Novel drug targets for the pharmacotherapy of benign prostatic hyperplasia (BPH)

Development of a P2X1-purinoceptor mediated contractile response in the aged mouse prostate gland through slowing down of ATP breakdown

AIMS

An age-related increase in prostatic smooth muscle tone is partly responsible for the lower urinary tract symptoms associated with benign prostatic hyperplasia (BPH). Changes in the effectors of prostatic smooth muscle contraction with age may play a role in the development of these symptoms. Using a mouse model of prostate contractility, this study investigated the effect of age on the different components of contractility in the prostate gland.

METHODS

The isometric force developed in response to electrical field stimulation or exogenously applied agonists by mouse prostates mounted in organ baths, was evaluated to determine the effect of age on contractile mechanisms. Changes with age in the rate of ATP breakdown and levels of the P2rx1 gene and P2X1-purinoceptor expression in mouse prostate were measured by a modified luciferin-luciferase assay, RT-PCR and western blot, respectively.

RESULTS

Nerve mediated contractile responses containing a component elicited by P2X1-purinoceptors were observed in prostates taken from aged mice, but not in prostates taken from young adult mice. Furthermore, the potency of the endogenous purinoceptor agonist ATP was 50-fold greater in aged mice, whereas the potency of its stable analogue α,β-metATP was unchanged. An age-related decrease in ATP metabolism was also observed.

CONCLUSIONS

With age, a purinergic contractile response to nerve stimulation develops in the mouse prostate gland due to a decrease in the rate of ATP breakdown. This may contribute to the increase in muscular tone observed in BPH and suggests that P2X1-purinoceptors are an additional target for the treatment of BPH.

Oral naftopidil suppresses human renal-cell carcinoma by inducing G(1) cell-cycle arrest in tumor and vascular endothelial cells

Renal cell carcinoma (RCC) is an angiogenesis-dependent and hypoxia-driven malignancy. As a result, several targeting agents are being investigated. However, the efficacy of current regimens is generally insufficient for their toxicity and poor overall response rates. We have recently reported that naftopidil exerts growth-inhibitory effects on human prostate cancer cells. In this study, we investigated the biochemical mechanisms by which naftopidil produces growth-inhibitory and antiangiogenic effects on RCC. We first tested the effects of naftopidil on the proliferation of ACHN and Caki-2 RCC cells. Next, we set up a model simulating the tumor microenvironment, in which ACHN cells were grafted onto the renal capsule of mice. We then tested the effects of naftopidil on human umbilical vein endothelial cells' cell proliferation and Matrigel plug vascularization. Finally, to establish the antitumor activity of naftopidil on RCC, we tested the antitumor effects of naftopidil on excised tumor specimens from 20 patients with RCC that were grafted beneath the renal capsule of mice. Naftopidil showed similar in vitro growth-inhibitory effects on all cell lines. Fluorescence-activated cell sorting analysis revealed an increase in G1 cell-cycle arrest in all naftopidil-treated cell lines. In vivo tumorigenic studies showed a significant reduction of ACHN tumor weight, Ki-67 index, and microvessel density (MVD) in naftopidil-treated mice. Naftopidil attenuated neovascularization in an in vivo Matrigel plug assay. Studies in mouse xenograft models also showed a significant MVD reduction in naftopidil-treated excised human RCC. The growth-inhibitory effects of naftopidil suggest it may be a novel anticancer agent and a potential preventive option for RCC.

Contractile signaling pathways in mouse prostate smooth muscle

BACKGROUND

Prostate smooth muscle plays an important role in the physiological ejection of prostatic fluid and also in the pathogenesis of benign prostate hyperplasia. Although mouse is the best genetically engineered animal model to identify potential molecular targets for human diseases, only fragmentary information is available for basic mechanism of mouse prostate contraction.

METHODS

Small smooth muscle tubular rings were excised from four mouse prostate lobes to measure their isometric contractions. High K(+) , noradrenaline (NA), or acetylcholine (ACh) was applied with and without various antagonists and/or inhibitors to examine the contractile signaling pathways.

RESULTS

Maximum amplitude of agonist-induced contractions varied greatly with different lobes but not with different locations or orientations within each lobe. Both NA and ACh produced large contractions in ventral and dorsal rings, whereas only small contractions were elicited in lateral and anterior rings. Combination of alpha-1 and muscarinic antagonists suppressed K(+) depolarization-induced contraction potently in ventral rings, but slightly in anterior rings. Blocking of either Ca(2+) -release or Ca(2+) -influx reduced agonist-induced contraction of ventral rings, however, a considerable amount of contractility remained even with both blockers. Inhibitors of ROCK and PKC partially inhibited NA-induced contractions, whereas a combination of Ca(2+) -blockers and Ca(2+) -sensitization inhibitors strongly suppressed the contraction.

CONCLUSIONS

The ejection of prostatic fluid is differentially regulated in each prostate lobe. In ventral prostate smooth muscle, Ca(2+) -release, Ca(2+) -influx, and ROCK- and PKC-mediated Ca(2+) -sensitizations are all involved in NA-induced contractions. This finding is a useful step toward the understanding of the phenotypic changes in the smooth muscle of BPH prostate.

Age-related changes in the innervation of the prostate gland: implications for prostate cancer initiation and progression

The adult prostate gland grows and develops under hormonal control while its physiological functions are controlled by the autonomic nervous system. The prostate gland receives sympathetic input via the hypogastric nerve and parasympathetic input via the pelvic nerve. In addition, the hypogastric and pelvic nerves also provide sensory inputs to the gland. This review provides a summary of the innervation of the adult prostate gland and describes the changes which occur with age and disease. Growth and development of the prostate gland is age dependent as is the occurrence of both benign prostate disease and prostate cancer. In parallel, the activity and influence of both the sympathetic and parasympathetic nervous system changes with age. The influence of the sympathetic nervous system on benign prostatic hyperplasia is well documented and this review considers the possibility of a link between changes in autonomic innervation and prostate cancer progression.

Shrinkage of experimental benign prostatic hyperplasia and reduction of prostatic cell volume by a gastrin-releasing peptide antagonist

Gastrin releasing-peptide (GRP) is a potent growth factor in many malignancies. Benign prostatic hyperplasia (BPH) is a progressive age-related proliferation of glandular and stromal tissues; various growth factors and inflammatory processes are involved in its pathogenesis. We have demonstrated that potent antagonists of GRP inhibit growth of experimental human tumors including prostate cancer, but their effect on models of BPH has not been studied. Here, we evaluated the effects of GRP antagonist RC-3940-II on viability and cell volume of BPH-1 human prostate epithelial cells and WPMY-1 prostate stromal cells in vitro, and in testosterone-induced BPH in Wistar rats in vivo. RC-3940-II inhibited the proliferation of BPH-1 and WPMY-1 cells in a dose-dependent manner and reduced prostatic cell volume in vitro. Shrinkage of prostates was observed after 6 wk of treatment with RC-3940-II: a 15.9% decline with 25 μg/d; and a 18.4% reduction with 50 μg/d (P < 0.05 for all). Significant reduction in levels of proliferating cell nuclear antigen, NF-κβ/p50, cyclooxygenase-2, and androgen receptor was also seen. Analysis of transcript levels of genes related to growth, inflammatory processes, and signal transduction showed significant changes in the expression of more than 90 genes (P < 0.05). In conclusion, GRP antagonists reduce volume of human prostatic cells and lower prostate weight in experimental BPH through direct inhibitory effects on prostatic GRP receptors. GRP antagonists should be considered for further development as therapy for BPH.

What makes the α(1A)-adrenoceptor gene express the α(1L)-adrenoceptor functional phenotype?

The α(1A)-adrenoceptor is therapeutically exploited because of its prevalence in the lower urinary tract. The pharmacology shown by this lower urinary tract α(1A)-adrenoceptor is different from that shown by other α(1A)-adrenoceptors, which has led to it being subclassified as an α(1L)-adrenoceptor. Only in the last few years was it shown that this pharmacologically distinct α(1L)-adrenoceptor is a product of the α(1A)-adrenoceptor gene. In this issue of the BJP, Nishimune et al. review the literature on α(1L)-adrenoceptor pharmacology and discuss the possible molecular mechanisms by which the α(1A)-adrenoceptor gene is able to produce two pharmacologically distinct adrenoceptor subtypes. Based primarily from their own research using cell lines transfected with α(1A)-adrenoceptors, they conclude that a protein that interacts with the receptor is the most plausible explanation. The challenge remains to identify any such interacting protein and show how it is able to change the pharmacology of the receptor for different ligands.

Activation of innate anti-viral immune response genes in symptomatic benign prostatic hyperplasia

Benign prostatic hyperplasia (BPH) is the most common urologic disease in men over age 50. Symptoms include acute urinary retention, urgency to urinate and nocturia. For patients with severe symptoms, surgical treatment is used to remove the affected tissue. Interestingly, the presence of histologic BPH does not always correlate with symptoms. The molecular basis of symptomatic BPH and how it differs from asymptomatic BPH is unknown. Investigation into the molecular players involved in symptomatic BPH will likely give insight into novel therapeutic, and potentially preventative, targets. We determined the expression of genes involved in the innate anti-viral immune response in tissues from patients undergoing surgery to alleviate the symptoms of BPH, and compared the results with prostate tissue with histologic BPH, but from patients with few urinary issues (asymptomatic BPH). We found that expression of complement factor I, apolipoprotein B mRNA-editing enzyme, catalytic polypeptide-like protein 3G, oligoadenylate synthetase 2 and interferon-induced tetratricopeptide 1, four genes whose protein products are involved in the innate anti-viral immune response, was significantly transcriptionally upregulated in symptomatic BPH. Additionally, we observe hypomethylation and concomitant expression of ancient retroviral-like sequences, the long interspersed nuclear element 1 retrotransposons, in symptomatic BPH when compared with normal prostate tissue. These findings merit further investigation into the anti-viral immune response in symptomatic BPH.