ADI – Modified arginine deiminase as anti-tumor drug

Arginine deiminase (ADI) produces depletion of arginine and has been studied as a potential antitumor drug for the treatment of arginine-auxotrophic tumors such as hepato-cellular carcinoma (HCC) and malignant melanoma. These tumors that are sensitive to arginine depletion do not express a certain key enzyme in the synthesis of arginine from citrulline. Recent data showed that a pegylated form of ADI inhibits human melanomas and HCCs in vitro and in vivo. Furthermore, studies on human lymphatic leukemia cell lines confirmed ADI´s anti-angiogenic activity.

The main limitation for in vivo applications of numerous ADIs lies in their pH-dependant activity profile. ADI from Pseudomonas plecoglossicida (PpADI) for example has a pH optimum at 6.5. A shift from 6.5 to 7.5 (physiological conditions) results in an activity drop of approximately 80%. In order to shift the pH optimum, a directed-evolution protocol based on an adapted citrulline screening protocol in microtiter-plate format was developed and validated by the present invention. A proof of concept for ADI engineering resulted in an improved pH optimum and increased resistance under physiological and slightly alkaline conditions.

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