CDK Inhibitors Roscovitine and CR8 Trigger Mcl-1 Down-Regulation and Apoptotic Cell Death in Neuroblastoma Cells

Abstract

Neuroblastoma (NB), the most frequent extracranial solid tumor of children accounting for nearly 15% of all childhood cancer mortality, displays overexpression of antiapoptotic Bcl-2 and Mcl-1 in aggressive forms of the disease. The clinical phase 2 drug roscovitine (CYC202, seliciclib), a relatively selective inhibitor of cyclin-dependent kinases (CDKs), and CR8, a recently developed and more potent analog, induce concentration-dependent apoptotic cell death of NB cells (average IC 50 values: 24.2 µM and 0.4 µM for roscovitine and CR8, respectively). Both roscovitine and CR8 trigger rapid downregulation of the short-lived survival factor Mcl-1 in the 9 investigated human NB cell lines. This effect was further analyzed in the human SH-SY5Y NB cell line. Down-regulation of Mcl-1 appears to depend on inhibition of CDKs rather than on interaction of roscovitine and CR8 with their secondary targets. CR8 is an adenosine triphosphate-competitive inhibitor of CDK9, and the structure of a CDK9/cyclin T/CR8 complex is described. Mcl-1 downregulation occurs both at the mRNA and protein levels. This effect can be accounted for by a reduction in Mcl-1 protein synthesis, under stable Mcl-1 degradation conditions. Mcl-1 down-regulation is accompanied by a transient increase in free Noxa, a proapoptotic factor. Mcl-1 down-regulation occurs independently of the presence or up-regulation of p53 and of the MYCN status. Taken together, these results suggest that the clinical drug roscovitine and its novel analog CR8 induce apoptotic tumor cell death by down-regulating Mcl-1, a key survival factor expressed in all NB cell lines. CDK inhibition may thus constitute a new approach to treat refractory high-risk NB.

Dual Targeting of Wild-Type and Mutant p53 by Small Molecule RITA Results in the Inhibition of N-Myc and Key Survival Oncogenes and Kills Neuroblastoma Cells In Vivo and In Vitro

“…Recent studies have shown a correlation between high expression of antiapoptotic factors Mcl-1 and Bcl-2 and resistance to therapy in neuroblastoma (6). Mcl-1 depletion via RNA interference induced apoptosis in neuroblastoma cell lines and sensitized them to cytotoxic chemotherapy, suggesting that Mcl-1, as well as Bcl-2, might be promising targets for neuroblastoma treatment (6,7).…”

Inhibition of NF-κB–Mediated Signaling by the Cyclin-Dependent Kinase Inhibitor CR8 Overcomes Prosurvival Stimuli to Induce Apoptosis in Chronic Lymphocytic Leukemia Cells

“…PHA76749, a dual cdc7/CDK9 inhibitor, also induces a reduction in Mcl-1 transcript expression causing apoptosis in CLL cells stimulated with CD154/IL-4, indicating that CDK9 targeting may be sufficient to induce CLL cell apoptosis in the lymph node microenvironment (37). As shown previously, Mcl-1 expression may also be regulated at the posttranscriptional level, due to the abrogation of Mcl-1 protein expression (16,30,37). Mcl-1 proteasomal degradation, coupled with maintenance or upregulation of proapoptotic, Mcl-1-binding partner Noxa upon treatment of cells with CR8, roscovitine, or PHA767491 can drive cells toward apoptosis (30,37).…”

“…Ã , P < 0.05; ÃÃ , P < 0.005; ÃÃÃ , P < 0.001. CR8 exhibited only a modest improvement as a CDK inhibitor compared with roscovitine, despite an enhanced ability to induce CLL apoptosis (19,30), whereas CR8 was less potent than flavopiridol at inhibiting CDK2 and CDK9 but induced CLL cell death in the same nanomolar range. These findings may reflect differences in the kinome each clincancerres.aacrjournals.org Downloaded from drug interacts with.…”

“…As shown previously, Mcl-1 expression may also be regulated at the posttranscriptional level, due to the abrogation of Mcl-1 protein expression (16,30,37). Mcl-1 proteasomal degradation, coupled with maintenance or upregulation of proapoptotic, Mcl-1-binding partner Noxa upon treatment of cells with CR8, roscovitine, or PHA767491 can drive cells toward apoptosis (30,37).…”

New Routes to Targeted Therapy of Intrahepatic Cholangiocarcinomas Revealed by Next-Generation Sequencing

“…Up to 25% of biliary tract tumors harbor CDKN2A mutations (as shown in the COSMIC database in November 2012).Tumors with loss of the CDKN2A/ CDKN2B locus may be sensitive to Cdk4/6 inhibitors, and clinical trials of these agents are currently under way for a variety of solid tumors. Of additional interest is the observation that, given the relatively frequent 21% rate of MCL1 focal gene amplification in the ICC cohort, CDK inhibitors may function by reducing MCL1 protein levels as their main mechanism of action [39].…”