Abstract 5597: Plinabulin boosts antitumor efficacy of topoisomerase inhibitor-based antibody-drug conjugates without or with immune checkpoint inhibitor

Abstract Background: Antibody drug conjugates (ADC) with topoisomerase inhibitors (TOP1-ADC) hold significant promise in cancer treatment. FDA-approved TOP1-ADC includes TROP2- or HER2-directed datopotamab deruxtecan (Dato-DXd) and trastuzumab deruxtecan (T-DXd), respectively. To boost ADC efficacy without overlapping toxicity, combination strategies including immune checkpoint inhibitors (ICI) are under active investigation. Plinabulin (Plin) is a first-in-class, differentiated tubulin binder that exerts anticancer activity primarily by activating GEF-H1-mediated pathways in dendritic cell (DC) maturation and T cell activation. In Dublin-3 phase 3 study, Plin/docetaxel outperformed docetaxel with significant OS/PFS/ORR benefits and doubling of 2- and 3-year survival rates, and reduced docetaxel induced neutropenia. In post-ICI settings given after radiation, Plin potentiates anti-PD-1 with significantly higher GEF-H1 immune activation in responders of mixed cancer types. Preclinically, Plin boosts irinotecan activity in human colon cancer models and reduces topotecan-induced neutropenia. Here we investigated Plin synergy with TOP1-ADC in-vitro, and with or without PD-1/L1 inhibitor pembrolizumab (Pembro) or atezolizumab (Atezo) in-vivo. Methods: For combinations in-vitro, HER2+ KPL-4 breast cancer cells were treated with Plin (1.46 - 46.8 nM), T-DXd (0.105 - 3.37 μM) or both. For combinations in-vivo, MC38 mouse colon adenocarcinoma cells overexpressing hTROP2 (hTROP2-MC38) or hHER2 (hHER2-MC38), were inoculated in B-hPD-1 or B-hPD-1/hPD-L1/hHER2 mice respectively, and antitumor activities of Plin (7.5 mg/kg) plus Dato-DXd (5 mg/kg) ± Pembro (0.3 mg/kg) or T-DXd (3 mg/kg) ± Atezo (8 mg/kg) were evaluated. Results: On HER2+ KPL-4 cells, Plin showed synergistic activity with T-DXd with median CI <1 at 1:1, 2:1 and 4:1 ratios (T-DXd:Plin). In hTROP2+ MC38 tumor model, Dato-DXd antitumor activity was significantly enhanced by Plin (doublet) and further boosted by Pembro (triplet) with complete response rates of 0%, 20% and 60% respectively. Compared to Dato-DXd plus Plin or Pembro groups, the triple combo most significantly delayed tumor growth (p=0.009 or 0.028) and improved animal overall survival, and was better tolerated than Dato-DXd+Pembro (10% vs. 40% mortality). In hHER2+ MC38 tumor model, only the triple combo group (T-DXd+Plin+Atezo) prolonged animal survival better than T-DXd alone (p=0.0256). Conclusions: Plinabulin is a Phase 3 novel agent clinically validated to promote DC maturation and T-cell activation, which provides a durable response by strengthening the cancer-immunity cycle when combined with ICI and neutropenia-limiting agents such as docetaxel and ADCs. Clinical investigations assessing plinabulin safety and efficacy combined with TOP1-ADC alone or plus ICI are highly encouraged. Citation Format: Yingjuan June Lu, Xiaoyan He, Weiwei Cheng, Zhengyan Zhang, James Tonra, Lan Huang. Plinabulin boosts antitumor efficacy of topoisomerase inhibitor-based antibody-drug conjugates without or with immune checkpoint inhibitor [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 5597.