The mechanism of this kinome reprogramming involved the proteolytic degradation

Moreover, like FTY720, this antitumor activity is mediated, in part, through the activation of PKC JNJ-7706621 price signaling. PKC plays an intriguing role in regulating apoptosis, eliciting either proapoptotic or antiapoptotic effects in a cell type and context specific manner. 27 In this study, we demonstrated that OSU 2S shared the ability of FTY720 to mediate PKC dependent apoptosis through NADPH dependent ROS production, and that caspase 3 not only represents a downstream effector of PKC, but also provides positive feedback by facilitating PKC activation via proteolytic cleavage. This unique mechanism might underlie the high potency of OSU 2S and FTY720 in mediating apoptotic death in HCC cells as somatic GST π gene silencing is a frequent feature of HCC leading to low antioxidant capacity.<br><br> 28 This premise was corroborated by the ability of siRNA induced repression of GST π to sensitize PLC5 cells, which exhibit high levels of endogenous GST π, to OSU 2S and FTY720 mediated growth inhibition. In contrast to the gain of S1P receptor agonist activity by FTY720 after SphK2 mediated phosphorylation, metabolic transformation of FTY720 to its phosphate derivative results in LDN193189 ic50 the loss of its antitumor activity. Since FTY720 is gradually phosphorylated and secreted, this inactivation/sequestration may explain the lower antiproliferative potency of FTY720 relative to OSU 2S, which is not phosphorylated by SphK2. Indeed, our data show that the suppression of SphK2 activity by pharmacological inhibition or knockdown of gene expression enhanced the antitumor activity of FTY720 to the same level as that of OSU 2S.<br><br> As a single agent in vivo, OSU 2S exhibited high tumor suppressive activity against both subcutaneous and intrahepatic HCC xenograft tumors through the activation of PKC and caspase dependent apoptosis without overt toxicity. The abdominal adhesions and peritonitis observed in drug treated mice were likely LY2228820 構造 a response to the chronic irritation associated with repeated i. p. injections of the agents. The angiocentric inflammation noted in the mesenteric vasculature of some mice may represent a localized hypersensitivity reaction to the compounds or a localized vascular toxicity, the significance of which is unclear. The mechanism for the lymphocyte reduction seen after prolonged treatment with 10 mg/kg OSU 2S is unknown, but is apparently independent of effects on S1P1 receptors as OSU 2S is devoid of S1P1 receptor targeted activity.<br><br> Moreover, this effect occurred at a dose that exceeds the 5 mg/kg dose needed to completely suppress tumor growth. Evaluation of PKC expression in a human TMA revealed lower PKC expression levels in HCC than in nonmalignant liver tissues, suggesting that the downregulated expression of this proapoptotic kinase may provide survival advantages. Our finding that shRNA mediated knockdown of PKC reduced the sensitivity of Huh7 cells to the antiproliferative effects of OSU 2S supports this premise. From a clinical perspective, the expression levels of PKC and GST π represent two key determinants for cellular sensitivity to OSU 2S, and thus may be useful as criteria for selecting patients for OSU 2S therapy, i. e.