Seliciclib (CYC202, R-Roscovitine) Induces Cell Death in Multiple Myeloma Cells by Inhibition of RNA Polymerase II–Dependent Transcription and Down-regulation of Mcl-1

Abstract

Seliciclib (CYC202, R-roscovitine) is a cyclin-dependent kinase (CDK) inhibitor that competes for the ATP binding site on the kinase. It has greatest activity against CDK2/cyclin E, CDK7/ cyclin H, and CDK9/cyclin T. Seliciclib induces apoptosis from all phases of the cell cycle in tumor cell lines, reduces tumor growth in xenografts in nude mice and is currently in phase II clinical trials. This study investigated the mechanism of cell death in multiple myeloma cells treated with seliciclib. In myeloma cells treated in vitro, seliciclib induced rapid dephosphorylation of the carboxyl-terminal domain of the large subunit of RNA polymerase II. Phosphorylation at these sites is crucial for RNA polymerase II-dependent transcription. Inhibition of transcription would be predicted to exert its greatest effect on gene products where both mRNA and protein have short half-lives, resulting in rapid decline of the protein levels. One such gene product is the antiapoptotic factor Mcl-1, crucial for the survival of a range of cell types including multiple myeloma. As hypothesized, following the inhibition of RNA polymerase II phosphorylation, seliciclib caused rapid Mcl-1 down-regulation, which preceded the induction of apoptosis. The importance of Mcl-1 was confirmed by short interfering RNA, demonstrating that reducing Mcl-1 levels alone was sufficient to induce apoptosis. These results suggest that seliciclib causes myeloma cell death by disrupting the balance between cell survival and apoptosis through the inhibition of transcription and down-regulation of Mcl-1. This study provides the scientific rationale for the clinical development of seliciclib for the treatment of multiple myeloma. (Cancer Res 2005; 65(12): 5399-407)

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

“…The molecular mechanism by which R-roscovitine achieves these promising results has not yet been elucidated. 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].…”

“…Importantly, R-roscovitine is capable of overcoming survival signals such as GM-CSF to promote neutrophil apoptosis in vitro and resolution of inflammation in established animal models. 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.…”

Analysis of cyclin B1 and CDK activity during apoptosis induced by camptothecin treatment

“…The reduction is likely indirectly due to inhibition of CDK7/CDK9 complexes, whose activities are required for transcription of a variety of mRNAs including cyclin B1 and anti-apoptotic genes (MacCallum et al, 2005). We then tested the role of cyclin B1 and cyclin E1 directly by blocking the expression by RNAi.…”

“…For example, roscovitine may enhance the activity of CPT derivatives in vivo (Abal et al, 2004), via its effects on transcription in addition to its effects upon CDK1 and CDK2 (MacCallum et al, 2005).…”

“…This property has lead to the development of inhibitors that are candidates for evaluation in preclinical and clinical studies. The biological mechanism of action of these compounds is not precisely known, however, it has been proposed that inhibition of distant Cdk1 family members such as Cdk7 and Cdk9 may lead to apoptosis (MacCallum et al, 2005). Further research is required to uncover the specific role of each Cdk complex in apoptosis.…”