R-Roscovitine simultaneously targets both the p53 and NF-κB pathways and causes potentiation of apoptosis: implications in cancer therapy

Abstract

Seliciclib (CYC202, R-Roscovitine) is a 2, 6, 9-substituted purine analog that is currently in phase II clinical trials as an anticancer agent. We show in this study that R-Roscovitine can downregulate nuclear factor-kappa B (NF-jB) activation in response to tumor necrosis factor (TNF)a and interleukin 1. Activation of p53-dependent transcription is not compromised when RRoscovitine is combined with TNFa. We characterize the molecular mechanism governing NF-jB repression and show that RRoscovitine inhibits the IjB kinase (IKK) kinase activity, which leads to defective IjBa phosphorylation, degradation and hence nuclear function of NF-jB. We further show that the downregulation of the NF-jB pathway is also at the level of p65 modification and that the phosphorylation of p65 at Ser 536 is repressed by R-Roscovitine. Consistent with repression of canonical IKK signaling pathway, the induction of NF-jB target genes monocyte chemoattractant protein, intercellular adhesion molecule-1, cyclooxygenase-2 and IL-8 is also inhibited by R-Roscovitine. We further show that treatment of cells with TNFa and RRoscovitine causes potentiation of cell death. Based on these results, we suggest the potential use of R-Roscovitine as a bitargeted anticancer drug that functions by simultaneously causing p53 activation and NF-jB suppression. This study also provides mechanistic insight into the molecular mechanism of action of R-Roscovitine, thereby possibly explaining its antiinflammatory properties. The p53 and nuclear factor-kappa B (NF-kB) pathways are two critical transcriptional regulatory networks deregulated in various human ailments including cancer and there has been a lot of evidence of cross-talk between these two pathways. 1 Activation of p53 is associated with cell cycle arrest and apoptosis while NF-kB activation is associated with cell survival. Hence, the cross-talk between these pathways must be finely tuned and regulated.p53 is one of the most extensively studied tumor suppressor proteins. 2 Loss or mutation of p53 function is correlated with increased cancer susceptibility. Hence, activating p53 has been a goal of several small molecule inhibitors currently being evaluated in the clinic.NF-kB is a transcription factor critical for the control of inflammation, apoptosis and cell proliferation. 3,4 Chronic inflammation by constitutively active NF-kB has been shown to contribute to the development of many cancers. 5 It is becoming apparent that deregulated activity of NF-kB is observed and causally linked to the development of several diseases that have an inflammatory component. 6,7 Hence, identification of NF-kB inhibitors has been the focus of several academic and pharmaceutical establishments. 6,7 Since p53 promotes cell death and NF-kB prevents cell death, an anticancer agent that simultaneously activates p53 and inhibits NF-kB would offer greater potential to target two cancer targets positively.One of the ways in which the p53 pathway has been successfully targeted is by using cyclin-dependent kinase (CDK) inhibi...

The cyclin‐dependent kinase inhibitor R‐roscovitine down‐regulates Mcl‐1 to override pro‐inflammatory signalling and drive neutrophil apoptosis

“…R-roscovitine is known to promote apoptosis in cancer cell lines by inhibition of RNA polymerase-II leading to down-regulation of the key survival protein Mcl-1 [24]. It has also been suggested that NF-kB activation at the level of IkB kinase kinase activity is inhibited by R-roscovitine [25]. Given that both Mcl-1 and NF-kB are key components of neutrophil survival regulation we were keen to address the hypothesis that R-roscovitine might act via similar mechanisms in the inflammatory neutrophil.…”

“…R-roscovitine has been investigated previously from an anticancer perspective and has been found to promote apoptosis in myeloma cell-lines by down-regulation of Mcl-1 [24]; indeed R-roscovitine and other CDK inhibitors are undergoing Phase I and II clinical trials for the treatment of various types of cancers. Recently, it was shown that R-roscovitine could directly inhibit NF-kB at late time-points in cancer cell-lines [25], a finding that, if applicable to neutrophils, might provide insight into the antiinflammatory properties of R-roscovitine. In this paper we show that R-roscovitine can overcome powerful pro-survival signals to promote neutrophil apoptosis, without directly affecting activation status or key signalling pathways, but by down-regulating the important pro-survival protein Mcl-1 at the level of transcription.…”

Zac1 is a histone acetylation-regulated NF-κB suppressor that mediates histone deacetylase inhibitor-induced apoptosis

“…The phosphorylation levels of these two sites are dramatically increased upon stimulation of NF-kB activity. 29,30 Moreover, studies show that tumor cell apoptosis induced by anticancer reagents is associated with decreased p65 phosphorylation at Ser536 residue, [31][32][33] suggesting that p65 Ser536 phosphorylation is important for maintaining cancer cell survival and can be inhibited by anticancer reagents. In this study we showed that not only phosphorylation of Ser536 but also phosphorylation of Ser468 is downregulated during HDAC inhibitor-induced apoptosis of EC cells.…”

Cyclin-Dependent Kinases (Cdk) as Targets for Cancer Therapy and Imaging

“…In vivo activity in mice bearing colorectal carcinoma xenografts, but also in hematopoietic progenitors (Mcclue et al, 2002;Raynaud et al, 2005;Song et al, 2007) and enhancement of antitumor effects of radiation and doxorubicin in combination with Rroscovitine was reported (Appleyard et al, 2009;Maggiorella et al, 2003). Like flavopiridol and other Cdk inhibitors with broad spectrum, several additional effects have been described for R-roscovitine in vitro: interruption of transcriptional elongation, interference with survival-associated pathways (IB kinase inhibition), induction of p53 phosphorylation and apoptosis (Alvi et al, 2005;Dey et al, 2008;Hahntow et al, 2004). A novel potent Cdk inhibitor with striking similarity to R-roscovitine regarding both chemical structure and cytotoxic properties is pyrazolo[1,5-a]pyrimidine derivative SCH 727965 (Parry et al, 2010).…”