Prostate Tumor Model Research Articles

Epidermal growth factor receptor content in rat prostatic adenocarcinoma: effects of endocrine treatment.

Epidermal growth factor receptor (EGF-R) was studied in Dunning prostatic cancer models using competitive binding assays and solution hybridization assay. EGF-R-binding capacity and mRNA were demonstrated in a hormone-sensitive R3327 prostatic tumor from both control and castrated animals while no such activity was found in the hormone-independent AT-1 tumors. Castration induced no quantitative changes in the EGF-R. Estrogen treatment induced a significant reduction of the binding capacity of EGF-R and its mRNA. It was concluded that EGF-R is present in the androgen-sensitive Dunning prostatic tumor models (R3327), but that the androgen-insensitive, undifferentiated AT-1 tumor lacks EGF-R expression. Endocrine treatment has no significant effect on the EGF-R in these tumor models.

Phase I?II study of the somatostatin analogue lanreotide in hormone-refractory prostate cancer

Lanreotide (BIM 32014), a somatulin analogue, was found to be as effective as castration in a rat prostate tumor model. Therapeutic benefit was also demonstrated in the hormone-resistant phase of this tumor model. The activity of lanreotide may be due to a reduction in the levels of growth factors such as insulin growth factor 1 (IGF1). A total of 30 patients with hormone-refractory prostate cancer were treated with a slow-release formulation of lanreotide. The mean age was 71 years. Patients were treated with one intramuscular injection of 30 mg BIM 23014 once a week and were followed for prostate-specific antigen (PSA) level evolution until disease progression or WHO grade 3 or 4 toxicity and for survival. The patients were treated for a mean duration of 12 weeks (range, 2-60 weeks). The performance status and bone pain were improved in 40% and 35% of patients respectively. In all, 20% of the patients had a decrease of > or = 50% in PSA levels and 16% showed a stabilization. The biological response was correlated with clinical improvement. The 1-year global survival rate was 72%, with the rate being 89% in the group of patients who were responders on PSA plasma level and 64% in patients with progressive disease. The response duration ranged from 16 to 60 weeks. Toxicity was minor, with transient grade I digestive side effects being noted in a few patients. Lanreotide given at 30 mg once a week to patients with metastatic hormone-refractory prostate cancer was well tolerated. The response rate was higher than that reported in recent published series. Higher doses of lanreotide should be evaluated.

Evaluation of the antitumour activity of coumarin in prostate cancer models.

Responses to coumarin have been reported for patients suffering from malignant melanoma, metastatic renal carcinoma and, recently, advanced prostate cancer. These data together with some experimental evidence for antiprostatic effect prompted us to study the activity of coumarin in various prostate tumour models and evaluate the endocrine properties of this drug. In rats no antiandrogenic activity was found. The growth of Noble Nb-R prostate tumours of the rat was strongly inhibited by coumarin (40 mg/kg; administered three times per week), whereas the hormonally more sensitive Dunning R3327-G rat prostate carcinoma did not respond to coumarin (40 mg) even when the drug was administered daily. Coumarin was also shown to possess antimetastatic activity in a Dunning R3327-MatLu tumour model. In this model small pieces of the hormone-independent tumour were implanted into the ear of the animal and later resected to mimic the clinical situation where primary tumours have been removed. The number of lung metastases was reduced significantly by 40%-50% following the administration of coumarin (40 mg daily).

Heat shock protein response in a prostate tumor model to interstitial thermotherapy: Implications for clinical treatment

Hyperthermia is being utilized individually and in conjunction with other therapies in treating malignant and benign tumors, though few studies have examined cellular effects of elevated temperatures in the prostate model. Highly conserved proteins of the 70 kDa heat shock protein family (HSP 70) are produced in response to environmental stresses, including heat, and are found in all organisms. HSPs are an indicator of cell damage, are associated with thermotolerance, and provide cells with transient resistance to subsequent thermal challenges. Transient thermotolerance is important in the determination of temperature, duration, and sequencing for treatments. This preliminary study analyzes the HSP 70 response of the Dunning R3327 adenocarcinoma model to a single 50 degrees C 1 hr treatment. Elevated HSP levels were found between 10 and 16 hr, returning to baseline by 24 hr. As some fractions of the cells are able to produce HSP 70 following treatment, the data suggest that currently utilized clinical temperatures (42-46 degrees C) administered for 1 hr are inadequate. HSP levels in response to hyperthermia, radiation, and chemotherapy may be useful in finding optimal treatment regimens for prostate cancer.

Ki‐67 expression and BrdUrd incorporation as markers of proliferative activity in human prostate tumour models

The validity of the use of the monoclonal antibodies Ki-67 and anti-BrdUrd to evaluate proliferative activity of human prostate tumour models was studied. Growth of the transplantable PC-82 and PC-EW prostate tumours, as assessed by tumour volume measurements, was significantly correlated with the proliferative activity as reflected by BrdUrd incorporation into DNA (r = 0.64 and r = 0.78, respectively). The proliferative activity of PC-82 tumours detected by Ki-67 antigen expression paralleled the pattern observed with BrdUrd (r = 0.51) and a significant correlation (r = 0.60) between the results obtained with both markers was found. In growing PC-82 and PC-EW tumours only small variations in the Ki-67 and BrdUrd indices were observed. In contrast, Ki-67 expression in regressing PC-82 tumours varied considerably (2.7 +/- 2.2%). The BrdUrd index in regressing PC-82 tumours showed less variation (1.3 +/- 0.2%), but part of the BrdUrd-positive cells were found in the stromal (murine) part of the regressing tissue. It is concluded that the Ki-67 and BrdUrd proliferation markers are reliable parameters to monitor changes in growth of prostate tumour lines, but that in slow growing or regressing tumours Ki-67 and BrdUrd data should be interpreted with caution.

The Effect of Interstitial Hyperthermia on the Dunning Prostate Tumor Model

The effect of hyperthermia was examined on the Dunning prostate tumor model in rats. Hyperthermia was created by heating self-regulating interstitial seeds with an external oscillating magnetic field. The seed alloy was comprised of 70% nickel and 30% copper. One treatment with 50C seeds for two hours did not provide significant delay in tumor growth compared to controls. However, regimens with two treatments separated by either 48hours or one week did cause significant delay (p = 0.0013 and p = 0.0096, respectively). These results suggest that an interstitial hyperthermia seed may provide an efficacious outpatient therapy for prostate cancer. Further, interstitial hyperthermia may be readily combined with existing radiotherapy with interstitial gold coated seeds to provide additive or synergistic anti-tumor effects.

Effects of adrenal androgens on the transplantable human prostate tumor PC-82.

The potential of the adrenal androgens androstenedione (A) and dehydroepiandrosterone (DHEA) to stimulate prostate tumor growth was investigated in the hormone-dependent human prostate tumor model PC-82, propagated in nude mice. Substitution of castrated mice bearing growth-arrested tumors with DHEA for 28 days, resulting in peripheral levels of 9.2 +/- 1.7 nmol/liter (mean +/- SEM), led to a decline of tumor burden comparable to that observed in castrated controls. Intratumor testosterone (T) and 5 alpha-dihydrotestosterone were similar to those detected in the castrated group. In contrast, high-dose A supplementation (peripheral level of 13.5 +/- 1.3 nmol/liter) in androgen ablated tumor-bearing mice resulted in tumor growth, although less pronounced than in T-resubstituted mice (T level of 18.8 +/- 1.5 nmol/l). Intraprostatic levels of androgens were not different between both groups. Substitution of castrated PC-82 tumor-bearing mice with low-dose A (2.5 +/- 0.4 nmol/l) neither stimulated growth of tumors nor did it lead to regression of PC-82 tumors. Proliferative activity as estimated by BrdU incorporation (S-phase cells) was not induced in these tumors. In conclusion, DHEA does not have a stimulatory effect on growth of PC-82 tumor tissue, but A is capable of inducing PC-82 tumor growth, most likely through peripheral conversion of A into T and 5 alpha-dihydrotestosterone.

The biological significance of low testosterone levels and of adrenal androgens in transplantable prostate cancer lines

The transplantable androgen-dependent human prostate tumor models PC-82 and PC-EW were used to study whether low levels of testosterone and androgens of adrenal origin were capable of stimulating the growth of prostatic carcinoma cells in these tumor models. At all circulating plasma testosterone levels applied in this study, much lower levels of dihydrotestosterone were found in PC-EW tumor tissue than in PC-82 tumor tissue. Nevertheless, both prostate tumor models had a similar threshold level of dihydrotestosterone for growth stimulation, i.e. 3-4 pmol/g tissue. This critical androgen level for tumor growth amounted to 2-3 times the tissue level found in castrated animals. At this threshold level approximately 2% of the cells showed proliferative activity, as assessed by bromodeoxyuridine incorporation into DNA. The adrenal androgen dehydroepiandrosterone did not stimulate PC-82 tumor growth, whereas androstenedione did induce a moderate increase in tumor volume. It is concluded that the adrenal androgen androstenedione exerts a stimulating effect on prostatic cancer cells when its conversion results in intra-tissue testosterone and dihydrotestosterone levels exceeding the threshold level for tumor growth.

Effects of low testosterone levels and of adrenal androgens on growth of prostate tumor models in nude mice

Two transplantable, androgen dependent prostate tumor models of human origin, PC-82 and PC-EW, were used to study the effect of low androgen levels and adrenal androgens on prostate tumor cell proliferation. Tumor load of the PC-82 and PC-EW tumors could be maintained constant when plasma testosterone levels were 0.8 and 0.9 nmol/l, respectively, corresponding with an intratissue 5α-dihydrotestosterone level of 3–4 pmol/g tissue. This critical androgen level for prostate tumor growth stimulation amounted to 2–3 times the castration level and proved to be similar for both tumor models. Relatively high levels of androstenedione resulted in physiological levels of plasma testosterone causing androgen concentrations in PC-82 tumor tissue exceeding the critical level for tumor growth. These results indicate that submaximal suppression of androgens can stop tumor growth in these prostate tumor models.

Androgen-primed chemotherapy—Experimental confirmation of efficacy

A current hypothesis suggests that androgen administration prior to chemotherapy (androgen priming) may potentiate tumor cytotoxicity in prostate cancer. The Dunning R3327G rat prostatic tumor model was used to test this concept experimentally. Control groups without priming included (1) intact untreated, (2) castrate alone and (3) castrate + chemotherapy (cyclophosphamide, 30 mg/kg/day for 2 days with repeat cycle in 25 days—CTX). Two experimental groups received androgens, one before and one after chemotherapy. Treatment effect was monitored by quantitating tumor volume and animal survival. Control groups receiving castration and chemotherapy had a retardation of tumor growth and a prolongation of survival when compared to untreated animals. Androgen priming before but not after chemotherapy enhanced the degree of tumor suppression. With the androgen-priming protocol, all androgen-primed tumors had regressed, 3 6 tumors had disappeared and 3 were only palpable. At the same time point, tumors in all the other groups were actively growing and had volumes greater than the initial values ( P < 0.01). Median survival was significantly prolonged in primed animals 191 vs 40 days for untreated animals and 150 days for the nonprimed castration + chemotherapy animals ( P < 0.02). These findings have been repeated with several replicate experiments. These observations confirm the hypothesis that androgen priming can potentiate chemotherapy in an experimental system.

Prostatic acid phosphatase in the serially transplantable human prostatic tumor lines PC-82 and PC-EW

The correlation between tumor volume of untreated tumor-bearing nude mice and serum concentration of prostatic acid phosphatase (PAP/RIA) was studied in the hormone-dependent serially transplantable human prostatic tumor models PC-82 and PC-EW. The normal serum level of PAP in control male nude mice without tumor was found to be 0.9 +/- 0.3 ng/ml. Elevated PAP serum concentrations were never found in animals without tumor (a highly specific diagnostic technique). A close correlation was observed between the concentration of PAP in the serum (range 0.3 to 154 ng/ml) and the tumor volume (range 10.0 to 6,530 mm3) of 104 untreated mice bearing a PC-82 or PC-EW human prostatic tumor. This correlation was comparable in both tumor lines (p less than 0.001). The positive effect of endocrine manipulation which resulted in tumor diameter decrease or growth arrest with regressive histological patterns, showed the normal PAP serum level, too. After successful treatment PAP was found to be normal, independent from the residual tumor mass. By contrast, in the event of only retarded tumor growth, the PAP level still correlated with the tumor burden.

Prediction of Metastatic Potential in an Animal Model of Prostate Cancer: Flow Cytometric Quantification of Cell Surface Charge

The natural history of clinically localized prostate cancer in individual patients is difficult to predict using currently available techniques. The majority of these patients will undergo treatment without knowledge of whether the tumor would have progressed during their lifetime. Because morepatients are being diagnosed yearly with early stage prostate cancers it is becoming increasingly important to delineate factors that will clarify which patients have tumors with invasive potential. Using the Dunning R-3327 rat prostate animal tumor model we have previously shown that an increase in cell surface charge, as measured by individual cell electrophoresis, is associated with an increase in metastatic ability. This electrophoretic technique is limited by the small number of cells that can be analzyed during each assay. Therefore, we adapted a flow cytometric method for measurement of cell surface change, utilizing a large molecule (cationized ferritin) that bindsquantitatively to the negative charges at the cell surface. With a fluorescent tag attached to the ferritin molecule, flow cytometric quantification of surface charge was possible, and this method was successful in identifying tumors with high metastatic ability in the Dunning prostate tumor model. (J. Urol., 142: 1338–1341, 1989)

Transplantable human prostatic carcinoma (PC-82) in athymic nude mice. III. Effects of estrogens on the growth of the tumor tissue.

The transplantable human prostatic tumor model (PC-82) in nude mice was used to evaluate the indirect and possibly direct effects of estrogens on the growth of prostatic tumor tissue. High (pharmalogical) doses of plasma estradiol (E2) were achieved in tumor-bearing mice by using E2-containing Silastic implants of different lengths. In comparison with the situation in men, in mice much higher concentrations of circulating E2 (exceeding 3 nmol/liter) were necessary to attain (near)-castrate levels of plasma testosterone (T). Treatment of tumor-bearing mice with a high dose of E2 resulted in tumor growth arrest and a subsequent decline of the tumor volume, which equals the effects of castration. No evidence was found that either of the two doses of E2 applied had any additive inhibitory effect on tumor growth when compared to castration alone. It was inferred from these findings that in the PC-82 tumor model, estrogens, rather than having a direct effect on the tumor tissue, mainly act indirectly by their suppressive effect on T secretion in the host animal. A different and unexpected result was obtained in castrated tumor-bearing mice treated with a combination of E2 and T. With both doses of E2 this type of treatment led to a smaller increase of the tumor volume compared with mice receiving T only, the result of the high dose being statistically significant. This antagonistic effect of the two steroids on the PC-82 tissue was paradoxically associated with a sharp increase of nuclear androgen receptor levels and a higher concentration of dihydrotestosterone in the tumor tissue. Plasma and tissue concentrations of T appeared to be unaltered. The present study of the PC-82 prostate tumor shows that only by careful monitoring of plasma steroid levels in tumor-bearing mice can conclusions about the effectiveness of hormonal treatment regimens, such as estrogen therapy, be drawn.

The effects of polyamine antimetabolites on polyamine-responsive case in kinase activity

The effects of two inhibitors of ornithine decarboxylase activity, ∝-difluoromethylornithine (DMFO) and (2R,5R) 6-heptyne-2,5 diamine (HDA), and an inhibitor of S-adenosylmethionine decarboxylase, methylglyoxal bis-guanylhydrazone (MGBG), were tested on casein kinase activity and endogenous phosphorylation in the cytosol fractions of mouse thyroid and a rat prostate tumor model, Dunning R 3327 MAT LyLu subline. When tested at 5 mM, spermine, DMFO, HDA, and MGBG stimulated mouse thyroid casein kinase activity by 230%, 14%, 65% and 106%, respectively. Similar responses were observed in prostate tumor cytosol. In mouse thyroid cytosol, spermine stimulates 32p incorporation primarily into 3 proteins (MW: 107, 88, and 56 kDa). At 5 mM, MGBG partially reproduces the effects of spermine; HDA is less effective and DMFO is without effect. Similar effects were observed on 3 proteins in prostate tumor cytosol with molecular weights of 91, 41, and 32 kDa. These data provide additional support for the hypothesis that the observed synergistic inhibitory effect of DMFO and MGBG on cell growth may not be due solely to the inhibition of polyamine blosynthesis. Our findings suggest that MGBG-mediated reduction in the phosphorylation of casein kinase substrate should be considered as one locus of action.

In vitro growth inhibition of Dunning rat prostate tumor by bone marrow factor.

Normal Copenhagen rat bone marrow was assayed for growth inhibition of cultured MAT LyLu rat prostate tumor cells. A marrow-derived factor was identified that had significant growth inhibitory activity in vitro against MAT LyLu as well as against DU-145 human prostate tumor and MBT-2 mouse bladder tumor cells but that was noninhibitory to normal rat fibroblasts. The factor was stable to degradation by acid, heat, freezing, trypsin, and carboxypeptidase B. The factor was nonreactive with Coomassie blue, and the molecular weight was estimated as less than 620 daltons. A similar factor was identified in normal human and normal rat sera. The presence of this factor in bone marrow may explain the absence of osseous metastases in the Dunning rat prostate tumor model.

Synthesis and biological activity of highly potent octapeptide analogs of somatostatin.

In the search for selective and long-acting analogs of somatostatin, nearly 200 compounds were synthesized by solid-phase methods, purified, and tested biologically. Among these octapeptides, some contained N-terminal (Formula: see text) were 177 times and 113 times more potent, respectively, than somatostatin in tests for inhibition of growth hormone release. These two octapeptides containing tyrosine and valine in positions 3 and 6, respectively, were more active and more selective than their Phe-3 and Thr-6 counterparts, D-Phe-Cys-Phe-D-Trp-Lys-Thr-Cys-Thr-NH2 and D-Phe-Cys-Phe-D-Trp-Lys-Thr-Cys-Trp-NH2. D-Phe-Cys-Tyr-D-Trp-Lys-Val-Cys-Thr-NH2 was also about 6 times more potent than its L-Trp-4 diastereoisomer. The analogs D-Phe-Cys-Tyr-Lys-Val-Cys-Thr-NH2 and D-Phe-Cys-Tyr-D-Trp-Lys-Val-Cys-Trp-NH2 showed a prolonged duration of action and were able to inhibit growth hormone release for at least 3 hr. Analogs of both Phe-3/Thr-6 and Tyr-3/Val-6 classes also suppressed the release of insulin and glucagon in rats and pentagastrin-induced secretion of gastric acid in dogs, but their potencies in these tests were much smaller than the growth-hormone-release inhibitory activity. Some of these analogs possessed antitumor activities as shown by the inhibition of growth of animal models of prostate, mammary, and ductal pancreatic tumors.

Methylglyoxal-bis(guanylhydrazone) in hormone-resistant adenocarcinoma of the prostate.

Methylglyoxal-bis(guanylhydrazone) (MGBG), an inhibitor of polyamine synthesis, was administered to 35 patients with hormone-resistant advanced adenocarcinoma of the prostate in doses of 500 or 600 mg/m2 per week intravenously. Of 31 patients with bidimensional measurable soft-tissue lesions, 25 had an adequate trial, defined as four or more doses. Six (24%; 95% confidence limits, 8% to 32%) patients achieved a partial remission (greater than or equal to 50% reduction in tumor size) in soft-tissue disease. Response was noted to start after one to two doses and persisted for a median of three months (range, 1 to 4 months). Toxicity was tolerable, and significant myelosuppression was not observed. The lack of response in osseous metastases may be secondary to the short duration of remission or to the presence or inducibility of the enzyme ornithine decarboxylase in bone. Since some animal prostatic cancer tumor models are sensitive to cytotoxic drugs that produce polyamine inhibition, clinical trials of MGBG combined with other inhibitors of the polyamine pathway should be explored.

Misonidazole as a Chemosensitizer in the Treatment of the Dunning Prostate Cancer Model

Utilizing a Dunning prostate tumor model, we investigated the ability of misonidazole, a compound with known radio sensitizing properties, to act as a chemosensitizer when administered in combination with the alkylating agent cyclophosphamide. This combination caused a decrease in tumor growth rate when compared to the growth of the tumor in animals receiving cyclophosphamide alone. However, only at toxic levels was this decrease statistically significant (p > 0.01).

Interstitial applications of laser irradiation in hematoporphyrin derivative-photosensitized Dunning R3327 prostate cancers.

Two prostate tumour models (Dunning R3327H and AT) were tested in rats to see if they were sensitive to hematoporphyrin-photoradiation therapy (HPD-PRT). The R3327H tumours were irradiated by implantation of a single fiber optic and the R3327 AT tumours were treated with implantation of four fiber optics simultaneously. Thermal measurements made at the tip of the fiber and up to 1 cm from the tip indicated temperature rises from 1.5 degree C to 20 degrees C at the tip and 0 degree to 8 degrees C distal to the tip, with power densities ranging from 100 mW to 500 mW. The R3327H tumour was controlled up to 8 weeks post-HPD-PRT, when the initial tumour size was 400-500 mm3. The R3327 AT tumours also respond to the HPD-PRT but a significant laser-induced thermal rise in the tumour is suspected.

Flow cytometry in prostatic adenocarcinoma

We have examined the reproducibility of DNA histograms produced by flow cytometry in two strains of the Dunning R3327 rat prostatic tumor model, determining the extent of variability between tumors in the same animal, from animal to animal within the same strain and from strain to strain. We have also investigated the ability of flow cytometry to monitor changes in DNA histograms produced by tumor age and hormonal manipulation. We have found that there is a considerable difference in aneuploidy in tumors from the two strains, and also much variability in its extent within each strain. While orchiectomy (ORCH) tended to decrease the extent of aneuploidy, this could only be reliably detected if each tumor acted as its own control, with sampling being done pre- and post-ORCH.