Biomedical subjects

G Halmos

Publications and source records attributed to G Halmos.

97 records · Page 6Linked to original sources

PubMed1993

Inhibition of growth of experimental prostate cancer in rats by LH-RH analogs linked to cytotoxic radicals.

The effects of hybrid cytotoxic LH-RH analogs, produced by linking anthraquinone or methotrexate to carrier LH-RH agonist [D-Lys6]LH-RH, were evaluated in Copenhagen-Fisher F1 rats bearing Dunning R-3327H prostate adenocarcinoma. The two cytotoxic LH-RH analogs T-98 [(D-Lys6)LH-RH coupled to glutaryl-2-(hydroxymethyl)anthraquinone (G-HMAQ)], and AJ-04 [(D-Lys6)LH-RH linked to methotrexate (MTX)], carrier [D-Lys6]LH-RH, or the free cytotoxic compounds MTX and G-HMAQ were administered from Alzet Osmotic minipumps for 7-8 weeks. The cytotoxic LH-RH analogs caused somewhat greater tumor growth inhibition than the carrier peptide, while anthraquinone or methotrexate alone, administered in equimolar doses, were ineffective. The inhibition of androgen sensitive organs (testes, ventral prostates, and seminal vesicles) was pronounced with both carrier and cytotoxic analogs, showing the latter to be fully hormonally active in suppressing the pituitary-gonadal axis. Histological changes were also evaluated. The inhibition of mitosis and the frequency of apoptosis were higher in tumors treated with AJ-04, T-98, [D-Lys6]LH-RH, or by castration than in those of controls. Serum hormone levels were lowered by both carrier peptide and cytotoxic analogs, LH being substantially depressed, and testosterone not detectable. These results and other findings indicate that LH-RH analogs containing cytotoxic radicals anthraquinone or methotrexate retain their hormonal activity after administration in vivo, and can effectively inhibit tumor growth. Extensive further studies are required on this new class of compounds, but apparent binding of cytotoxic LH-RH analogs to tumors such as prostate cancer, which have receptors for LH-RH, could greatly reduce peripheral toxicity of chemotherapeutic agents. This approach, based on targeted chemotherapy, might be of practical therapeutic importance for the management of advanced prostate cancers, which eventually relapse after palliative hormonal therapy.

Adenocarcinoma↗

PubMed1993

Inhibition of growth of the human malignant glioma cell line (U87MG) by the steroid hormone antagonist RU486.

Treatment of nude mice bearing xenografts of the human malignant glioma U87MG cell line with the steroid hormone antagonist RU486 for 4 weeks resulted in a significant and dose-dependent suppression of tumor volume and weight. Receptor analyses of tumor cytosol preparations demonstrated a single class of high affinity binding sites for dexamethasone, but the absence of receptors for progesterone. RU486 also nullified the stimulatory effect of dexamethasone on proliferation of U87MG cells in vitro. These results indicate that the growth of U87MG human malignant glioma is dependent on corticoids. The antiproliferative effect of RU486 appears to be due to the inhibition of binding of glucocorticoid hormones to their receptor proteins. Our results suggest a new therapy for some brain tumors, such as malignant gliomas based on the steroid hormone antagonist RU486.

Animals↗

PubMed1993

Use of radioreceptor assay and cell superfusion system for in vitro screening of analogs of growth hormone-releasing hormone.

In the search for more active agonists and antagonists of human growth hormone-releasing hormone (hGH-RH), various analogs are being synthesized. In order to follow the binding affinity of these analogs, we have developed a sensitive in vitro radioreceptor assay for GH-RH based on binding of labeled [His1,Nle27]hGH-RH(1-32)NH2 to rat anterior pituitary membrane homogenates by adapting and modifying earlier methods. Scatchard analysis of saturation binding data demonstrated the presence of a single class of specific binding sites for GH-RH in membranes of rat anterior pituitaries with a Bmax of 33.3 +/- 5.2 fmol/mg protein and an apparent Kd of 0.19 +/- 0.02 nM. In displacement analyses, we compared the binding affinity of [His1,Nle27]hGH-RH(1-32)NH2 with its iodinated derivative. No significant differences were detected in IC50 concentrations ranging from 0.97 to 3.4 nM between labeled and nonlabeled hGH-RH analogs. These findings demonstrate the validity of the radioreceptor assay. To evaluate the biological activities of hGH-RH derivatives, we applied a sensitive, dispersed rat pituitary cell superfusion system. This dynamic in vitro system eliminates the drawbacks of the static pituitary cell culture. No differences were observed in biological activities of the iodinated and noniodinated hGH-RH analogs. GH-releasing activity obtained from the superfusion assay correlated well with GH-RH receptor binding affinity for all nonlabeled and labeled hGH-RH analogs examined. These two methods are fast, simple, and relatively inexpensive, and provide quantitative data on receptor affinities, biological activities, and hence structure-affinity and structure-activity relationships. Joint use of these two in vitro systems appears to be suitable for screening newly synthesized GH-RH analogs.

Animals↗

PubMed1992

Growth inhibition of estrogen-dependent and estrogen-independent MXT mammary cancers in mice by the bombesin and gastrin-releasing peptide antagonist RC-3095.

BACKGROUND: Many breast cancers are estrogen independent, and even in patients who initially respond to estrogen suppression therapy, the regression is often temporary. We have recently shown that antagonists of bombesin and gastrin-releasing peptide, including RC-3095, inhibit the growth of pancreatic, colonic, and prostatic cancers in experimental animals. This effect was associated with a substantial decrease in epidermal growth factor (EGF) receptor levels in pancreatic and colon cancers. PURPOSE: In view of these findings, we investigated the effects of our synthetic bombesin and gastrin-releasing peptide receptor antagonist D-Tpi6,Leu13 psi (CH2NH)-Leu14 bombesin(6-14) (RC-3095) on the growth of hormone-dependent and hormone-independent MXT mouse mammary cancers in vivo. METHODS: Female (C57BL x DBA/2)F1 mice bearing estrogen-dependent or estrogen-independent MXT mammary carcinomas were treated with small doses (20 micrograms/d) of RC-3095 administered from osmotic minipumps. Separate groups of mice with estrogen-independent tumors received RC-3095, bombesin, or gastrin-releasing peptide(14-27) at 20 micrograms/d. We determined tumor volume and weight, mitotic index, apoptosis (programmed cell death), and argyrophilic nucleolar organizer regions, an indicator of tumor cell proliferation. Levels of receptors for EGF and bombesin were measured in tumor membrane fractions. RESULTS: Growth of both estrogen-dependent and estrogen-independent MXT breast cancers was significantly inhibited by RC-3095. Bombesin or gastrin-releasing peptide had no effect on the growth of estrogen-independent tumors. Inhibition of tumor cell proliferation was indicated by a 45%-65% reduction in tumor volume, a 35%-58% reduction in tumor weight, and statistically significant decreases in argyrophilic nucleolar organizer region counts after treatment with RC-3095. In estrogen-independent cancers, tumor inhibition was associated with a decrease in the capacity of EGF receptors from 0.21 +/- 0.016 pmol/mg membrane protein in controls to 0.03 +/- 0.003 pmol/mg membrane protein in the RC-3095-treated group. CONCLUSIONS: This is the first demonstration of inhibitory effects of bombesin and gastrin-releasing peptide antagonists on the growth of breast cancers in vivo. IMPLICATIONS: These findings suggest that bombesin antagonists should be considered for breast cancer therapy.

Animals↗

PubMed1992

Short-chain analogs of luteinizing hormone-releasing hormone containing cytotoxic moieties.

Five hexapeptide and heptapeptide analogs of luteinizing hormone-releasing hormone (LH-RH) were synthesized for use as carriers for cytotoxic compounds. These short analogs were expected to enhance target selectivity of the antineoplastic agents linked to them. Native LH-RH-(3-9) and LH-RH-(4-9) containing D-lysine and D-ornithine at position 6 were amidated with ethylamine and acylated on the N terminus. The receptor-binding affinity of one hexapeptide carrier AJ-41 (Ac-Ser-Tyr-D-Lys-Leu-Arg-Pro-NH-Et) to human breast cancer cell membranes was similar to that of [D-Trp6]LH-RH. Alkylating nitrogen mustards (melphalan, Ac-melphalan), anthraquinone derivatives including anticancer antibiotic doxorubicin, antimetabolite (methotrexate), and cisplatin-like platinum complex were linked to these peptides through their omega-amino group at position 6. The hybrid molecules showed no LH-RH agonistic activity in vitro and in vivo but had nontypical antagonistic effects on pituitary cells in vitro at the doses tested. These analogs showed a wide range of receptor-binding affinities to rat pituitaries and cell membranes of human breast cancer and rat Dunning prostate cancer. Several of these conjugates exerted some cytotoxic effects on MCF-7 breast cancer cell line.

Amino Acid Sequence↗

PubMedDate not supplied

Combination treatment of nitrosamine-induced pancreatic cancers in hamsters with analogs of LH-RH and a bombesin/GRP antagonist.

Analogs of luteinizing hormone-releasing hormone (LH-RH) and bombesin/gastrin-releasing peptide were previously shown to inhibit the growth of experimental pancreatic cancers. In the present study, in an attempt to increase the efficacy of therapy, female Syrian golden hamsters with N-nitrosobis(2-oxopropyl)amine-induced pancreatic cancers were treated for 2 mo with a combination of LH-RH agonist [D-Trp6]LH-RH or antagonist [Ac-D-Nal(2)1, D-Phe(4Cl)2, D-Pal(3)3, D-Cit6-Ala10]LH-RH (SB-75) and bombesin/GRP antagonist D-Tpi6, Leu13 psi(CH2NH)Leu14bombesin(6-14) (RC-3095). The results were compared to those obtained by treatment with same doses of single peptides. LH-RH analogs and bombesin antagonist given alone significantly reduced the number of tumorous animals and decreased weight of pancreata by 46-71% and weight of tumorous pancreas by 38-64%. Histology showed lower mitotic activity and a decreased number of AgNORs in tumor cells from treated animals. Enhanced apoptosis was also observed after treatment with the LH-RH analogs. Combination therapy had no superior inhibitory effect on tumors compared to single peptides, by practically all the parameters analyzed. The reasons for this lack of potentiation are not clear. The tumor inhibitory effect of bombesin antagonists appears to be mediated by interference with EGF-receptor mechanisms. In the present study, although a significant downregulation of EGF-receptors was found in tumors treated with combination, the decrease in binding capacity for EGF was maximal in the group treated with RC-3095 alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMedDate not supplied

Growth inhibition of experimental pancreatic cancers and sustained reduction in epidermal growth factor receptors during therapy with hormonal peptide analogs.

Reduction in receptors for epidermal growth factor (EGF) in cancers appears to be one of the principal mechanisms through which peptide hormone analogs can inhibit tumor growth. In this study, hamsters with nitrosamine-induced pancreatic cancers were treated for 8 weeks with bombesin/gastrin-releasing peptide (GRP) antagonist RC-3095, somatostatin analog RC-160 or the luteinizing hormone-releasing hormone antagonist Cetrorelix, using sustained delivery systems releasing 20, 35 and 20 microg analog/ day respectively. To establish the pattern of changes in the number and affinity of EGF receptors on tumors, groups of animals were sacrificed at regular intervals during therapy. Chronic treatment with RC-3095 or Cetrorelix resulted in an early (day 10) and sustained reduction (71% or 69% respectively) in EGF receptors on pancreatic tumors. In contrast, RC-160 decreased receptor concentration by 60% only after 20 days. Among the histological characteristics of proliferation, the decrease in argyrophilic nucleolar organizer regions, but not apoptotic and mitotic indices, showed a correlation with the fall in EGF receptors. The concentration of the receptors returned to the control level 4 days after cessation of chronic treatment with RC-3095. The effect of single injections of RC-3095, RC-160 and Cetrorelix on EGF receptors was also investigated. RC-160 decreased the number of EGF receptors on pancreatic cancers by 31% 3 h after administration, but the receptors had returned to normal level at 6 h. RC-3095 and Cetrorelix caused a 67% and 59% decline, respectively, in EGF receptors only 6 h after injection and the concentration of receptors remained low for 24 h. Thus, the pattern of downregulation of EGF receptors in pancreatic cancers appears to depend on the peptide used for therapy. Since the antitumor effect may be the result of the fall in EGF receptors in cancers, information on the time course of changes in these receptors during treatment with these analogs may lead to an improvement in therapeutic regimens.

Animals↗