Agshin F. Taghiyev

Mechanisms of Ascorbate-Induced Cytotoxicity in Pancreatic Cancer

Purpose: Pharmacologic concentrations of ascorbate may be effective in cancer therapeutics. We hypothesized that ascorbate concentrations achievable with i.v. dosing would be cytotoxic in pancreatic cancer for which the 5-year survival is <3%. Experimental Design: Pancreatic cancer cell lines were treated with ascorbate (0, 5, or 10 mmol/L) for 1 hour, then viability and clonogenic survival were determined. Pancreatic tumor cells were delivered s.c. into the flank region of nude mice and allowed to grow at which time they were randomized to receive either ascorbate (4 g/kg) or osmotically equivalent saline (1 mol/L) i.p. for 2 weeks. Results: There was a time- and dose-dependent increase in measured H2O2 production with increased concentrations of ascorbate. Ascorbate decreased viability in all pancreatic cancer cell lines but had no effect on an immortalized pancreatic ductal epithelial cell line. Ascorbate decreased clonogenic survival of the pancreatic cancer cell lines, which was reversed by treatment of cells with scavengers of H2O2. Treatment with ascorbate induced a caspase-independent cell death that was associated with autophagy. In vivo, treatment with ascorbate inhibited tumor growth and prolonged survival. Conclusions: These results show that pharmacologic doses of ascorbate, easily achievable in humans, may have potential for therapy in pancreatic cancer. Clin Cancer Res; 16(2); 509–20

MicroRNA-34 mediates AR-dependent p53-induced apoptosis in prostate cancer

We investigated whether knocking down AR expression effects apoptosis after treatment with different apoptosis-inducing agents. We found that siRNA AR (si-AR) significantly decreased apoptosis induced by topoisomerase inhibitors doxorubicin (DOX) and camptothecin (Campt). It is known that DNA double-strand break inducing agents leads to activation (phosphorylation) of p53 that in turn regulates the expression of a variety of apoptosis-related genes including microRNA(miR)-34a and 34b/c. We found that DOX induced 5 phosphorylation sites of p53 (Ser15, 20, 37, 46, and 392); all of these sites were inhibited by si-AR. Subsequently we identified three kinases, SPAK, MDC1, and CaMKII that are under AR control and two of them, MDC1 and CaMKII, apparently participate in p53 upstream events that resulted in p53 inhibition. Using qPCR we showed that the level of miR-34a increased by 3-fold after DOX, but no increase was found with si-AR. MiR-34c expression increased 27 fold after DOX and only by 2.7 times with si-AR. It appears that AR-dependent inhibition of p53 resulted in suppression of miR-34a and -34c expression. Importantly, DOX did not induce miR-34 in LNCaP grown in an androgen free medium or in AR-negative prostate cancer cell lines, DU145 and PC3. To directly investigate the role of miR-34 in DOX-mediated apoptosis, we transfected cells with anti-miR-34 oligonucleotides or with miR-34. We found that inhibition of individual miR-34, either 34a or 34c, or forced over expression of miR-34a or miR-34c did not modulate DOX-mediated apoptosis. Only simultaneous inhibition or forced over expression of both miR-34 resulted in modulation of DOX-mediated apoptosis. Taken together, our data indicate that cooperation between miR-34a and 34c plays an important role in AR-dependent p53-mediated apoptosis in prostate cancer.

Androgen regulates apoptosis induced by TNFR family ligands via multiple signaling pathways in LNCaP

It has been suggested in many studies that combined treatment with chemotherapeutic agents and apoptosis-inducing ligands belonging to TNFR family is a more effective strategy for cancer treatment. However, the role of androgen regulation of TNFR family-induced apoptosis in prostate cancer is poorly understood. In this study, we investigated the dose-dependent effects of androgen on TNF-α and TRAIL-mediated apoptosis in LNCaP. To investigate the interaction between the androgen receptor (AR) and the caspase-2 gene, chromatin immunoprecipitation analysis was used, and we are the first to identify that AR interacts in vivo with an androgen-responsive elements in intron 8 of caspase-2 gene. We have found that DHT inhibited apoptosis in dose-dependent manner. There is a direct, androgen-dependent correlation between the levels of activated Akt and caspase activation after treatment with TNF-α and TRAIL. We have also found that there are at least two different regulatory mechanisms of p53 expression by androgen: at the gene and protein levels. At the same time, the level of AR was found to be higher in LNCaP-si-p53 compared to LNCaP-mock cells. These data indicate that there is a mutual regulation of expression between p53 and AR. Our study suggests that androgen-dependent outcome of apoptotic treatment can occur, at least in part, via the caspase-2, Akt and p53-mediated pathways.

Calcium/calmodulin-dependent kinase II plays an important role in prostate cancer cell survival

It has recently been shown that the androgen receptor (AR) is the main factor that required for prostate cancer cells survival. We show that knocking down AR expression by siRNA induces PI3K-independent activation of Akt, which was mediated by calcium/calmodulin-dependent kinase II (CaMKII). We further show, for the first time, that prostate cancer cells express β, γ, and δ CaMKII genes, and the expression of these genes is under the control of AR activity: active AR in the presence of androgens inhibits CaMKII gene expression whereas inhibition of AR activity results in elevated level of kinase activity and in enhanced expression of CaMKII-β and –γ genes. Overexpression of CaMKII genes results in resistance to apoptosis induced by KN-93, a CaMKII inhibitor, or wortmanninn, a PI3K/Akt inhibitor, in combination with doxorubicin, thapsigargin and TRAIL. Moreover, overexpression of CaMKII increases secretion of prostate specific antigen and promotes cell growth of LNCaP in steroid-free condition. Our data show that there is cross-talk between AR- and CaMKII-mediated pathways. The results of this study suggest that CaMKII is an important player in prostate cancer cells ability to escape apoptosis under androgen ablation and facilitate the progression of prostate cancer cells to an androgen-independent state.

Mechanisms of Cell Death Induced by Histone Deacetylase Inhibitors in Androgen Receptor–Positive Prostate Cancer Cells

Histone deacetylase inhibitors (HDACI) are potential therapeutic agents that inhibit tumor cell growth and survival. Although there are several publications regarding the effects of HDACIs on prostate cancer cell growth, their mechanism(s) of action remains undefined. We treated several human prostate cancer cell lines with the HDACI trichostatin A and found that trichostatin A induced cell death in androgen receptor (AR)–positive cell lines to higher extent compared with AR-negative cell lines. We then discovered that trichostatin A and other HDACIs suppressed AR gene expression in prostate cancer cell lines as well as in AR-positive breast carcinoma cells and in mouse prostate. Trichostatin A also induced caspase activation, but trichostatin A–induced AR suppression and cell death were caspase independent. In addition, we found that doxorubicin inhibited AR expression, and p21 protein completely disappeared after simultaneous treatment with trichostatin A and doxorubicin. This effect may be attributed to the induction of protease activity under simultaneous treatment with these two agents. Further, simultaneous treatment with trichostatin A and doxorubicin increased cell death in AR-positive cells even after culturing in steroid-free conditions. The protease/proteasome inhibitor MG132 protected AR and p21 from the effects of trichostatin A and doxorubicin and inhibited trichostatin A–induced cell death in AR-positive prostate cells. Taken together, our data suggest that the main mechanism of trichostatin A–induced cell death in AR-positive prostate cancer is inhibition of AR gene expression. The synergistic effect of simultaneous treatment with trichostatin A and doxorubicin is mediated via inhibition of AR expression, induction of protease activity, increased expression of p53, and proteolysis of p21. (Mol Cancer Res 2006;4(2):113–23)

Development and translational imaging of a TP53 porcine tumorigenesis model

Cancer is the second deadliest disease in the United States, necessitating improvements in tumor diagnosis and treatment. Current model systems of cancer are informative, but translating promising imaging approaches and therapies to clinical practice has been challenging. In particular, the lack of a large-animal model that accurately mimics human cancer has been a major barrier to the development of effective diagnostic tools along with surgical and therapeutic interventions. Here, we developed a genetically modified porcine model of cancer in which animals express a mutation in TP53 (which encodes p53) that is orthologous to one commonly found in humans (R175H in people, R167H in pigs). TP53(R167H/R167H) mutant pigs primarily developed lymphomas and osteogenic tumors, recapitulating the tumor types observed in mice and humans expressing orthologous TP53 mutant alleles. CT and MRI imaging data effectively detected developing tumors, which were validated by histopathological evaluation after necropsy. Molecular genetic analyses confirmed that these animals expressed the R167H mutant p53, and evaluation of tumors revealed characteristic chromosomal instability. Together, these results demonstrated that TP53(R167H/R167H) pigs represent a large-animal tumor model that replicates the human condition. Our data further suggest that this model will be uniquely suited for developing clinically relevant, noninvasive imaging approaches to facilitate earlier detection, diagnosis, and treatment of human cancers.

Death Receptor-Induced Cell Death in Prostate Cancer

Prostate cancer mortality results from metastasis and is often coupled with progression from androgen‐dependent to androgen‐independent growth. Unfortunately, no effective treatment for metastatic prostate cancer increasing patient survival is available. The absence of effective therapies reflects in part a lack of knowledge about the molecular mechanisms involved in the development and progression of this disease. Apoptosis, or programmed cell death, is a cell suicide mechanism that enables multicellular organisms to regulate cell number in tissues. Inhibition of apoptosis appears to be a critical pathophysiological factor contributing to the development and progression of prostate cancer. Understanding the mechanism(s) of apoptosis inhibition may be the basis for developing more effective therapeutic approaches. Our understanding of apoptosis in prostate cancer is relatively limited when compared to other malignancies, in particular, hematopoietic tumors. Thus, a clear need for a better understanding of apoptosis in this malignancy remains. In this review we have focused on what is known about apoptosis in prostate cancer and, more specifically, the receptor/ligand‐mediated pathways of apoptosis as potential therapeutic targets.

Trichostatin a (TSA) sensitizes the human prostatic cancer cell line DU145 to death receptor ligands treatment

The human prostatic carcinoma cell line DU145 has previously been found to be resistant to treatment with TNF-family ligands. However, TRAIL, TNF-α, and anti-Fas antibodies (Ab) treatment in combination with the histone deacetylase inhibitor Trichostatin A (TSA) converted the phenotype of DU145 from resistant to sensitive. TSA induced 15% cell death but simultaneous treatment with TRAIL, TNF-α, and anti-Fas Ab resulted in 55%, 70%, and 40% cell death, respectively. Simultaneous treatment did not increase the level of TSA-induced histone acetylation, but induced the release of acetylated histones from chromatin into the cytosol. This release was caspase dependent since it was abrogated by Z-VAD-fmk. In addition, treatment with TSA induced caspase-9 activation and resulted in the release of cytochrome c and Smac/DIABLO from mitochondria. To further investigate the role of caspase-9 in TSA-mediated apoptosis we used two different approaches: 1) cells were pretreated with the caspase-9 inhibitor Z-LEHD-fmk, and 2) cells were transfected with a dominant-negative form of caspase-9. Both approaches gave similar results: cells became resistant to treatment with TSA. These data indicate that TSA mediates its effect via the mitochondrial pathway. This was confirmed by examining DU145 overexpressing Bcl-2. These transfectants were resistant to TSA treatment. Taken together, our data shows that only simultaneous treatment with TNF-family ligands and TSA in DU145 resulted in caspase activity sufficient to induce apoptosis. The combination of TSA and TNF-family ligands could potentially be the basis for the treatment of prostate cancer.

Bisindolylmaleimide IX Facilitates Tumor Necrosis Factor Receptor Family-mediated Cell Death and Acts as an Inhibitor of Transcription

Bisindolylmaleimides (Bis) were originally described as protein kinase C inhibitors. Several studies have shown that Bis potentiate tumor necrosis factor (TNF) receptor family-mediated apoptosis in lymphoid and dendritic cells, but the inhibition of protein kinase C cannot account for these effects (Zhou, T., Song, L., Yang, P., Wang, Z., Lui, D., and Jope, R. S. (1999) Nat. Med. 5, 42–48). We investigated the effect of four Bis derivatives (I, II, VIII, and IX) in human prostatic carcinoma cell lines and found that Bis IX was the most potent inducer of apoptosis under simultaneous treatment with TNF-α, agonistic anti-Fas monoclonal antibody, and TNF-related apoptosis-inducing ligand (TRAIL). Bis IX synergistically induced caspase activity in combination with apoptosis-inducing ligands and converted the phenotype of cell lines from apoptosis-resistant to -sensitive. Bis IX induced p53 accumulation in LNCaP (lymph node carcinoma of prostate), which expresses wild-type p53 that was not accompanied by the induction of p53-responsive genes, p21/WAF1, and Mdm2. Moreover, the induction of p21/WAF1 and Mdm2 by doxorubicin was abrogated by simultaneous treatment with Bis IX. These effects apparently result from general inhibition of transcription by Bis IX. We have shown by Northern blot analysis that the transcription activity of the hygromycin gene after transient transfection of pcDNA3.1-Hygro plasmid in 293 and HeLa cells was inhibited by Bis IX in a dose-dependent manner. Moreover, DNA binding activity of Bis IX was prevented by actinomycin D, suggesting that actinomycin D and Bis IX have similar mechanisms of interaction with DNA. In addition, we found that actinomycin D and Bis IX induced caspase activity to the same extent during TRAIL-mediated apoptosis. In summary, these results suggest that Bis IX potentiates TNF receptor family-mediated cell death in part as an inhibitor of transcription.

TRAIL-DISC Formation Is Androgen-Dependent in the Human Prostatic Carcinoma Cell Line LNCaP

We and others have previously described that the androgen-responsive human prostatic carcinoma cell line LNCaP is resistant to TRAIL and that TRAIL-mediated apoptosis in LNCaP is PI3K/Akt-dependent. In this study, we found that LNCaP remained resistant to treatment with TRAIL after androgen deprivation even in the presence of the PI3K/Akt pathway inhibitor wortmannin. This resistance was determined by failure to form the TRAIL-DISC and by decreased TRAIL-R1 and TRAIL-R2 levels after androgen deprivation; the capacity of TRAIL to induce DISC formation was completely restored in the presence of DHT. TRAIL and wortmannin together accelerated processing of caspase-8 on the DISC and apparently the release of caspase-8 from the DISC into the cytoplasm. Surprisingly, we found that wortmannin decreased the total amount of TRAIL-R1, but not TRAIL-R2, in the cells as well as the amount of TRAIL-R1 precipitated by TRAIL. Our data suggest that TRAIL-DISC formation and sensitivity to TRAIL treatment are androgen-dependent in LNCaP.