Effect of early exposure of flutamide on subsequent growth of transplantable rat prostatic tumor (dunning R-3327)

Rat transplantable prostatic tumors (Dunning R-3327) were treated with flutamide before tumors grew palpable, in order to examine the effect of short term treatment of antiandrogen for prostatic cancer in latent period on the growth after appearance of tumor. Flutamide delayed an appearance of the tumor nodule and retarded the growth rate in proportion as treatment began earlier. Flutamide also reduced final tumor volume. Flutamide-treated tumors histologically consisted of small or dilated glandular structure with an increase in stromal area, but androgen receptors were preserved. Flutamide-treated tumor showed slow growth with androgen sensitivity when transplanted to intact rats, showing prolonged influences of antiandrogen on tumor growth. There was no significant difference between flutamide-treated and control groups in weight of accessory sex organs and serum androgen or estrogen levels. In conclusion, flutamide treatment may retard an appearance of prostatic cancer concomitant in benign prostatic hyperplasia. © 1994 Wiley-Liss, Inc.     

Murine monoclonal antibodies reactive with a variety of androgen independent Dunning rat prostate adenocarcinoma sublines also reactive with human prostate adenocarcinoma

Murine hybridoma-derived monoclonal antibody (MCA) to Dunning rat prostate adenocarcinoma R-3327HIS (androgen independent type) has been produced by fusing P3x63 Ag8-653 myeloma cells with splenocytes of BALB/c mice which were immunized with R-3327HIS tumor cell membranes. One monoclonal antibody designated MCA-R1 (IgG2a subtype) produced an intense immunostaining of various androgen independent Dunning rat prostate tumor sublines (HIS, HIM, HIF, AT-1, AT-2, AT-3, MAT-Lu and MAY-Ly-Lu), but did not stain other tumors of rat origin or normal rat tissues. Marginal immunostaining was detected in the androgen responsive R-3327H and R-3327G tumor subline. Although MCA-R1 antibody did not react with the regressed prostate tumor of R-3327H or R-3327G, it strongly reacted with the relapsed prostate tumor from either R-3327H or R-3327G tumor derived from rats were treated with diethyl stilbestrol (DES) or castration. MCA-R1 antibody also produced a strong cross-reaction with human prostate adenocarcinoma. Like the Dunning rat tumor, human adenocarcinoma exhibited distinct immunostaining patterns with respect to intracellular localization among well differentiated, moderately differentiated and poorly differentiated tumor. Benign prostatic hyperplasia or other normal tissues did not stain. Immunofluorescence, immunoprecipitation, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and radioautographic analysis revealed that the Dunning rat prostate tumor antigen recognized (m.wt. 50 and 120 Kd) by MCA-R1 antibody are localized on both cell surface and in the cytoplasm. This MCA may represent a potential reagent for the study of tumor biology and immunotherapy of prostate tumor.     

Response of rat and human prostatic cancers to the novel 5 alpha-reductase inhibitor, SK&F 105657.

The response of two androgen-responsive rat prostatic cancers (i.e., Dunning R-3327 H and G sublines) and one androgen-responsive human prostatic cancer (i.e., PC-82) to the 5 alpha-reductase inhibitor, SK&F 105657, was tested in vivo. SK&F 105657 was administered orally twice a day at a dose of 25 or 50 mg/kg/dose. The rat R-3327 G tumor and the human PC-82 tumor have a low to undetectable level of tissue 5 alpha-reductase activity and both responded to SK&F 105657 treatment with a reproducible inhibition of tumor growth. Associated with this antitumor effect was a major decrease (i.e., greater than 70%) in tissue dihydrotestosterone (DHT) content in both tumors. By contrast, the rat R-3327 H prostatic cancer has a much higher level of tissue 5 alpha-reductase activity, and neither tumor DHT content nor growth of the tumor was inhibited by treatment with SK&F 105657. Drug treatment of rats bearing R-3227 H tumors resulted in a similar reduction in the DHT content, wet weight, and DNA content of the ventral prostate as that produced in R-3327 G tumor-bearing rats which experienced an antitumor response. These results suggest that SK&F 105657 can produce antitumor effects if a substantial reduction in tissue DHT is achieved. Such reduction in tissue DHT, secondary to inhibition of the tissue 5 alpha-reductase enzyme, appears to be more difficult to achieve in tumors than in the normal prostate. In order to achieve such a DHT reduction in tumor tissue, prostatic cancers with low 5 alpha-reductase activity could be treated with SK&F 105657 on a dose regimen that lowers serum DHT to surgical castration levels, while concomitantly inhibiting the already low tumor tissue 5 alpha-reductase activity.     

Retinoic acid binding protein in normal and neoplastic rat prostate

Sucrose density gradient analysis of cytosol from normal and neoplastic rat prostatic tissues exhibited a peak of (³H) retinoic acid binding in the 2S region, corresponding to the cytoplasmic retinoic acid binding protein (cRABP). In the Fisher-Copenhagen FI rat, cRABP was present in the lateral lobe, but could not be detected in the ventral nor in the dorsal prostatic lobes. Four sublines of the R-3327 rat prostatic tumor contained similar levels of this binding protein. The absence of cRABP in the normal tissue of origin of the R-3327 tumor, the rat dorsal prostate, and reappearance in the neoplastic tissues follows a pattern described in other human and animal tumors. The occurrence of cRABP in the well-differentiated as well as in the anaplastic R-3327 tumors in which markers which reflect a state of differentiation and hormonal regulation, such as androgen receptor, 5a reductase, and secretory acid phosphatase are either markedly reduced or absent, points to cRABP as a marker of malignant transformation.     

The relationship of androgen receptor levels to androgen responsiveness in the Dunning R3327 rat prostate tumor sublines

The objective of this study was to determine whether androgen receptor levels in a transplantable animal model of prostatic adenocarcinoma correlated with androgen responsiveness of the tumor. This is the first comparative study of androgen receptor levels in 3 subcellular compartments (cytosol, nuclear salt-extractable and nuclear salt-resistant fractions) of 4 Dunning R3327 rat prostatic adenocarcinoma sublines that vary in their response to androgen ablation. Tumors were harvested from intact adult male rats in order to best approximate the human clinical setting in which receptor levels are quantitated prior to androgen ablative therapy. Only the nuclear salt-resistant (nuclear matrix) and total nuclear androgen receptor contents were significantly different among all tumor sublines. The properties of the tumors studied and their nuclear salt-resistant androgen receptor levels were as follows: H tumor--well-differentiated, slow growing, androgen-dependent, 63 +/- 11 fmol./mg. DNA; HI tumor--well-differentiated, slow growing, androgen-insensitive, 19 +/- 8 fmol./mg. DNA; G tumor--poorly-differentiated, fast growing, androgen-sensitive, 195 +/- 42 fmol./mg. DNA; and AT-2 tumor--anaplastic, fast growing, androgen-insensitive, no detectable receptors. There was no apparent quantitative relationship between androgen receptor content and tumor growth rates, which varied considerably irrespective of the androgen responsiveness of the tumor. However, there was a qualitative relationship between nuclear salt-resistant or total nuclear receptor content and androgen responsiveness. Higher levels of receptor (H and G tumor sublines) were associated with responsiveness to androgen ablation (cessation or slowing of growth, respectively), whereas lower levels of receptor (HI and AT-2 sublines) were associated with androgen insensitivity. These observations, based on relatively homogeneous tumors, may have important implications for human prostatic cancers which appear to be composed of heterogeneous cell populations.     

Enzyme activity and distribution in rat prostatic adenocarcinoma

The activity and distribution of acid phosphatase, alkaline phosphatase, nonspecific esterases, beta-glucuronidase, and aminopeptidase were examined in the transplantable R-3327 rat prostatic adenocarcinoma and compared with those in the four prostatic lobes of the rat. Both the well and poorly differentiated tumor cells in R-3327 carcinoma were characterized by high activities of beta-glucuronidase and aminopeptidase. The poorly differentiated cells had a high alkaline phosphatase activity. The enzymatic profile of the R-3327 adenocarcinoma closely resembled that of the anterior and dorsal prostate. The origin of the tumor in one of these prostatic lobes is probable, but not certain.     

Evidence for the association between blood prolactin and androgen receptors in BPH

The purpose of this study was to investigate the relationship between prostatic androgen receptors and plasma prolactin and testosterone in patients with benign prostatic hyperplasia. Cytosolic and KCl extractable nuclear androgen receptors were measured in 22 patients and these were in turn correlated to the hormone concentrations in blood specimens taken on the morning before the day of operation. The mean +/- S.E.M. concentrations of cytoplasmic androgen receptors, KCl extractable nuclear androgen receptors, plasma testosterone and plasma prolactin were respectively 115 +/- 18 fmoles/gm. tissue, 198 +/- 40 fmoles/gm. tissue, 15.6 +/- 1.2 nmol./l. and 128 +/- 17 mU/l. Plasma prolactin was highly correlated with cytosolic androgen receptors (r = 0.784, p less than 0.01; no. = 15) though not with nuclear androgen receptors (r = 0.453, p greater than 0.05; no. = 15). However, when the androgen receptor levels were expressed as fmoles/mg. protein both cytosolic and nuclear levels were proportional to plasma prolactin (p less than 0.01 and p less than 0.02 for both the cytosolic and nuclear receptors respectively; no. = 15). There was no correlation between either cytosolic and nuclear androgen receptors and plasma testosterone levels. The results suggest that plasma prolactin may be involved in the regulation of androgen receptor content in the benign prostate.     

1,2-Bis(2,6-dichloro-4-hydroxyphenyl)ethylenediamine] dichloro-platinum(II): an endocrine-active platinum complex with a specific prostatic tumor-inhibiting activity

[1,2-Bis(2,6-dichloro-4-hydroxyphenyl)ethylenediamine]dichloro-platinum (II), (C), a platinum complex with endocrine activity and a specific effect on hormone-dependent mammary tumors, was tested for its tumor-inhibitory activity in the hormone-sensitive R 3327 and Nb prostate carcinoma models of the rat and for its endocrine activities in comparison to the ligand L and diethylstilbestrol (DES). Established tumors of the R 3327 prostate tumor were strongly inhibited by C. Its effect equaled that of DES and was significantly better than that of L. Accessory sex organ weights and testosterone levels were strongly reduced by C as well as L. This antigonadotrophic effect, which is almost comparable to DES, was confirmed in 10 day experiments with intact, mature mice and rats, whereas a direct antiandrogenic activity was not given. A part of the antitumor action of C is therefore due to this antigonadotrophic activity. Affinities to estrogen, progesterone, and androgen receptors, however, were very low. The hormone-sensitive Noble Nb-R prostatic carcinoma was almost completely inhibited by C, whereas L had only a weak effect. As C has no significant effect on the hormone-independent R 3327 HI prostate tumor and as its effect on hormone-dependent tumors is significantly better than that of the ligand L in spite of their similar endocrine properties, an apparently specific antiproliferative effect of C only on hormone-dependent prostate tumors is obvious. This was further shown in a long-term experiment with the R 3327 prostate carcinoma. Whereas tumors in the castration group relapsed from androgen ablation and exerted a progressive tumor growth, therapy with C almost completely prevented this relapse phenomenon. After 25 weeks of treatment, C inhibited tumor growth by 90% compared to castration. Owing to these results, this new endocrine active platinum complex with an apparently specific effect on hormone-dependent prostate tumors can be of value for the therapy of the prostatic carcinoma.     

Expression of ras proto-oncogenes in the Dunning R3327 rat prostatic adenocarcinoma system

Steady-state levels of c-Ha-ras mRNA were measured in eight sublines of the Dunning R3327 rat prostatic adenocarcinoma. As a control, normal dorsal prostate tissue was studied. Increased expression of c-Ha-ras is associated with tumor progression in one lineage of the Dunning R3327 system (H to AT1 to MAT-Lu and MAT-Ly-Lu). Here ras mRNA increases as the tumor advances from androgen dependence and a high degree of differentiation to an anaplastic aneuploid phenotype with high metastatic potential. However, in the other Dunning lineage (H to HI to HI-F to AT3), expression of c-Ha-ras is variable and does not correlate with tumor progression. Immunocytochemistry showed that levels of the c-Ha-ras p21 protein paralleled steady-state mRNA levels in variants. Transfection assays, using NIH/3T3 cells, suggested that the ras loci were not activated in the R3327 tumors. Levels of c-Ki-ras mRNA were also measured in the Dunning tumors; these did not correlate with tumor progression in either lineage. Expression of N-ras mRNA was not detected in the Dunning tumors.     

Efficacy and advantages in the use of low doses of Anandron and estrogen combination in the treatment of prostate cancer

Treatment effects of RU 23908 antiandrogen (Anandron) and estrogen in low doses on hormone-dependent rat prostatic adenocarcinoma (R3327-H) were investigated. Tumor-bearing Copenhagen rats were treated for 6 weeks with 8 micrograms Anandron and 1 microgram estradiol-17 beta every two days. Reduction and counteraction of androgen synthesis and action was established by an observed decline in serum testosterone level and by changes in both histology and weight of androgen target organs. Prostate tumor growth rate was significantly retarded in rats treated with Anandron/Estradiol combination compared to untreated intact control and was equal to the slow growth rate in castrate tumor-bearing animals. Tumor histology changes during treatment correlated with the observed growth rate retardation. Areas of necrosis, metaplasia, and acellularity were more frequently observed in tumors of Anandron/Estradiol-treated compared to castrated rats. These results suggest that low doses of Anandron and estrogen can effectively be combined as a complete androgen counteracting therapy for hormone-dependent prostatic carcinoma with minimal undesired side effects.     

Decreased prostatic secretory function in canine benign prostatic hyperplasia is not due to decreased levels of muscarinic cholinergic receptors

The ejaculatory volume and the prostatic secretory capacity (ml. ejaculate per gm. prostate wet weight) were determined for a group of dogs with normal and hyperplastic prostates. The ejaculatory volume and prostatic secretory capacity in dogs with BPH were decreased by 70 per cent and 80 per cent respectively, compared to dogs with normal prostates. Radioligand receptor binding using [3H]N-methylscopolamine, a muscarinic cholinergic antagonist, was performed on a similar group of dogs with normal and hyperplastic prostates. The mean equilibrium dissociation constant for the binding of [3H]N-methylscopolamine to homogenates obtained from normal and hyperplastic prostates was 0.21 nM. and 0.19 nM. respectively, demonstrating that the affinity of the receptor binding sites was not altered by the development of BPH. The tissue density of the muscarinic cholinergic receptors (fmol. per mg. prostate wet weight) and the cellular density of these receptors (fmol. per mg. DNA) were not significantly different in normal and hyperplastic prostates. These data indicate that the dramatic reduction in prostatic secretory capacity associated with canine BPH is not related to changes in the muscarinic cholinergic receptor binding capacity.     

Inhibitory effects of estracyt on R-3327 rat prostatic carcinoma

Estracyt (estramustine phosphate) injected intraperitoneally, 100 mg. per Kg. three days a week for four weeks, retarded growth of the R-3327 tumor in intact rats and in orchiectomized rats given androgen. The growth inhibition was accomplished by reduction of tumor deoxyribonucleic acid concentration and of the activities of acid phosphatase, leucine aminopeptidase, and other hydrolases. Histologic examination revealed cellular necrosis particularly prominent in the orchiectomized, androgen-treated rats. Estracyt did not affect the uptake of ⁶⁵Zn in the tumors but markedly reduced the high uptake in the dorsolateral prostate. There was no accumulation of ³H or ¹⁴C in the tumors after intravenous administration of 3H, ¹⁴C-labeled Estracyt, but the isotope concentrations decreased much in the same way as they decreased in the dorsolateral prostate. The isotopes were retained in the ventral prostate, where their concentrations were approximately twenty times higher than those in the muscle four hours after injection. The results demonstrate the value of the R-3327 tumor in the evaluation of drugs of potential clinical use for the treatment of prostatic cancer. The results also show that Estracyt has an antitumor effect which is not dependent on the antigonadotropic action of the drug.     

Autoradiographic localization of estrogen and androgen target cells in human and rat prostate carcinoma

The distribution of estrogen target cells within the Dunning R3327-H rat prostate tumor following intravenous injection of tritiated estradiol into rat hosts was compared to the distribution obtained following incubation of a 2 mm. sample of the tumor with tritiated estradiol in organ culture. No difference was observed, indicating that the in vitro method was an effective approach for autoradiographic analysis of tumor biopsy samples. Subsequently, tumor samples were excised from solid tumors of R3327-H and R3327-MAT LyLu tumors growing in Copenhagen rats. These tumor models were chosen as representatives of hormone sensitive (R3327-H) and hormone insensitive (R3327-MAT LyLu) tumors. Normal rat dorsal prostate and human tumor biopsy samples were also studied. Autoradiographic studies were performed in vitro utilizing tritiated estradiol and tritiated dihydrotestosterone to compare the distribution of estrogen and androgen target cells. The present research demonstrated that 1) similar patterns of nuclear uptake of steroids are obtained with in vivo and in vitro autoradiographic techniques, 2) estradiol receptors occur primarily in extra-acinar epitheloid cells in both rat and human prostate carcinomas, 3) these epithelioid cells are not characteristic of the normal rat dorsal prostate, 4) androgen receptors occur in both acinar and stromal epithelioid cells in rat and primarily in acinar epithelial cells in human tumors and 5) in vitro autoradiographic methods can provide insight into differences in sensitivity to steroids which may be of diagnostic importance in the treatment of cancer.     

The timing of androgen ablation therapy and/or chemotherapy in the treatment of prostatic cancer

The effect of varying the timing of androgen ablation alone and in combination with chemotherapy on tumor growth rate and host survival has been studied using the serially transplantable Dunning R-3327 H rat prostatic adenocarcinoma as a model. These studies have demonstrated three basic points: 1) When either androgen ablation or Cytoxan chemotherapy are given as a single agent treatment, they are both most effective when given as early as possible; 2) when androgen ablation is combined with Cytoxan chemotherapy, it is most effective when both therapies are begun simultaneously and as early as possible; and 3) when androgen ablation and Cytoxan treatment are begun simultaneously and early, it is possible to increase survival above that found for either treatment when given optimally as single modalities (ie, such simultaneous early treatment enhances the individual therapeutic effectiveness of both treatments).     

Androgen signal transduction and prostatic carcinoma

Summary In the prostate, androgen action affects the growth of the gland, its morphology, and regulation of protein expression. Endocrine therapy of non-organ-confined tumors is based on the androgen dependence of the vast majority of prostatic carcinomas. Although initial response rates are high, this therapy is only temporarily effective. Critical molecular changes ultimately resulting in androgen independence of tumor cells are unknown at this time. The androgen signal-transduction cascade and its central element, the androgen receptor (AR), are possible targets for such changes. Immunohistological analysis using anti-AR antibodies has revealed the presence of AR in a vast majority of therapy-responsive as well as therapy-unresponsive prostatic carcinomas, indicating that loss of AR expression is not the reason for androgen independence. On the other hand, molecular-biology studies have revealed qualitative and quantitative impairment of AR expression in prostatic tumor cell lines that represent very late stages of prostatic carcinoma development. Mutant ARs were detected in the prostatic tumor cell line LNCaP and in two specimens from primary prostatic tumors. The LNCaP mutant AR as well as mutant AR715met, one of the mutant receptors detected in tumor tissue, show a gain of function as compared with the wild-type receptor. In addition to androgens, the natural activators of the AR, the LNCaP receptor is activated also by progestagenic and estrogenic steroids and by the nonsteroidal antiandrogen flutamide. AR715met is activated by adrenal androgens and progesterone in addition to androgens. Although determination of the frequency of point mutations in late prostatic carcinoma requires further investigation, these data imply that tumor progression in an androgen-ablated environment may be accompanied by aberrant AR activation.     

Androgen receptor binding characteristics in the cytosol of the rat dorsolateral prostate gland and the dunning R-3327 prostatic adenocarcinoma

The incidence of prostatic cancer is highly correlated with advanced age, and it has been suggested that changes in androgen binding may be important in age-associated alterations in growth regulatory mechanisms of prostatic epithelial cells. In this study the effects of age on androgen binding characteristics in the dorsolateral prostate glands of young and aged Copenhagen rats were determined and the binding properties in the Dunning R3327/130 subline of rat prostatic adenocarcinoma were characterized. Tritium-labeled and nonlabeled methyltrienolone analogs (R1881) were used to study the binding properties of 5α-dihydrotestosterone receptor in the cytosol of tumors and prostate glands. Binding of R1881 was low but specific for the androgen receptor as shown by competition studies in which nonlabeled R1881, 5α-dihydrostestosterone, and testosterone competed successfully with ³H-R1881 for binding sites, but 17β-estradiol and low levels of progesterone did not. In Copenhagen dorsolateral prostate, Scatchard analysis suggested a single class of binding sites. In young animals (three to five months) the average binding capacity was 10.36 fmol/mg cytosol protein with a dissociation constant (K_d) of 2.28 nmol/L. The dorsolateral prostate of aged rats (11–16 months) showed no significant difference in specific binding characteristics as compared to the younger age group. Specific binding of ³H-R1881 in R3327/130 tumor was saturable with a single class of high-affinity binding sites having an average binding capacity of 64.77 fmol/mg cytosol protein and a K_d of 2.76 nmol/L. These data show that the tumor had approximately 6.5 times the number of binding sites as did the normal Copenhagen rat dorsolateral prostate gland. However, no age-related changes were detected through 11–16 months of age in the androgen binding characteristics of normal rat dorsolateral prostate gland that could be correlated with the higher concentration of androgen binding sites in the R3327/130 tumor subline.     

Effect of adrenalectomy,flutamide, and leuprolide on the growth of the dunning rat R-3327 prostatic carcinoma

The R-3327 prostatic tumor implanted in the male Copenhagen x Fischer F₁ rat continues to grow because androgen is being supplied from an endogenous source. It follows that regimens which decrease the availability of androgen will retard the growth rate of the tumor. These experiments showed that castration, the antiandrogen flutamide, and the luteinizing hormone-releasing hormone (LHRH) agonist leuprolide inhibited tumor growth. Adrenalectomy alone had no significant effect on tumor size and did not further retard the growth of the tumor in castrated rats. Further, under the conditions of this study, there was no significant difference in tumor growth rates between the groups of rats treated with either flutamide alone or flutamide combined with leuprolide. Total ablation of androgen may not be needed for maximal inhibition of tumor growth.     

Differential effects of prolactin on rat dorsolateral prostate and R3327 prostatic tumor sublines

Many investigators have reported effects of the pituitary hormone, prolactin, on the physiology and biochemistry of the rat prostate gland, particularly the lateral or dorsolateral lobe. The Dunning R3327H is a transplantable rat prostatic adenocarcinoma derived from a spontaneous tumor of the Copenhagen rat dorsolateral prostate. This study describes and compares morphological and physiological effects of prolactin on rat dorsolateral prostate and two sublines of the Dunning tumor. Ectopic pituitary grafts were used to induce chronic hyperprolactinemia in castrated rats receiving androgen supplement to provide a relatively controlled hormonal environment in which the effects of prolactin were maximally and consistently observed. Gravimetric and biochemical analyses, as well as ultrastructural study, provided evidence of prolactin's stimulatory effect on dorsolateral prostate growth and secretory activity. Hyperprolactinemia stimulated the growth of the well-differentiated, androgen-dependent R3327/3219 tumor subline with an increase in weight, volume and the total content of DNA, protein and zinc. There were no changes in tumor morphology. In contrast, the anaplastic androgen-independent R3327/150 tumor subline did not respond to graft-induced hyperprolactinemia. This differential response of the two R3327 tumor sublines attests to the complexity of prolactin's effects on prostatic tissue and to the extent of the deterioration of endocrine control that often accompanies tumor progression. Prolactin binding in the R3327 sublines was studied using immunohistochemical staining and radioligand assay, but produced complex results which raise questions about the discrepancy between hormone binding and biological action of prolactin in prostatic tissues.     

Characterization of peripheral benzodiazepine receptors in rat prostatic adenocarcinoma

Using PK 11195, a high affinity ligand for peripheral benzodiazepine receptors (PBZr), binding sites in isolated mitochondrial (m-fraction) and microsomal fractions (p-fraction) from R-3327 Dunning AT-1 tumors, ventral and dorsolateral prostate were studied. Binding of PK 11195 in both m- and p-fractions from AT-1 tumors, but only in m-fraction from ventral and dorsolateral prostate, was specific, saturable, and of high affinity. The PBZr density in m-fraction from AT-1 tumors was 6-fold and 20-fold higher than that in ventral and dorsolateral prostate, respectively. The receptor density in p-fraction from AT-1 tumors was approximately 25% of that found in the m-fraction. Clear differences were observed in the competition by both diazepam and flunitrazepam for binding sites in m- and p-fractions from tumors. These data indicate that the receptors were not only localized to the mitochondria, but were also present in considerable amounts in the microsomal fractions. The unusually high amounts of receptors in the fast growing anaplastic prostatic tumor suggest their involvement in the regulation of cell proliferation and possibly in tumorigenesis. © 1994 Wiley-Liss, Inc.     

Effect of castration, DES, flutamide, and the 5 alpha-reductase inhibitor, MK-906, on the growth of the Dunning rat prostatic carcinoma, R-3327.

Male rats bearing implants of the Dunning rat prostatic carcinoma, R-3327, were used in a 42-day study to determine the effect of castration or orally administered flutamide (FL), DES (diethylstilbestrol) or the 5 alpha-reductase inhibitor, MK-906, on the growth of this androgen-responsive cancer. The rate of growth and final weights of the tumor and the ventral prostate (VP) were all reduced (P less than 0.05) by castration. Flutamide (25 mg/kg/day) significantly decreased tumor and VP weights in intact rats and castrates given 100 micrograms/day (SC) of testosterone propionate (TP) or dihydrotestosterone propionate (DHTP). It also significantly retarded tumor growth rate in TP- or DHTP-treated castrates and was marginally effective in intact animals. DES (100 micrograms/kg/day) reduced (P less than 0.05) tumor and VP weights of intact rats but did not significantly affect tumor growth rate or weight in castrates given TP or DHTP. These results indicated that the effect of DES on tumor growth is caused by its inhibition of the secretion or release of the gonadotropins necessary for testicular androgen production. MK-906 (25 mg/kg/day) affected neither the gross nor the histomorphology of the tumor in intact rats or castrates given TP or DHTP. Further, it caused no histological changes in the testes of intact rats. It did, however, significantly reduce VP weight in intact animals and TP-treated castrates but not in those given DHTP. This illustrates that the anti-androgenicity of MK-906 stems from its inhibition of DHT formation. The failure of MK-906 to influence tumor growth in the TP-treated castrates strongly suggests that the R-3327 tumor can respond to testosterone directly. If that is true, then its growth is unlikely to be affected by a pure 5 alpha-reductase inhibitor such as MK-906. In ancillary experiments, tumors from MK-906-treated animals were found to have reduced levels of DHT and, when assayed in vitro, to have a reduced capacity to convert [3H]-T to [3H]-DHT.