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Introduction: Protein kinases are involved in various cellular functions including metabolism, cell cycle regulation, survival, and differentiation. Dysregulation of protein kinases is implicated in various processes of carcinogenesis. The advent of protein kinase inhibitors in cancer therapy has led to a paradigm shift in how we treat cancer. There are several protein kinase inhibitors that have been approved by FDA in the last few decades. Areas Covered: This article provides a review of the clinical benefits and side effect profiles of FDA approved protein kinase inhibitors as of December 2017 for the well-known oncogenic protein kinases. The role of the respective oncogenic protein kinases in carcinogenesis and cancer progression were searched in PubMed and discussed. The relevant and landmark clinical trials mostly phase III trials of protein kinase inhibitors leading up to the FDA approval were PubMed searched and discussed. Expert Commentary: Further understanding of the molecular origin of cancers would help us identify new targets, while clinical trials trying to identify the appropriate sequence of available kinase inhibitor would make better use of current protein kinase inhibitor armamentarium. Also, testing these drugs in the adjuvant setting in patients with high risk of recurrence might offer some clinical benefit. Development of resistance, side effects and cost are major limitations of protein kinase inhibitors, therefore understanding of the molecular mechanisms of resistance and designing protein kinase inhibitors to obviate the resistance would help overcome the resistance. Finally, collaboration between international organizations for cancer research and voluntary and charity organizations might help reduce the cost.

Celastrol, a plant triterpene has attracted great interest recently, especially for its potential anti-inflammatory and anti-cancer activities. In the present report, we investigated the effect of celastrol on proliferation of various cancer cell lines. The mechanism, by which this triterpene exerts its apoptotic effects, was also examined in detail. We found that celastrol inhibited the proliferation of wide variety of human tumor cell types including multiple myeloma, hepatocellular carcinoma, gastric cancer, prostate cancer, renal cell carcinoma, head and neck carcinoma, non-small cell lung carcinoma, melanoma, glioma, and breast cancer with concentrations as low as 1 μM. Growth inhibitory effects of celastrol correlated with a decrease in the levels of cyclin D1 and cyclin E, but concomitant increase in the levels of p21 and p27. The apoptosis induced by celastrol was indicated by the activation of caspase-8, bid cleavage, caspase-9 activation, caspase-3 activation, PARP cleavage and through the down regulation of anti-apoptototic proteins. The apoptotic effects of celastrol were preceded by activation of JNK and down-regulation of Akt activation. JNK was needed for celastrol-induced apoptosis, and inhibition of JNK by pharmacological inhibitor abolished the apoptotic effects. Overall, our results indicate that celastrol can inhibit cell proliferation and induce apoptosis through the activation of JNK, suppression of Akt, and down-regulation of anti-apoptotic protein expression.

Cancer is one of the leading causes of death in the United States and around the world. Most modern drug-targeted therapies, besides being enormously expensive, are associated with serious side effects and morbidity. Still, the search continues for an ideal treatment that has minimal side effects and is cost-effective. Indeed, the design and development of chemopreventive agents that act on specific and/or multiple molecular and cellular targets is gaining support as a rational approach to prevent and treat cancer. We present evidence on numerous dietary agents identified from fruits and vegetables that act on multiple signal transduction and apoptotic cascades in various tumor cells and animal models. Some of the most interesting and well documented are turmeric (curcumin), resveratrol, silymarin, EGCG, and genistein. This review will provide an insight on the cellular and molecular mechanism(s) by which dietary agents modulate multiple signaling and apoptotic pathways in tumor cells and elucidate the role of these agents in both prevention and treatment of cancer.

BACKGROUND AND PURPOSEActivation of pro-inflammatory transcription factors NF-kB and signal transducer and activator of transcription 3 (STAT3) is one of the major contributors to both pathogenesis and chemoresistance in multiple myeloma (MM), which results in high mortality rate. Thus, in the present study, we investigated whether celastrol could suppress the proliferation and induce chemosensitization of MM cells by interfering with NF-kB and STAT3 activation pathways. EXPERIMENTAL APPROACHThe effects of celastrol were investigated using both a virtual predictive tumour cell system and different MM cell lines resistant to doxorubicin, melphalan and bortezomib. KEY RESULTSCelastrol inhibited the proliferation of MM cell lines regardless of whether they were sensitive or resistant to bortezomib and other conventional chemotherapeutic drugs. It also synergistically enhanced the apoptotic effects of thalidomide and bortezomib. This correlated with the down-regulation of various proliferative and anti-apoptotic gene products including cyclin D1, Bcl-2, Bcl-xL, survivin, XIAP and Mcl-1. These effects of celastrol were mediated through suppression of constitutively active NF-kB induced by inhibition of IkBa kinase activation; and the phosphorylation of IkBa and of p65. Celastrol also inhibited both the constitutive and IL6-induced activation of STAT3, which induced apoptosis as indicated by an increase in the accumulation of cells in the sub-G1 phase, an increase in the expression of pro-apoptotic proteins and activation of caspase-3. CONCLUSIONS AND IMPLICATIONSThus, based on our experimental findings, we conclude that celastrol may have great potential as a treatment for MM and other haematological malignancies.