Vinblastine sensitizes leukemia cells to cyclin-dependent kinase inhibitors, inducing acute cell cycle phase-independent apoptosis

Abstract

The efficacy of many chemotherapeutic agents can be attenuated by expression of the anti-apoptotic proteins Bcl-2, Bcl-X(L) and Mcl-1. Flavopiridol and dinaciclib are cyclin-dependent kinase 7 and 9 inhibitors that transcriptionally inhibit expression of Mcl-1. We have investigated the ability of flavopiridol and dinaciclib to sensitize a panel of leukemia cell lines to vinblastine and paclitaxel. Both drugs acutely sensitized most of the leukemia lines to vinblastine, with 100% apoptosis in 4 h. Furthermore, dinaciclib sensitized freshly isolated chronic lymphocytic leukemia cells to vinblastine. This rapid induction of apoptosis was attributed to vinblastine-mediated activation of JNK because (a) flavopiridol and dinaciclib failed to induce apoptosis when combined with non-JNK activating concentrations of vinblastine; (b) JNK inhibitors suppressed JNK activity and prevented apoptosis; (c) flavopiridol did not potentiate apoptosis induced by paclitaxel which does not activate JNK in these cells; and (d) Jurkat cells failed to activate JNK in response to vinblastine and were not sensitive to combinations of vinblastine and flavopiridol or dinaciclib. The rapid induction of apoptosis by this combination in multiple cell systems but not in normal lymphocytes provides justification for performing a clinical trial to assess the efficacy in patients.

Rapid induction of apoptosis in chronic lymphocytic leukemia cells by the microtubule disrupting agent BNC105

“…6 and unpublished data). 4,6 In this patient's cells, BNC105 activated JNK, c-Jun, and ATF2 and induced ATF3 but had no impact on Noxa protein (Fig. 6A).…”

“…The mean apoptotic death with 100 nmol/L BNC105 was 46% as compared to our previous studies showing 100 nmol/L vinblastine resulted in a mean of 22% apoptosis, and 1 mmol/L vinblastine yielding a mean of 36% apoptosis. 4,6 A time course of 10 nmol/L BNC105 exposure shows PARP cleavage beginning at 6 h with complete cleavage at 12-24 h as compared to spontaneous cleavage reaching »50% in 48 h (Fig. 1D).…”

“…6 The mechanism of this rapid apoptosis is associated with 2 separate pathways: induction of the pro-apoptotic Bcl-2 family member Noxa, and activation of c-Jun N-terminal kinase (JNK). 3,4,6 Noxa is known to inhibit the anti-apoptotic proteins Mcl-1 and Bfl-1, while we surmise the target for JNK is either the anti-apoptotic Bcl-2 or Bcl-X proteins or a step in their ability to suppress apoptosis. The rapid onset of apoptosis is only observed in some leukemia cell lines, but it can be induced in other leukemia when combined with alternate approaches to inhibit anti-apoptotic Bcl-2 family proteins.…”

“…6 In contrast, vinblastine sensitizes most leukemia to the CDK1/2/5/9 inhibitor dinaciclib in a JNKdependent but Noxa-independent manner. 4 This latter pathway is due to dinaciclib-mediated inhibition of global transcription, such that Mcl-1, whose mRNA and protein are short lived, decreases very rapidly. Importantly, these drug combinations did not kill normal leukocytes suggesting potential selectivity for leukemic cells.…”

“…Recently, we demonstrated that these drugs can induce apoptosis rapidly from all phases of the cell cycle, and even in post-mitotic quiescent cells (e.g., peripheral CLL). [3][4][5] This rapid apoptosis still requires microtubule dissociation as it also occurs with combretastatin A4 (CA4) which targets the colchicine site on tubulin, but not with paclitaxel which stabilizes microtubules. 6 The mechanism of this rapid apoptosis is associated with 2 separate pathways: induction of the pro-apoptotic Bcl-2 family member Noxa, and activation of c-Jun N-terminal kinase (JNK).…”