Antiandrogen effects in models of androgen responsive cancer

Large fragment of the probasin promoter targets high levels of transgene expression to the prostate of transgenic mice

BACKGROUND

Androgen regulation and prostate-specific expression of targeted genes in transgenic mice can be controlled by a small DNA fragment of the probasin (PB) promoter (-426 to +28 base pairs, bp). Although the small PB fragment was sufficient to direct prostate-specific expression, the low levels of transgene expression suggested that important upstream regulatory sequences were missing.

METHODS

To enhance transgene expression, a large fragment of the PB promoter (LPB, -11,500 to +28 bp) was isolated, linked to the bacterial chloramphenicol acetyl transferase (CAT) gene, and microinjected into CD1 mouse oocytes to generate transgenic mouse lines.

RESULTS

As shown by the immunohistochemical studies, CAT gene expression was restricted to the prostatic epithelial cells in a tissue-specific manner. High levels of CAT gene expression were observed in two of the six LPB-CAT transgenic lines. In Line 1, developmental regulation of LPB-CAT was detected early, from 1 to 4 weeks of age, with the activity of CAT increasing from 3 to 40,936 dpm/min/mg protein. Upon sexual maturation and elevated serum androgen levels (7 weeks of age), a further 18-fold rise in CAT activity occurred. Hormone ablation by castration in mature mice dramatically reduced transgene expression, whereas treatment with androgens returned LPB-CAT expression to precastration levels. In contrast, treatment with glucocorticoids had no significant effect on CAT gene expression. Zinc treatment of the castrated animals also increased LPB-CAT expression three- to four-fold in two prostatic lobes.

CONCLUSIONS

This study demonstrates that important regulatory DNA sequences located in the LPB fragment contribute to tissue-specific expression and greatly increase levels of transgene expression induced by androgens and zinc.

Antiproliferative activity of casodex (ICI 176.334) in hormone-dependent tumours

The nonsteroidal antiandrogen casodex has been described as a peripherally selective drug for the treatment of prostatic cancer. In this study we determined its activity in various models of hormone-dependent malignancies including those of the prostate and the breast. Analysis of endocrine effects in rats after 15 days of treatment revealed a strong reduction of the weights of prostates and seminal vesicles and a significant rise of testosterone serum levels as a result of the interference with central feedback mechanisms. The growth of androgen-sensitive human LNCaP/FGC prostate cancer cells was strongly inhibited by casodex. Unlike hydroxyflutamide, casodex was also active in hormone-depleted medium. The inhibitory effect was overcome by addition of testosterone propionate, which indicates an androgen-receptor-mediated mode of action. In rats bearing Dunning R3327-G prostate carcinomas casodex exerted a strong antitumour effect at the beginning of therapy. However, after 4 weeks of treatment tumours resumed growth whereas diethylstilboestrol-treated tumours remained static. In MXT-M3.2 mouse mammary tumours with significant quantities of androgen receptors casodex was also effective in inhibiting tumour growth. After 6 weeks of treatment, tumour weights were reduced by 69% whereas uterine weights were significantly increased, possibly because of a progestin-like activity of the drug. Csodex is very active in various models of hormone-dependent carcinomas. However, the limited duration of action in prostatic tumours and the incomplete growth inhibition in mammary tumours suggest that it should be used only combination with other endocrine therapies.

A randomized double-blind study evaluating Anandron associated with orchiectomy in stage D prostate cancer

A randomized double-blind study with a 3-yr follow-up comparing the two arms "orchiectomy + Anandron (300 mg)" vs "orchiectomy + placebo" in 125 patients with stage D prostate cancer has confirmed the beneficial effects of the combined Anandron therapy on subjective parameters and on the best objective response (NPCP criteria), although these effects were not statistically significant, but failed to detect any improvement in time-to-disease progression or survival. Comparison with the results of other trials emphasizes the urgent need to establish suitable prognostic factors by further clinical research before evaluating the benefits of individual drugs.

Pharmacokinetics of the recombinant fusion protein DAB486IL-2 in animal models

The kinetics of the in vitro cytotoxicity of DAB486IL-2, a genetically engineered fusion protein containing a portion of diphtheria toxin and human interleukin-2, were examined in the C91/PL cell line, which constitutively expresses IL-2 receptors. Maximal inhibition of protein synthesis was observed by 4-6 h after DAB486IL-2 addition at a concentration of 300 ng/ml. The tissue distribution, urinary excretion, and plasma pharmacokinetics of DAB486IL-2 in the rat and its plasma pharmacokinetics in the monkey were also examined. In rats the primary site of distribution of [35S]-DAB486IL-2 outside the vasculature appears to be the liver, followed by the kidney, spleen, and lung. Persistence of radioactive material in the liver and urinary excretion of metabolic degradation products suggest that labeled protein is metabolized by hepatic tissue. Following i.v. bolus administration of DAB486IL-2, the initial serum half-life for both the rat and the monkey was approximately 5 min. The overall clearance rate of drug for the two species differed, with DAB486IL-2 being cleared from circulation 2-3 times more rapidly in the monkey. Presence of high levels of neutralizing antibodies to diphtheria toxin in the rat significantly influenced the clearance of bioactive DAB486IL-2. However, the question as to whether the presence of in vitro biological activity for the molecule is masked by the presence of antibodies cannot be clearly answered.