Phase II Testing of ADI-PEG in Hepatocellular Carcinoma

Amino acid deprivation therapy is an effective means for the treatment of some forms of cancer. Recently it has been found that human hepatocellular carcinomas (HCC) cell lines appear to require arginine for growth. Arginine is not an essential amino acid for human adults or infants as it can be synthesized from citrulline (for review see Rogers 1994). Therefore, selective elimination of arginine from the circulation may be a means of treating patients with metastatic melanoma or non resectable HCC. The enzyme arginine deiminase (ADI) metabolizes arginine into citrulline (Cunin 1986). However, ADI is only found in microbes and not in humans. ADI is therefore, highly immunogenic and has a short serum half-life following injection. These potential drawbacks (microbial source and thus viewed as foreign by the human immune system, and a short serum half-life) can be overcome by covalent attachment of polyethylene glycol (PEG) to argininedeiminase and termed this drug ADI-PEG 20. ADI-PEG 20 appears to be an effective anti-cancer treatment for human HCC. Pharmacokinetic and pharmacodynamic data indicates a once a week injection of 160 IU/m2 of ADI-PEG 20 eliminates all detectable arginine from the circulation for at least 7 days. This treatment appears to be well tolerated. The purpose of this study is to determine the efficacy of this treatment in patients with HCC. Efficacy is a primary end point of this study. No patients will recieve placebo.