Abstract A081: Phase I study of mesothelin-targeted immunotoxin LMB-100 given as a long infusion

Abstract

Abstract Purpose: LMB-100 recombinant immunotoxin consists of a mesothelin-binding Fab for targeting and a modified Pseudomonas exotoxin A payload. Previous Phase 1 clinical testing of a 30-minute LMB-100 infusion format identified dose-limiting toxicity (DLT) of capillary leak syndrome (CLS) and a serum half-life of ~60 minutes. Pre-clinical data suggested that extending infusion time could improve anti-tumor efficacy by increasing tumor cell duration of exposure to LMB-100. The primary objective of this study was to determine the safety and tolerability of administering LMB-100 over a longer infusion time. We hypothesized that reduced CMAX would result in decreased severity of off-target toxicities like CLS without decreasing anti-tumor activity. Patients and Methods: Patients (n = 15) with pancreatic adenocarcinoma and other mesothelin-expressing solid tumors (n = 3; mesothelioma, colon adenocarcinoma, ampullary carcinoma) treated on 3 dose levels received long infusion (24-48 hours) LMB-100 (65 or 100 mcg/kg/day) with or without a loading dose (40 mcg/kg over 30 minutes) for up to 2 cycles. Safety and tolerability, pharmacokinetics, immunogenicity and anti-tumor activity were assessed. Results: DLT of proteinuria (grade 3) was observed in 1 of 6 patients receiving 100 mcg/kg/day over 48 hours with pre-load. Three of 6 patients at this dose level developed significant CLS (>5 kg weight gain from fluid edema) that was not dose-limiting. No CLS was observed in the 6 patients who received 100 mcg/kg over 24 hours on days 1 and 4 with pre-load. Increased immunogenicity was observed with the long infusion compared to standard administration format: 8 of 9 patients receiving 2nd cycle treatment had undetectable plasma LMB-100 concentration during this cycle that was associated with the development of high titer anti-LMB-100 antibodies. Progressive disease was observed in 11 of 12 evaluable patients, and none of 8 evaluable patients with pancreatic adenocarcinoma had a clinically significant decline in CA 19-9 tumor marker. Conclusions: Long infusion format of delivery for LMB-100 can reduce CLS but increases immunogenicity. No anti-tumor activity was observed. Citation Format: Christine Alewine, Mehwish Iqra Ahmad, Cody J Peer, Seth Steinberg, William D Figg, Raffit Hassan, Ira Pastan. Phase I study of mesothelin-targeted immunotoxin LMB-100 given as a long infusion [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr A081. doi:10.1158/1535-7163.TARG-19-A081