Phosphodiesterase Type 5 Inhibitors Synergize Vincristine in Killing Castration-Resistant Prostate Cancer Through Amplifying Mitotic Arrest Signaling

Abstract

Combination therapies that display cancer-killing activities through either coexistent targeting of several cellular factors or more efficient suppression of a specific pathway are generally used in cancer treatment. Sildenafil, a specific phosphodiesterase type 5 (PDE5) inhibitor, has been suggested to display both cardioprotective and neuroprotective activities that provide a rationale for the combination with vincristine on the treatment against castration-resistant prostate cancer (CRPC). In the present work, vincristine arrested cells in the metaphase stage of mitosis. Vincristine-induced mitotic arrest was identified by Cdk1 activation (i.e., increased Cdk1 Thr161 phosphorylation and decreased Cdk1 Tyr15 phosphorylation), cyclin B1 upregulation, and increased phosphorylation of multiple mitotic proteins and stathmin. Sildenafil synergistically potentiated vincristine-induced mitotic arrest and a dramatic increase of mitotic index. Furthermore, sildenafil potentiated vincristine-induced mitochondrial damage, including Mcl-1 downregulation, Bcl-2 phosphorylation and downregulation, Bak upregulation and loss of mitochondrial membrane potential, and sensitized caspase-dependent apoptotic cell death. Sildenafil-mediated synergistic effects were mimicked by other PDE5 inhibitors including vardenafil and tadalafil, and also by PDE5A knockdown in cells, suggesting PDE5-involved mechanism. Notably, sildenafil amplified vincristine-induced phosphorylation and cleavage of BUBR1, a protein kinase in spindle assembly checkpoint (SAC) function and chromosome segregation. Sildenafil also significantly decreased kinetochore tension during SAC activation. Moreover, sildenafil synergized with vincristine on suppressing tumor growth in an in vivo model. In conclusion, the data suggest that sildenafil, in a PDE5-dependent manner, potentiates vincristine-induced mitotic arrest signaling, and sensitizes mitochondria damage–involved apoptosis in CRPC. Both in vitro and in vivo data suggest the combination potential of PDE5 inhibitors and vincristine on CRPC treatment.

The Potential Role of Sildenafil in CancerManagement Through EPR Augmentation

“…Further exploration in the molecular pathways responsible for this phenomenon identified a lower percentage of Ki67-positive nuclei and a higher frequency of cleaved caspase-3 positive cells relative to groups treated with monotherapy, thus promoting apoptosis and tumor regression [50]. Likewise, Hsu, J.-L. et al reported the synergestic effects between vincristine and sildenafil in PC-3-derived cancer xenografts in nude mice demonstrating a decrease in tumor weight relative to the single chemotherapeutic agent [46]. 4.…”

“…The effect of co-administration of vincristine and sildenafil on PC-3 and DU145 human prostate cancer cell lines showed that a significant increase in vincristine-induced mitotic arrest and mitotic index [46]. The probability of cells being held in metaphase were dramatically increased in presence of sildenafil.…”

“…Interestingly, the phosphorylation of Bcl-2 with caspase activation amplification including caspase-3, -8, and -9, and cleavage of poly [ADP-ribose] polymerase 1 (PARP-1), a caspase-3 substrate, was markedly increased when sildenafil was co-administered with vincristine. Additionally, sildenafil was shown to enhance vincristine-induced perturbation of microtubule-kinetochore interactions incurring higher apoptotic effects [46]. Roberts, J. L. et al reported that combination therapy of curcumin and sildenafil may induce gastrointestinal tumor cell death in HCT116, HT29, HuH7, HEP3B and HEPG2 human gastrointestinal tumor cells through endoplasmic reticulum stress, reactive oxygen/nitrogen species and increasing autophagosome and autolysosome levels prompting cancer cellular death [47].…”

The Potential Role of Sildenafil in Cancer Management through EPR Augmentation

“…The effect of coadministration of vincristine and sildenafil on PC-3 and DU145 human prostate cancer cell lines showed that a significant increase in vincristine-induced mitotic arrest and mitotic index [ 46 ]. The probability of cells being held in metaphase was dramatically increased in presence of sildenafil.…”

New Approaches in Oncology for Repositioning Drugs: The Case of PDE5 Inhibitor Sildenafil

“…Combining vincristine with sildenafil (10-25µM) is an approach to achieving greater efficacy at lower doses to reduce toxicity. Sildenafil has been shown to synergistically amplify the action of vincristine on tumor cells both in vitro (PC-3 and DU-145 cell lines) and in vivo (65).…”