midostaurin and Gastrointestinal-Stromal-Tumors

Approximately 90 % of gastrointestinal tumors (GISTs) harbor an activating mutation in KIT or PDGFR alpha oncogene known to confer imatinib sensitivity. Imatinib is a tyrosine kinase inhibitor of KIT and PDGFRs that yields a 6-months progression-free survival (PFS) rate of 80 % in patients with advanced GISTs. Several studies have shown that response to imatinib in GIST patients mainly depends on the mutational status of KIT or PDGFR alpha. Moreover, most if not all patients treated with imatinib for advanced GIST will secondarily develop progressive disease under treatment. In the majority of cases, such progressions are the result of acquired resistance due to occurrence of secondary C-KIT mutations; especially for GIST with primary exon 11 mutations. Sunitinib is another approved drug and an inhibitor of multiple tyrosine kinases including KIT, PDGFR alpha as well as PDGFR beta and VEGFRs which are associated with angiogenesis. Sunitinib, in phase II and III trials was associated with durable clinical benefit in nearly 25 % of patients with advanced GIST resistant/intolerant to imatinib. Clearly, a better knowledge of the molecular mechanisms underlying the resistance to imatinib as well as the development of a new class of broad-spectrum tyrosine kinase inhibitors may allow in the near future new individualized therapeutic strategies for GISTs patients.

Topics: Antineoplastic Agents; Benzamides; Benzenesulfonates; Disease Progression; Drug Resistance, Neoplasm; Gastrointestinal Stromal Tumors; Humans; Imatinib Mesylate; Indoles; Mutation; Neoplasm Proteins; Niacinamide; Oligonucleotides; Phenylurea Compounds; Phthalazines; Piperazines; Piperidines; Protein Kinase Inhibitors; Proto-Oncogene Proteins c-kit; Pyridines; Pyrimidines; Pyrroles; Receptor, Platelet-Derived Growth Factor alpha; Sorafenib; Staurosporine; Sunitinib; Thiazoles

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal cancer of teh gastrointestinal tract. They are characterized by the expression of KIT. Therapeutically, metastatic GISTs are effectively treated by imatinib, a tyrosine kinase inhibitor (TKI) with activity against KIT and platelet-derived growth factor receptor. Gastrointestinal stromal tumors refractory to standard therapy with imatinib are a clinical challenge. This has lead to the clinical testing of a variety of agents used alone or in combination with other TKIs. Sunitinib, a multitargeted TKI, is the first drug available fort eh treatment of these patients. Additional trials are ongoing, evaluating the efficacy of the novel KIT TKIs AMG 706 and AMN 107 (nilotinib). RAD001, PKC412, and bavacizumab are being tested in conjunction with imatinib. Lastly, the heat-shock protein-90 inhibitor IPI-540 is also in phase I evaluation in imatinib-refractory patients with GIST. The future management of GIST is likely to be altered by the availability of more agents and by better biologic understanding of the patient populations each agent best treats.

Topics: Antibodies, Monoclonal; Antibodies, Monoclonal, Humanized; Antineoplastic Agents; Benzamides; Bevacizumab; Clinical Trials as Topic; Dasatinib; Drug Resistance, Neoplasm; Everolimus; Gastrointestinal Stromal Tumors; Humans; Imatinib Mesylate; Immunosuppressive Agents; Indoles; Niacinamide; Oligonucleotides; Piperazines; Protein Kinase Inhibitors; Proto-Oncogene Proteins c-kit; Pyrimidines; Pyrroles; Sirolimus; Staurosporine; Sunitinib; Thiazoles

Gastrointestinal stromal tumors (GISTs) are prototypes of stem cell factor receptor (c-KIT)-driven cancer. Two receptor tyrosine kinases, c-KIT and fms-tyrosine kinase (FLT3), are frequently mutated in acute myeloid leukemia (AML) patients, and these mutations are associated with poor prognosis. In this study, we discovered a multitargeted tyrosine kinase inhibitor, compound

Topics: Animals; Antineoplastic Agents; Apoptosis; Cell Proliferation; Female; fms-Like Tyrosine Kinase 3; Gastrointestinal Neoplasms; Gastrointestinal Stromal Tumors; Humans; Leukemia, Myeloid, Acute; Male; Mice; Mice, Inbred ICR; Mice, Inbred NOD; Mice, Nude; Mice, SCID; Mutation; Phosphorylation; Protein Kinase Inhibitors; Proto-Oncogene Proteins c-kit; Pyrimidines; Rats, Sprague-Dawley; Tumor Cells, Cultured; Xenograft Model Antitumor Assays

Certain mutations within c-KIT cause constitutive activation of the receptor and have been associated with several human malignancies. These include gastrointestinal stromal tumors (GIST), mastocytosis, acute myelogenous leukemia, and germ cell tumors. The kinase inhibitor imatinib potently inhibits c-KIT and is approved for treatment of GIST. However, secondary point mutations can develop within the kinase domain to confer resistance to imatinib and cause drug-resistant relapse. A common mutation, which results in a V654A substitution, has been documented in imatinib-resistant GIST patients. We expressed c-KIT cDNA constructs encoding the V654A substitution alone and in combination with a typical activating exon 11 mutation characteristic of GIST, V560G, in factor-dependent FDC-P1 cells. The V654A substitution alone resulted in enhanced proliferation in c-KIT ligand (stem cell factor) but not factor independence. Cells expressing the double mutant were, like those expressing single V560G mutant c-KIT, factor independent. Analysis of cellular proliferation in the presence of imatinib showed that the V654A substitution alone conferred resistance. The difference in sensitivity was especially pronounced for cells expressing single mutant V560G c-KIT compared with double mutant V560G/V654A c-KIT. The findings were supported by studies of c-KIT phosphorylation. Analysis of the crystal structure of imatinib in complex with the kinase domain of c-KIT predicts that the V654A substitution directly affects the binding of imatinib to the receptor. Alternative c-KIT inhibitors, nilotinib (AMN107) and PKC412, were also less active on V560G/V654A c-KIT than on the V560G single mutant; however, nilotinib, like imatinib, potently inhibited the V560G mutant. PKC412 strongly inhibited imatinib-resistant D816V c-KIT.

Topics: Animals; Antineoplastic Agents; Apoptosis; Benzamides; Cell Proliferation; Cells, Cultured; Drug Resistance, Neoplasm; Exons; Fluorescent Antibody Technique; Gastrointestinal Stromal Tumors; Humans; Imatinib Mesylate; Immunoprecipitation; Mice; Mutation; Myeloid Progenitor Cells; Phosphorylation; Piperazines; Protein Kinase Inhibitors; Protein-Tyrosine Kinases; Proto-Oncogene Proteins c-kit; Pyrimidines; Staurosporine

Activating mutations in platelet-derived growth factor receptor alpha (PDGFRA) have been reported in a subset of gastrointestinal stromal tumor (GIST) patients who do not express the mutant stem cell factor receptor c-kit. The responsiveness of mutant PDGFRA-positive GIST to imatinib depends on the location of the PDGFRA mutation; for example, the V561D juxtamembrane domain mutation is more sensitive to imatinib than the D842V kinase domain mutation. In this study, we compare the effects of 3 tyrosine kinase inhibitors, PKC412 and nilotinib, and imatinib, on 2 GIST-related PDGFRA mutants, V561D and D842V, which possess differential sensitivity to imatinib.. The effects of PKC412, nilotinib, and imatinib, alone and in combination, were evaluated via in vitro proliferation studies performed with V561D- or D842V-PDGFRA mutants. The effects of nilotinib and PKC412, alone and combined, were investigated in vivo.. PKC412 potently inhibited the V561D-PDGFRA mutant in vitro and the D842V-PDGFRA mutant in vitro and in vivo. Both imatinib and nilotinib displayed potent activity in vitro against the V561D-PDGFRA mutant but were significantly less efficacious against D842V-PDGFRA. However, when combined with either imatinib or PKC412, nilotinib showed no evidence for antagonism and acted in a cooperative fashion against D842V-PDGFRA.. Our findings support the clinical testing of PKC412 for treatment of mutant PDGFRA-GIST. The data also support the use of nilotinib as a treatment option for V561D-PDGFRA-associated GIST, although the reduced sensitivity of D842V-PDGFRA probably limits the potential of nilotinib monotherapy for D842V-PDGFRA-associated GIST.

Topics: Animals; Antineoplastic Combined Chemotherapy Protocols; Benzamides; Cell Line; Cell Proliferation; Dose-Response Relationship, Drug; Drug Resistance, Neoplasm; Gastrointestinal Stromal Tumors; Imatinib Mesylate; Male; Mice; Mice, Nude; Phosphorylation; Piperazines; Point Mutation; Protein Kinase Inhibitors; Pyrimidines; Receptor, Platelet-Derived Growth Factor alpha; Staurosporine; Tyrosine; Xenograft Model Antitumor Assays

Resistance is a major challenge in the treatment of patients with gastrointestinal stromal tumors (GISTs). We investigated the mechanisms of resistance in patients with progressive GISTs with primary KIT mutations and the efficacy of the kinase inhibitor PKC412 for the inhibition of imatinib-resistant mutants.. We performed a cytogenetic analysis and screened for mutations of the KIT and PDGFRA kinase domains in 26 resistant GISTs. KIT autophosphorylation status was assessed by Western immunoblotting. Imatinib-resistant GIST cells and Ba/F3 cells expressing these mutant proteins were tested for sensitivity to imatinib and PKC412.. Six distinct secondary mutations in KIT were detected in 12 progressive tumors, with V654A and T670I found to be recurrent. One progressive tumor showed acquired PDGFRA -D842V mutation. Amplification of KIT or KIT / PDGFRA was found in 2 patients. Eight of 10 progressive tumors available for analysis showed phosphorylated KIT. Two remaining progressive tumors lost KIT protein expression. GIST cells carrying KIT -del557-558/T670I or KIT -InsAY502-503/V654A mutations were resistant to imatinib, while PKC412 significantly inhibited autophosporylation of these mutants. Resistance to imatinib and sensitivity to PKC412 of KIT -T670I and PDGFRA -D842V mutants was confirmed using Ba/F3 cells.. This study shows the high frequency of KIT/PDGFRA kinase domain mutations in patients with secondary resistance and defines genomic amplification of KIT / PDGFRA as an alternative cause of resistance to the drug. In a subset of patients, cancer cells lost their dependence on the targeted tyrosine kinase. Our findings show the sensitivity of the imatinib-resistant KIT -T670I and KIT -V654A and of PDGFRA -D842V mutants to PKC412.

Topics: Adult; Aged; Antineoplastic Agents; Benzamides; Drug Resistance, Neoplasm; Exons; Female; Gastrointestinal Stromal Tumors; Humans; Imatinib Mesylate; Male; Middle Aged; Mutation; Piperazines; Proto-Oncogene Proteins c-kit; Pyrimidines; Receptor, Platelet-Derived Growth Factor alpha; Staurosporine