Prostate cancer cells regulate growth and differentiation of bone marrow endothelial cells through TGFbeta and its receptor, TGFbetaRII

Oncolyic Virotherapy for Prostate Cancer: Lighting a Fire in Winter

As the most common cancer of the genitourinary system, prostate cancer (PCa) is a global men's health problem whose treatments are an urgent research issue. Treatment options for PCa include active surveillance (AS), surgery, endocrine therapy, chemotherapy, radiation therapy, immunotherapy, etc. However, as the cancer progresses, the effectiveness of treatment options gradually decreases, especially in metastatic castration-resistant prostate cancer (mCRPC), for which there are fewer therapeutic options and which have a shorter survival period and worse prognosis. For this reason, oncolytic viral therapy (PV), with its exceptional properties of selective tumor killing, relatively good safety in humans, and potential for transgenic delivery, has attracted increasing attention as a new form of anti-tumor strategy for PCa. There is growing evidence that OV not only kills tumor cells directly by lysis but can also activate anticancer immunity by acting on the tumor microenvironment (TME), thereby preventing tumor growth. In fact, evidence of the efficacy of this strategy has been observed since the late 19th century. However, subsequently, interest waned. The renewed interest in this therapy was due to advances in biotechnological methods and innovations at the end of the 20th century, which was also the beginning of PCa therapy with OV. Moreover, in combination with chemotherapy, radiotherapy, gene therapy or immunotherapy, OV viruses can have a wide range of applications and can provide an effective therapeutic result in the treatment of PCa.

Molecular signaling pathways mediating osteoclastogenesis induced by prostate cancer cells

Background

Advanced prostate cancer commonly metastasizes to bone leading to osteoblastic and osteolytic lesions. Although an osteolytic component governed by activation of bone resorbing osteoclasts is prominent in prostate cancer metastasis, the molecular mechanisms of prostate cancer-induced osteoclastogenesis are not well-understood.

Methods

We studied the effect of soluble mediators released from human prostate carcinoma cells on osteoclast formation from mouse bone marrow and RAW 264.7 monocytes.

Results

Soluble factors released from human prostate carcinoma cells significantly increased viability of naïve bone marrow monocytes, as well as osteoclastogenesis from precursors primed with receptor activator of nuclear factor κ-B ligand (RANKL). The prostate cancer-induced osteoclastogenesis was not mediated by RANKL as it was not inhibited by osteoprotegerin (OPG). However inhibition of TGFβ receptor I (TβRI), or macrophage-colony stimulating factor (MCSF) resulted in attenuation of prostate cancer-induced osteoclastogenesis. We characterized the signaling pathways induced in osteoclast precursors by soluble mediators released from human prostate carcinoma cells. Prostate cancer factors increased basal calcium levels and calcium fluctuations, induced nuclear localization of nuclear factor of activated t-cells (NFAT)c1, and activated prolonged phosphorylation of ERK1/2 in RANKL-primed osteoclast precursors. Inhibition of calcium signaling, NFATc1 activation, and ERK1/2 phosphorylation significantly reduced the ability of prostate cancer mediators to stimulate osteoclastogenesis.

Conclusions

This study reveals the molecular mechanisms underlying the direct osteoclastogenic effect of prostate cancer derived factors, which may be beneficial in developing novel osteoclast-targeting therapeutic approaches.

Systemic delivery of oncolytic adenoviruses targeting transforming growth factor-β inhibits established bone metastasis in a prostate cancer mouse model

We have examined whether Ad.sTβRFc and TAd.sTβRFc, two oncolytic viruses expressing soluble transforming growth factor-β receptor II fused with human Fc (sTGFβRIIFc), can be developed to treat bone metastasis of prostate cancer. Incubation of PC-3 and DU-145 prostate tumor cells with Ad.sTβRFc and TAd.sTβRFc produced sTGFβRIIFc and viral replication; sTGFβRIIFc caused inhibition of TGF-β-mediated SMAD2 and SMAD3 phosphorylation. Ad(E1-).sTβRFc, an E1(-) adenovirus, produced sTGFβRIIFc but failed to replicate in tumor cells. To examine the antitumor response of adenoviral vectors, PC-3-luc cells were injected into the left heart ventricle of nude mice. On day 9, mice were subjected to whole-body bioluminescence imaging (BLI). Mice bearing hind-limb tumors were administered viral vectors via the tail vein on days 10, 13, and 17 (2.5×10(10) viral particles per injection per mouse, each injection in a 0.1-ml volume), and subjected to BLI and X-ray radiography weekly until day 53. Ad.sTβRFc, TAd.sTβRFc, and Ad(E1-).sTβRFc caused significant inhibition of tumor growth; however, Ad.sTβRFc was the most effective among all the vectors. Only Ad.sTβRFc and TAd.sTβRFc inhibited tumor-induced hypercalcemia. Histomorphometric and synchrotron micro-computed tomographic analysis of isolated bones indicated that Ad.sTβRFc induced significant reduction in tumor burden, osteoclast number, and trabecular and cortical bone destruction. These studies suggest that Ad.sTβRFc and TAd.sTβRFc can be developed as potential new therapies for prostate cancer bone metastasis.

Angiocrine factors modulate tumor proliferation and motility through EphA2 repression of Slit2 tumor suppressor function in endothelium

It is well known that tumor-derived proangiogenic factors induce neovascularization to facilitate tumor growth and malignant progression. However, the concept of "angiocrine" signaling, in which signals produced by endothelial cells elicit tumor cell responses distinct from vessel function, has been proposed, yet remains underinvestigated. Here, we report that angiocrine factors secreted from endothelium regulate tumor growth and motility. We found that Slit2, which is negatively regulated by endothelial EphA2 receptor, is one such tumor suppressive angiocrine factor. Slit2 activity is elevated in EphA2-deficient endothelium. Blocking Slit activity restored angiocrine-induced tumor growth/motility, whereas elevated Slit2 impaired growth/motility. To translate our findings to human cancer, we analyzed EphA2 and Slit2 expression in human cancer. EphA2 expression inversely correlated with Slit2 in the vasculature of invasive human ductal carcinoma samples. Moreover, analysis of large breast tumor data sets revealed that Slit2 correlated positively with overall and recurrence-free survival, providing clinical validation for the tumor suppressor function for Slit2 in human breast cancer. Together, these data support a novel, clinically relevant mechanism through which EphA2 represses Slit2 expression in endothelium to facilitate angiocrine-mediated tumor growth and motility by blocking a tumor suppressive signal.

SKI-606 (Bosutinib) blocks prostate cancer invasion, growth, and metastasis in vitro and in vivo through regulation of genes involved in cancer growth and skeletal metastasis

In the current study, we have examined the efficacy of a Src/Abl kinase inhibitor SKI-606 (Bosutinib) for its effect on prostate cancer growth and skeletal metastasis. Treatment of highly invasive human prostate cancer cells PC-3 and DU-145 with different doses of SKI-606 decreased Src activation, cell proliferation, migration, and invasion as determined by Matrigel Boyden chamber invasion assay. For in vivo studies, PC-3 cells were inoculated through s.c. or i.t. route into male BALB/c nu/nu or Fox Chase severe combined immunodeficient mice, respectively. Experimental animals treated with SKI-606 developed tumors of a significantly smaller volume and a significant decrease (50%) in experimental skeletal lesion area. A marked increase (32%) in bone volume to tumor volume ratio was also seen by micro-computed tomography analysis of tibias from control and experimental groups of animals. Western blot analysis showed the ability of SKI-606 to significantly decrease the phosphorylation of signaling molecules (AKT, mitogen-activated protein kinase, focal adhesion kinase) and the expression of tumor progression-associated genes uPAR, MMP-2, MMP-9, N-cadherin, fibronectin, BMP-2 (bone morphogenetic protein 2), BMP-6 (bone morphogenetic protein 6), IL-8 (interleukin 8), and TGF-beta (transforming growth factor beta) in prostate cancer cells. SKI-606 is currently in clinical trials for breast cancer and chronic myelogenous leukemia. Results from these studies provide convincing evidence for evaluating its efficacy in prostate cancer patients.

Breast cancer-derived factors stimulate osteoclastogenesis through the Ca2+/protein kinase C and transforming growth factor-beta/MAPK signaling pathways

Breast cancer commonly metastasizes to bone where its growth depends on the action of bone-resorbing osteoclasts. We have previously shown that breast cancer cells secrete factors able to directly stimulate osteoclastogenesis from receptor activator of nuclear factor kappaB ligand (RANKL)-primed precursors and that transforming growth factor-beta (TGFbeta) plays a permissive role in this process. Now, we evaluate the signaling events triggered in osteoclast precursors by soluble factors produced by MDA-MB-231 human breast carcinoma cells. In mouse bone marrow cultures and RAW 264.7 murine monocytic cells, MDA-MB-231-derived factors increased osteoclast number, size, and nucleation. These factors failed to induce Smad2 phosphorylation, and short interfering RNAs against Smad4 did not affect their ability to induce osteoclastogenesis. In contrast, MDA-MB-231 factors induced phosphorylation of p38 and ERK1/2, and pharmacological inhibitors against p38 (SB203580) and MEK1/2 (PD98059) impeded the osteoclastogenic effects of cancer-derived factors. Neutralizing antibodies against TGFbeta attenuated p38 activation, whereas activation of ERK1/2 was shortened in duration, but not decreased in amplitude. ERK1/2 phosphorylation induced by cancer-derived factors was blocked by MEK1/2 inhibitor, but not by Ras (manumycin A) or Raf (GW5074) inhibitors. Inhibition of protein kinase Calpha using Gö6976 prevented both ERK1/2 phosphorylation and osteoclast formation in response to MDA-MB-231-derived factors. Using microspectrofluorimetry of fura-2-AM-loaded osteoclast precursors, we have found that cancer-derived factors, similar to RANKL, induced sustained oscillations in cytosolic free calcium. The calcium chelator BAPTA prevented calcium elevations and osteoclast formation in response to MDA-MB-231-derived factors. Thus, we have shown that breast cancer-derived factors induce osteoclastogenesis through the activation of calcium/protein kinase Calpha and TGFbeta-dependent ERK1/2 and p38 signaling pathways.

Dysfunctional transforming growth factor-beta receptor II accelerates prostate tumorigenesis in the TRAMP mouse model

The contribution of a dysfunctional transforming growth factor-beta type II receptor (TGF beta RII) to prostate cancer initiation and progression was investigated in an in vivo mouse model. Transgenic mice harboring the dominant-negative mutant TGF-beta type II receptor (DNTGF beta RII) in mouse epithelial cell were crossed with the TRAMP prostate cancer transgenic mouse to characterize the in vivo consequences of inactivated TGF-beta signaling on prostate tumor initiation and progression. Histopathologic diagnosis of prostate specimens from the TRAMP+/DNTGF beta RII double transgenic mice revealed the appearance of early malignant changes and subsequently highly aggressive prostate tumors at a younger age, compared with littermates TRAMP+/Wt TGF beta RII mice. Immunohistochemical and Western blotting analysis revealed significantly increased proliferative and apoptotic activities, as well as vascularity and macrophage infiltration that correlated with an elevated vascular endothelial growth factor and MCP-1 protein levels in prostates from TRAMP+/DNTGF beta RII+ mice. An epithelial-mesenchymal transition (EMT) effect was also detected in prostates of TRAMP+/DNTGF beta RII mice, as documented by the loss of epithelial markers (E-cadherin and beta-catenin) and up-regulation of mesenchymal markers (N-cadherin) and EMT-transcription factor Snail. A significant increase in the androgen receptor mRNA and protein levels was associated with the early onset of prostate tumorigenesis in TRAMP+/DNTGF beta RII mice. Our results indicate that in vivo disruption of TGF-beta signaling accelerates the pathologic malignant changes in the prostate by altering the kinetics of prostate growth and inducing EMT. The study also suggests that a dysfunctional TGF beta RII augments androgen receptor expression and promotes inflammation in early stage tumor growth, thus conferring a significant contribution by TGF-beta to prostate cancer progression.

Targeting TGF-beta in prostate cancer: therapeutic possibilities during tumor progression

BACKGROUND

TGF-beta regulates prostate growth by inhibiting epithelial cell proliferation and inducing apoptosis through eliciting a dynamic signaling pathway. In metastatic prostate cancer, however, TGF-beta serves as a tumor promoter. TGF-beta engages Smad-dependent and Smad-independent mechanisms to exert its action. During prostate tumorigenesis, prostate cells exhibit loss or mutation of TGF-beta transmembrane receptors. Increased production of TGF-beta causes immunosuppression, extracellular matrix degradation, epithelia to mesenchymal transition and angiogenesis that promotes tumor cell invasion and metastasis.

OBJECTIVE

The molecular basis for effective therapeutic targeting of TGF-beta must be directed towards the double-edge-sword nature of the cytokine: inhibiting the TGF-beta tumor promoter capabilities in advanced metastatic prostate cancer, although retaining the growth-inhibitory abilities exhibited in early stages of prostate tumorigenesis.

RESULTS/CONCLUSION

The current understanding of the therapeutic possibilities of targeting TGF-beta signaling during prostate tumor progression is built on preclinical studies. Studies targeting TGF-beta signaling pathway for the treatment of several human malignancies include the use of neutralizing antibodies, antisense oligonucelotides and small molecule inhibitors of kinase activity of the receptor complex. This review focuses on exploiting the therapeutic potential of targeting TGF-beta signaling in the context of its contribution to prostate cancer initiation and progression to metastasis.

Osteoclast precursors acquire sensitivity to breast cancer derived factors early in differentiation

The development of osteolytic breast cancer bone metastases relies on the ability of tumor cells to stimulate the formation of bone-resorbing osteoclasts. We have studied the effects of soluble factors produced by MDA-MB-231 breast carcinoma cells on osteoclast formation from human monocytic precursors and RAW 264.7 monocytic cells. Although factors produced by breast cancer cells were ineffective in inducing osteoclast formation from monocytes, priming with RANKL for 1-3 days dramatically increased receptiveness of osteoclast precursors to cancer-derived factors, which enhanced osteoclast formation 2-3 fold in the absence of supporting cell types. Osteoclasts formed by exposure to cancer factors expressed proteases critical for bone resorption, cathepsin K and matrix metalloproteinase 9, and were capable of resorbing calcified matrices. Expression of key osteoclastogenic transcription factor NFATc1 in osteoclast precursors was dramatically increased by short treatment with RANKL. NFATc1 was localized in the nuclei of primed osteoclast precursors when RANKL was present; however removal of RANKL led to rapid nuclear export of NFATc1. Cancer-derived factors were able to substitute for RANKL in supporting nuclear localization of NFATc1. Using neutralizing antibodies against TGFbeta, and a kinase inhibitor targeting the TGFbeta type I receptor, we identified TGFbeta as a permissive factor, required for the effects of breast cancer cells on NFATc1 nuclear accumulation and osteoclast formation. Our data suggest that, during differentiation, osteoclast precursors acquire the competency to respond to factors secreted by breast cancer cells, which may serve to promote tumor growth at skeletal sites undergoing active bone turnover.

Smad3 is overexpressed in advanced human prostate cancer and necessary for progressive growth of prostate cancer cells in nude mice

PURPOSE

The purpose of this study was to investigate the potential role of Smad3, a key mediator of transforming growth factor-beta signaling, in progression of prostate cancer.

EXPERIMENTAL DESIGN

Expression of Smad proteins was determined in human prostate cancer tissue array and cell lines. Growth and metastasis of cells overexpressing dominant-negative Smad3 (Smad3D) were studied to determine its role in tumor progression in mice. Cell growth, apoptosis, and expression of angiogenic molecules in tumor lesions were studied to determine potential pathways that Smad3 promotes tumor progression.

RESULTS

Smad3 was overexpressed in human prostate cancer, which correlated with Gleason score and expression of proliferating cell nuclear antigen. Androgen-independent PC-3MM2 and DU145 cells expressed much higher levels of Smad3 than did androgen-dependent LNCaP, 22Rv1, and LAPC-4 cells. Overexpression of Smad3D in PC-3MM2 cells (PC-3MM2-Smad3D) had minimal direct effects on cell growth but attenuated effects of transforming growth factor-beta1 on gene expression and cell growth. Overexpression of Smad3D did not significantly alter tumor incidence but reduced tumor growth rate and metastasis incidence. Most cells in the control tumors, but not PC-3MM2-Smad3D tumors, were positively stained by an antibody to proliferating cell nuclear antigen. Microvessels and expression of angiogenic molecule interleukin-8 were significantly reduced in tumors from PC-3MM2-Smad3D cells. PC-3MM2-Smad3D tumors also expressed lower levels of vascular endothelial growth factor and platelet-derived growth factor.

CONCLUSIONS

These data suggest that Smad3, through regulating angiogenic molecule expression in tumor cells, is critical for progression of human prostate cancer.