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Enzastaurin (LY317615) is a novel serine/threonine kinase inhibitor, targeting Protein Kinase C-beta (PKC-β), and PI3K/AKT pathways to inhibit angiogenesis and tumor cell proliferation. The aims of this study were to determine whether Enzastaurin has direct antitumor activity against freshly explanted tumor cells and to correlate mRNA expression of genes related to the proposed mechanism of action of enzastaurin with in vitro chemosensitivity.Freshly biopsied tumor cells were studied using soft-agar cell cloning experiments (SACCE) to determine the in vitro chemosensitivity to enzastaurin. An aliquot of the same tumor specimens was shock-frozen and total RNA was isolated for standardized multiplex rt-PCR experiments for gene expression of PKC-β1, PKC-β2, IL-8, IL-8RA, IL-8RB, Glycogen Synthase Kinase 3 beta (GSK-3β) and TGF-β1. Correlations, threshold optimization, sensitivity, specificity, and efficiency were analyzed using the appropriate statistical methodologies.Seventy-two tumor samples were collected and 63 were fully evaluable. Low levels of mRNA expression of GSK-3β and high levels of mRNA expression of IL-8 were highly significantly correlated with chemosensitivity to enzastaurin. Optimization analyses demonstrated threshold values of 4,000 copies for IL-8 and three copies for GSK-3β relative to 104 copies of β-actin. However, no correlation between mRNA expression of PKC-β1, PKC-β2, IL-8RA, IL-8RB and chemosensitivity to enzastaurin was observed. Expression of TGF-β1 mRNA was not detectable in the specimens investigated.mRNA expression levels of IL-8 and GSK-3β correlate with antitumor activity of enzastaurin. These results form a rational basis for clinical trials to evaluate the expression of these genes as potential predictors for treatment outcome after enzastaurin chemotherapy.