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The microphthalmia-associated transcription factor (MITF) is indispensable for the viability of melanocytic cells, is an oncogene in melanoma and has a cell type-specific expression pattern. As the modulation of MITF activity by direct chemical targeting remains a challenge, we assessed a panel of drugs for their ability to downregulate MITF expression or activity by targeting its upstream modulators. We found that the multi-kinase inhibitors midostaurin and sunitinib downregulate MITF protein levels. To identify the target molecules shared by both the drugs in melanocytic cells, a chemical proteomic approach was applied and AMP-activated kinase (AMPK) was identified as the relevant target for the observed phenotype. RNA interference and chemical inhibition of AMPK led to a decrease in MITF protein levels. Reduction of MITF protein levels was the result of proteasomal degradation, which was preceded by enhanced phosphorylation of MITF mediated by ERK. As expected, downregulation of MITF protein levels by AMPK inhibition was associated with decreased viability. Together, these results identify AMPK as an important regulator for the maintenance of MITF protein levels in melanocytic cells. [ABSTRACT FROM AUTHOR]

Resistance to the BCR-ABL tyrosine kinase inhibitor imatinib poses a pressing challenge in treating chronic myeloid leukemia (CML). This resistance is often caused by point mutations in the ABL kinase domain or by overexpression of LYN. The second-generation BCR-ABL inhibitor INNO-406 is known to inhibit most BCR-ABL mutants and LYN efficiently. Knowledge of its full target spectrum would provide the molecular basis for potential side effects or suggest novel therapeutic applications and possible combination therapies. We have performed an unbiased chemical proteomics native target profile of INNO-406 in CML cells combined with functional assays using 272 recombinant kinases thereby identifying several new INNO-406 targets. These include the kinases ZAK, DDR1/2 and various ephrin receptors. The oxidoreductase NQO2, inhibited by both imatinib and nilotinib, is not a relevant target of INNO-406. Overall, INNO-406 has an improved activity over imatinib but a slightly broader target profile than both imatinib and nilotinib. In contrast to dasatinib and bosutinib, INNO-406 does not inhibit all SRC kinases and most TEC family kinases and is therefore expected to elicit fewer side effects. Altogether, these properties may make INNO-406 a valuable component in the drug arsenal against CML. [ABSTRACT FROM AUTHOR]

Background The multikinase inhibitor dasatinib exerts growth-inhibitory effects in patients with imatinib-resistant chronic myeloid leukaemia (CML). In first clinical trials, side effects of dasatinib, 140 mg daily, were reported to be mild and tolerable. Patients and methods We examined the side effect profile in 16 patients with imatinib-resistant CML who received 140 mg dasatinib daily in our center. Results Dasatinib produced substantial and sometimes severe or even life-threatening side effects with ≥ 10% body weight loss (6/16 patients), pleural effusions grade II or higher (12/16) and infectious complications (12/16), including atypical infections not seen in imatinib-treated patients. One patient developed Epstein–Barr-Virus-positive mucosal leucoplakia, one died from pneumonia caused by pneumocystis carinii and three patients developed a skin-cancer. Most events were recorded within the first 2 years of therapy, only skin tumours developed after the second year. In ex vivo experiments performed in dasatinib-treated patients, transient suppression of IgE-dependent activation of blood basophils and TcR-dependent activation of T-lymphocytes was found. Moreover, in drug-binding studies, dasatinib was found to bind to several key kinase-targets of the immune system including Lyn and Btk, in mast cell, basophil, B-cell and T-cell lines. Conclusion Dasatinib acts not only anti-neoplastic in CML but may also act as an immunosuppressive agent when applied at 140 mg daily, and produces frequent pleural effusions and weight loss in advanced CML. [ABSTRACT FROM AUTHOR]

The detailed molecular mechanism of action of second-generation BCR–ABL tyrosine kinase inhibitors, including perturbed targets and pathways, should contribute to rationalized therapy in chronic myeloid leukemia (CML) or in other affected diseases. Here, we characterized the target profile of the dual SRC/ABL inhibitor bosutinib employing a two-tiered approach using chemical proteomics to identify natural binders in whole cell lysates of primary CML and K562 cells in parallel to in vitro kinase assays against a large recombinant kinase panel. The combined strategy resulted in a global survey of bosutinib targets comprised of over 45 novel tyrosine and serine/threonine kinases. We have found clear differences in the target patterns of bosutinib in primary CML cells versus the K562 cell line. A comparison of bosutinib with dasatinib across the whole kinase panel revealed overlapping, but distinct, inhibition profiles. Common among those were the SRC, ABL and TEC family kinases. Bosutinib did not inhibit KIT or platelet-derived growth factor receptor, but prominently targeted the apoptosis-linked STE20 kinases. Although in vivo bosutinib is inactive against ABL T315I, we found this clinically important mutant to be enzymatically inhibited in the mid-nanomolar range. Finally, bosutinib is the first kinase inhibitor shown to target CAMK2G, recently implicated in myeloid leukemia cell proliferation.Leukemia (2009) 23, 477–485; doi:10.1038/leu.2008.334; published online 27 November 2008 [ABSTRACT FROM AUTHOR]