Mechanisms of Action of a Dual Cdc7/Cdk9 Kinase Inhibitor against Quiescent and Proliferating CLL Cells

Abstract

In chronic lymphocytic leukemia (CLL) the proliferation rate and resistance to drug-induced apoptosis are recognized as important factors in the outcome of treatment. In this study, we assess the activity and the mechanism of action of the prototype cell division cycle kinase 7 (Cdc7) inhibitor, PHA-767491, which inhibits the initiation of DNA replication but also has cyclin-dependent kinase 9 (Cdk9) inhibitory activity. We have studied the effects of this dual Cdc7/Cdk9 inhibitor in both quiescent CLL cells and CLL cells that have been induced to proliferate using a cellular coculture system that mimics the lymph node microenvironment. We find that this compound, originally developed as a DNA replication inhibitor, is particularly active in promoting mitochondrial dependent apoptosis in quiescent CLL cells purified from peripheral blood of patients regardless of recognized risk factors. In this setting, apoptosis is preceded by a decrease in the levels of Mcl-1 protein and transcript possibly due to inhibition of Cdk9. Following stimulation by CD154 and interleukin-4, CLL cells become highly chemoresistant, reenter into the cell cycle, reexpress Cdc7 kinase, a key molecular switch for the initiation of DNA replication, replicate their DNA, and undergo cell division. In this context, treatment with PHA-767491 abolished DNA synthesis by inhibiting Cdc7 but is less effective in triggering cell death, although Mcl-1 protein is no longer detectable. Thus, dual Cdc7/Cdk9 inhibition has the potential to target both the quiescent and actively proliferating CLL populations through two distinct mechanisms and may be a new therapeutic strategy in CLL. Mol Cancer Ther; 10(9); 1624-34. Ó2011 AACR.

Pro‐survival signal inhibition by CDK inhibitor dinaciclib in Chronic Lymphocytic Leukaemia

“…The downregulation of these and other proteins by dinaciclib, including AKT, IκBα and NF-κB, could be due to its ability to regulate transcription (Alvi, et al 2005, Natoni, et al 2011 particularly, the inhibition on CDK9, which targets RNA polymerase II activity (Oelgeschläger 2002). Thus, repression of transcription has been considered as a mechanism that explains how CDK inhibitors kill cancer cells (Alvi, et al 2005, Natoni, et al 2011.…”

“…Thus, repression of transcription has been considered as a mechanism that explains how CDK inhibitors kill cancer cells (Alvi, et al 2005, Natoni, et al 2011.…”

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

“…CR8 treatment reduces Mcl-1 transcripts, mainly by inhibiting CDK9-mediated phosphorylation of RNA polymerase II (19). 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).…”

Toward personalized therapy for chronic lymphocytic leukemia

“…2,3 Moreover, the simultaneous coexistence of two populations of CLL cellsquiescent in peripheral blood and highly proliferative in patient's bone marrow germinal centers, requires therapy effective for both resting and cycling CLL cell populations. [4][5][6] Over the past 20 years, an improvement in CLL treatment has occurred by…”

“…12 Some of them reflect their action toward uncycling and cycling cell populations. 6,7,12 Despite the increasing number of clinical diagnostic parameters and overall improvement of patients' response to therapy, there are still patients who display a poor reaction to administered drugs. 13,14 The results revealed that in the group of CLL patients treated previously with chlorambucil or fludarabine, an reveal their predictive value for clinical response for CLL patients much earlier, after ex vivo testing of their PBMC sensitivity to planned treatment options.…”