Abstract C030: A new low potency DNA guanine monoalkylating ADC payload with enhanced i n vivo tolerability

Abstract

Although five Antibody-Drug Conjugates (ADCs) have been approved and over eighty others are in development, the majority contain payloads belonging to two classes: tubulin inhibitors and DNA interactive agents. Most DNA-interactive payloads (e.g., the PBD dimers and IGNs) have potent cytotoxicity but ADCs containing them have high hydrophobicity and a narrow therapeutic window. Thus, there is interest in developing novel payloads which benefit from similar in vivo efficacy but possess lower hydrophobicity and a substantially wider Therapeutic Window (TW). The pyridinobenzodiazepines (PDDs) are a new class of sequence-selective, DNA guanine monoalkylating ADC payload which contain a polyheterocyclic chain with sufficient span to guide them to specific DNA sequences (e.g., transcription factor binding sites). The lead high potency PDD payload (FGX2-62) is active in vitro in the picomolar range in a wide panel of cell-lines, is easily conjugated and has in vivo potency at sub-mg/kg levels in ADC form. Within the PDD platform, we have now developed a lower potency DNA monoalkylator with substantially superior in vivo properties to other DNA alkylating agents. FGX20-75 is active in the low nanomolar range (e.g., 2.1 nM in the gastric cell-line SW48, 72 hour incubation), but is sufficiently hydrophilic to allow efficient conjugation at DARs > 4. The increase in loading compared to other DNA-interactive payloads compensates for the drop in potency of FGX20-75, resulting in a potent ADC with substantially increased tolerability. ADCs have been generated by conjugating a maleimide-linked analogue of FGX20-75 to the EGFR-targeting antibody Cetuximab with DAR of 4.2. The ADCs exhibit significant in vivo efficacy compared to other DNA-interactive payloads, and a substantially increased tolerability profile. A maximum tolerated dose (MTD) has not yet been reached at 35 mg/kg (single dose, CD1 mice). The favourable hydrophobicity profile of the low potency alkylator (FGX20-75) and its ease of conjugation to antibodies, along with the significant in vivo efficacy and tolerability of the ADCs produced, suggest that this low potency DNA-alkylating payload represents a promising new approach in ADC development. Citation Format: Nicolas Veillard, Paolo Andriollo, Francesco Cascio, Paul J. M. Jackson, David E. Thurston. A new low potency DNA guanine monoalkylating ADC payload with enhanced in vivo tolerability [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr C030. doi:10.1158/1535-7163.TARG-19-C030