Thomas E. Smithgall, PhD

Src family kinases, HIV Nef, and AIDS.  Our group continues to explore the interaction of Src-family kinases with Nef, an HIV accessory protein essential for AIDS progression.  Nef binds directly to the SH3 domains of several Src-family members found in HIV target cells (Hck, Lyn and c-Src), leading to constitutive kinase activation.  In collaboration with the University of Pittsburgh Drug Discovery Institute, we are actively running in vitro and cell-based high-throughput screens of chemical libraries to identify selective inhibitors of the Nef:Hck complex. We have identified several new classes of Nef-dependent compounds with potent anti-HIV activity in vitro. These compounds represent exciting new tools for exploring the role of Nef-mediated Src-family kinase signaling in HIV pathogenesis as well as leads for anti-HIV drug development.  We are also exploring the structural biology of Nef in complex with Src family kinases and in the presence of small molecule inhibitors.

Src family kinases, Bcr-Abl and chronic myelogenous leukemia (CML).  Selective targeting of Bcr-Abl, the tyrosine kinase oncoprotein responsible for CML, with the Abl kinase inhibitor imatinib is very effective in the chronic phase of the disease.  However relapse due to drug resistance is an emerging problem resulting most often Bcr-Abl kinase domain mutations that impact drug binding.  Clinical imatinib resistance also results from hyperactivation of Src-family kinases in CML cells.  We discovered that Src-family kinases directly phosphorylate the Bcr-Abl SH3 domain, preventing the docking of this domain to its regulatory position on the SH2-kinase linker within the Abl kinase core. This finding suggests that Abl SH3:linker interactions persist in the context of Bcr-Abl, despite its constitutive kinase activity. This observation has led us to question whether enhanced SH3:linker interaction can allosterically inhibit both wild-type and drug-resistant forms of Bcr-Abl. To this end, we have developed Abl kinase variants in which SH3:linker interaction has been enhanced, and found that they show dramatically reduced kinase activity and enhanced inhibitor sensitivity.  We are currently developing screening assays to identify small molecules that induce this same allosteric effect as a new approach to selective inhibition of Bcr-Abl.

The c-Fes tyrosine kinase as a drug target in cancer.  The c-fes proto-oncogene encodes a non-receptor tyrosine kinase with unique regulatory features, including N-terminal F-BAR and coiled-coil domains.  Fes kinase activity is normally tightly controlled and contributes to the growth and differentiation of hematopoietic, endothelial and neuronal cells.  Unscheduled activation of Fes contributes to the development of several forms of cancer, including acute myeloid leukemia and multiple myeloma.  We are actively pursuing discovery of small molecule inhibitors selective for c-Fes, which will be useful tools to explore the role of this kinase in both normal biology and cancer.