Abstract 6753: Exploring new approaches to widening of the therapeutic index of ADCs with dual-payload design and combination with a novel HMA

Abstract Antibody-drug conjugates (ADCs) have revolutionized targeted cancer therapy by delivering potent cytotoxic agents directly to tumor cells. Recent approvals of ADCs such as trastuzumab deruxtecan, sacituzumab govitecan have significantly improved patient treatment options, underscoring the clinical potential of this therapeutic class. However, single-payload ADCs often face limitations in efficacy. Tumor heterogeneity poses a significant challenge, as targeting cancer cells with a single cytotoxic mechanism may not sufficiently overcome resistance or achieve optimal therapeutic outcomes. These limitations call for the development of novel strategies that widen the therapeutic index by increasing the Maximum Tolerated Dose (MTD) and lowering the Minimum Effective Dose (MED). We have designed and synthesized a novel dual-payload ADC combining two distinct cytotoxic agents: a potent topoisomerase I inhibitor (Top1i) and a microtubule-disrupting agent. This innovative approach allows for a synergistic therapeutic effect, leveraging the complementary mechanisms of action of both payloads within a single ADC. In vitro cell viability was determined using the CellTiter-Glo assay against the NCI-N87 and MDA-MB-468 cell lines. These studies demonstrated robust potency of the dual-payload ADC across multiple cancer cell lines. In vivo efficacy studies were conducted in HER2-expressing NCI-N87 gastric cancer xenograft model. The tumor-bearing mice were treated with various doses of dual-payload ADC, single-payload ADC, or saline control. Notably, dual-payload ADC displayed superior efficacy compared to single-payload ADC, achieving a tumor growth inhibition (TGI) of 103% (p < 0.05). This demonstrates superior tumor growth inhibition of the dual-payload ADC compared to a Top1i-based single-payload ADC and a more favorable safety profile compared to a microtubule inhibitor-based single-payload ADC. Pharmacokinetic (PK) profiling and non-GLP toxicity studies are currently underway to further characterize its suitability for clinical development. Moreover, we have explored combination strategies to further augment the therapeutic index. One promising approach involves the combination of the ADC with NTX-301, a novel 4′-thio-modified analog of decitabine (DAC). NTX-301 enhances p53 stabilization more effectively than DAC, potentially improving the ADC’s efficacy through synthetic lethality with BCL2 inhibition. Preliminary data suggest that the ADC+NTX-301 combination produces greater synergy and a more favorable therapeutic index than ADC combinations with traditional hypomethylating agents (HMAs). In this study, we present novel strategies to enhance the therapeutic index of ADCs through a dual-payload design and combination with NTX-301. These results highlight the potential of both approaches for further development in cancer treatment. Citation Format: Younghwa Chun, Areum Go, Byeong Sung Lee, Seunggun Shin, Sohui Kweon, Hyemin Han, JaeHyeon Lee, Suhyun Park, Ha Young Lee, Min Young Lee, Hyun Yong Cho, Doo Young Jung. Exploring new approaches to widening of the therapeutic index of ADCs with dual-payload design and combination with a novel HMA [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6753.