Abstract 232: An antibody-drug conjugate carrying a microtubule inhibitor and a DNA alkylator exerts both mechanisms of action on tumor cells

Antibody-drug conjugates (ADCs) consist of a tumor-targeted antibody, a drug (payload) with specified mechanism of action, and the chemical framework for attaching them to each other. By selective delivery of the payload to the tumor and not to normal tissues, ADCs can provide greater efficacy and tolerability than systemic chemotherapies, which can translate to longer duration of treatment and response, as well as more options for combination therapies without the concern of overlapping toxicity. To preempt potential resistance to therapy, we have engineered a dual-payload ADC (DP-ADC) that delivers two mechanistically distinct payloads to a single target cell. To build a precision dual payload-ADC (DP-ADC), we leveraged our Synthemer platform, which enables us to chemically attach the payloads to a synthetic scaffold in a defined manner, and then to chemically attach the loaded scaffold to the antibody. This approach allows for unambiguous control of architecture and ratio of the payloads: the payloads are incorporated in a fixed ratio into the scaffold and subsequently into the ADC. Moreover, the synthetic design also allows for selection of solubilizing groups and charge compensation for each payload, allowing for optimal properties of the ADC. Our prototype DP-ADC combines the microtubule inhibitor auristatin F hydroxypropyl amide (AF-HPA) with the DNA monoalkylator I-BiP (related to pyrrolobenzodiazepine), at a payload ratio of 3:1. The drug-to-antibody ratio (DAR) was 12 AF-HPA and 4 I-BiP (16 total), achieved by conjugating 4 of the loaded dual-payload scaffolds to the antibody. The DP-ADC exhibited comparable antigen binding to the unconjugated antibody, and cytotoxic potency comparable to both single-payload ADCs alone. Using cell-based assays that specifically probe the mechanism of action of each payload, we demonstrated that the DP-ADC exerted both expected mechanisms of action on the tumor cell in a target-dependent manner. Considerations for the selection of payload combinations will also be presented. While synergistic action is typically assumed to be preferred if not required, a recent study demonstrated that the observed clinical benefit of most combinations can be explained by the drugs’ independent modes of action, not synergy. Indeed, AF-HPA and I-BiP did not exhibit synergy in cytotoxicity studies in cancer cell lines, yet their combination in a DP-ADC is still expected to confer potential clinical benefit over either single-payload ADC across a patient population. Citation Format: Jeremy R. Duvall, Marc Damelin, Mariya V. Kozytska, Barrett J. Nehilla, Marina Protopopova, Patrick R. Conlon, LiuLiang Qin, Mark Nazzaro, Josh D. Thomas, Qingxiu Zhang, Dorin Toader, Timothy B. Lowinger. An antibody-drug conjugate carrying a microtubule inhibitor and a DNA alkylator exerts both mechanisms of action on tumor cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 232.