A phase I study of mesothelin-targeted immunotoxin LMB-100 in combination with nab-paclitaxel for patients with previously treated advanced pancreatic cancer

307 Background: LMB-100 is a Pseudomonas exotoxin A-based immunotoxin that targets mesothelin (MSLN). MSLN is expressed by >75% of pancreatic adenocarcinomas (PDAC). LMB-100 kills MSLN-expressing cells by irreversibly modifying elongation factor-2 to halt protein synthesis. Phase I studies of LMB-100 defined the maximum tolerated dose (MTD) of 140 mcg/kg IV given on D1, 3 and 5 of a 21-day cycle. Development of anti-drug antibodies (ADAs) limited patient drug exposure beyond cycle 2. Our pre-clinical data showed that combination of LMB-100 with a taxane resulted in synergistic anti-tumor activity. Methods: We conducted a phase I single center study (standard 3+3 design) to determine the MTD of LMB-100 given with nab-paclitaxel in patients with previously treated advanced PDAC. LMB-100 was given on D1, 3 and 5 of a 21-day cycle, and nab-paclitaxel (125 mg/m2) on D1 and D8. Initial patients could receive a maximum of 4 cycles, but subsequently a 2-cycle maximum was employed. Results: Fourteen patients (median age 58) were enrolled. Two of 6 patients experienced DLTs at the 100 mcg/kg dose of LMB-100 (myalgia- 2 pts, fatigue- 1 pt, hypotension- 1 pt; all grade 3). One of 8 patients had DLT at the 65 mcg/kg dose (edema, urine output decrease- both grade 3). Other toxicities related to LMB-100 included hypoalbuminemia, edema-associated weight gain, hyponatremia, fatigue, drug fever, infusion-related reaction, hypophosphatemia, nausea and anorexia. One patient died on treatment from complications of bowel perforation attributed to cancer. All patients achieved detectable serum levels of LMB-100 during the first cycle, even those with pre-existing ADAs, and 5 of 8 did so during cycle 2. One patient receiving the 65 mcg/kg dose had a confirmed partial response, and CA 19-9 dropped by > 50% in 5 of 8 evaluable patients. Conclusions: MTD of LMB-100 is 65 mcg/kg given with nab-paclitaxel on this schedule. Anti-tumor activity was observed. A phase II cohort is currently being accrued. Clinical trial information: NCT02810418.