Strategic combination therapy overcomes tyrosine kinase coactivation in adrenocortical carcinoma.

BACKGROUND: Coactivation of tyrosine kinase limits the efficacy of tyrosine kinase inhibitors. We hypothesized that a strategic combination therapy could overcome tyrosine kinase coactivation and compensatory oncogenic signaling in patients with adrenocortical carcinoma (ACC). METHODS: We profiled 88 tyrosine kinases before and after treatment with sunitinib in H295R and SW13 ACC cells. The effects of monotherapy and strategic combination regimens were determined by the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (ie, MTS) assay. RESULTS: The minimum inhibitory concentrations (IC(min)) of sunitinib quenched its primary targets: FLT-3, VEGFR-2, and RET. In contrast, ERK, HCK, Chk2, YES, CREB, MEK, MSK, p38, FGR, and AXL were hyperactivated. Monotherapy with sunitinib or PD98059 at their IC(min) reduced proliferation by 23% and 19%, respectively, in H295R cells and by 25% and 24%, respectively, in SW13 cells. Sunitinib and PD98059 in combination decreased proliferation by 68% and 64% in H295R and in SW13 cells, respectively (P < .05 versus monotherapy). The effects of combination treatment exceeded the sum of the effects observed with each individual agent alone. CONCLUSION: We describe the first preclinical model to develop strategic combination therapy to overcome tyrosine kinase coactivation in ACC. Because many tyrosine kinase inhibitors are readily available, this model can be immediately tested in clinical trials for patients with advanced ACC.

Interaction among GSK-3, GBP, axin, and APC in Xenopus axis specification.

Glycogen synthase kinase 3 (GSK-3) is a constitutively active kinase that negatively regulates its substrates, one of which is beta-catenin, a downstream effector of the Wnt signaling pathway that is required for dorsal-ventral axis specification in the Xenopus embryo. GSK-3 activity is regulated through the opposing activities of multiple proteins. Axin, GSK-3, and beta-catenin form a complex that promotes the GSK-3-mediated phosphorylation and subsequent degradation of beta-catenin. Adenomatous polyposis coli (APC) joins the complex and downregulates beta-catenin in mammalian cells, but its role in Xenopus is less clear. In contrast, GBP, which is required for axis formation in Xenopus, binds and inhibits GSK-3. We show here that GSK-3 binding protein (GBP) inhibits GSK-3, in part, by preventing Axin from binding GSK-3. Similarly, we present evidence that a dominant-negative GSK-3 mutant, which causes the same effects as GBP, keeps endogenous GSK-3 from binding to Axin. We show that GBP also functions by preventing the GSK-3-mediated phosphorylation of a protein substrate without eliminating its catalytic activity. Finally, we show that the previously demonstrated axis-inducing property of overexpressed APC is attributable to its ability to stabilize cytoplasmic beta-catenin levels, demonstrating that APC is impinging upon the canonical Wnt pathway in this model system. These results contribute to our growing understanding of how GSK-3 regulation in the early embryo leads to regional differences in beta-catenin levels and establishment of the dorsal axis.

Mitogen-activated protein kinase translocates into the germinal vesicle and induces germinal vesicle breakdown in porcine oocytes.

The role of mitogen-activated protein kinase (MAPK) in the meiotic resumption of porcine oocytes was examined. First, using indirect immunofluorescence staining with a specific antibody against rat MAPK, we monitored the dynamics of the subcellular distribution of MAPK during meiosis initiation. We found that the inactive MAPK was already present in immature oocytes arrested at the G2 stage and that this inactive kinase was localized exclusively in the cytoplasm. At the G2/M transition stage, part of the MAPK moved into the germinal vesicle (GV) before germinal vesicle breakdown (GVBD). In addition, immunoblot analysis showed that the nuclear MAPK existed in an active form. To determine whether this active MAPK could induce GVBD, we microinjected active MAPK into immature porcine oocytes. The active MAPK injected into the cytoplasm was quickly inactivated and could not accelerate GVBD. In contrast, MAPK injection into the GV markedly accelerated GVBD. These results show that in porcine oocytes, 1) inactive MAPK localizes in the cytosol of immature GV oocytes, 2) part of the activated MAPK translocates into the GV just before GVBD, and 3) exogenous MAPK maintains its activity level in the GV and induces GVBD, indicating that MAPK mediates the maturation-inducing signal from the cytoplasm into the nucleus and induces meiosis reinitiation.