Molecular insights into the microtubules depolymerizing activity of the IL-8 receptor B antagonist SB225002.

OBJECTIVE: We have previously reported the novel off-target microtubules destabilizing activity of SB225002, a compound that was originally designed as a selective and potent IL-8 receptor B antagonist. In the present study we investigated the reversibility of SB225002 antimitotic effect and provided additional mechanistic insights underlying cell death induction in SW480 human colorectal adenocarcinoma cells. MATERIALS AND METHODS: Mitotically arrested cells by SB225002 treatment were isolated by shake-off, and their identity was verified by both flow cytometry and immunoblotting. The reversibility of SB225002 antimitotic effects was investigated by flow cytometry and immunoblotting. Prometaphase arrested cells were imaged via indirect immunofluorescence and confocal microscopy. Activation of CHK1 in mitotically arrested cells was assessed by immunoblotting, and the relationship between CHK1 and mitotic arrest was examined via siRNA-mediated knockdown of CHK1. JNK signaling was evaluated via immunoblotting as well as pharmacological inhibition, followed by flow cytometry. The role of reactive oxygen species (ROS) in cytotoxicity was evaluated by ROS scavenging and flow cytometry. RESULTS: Following SB225002 washout, the mitotic checkpoint was abrogated, and cell cycle perturbations were gradually restored with induction of cell death. Mechanistically, CHK1 checkpoint was activated by SB225002 and occurred downstream of the mitotic checkpoint. In addition, SB225002 activated JNK signaling which contributed to cell death and restrained polyploidy. Furthermore, SB225002 increased intracellular ROS which played a role in mediating SB225002 cytotoxicity. CONCLUSIONS: Findings of the present study warrants further development of SB225002 as a lead compound that uniquely targets microtubules dynamics and IL-8 signaling.

Mitigation of doxorubicin-induced cardiotoxicity by dichloroacetate: potential roles of restoration of PGC-1α/SIRT3 signaling and suppression of oxidative stress and apoptosis.

OBJECTIVE: Doxorubicin (DOX) is an effective chemotherapeutic agent used in the treatment of various neoplasms. Nevertheless, its therapeutic efficacy is hampered by life-threatening heart failure. Therefore, the current study was undertaken to investigate whether dichloroacetate (DCA), a metabolic and mitochondrial modulator, when administered at a therapeutically feasible dose could potentially reverse acute DOX cardiotoxicity. Furthermore, the possible underlying mechanisms of cardioprotection were also assessed. MATERIALS AND METHODS: Different techniques were performed to assess cardiac injury like echocardiography, histopathology, transmission electron microscope, biomarkers of cardiac injury, and oxidative stress markers. Further, the expression levels of mRNA and protein were quantified by PCR and immunohistochemistry, respectively. RESULTS: Echocardiography showed that mice that received DOX/DCA combination were protected against heart failure. Additionally, histopathology and transmission electron microscopy revealed structural damage alleviation by DOX/DCA combination, which was confirmed biochemically via significant suppression of elevated CK-MB and AST levels. Mechanistically, DOX dysregulated the expression of PGC-1α and SIRT-3 genes which are key to normal mitochondrial functioning. Of note, co-treatment with DCA effectively restored PGC-1α/SIRT-3 signaling and normalized the mitochondrial DNA index. Moreover, events downstream of DOX-triggered mitochondrial dysfunction such as oxidative stress and p53-dependent apoptosis were all abrogated by combination with DCA. CONCLUSIONS: The present study is the first to provide in vivo evidence that DCA is effective in protecting against acute DOX cardiotoxicity. Additionally, the study highlights the potential of administering metabolic modulators to safeguard against DOX cardiotoxicity.

Mechanisms of enhancement of TRAIL tumoricidal activity against human cancer cells of different origin by dipyridamole.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has emerged as an attractive cytokine that selectively targets cancer cells, however its efficacy has been challenged by a number of resistance mechanisms. Therefore, the current study investigated the potential of dipyridamole to enhance TRAIL efficacy and the probable underlying mechanisms. Dipyridamole dramatically sensitized p53-mutant human cancer cell lines: SW480, MG63 and DU145, to the antitumor activity of TRAIL, as evidenced by enabling TRAIL to efficiently cleave initiator and executioner caspases. Although dipyridamole upregulated both DR4 and DR5 and increased their cell surface expression, RNA interference revealed a preferential dependence on DR5. Moreover, dipyridamole inhibited survivin expression and its important consequences were confirmed by small interfering RNA. Mechanistically, dipyridamole induced transcriptional shutdown of survivin expression accompanying G(1) arrest that was characterized by downregulation of D-type cyclins and cdk6. In addition, a transcriptional mechanism powered by CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP) induction was responsible for DR5 upregulation by dipyridamole. Importantly, dipyridamole-induced enhancement of TRAIL efficacy and alterations of protein expression were independent of either protein kinase A or protein kinase G. In conclusion, findings of the present study described novel mechanisms of dipyridamole action and highlighted its promising use as a potential enhancer of TRAIL efficacy.