PA289：一种同类首创的前药载荷，具有新型作用机制和良好的疗效/安全性特征

Background: PA289 is a novel seco-CBI based linker-payload with a differentiated protein alkylation (ProAlk) mechanism of action, killing cells via alkylation of cytosolic proteins​ (Wirth et al , 2012). It uses IKSUDA's stable, cysteine-specific PermaLink conjugation technology and glucuronide triggers to enhance tolerability. Tumor overexpressed lysosomal glucuronidase leads to selective activation after ADC uptake and limits systemic release of the active payload. PA289's unique MOA and prodrug format lead to controlled activation support improved therapeutic performance and help address the clinical challenge of ADC sequencing. Methods: The prodrug linker-payload PA289 was conjugated using PermaLink technology to generate ADCs with a drug to antibody ratio of approximately 4. In vitro cell-killing and bystander activity was evaluated by CellTiter-Glo assay and impact on cell cycle was determined by propidium iodide staining. An HMGB1 ELISA was used to monitor immunogenic cell death. Induction of apoptosis was measured by Caspase-Glo® 3/7 assay. Efficacy studies were conducted in immunodeficient mice engrafted with human cancer xenografts. Toxicology studies were conducted in cynomolgus monkeys. Results: The free payload shows potent in vitro activity against 248 cancer cell lines from 15 solid cancer indications (IC50 from 1-100 pM). Both the free payload and a PA289 ADC induce S-phase cell cycle arrest and apoptosis in vitro . The payload triggers immunogenic cell death and, unlike MMAE or deruxtecan, is a poor substrate for ABCB1 and ABCG2 drug efflux pumps. A PA289 ADC demonstrates stronger bystander cell-killing than an MMAE-ADC in co-cultures in vitro . Both the payload and a PA289 ADC retain activity against a trastuzumab deruxtecan-resistant cell line in vitro . This latter finding was confirmed in vivo, where a PA289 ADC shows durable tumor regressions in a trastuzumab deruxtecan-resistant xenograft. PA289 ADCs against multiple targets are active in vivo across several lung, esophageal and breast cancer xenograft models with a single dose of 0.3 mg/kg and show 10 to 20-fold greater potency than clinical benchmark ADCs with topoisomerase I inhibitor payloads. Despite this high in vivo potency, a PA289 ADC was well-tolerated in cynomolgus monkeys at 8 mg/kg (single dose) and 5 mg/kg repeat dose (Q3Wx2), with minimal test-article related findings. Conclusions: PA289 is an ADC linker-payload with a unique protein alkylation mechanism and a novel glucuronide prodrug design, showing strong in vitro potency and low susceptibility to drug efflux pumps. PA289-based ADCs demonstrate superior in vivo activity compared with deruxtecan ADCs across multiple tumor models, with excellent tolerability in monkeys at doses well above those required for durable tumor regressions.