New standards in the chemotherapy of metastatic hormone-refractory prostate cancer

A novel microtubule-modulating agent induces mitochondrially driven caspase-dependent apoptosis via mitotic checkpoint activation in human prostate cancer cells

Hormone-refractory prostate cancer, its skeletal metastasis and complications remain a therapeutic challenge. Here we show that treatment with (S)-3-((R)-9-bromo-4-methoxy-6-methyl-5,6,7,8-tetrahydro-[1,3]dioxolo[4,5-g]isoquinolin-5-yl)-6,7-dimethoxyiso-benzofuran-1(3H)-one (EM011), the brominated analogue of a plant-derived non-toxic antitussive alkaloid, noscapine, achieved significant inhibition of hormone-refractory human prostate cancer implanted intratibially in the bone as shown by non-invasive, real-time bioluminescent imaging of tumour growth in nude mice. Mechanistically, in vitro data suggested that the antiproliferative and proapoptotic effects of EM011 in human prostate cancer cell lines were through blockade of cell-cycle progression by impairing the formation of a bipolar spindle apparatus. The G2/M arrest was accompanied by activation of the mitotic checkpoint, a pre-requisite for induction of optimal apoptosis. Attenuation of mitotic checkpoint by siRNA duplexes led to a reduction in mitotic arrest and subsequent apoptosis. Our results further demonstrated participation of an intrinsic mitochondrially mediated apoptotic pathway that ultimately triggered caspase-driven EM011-induced apoptosis. EM011 did not exert any detectable toxicity in normal tissues with frequently dividing cells such as the gut and bone marrow. Thus, these data warrant further evaluation of EM011 for the management of prostate cancer.

Garlic-derived S-allylmercaptocysteine is a novel in vivo antimetastatic agent for androgen-independent prostate cancer

PURPOSE

There is epidemiologic evidence that high garlic consumption decreases the incidence of prostate cancer, and compounds isolated from garlic have been shown to have cancer-preventive and tumor-suppressive effects. Recent in vitro studies in our laboratory have shown that garlic-derived organosulfur compound S-allylmercaptocysteine suppresses invasion and cell motility of androgen-independent prostate cancer cells via the up-regulation of cell-adhesion molecule E-cadherin. S-allylmercaptocysteine is therefore a potential antimetastatic drug with broad clinical applications that we tested in vivo for the first time in this study.

EXPERIMENTAL DESIGN

We used a newly established fluorescent orthotopic androgen-independent prostate cancer mouse model to assess the ability of S-allylmercaptocysteine to inhibit tumor growth and dissemination.

RESULTS

We showed that oral S-allylmercaptocysteine not only inhibited the growth of primary tumors by up to 71% (P < 0.001) but also reduced the number of lung and adrenal metastases by as much as 85.5% (P = 0.001) without causing notable toxicity. This metastatic suppression was accompanied by a 91% reduction of viable circulating tumor cells (P = 0.041), suggesting that S-allylmercaptocysteine prevents dissemination by decreasing tumor cell intravasation.

CONCLUSIONS

Our results provide in vivo evidence supporting the potential use of S-allylmercaptocysteine as an E-cadherin up-regulating antimetastatic agent for the treatment of androgen-independent prostate cancer. This is the first report of the in vivo antimetastatic properties of garlic, which may also apply to other cancer types.

Patupilone (epothilone B, EPO906) inhibits growth and metastasis of experimental prostate tumors in vivo

BACKGROUND

Microtubule agents appear promising for the treatment of prostate cancer. Patupilone (epothilone B), a highly potent non-taxane microtubule stabilizing agent, was evaluated in models of androgen-independent prostate cancer.

METHODS

Patupilone was administered to athymic mice bearing human prostate cancer xenografts (subcutaneous DU 145 and PC-3M, orthotopic PC-3M).

RESULTS

One 4 mg/kg patupilone administration produced transient regression of DU 145 tumors, while two weekly administrations of 2.5 mg/kg produced stable disease followed by protracted regression, however with more pronounced body weight loss. Taxol (15 mg/kg every other day) weakly inhibited tumor growth, but with less body weight loss. Patupilone (5 mg/kg) produced protracted growth inhibition of subcutaneous PC-3M tumors, with transient body weight loss. In mice with orthotopic PC-3M tumors, 4 or 5 mg/kg/week patupilone impaired primary tumor growth, abrogated metastases and enhanced survival, with only transient body weight loss.

CONCLUSIONS

These data suggest that patupilone holds promise for prostate cancer treatment.