Mohammad Azam

Chronic myelogenous leukemia (CML) is a myeloproliferative disease that accounts for ~ 20% of all cases of leukemia. CML is associated with the translocation (9;22), resulting in the generation of the BCR-ABL chimeric gene. Numerous experimental models have established that the BCR-ABL oncoprotein is sufficient to induce CML. Studies from several groups have shown that the enhanced tyrosine kinase activity of BCR-ABL is responsible for its oncogenic activity. For this reason, STI-571 (Gleevec) was designed, which functions by competitive inhibtion of the ATP-binding site of the kinase domain, leading to reduced phosphorylation of proteins involved in BCR-ABL signaling. STI-571 causes growth arrest or apoptosis in BCR-ABL expressing cells but has minimal effects on normal cells. Phase I trials of STI-571 showed remission in patients in chronic phase as well as blast crisis. While, responses in chronic phase are durable, in blast crisis remission lasted only a few months, despite continued drug treatment. Relapses were due to the reactivation of BCR-ABL kinase activity either through the amplification of BCR-ABL (n=3) or through point mutation in the Abl-kinase domain (n=6) leading to reduced/lost affinity of the substrate (STI-571). To date only a limited number of resistant patients have been analyzed and only a single mutation has been observed. We wish to explore whether other mutations in BCR-ABL may confer resistance to STI-571. Using a novel set of retroviral vectors designed in our laboratory that facilitates rescue of cDNAs from rare clones of cells, I propose to screen a random mutation library of the Abl-kinase domain of BCR-ABL for resistance to STI-571. Moreover, a site directed mutation approach against the STI-571 binding region and its analysis in drug tolerance will also be undertaken. These studies will provide an understanding of the potential range of genetic variation in BCR-ABL that accounts for STI-571 resistance, and will contribute to the development of diagnostic tools and the next generation of rationally designed kinase inhibitors.



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		Mohammad Azam, Ph.D. Biochemistry and Molecular Biology Jawaharlal Nehru University, New Delhi, India - 1999 Instructor in Pediatrics
		Chronic myelogenous leukemia (CML) is a myeloproliferative disease that accounts for ~ 20% of all cases of leukemia. CML is associated with the translocation (9;22), resulting in the generation of the BCR-ABL chimeric gene. Numerous experimental models have established that the BCR-ABL oncoprotein is sufficient to induce CML. Studies from several groups have shown that the enhanced tyrosine kinase activity of BCR-ABL is responsible for its oncogenic activity. For this reason, STI-571 (Gleevec) was designed, which functions by competitive inhibtion of the ATP-binding site of the kinase domain, leading to reduced phosphorylation of proteins involved in BCR-ABL signaling. STI-571 causes growth arrest or apoptosis in BCR-ABL expressing cells but has minimal effects on normal cells. Phase I trials of STI-571 showed remission in patients in chronic phase as well as blast crisis. While, responses in chronic phase are durable, in blast crisis remission lasted only a few months, despite continued drug treatment. Relapses were due to the reactivation of BCR-ABL kinase activity either through the amplification of BCR-ABL (n=3) or through point mutation in the Abl-kinase domain (n=6) leading to reduced/lost affinity of the substrate (STI-571). To date only a limited number of resistant patients have been analyzed and only a single mutation has been observed. We wish to explore whether other mutations in BCR-ABL may confer resistance to STI-571. Using a novel set of retroviral vectors designed in our laboratory that facilitates rescue of cDNAs from rare clones of cells, I propose to screen a random mutation library of the Abl-kinase domain of BCR-ABL for resistance to STI-571. Moreover, a site directed mutation approach against the STI-571 binding region and its analysis in drug tolerance will also be undertaken. These studies will provide an understanding of the potential range of genetic variation in BCR-ABL that accounts for STI-571 resistance, and will contribute to the development of diagnostic tools and the next generation of rationally designed kinase inhibitors.
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