ABL1 kinase as a tumor suppressor in AML1-ETO and NUP98-PMX1 leukemias.

Deletion of ABL1 was detected in a cohort of hematologic malignancies carrying AML1-ETO and NUP98 fusion proteins. Abl1-/- murine hematopoietic cells transduced with AML1-ETO and NUP98-PMX1 gained proliferation advantage when compared to Abl1 + /+ counterparts. Conversely, overexpression and pharmacological stimulation of ABL1 kinase resulted in reduced proliferation. To pinpoint mechanisms facilitating the transformation of ABL1-deficient cells, Abl1 was knocked down in 32Dcl3-Abl1ko cells by CRISPR/Cas9 followed by the challenge of growth factor withdrawal. 32Dcl3-Abl1ko cells but not 32Dcl3-Abl1wt cells generated growth factor-independent clones. RNA-seq implicated PI3K signaling as one of the dominant mechanisms contributing to growth factor independence in 32Dcl3-Abl1ko cells. PI3K inhibitor buparlisib exerted selective activity against Lin-cKit+ NUP98-PMX1;Abl1-/- cells when compared to the Abl1 + /+ counterparts. Since the role of ABL1 in DNA damage response (DDR) is well established, we also tested the inhibitors of ATM (ATMi), ATR (ATRi) and DNA-PKcs (DNA-PKi). AML1-ETO;Abl1-/- and NUP98-PMX1;Abl1-/- cells were hypersensitive to DNA-PKi and ATRi, respectively, when compared to Abl1 + /+ counterparts. Moreover, ABL1 kinase inhibitor enhanced the sensitivity to PI3K, DNA-PKcs and ATR inhibitors. In conclusion, we showed that ABL1 kinase plays a tumor suppressor role in hematological malignancies induced by AML1-ETO and NUP98-PMX1 and modulates the response to PI3K and/or DDR inhibitors.

DNA polymerase θ protects leukemia cells from metabolically induced DNA damage.

Leukemia cells accumulate DNA damage, but altered DNA repair mechanisms protect them from apoptosis. We showed here that formaldehyde generated by serine/1-carbon cycle metabolism contributed to the accumulation of toxic DNA-protein crosslinks (DPCs) in leukemia cells, especially in driver clones harboring oncogenic tyrosine kinases (OTKs: FLT3(internal tandem duplication [ITD]), JAK2(V617F), BCR-ABL1). To counteract this effect, OTKs enhanced the expression of DNA polymerase theta (POLθ) via ERK1/2 serine/threonine kinase-dependent inhibition of c-CBL E3 ligase-mediated ubiquitination of POLθ and its proteasomal degradation. Overexpression of POLθ in OTK-positive cells resulted in the efficient repair of DPC-containing DNA double-strand breaks by POLθ-mediated end-joining. The transforming activities of OTKs and other leukemia-inducing oncogenes, especially of those causing the inhibition of BRCA1/2-mediated homologous recombination with and without concomitant inhibition of DNA-PK-dependent nonhomologous end-joining, was abrogated in Polq-/- murine bone marrow cells. Genetic and pharmacological targeting of POLθ polymerase and helicase activities revealed that both activities are promising targets in leukemia cells. Moreover, OTK inhibitors or DPC-inducing drug etoposide enhanced the antileukemia effect of POLθ inhibitor in vitro and in vivo. In conclusion, we demonstrated that POLθ plays an essential role in protecting leukemia cells from metabolically induced toxic DNA lesions triggered by formaldehyde, and it can be targeted to achieve a therapeutic effect.

TET2 and DNMT3A Mutations Exert Divergent Effects on DNA Repair and Sensitivity of Leukemia Cells to PARP Inhibitors.

Somatic variants in TET2 and DNMT3A are founding mutations in hematological malignancies that affect the epigenetic regulation of DNA methylation. Mutations in both genes often co-occur with activating mutations in genes encoding oncogenic tyrosine kinases such as FLT3ITD, BCR-ABL1, JAK2V617F , and MPLW515L , or with mutations affecting related signaling pathways such as NRASG12D and CALRdel52 . Here, we show that TET2 and DNMT3A mutations exert divergent roles in regulating DNA repair activities in leukemia cells expressing these oncogenes. Malignant TET2-deficient cells displayed downregulation of BRCA1 and LIG4, resulting in reduced activity of BRCA1/2-mediated homologous recombination (HR) and DNA-PK-mediated non-homologous end-joining (D-NHEJ), respectively. TET2-deficient cells relied on PARP1-mediated alternative NHEJ (Alt-NHEJ) for protection from the toxic effects of spontaneous and drug-induced DNA double-strand breaks. Conversely, DNMT3A-deficient cells favored HR/D-NHEJ owing to downregulation of PARP1 and reduction of Alt-NHEJ. Consequently, malignant TET2-deficient cells were sensitive to PARP inhibitor (PARPi) treatment in vitro and in vivo, whereas DNMT3A-deficient cells were resistant. Disruption of TET2 dioxygenase activity or TET2-Wilms' tumor 1 (WT1)-binding ability was responsible for DNA repair defects and sensitivity to PARPi associated with TET2 deficiency. Moreover, mutation or deletion of WT1 mimicked the effect of TET2 mutation on DSB repair activity and sensitivity to PARPi. Collectively, these findings reveal that TET2 and WT1 mutations may serve as biomarkers of synthetic lethality triggered by PARPi, which should be explored therapeutically. SIGNIFICANCE: TET2 and DNMT3A mutations affect distinct DNA repair mechanisms and govern the differential sensitivities of oncogenic tyrosine kinase-positive malignant hematopoietic cells to PARP inhibitors.

TGFßR-SMAD3 Signaling Induces Resistance to PARP Inhibitors in the Bone Marrow Microenvironment.

Synthetic lethality triggered by PARP inhibitor (PARPi) yields promising therapeutic results. Unfortunately, tumor cells acquire PARPi resistance, which is usually associated with the restoration of homologous recombination, loss of PARP1 expression, and/or loss of DNA double-strand break (DSB) end resection regulation. Here, we identify a constitutive mechanism of resistance to PARPi. We report that the bone marrow microenvironment (BMM) facilitates DSB repair activity in leukemia cells to protect them against PARPi-mediated synthetic lethality. This effect depends on the hypoxia-induced overexpression of transforming growth factor beta receptor (TGFßR) kinase on malignant cells, which is activated by bone marrow stromal cells-derived transforming growth factor beta 1 (TGF-ß1). Genetic and/or pharmacological targeting of the TGF-ß1-TGFßR kinase axis results in the restoration of the sensitivity of malignant cells to PARPi in BMM and prolongs the survival of leukemia-bearing mice. Our finding may lead to the therapeutic application of the TGFßR inhibitor in patients receiving PARPis.

LDL cholesterol counteracts the antitumour effect of tyrosine kinase inhibitors against renal cell carcinoma.

BACKGROUND: Treatment with tyrosine kinase inhibitors (TKIs) significantly improves survival of patients with renal cell carcinoma (RCC). However, about one-quarter of the RCC patients are primarily refractory to treatment with TKIs. METHODS: We examined viability of RCC and endothelial cells treated with low-density lipoprotein (LDL) and/or TKIs. Next, we validated the potential role of PI3K/AKT signalling in LDL-mediated TKI resistance. Finally, we examined the effect of a high-fat/high-cholesterol diet on the response of RCC xenograft tumours to sunitinib. RESULTS: The addition of LDL cholesterol increases activation of PI3K/AKT signalling and compromises the antitumour efficacy of TKIs against RCC and endothelial cells. Furthermore, RCC xenograft tumours resist TKIs in mice fed a high-fat/high-cholesterol diet. CONCLUSIONS: The ability of renal tumours to maintain their cholesterol homoeostasis may be a critical component of TKI resistance in RCC patients.

Non-NAD-Like poly(ADP-Ribose) Polymerase-1 Inhibitors effectively Eliminate Cancer in vivo.

The clinical potential of PARP-1 inhibitors has been recognized >10years ago, prompting intensive research on their pharmacological application in several branches of medicine, particularly in oncology. However, natural or acquired resistance of tumors to known PARP-1 inhibitors poses a serious problem for their clinical implementation. Present study aims to reignite clinical interest to PARP-1 inhibitors by introducing a new method of identifying highly potent inhibitors and presenting the largest known collection of structurally diverse inhibitors. The majority of PARP-1 inhibitors known to date have been developed as NAD competitors. NAD is utilized by many enzymes other than PARP-1, resulting in a trade-off trap between their specificity and efficacy. To circumvent this problem, we have developed a new strategy to blindly screen a small molecule library for PARP-1 inhibitors by targeting a highly specific rout of its activation. Based on this screen, we present a collection of PARP-1 inhibitors and provide their structural classification. In addition to compounds that show structural similarity to NAD or known PARP-1 inhibitors, the screen identified structurally new non-NAD-like inhibitors that block PARP-1 activity in cancer cells with greater efficacy and potency than classical PARP-1 inhibitors currently used in clinic. These non-NAD-like PARP-1 inhibitors are effective against several types of human cancer xenografts, including kidney, prostate, and breast tumors in vivo. Our pre-clinical testing of these inhibitors using laboratory animals has established a strong foundation for advancing the new inhibitors to clinical trials.

Piperlongumine and its analogs down-regulate expression of c-Met in renal cell carcinoma.

The c-Met protein, a transmembrane receptor tyrosine kinase, is the product of a proto-oncogene. Its only known ligand, hepatocyte growth factor (HGF), regulates cell growth, motility, migration, invasion, proliferation, and angiogenesis. The aberrant expression of c-Met is often associated with poor prognosis in multiple cancers, including renal cell carcinoma (RCC). Silencing or inactivation of c-Met leads to decreased viability of cancer cells, thereby making ablation of c-Met signaling an attractive concept for developing novel strategies for the treatment of renal tumors. Naturally-occurring products or substances are the most consistent source of drug development. As such, we investigated the functional impact of piperlongumine (PL), a naturally occurring alkaloid present in the Long pepper (Piper longum) on c-Met expression in RCC cells and demonstrated that PL and its analogs rapidly reduce c-Met protein and RNA levels in RCC cells via ROS-dependent mechanism. PL-mediated c-Met depletion coincided with the inhibition of downstream c-Met signaling; namely Erk/MAPK, STAT3, NF-κB and Akt/mTOR. As such, PL and PL analogs hold promise as potential therapeutic agents for the treatment of metastatic RCC and the prevention of postoperative RCC recurrence.

Minor grove binding ligands disrupt PARP-1 activation pathways.

PARP-1 is a nuclear enzyme regulating transcription, chromatin restructuring, and DNA repair. PARP-1 is activated by interaction with NAD+, DNA, and core histones. Each route of PARP-1 activation leads to somewhat different outcomes. PARP-1 interactions with core histones control PARP-1 functions during transcriptional activation in euchromatin. DNA-dependent regulation of PARP-1 determines its localization in heterochromatin and PARP-1-dependent silencing. Here we address the biological significance of DNA-dependent PARP-1 regulation in vitro and in vivo. We report that minor grove binding ligands (MGBLs) specifically target PARP-1 interaction with DNA, and, hence, the DNA-dependent pathway of PARP-1 activation. By obstructing its interaction with DNA molecules, MGBLs block PARP-1 activity in vitro and in vivo, as we demonstrate using Drosophila, as well as human cancer-derived cells. We also demonstrate synergistic inhibition of PARP-1, combining MGBLs with conventional NAD+-dependent inhibitors in human cancer cells. These results suggest that combining different classes of PARP-1 inhibitors can precisely modulate PARP-1 activity in living cells, thus holding promise for new avenues of cancer treatment.

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

BACKGROUND: 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. METHODS: NF-κB activity was evaluated using Luciferase reporter assays and Western blot analysis of p50 and p65 nuclear translocation. IL-6, IL-8, and MMP-9 levels were assessed using ELISA. Cellular adhesion and invasiveness properties of prostate cancer cells treated with PL were also assessed. RESULTS: NF-κB DNA-binding activity was directly down-regulated with increasing concentrations of PL, along with decreased nuclear translocation of p50 and p65 subunits. Expression of IL-6, IL-8, MMP-9, and ICAM-1 was attenuated, and a decrease of cell-to-matrix adhesion and invasiveness properties of prostate cancer cells were observed. CONCLUSIONS: PL-mediated inhibition of NF-κB activity decreases aggressive growth characteristics of prostate cancer cells in vitro.

Piperlongumine induces rapid depletion of the androgen receptor in human prostate cancer cells.

BACKGROUND: 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. METHODS: Expression and transcriptional activity of AR was examined by western blotting and luciferase reporter assay, respectively. CellTiter Blue assay was utilized to quantify cell proliferation. Reactive oxygen species (ROS) generation was examined by staining cells with a ROS indicator CM-H(2) DCFDA, followed by flow cytometry analysis. RESULTS: The results of our experiments demonstrate that PL rapidly reduces AR protein levels in PC cells via proteasome-mediated ROS-dependent mechanism. Moreover, PL effectively depletes a modified AR lacking the ligand-binding domain, shedding light on a new paradigm in the treatment approach to prostatic carcinoma that expresses mutated constitutively active AR. Importantly, PL effectively depletes AR in PC cells at low micromolar concentrations, while concurrently exerting a significant inhibitory effect on AR transcriptional activity and proliferation of PC cells. CONCLUSIONS: Our investigation demonstrates for the first time that PL induces rapid depletion of the AR in PC cells. As such, PL may afford novel opportunities for both prevention and treatment of prostatic malignancy.

The effect of 5-aminolevulinic acid and its derivatives on protoporphyrin IX accumulation and apoptotic cell death in castrate-resistant prostate cancer cells.

OBJECTIVE: To examine whether pharmacologically relevant zinc-binding agents are capable of depleting X-linked inhibitor of apoptosis protein in tumor cells. Our prior work reveals that treatment with zinc-chelating agents induces selective downregulation of the X-linked inhibitor of apoptosis protein in cancer cells of various origins. A precursor of the heme synthetic pathway, 5-aminolevulinic acid, is metabolized to protoporphyrin IX, which is highly reactive with zinc. We assessed whether modified versions of 5-aminolevulinic acid with lipophilic side chains can enhance efficacy and selectivity with respect to protoporphyrin IX accumulation, X-linked inhibitor of apoptosis protein depletion, and tumor necrosis factor-related apoptosis-inducing ligand-mediated apoptosis in human castration-resistant prostate cancer cells. METHODS: Seven modified versions of 5-aminolevulinic acid (5 esters and 2 amides) were synthesized. Levels of endogenous protoporphyrin IX were examined by flow cytometry. X-linked inhibitor of apoptosis protein expression was examined by Western blotting. terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling assay was used to assess cell apoptosis. Results were compared qualitatively. RESULTS: Accumulation of endogenous protoporphyrin IX by castration-resistant prostate cancer cells was shown to be directly related to the carbon chain length of the esterified 5-aminolevulinic acid derivatives. In fact, treatment with 5-aminolevulinic acid-HE was superior to that achieved by 5-aminolevulinic acid with respect to X-linked inhibitor of apoptosis protein downregulation. 5-aminolevulinic acid and 5-aminolevulinic acid-HE in combination with tumor necrosis factor-related apoptosis-inducing ligand significantly enhanced apoptotic cell death in castration-resistant prostate cancer cell lines. CONCLUSION: Esterified derivatives of 5-aminolevulinic acid alone or in combination with other agents may provide therapeutic opportunities in the treatment of castration-resistant prostate cancer by harnessing apoptotic pathways that are triggered by cellular zinc imbalance.

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.

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

BACKGROUND: 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 docetaxel's pharmacokinetic activity in vitro and in vivo. METHODS: Liver CYP3A4 enzymatic activity was measured by fluorescence. In vivo docetaxel pharmacokinetic activity was analyzed by liquid chromatography. An in vivo xenograft model of human CRPC was utilized to assess the anti-tumor effect of docetaxel when co-administered with piperine. RESULTS: Inhibition of hepatic CYP3A4 activity resulted in an increased area under the curve, half-life and maximum plasma concentration of docetaxel when compared to docetaxel alone administration. The synergistic administration of piperine and docetaxel significantly improved the anti-tumor efficacy of docetaxel in a xenograft model of human CRPC. CONCLUSIONS: Docetaxel is one of the most widely used cytotoxic chemotherapeutic agents and is currently the mainstay treatment for metastatic CRPC. Dietary constituents are important agents modifying drug metabolism and transport. In our studies, dietary consumption of piperine increases the therapeutic efficacy of docetaxel in a xenograft model without inducing more adverse effects on the treated mice.

Interleukin-6: a potential biomarker of resistance to multitargeted receptor tyrosine kinase inhibitors in castration-resistant prostate cancer.

OBJECTIVE: To determine if cellular interleukin-6 production predicts response to tyrosine kinase inhibitors (TKIs). As clinical experience using TKIs in patients with castration-resistant prostate cancer (CRPC) matures, Phase II trials show a heterogeneous response to sunitinib in CRPC patients. Change in serum prostate-specific antigen (PSA) level has proven unreliable for prediction of CRPC response to TKIs. Interleukin-6 (IL-6), a critical mediator of prostate cancer pathogenesis, has been shown to rise in patients with disease progression. As such, we investigated whether cellular IL-6 production can predict TKI response in both in vitro and in vivo models. METHODS: IL-6 mRNA levels and protein expression were examined by reverse transcriptase-polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. Apoptosis was examined using the terminal dUTP nick-end labeling assay. For in vivo studies, a CRPC xenograft model in C.B17/Icr-scid mice was used. RESULTS: PC-3 and DU-145 CRPC cell lines exhibited a heterogeneous response to sunitinib and pazopanib. Dose-dependent reduction of IL-6 was observed in TKI-sensitive DU-145 cells. In contrast, the TKI-resistant PC-3 cells failed to suppress IL-6 secretion. Instead, in the presence of tumor necrosis factor-alpha, IL-6 rose significantly upon administration of TKIs. Findings of in vitro experiments were confirmed in an in vivo mouse model of CRPC. CONCLUSION: Sensitivity of CRPC cells to TKIs is heterogeneous. These findings are consistent with results of recently published Phase II clinical trials using sunitinib in patients with CRPC. A substantial rise in IL-6 occurs both in vitro and in vivo in the presence of TKIs in resistant PC-3 cells but not in TKI-sensitive DU-145 cells. These findings suggest that IL-6 may represent a biomarker for TKI resistance in patients with CRPC.

Reversal of epigenetic silencing of AP-2alpha results in increased zinc uptake in DU-145 and LNCaP prostate cancer cells.

Zinc accumulation is lost during prostate carcinogenesis. Recent studies reveal a strong association between prostate cancer progression and the downregulation of the zinc uptake transporters hZip1 and hZip3. The aim of this work was to assess the involvement of epigenetic processes in the disruption of zinc uptake homeostasis in prostate adenocarcinoma. In this report, we demonstrate an increase in hZip1 and hZip3 zinc transporters' expression and zinc uptake by the prostate cancer cells DU-145 and LNCaP in response to 5-aza-2'-deoxycytidine. This effect is due to demethylation of the promoter region of the activator protein (AP)-2alpha protein, which is crucial for hZip1 and hZip3 genes expression. Loss of AP-2alpha expression in DU-145 and LNCaP prostate cancer cells is due to hypermethylation of its promoter region. Similarly, we found higher AP-2alpha promoter methylation levels in clinical samples of early-stage prostate adenocarcinoma when compared with adjacent non-malignant prostate tissue. Taken together, our findings provide a better understanding of the epigenetic mechanisms that are involved in the loss of AP-2alpha protein in prostate cancer cells which lead to decreased cellular zinc uptake-a sine qua non of prostate cancer development.

Are all multi-targeted tyrosine kinase inhibitors created equal? An in vitro study of sunitinib and pazopanib in renal cell carcinoma cell lines.

OBJECTIVES: We examined the in vitro cellular effects of the multi-targeted receptor tyrosine kinase inhibitors (TKIs) sunitinib and pazopanib on a series of human renal cell carcinoma (RCC) cell lines. METHODS: The human RCC cell lines 769-P, 786-O, HRC-24, HRC-31, HRC-45, HRC-78, SK-26B, and SK-45 were treated with varying concentrations of sunitinib and pazopanib. Cellular proliferation and cellular death were assessed using the CellTiter-Blue Cell Viability Assay and the TUNEL assay, respectively. Effective doses (ED) for inhibition of cellular proliferation or induction of apoptosis were calculated for sunitinib and pazopanib in each RCC cell line. RESULTS: Both sunitinib and pazopanib exhibited anti-proliferative activity to varying degree against all human RCC cell lines; however, sunitinib's effects were achieved at significantly lower concentrations. Moreover, sunitinib had a direct pro-apoptotic effect on all tested cell lines, while pazopanib failed to induce apoptosis in any of the examined human RCC cell lines even at maximal concentrations. CONCLUSIONS: Although sunitinib and pazopanib are often used interchangeably in the clinical setting, our results suggest that in-vitro biological activity of the two agents differs. Sunitinib exhibits a cytotoxic effect on RCC cell lines, while pazopanib's activity is solely cytostatic. These data may be clinically relevant given the current lack of comparative in-vivo studies between the two agents.

Docetaxel-mediated apoptosis in myeloid progenitor TF-1 cells is mitigated by zinc: potential implication for prostate cancer therapy.

BACKGROUND: Docetaxel-based combination chemotherapy is approved by the FDA for the treatment of metastatic castration-resistant prostate cancer. Unfortunately, docetaxel's efficacy is significantly limited by its considerable toxicity on hematopoietic progenitor cells, thus necessitating dose reduction or even discontinuation of the chemotherapy. Induction of pre-mitotic arrest protects cells against docetaxel-mediated toxicity and affords therapeutic opportunities. METHODS: Cell cycle progression was examined by propidium iodide staining. Zinc uptake was determined by FluoZin-3 AM staining. Apoptotic DNA fragmentation was detected using APO-BRDU kit. RESULTS: In the course of our current work, we treated the myeloid progenitor TF-1 cells and the castration-resistant PC-3 and DU-145 prostate cancer cells with physiologically relevant concentrations of zinc. In doing so, we were able to prevent docetaxel-mediated mitotic arrest in zinc accumulating myeloid progenitor TF-1 cells but not in castration-resistant PC-3 and DU-145 prostate cancer cells. Moreover, pre-treatment with zinc abolished docetaxel-induced apoptosis in TF-1 cells, whereas such treatment had no effect on apoptosis in PC-3 and DU-145 prostate cancer cells. CONCLUSIONS: Our results suggest that zinc can protect myeloid progenitor cells against docetaxel-induced toxicity without compromising the drug's anti-tumor activity.

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

BACKGROUND: Cadmium 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. RESULTS: In 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-kappaB-independent, proteasome-mediated mechanism and coincides with an increased sensitivity of prostate cancer cells to TNF-alpha-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. CONCLUSIONS: Selection of cadmium-resistant cells could represent an adaptive survival mechanism that may contribute to progression of prostatic malignancies.

Transcriptional regulation of the major zinc uptake protein hZip1 in prostate cancer cells.

hZip1 has been characterized as the major zinc uptake transporter regulating the accumulation of zinc in prostate cells. The mechanisms regulating expression of hZip1 have not been described. To explore the mechanisms of transcriptional regulation of the hZip1 gene, we determined the putative promoter sequence for hZip1 and identified the potential transcription start site within the predicted hZip1 promoter region. To further characterize the promoter region for basal hZip1 transcription, 3' and 5' deletion constructs and constructs with mutated binding sites for putative transcription factors were generated by PCR amplification and assessed for transcriptional activity with a luciferase reporter assay in PC-3 prostate cancer cells. The ability of the specific transcription factors to bind the hZip1 core promoter was confirmed by EMSA, GelSupershift and ChIP assays. Our experiments identified the core promoter region responsible for constitutive expression of hZip1 and demonstrated critical roles for SP1 and CREB1 in transcriptional regulation of the hZip1 gene in prostate cancer cells.