Secretion of epidermal growth factor and related polypeptides by the DU 145 human prostate cancer cell line

Epidermal growth factor: receptor binding and effects on the sex accessory organs of sexually mature male mice

The role of epidermal growth factor (EGF) in maintaining the integrity of the male sex accessory glands was investigated in the mouse. In the sexually mature male C3H mouse, EGF levels were highest in the submandibular gland, followed by the seminal vesicles and the prostate. Twenty eight days after sialoadenectomy (Sx), EGF fell below detectable limits in the serum and in the seminal vesicles. However, the prostate still retained 22% of its immunoreactive EGF. There was a seven-fold increase in serum testosterone after sialoadenectomy. Despite this drastic rise in testosterone, both prostatic and seminal vesicular weights were reduced, serum levels of LH were suppressed only by 37% and FSH levels were not altered. All these changes were abolished by the simultaneous administration of exogenous EGF at 100 micrograms./kg./day for 28 days. Both prostatic and seminal vesicular membranes contained binding sites for 125I-EGF. Binding was maximal after one hour of incubation at room temperature. Two classes of binding sites were shown for either organ (Kd = 1.2 nM, n = 56 fmol/mg. and Kd = 74 nM, n = 540 fmol/mg. for prostate; Kd = 0.9 nM, n = 29 fmol/mg. and Kd = 93 nM, n = 150 fmol/mg. for seminal vesicle). The binding of 125I-EGF was displaced by excess EGF and TGF-alpha but not by insulin, ILGF-2 and PDGF. These data suggest that EGF may have an important role in maintaining the integrity of the seminal vesicle and the prostate in the mouse. While the seminal vesicle appears to acquire EGF by uptake from the environment, the prostate may have the ability to synthesize EGF locally.

Therapeutic response to somatostatin analogue, BIM 23014, in metastatic prostatic cancer

Metastatic prostate cancer is well known to respond to hormonal manipulations, but once progression occurs new treatment modalities are required. Specific and systemic antitumour therapy is preferable to local treatments such as radiotherapy in such patients. The finding that somatostatin analogue, BIM 23014, inhibits prostatic tumour growth in animal models is of great interest. We treated 25 poor risk patients with progressive metastatic prostate cancer. Sixteen had also failed to respond to 'total androgen blockade'. Two patients have achieved a partial remission, one of which is maintained at over 30 months, and three had stable disease for over 6 months. Side effects have consisted of mild diarrhoea and abdominal cramp in the first few days of treatment in a minority of the patients. These results are encouraging and further randomized studies are in progress.

Divergent responses to epidermal growth factor in hormone sensitive and insensitive human prostate cancer cell lines

The present study was undertaken to compare the relationship between response to exogenous epidermal growth factor (EGF) and the expression of the EGF-receptor (EGF-R) in an androgen sensitive (LNCaP) and insensitive (DU145) prostate cancer cell line. Although both cell lines demonstrated a single EGF-R binding site of similar high affinities (mean dissociation constant (Kd) +/- S.D. for DU145 = 1.0 +/- 0.6 nmol l-1; LNCaP = 2.8 +/- 2.2 nmol l-1) the number of binding sites (RT) for the hormone insensitive DU145 cells (mean +/- S.D. = 2.5 +/- 1.0 x 10(5) sites/cell) and 10-fold greater than that expressed in the androgen responsive LNCaP cell line (mean +/- S.D. = 2.0 +/- 1 x 10(4) sites/cell). Additionally exogenous EGF only minimally affected the growth and DNA synthesis of DU145 cells whereas LNCaP cells showed a significant response which was dose dependent. The autologous production of EGF-like molecules by DU145 cells is believed to reduce the cells needs for exogenous mitogens, thereby rendering the cells autostimulatory. Treatment of LNCaP cells with Mibolerone--a synthetic androgen--did not affect either the expression of the EGF receptor or the proliferative response observed with EGF. Western blot analysis, using monoclonal antibodies directed against the EGF receptor revealed a band of approximately 170 kD with DU145 cell lysates but the LNCaP EGF receptor was not detected using this technique.

Interactions between epidermal growth factor-mediated autocrine regulation and linoleic acid-stimulated growth of a human prostate cancer cell line

Human prostate cancer (PC) cell lines possess epidermal growth factor (EGF) receptors and secrete EGF-related polypeptides. We used an EGF receptor-blocking antibody (anti-EGF.R) to demonstrate a functional autocrine loop, as well as the interaction between this and the effects of linoleic acid (LA), an omega-6 fatty acid, on PC cell growth. The anti-EGF.R competed effectively with [125I]EGF for receptors on DU145 PC cells, and on a high-passage DU145 variant (DU145M); when added to the culture medium, it suppressed both DU145 and DU145M cell growth in a dose-dependent manner. LA, a precursor for eicosanoid synthesis, had little effect on DU145 cell growth rate but stimulated DU145M growth in a concentration-related manner over a range of 0.25-2.0 micrograms/ml. anti-EGF.R (10(-9) M) caused suppression of LA-stimulated growth of DU145M cells in serum-free medium, which was prevented by the addition of 2 nM EGF. We conclude that an EGF.R-mediated autocrine loop is involved in PC cell growth regulation and that at least one site of action may be the synthesis of eicosanoids from their LA precursor.

Inhibition of growth of PC-82 human prostate cancer line xenografts in nude mice by bombesin antagonist RC-3095 or combination of agonist [D-Trp6]-luteinizing hormone-releasing hormone and somatostatin analog RC-160

The effects of treatment with a bombesin receptor antagonist [D-Tpi6, Leu13 psi (CH2NH) Leu14]BN(6-14)(RC-3095) and the combination of an agonist of luteinizing hormone-releasing hormone [D-Trp6]-LH-RH and somatostatin analog D-Phe-Cys-Tyr-D-Trp-Lys-Val- Cys-Trp-NH2 (RC-160) were studied in nude mice bearing xenografts of the hormone-dependent human prostate tumor PC-82. During the 5 weeks of treatment, tumor growth was decreased in all treated groups compared with controls. Bombesin antagonist RC-3095 and the combination of [D-Trp6]-LH-RH and RC-160 caused a greater inhibition of tumor growth than [D-Trp6]-LH-RH or RC-160 alone as based on measurement of tumor volume and percentage change in tumor volume. The largest decrease in tumor weight was also seen in the groups treated with the bombesin antagonist and with the combination of RC-160 and [D-Trp6]-LH-RH. Serum prostatic-specific antigen levels were greatly decreased, and insulin-like growth factor I (IGF-I) as well as growth hormone levels were reduced in all treated groups. Specific binding sites for [D-Trp6]-LH-RH, epidermal growth factor (EGF), IGF-I, and somatostatin (SS-14) were found in the tumor membranes. Receptors for EGF were significantly down-regulated by treatment with the bombesin antagonist or RC-160. Combination of LH-RH agonists with somatostatin analog RC-160 might be considered for improvement of hormonal therapy for prostate cancer. The finding that bombesin antagonist RC-3095 inhibits the growth of PC-82 prostate cancer suggests the merit of further studies to evaluate the possible usefulness of antagonists of bombesin in the management of prostatic carcinoma.

Endogenous secretion of epidermal growth factor peptides stimulates growth of DU145 prostate cancer cells

The growth rate of DU145 prostate cancer cells in vitro is slowed considerably by changing the growth medium every 24 h, suggesting dependence upon endogenously-secreted growth factors. Because previous studies have identified epidermal growth factor (EGF) in the conditioned medium from DU145 cells, [35S]labeled EGF was selectively immunoprecipitated from the culture medium at 24-h intervals for quantitation. Under the culture conditions used, there was an initial phase of slow growth, the EGF level secreted per cell was highest on day 3 after plating, and an increase in cell number was most evident between days 3 and 4. Finally, growth was assayed under culture conditions where the medium was replaced every 24 h with fresh medium in the absence or presence of 10 ng/ml added EGF. The EGF was able to increase the cell growth up to the levels seen in cultures where the medium was unchanged during the entire period. We interpret these results as evidence that endogenously secreted EGF-like growth factors participate in an autocrine growth stimulation of DU145 cells.

Benign prostatic hyperplasia--video image analysis and its relationship to androgen and epidermal growth factor receptor expression

Androgens are essential for the development and maintenance of the prostate. However, prostatic growth may be mediated by epidermal growth factor (EGF) and the expression of the EGF receptor (EGFR) may be influenced by the androgenic milieu. We have characterized the expression of cytosolic androgen receptor (ARc), nuclear salt extractable androgen receptor (ARn) and EGFR in 89 consecutive cases of benign prostatic hyperplasia, 84 of which were treated by transurethral prostatic resections. Image analysis morphometry was performed on the histological sections to determine the epithelial content of the gland. Our results indicate that there is a vast heterogeneity of receptor expression in benign prostatic hyperplasia. Expression of ARc ranged from zero to 1312 fmol/gm. tissue (mean +/- SD 265 +/- 290), ARn ranged from zero to 531 fmol/gm. tissue (mean +/- SD 145 +/- 98) and EGFR ranged from zero to 316 fmol/gm. tissue (mean +/- SD 121 +/- 76). A statistically significant association was found between expression of ARn and EGFR, and these were both significantly correlated with the epithelial content of the gland.

Inhibition of prostatic tumor cell proliferation by suramin: alterations in TGF alpha-mediated autocrine growth regulation and cell cycle distribution

Suramin is a trypanocidal drug that has generated recent interest as an antineoplastic agent because of its ability to inhibit the binding of growth factors to their cell surface receptors. Our studies, and others, suggest that the androgen-independent human prostatic carcinoma cell lines PC3 and DU145 proliferate via autocrine growth mechanisms mediated by transforming growth factor alpha (TGFa) and its receptor, the epidermal growth factor (EGF) receptor. The present studies were designed to evaluate the ability of suramin to inhibit PC3 and DU145 proliferation by interfering with TGFa-mediated autocrine growth. Suramin induced a dose-dependent reduction of prostatic tumor cell proliferation which was reversed by removal of suramin from the culture medium. 3H-thymidine release studies showed that suramin had little direct cytotoxicity to either cell line. These findings suggest that the effects of suramin are mediated by cytostatic, rather than cytotoxic, mechanisms. Suramin also interfered with TGFa-mediated growth mechanisms. Specifically, suramin reduced the specific binding of TGFa to PC3 and DU145 cells. Additionally, the inhibitory effect of suramin on DU145 was reversed by cultivation of cells in the presence of excess TGFa. Further investigations revealed that suramin increased the percentage of cells in the S phase of the cell cycle for both cell lines. These studies show that the inhibitory effect of suramin on PC3 and DU145 cell growth is mediated, in part, by alteration of TGFa-mediated autocrine growth mechanisms and cell cycle kinetics.

Autocrine regulation of DU145 human prostate cancer cell growth by epidermal growth factor-related polypeptides

The DU145 human prostate cancer cell line possesses epidermal growth factor (EGF) receptors and synthesizes both EGF and the related polypeptide transforming growth factor-alpha (TGF-alpha). A monoclonal antibody to the EGF receptor was used to determine whether these characteristics were indicative of a functional autocrine regulatory system. This antibody competed effectively with [125I]EGF for binding to DU145 cell binding sites over a 1 x 10(-11) to 1 x 10(-7) M concentration range, and did so with a capability similar to that of the two natural ligands. It inhibited growth of these cells in both 3% fetal bovine serum-supplemented and serum-free medium; in experiments with incubation times of 3-5 days there was a 45-50% reduction in cell number. Growth suppression by the EGF receptor blockade of cells plated at a density of 1.5 x 10(4) cells/ml/well was reversed competitively by the addition of EGF to the medium; 0.3 nM completely eliminated the inhibitory effect of a 1 x 10(-9) M antibody concentration. It is concluded that DU145 cell growth is regulated by an EGF-mediated autocrine loop.

Effects of fatty acids and eicosanoid synthesis inhibitors on the growth of two human prostate cancer cell lines

Dietary fatty acids (FAs) may be involved in the carcinogenic process within the prostate gland and progression to clinically manifest disease. We have shown that growth of the androgen-unresponsive PC-3 human prostate cancer cell line is stimulated in vitro by the presence of linoleic acid (LA), an omega-6 polyunsaturated FA. The response was positively related to the FA concentration over the entire range examined (5-750 ng/ml). Conversely, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), two omega-3 FAs present in fish oils, inhibited PC-3 cell growth in a dose-dependent manner; both were equally effective, with an approximately 65% reduction in growth occurring at a concentration of 2.0 micrograms/ml (P less than 0.001). The DU 145 human prostate cancer cell line, which is also androgen-unresponsive, showed no growth response to LA and was less susceptible to growth inhibition when cultured in the presence of omega-3 FAs. Growth experiments with indomethacin, esculetin, and piroxicam, pharmacological inhibitors of eicosanoid biosynthesis with differing sites of action, indicated that human prostate cancer cell growth requires intact metabolic pathways for both leukotriene and prostaglandin production.

Density-dependent regulation of epidermal growth factor receptor expression in DU 145 human prostate cancer cells

Androgen-independent prostate cancer cells may rely on an autocrine loop for growth stimulation, and have been shown to express both the epidermal growth factor receptor (EGFR) and its stimulatory ligands. We have shown here that DU 145 prostate cancer cells have a decreased amount of EGFR in confluent cultures when compared to levels seen in subconfluent cultures. This down-regulation of EGFR numbers is not due to cell proliferation or nutrient depletion, but can be correlated only with whether cell-cell contact exists throughout the culture. This is reminiscent of the situation existing in some tumors whereby EGFR expression is higher in cells at the invading margins of the tumor.

Production and response of a human prostatic cancer line to transforming growth factor-like molecules

Serum-free media conditioned by the androgen insensitive human prostate cancer cell line DU145 showed immunological transforming growth factor-alpha (TGF alpha) activity, as well as competing activity in epidermal growth factor (EGF) radioreceptor assays (RRA). Furthermore, there were factors in the conditioned media which inhibited and stimulated DNA synthesis by DU145 cells in a dose-dependent fashion. Fractionation of the concentrated conditioned media by reverse-phase high performance liquid chromatography revealed several peaks containing EGF-like competitive activity only one of which demonstrated TGF alpha activity. However, none of the peaks corresponded to immunoreactive EGF. Measurement of EGF receptors on DU145 cells by competition and saturation analysis revealed high levels of receptors (mean +/- s.d. = 2.5 +/- 1 x 10(5) surface receptors per cell) which were of high affinity (Kd +/- s.d. = 1.0 +/- 0.5 nmol l-1). Although DU145 cells express high levels of EGF receptors, DNA synthesis was only minimally affected by exogenous EGF and TGF alpha.

Production of epidermal growth factor and transforming growth factor-alpha by the androgen-responsive LNCaP human prostate cancer cell line

Epidermal growth factor (EGF)-related polypeptides may be involved in the growth of human prostate cancer cells, and in the androgen stimulation of hormone-responsive prostatic carcinomas. We have shown that androgen-responsive LNCaP cells, like the autonomous DU 145 human prostate cancer cell line, synthesize and secrete EGF and related polypeptides, including immunoreactive transforming growth factor-alpha (TGF-alpha). As determined by radioimmunoassay, intracellular EGF levels were approximately 100 times those of TGF-alpha, but together these accounted for less than half of the total EGF-like polypeptides detected in a radioreceptor assay. Although LNCaP cell growth was stimulated by dihydrotestosterone (DHT), there was no evident effect on immunoreactive EGF levels in the medium after correction for cell number. Moreover, metabolic labeling experiments showed no effect of the androgen on EGF synthesis by LNCaP cells. Gel filtration chromatography of conditioned medium showed both high molecular weight species and the mature 6,000 dalton form of immunoreactive EGF. We conclude that although LNCaP prostate cancer cell growth is stimulated by DHT, it is unlikely that it is mediated directly via increased EGF synthesis by the tumor cells.