We describe a strategy to comprehend signaling pathways active in lung cancer cells and targeted by dasatinib employing chemical proteomics to identify direct interacting proteins combined with immunoaffinity purification of tyrosine phosphorylated peptides corresponding to activated tyrosine kinases. We identified nearly 40 different kinase targets of dasatinib. These include SFK members (LYN, SRC, FYN, LCK, YES), non-receptor tyrosine kinases (FRK, BRK, ACK), and receptor tyrosine kinases (Ephrin receptors, DDR1, EGFR). Using quantitative phosphoproteomics we identified peptides corresponding to autophosphorylation sites of these tyrosine kinases that are inhibited in a concentration-dependent manner by dasatinib. Using drug resistant gatekeeper mutants, we show that SFK kinases, particularly SRC and FYN, as well as EGFR are relevant targets for dasatinib action. The combined mass spectrometry based approach described here provides a system-level view of dasatinib action in cancer cells and suggests both functional targets and rationale combinatorial therapeutic strategies.

Excitatory amino acid transmission has been proposed as the principal synaptic mechanism for distribution of information through corticocortical and thalamocortical pathways. The following study utilized a double labeling paradigm, using antibodies that recognize non-NMDA ionotropic glutamate receptor subunits and other neuronal markers, to further define, quantitatively, the subclasses of neurons that contain immunoreactivity for the AMPA/kainate and kainate receptor subunits in the monkey prefrontal cortex. Double labeling with an antibody that recognizes common epitopes in AMPA/kainate subunits GluR2 and GluR3 (GluR2/3) in combination with an antibody that recognizes the kainate receptor subunits GluR5, GluR6, and GluR7 (GluR5/6/7) demonstrated that immunoreactivity for these two receptor classes was highly colocalized in a great majority of the pyramidal neurons in this region but present in only a minority of neurochemically identified subclasses of GABAergic interneurons. Furthermore, GluR2/3 immunoreactivity had principally a somatic distribution whereas GluR5/6/7 labeling was predominately found in the perikarya and/or particular dendritic domains. In contrast, intense GluR1 labeling was observed in a small subpopulation of interneurons and low GluR1 immunoreactivity was present in many other cortical neurons. These results demonstrate that there is a high degree of specificity in the distribution of AMPA/kainate and kainate receptor-class proteins to subclasses of neurons within the neocortex. A neuron's combination of excitatory amino acid receptor subunits may regulate its response to excitatory inputs and further defines the role of identified subclasses of neurons in the complex circuitry of the cerebral cortex and may also indicate the basis for the apparent cellular selectivity of excitotoxic degenerative processes.

Activating mutations in the epidermal growth factor receptor (EGFR) selectively activate signal transducers and activators of transcription (STAT) and Akt survival signaling pathways important in lung cancer cell growth and survival. Many kinases, such as EGFR, rely on heat shock protein 90 (Hsp90) chaperone function for conformational maturation and proper function. Histone deacetylase inhibitors (HDACi) have been suggested to regulate signaling protein interactions via modulation of protein chaperone function through Hsp90. For these reasons, we evaluated the effect of a HDACi in lung cancer cells with defined EGFR status. Cell lines with defined EGFR status and sensitivity to EGFR tyrosine kinase inhibitors were exposed to the HDACi LBH589, and the effects on cell survival, proliferation, and downstream signaling were evaluated. LBH589 resulted in increased acetylation of Hsp90 and reduced association of Hsp90 with EGFR, Akt, and STAT3. LBH589 selectively depleted proteins important in signaling cascades in cell lines harboring EGFR kinase mutations, such as EGFR, STAT3, and Akt, and these cells underwent apoptosis following exposure to LBH589. In addition, we found depletion of STAT3-dependent survival proteins, including Bcl-xL, Mcl-1, and Bcl-2. Conversely, LBH589 had little effect on apoptosis in cells not dependent on EGFR for survival, no changes were identified in the expression of EGFR or other survival proteins, and the predominant effect was cell cycle arrest rather than apoptosis. A 10-fold increase in LBH589 was necessary to observe durable depletion of EGFR and Akt in cells not harboring EGFR mutation. Treatment of cells with erlotinib and LBH589 resulted in synergistic effects on lung cancer cells dependent on EGFR for growth and/or survival. Based on these results, LBH589 can acetylate Hsp90, deplete EGFR and other key survival signaling proteins, and trigger apoptosis only in lung cancer cells harboring EGFR mutations. Therefore, EGFR mutation status may be predictive of outcome with LBH589 and possibly other HDACi. [Mol Cancer Ther 2007;6(9):2515 -24]