Abstract PS2-12-01: Washout Efficiency in Cancer Drug Development: A Strategy to Minimize Toxicity

Abstract Introduction Cytotoxic anticancer drugs, such as microtubule-targeting agents (MTAs), are widely used in cancer treatment due to their ability to inhibit cell division. However, these drugs often cause significant side effects because they lack specificity for cancer cells, leading to toxicity in normal tissues. This challenge limits the therapeutic potential of MTAs. Enhancing drug selectivity for cancer cells while minimizing toxicity to normal cells is crucial. One promising strategy to achieve this is improving washout efficiency, where cancer cells retain the drug's effects longer than normal cells. CMPD1, a dual-target inhibitor that disrupts the p38-MK2 signaling pathway and microtubule dynamics, has shown potential to selectively target cancer cells, offering a novel approach to improve MTA efficacy with reduced toxicity. Methods To evaluate the efficacy and safety of CMPD1, we conducted a series of in vitro and in vivo experiments. In vitro, we used live-cell imaging, cell cycle analysis, and apoptosis assays to compare the effects of CMPD1 on several breast cancer cell lines (MDA-MB-231, CAL-51) and normal cell lines (MCF10A, RPE1). We specifically assessed how CMPD1 impacts mitotic progression and cell viability in cancer cells versus normal cells. Additionally, we performed washout assays to study the difference in drug retention and the subsequent effects on cell cycle progression between cancer and normal cells. In vivo experiments involved xenograft mouse models of breast cancer where we evaluated tumor growth, weight loss, and organ toxicity, comparing the effects of CMPD1 with those of the standard chemotherapeutic agent, Taxol. Blood markers and histological analysis of liver and kidney tissues were performed to assess any adverse effects caused by treatment. Results CMPD1 demonstrated a striking ability to preferentially induce mitotic defects in cancer cells while sparing normal cells. This selective activity was further confirmed through washout assays, where CMPD1-treated cancer cells exhibited prolonged mitotic arrest even after the drug was removed, whereas normal cells quickly resumed mitosis following drug washout. This differential washout efficiency between cancer and normal cells underpinned CMPD1's enhanced specificity for cancer cells. In animal models, CMPD1 effectively suppressed tumor growth at doses much lower than those required for Taxol, with minimal adverse effects on the mice. Notably, CMPD1-treated animals did not experience significant weight loss, and no liver or kidney damage was observed, contrasting sharply with the Taxol group, which showed marked organ damage and significant weight loss. Blood analysis revealed that CMPD1 treatment did not induce a significant drop in white blood cell count, a common side effect seen with Taxol. These findings suggest that CMPD1's superior washout efficiency may contribute to its ability to selectively target cancer cells, while minimizing systemic toxicity and adverse side effects. Conclusion CMPD1’s differential washout efficiency in cancer versus normal cells enhances its specificity and reduces off-target toxicity. This mechanism makes CMPD1 a promising candidate for cancer therapy, offering potent efficacy with minimal side effects. These findings suggest that improving washout efficiency could be a key strategy in developing safer and more effective anticancer drugs. Citation Format: M. Takada, M. Yu, Y. Chen, M. Otsuka, A. Suzuki. Washout Efficiency in Cancer Drug Development: A Strategy to Minimize Toxicity abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS2-12-01.