Abstract
295 Background: ADI-PEG 20 (A) is a pegylated form of arginine depleting enzyme, arginine deaminase. Normal cells synthesise arginine using the enzyme argininosuccinate synthetase (ASS). A selectively targets malignant cells which lack ASS. A has shown encouraging pre clinical activity as monotherapy in PC, and synergistic activity with gem and taxanes. Methods: Eligibility: Metastatic PC, up to one line of prior treatment (dose escalation cohort:ct) no prior treatment (expansion ct), ECOG 0-1.Treatment: gem 1,000 mg/m2, nab-P 125mg/m2 3 out of 4 weeks, A 18 mg IM weekly (ct 1), A 36mg weekly (ct 2 and expansion ct). Primary endpoint: determine MTD of A in combination with nab-P and gem. Statistical plan: Single arm, non-randomized, open-label, phase IB, standard 3 + 3 dose escalation with expansion ct of 9 patients at MTD. Secondary endpoints: progression-free survival (PFS), response rate, overall survival (OS), safety, tolerability, blood and archival tumor analyses for ASS expression and immunogenicity. Pts treated at MTD and on expansion cohort were eligible for primary and secondary endpoints. Results: Between 11/14 and 09/15, 18 pts enrolled. 4 pts (22%) had 1 prior line of therapy. Toxicity attributable to A was limited to grade 1 rash/erythema at injection site (n = 3). Cohort 2 was expanded to 6 pts due to DLT of elevated LFTs, no further DLTs observed. ≥ grade 3 toxicity attributable to gem and/or nab-P included elevation in AST/ALT, hematologic toxicity, fatigue, diarrhea, neutropenic fever, alopecia as expected. No A related grade 3-5 toxicities were observed. Response: 6 pts (40%) PR, including one previously treated pt, 8 pts (53%) stable disease (SD), 1 pt inevaluable. Two pts continue on study, median PFS 6.5 months (95% CI 5.3 – 15.2), median OS 11.3 months (95% CI 4.9- . ). Eight of 15 pts treated at MTD received 2nd-line chemotherapy at progression. Five of 11 archival tumors samples tested for ASS1 expression by IHC were deficient. Conclusions: A was well tolerated in combination with gem and nab-P. Activity was observed in treated and untreated pts, and in pts with ASS deficient and proficient tumors; synergy of A with cytotoxics may be independent of ASS status and future investigation in an unselected population is warranted. Clinical trial information: NCT02101580.
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