A single amino acid exchange inverts susceptibility of related receptor tyrosine kinases for the ATP site inhibitor STI-571.
ABSTRACT The tyrosine kinase inhibitor STI-571 potently blocks BCR-Abl, platelet-derived growth factor (PDGF) alpha- and beta-receptors, and c-Kit kinase activity. Flt3, a receptor tyrosine kinase closely related to PDGF receptors and c-Kit is, however, not inhibited by STI-571. Sequence alignments of different kinases and indications from the crystal structure of the STI-571 Abl kinase complex revealed amino acid residues that are probably crucial for this activity profile. It was predicted that Flt3 Phe-691 in the beta5 strand may sterically prevent interaction with STI-571. The point mutants Flt3 F691T and PDGFbeta-receptor T681F were constructed, and kinase assays showed that the Flt3 mutant but not the PDGFbeta-receptor mutant is inhibited by STI-571. Docking of STI-571 into computer models of the PDGFbeta-receptor and Flt3 kinase domains and comparison with the crystal structure of the STI-571 Abl kinase complex indicated very similar binding sites among the three nonphosphorylated kinases, suggesting corresponding courses of their Asp-Phe-Gly motifs and activation loops. Accordingly, we observed reduced sensitivity of preactivated compared with nonactivated PDGFR-beta for the inhibition by STI-571. Courses of the activation loop that collide with STI-571 binding explain its inactivity at other kinases as the insulin receptor. The binding site models of PDGFR-beta and Flt3 were applied to predict structural approaches for more selective PDGFbeta-receptor inhibitors.
- SourceAvailable from: Margherita Nannini[show abstract] [hide abstract]
ABSTRACT: Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumors of the gastrointestinal tract. Most GIST harbor a mutation affecting either the KIT or PDGFRA genes, whereas a small subgroup of tumors is wild type for mutations.Mutation of tyrosine kinase receptors is a mechanism of drug resistance that can occur either at the beginning of treatment (primary resistance) or during the course of therapy (secondary resistance). In addition, mutational status can predict the response to treatment with tyrosine kinase inhibitors, but the role of mutational status as a prognostic factor remains controversial.Evidence of a potential role of mutational status as a prognostic factor has emerged over the past decade. The presence of KIT exon 11 insertion/deletion involving either one or both Trp557-Lys558 amino acids correlates with a poorer clinical outcome if compared to patients with tumors wild type for KIT exon 11 mutations. A malignant clinical behavior has also been documented for KIT exon 13 and KIT exon 9 mutant GIST. Patients with GIST harboring a PDGFRA mutation seem to have a better prognosis than the others.The aim of this paper is to review the clinical significance of tyrosine kinase mutational status.Journal of Translational Medicine 01/2011; 9:75. · 3.46 Impact Factor
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ABSTRACT: Acute myeloid leukemia (AML) is a hematologic malignancy with a poor prognosis. Approximately one quarter of the patients with AML also carry an internal tandem duplication (ITD) mutation in the gene encoding FMS-like tyrosine kinase 3 (FLT3), which has a significantly deleterious impact on prognosis. The ITD mutation renders FLT3 constitutively active and leads to uncontrolled proliferation of the leukemic blast. Over the course of the last decade, a variety of compounds have been developed in preclinical and clinical studies as potent inhibitors of FLT3. Many of the earlier agents under investigation, such as lestaurtinib, midostaurin, and sunitinib, were initially developed as inhibitors of other tyrosine kinases and as targeted therapies in a variety of malignancies. These compounds have been demonstrated to have some efficacy in clinical trials of AML, mainly manifesting as transient decreases in circulating blasts correlating with effective in vivo suppression of the FLT3 target. Nevertheless, the cumbersome pharmacokinetics of some compounds and the suboptimal specificity and potency of others have limited their therapeutic efficacy. In the last few years, newer, more potent and specific agents have been under investigation, with the leading example being AC220. This agent has shown significant promise in early phases of clinical investigation, and is currently in more advanced clinical trials. Hope remains that FLT3 inhibition will be become an effective therapeutic adjunct to our current treatment approach to AML.The Oncologist 07/2011; 16(8):1162-74. · 4.10 Impact Factor
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ABSTRACT: Acute myeloid leukemia (AML) is an aggressive hematologic malignancy which is cured in a minority of patients. A FLT3-internal tandem duplication (ITD) mutation, found in approximately a quarter of patients with de novo AML, imparts a particularly poor prognosis. Patients with FLT3-ITD AML often present with more aggressive disease and have a significantly higher propensity for relapse after remission. The therapeutic approach for these patients has traditionally included intensive induction chemotherapy, followed by consolidative chemotherapy or hematopoietic cell transplantation (HCT). In recent years, multiple small molecule inhibitors of the FLT3 tyrosine kinase have been studied preclinically and in clinical trials. The earlier generation of these agents, often non-specific and impacting a variety of tyrosine kinases, produced at best transient peripheral blood responses in early clinical trials. Additionally, the combination of FLT3 inhibitors with cytotoxic regimens has not, as of yet, demonstrated an improvement in overall survival. Nevertheless, multiple current trials, including those with sorafenib, lestaurtinib, and midostaurin, continue to study the combination of FLT3 inhibitors with standard chemotherapy. Factors such as sustained FLT3 inhibition, protein binding, pharmacokinetics, and the presence of elevated FLT3-ligand levels appear to significantly impact the potency of these agents in vivo. In recent years, the development of more specific and potent agents has generated hope that FLT3 inhibitors may play a more prominent role in the treatment of FLT3-ITD AML in the near future. Nevertheless, questions remain regarding the optimal timing and schedule for incorporation of FLT3 inhibitors. The suitability, type, and timing of allogeneic HCT in the therapeutic approach for these patients are also issues which require further study and definition. Recent retrospective data appears to support the efficacy of allogeneic HCT in first complete remission, possibly due to a graft versus leukemia effect. However, larger prospective studies are necessary to further elucidate the role of HCT and its potential combination with FLT3 inhibitor therapy. We are hopeful that current clinical investigation will lead to an optimization and improvement of outcomes for these patients.American journal of blood research. 01/2011; 1(2):175-89.