Design, engineering, and characterization of a novel long-acting (Pegylated) single isomer human arginase for arginine depriving anticancer treatment

• Published in: Journal of clinical oncology Vol. 37; no. 15_suppl; p. 3090
• Main Authors: Yu, Kuo-Ming, Pang, Tammy Pui-Shi, Cutler, Murray, Lau, Johnson Yiu-Nam, Lo, Thomas Wai-Hung, Leung, Thomas Yun-Chung
• Format: Journal Article
• Language: English
• Published: 20.05.2019
• ISSN: 0732-183X; 1527-7755
• DOI: 10.1200/JCO.2019.37.15_suppl.3090

Abstract only 3090 Background: Arginine deprivation therapy is an attractive strategy to treat arginine-auxotrophic cancers with deficient expression of argininosuccinate synthetase, argininosuccinate lyase or ornithine transcarbamylase. We have designed and engineered a novel human arginase with single site pegylation exerting excellent preclinical pharmacologic profile to serve as a new class of therapy. Methods: Human arginase has three cysteines (at position 45, 168, 303) and none of them is in or close to the active site. Two cysteines were mutated to serines, leaving the only cysteine at 45 for the simple and cost-effective synthesis of a single isoform of pegylated human arginase. Different forms of PEG moieties were evaluated for the selection of a drug candidate (PT01), followed by extensive characterization. Results: Converting Cys at 168 and 303 to serine impacted least on enzymatic activity (with cobalt cation). Pegylation with different sizes and shapes showed that 20 and 40 kDa (linear and branched) had similar PK/PD profile without damaging enzymatic activity. Therefore, arginase modified with a linear 20 kDa PEG was chosen as the candidate. A single 0.4 mg/kg IV dose of PT01 in rats induced 4 days of near complete plasma arginine depletion, while 6–7 days of depletion between 1.2 and 2 mg/kg. Plasma arginine levels were reversible. First-order clearance of both plasma PT01 concentration and activity suggested a terminal half-life of about 20 hours. In vitro assay showed very potent cytotoxicity at sub-nM level against various cell lines of breast, prostate, and pancreas in origins. In two mouse cancer models (hard-to-cure pancreas and castration-resistant prostate), weekly infusion at 5 and 10 mg/kg induced significant tumor growth inhibition of 44-67%. All mice experienced dose-dependent but rapidly reversible weight loss following each weekly dose. Conclusions: A novel single isoform of pegylated human arginase was created, showing excellent enzymatic activity, PK/PD profiles, and cytotoxicity in vitro. Mouse xenograft models showed good tumor growth inhibition activity with tolerable toxicity as manifested on transient weight loss during therapy.