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Maritoclax and dinaciclib inhibit MCL-1 activity and induce apoptosis in both a MCL-1-dependent and -independent manner.

Varadarajan S, Poornima P, Milani M, Gowda K, Amin S, Wang HG, Cohen GM - Oncotarget (2015)

Bottom Line: Furthermore, maritoclax induced extensive mitochondrial fragmentation, and a Bax/Bak- but MCL-1-independent accumulation of mitochondrial reactive oxygen species (ROS), with an accompanying loss of complexes I and III of the electron transport chain.ROS scavengers, such as MitoQ, could not salvage maritoclax-mediated effects on mitochondrial structure and function.Although dinaciclib is clearly not a specific MCL-1 inhibitor, its ability to rapidly downregulate MCL-1 may be beneficial in many clinical settings, where it may reverse chemoresistance or sensitize to other chemotherapeutic agents.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Clinical Cancer Medicine, University of Liverpool, Liverpool, UK.

ABSTRACT
The anti-apoptotic BCL-2 family proteins are important targets for cancer chemotherapy. Specific and potent inhibitors of the BCL-2 family, such as ABT-263 (navitoclax) and ABT-199, are only effective against some members of the BCL-2 family but do not target MCL-1, which is commonly amplified in tumors and associated with chemoresistance. In this report, the selectivity and potency of two putative MCL-1 inhibitors, dinaciclib and maritoclax, were assessed. Although both compounds induced Bax/Bak- and caspase-9-dependent apoptosis, dinaciclib was more potent than maritoclax in downregulating MCL-1 and also in inducing apoptosis. However, the compounds induced apoptosis, even in cells lacking MCL-1, suggesting multiple mechanisms of cell death. Furthermore, maritoclax induced extensive mitochondrial fragmentation, and a Bax/Bak- but MCL-1-independent accumulation of mitochondrial reactive oxygen species (ROS), with an accompanying loss of complexes I and III of the electron transport chain. ROS scavengers, such as MitoQ, could not salvage maritoclax-mediated effects on mitochondrial structure and function. Taken together, our data demonstrate that neither dinaciclib nor maritoclax exclusively target MCL-1. Although dinaciclib is clearly not a specific MCL-1 inhibitor, its ability to rapidly downregulate MCL-1 may be beneficial in many clinical settings, where it may reverse chemoresistance or sensitize to other chemotherapeutic agents.

No MeSH data available.


Related in: MedlinePlus

Maritoclax-mediated mitochondrial effects occur independent of Bax/Bak- and MCL-1(A) MEFs deficient in either Bax/Bak (DKO) or MCL-1 along with their wild type counterparts were grown on coverslips, exposed for 4 h to maritoclax (10 μM), stained with antibody against HSP60 and subjected to confocal microscopy. Scale bar – 10 μm. (B) MEFs deficient in either Bax/Bak (DKO) or MCL-1 along with their wild type counterparts exposed to maritoclax (10 μM) for the indicated times, were immunoblotted with the indicated antibodies. (C and D) MEFs deficient in either Bax/Bak (DKO) (C) or MCL-1 (D) along with their wild type counterparts were exposed to maritoclax (10 μM) for the indicated times and mitochondrial accumulation of ROS assessed. Error bars represent the Mean ± SEM from three independent experiments.
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Figure 6: Maritoclax-mediated mitochondrial effects occur independent of Bax/Bak- and MCL-1(A) MEFs deficient in either Bax/Bak (DKO) or MCL-1 along with their wild type counterparts were grown on coverslips, exposed for 4 h to maritoclax (10 μM), stained with antibody against HSP60 and subjected to confocal microscopy. Scale bar – 10 μm. (B) MEFs deficient in either Bax/Bak (DKO) or MCL-1 along with their wild type counterparts exposed to maritoclax (10 μM) for the indicated times, were immunoblotted with the indicated antibodies. (C and D) MEFs deficient in either Bax/Bak (DKO) (C) or MCL-1 (D) along with their wild type counterparts were exposed to maritoclax (10 μM) for the indicated times and mitochondrial accumulation of ROS assessed. Error bars represent the Mean ± SEM from three independent experiments.

Mentions: Although maritoclax-mediated effects on mitochondrial fragmentation and ROS accumulation were consistent with the purported roles of MCL-1, we wished to assess whether maritoclax induced such changes in a Bax/Bak- and MCL-1- dependent manner. Maritoclax induced extensive mitochondrial fragmentation in both DKO and MCL-1 MEFs, to a similar extent as their wild type counterparts (Fig. 6A), thus suggesting that maritoclax-induced mitochondrial fragmentation occurred irrespective of Bax/Bak and MCL-1 status. In agreement with the microscopic observation of mitochondrial fragmentation, maritoclax resulted in a loss of high molecular weight isoforms of OPA1 in cells that lacked either Bax/Bak or MCL-1 (Fig. 6B). However, the loss of ETC components observed following maritoclax in wild type cells, seem to diminish in the DKO cells, suggesting an involvement of Bax/Bak in accelerating maritoclax-mediated loss of ETC components (Fig. 6B). Maritoclax-mediated rapid accumulation of mitochondrial ROS also occurred in a Bax/Bak-dependent manner, which raised the possibility that the mitochondrial ROS were responsible for the loss of the ETC components (Fig. 6C). However, a similar extent of protection either from the loss of ETC components or mitochondrial ROS accumulation was not observed in the MCL-1 MEFs, thus ruling out MCL-1 in these events (Figs. 6B and 6D). Moreover, maritoclax induced a greater accumulation of mitochondrial ROS in cells lacking MCL-1 (Fig. 6D), similar to the cell death effects observed in these cells (Fig. 2D).


Maritoclax and dinaciclib inhibit MCL-1 activity and induce apoptosis in both a MCL-1-dependent and -independent manner.

Varadarajan S, Poornima P, Milani M, Gowda K, Amin S, Wang HG, Cohen GM - Oncotarget (2015)

Maritoclax-mediated mitochondrial effects occur independent of Bax/Bak- and MCL-1(A) MEFs deficient in either Bax/Bak (DKO) or MCL-1 along with their wild type counterparts were grown on coverslips, exposed for 4 h to maritoclax (10 μM), stained with antibody against HSP60 and subjected to confocal microscopy. Scale bar – 10 μm. (B) MEFs deficient in either Bax/Bak (DKO) or MCL-1 along with their wild type counterparts exposed to maritoclax (10 μM) for the indicated times, were immunoblotted with the indicated antibodies. (C and D) MEFs deficient in either Bax/Bak (DKO) (C) or MCL-1 (D) along with their wild type counterparts were exposed to maritoclax (10 μM) for the indicated times and mitochondrial accumulation of ROS assessed. Error bars represent the Mean ± SEM from three independent experiments.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
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Figure 6: Maritoclax-mediated mitochondrial effects occur independent of Bax/Bak- and MCL-1(A) MEFs deficient in either Bax/Bak (DKO) or MCL-1 along with their wild type counterparts were grown on coverslips, exposed for 4 h to maritoclax (10 μM), stained with antibody against HSP60 and subjected to confocal microscopy. Scale bar – 10 μm. (B) MEFs deficient in either Bax/Bak (DKO) or MCL-1 along with their wild type counterparts exposed to maritoclax (10 μM) for the indicated times, were immunoblotted with the indicated antibodies. (C and D) MEFs deficient in either Bax/Bak (DKO) (C) or MCL-1 (D) along with their wild type counterparts were exposed to maritoclax (10 μM) for the indicated times and mitochondrial accumulation of ROS assessed. Error bars represent the Mean ± SEM from three independent experiments.
Mentions: Although maritoclax-mediated effects on mitochondrial fragmentation and ROS accumulation were consistent with the purported roles of MCL-1, we wished to assess whether maritoclax induced such changes in a Bax/Bak- and MCL-1- dependent manner. Maritoclax induced extensive mitochondrial fragmentation in both DKO and MCL-1 MEFs, to a similar extent as their wild type counterparts (Fig. 6A), thus suggesting that maritoclax-induced mitochondrial fragmentation occurred irrespective of Bax/Bak and MCL-1 status. In agreement with the microscopic observation of mitochondrial fragmentation, maritoclax resulted in a loss of high molecular weight isoforms of OPA1 in cells that lacked either Bax/Bak or MCL-1 (Fig. 6B). However, the loss of ETC components observed following maritoclax in wild type cells, seem to diminish in the DKO cells, suggesting an involvement of Bax/Bak in accelerating maritoclax-mediated loss of ETC components (Fig. 6B). Maritoclax-mediated rapid accumulation of mitochondrial ROS also occurred in a Bax/Bak-dependent manner, which raised the possibility that the mitochondrial ROS were responsible for the loss of the ETC components (Fig. 6C). However, a similar extent of protection either from the loss of ETC components or mitochondrial ROS accumulation was not observed in the MCL-1 MEFs, thus ruling out MCL-1 in these events (Figs. 6B and 6D). Moreover, maritoclax induced a greater accumulation of mitochondrial ROS in cells lacking MCL-1 (Fig. 6D), similar to the cell death effects observed in these cells (Fig. 2D).

Bottom Line: Furthermore, maritoclax induced extensive mitochondrial fragmentation, and a Bax/Bak- but MCL-1-independent accumulation of mitochondrial reactive oxygen species (ROS), with an accompanying loss of complexes I and III of the electron transport chain.ROS scavengers, such as MitoQ, could not salvage maritoclax-mediated effects on mitochondrial structure and function.Although dinaciclib is clearly not a specific MCL-1 inhibitor, its ability to rapidly downregulate MCL-1 may be beneficial in many clinical settings, where it may reverse chemoresistance or sensitize to other chemotherapeutic agents.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Clinical Cancer Medicine, University of Liverpool, Liverpool, UK.

ABSTRACT
The anti-apoptotic BCL-2 family proteins are important targets for cancer chemotherapy. Specific and potent inhibitors of the BCL-2 family, such as ABT-263 (navitoclax) and ABT-199, are only effective against some members of the BCL-2 family but do not target MCL-1, which is commonly amplified in tumors and associated with chemoresistance. In this report, the selectivity and potency of two putative MCL-1 inhibitors, dinaciclib and maritoclax, were assessed. Although both compounds induced Bax/Bak- and caspase-9-dependent apoptosis, dinaciclib was more potent than maritoclax in downregulating MCL-1 and also in inducing apoptosis. However, the compounds induced apoptosis, even in cells lacking MCL-1, suggesting multiple mechanisms of cell death. Furthermore, maritoclax induced extensive mitochondrial fragmentation, and a Bax/Bak- but MCL-1-independent accumulation of mitochondrial reactive oxygen species (ROS), with an accompanying loss of complexes I and III of the electron transport chain. ROS scavengers, such as MitoQ, could not salvage maritoclax-mediated effects on mitochondrial structure and function. Taken together, our data demonstrate that neither dinaciclib nor maritoclax exclusively target MCL-1. Although dinaciclib is clearly not a specific MCL-1 inhibitor, its ability to rapidly downregulate MCL-1 may be beneficial in many clinical settings, where it may reverse chemoresistance or sensitize to other chemotherapeutic agents.

No MeSH data available.


Related in: MedlinePlus