Similarities in the modulation of pituitary and prostatic FSH by inhibin and related peptides

Follicle-stimulating hormone promotes growth of human prostate cancer cell line-derived tumor xenografts

Chemical castration in prostate cancer can be achieved with gonadotropin-releasing hormone (GnRH) agonists or antagonists. Their effects differ by the initial flare of gonadotropin and testosterone secretion with agonists and the immediate pituitary-testicular suppression by antagonists. While both suppress luteinizing hormone (LH) and follicle-stimulating hormone (FSH) initially, a rebound in FSH levels occurs during agonist treatment. This rebound is potentially harmful, taken the expression of FSH receptors (R) in prostate cancer tissue. We herein assessed the role of FSH in promoting the growth of androgen-independent (PC-3, DU145) and androgen-dependent (VCaP) human prostate cancer cell line xenografts in nude mice. Gonadotropins were suppressed with the GnRH antagonist degarelix, and effects of add-back human recombinant FSH were assessed on tumor growth. All tumors expressed GnRHR and FSHR, and degarelix treatment suppressed their growth. FSH supplementation reversed the degarelix-evoked suppression of PC-3 tumors, both in preventive (degarelix and FSH treatment started upon cell inoculation) and therapeutic (treatments initiated 3 weeks after cell inoculation) setting. A less marked, though significant FSH effect occurred in DU145, but not in VCaP xenografts. FSHR expression in the xenografts supports direct FSH stimulation of tumor growth. Testosterone supplementation, to maintain the VCaP xenografts, apparently masked the FSH effect on their growth. Treatment with the LH analogue hCG did not affect PC-3 tumor growth despite their expression of luteinizing hormone/choriongonadotropin receptor. In conclusion, FSH, but not LH, may directly stimulate the growth of androgen-independent prostate cancer, suggesting that persistent FSH suppression upon GnRH antagonist treatment offers a therapeutic advantage over agonist.

Expression and cellular localization of follicle-stimulating hormone receptor in normal human prostate, benign prostatic hyperplasia and prostate cancer

PURPOSE

FSH, identified as an endogenous product of the prostate, is a glycoprotein with proliferative activity. Increasing evidence of autocrine/paracrine activities of gonadotropins at extragonadal sites led us to investigate the gene expression and cellular localization of FSH-R in normal and diseased human prostates.

MATERIALS AND METHODS

Prostate specimens, including normal gland, BPH, PCa and human androgen refractory (PC3) and androgen dependent (LNCaP) prostate cancer cell lines (European Collection of Cell Cultures, Salisbury, United Kingdom), were analyzed for FSH-R expression by semiquantitative and real-time reverse transcriptase-polymerase chain reaction and immunohistochemistry. We also evaluated cyclic adenosine monophosphate production by cultured PC3 and LNCaP stimulated with human FSH.

RESULTS

Little FSH-R expression was seen in 9 of 13 normal and 8 of 15 BPH specimens. Of 30 PCa samples 21 were FSH-R positive with generally higher expression compared to normal prostate and BPH samples. Real-time reverse transcriptase-polymerase chain reaction of matched normal/tumor pairs confirmed higher FSH-R mRNA expression in PCa. PC3 cells expressed FSH-R, while LNCaP cells were FSH-R negative. FSH-R protein was mainly localized in the glandular epithelium and in some stromal cells in normal prostate, BPH and PCa specimens. PC3 cells expressed FSH-R protein and their treatment with FSH induced a significant increase in cyclic adenosine monophosphate production.

CONCLUSIONS

These results indicate that a subset of PCa expresses FSH-R mRNA and protein at levels higher than those of normal and hyperplastic tissues that express FSH-R. This suggests that FSH might contribute to some cases of PCa via a receptor mediated mechanism.

Prostate secretory protein of 94 amino acids (PSP-94) and its peptide (PCK3145) as potential therapeutic modalities for prostate cancer

This review focuses on the promising roles of prostate secretory protein of 94 amino acids (PSP-94) and one of its derived peptides (PCK3145) as potential therapeutic modalities for prostate cancer and its associated complications. Evaluation of these compounds was carried out in vitro and in vivo using syngeneic models of rat prostate cancer. Overproduction of parathyroid hormone-related protein (PTHrP) results in the development of hypercalcemia of malignancy in several malignancies including prostate cancer. In order to evaluate the effect of PSP-94 and PCK3145 on prostate cancer progression, the rat Dunning R3227 MatLyLu cell line transfected with full-length cDNA encoding PTHrP (MatLyLu-PTHrP) was used. As the main pathogenetic factor of hypercalcemia of malignancy, overexpression of PTHrP was aimed at mimicking the hypercalcemic nature seen in patients suffering from late-stage cancer. In vitro studies showed that PSP-94 and PCK3145 can cause a dose-dependent inhibition in the growth of MatLyLu-PTHrP cells. For in vivo studies, male Copenhagen rats were inoculated either s.c. into the right flank or directly into the left ventricle via intracardiac (i.c.) inoculation with MatLyLu-PTHrP cells. In these models, s.c. injection of MatLyLu cells results in the development of primary tumor growth, whereas i.c. inoculation routinely results in the development of experimental skeletal metastases in the lumbar vertebrae causing hind-limb paralysis. Administration of PSP-94 and PCK3145 into tumor-bearing animals resulted in a dose-dependent inhibition of primary tumor growth, and tumoral and plasma PTHrP levels, and in the reduction of plasma calcium levels. Additionally, treatment with PSP-94 or PCK3145 caused an inhibition of skeletal metastases resulting in a significant delay in the development of hind-limb paralysis. Interestingly, equimolar concentrations of PCK3145 were shown to be more effective in delaying the development of experimental skeletal metastases as compared to PSP-94. One of the possible mechanisms of action of these modalities is through the induction of apoptosis which was observed by both in-vitro and in-vivo analyses of MatLyLu-PTHrP cells and tumors. Several intracellular mechanisms can also be involved in inhibiting PTHrP production and anti-tumor effects of PSP-94 and PCK3145. Collectively, these studies warrant the continued clinical development of these agents as therapeutic agents for patients with hormone-refractory prostate cancer.

A synthetic 15-mer peptide (PCK3145) derived from prostate secretory protein can reduce tumor growth, experimental skeletal metastases, and malignancy-associated hypercalcemia

In previous studies, we have shown that prostate secretory protein (PSP-94) can reduce prostate cancer growth in vivo. In the current study, we identified the amino acid sequence of PSP-94 that is required for eliciting this response. For these studies, we used rat prostate cancer Mat Ly Lu cells overexpressing parathyroid hormone-related protein (PTHrP), which is the main pathogenetic factor responsible for hypercalcemia of malignancy. Synthetic peptides corresponding to amino acids 7-21 (PCK721), 31-45 (PCK3145), and 76-94 (PCK7694) of PSP-94 were synthesized. Only PCK3145 showed a significant reduction in tumor cell proliferation. For in vivo studies, syngenic male Copenhagen rats were inoculated s.c. with Mat Ly Lu cells overexpressing PTHrP into the right flank or into the left ventricle via intracardiac injection, which results in experimental metastases to the lumbar vertebrae causing hind-limb paralysis. Animals were infused with different doses (1, 10, and 100 microg/kg/day) of peptides for 15 days, and the effect of these treatments on tumor volume, skeletal metastases, or development of hind-limb paralysis was determined. Treatment with PCK3145 resulted in a dose-dependent decrease in tumor volume and delay in the development of skeletal metastases. Bone histomorphometry showed that after intracardiac inoculation of tumor cells, the highest dose of PCK3145 (100 microg/kg/day) resulted in reducing skeletal tumor burden, which delayed the development of hind-limb paralysis. Treatment with PCK3145 led to reduction of plasma calcium and PTHrP levels and a significant decrease in PTHrP levels in the primary tumors and in vertebrae of experimental animals. These effects of PCK3145 were due to its ability to promote tumor cell apoptosis. Collectively, the results of these studies have demonstrated the ability of a small peptide derived from PSP-94 to reduce tumor volume and experimental skeletal metastases-results that will be highly beneficial in the continued development of this peptide as a novel therapeutic agent for patients with hormone refractory, late-stage prostate cancer.

Advancing perspectives on prostate cancer: multihormonal influences in pathogenesis

Nonandrogenic hormones are implicated in the growth and function of the prostate, which is itself an endocrine gland that synthesizes and secretes hormones and growth factors, including follicle-stimulating hormone (FSH) and prostatic inhibin peptide (PIP). Findings of increased FSH concentrations and receptor expression in diseased prostate tissue suggest a role for FSH in prostate cancer growth. Not only does PIP suppress circulating levels of FSH, but it responds to and modulates prostatic FSH, suggesting a close interlinkage of these compounds in controlling both healthy and diseased prostate cells. Other focuses of endocrinologic research include androgen receptors, vitamin D, growth factors (including insulin-like growth factors I and II), and retinoids. Issues such as optimal therapy timing, intermittent administration, and the adoption of a multihormonal approach to the management of prostate cancer remain to be resolved.

Decreased immunoexpression of prostate inhibin peptide in prostatic carcinoma: a study with monoclonal antibody

Prostate inhibin peptide (PIP) is a follicle-stimulating hormone (FSH) regulating peptide produced by the prostate. The mechanism of its endocrine role in regulating prostate growth is believed to be androgen-independent but FSH-dependent. Previous studies using polyclonal antibody proposed PIP as a prostatic-specific marker in cancer diagnosis. However, the recently available monoclonal antibody has not yet been evaluated. Paraffin sections of 72 prostatectomy specimens for prostate cancer with or without hormonal blockage therapy and 10 nonneoplastic prostate tissues from autopsy were stained by using PIP monoclonal antibody (clone: 4A6A6) with the avidin-biotin complex method. PIP reactivity was semiquantitatively estimated in prostatic carcinoma (PCA), prostatic intraepithelial neoplasia (PIN), benign prostatic hyperplasia (BPH) and normal tissue in each case when ever present. Statistical analyses were performed accordingly. PIP expression is predominantly cytoplasmic. Urothelium, seminal vesicles, inflamed prostatic glands, basal cells, and squamous metaplasia were negative for PIP. Average percentage of cells expressing PIP was significantly decreased in PIN (40%) and PCA (14%) when compared with BPH (81%) and normal tissue (68%). There was no correlation of tumor PIP level with patient's age, tumor size, Gleason score, tumor stage, or the usage of preoperative hormonal blockage therapy. PIP monoclonal antibody should be used with caution as a prostate-specific marker in surgical pathology. The mechanism for this alteration and the effect of PIP on prostatic tumor growth, particularly in patients under a variety of hormonal therapies, needs further study.

Human seminal plasma beta-microseminoprotein: its purification, characterization, and immunohistochemical localization

beta-Microseminoprotein was very efficiently purified from human seminal plasma with only three steps including DEAE-Sephacel and Zinc-chelate Sepharose CL-6B column chromatography. The purified protein was a non-glycoprotein with a molecular weight (M(r)) of 19,000 and 17,000 on gel filtration and reduced SDS-PAGE, respectively. The protein gave six bands from M(r) 15,600 to 25,500 on non-reduced SDS-PAGE. The characterization including the molecular weight, amino acid sequence of N-terminus and concentrations in various body fluids is discussed. Furthermore, the immunohistochemical localization of the protein among various human tissues is demonstrated.

Effect of transurethral resection of prostate on plasma hormone levels in benign prostatic hyperplasia

Circulating levels of pituitary and adrenal hormones were measured in patients with benign prostatic hyperplasia before and after transurethral resection of the prostate (TURP). TURP caused a significant increase in plasma LH levels 2 weeks and 3 weeks after surgery. The plasma prolactin level decreased significantly 3 weeks after prostatectomy but plasma concentrations of FSH and ACTH were unchanged. TURP did not alter circulating levels of aldosterone, cortisol, DHEA-S and testosterone. These data suggest that the human prostate has a role in regulating the pituitary secretion of LH and prolactin.

Effect of prostatic inhibin peptide (PIP) on prostate cancer cell growth in vitro and in vivo

Prostatic inhibin peptide (PIP), is a 94 amino acid protein which is secreted by the prostate gland in an androgen-independent manner. Previously, it has been demonstrated that PIP appears to inhibit follicle-stimulating-hormone (FSH) secretion by the pituitary and prostate glands. In vitro, the Dunning R3327 rat prostate cancer cell line MAT-LyLu (MLL) cells and the human prostate cancer cell line PC-3, are stimulated to grow in response to exogenous FSH and these effects are blocked by PIP. In vivo, PIP inhibits the growth of the highly metastatic MLL prostate cancer cell line. A comparison of hormone levels in control and PIP-treated rats demonstrates a significant inhibition of FSH in treated animals. It appears that, in vivo, PIP may inhibit prostate cancer growth by inhibiting FSH. PIP may represent a novel hormonal treatment for prostate cancer.

Passive immunization against prostatic 'inhibin' peptide as a male contraceptive

Passive immunization of adult male hamsters for 12 weeks against peptide (As-PIP), a sperm coating antigen, resulted in selective elevation of the blood levels of FSH, impairment of spermatogenesis, and complete infertility when males were mated with normal cycling females. Passive immunization of male marmosets with As-PIP for 8 weeks was also effective and was reversible, without causing any obvious change in mating behaviour. These preliminary studies in hamsters and marmosets indicate that antibodies to a prostatic 'inhibin' peptide represent a promising new approach to male contraception.