High-Content, High-Throughput Analysis of Cell Cycle Perturbations Induced by the HSP90 Inhibitor XL888

BACKGROUND: Many proteins that are dysregulated or mutated in cancer cells rely on the molecular chaperone HSP90 for their proper folding and activity, which has led to considerable interest in HSP90 as a cancer drug target. The diverse array of HSP90 client proteins encompasses oncogenic drivers, cell cycle components, and a variety of regulatory factors, so inhibition of HSP90 perturbs multiple cellular processes, including mitogenic signaling and cell cycle control. Although many reports have investigated HSP90 inhibition in the context of the cell cycle, no large-scale studies have examined potential correlations between cell genotype and the cell cycle phenotypes of HSP90 inhibition. METHODOLOGY/PRINCIPAL FINDINGS: To address this question, we developed a novel high-content, high-throughput cell cycle assay and profiled the effects of two distinct small molecule HSP90 inhibitors (XL888 and 17-AAG [17-allylamino-17-demethoxygeldanamycin]) in a large, genetically diverse panel of cancer cell lines. The cell cycle phenotypes of both inhibitors were strikingly similar and fell into three classes: accumulation in M-phase, G2-phase, or G1-phase. Accumulation in M-phase was the most prominent phenotype and notably, was also correlated with TP53 mutant status. We additionally observed unexpected complexity in the response of the cell cycle-associated client PLK1 to HSP90 inhibition, and we suggest that inhibitor-induced PLK1 depletion may contribute to the striking metaphase arrest phenotype seen in many of the M-arrested cell lines. CONCLUSIONS/SIGNIFICANCE: Our analysis of the cell cycle phenotypes induced by HSP90 inhibition in 25 cancer cell lines revealed that the phenotypic response was highly dependent on cellular genotype as well as on the concentration of HSP90 inhibitor and the time of treatment. M-phase arrest correlated with the presence of TP53 mutations, while G2 or G1 arrest was more commonly seen in cells bearing wt TP53. We draw upon previous literature to suggest an integrated model that accounts for these varying observations

Effect of enzastaurin on cell signaling, proliferation and apoptosis in breast cancer cell lines

14121 Background: Enzastaurin, an acyclic bisindolylmaleimide, is a potent selective serine/threonine kinase inhibitor that inhibits PKCβ, targets the PI3K/AKT pathway, and inhibits GSK3β phosphorylation. Enzastaurin induced apoptosis and decreased proliferation of various cancer lines, and decreased VEGF expression and microvessel density in human tumor xenografts. In animal models, enzastaurin had antitumor/antiangiogenic activity in non-small-cell lung, colon, renal cell, hepatocellular, and other cancers. Therefore, we sought to determine enzastaurin’s impact on cellular PKCβ-mediated signaling in breast cancer cells. Secondarily, we sought to determine the induction of the apoptotic cascade by enzastaurin. Methods: Breast cancer cell lines MCF-7, BT-474, MDA-MB-435 and SK-BR-3 were treated with differing enzastaurin concentrations. Western-Blot analyses were performed to examine PKCβ, phospho-GSK3β and caspase 9 expressions. The phenotype and proliferation of enzastaurin-treated cells were also monitored by fluorescence microscopy. Results: Treating all 4 cancer cell lines with ascending enzastaurin doses (0.1–10 μM) led to a significant downregulation of GSK3β phosphorylation (2–17%) compared to control cells. A 48–72 hr incubation with increasing enzastaurin doses also reduced the PKCβ expression significantly (5–50%). Moreover, a dose- dependent reduction of cell proliferation to levels of 15–40% compared to control cells with the highest enzastaurin concentration was detectable. We also saw a marked pro-caspase 9 reduction (0–30%) after enzastaurin compared to control cells. The microscopic inspection of treated cells phenotypically confirmed increasing apoptosis-induced cell death. Conclusions: Enzastaurin has a significant antiproliferative effect in different breast cancer cells. Moreover, enzastaurin suppresses GSK3β phosphorylation, suggesting that it may be a reliable pharmacodynamic marker for enzastaurin activity in breast cancer cells; however, more preclinical analysis is needed. Our study provides evidence for enzastaurin’s potential to directly suppress breast cancer cell proliferation and to induce tumor cell death by apoptotic induction. No significant financial relationships to disclose. </jats:p