L-Asparaginase - Perspectives On The Mechanisms Of Action And Resistance

L-Asparaginase, the enzyme that hydrolyzes asparagine to yield aspartic acid and ammonia, is isolated from various bacterial sources and is an effective and well-accepted chemotherapeutic agent, especially in the treatment of pediatric acute lymphoblastic leukemia. The enzyme works by depleting the tumor of its source of asparagine from the circulation, as tumors specifically of lymphoid origin are incapable of intracellular asparagine synthesis and are L-asparaginase-sensitive upon presentation. Despite its effectiveness, however, the use of L-asparaginase as a chemotherapeutic agent is somewhat limited because of its toxicity and spontaneous acquisition of resistance to this enzyme by the tumor cells. Numerous side effects of L-asparaginase treatment have been reported and present a clinical challenge. Resistance to L-asparaginase occurs often and is highly correlated with an increase in the cellular production of asparagine synthetase, the enzyme responsible for asparagine biosynthesis. inactivation of asparagine synthetase in resistant tumor cells renders them sensitive to L-asparaginase treatment. Different strategies to inhibit intracellular asparagine synthetase are being used to overcome L-asparaginase resistance. Additional resistance can occur due to immunologic reactions to the foreign protein. Strategies of chemical modification of L-asparaginase have been used successfully to diminish the immunogenicity of the enzyme and enhance its utility in treatment of acute lymphoblastic leukemia