The addition of ADI-PEG 20, a pegylated form of an arginine-depleting enzyme, to nab-paclitaxel and gemcitabine has encouraging activity in patients with advanced pancreatic adenocarcinoma while demonstrating minimal additional toxicity over that with cytotoxic therapy alone.
Maeve A. Lowery, MD
The addition of ADI-PEG 20, a pegylated form of an arginine-depleting enzyme, to nab-paclitaxel (Abraxane) and gemcitabine has encouraging activity in patients with advanced pancreatic adenocarcinoma while demonstrating minimal additional toxicity over that with cytotoxic therapy alone.
In an open-label, single-arm phase Ib dose-escalation trial, 7 of 18 patients (39%) treated with various doses of ADI-PEG 20 combined with nab-paclitaxel and gemcitabine experienced partial response (PR) per RECIST v1.1 criteria, and 10 patients (56%) had stable disease (SD), according to data presented at the 2017 Gastrointestinal Cancers Symposium in San Francisco.1Seven patients experienced ≥3 toxicity that was considered to be potentially caused by ADI-PEG 20, including neutropenia in 4 patients.
Data from the phase Ib clinical trial were presented in poster format by Maeve A. Lowery, MD, a medical oncologist at Memorial Sloan Kettering Cancer Center in New York City, and colleagues.
Pancreatic cancers are often deficient in argininosuccinate synthetase (ASS), the rate-limiting enzyme involved in arginine synthesis. Arginine has multiple intracellular roles, including nitric oxide formation and protein biosynthesis. In a preclinical study, arginine depletion with ADI-PEG 20 has been shown to be synthetically lethal with ASS deficiency.2Synergy between ADA-PEG 20 and docetaxel has also been demonstrated in both preclinical studies and in a phase I study of patients with various solid tumors.
For the phase Ib study presented by Lowery, 9 patients with metastatic pancreatic cancer who received up to 1 line of prior treatment were enrolled. The dose of ADI-PEG 20 was escalated using a 3+3 design in which cohorts of 3 to 6 patients were enrolled to 1 of 3 dose levels of ADI-PEG 20 (9, 18, or 36 mg/m2) with gemcitabine and nab-paclitaxel. After the recommended phase II dose was established, an additional 9 patients with untreated disease were treated at this dose level. Four patients (44%) in the dose escalation phase received prior 5-fluorouracil-based chemotherapy for metastatic disease.
Of the 6 patients who received 36 mg/m2of ADI-PEG 20 in the dose-escalation phase, 1 had a dose-limiting grade 3 liver toxicity, which was considered potentially to be related to the study drug. The recommended phase II dose of ADI-PEG 20 was set at 36 mg/m2.
Fifteen patients were treated at the recommended phase II dose. Best response among these 15, per RECIST v1.1 criteria, was PR in 6 patients (40%) and SD in 8 (53%). One patient came off the study due to disease progression. Four patients (26.7%) had SD ≥8 weeks, and the disease control rate at 24 weeks was 47%. The median progression-free survival was 6.5 months and 3 of the 15 patients (20%) were progression-free at 12 months. Two patients remained on study. The median overall survival was 11.3 months (95% CI, 4.9 months to not reached).
The authors measured ASS expression and found that median levels were 20% to 95% among the 4 patients with a confirmed PR, and ranged from 5% to 95% in those with SD. Arginine depletion was also confirmed in responders; the median duration of depletion to ≤10µm was 16 weeks for patients with PR and 13 weeks for patients with SD.
Overall, 7 patients (39%) had ≥3 toxicity that was considered potentially related to ADI-PEG 20, including 4 (22%) with neutropenia, 3 (17%) with lymphopenia, and 1 (5%) with thrombocytopenia. Six patients (33%) reported a rash, predominantly at the injection site, all of which were grade 1 or 2. There were no systemic allergic reactions or seizures attributed to ADI-PEG 20.
“Preliminary assessment of efficacy among patients treated at the maximally tolerated dose [36 mg/m2] is encouraging, with responses observed in ASS1-deficient and -proficient tumors,” the authors indicated. A phase II trial comparing this regimen to chemotherapy alone in patients with advanced pancreas adenocarcinoma is planned.