleashing the Power of DNA-Targeted Therapy: The Potential of DGN462-Loaded ADCs in Combating Human Cancers

A novel class of cytotoxic agents, termed IGNs, has been introduced for antibody-drug conjugates (ADCs), offering a distinct DNA-alkylating mechanism. These agents are composed of indolino-benzodiazepine dimers, with di-imine IGNs capable of DNA crosslinking and alkylation, and mono-imine IGNs inducing only alkylation. The mono-imine IGN, DGN462, was identified as a lead candidate due to its favorable tolerability in mice, with a maximum tolerated dose of 40 mg/kg and no delayed toxicity.

DGN462's DNA-alkylating capability was confirmed through the formation of covalent DNA adducts, specifically by alkylating the C2-amino group of guanine. This resulted in a slowed progression through the S-phase and a cell cycle arrest in the G2/M phase, in a dose-dependent manner.

The DGN462 ADCs, with approximately 3 molecules of DGN462 per antibody and a cleavable linker, exhibited high monomer content, low free drug levels, and symmetrical mass distribution. These conjugates demonstrated high potency and antigen specificity in vitro against various cell types, including those expressing PgP, with IC50 values ranging from 2 pM to 3 nM. The ADCs also showed bystander activity, suggesting that metabolites released from target cancer cells can eliminate nearby antigen-negative cells, which could be advantageous in treating solid tumors with heterogeneous antigen expression.

In vivo studies revealed that a CD33-targeting DGN462 ADC was highly effective against AML xenografts, with a minimal efficacious dose of 0.6 mg/kg, while a non-targeting control showed no activity. Similarly, an epidermal growth factor receptor-targeting DGN462 ADC displayed high activity and specificity against a head and neck squamous cell carcinoma model, with a minimal efficacious dose of 1.6 mg/kg. The intact conjugate had a half-life of about 90 hours in mice, with bioactivity maintained up to 72 hours post dosing, indicating active retention in vivo.

DGN462 ADCs have shown a favorable safety profile and a potent DNA-alkylating mechanism, suggesting potential efficacy in tumors that are less sensitive to tubulin agents, exhibit heterogeneous antigen expression, and/or have PgP-mediated drug resistance. The research was presented at the 105th Annual Meeting of the American Association for Cancer Research and published in Cancer Research.