It is well known that androgen deprivation is the cornerstone of initial therapy for metastatic prostate cancer. Once metastatic prostate cancer progresses in the face of hormonal therapy, it is classified as being androgen independent. Therapeutic options for patients with androgen independent prostate cancer are extremely limited. In particular, cytotoxic chemotherapy has provided minimal benefit. The purpose of this project is to perform translational research to develop new agents, and/or therapeutic maneuvers, that appear to have antitumor activity in prostate cancer. To achieve this goal, we have become extensively involved in the efforts to understand the biology of prostate cancer. Currently, we are attempting to correlate biological variables associated with prostate cancer and response to therapy (e.g., mutated androgen receptor, CAG repeats and microvessel count). The Molecular Pharmacology Section reported the first confirmation of the therapeutic efficacy of flutamide withdrawal, as well as the enhanced activity of simultaneous adrenal suppression. It has been hypothesized that the clinical improvement associated with flutamide is a result of the presence of a mutation within the ligand-binding domain of the androgen receptor. As we and others have reported, the human prostate cancer cell line LNCaP, which expresses such a mutated receptor, is stimulated to grow by hydroxy-flutamide, the active metabolite of flutamide. We believe that the mutation in the ligand-binding domain of the androgen receptor causes these normally antagonistic compounds to behave as androgen agonists. Whether this phenomenon is unique to the LNCaP cell line or is also responsible for the observations made in vivo is unknown. This question is being actively pursued in our section. More recently, we have initiated experiments in an attempt to determine which genes are regulated by the androgen receptor. In particular, we are interested in a polymorphism in the AR (a trinucleotide repeat in exon 1 -- CAG repeat). Clinically we have attempted to develop novel agents that alter the biology of the cancer. Specifically, we have been interested for many years in inhibiting angiogenesis as a means to treat prostate cancer. The progression of prostate cancer from a latent to an aggressive form depends on the acquisition of the angiogenic phenotype. Without angiogenesis, the primary prostate tumor is confined to 1-2 mm in size, and remains indolent. Angiogenesis is also required at sites of secondary colonizations in order for prostate cancer metastases to proliferate and expand. Prostate tumors found in autopsy specimens from men without clinical prostate cancer have very low blood vessel content, compared to prostate cancer specimens from men with clinically-evident disease. Siegal and colleagues reported that microvessel density (MVD) was significantly higher in prostate cancer tissue, than in adjacent hyperplastic or benign tissue. Numerous studies have been conducted to evaluate the use of MVD in prostate cancer samples as a prognostic and/or diagnostic marker. Most studies have demonstrated that MVD does help predict pathological stage and patient outcome. Using specimens from radical prostatectomies, Weidner et al., correlated increased angiogenesis in primary tumor specimens with metastatic disease. Several other studies also found MVD to independently predict the outcome of patients with prostate cancer. A recent study did not find MVD to be a useful prognostic indicator for men with clinically localized prostate cancer. Angiogenesis is driven by an imbalance of positive and negative regulators. One of the most potent positive regulators of angiogenesis is the vascular endothelial growth factor (VEGF). Prostate cancer cells produce VEGF at very high concentrations compared to normal prostate tissue. Such elevated levels of VEGF contribute to prostate cancer progression by inducing angiogenesis in the stroma via paracrine signalling. Using different sublines of LNCap cell lines, Balbay and colleagues demonstrated that the metastatic potential of human prostate cancer cell lines in an athymic mice model correlated with their VEGF expression. VEGF production is regulated by androgens in both normal and malignant prostate tissues. When prostate cancer cells progress to an androgen-independent state, VEGF regulation by androgens is also lost. Cellular hypoxia then becomes the main regulator of VEGF. VEGF acts upon two high affinity tyrosine kinase family receptors, Flt-1/ VEGFR-1 and Flk-1/ VEGFR-2. While previously believed to be specific to endothelial cells, these VEGF receptors have recently been localized to several types of tumors, including prostate. A recent study reports that Flt-1 is present in BPH and PIN, but lost in prostate cancer cells and with tumor dedifferentiation, implicating a role for this receptor in prostatic transformation to malignancy. Another member of the VEGF family, VEGF C, which binds to VEGF receptor-3 (VEGFR-3/ Flt-4) is also produced by prostate cancer cells and has recently been implicated in lymph node metastasis. Thus, the strong interplay between prostate cancer progression and angiogenesis are quickly being realized as this field unfolds. Antiangiogenic agents which we have clinically evaluated include: suramin, CAI, thalidomide, TNP-470, COL3, and somatuline. Currently, we are assessing docetaxel with or without thalidomide, and ketoconazole with or without alendronate (an MMP inhibitor) in patients with androgen indepedent prostate cancer. We have initiated a phase I clinical trial with CC5013 and 2ME (angiogenesis inhibitors). More recently, we have synthesized 80 analogs of thalidomide and have evaluated them using four in vitro models to assess activity in the inhibition of angiogenesis (rat aorta model, human saphenous vein model, cultured endothelial cells, and tube formationassay). We have identified the most potent of these and have patented them. We are in the process of developing them and taking them into xenograft models. These compounds appear to be extremely active with minimal side effects in initial preclinical toxicology studies.
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