In another recent phase II trial of weekly docetaxel with thalidomide in 75 patients with metastatic AIPC (Figg et al, 2001b), 50% of patients receiving docetaxel/thalidomide and 35% of those receiving docetaxel alone had a PSA decrease of at least 50%. While the median overall survival and 18-month survival in docetaxel group were 15.9 months and 47.2%, respectively, the 18-month survival in combination group was 69.3%, and the median overall survival has not been reached in this group (Dahut et al, 2004). This result strongly suggests that the combination of a cytotoxic agent with an angiogenesis inhibitor is a promising area of investigation for prostate cancer management. Thalidomide was well tolerated in vast majority of patients. Constipation, dizziness, edema, fatigue and rebound insomnolence after coming off study were the most common side effects. Thrombotic events occurred in the thalidomide/docetaxel combination treatment that can be prevented by prophylactic low molecular weight heparin (Horne et al, 2003).

Thalidomide is now undergoing many clinical trials for the treatment of a wide variety of tumors. At the NCI, a double-blinded randomized phase III study of thalidomide versus placebo in patients with stage D0 androgen dependent prostate cancer was recently initiated. The goal of this study is to determine if thalidomide can improve the efficacy of the LHRH agonist in hormone-responsive patients with a rising PSA after primary definitive therapy (surgery or radiation) for prostate cancer.

CC-5013, a-(3-aminophthalimido) glutarimide, is an analogue of thalidomide. In vitro studies have shown that CC-5013 is more potent than thalidomide in inhibiting TNF-a production and MM cell proliferation (Celgene Corporation, Inc, unpublished data). In the rat aortic ring angiogenesis assay, CC-5013 demonstrated a potent inhibitory effect on microvessel outgrowth (Figg et al, 2002). In vivo, CC-5013 showed the inhibitory effects on growth of MM cell line (HS-Sultan). Furthermore, according to preliminary non-clinical and clinical studies conducted to date, CC-5013 appears to lack the sedative and teratogenic activity of thalidomide.

In two phase I studies in MM, a total of 39 patients with relapsed or refractory disease have been treated with CC-5013. Patients received doses ranging from 5 mg to 50 mg daily of CC-5013. It was well tolerated with principal side effects being bone marrow suppression, myalgia, fatigue, headache, constipation, diarrhea, ringing in ears, lightheadedness, and mild elevated LFT and creatinine. In one study conducted at the University of Arkansas, myeloma response was seen at the higher dosages of CC-5013. Four of 15 patients had a greater than 25% reduction (1 patient > 75%) in paraprotein level. Ten of 14 evaluable patients treated at the Dana Farber Cancer Center responded to the drug, including 3 patients with > 50% and 7 patients with 25-50% reduction in paraprotein level. At the NCI, a phase I trial of CC-5013 is currently conducting in patients with solid tumors, including metastatic AIPC, to further study its clinical antitumor activity.

B. Matrix metalloproteinase inhibitors (MMPs)

In recently years, several MMPs inhibitors, such as batimastat, marimastat, prinomastat, and COL-3, have been developed as anticancer drugs and are being actively evaluated in preclinical studies and ongoing clinical trials (Nemunaitis et al, 1998; Macaulay et al, 1999; Heath et al, 2001; Rudek et al, 2001; Ahmann et al, 2002). Batimastat is almost completely insoluble, and consequently, has a very poor bioavailability with oral route. Therefore, the clinical usage of batimastat is limited.

Marimastat has a broad-spectrum inhibitory activity against most of the major MMPs; including MMP2 and MMP9 (Nemunaitis et al, 1998). Marimastat is almost completely absorbed after oral administration with a half-life of approximately 15 hours. It has been evaluated extensively in clinical trials in different solid tumors with promising activity in patients with pancreatic and colorectal cancer. A total of 88 patients with advanced metastatic prostate cancer were evaluated in 6 phase I trials. Marimastat was administrated orally for 4 weeks. The therapeutic response was measured by decrease in the rate of rise of serum PSA. In these studies Marimastat was demonstrated to reduce the rate of rise of serum PSA in a dose-dependent manner (Nemunaitis et al 1998 However, the significance in the change of the PSA slope is unclear. Marimastat has been well tolerated. The principal side effect was dose-related joint pain and stiffness.

Prinomastat is a selective inhibitor of MMP2/MMP3/MMP9. It has been demonstrated that prinomastat inhibits the growth of PC-3 cells in an animal model (Shalinsky et al, 1999). Prinomastat was well tolerated with principal side effect being mild musculoskeletal toxicity in early clinical trials. In a recent phase III trial, 406 patients with chemotherapy-naive AIPC were randomized into mitoxantrone/prednisone with or without prinomastat. No significant difference in PSA response rate, progression-free survival, or overall survival in two groups was observed (Ahmann et al, 2002). While this result showed no benefit by addition of prinomastat to chemotherapy in AIPC, it does not preclude the use of Prinomastat in the treatment of early stage of prostate cancer.

Alendronate, a bisphosphonate and an inhibitor of osteoclastic bone resorption, has been shown to decrease MMP2 and MMP9 secretion in animal models (39). Also, recent studies demonstrated that bisphosphonates have antitumor effect in vivo animal systems and promoting apoptosis of tumor cells in vitro (Diel et al, 1998; Powles et al, 1998). Stearns et al evaluated the combination of alendronate and paclitaxol on human PC3ML cell bone metastases in SCID mice (Stearns et al, 1996). The pretreatment of SCID mice with alendronate partially blocked the establishment of bone metastases by PC3ML cells and resulted in tumor formation in the peritoneum and other soft tissues. When used separately, alendronate and paclitaxel partially inhibited MMP2 production, but the combination totally blocked protease production and release. Based on these preclinical results, the NCI recently completed a randomized phase II trial of ketoconazole (KT) and alendronate (AL) versus KT in 72 patients with progressive AIPC metastatic to bone. The proportion of patients with a > 50% decline in PSA was similar in the 2 groups (47.2% in KT/AL group vs 44.4% in KT group). However, there was a strong trend toward a prolonged duration of response in KT/AL group compared to ketoconazole group (median, 8.9months vs 6.3 months, respective; p=0.055), and more patients in KT/AL group have not progressed (Liu et al, 2002). This result suggests that alendronate, a potential antiangiogenic agent, improves duration of response in patients with AIPC treated with ketoconazole.

C. TNP-470

TNP-470, a semi-synthetic derivative of fumagillin, was one of the first antiangiogenic compounds to undergo clinical testing (Kruger et al, 2000). Fumagillin is an antibiotic secreted by Aspergillus fumigatus fresenius (Ingber et al, 1990). It was subsequently found that fumagillin is a very potent inhibitor of endothelial cell proliferation in vitro and tumor-induced angiogenesis in vivo (Ingber et al, 1990; Kruger et al, 2000). However, the clinical utility of fumagillin was limited because it caused profound weight loss in animal studies. Therefore, several synthetic analogues were developed, and among these, TNP-470 has shown the least toxicity with the greatest antiangiogenic activity (Ingber et al 1990; Kusaka et al, 1991). In vitro studies revealed that TNP-470 inhibited endothelial cell proliferation in a very low concentration (Kusaka et al, 1994). In vivo, TNP-470 has been demonstrated to be a potent antiangiogenic agent in the chick chorioallantoic assay, rat corneal micropocket assay, and in the rat blood vessel organ culture assay (Ingber et al, 1990; Kusaka et al, 1991; Kruger et al, 2000). Furthermore, TNP-470 inhibited the growth of Lewis lung carcinoma, B16 melanoma, and other tumors in animal models (Ingber et al, 1990; Kusaka et al, 1991; O’Reilly et al, 1995). The molecular target of TNP-470 appears to involve transcription inhibition of specific cyclin-dependent kinase (cdk) and cyclin gene family members (Koyama et al, 1996). It might also inhibit cdc2 and cdk2 kinase activation in endothelial cells (Kato et al, 1994).

Several phase I studies of TNP-470 have been completed in patients with Kaposi’s sarcoma, renal cell carcinoma, brain cancer, breast cancer, cervical cancer and prostate cancer (Figg et al, 1997; Bhargava et al, 1999; Stadler et al, 1999; Logothetis et al, 2001). These phase I trials often showed that TNP-470 resulted in minor objective responses and was well tolerated. The major dose-limiting toxicities were reversible neurotoxicities, including fatigue, asthenia, nystagmus, diplopia, ataxia, depression and loss of concentration. Interestingly, although antitumor activity was not documented in patients with AIPC, TNP-470 caused a transient increase of serum PSA. It was subsequently found that TNP-470 enhances PSA transcription in vitro culture systems (Horti er al, 1999).

D. 2-methoxyestradiol

2-methoxyestradiol (2ME) is a natural metabolite of the endogenous estrogens estradiol-17b and 17-ethynylestradiol (Seegers et al, 1989). In contrast to most estrogens, 2-ME has been shown in preclinical studies to be potentially efficacious in the treatment of cancer. In vitro, 2ME has potent antiproliferative activity in many human cancer cell lines, including Hela cells, Jurkat leukemia cells, and neuroblastoma cells (Seegers et al, 1989, Cushman et al, 1995, and Nakagawa-Yagi et al, 1996). Human breast cancer cell lines are particular sensitive to the cytotoxic effect of 2-ME irrespective of the estrogen receptor status. In vivo, 2-ME has potent activity in primary and metastatic tumor models. Its activity was evident in xenograft models derived from a non-estrogen-dependent human breast tumor cell line (MDA MB-435), MethA sarcoma, B16 melanoma, neuroblastoma, and myeloma (Fotsis et al, 1994, Klauber et al, 1997; Arbiser et al, 1999; Schumacher et al, 2001).

The mechanism of action of 2-ME has not yet been determined, but studies have shown that 2-ME has a potent inhibitory effect on the proliferation of blood-vessel endothelial cells in vitro (Fotsis et al, 1994). Additional studies have demonstrated that 2-ME causes apoptosis in cultured arterial endothelial cells and inhibits the migration of these vascular endothelial cells (Yue et al, 1997). In vivo, 2-ME has been shown to be a potent antiangiogenic agent in tumor vasculature studies and many other models (Fotsis et al, 1994, Klauber et al, 1994; Zhu et al, 1998). A phase I clinical trial of 2-ME in metastatic breast cancer patients was recently initiated (Miller et al, 2001). To date 2-ME has been well tolerated, and no dose-limiting toxicity noted. 2-ME treatment did not alter hormonal status in these patients. Ten out fifteen patients had stable disease. At the NCI, we are currently conducting a phase I trial of 2-ME in patients with solid tumors, including metastatic AIPC, to further explore its clinical benefit, biological as well as molecular activities.

VI. VEGF antibody and inhibitors

VEGF and its receptors play a pivotal role in the regulation of angiogenesis (Folkman et al, 2001 and Liekens, 2001). Therefore, inhibition of VEGF and /or its receptor activity can have a potential benefit in cancer treatment. Recombinant humanized anti-VEGF (RhuMAb VEGF, bevacizumab, Avastin (Genetech)) is a monoclonal IgG antibody. In vivo animal models, it has potent anti-VEGF activity, and suppresses the growth of a broad spectrum of human cancer cell lines (Kim et al, 1993; Warren et al, 1995; Mordenti et al, 1999). Several phase I trials showed that bevacizumab was well tolerated with minimal toxicity. A phase II trial of bevacizumab was conducted in patients with AIPC (Bok et al, 1999). Bevacizumab showed no significant effects on PSA or clinical benefits. Therefore, further studies of this antibody likely will focus on early stage disease, adjuvant treatment, or in combination with other treatment modalities. Dr. Picus reported that a phase II trial combining docetaxel, estramustine and bevacizumab resulted in 79% of patients having a > 50% decrease in PSA and 42% had a partial response. Survival and disease progression have not yet been assessed. (Picus, 2004)

Cetuximab (IMC-C225, anti-EGFR MAb, Erbitux (Imclone, Bristol-Meyers Squibb Oncology)) was studied alone and in combination with paclitaxel in a murine model. Cetuximab alone and in combination significantly decreased growth of the PC-3M-LN4, in vivo. A decreased serum concentration of interleukin-8 as well as a decrease in MVD, and tumor cell proliferation and an enhanced of apoptosis were all enhanced by coadministration of paclitaxel (Karahima, 2002).

Semaxanib (SU5416) is a potent VEGF receptor inhibitor. It inhibits VEGF-mediated FLK1 signaling and endothelial cell proliferation in vitro culture systems (Millauer et al, 1993). In vivo, SU5416 has been demonstrated to inhibit the growth of several type of tumors in animal models (millauer et al, 1996). SU5416 has been tested in phase I studies, in combination with androgen ablation and radiation therapy, and in a phase II study with dexamethasone combination in patients with AIPC. Dose-limiting toxicities in phase I studies consisted headache, fatigue, change in voice, nausea and vomiting, as well as allergic reactions (Cropp et al, 1999). Although SU5416 had promising results in preclinical models, it was withdrawn recently due to its lack of efficacy in clinical trials.

A. Cyclooxygenases inhibitors

Prostaglandins and their derivatives are signaling lipophilic molecules that regulate many physiologic processes including the inflammatory response, platelet aggression, clot formation, and gastric cyto-protection (Dang et al, 2002). Cyclooxygenases (COXs) are key enzymes in the conversion of arachidonic acid to prostagladins. There are two isoforms of the COXs. COX-1 is a constitutive enzyme that is present in most normal tissues and is responsible for local prostaglandin synthesis. In contrast, COX-2 is an inducible form that is normally only expressed at a low level in some tissues, such as brain and kidney. COX-2 synthesis is induced by a variety of stimuli, including inflammatory cytokines, growth factors, oncogenes (HER2/neu and Src), tumor promoters and carcinogens (Kosaka et al, 1994; Vadlamudi et al, 1999; Dang et al, 2002). Studies showed that excessive COX-2 overexpression occurs in colorectal, lung, gastric, breast, prostate and many other solid tumors (Eberhart et al, 1994; Ristimaki et al, 1997; Hida et al, 1998; Hwang et al, 1998; Gupta et al, 2000; Dang et al, 2002). Also, accumulating evidence suggests that elevated prostaglandin expression is associated with tumor growth, metastatic potential and recurrence in a variety spectrum of tumor types. Uotila et al showed that the expression of COX-2 in prostate cancer cells is higher compared with normal glandular epithelial of control prostates (Uotila et al, 2001). Although the mechanism is unclear, overexpression of COX-2 may affect different steps in the process of carcinogenesis, such as immune regulation, cell invasion and proliferation, or apoptosis. Recently, studies demonstrated that there is a strong link between COX-2 expression and hypoxia-induced tumor angiogenesis (Liu et al, 1998). Therefore, COX-2 overexpression may increase tumor blood supply and contribute to tumor growth.

In prostate cancer, studies have shown that COX-2 inhibitors could induce apoptosis in prostate cancer cells in vitro (Liu et al, 1998). In addition, Celecoxib, an elective COX-2 inhibitor, has been shown to be a potent antitumor and a chemoprevention agent in a DMBA-induced rat mammary tumor model (Alshafie et al, 2000). Furthermore, Kirschenbaum et al reported that the COX-2 inhibitors decrease MVD and angiogenesis in prostate cancer tumor models (Liu et al, 2000). Based upon these preclinical observations, COX-2 inhibitors, the potential antiangiogenesis agents, have been tested as chemoprevention as well as treatment modalities. Several clinical trials reported that Celecoxib and other NSAIDs have chemoprevention effects on intestinal adenomas in patients with familial adenomatous polyposis (FAP) (Waddell, et al, 1983, Hawk et al, 1999; Steinbach et al, 2000). Currently, exisulind, a COX-1/COX-2 inhibitor, is being evaluated in phase I/II trials in prostate cancer patients, either as a single agent or in combination with docetaxel. Also, a neoadjuvant trial is currently conducting in prostate cancer, in which patients are randomized to receive either celecoxib or placebo prior to radical prostatectomy. The results of these trials will help to determine the future role of COX-2 inhibitors in the treatment and chemoprevention of prostate cancer.

VII. Conclusion

Antiangiogenesis, a new treatment and prevention strategy in patients with prostate cancer and other tumors, is being developed as either monotherapy or a combination therapy. While preclinical models appeared very promising, with the exception of a few agents, early clinical studies of angiogenesis inhibitors in patients with prostate cancer exhibited disappointed results. Most clinical studies reported that no complete angiosuppression or clinical benefit can be obtained. However, it is too early to conclude that they are ineffective since they have been used only in late stage metastatic prostate cancer. In addition, lack of effectiveness is these trials is not surprising since multiple steps and a variety of factors required for angiogenesis, and by inhibiting one factor is insufficient. Therefore, it is possible that synergistic anti-tumor effects can be obtained by targeting of multiple points in the angiogenic cascade, or by combining angiogenesis inhibitors with radiation therapy, hormonal ablation or cytotoxic therapies. It is expected that within the next decade, these combinations will provide new modalities in the treatment of prostate cancer.

Acknowledgements

This work is supported by the intramural program of the National Cancer Institute.

This is a US government work. There are no restrictions on its use.

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Review Article

Received: 15 April 2004; Accepted: 26 April 2004; electronically published: May 2004

I. Introduction

II. Regulation of angiogenesis

III. Matrix metalloproteinase and angiogenesis

IV. Angiogenesis and prostate cancer

V. Antiangiogenesis

VI. VEGF antibody and inhibitors

VII. Conclusion

Acknowledgements

References