Novel cytotoxic and biological agents for prostate cancer: Where will the money be in 2005?

Combined In vivo Effect of A12, a Type 1 Insulin-Like Growth Factor Receptor Antibody, and Docetaxel against Prostate Cancer Tumors

PURPOSE

A human type 1 insulin-like growth factor receptor antibody (A12) has been shown to effectively inhibit human xenograft tumor growth, including androgen-dependent and androgen-independent prostate tumors. Docetaxel, either as a single agent or combined with others, has shown a survival benefit in prostate cancer patients. Based on these data, we investigated the combined in vivo effect of A12 and docetaxel on human androgen-independent and osseous prostate tumor growth.

EXPERIMENTAL DESIGN

To study human androgen-independent prostate cancer model, LuCaP35V tumors were implanted s.c. into castrated severe combined immunodeficient mice. When tumors reached about 100 mm3, animals were treated with vehicle control docetaxel (10 or 20 mg/kg) and docetaxel in combination with A12 (40 microg/kg) for 4 weeks. To study human osseous prostate cancer model, LuCaP 23.1 tumors were implanted intratibiae. When serum prostate-specific antigen reached 5 to 10 ng/mL, treatments were initiated.

RESULTS

A12 markedly augmented the inhibition of docetaxel on tumor growth. When docetaxel is combined with A12, the inhibition of tumor growth continued after treatment cessation, which was associated with continued apoptosis and decreased proliferation of tumor cells. Gene expression profiles indicated that the posttreatment suppression of tumor growth may be due to enhanced negative regulation of cell cycle progression- and/or cell survival-associated genes, some of which have been shown to induce resistance to docetaxel.

CONCLUSIONS

Our findings suggest that targeting type 1 insulin-like growth factor receptor can enhance the therapeutic effect of docetaxel on advanced prostate cancer. Our findings also suggest a potential mechanism to improve the treatment efficacy of docetaxel in prostate cancer.

Chemotherapy for advanced prostate cancer: docetaxel and beyond

To place appropriately into context the current status of chemotherapy as a management option for patients with hormone-refractory metastatic prostate cancer, it is important to reflect on the widely held historical belief that advanced prostate cancer is a chemotherapeutic-insensitive neoplasm. This article focuses on three disease subsets: (1)metastatic, hormone-refractory, chemotherapy-naive prostate cancer;(2) metastatic, hormone-refractory, progressive prostate cancer after frontline chemotherapy; and (3) locally advanced prostate cancer. Yagoda and Petrylak evaluated the results of 26 phase II trials of antineoplastics in advanced prostate cancer published between 1987 and 1991 and found the average objective response rate was less than 10% with only a few studies having response rates in the 10% to 20%range.

The Role of Serotonin (5-Hydroxytryptamine 1A and 1B ) Receptors in Prostate Cancer Cell Proliferation

PURPOSE

Serotonin (5-hydroxytryptamine), a monoamine neurotransmitter released by prostate neuroendocrine cells, has a fundamental role in tumor growth, differentiation and gene expression. We investigated the effect of 5-hydroxytryptamine and 5-hydroxytryptamine antagonists on the growth of prostate cancer cells and we identified 5-hydroxytryptamine receptor expression in PC3 cells and in human hormone refractory prostate cancer tissue.

MATERIALS AND METHODS

A total of 12 preparations of hormone refractory PC3 human prostate cancer cells were incubated with 5-hydroxytryptamine, or the 5-hydroxytryptamine receptor antagonists 5-hydroxytryptamine1A, 1B, 1D, 2, 3 or 4. After 72 hours cell viability was assessed using the crystal violet assay. PC3 cells treated with 5-hydroxytryptamine1A and 1B antagonists were investigated for apoptosis using flow cytometry. PC3 cells and sections of hormone refractory human prostate cancer tissue were studied by immunohistochemistry and Western blot analysis.

RESULTS

In PC3 cells 5-hydroxytryptamine caused dose dependent proliferation with a maximum increase of 15% in 12 preparations at a concentration of 10(-8) M at 72 hours compared to controls (p < 0.0001). At a concentration of 10(-4) M at 72 hours the 5HT1A antagonist NAN-190 hydrobromide and the 5-hydroxytryptamine1B antagonist SB224289 HCl (Tocris Laboratories, Bristol, United Kingdom) induced a 20% and 78% inhibitory effect, respectively, on PC3 cell growth compared to that in controls (p < 0.0001). In PC3 cells 5-hydroxytryptamine1A and 1B antagonists demonstrated apoptosis after 24 and 48 hours of incubation. Immunostaining for 5-hydroxytryptamine1A and 1B receptors was seen in PC3 cells and prostate cancer tissue. Western blot analysis demonstrated 5-hydroxytryptamine1A and 1B receptor proteins with 46 and 43 kDa bands, respectively.

CONCLUSIONS

In PC3 prostate cancer cells 5-hydroxytryptamine1A and to a greater extent 5-hydroxytryptamine1B antagonists significantly inhibit growth and induce apoptosis. To our knowledge growth inhibition caused by the 5-hydroxytryptamine1B antagonist SB224289 HCl is a novel finding, as is apoptosis caused by the 2 antagonists 5-hydroxytryptamine1A and 1B. This effect is most likely mediated via 5-hydroxytryptamine1A and 1B receptors. Therefore, our results imply that 5-hydroxytryptamine1A and in particular 5-hydroxytryptamine1B receptor antagonists warrant further investigations as potential anti-neoplastic agents.

Tissue inhibitor of metalloproteinase-3 induces apoptosis in prostate cancer cells and confers increased sensitivity to paclitaxel

Prostate cancer is the most common cancer and the second leading cause of cancer-related death in American men. To investigate the possible usefulness of tissue inhibitor of metalloproteinase-3 (TIMP-3) in prostate cancer gene therapy, we used an adenovirus expressing TIMP-3 to assess its role as an apoptosis trigger in highly metastatic prostate cancer cell lines PC-3 and DU-145. We showed that TIMP-3 alone induced apoptotic cell death which was triggered by mitochondrion-mediated caspase-3 activation. In combination treatment, we found that adenovirus-mediated expression of TIMP-3 greatly sensitised prostate cancer cells to chemotherapeutic drug paclitaxel, indicating a superadditive or synergistic effect of TIMP-3 and cytostatic treatment on prostate cancer cell death. The proper combination of adenovirus-mediated expression of TIMP-3 with conventional chemotherapeutic drug(s) could have potential benefits in treating highly metastatic prostate cancer.

Changing perspectives of the role of chemotherapy in advanced prostate cancer

The use of cytotoxic chemotherapy in advanced prostate adenocarcinoma has been validated by the recent demonstration of survival benefit in two large randomized phase III trials. Before publication of these landmark trials, SWOG 9916 and TAX 327, no chemotherapeutic regimen had shown survival benefit in the treatment of androgen independent prostate cancer (AIPC). These trials provide new encouragement for the use of chemotherapy in all stages of disease. Improved communication between medical and urologic oncologists and early patient referral for clinical trial participation remains essential for identifying new chemotherapeutic regimens with improved activity in AIPC and for defining the role of chemotherapy in earlier-stage disease. This article discusses the role of chemotherapy as the current standard of care for the treatment of AIPC and provides a historical perspective of the trials that preceded the development of current docetaxel-based regimens.

Pathogenesis and treatment of prostate cancer bone metastases: targeting the lethal phenotype

Traditionally, prostate cancer treatment, as well as all cancer treatment, has been designed to target the tumor cell directly via various hormonal and chemotherapeutic agents. Recently, the realization that cancer cells exist in complex microenvironments that are essential for the tumorigenic and metastatic potential of the cancer cells is starting the redefine the paradigm for cancer therapy. The propensity of prostate cancer cells to metastasize to bone is leading to the design of novel therapies targeting both the cancer cell as well as the bone microenvironment. Tumor cells in the bone interact with the extracellular matrix, stromal cells, osteoblasts, osteoclasts, and endothelial cells to promote tumor-cell survival and proliferation leading to a lethal phenotype that includes increased morbidity and mortality for patients with advanced prostate cancer. Several strategies are being developed that target these complex tumor cell-microenvironment interactions and target the signal transduction pathways of other cells important to the development of metastases, including the osteoclasts, osteoblasts, and endothelial cells of the bone microenvironment. Current and new therapies in metastatic prostate cancer will comprise a multitargeted approach aimed at both the tumor cell and the tumor microenvironment. Here, we review the current therapeutic strategies for targeting the prostate cancer-bone microenvironment and several single- and multiagent targeted approaches to the treatment of advanced prostate cancer that are under development.

Chemotherapy for metastatic disease: current status

Chemotherapy now has an established role in the treatment of hormone-refractory metastatic prostate cancer. This review summarises the results of the latest trials and discusses ongoing studies investigating the role of chemotherapy earlier in the disease.