Konstantin Golovine

Methylseleninic acid sensitizes prostate cancer cells to TRAIL-mediated apoptosis

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a cytotoxic agent that preferentially induces apoptosis in a variety of human cancer cells. Unfortunately, some tumor cells remain resistant to TRAIL. Therefore, agents that sensitize malignant cells to TRAIL-mediated cell death might be of particular importance for the development of novel antitumor therapeutic regimens. Recent studies establish a critical role of selenium in prostate cancer prevention in vitro and in vivo. Here, we demonstrate that concomitant administration of TRAIL and methylseleninic acid (MSA) produces synergistic effects on the induction of apoptosis in androgen-dependent LNCaP and androgen-independent DU-145 prostate cancer cells. MSA rapidly and specifically downregulates expression of the cellular FLICE inhibitory protein, a negative regulator of death receptor signaling. In addition, we demonstrate that the synergistic effects of MSA and TRAIL result from the activation of the mitochondrial pathway-mediated amplification loop. Addition of MSA effectively blocked TRAIL-mediated BAD phosphorylation at Ser112 and Ser136 in DU-145 cells and was accompanied by induction of the mitochondrial permeability transition and release of apoptogenic cytochrome c and Smac/DIABLO proteins from the mitochondria and into the cytosol. These results suggest that selenium-based dietary compounds may help to overcome resistance to TRAIL-mediated apoptosis in prostate cancer cells.

Zinc chelation induces rapid depletion of the X-linked inhibitor of apoptosis and sensitizes prostate cancer cells to TRAIL-mediated apoptosis

The X-linked inhibitor of apoptosis (XIAP), the most potent member of the inhibitor of apoptosis protein (IAP) family of endogenous caspase inhibitors, blocks the initiation and execution phases of the apoptotic cascade. As such, XIAP represents an attractive target for treating apoptosis-resistant forms of cancer. Here, we demonstrate that treatment with the membrane-permeable zinc chelator, N,N,N′,N′,-tetrakis(2-pyridylmethyl) ethylenediamine (TPEN) induces a rapid depletion of XIAP at the post-translational level in human PC-3 prostate cancer cells and several non-prostate cell lines. The depletion of XIAP is selective, as TPEN has no effect on the expression of other zinc-binding members of the IAP family, including cIAP1, cIAP2 and survivin. The downregulation of XIAP in TPEN-treated cells occurs via proteasome- and caspase-independent mechanisms and is completely prevented by the serine protease inhibitor, Pefabloc. Finally, our studies demonstrate that TPEN promotes activation of caspases-3 and -9 and sensitizes PC-3 prostate cancer cells to TRAIL-mediated apoptosis. Taken together, our findings indicate that zinc-chelating agents may be used to sensitize malignant cells to established cytotoxic agents via downregulation of XIAP.

Piperlongumine promotes autophagy via inhibition of Akt/mTOR signalling and mediates cancer cell death

Background:The Akt/mammalian target of rapamycin (mTOR) signalling pathway serves as a critical regulator of cellular growth, proliferation and survival. Akt aberrant activation has been implicated in carcinogenesis and anticancer therapy resistance. Piperlongumine (PL), a natural alkaloid present in the fruit of the Long pepper, is known to exhibit notable anticancer effects. Here we investigate the impact of PL on Akt/mTOR signalling.Methods:We examined Akt/mTOR signalling in cancer cells of various origins including prostate, kidney and breast after PL treatment. Furthermore, cell viability after concomitant treatment with PL and the autophagy inhibitor, Chloroquine (CQ) was assessed. We then examined the efficacy of in vivo combination treatment using a mouse xenograft tumour model.Results:We demonstrate for the first time that PL effectively inhibits phosphorylation of Akt target proteins in all tested cells. Furthermore, the downregulation of Akt downstream signalling resulted in decrease of mTORC1 activity and autophagy stimulation. Using the autophagy inhibitor, CQ, the level of PL-induced cellular death was significantly increased. Moreover, concomitant treatment with PL and CQ demonstrated notable antitumour effect in a xenograft mouse model.Conclusions:Our data provide novel therapeutic opportunities to mediate cancer cellular death using PL. As such, PL may afford a novel paradigm for both prevention and treatment of malignancy.

Overexpression of the zinc uptake transporter hZIP1 inhibits nuclear factor-kappaB and reduces the malignant potential of prostate cancer cells in vitro and in vivo.

Purpose: Intracellular zinc levels and expression of the zinc uptake transporter, hZIP1, are markedly down-regulated in prostate adenocarcinomatous tissue compared with normal prostate tissue. Our previous studies have shown that zinc inhibits nuclear factor-κB (NF-κB) activity and reduces the malignant potential of prostate cancer cells in vitro. In this study, we investigate the functional effect of hZIP1 overexpression on NF-κB activity and tumorigenic potential in human prostate cancer cells in vitro and in vivo. Experimental Design: NF-κB activity in PC-3 prostate cancer cells was examined by Western blotting and luciferase assay. ELISA was used to examine the expression of tumorigenic cytokines. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling, adhesion, and invasiveness assays were used to assess the malignant potential of tumor cells. The effect of hZIP1 overexpression on prostate tumor progression in vivo was assessed using a xenograft model. Results: Overexpression of the hZIP1 transporter in PC-3 cells results in significant inhibition of NF-κB activity in the presence of physiologic levels of zinc. NF-κB inhibition coincides with a reduction in expression of several NF-κB controlled prometastatic and antiapoptotic factors as well as sensitization of the cells to etoposide and tumor necrosis factor-mediated apoptosis-inducing ligand-mediated cell death. Moreover, overexpression of the hZIP1 transporter induces regression of prostate tumor growth in a xenograft model. Conclusions: Our results show that hZIP1 overexpression has a functional effect on the malignant potential of prostate cancer cells via inhibition of NF-κB-dependent pathways and support the concept that hZIP1 may function as a tumor suppressor gene in prostate cancer.

Modulation of Akt/mTOR Signaling Overcomes Sunitinib Resistance in Renal and Prostate Cancer Cells

Tyrosine kinase inhibitors exhibit impressive activity against advanced renal cell carcinoma. However, recent clinical studies have shown an equivocal response to sunitinib in patients with castration-resistant prostate cancer. The tumor suppressor PTEN acts as a gatekeeper of the phosphoinositide 3-kinase (PI3K)/Akt/mTOR cell–survival pathway. Our experiments showed that PTEN expression inversely correlates with sunitinib resistance in renal and prostate cancer cells. Restoration of PTEN expression markedly increases sensitivity of tumor cells to sunitinib both in vitro and in vivo. In addition, pharmacologic manipulation of PI3K/Akt/mTOR signaling with PI3K/mTOR inhibitor, GDC-0980, mTOR inhibitor, temsirolimus, or pan-Akt inhibitor, GSK690693, was able to overcome sunitinib resistance in cancer cells. Our findings underscore the importance of PTEN expression in relation to sunitinib resistance and imply a direct cytotoxic effect by sunitinib on tumor cells in addition to its antiangiogenic actions. Mol Cancer Ther; 11(7); 1510–7. ©2012 AACR.

Co-administration of piperine and docetaxel results in improved anti-tumor efficacy via inhibition of CYP3A4 activity†

Docetaxel is the mainline treatment approved by the FDA for castration‐resistant prostate cancer (CRPC) yet its administration only increases median survival by 2–4 months. Docetaxel is metabolized in the liver by hepatic CYP3A4 activity. Piperine, a major plant alkaloid/amide, has been shown to inhibit the CYP3A4 enzymatic activity in a cell‐free system. Thus, we investigated whether the co‐administration of piperine and docetaxel could increase docetaxels pharmacokinetic activity in vitro and in vivo.

Depletion of intracellular zinc increases expression of tumorigenic cytokines VEGF, IL-6 and IL-8 in prostate cancer cells via NF-κB-dependent pathway

Zinc accumulation diminishes early in the course of prostate malignancy and continues to decline during progression toward hormone‐independent growth. In contrast, constitutive levels of NF‐κB activity increase during progression of prostate cells toward greater tumorigenic potential. We have reported previously that physiological levels of zinc suppress NF‐κB activity in prostate cancer cells and reduce expression of pro‐angiogenic and pro‐metastatic cytokines VEGF, IL‐6, IL‐8, and MMP‐9 associated with negative prognostic features in prostate cancer.

Piperlongumine inhibits NF-κB activity and attenuates aggressive growth characteristics of prostate cancer cells

Elevated NF‐κB activity has been previously demonstrated in prostate cancer cell lines as hormone‐independent or metastatic characteristics develop. We look at the effects of piperlongumine (PL), a biologically active alkaloid/amide present in piper longum plant, on the NF‐κB pathway in androgen‐independent prostate cancer cells.

Piperlongumine Induces Rapid Depletion of the Androgen Receptor in Human Prostate Cancer Cells

Androgen receptor (AR) signaling is regarded as the driving force in prostate carcinogenesis, and its modulation represents a logical target for prostate cancer (PC) prevention and treatment. Natural products are the most consistent source of small molecules for drug development. In this study, we investigate the functional impact of piperlongumine (PL), a naturally occurring alkaloid present in the Long pepper (Piper longum), on AR expression in PC cells and delineate its mechanism of action.

Cadmium down-regulates expression of XIAP at the post-transcriptional level in prostate cancer cells through an NF-κB-independent, proteasome-mediated mechanism

BackgroundCadmium has been classified as a human carcinogen, affecting health through occupational and environmental exposure. Cadmium has a long biological half-life (>25 years), due to the flat kinetics of its excretion. The prostate is one of the organs with highest levels of cadmium accumulation. Importantly, patients with prostate cancer appear to have higher levels of cadmium both in the circulation and in prostatic tissues.ResultsIn the current report, we demonstrate for the first time that cadmium down-regulates expression of the X-linked inhibitor of apoptosis protein (XIAP) in prostate cancer cells. Cadmium-mediated XIAP depletion occurs at the post-transcriptional level via an NF-κB-independent, proteasome-mediated mechanism and coincides with an increased sensitivity of prostate cancer cells to TNF-α-mediated apoptosis. Prolonged treatment with cadmium results in selection of prostate cancer cells with apoptosis-resistant phenotype. Development of apoptosis-resistance coincides with restoration of XIAP expression in cadmium-selected PC-3 cells.ConclusionsSelection of cadmium-resistant cells could represent an adaptive survival mechanism that may contribute to progression of prostatic malignancies.