Abstract 4426: Novel tumor microenvironment (TME)-activated, pan-RASi and Topo1i dual-payload linker enables safe broad RAS inhibition and overcomes Topo1i resistance

Abstract Pan-RAS inhibitors target RAS mutations in tumor cells but also affect wild-type RAS in normal tissues. Consequently, pan-RASi-related skin toxicities such as rash and acneiform dermatitis commonly occur, narrowing their therapeutic window. QHL-P1711 is a potent pan-RAS inhibitor which effectively suppresses the proliferation of wild type NRAS and HRAS tumor cells and tumor cells with KRASG12C, KRASG12D and KRASG12V mutations. In cytotoxicity assays, QHL-P1711 demonstrated synergistic effects with DXd (a Topo1 inhibitor) in MIA PaCA-2G12C, AGSG12D and Capan-1G12V tumor cells.TMEAlinker is a clinically validated, selectively activated linker in the tumor microenvironment (TME) by legumain, an active protease highly overexpressed in the TME while exhibiting negligible expression in skin endothelial cells. By using the dual-payload TMEAlinker, both pan-RASi (QHL-P1711) and DXd can be conjugated to an EGFR-TROP2 bispecific antibody to construct a dual-payload ADC EGFR-TROP2-TMEAlinker-RASi-DXd (IMD2146). The highly hydrophilic dual-payload TMEAlinker effectively addressed CMC challenges and enabled homogeneous formation of dual-payload ADCs with a drug-to-antibody ratio (DAR) of 8+8.IMD2146 exhibited superior efficacy than single-payload ADCs and pan-RAS inhibitor treatment at equivalent pan-RASi molar doses in the NCL-H1975 tumor model. Notably, IMD2146 retained antitumor activity in the PA-1 Topo1i-resistant tumor model, whereas the single-payload ADC (EGFR-TROP2-TMEAlinker-DXd) showed no efficacy. In human plasma at 37 °C, 1% of free pan-RASi was released after 7 days of incubation of IMD2146, indicating excellent plasma stability. In preclinical toxicology studies in cynomolgus monkeys, IMD2146 was well tolerated after repeated dosing at 50 mg/kg. Pharmacokinetic analysis in cynomolgus monkeys revealed high plasma concentrations of IMD2146 with minimal levels of free pan-RASi and free DXd, further confirming its stability in circulation.In summary, these results demonstrate that the dual-payload TMEAlinker design provides a novel strategy to achieve systemic safety with broad RAS inhibition while effectively overcoming Topo1i resistance. This approach integrates precise TME activation with dual-mechanism targeting, offering a promising therapeutic platform for RAS-driven tumors while minimizing systemic toxicity. Citation Format: Zhengsong Gu, Cheng Liu, Yuan Liu. Novel tumor microenvironment (TME)-activated, pan-RASi and Topo1i dual-payload linker enables safe broad RAS inhibition and overcomes Topo1i resistance abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 4426.