Temporal changes in the clinical approach to diagnosing prostate cancer.

The diagnosis and detection of prostate cancer has undergone profound changes over the past three decades, due primarily to the development and widespread clinical use of prostate-specific antigen (PSA) testing. These changes have led to substantial differences in the prostate cancer phenotype. It is important to understand these changes to develop appropriate treatment options for contemporarily diagnosed prostate cancer. We explored a group of four temporal changes in prostate cancer detection that occurred after the advent of PSA testing. Through changes in the use of PSA testing, performance of prostate biopsy, application of PSA testing in different age groups, and pathologic tumor grading, a significant increase in detection of potentially inconsequential prostate cancers has occurred. The prostate cancer of 2011 is generally a smaller, lower-grade tumor and more often observed in younger men. These changes in detection will allow for increased use of active surveillance for prostate cancer.

TGF-beta promotion of Gli2-induced expression of parathyroid hormone-related protein, an important osteolytic factor in bone metastasis, is independent of canonical Hedgehog signaling.

Breast cancer frequently metastasizes to bone, in which tumor cells receive signals from the bone marrow microenvironment. One relevant factor is TGF-ß, which upregulates expression of the Hedgehog (Hh) signaling molecule, Gli2, which in turn increases secretion of important osteolytic factors such as parathyroid hormone-related protein (PTHrP). PTHrP inhibition can prevent tumor-induced bone destruction, whereas Gli2 overexpression in tumor cells can promote osteolysis. In this study, we tested the hypothesis that Hh inhibition in bone metastatic breast cancer would decrease PTHrP expression and therefore osteolytic bone destruction. However, when mice engrafted with human MDA-MB-231 breast cancer cells were treated with the Hh receptor antagonist cyclopamine, we observed no effect on tumor burden or bone destruction. In vitro analyses revealed that osteolytic tumor cells lack expression of the Hh receptor, Smoothened, suggesting an Hh-independent mechanism of Gli2 regulation. Blocking Gli signaling in metastatic breast cancer cells with a Gli2-repressor gene (Gli2-rep) reduced endogenous and TGF-ß-stimulated PTHrP mRNA expression, but did not alter tumor cell proliferation. Furthermore, mice inoculated with Gli2-Rep-expressing cells exhibited a decrease in osteolysis, suggesting that Gli2 inhibition may block TGF-ß propagation of a vicious osteolytic cycle in this MDA-MB-231 model of bone metastasis. Accordingly, in the absence of TGF-ß signaling, Gli2 expression was downregulated in cells, whereas enforced overexpression of Gli2 restored PTHrP activity. Taken together, our findings suggest that Gli2 is required for TGF-ß to stimulate PTHrP expression and that blocking Hh-independent Gli2 activity will inhibit tumor-induced bone destruction.

Maspin reduces prostate cancer metastasis to bone.

Maspin is a serine protease inhibitor with anti-tumor activity, including inhibition of tumor growth, angiogenesis, invasion, motility, and metastasis. Normal mammary and prostate cells express maspin at high levels. In contrast, breast and prostate cancer tissue samples and cell lines exhibit reduced or no expression of the maspin transcript. Previously we have demonstrated that introduction of an intact chromosome 18 into the bone-derived metastatic prostate cancer cell line, PC-3, resulted in reduced in vitro growth and in vivo metastatic potential. The goal of this study was to determine whether maspin is the tumor/metastasis suppressor on chromosome 18 responsible for this phenotype. To investigate whether maspin, when produced at endogenous levels, is capable of inhibiting metastasis to bone we transfected a bacterial artificial chromosome (BAC) genomic clone containing the maspin gene into PC-3 cells that aggressively metastasize to bone in an animal model. The BAC transfected PC-3 cells exhibited an in vitro phenotype consistent with maspin acting as a tumor suppressor. Analysis of the PC-3 maspin transfectants in an in vivo bone metastasis assay resulted in significant reduction of the number and severity of skeletal metastasis, compared with parental PC-3 cells. However, maspin had no effect on the ability of PC-3 cells to metastasize to extra-skeletal sites in this model. These results indicate that maspin expression likely plays a role in reducing the tumor cell's ability to seed to bone or in inhibition of growth in the bone microenvironment. However, it does not affect the ability to metastasize to distant sites.

Caspase-2 deficiency enhances aging-related traits in mice.

Alteration of apoptotic activity has been observed in a number of tissues in aging mammals, but it remains unclear whether and/or how apoptosis may affect aging. Caspase-2 is a member of the cysteine protease family that plays a critical role in apoptosis. To understand the impact of compromised apoptosis function on mammalian aging, we conducted a comparative study on caspase-2 deficient mice and their wild-type littermates with a specific focus on the aging-related traits at advanced ages. We found that caspase-2 deficiency enhanced a number of traits commonly seen in premature aging animals. Loss of caspase-2 was associated with shortened maximum lifespan, impaired hair growth, increased bone loss, and reduced body fat content. In addition, we found that the livers of caspase-2 deficient mice had higher levels of oxidized proteins than those of age-matched wild-type mice, suggesting that caspase-2 deficiency compromised the animal's ability to clear oxidatively damaged cells. Collectively, these results suggest that caspase-2 deficiency affects aging in the mice. This study thus demonstrates for the first time that disruption of a key apoptotic gene has a significant impact on aging.

The hedgehog signaling molecule Gli2 induces parathyroid hormone-related peptide expression and osteolysis in metastatic human breast cancer cells.

Parathyroid hormone-related peptide (PTHrP) is a major factor involved in tumor-induced osteolysis caused by breast cancers that have metastasized to bone. However, the molecular mechanisms that mediate PTHrP production by breast cancer cells are not entirely clear. We hypothesized that Gli2, a downstream transcriptional effector of the Hedgehog (Hh) signaling pathway, regulates PTHrP expression in metastatic breast cancer because the Hh pathway regulates physiologic PTHrP expression in the developing growth plate. Here, we show that Gli2 is expressed in several human cancer cell lines that cause osteolytic lesions in vivo and produce PTHrP (MDA-MB-231, RWGT2, and PC-3) but is not expressed in nonosteolytic cancer cell lines that do not secrete PTHrP (MCF-7, ZR-75, and T47D). Transient expression of Gli2 in MDA-MB-231 and MCF-7 breast cancer cells increased PTHrP promoter-luciferase activity dose dependently. Stable expression of Gli2 in MDA-MB-231 cells resulted in an increase in PTHrP protein in the conditioned medium. Alternatively, MDA-MB-231 cells stably transfected with Gli2-EnR, a repressor of Gli2 activity, exhibited a 72% to 93% decrease in PTHrP mRNA by quantitative real-time PCR when compared with control cells. To examine the effects of Gli2 on breast cancer-mediated osteolysis in vivo, athymic nude mice were inoculated with MDA-MB-231 cells stably expressing Gli2 or the empty vector. Following tumor cell inoculation via the left cardiac ventricle, Gli2-expressing tumors caused significantly more osteolysis. Together, these data suggest that PTHrP expression and osteolysis in vivo in human breast cancer cells is driven at least in part by Gli2.

Molecular mechanisms of breast cancer metastases to bone.

Bone metastases lead to hypercalcemia, bone pain, fractures, and nerve compression. They cause increased morbidity and mortality in patients with advanced breast cancer. Animal models reproduce many of the features seen in patients with breast cancer and permit identification of tumor- and bone-derived factors important in skeletal metastasis. These factors provide novel targets for therapeutic interventions. Specific tumor-bone molecular interactions mediated by these factors drive a vicious cycle that perpetuates skeletal metastases. In breast cancer, osteolytic metastases are most common, but mixed and osteoblastic metastases occur in a significant number of patients. Parathyroid hormone-related protein is a common osteolytic factor, and vascular endothelial growth factor and interleukins 8 and 11 also contribute. Osteoblastic metastases can be caused by tumor-secreted endothelin-1 (ET-1), but there are a variety of other potential osteoblastic factors. Stimulation of osteoblasts can paradoxically increase osteoclast function, as bone-synthesizing osteoblasts are the main regulators of bone-destroying osteoclasts. Coexpression of osteolytic and osteoblastic factors can thus produce mixed metastases or increased osteolysis. Cancer treatments, especially sex steroid deprivation therapies, stimulate bone loss. Bone resorption results in the release of bone growth factors, which may unintentionally increase the formation of bone metastases by activating the vicious cycle. Clinically approved bisphosphonates prevent bone resorption and reduce the release of bone growth factors. Parathyroid hormone-related protein-neutralizing antibody, inhibitors of the receptor activator of nuclear factor-kB ligand pathway, and ET-1 receptor antagonists are in clinical trials. These agents act on bone cells rather than tumor cells. Recent experiments identify new potential targets for prevention of bone metastases.

Actions of bisphosphonates in animal models of breast cancer.

The skeleton is the most common site of breast cancer metastases. These bone metastases are usually osteolytic and cause significant morbidity. Bisphosphonates, potent inhibitors of bone resorption, reduce skeletal morbidity in breast cancer patients with bone metastases. Animal studies with bisphosphonates are crucial to understanding the mechanisms by which these compounds affect bone and tumor cells in vivo. Such animal models of breast cancer that are used to test the efficacy of bisphosphonates are discussed. These studies may offer insight into the treatment of other tumor types that frequently metastasize to bone.