Phase I study of mesothelin-targeted immunotoxin LMB-100 in combination with tofacitinib in persons with pancreatobiliary cancer or other mesothelin expressing solid tumors.

Abstract

TPS452 Background: LMB-100 recombinant immunotoxin consists of a mesothelin-binding Fab for targeting with a modified Pseudomonas exotoxin A payload. Formation of anti-drug antibodies (ADAs) is thought to contribute significantly to limited clinical efficacy of LMB-100 seen in prior clinical trials. Most patients develop clinically meaningful ADAs after 1-2 cycles of LMB-100, resulting in rapid neutralization of LMB-100 during subsequent cycles and undetectable plasma drug levels. Tofacitinib is an oral Janus Kinase-1 and -3 (JAK) inhibitor approved by the FDA for the treatment of rheumatoid arthritis and ulcerative colitis. Pre-clinical studies have shown that tofacitinib can prevent the formation of ADAs against recombinant immunotoxin (Onda et al. Journal of Immunology 2014), and that co-administration of tofacitinib with LMB-100 increases immunotoxin serum half- life in mice and anti-tumor efficacy (Simon et al. JCI Insight 2019). We hypothesize that co-administration of tofacitinib with LMB-100 will prevent or delay the formation of high titer ADAs to LMB-100, such that 2 effective cycles of immunotoxin can be administered to patients. Methods: This phase I clinical trial consists of a dose escalation phase using 3+3 design to determine the maximum tolerated dose (MTD) of LMB-100 that can be administered with tofacitinib in participants (n = 18 max) with mesothelin-expressing solid tumors, followed by a dose expansion phase at the MTD for participants (n = 15) with pancreatic adenocarcinoma or extrahepatic cholangiocarcinoma. The primary objective of the expansion phase is to determine whether co-administration of tofacitinib delays formation of neutralizing anti-LMB-100 ADAs for cycle 2 of treatment as measured by LMB-100 plasma drug levels. A positive outcome will be reached if percent of participants achieving threshold LMB-100 drug levels during cycle 2 increases from 50% to 80% (83.6% probability if >10 of 15 evaluable participants meet this milestone). Plasma drug levels during cycle 3 will also be analyzed as a secondary endpoint. Key inclusion criteria include adults with histologically confirmed previously treated solid tumor malignancies. Participants will receive tofacitinib 10 mg twice daily on days 1-10 and LMB-100 at 65, 100, or 140 mcg/kg on days 4, 6 and 8 of a 21-day cycle. The dose escalation phase has been completed and enrollment onto dose expansion phase is ongoing. Clinical trial information: NCT04034238.