Biomedical subjects

G Halmos

Publications and source records attributed to G Halmos.

At least 37 records · Page 2Linked to original sources

PubMed2000

The presence of receptors for bombesin/GRP and mRNA for three receptor subtypes in human ovarian epithelial cancers.

Bombesin-like peptides can function as autocrine or paracrine growth factors and stimulate the growth of various cancers. The antagonists of bombesin/gastrin-releasing peptide (GRP) suppress the proliferation of diverse tumors including ovarian cancer by mechanisms likely mediated by bombesin receptors. In this study, we used the reverse transcription-polymerase chain reaction (RT-PCR) method to evaluate the mRNA expression of three bombesin receptor subtypes: gastrin-releasing peptide receptor (GRPR), neuromedin B receptor (NMBR), and bombesin receptor subtype 3 (BRS-3), in 22 specimens of human epithelial ovarian cancer and in two human ovarian cancer lines. Of the 22 ovarian cancer specimens analyzed, 17 tumors ( approximately 77%) expressed mRNA for GRPR, 19 ( approximately 86%) showed NMBR mRNA and six ( approximately 27%) revealed BRS-3 mRNA. Thus, 14 of 22 specimens ( approximately 64%) expressed mRNAs for both GRPR and NMBR, and five ( approximately 23%) expressed all three subtypes. The expression of GRPR appeared to be greater in poorly differentiated ovarian carcinomas. A higher incidence of BRS-3 expression was observed in samples with tumor Stage IV (4/4, 100%) compared with Stage III (1/17, approximately 6%). mRNA for both GRPR and NMBR was also detected in OV-1063 and UCI-107 human ovarian cancer xenografts, but BRS-3 was found only in OV-1063, which originated from a metastatic tumor. In addition, functional receptors for bombesin/GRP were found in eight of 11 ovarian cancer specimens investigated and in both ovarian cancer lines by receptor binding assay. Our study indicates that GRPR and NMBR are widely distributed in human ovarian carcinomas with BRS-3 being found in Stage IV tumors. Some approaches based on bombesin/GRP receptor antagonists or targeted bombesin analogs could be considered for treatment of ovarian cancers.

Aged↗

PubMed2000

Inhibition of metastatic renal cell carcinomas expressing somatostatin receptors by a targeted cytotoxic analogue of somatostatin AN-238.

The effectiveness of chemotherapy targeted to somatostatin (SST) receptors based on cytotoxic SST analogue AN-238, consisting of 2-pyrrolinodoxorubicin (AN-201) linked to SST carrier octapeptide, was investigated in human renal cell carcinomas (RCCs). SST receptors, which showed high-affinity binding for AN-238, were found in the SW-839 RCC line with sst2A subtype and in the 786-0 RCC line, which expressed the sst5 subtype. CAKI-1 RCC, which does not express sst2A or sst5, was used as a negative control for testing the specificity of SST receptor targeting. Using microsatellite analysis, AN-238 was shown to selectively inhibit the proliferation of 786-0 line, but not the CAKI-1 RCC line in vitro. The effects of three i.v. injections of 150 nmol/kg of AN-238 or AN-201, given on days 1, 8, and 21, were evaluated in groups of nude mice bearing s.c. xenografts of SW-839 and 786-0 RCC. After 5 weeks, the volumes of SW-839 and 786-0 RCC tumors were decreased by 67.2 (P < 0.05) and 78.3% (P < 0.01), respectively, whereas AN-201 had no significant effect on tumor growth. The inhibition of SST receptor-negative CAKI-1 tumors by AN-238 was only marginal. To investigate the efficacy of SST receptor-targeted chemotherapy in metastatic RCC, three i.v. injections of AN-238 or AN-201 at 150 nmol/kg were given at biweekly intervals to nude mice implanted with 786-0 tumors under the renal capsule. After 6 weeks, the weight of orthotopic tumors treated with AN-238 (55.3 +/- 44.3 mg) was significantly lower (87% reduction; P < 0.001) than that in the control group (414.2 +/- 41.0 mg) or in animals given AN-201 (270.2 +/- 603 mg; P < 0.05). Five of six animals (83%), both in the control and the AN-201 group, developed metastases to lymph nodes, but only one of seven mice (14%) given AN-238 showed lymphatic spread. Lung metastases were found in 83% of controls and 50% of AN-201 treated animals, but none occurred in mice treated with AN-238. This study demonstrates that targeted cytotoxic SST analogue AN-238 provides an effective therapy for chemoresistant neoplasms such as RCC. Because most clinical RCCs express SST receptors, this treatment modality might be beneficial to patients with metastatic disease.

Animals↗

PubMed2000

Inhibition of growth of MDA-MB-468 estrogen-independent human breast carcinoma by bombesin/gastrin-releasing peptide antagonists RC-3095 and RC-3940-II.

BACKGROUND: The growth of breast carcinoma is promoted by autocrine growth factors such as the bombesin (BN)-like peptides and epidermal growth factor (EGF). The stimulatory action of BN-like peptides can be blocked by the use of BN/gastrin-releasing peptide (GRP) antagonists. METHODS: The authors investigated the effects of synthetic BN/GRP antagonists RC-3095 and RC-3940-II on tumor growth and the expression of mRNA for EGF receptors and three BN receptor subtypes in MDA-MB-468 human breast carcinoma. Athymic nude mice with xenografts of MDA-MB-468 human breast carcinoma were injected subcutaneously for 6 weeks with RC-3940-II at doses of 20 or 40 microg/day. In another study, the effects of RC-3940-II and RC-3095 were compared. RESULTS: RC-3940-II caused a significant and dose-dependent growth inhibition of MDA-MB-468 tumors in nude mice; therapy with either dose of RC-3940-II significantly (P<0.01) reduced the mean final tumor volume and weight compared with controls. RC-3940-II induced a persistent regression of > 50% of all tumors. One of 3 tumors treated with 20 microg of RC-3940-II and 3 of 5 tumors treated with 40 microg were found to have regressed completely by the end of the study. When RC-3940-II and RC-3095 were compared at the dose of 20 microg/day, both powerfully suppressed growth of MDA-MB-468 tumors, with RC-3940-II causing a complete regression of 2 tumors and RC-3095 a complete regression of 1 tumor. Receptor analyses of untreated MDA-MB-468 tumors revealed an overexpression of EGF receptors and two classes of binding sites for BN/GRP. mRNAs for receptors of GRP, neuromedin B, and BN receptor subtype-3 were detected by reverse transcriptase-polymerase chain reaction. CONCLUSIONS: A virtual arrest of growth or regression of MDA-MB-468 human breast carcinoma after therapy with RC-3940-II and RC-3095 indicates that these BN/GRP antagonists could provide a new treatment modality for breast tumors expressing BN and EGF receptors.

Animals↗

PubMed2000

Presence of receptors for bombesin/gastrin-releasing peptide and mRNA for three receptor subtypes in human prostate cancers.

BACKGROUND: Bombesin-like peptides can function as autocrine or paracrine growth factors and stimulate the growth of some cancer cells, including human prostate cancer. Three bombesin receptor subtypes, termed gastrin-releasing peptide receptor (GRPR), neuromedin B receptor (NMBR), and bombesin receptor subtype 3 (BRS-3), have been identified in rodents and humans. METHODS: We investigated the presence and characteristics of the functional receptors for bombesin/GRP in human prostate adenocarcinoma specimens by radio-receptor assay and the mRNA expression of the three bombesin receptor subtypes by RT-PCR. RESULTS: Of the 80 specimens of primary prostate cancer examined by receptor binding assays, 50 ( approximately 63%) showed high-affinity, low-capacity binding sites for bombesin/GRP, and 12 of these 50 receptor-positive specimens also showed a second binding site. Of the 22 prostate cancer specimens analyzed by RT-PCR, 20 (91%) expressed GRPR mRNA, 3 (14%) showed NMBR mRNA, and 2 ( approximately 9%) revealed BRS-3 mRNA. No correlation was observed between receptor expression and patients' age or pathological data. CONCLUSIONS: The detection of a wide distribution of bombesin/GRP receptors in human prostate carcinomas supports the view that they may be involved in modulation of tumor progression and suggests that approaches based on binding of bombesin receptor antagonists or new targeted cytotoxic bombesin analogs to prostate cancers could be considered for the therapy.

Adenocarcinoma↗

PubMed2000

Antagonistic actions of analogs related to growth hormone-releasing hormone (GHRH) on receptors for GHRH and vasoactive intestinal peptide on rat pituitary and pineal cells in vitro.

Peptide analogs of growth hormone-releasing hormone (GHRH) can potentially interact with vasoactive intestinal peptide (VIP) receptors (VPAC(1)-R and VPAC(2)-R) because of the structural similarities of these two hormones and their receptors. We synthesized four new analogs related to GHRH (JV-1-50, JV-1-51, JV-1-52, and JV-1-53) with decreased GHRH antagonistic activity and increased VIP antagonistic potency. To characterize various peptide analogs for their antagonistic activity on receptors for GHRH and VIP, we developed assay systems based on superfusion of rat pituitary and pineal cells. Receptor-binding affinities of peptides to the membranes of these cells were also evaluated by radioligand competition assays. Previously reported GHRH antagonists JV-1-36, JV-1-38, and JV-1-42 proved to be selective for GHRH receptors, because they did not influence VIP-stimulated VPAC(2) receptor-dependent prolactin release from pituitary cells or VPAC(1) receptor-dependent cAMP efflux from pinealocytes but strongly inhibited GHRH-stimulated growth hormone (GH) release. Analogs JV-1-50, JV-1-51, and JV-1-52 showed various degrees of VPAC(1)-R and VPAC(2)-R antagonistic potency, although also preserving a substantial GHRH antagonistic effect. Analog JV-1-53 proved to be a highly potent VPAC(1) and VPAC(2) receptor antagonist, devoid of inhibitory effects on GHRH-evoked GH release. The antagonistic activity of these peptide analogs on processes mediated by receptors for GHRH and VIP was consistent with the binding affinity. The analogs with antagonistic effects on different types of receptors expressed on tumor cells could be utilized for the development of new approaches to treatment of various human cancers.

Amino Acid Sequence↗

PubMed2000

Veratridine-evoked release of dopamine from guinea pig isolated cochlea.

Dopamine released from the lateral olivocochlear efferent system is thought to inhibit the toxic effect of the extreme glutamate outflow from the inner hair cells during ischemia or acoustic trauma. Using in vitro microvolume superfusion, we have studied the release of [(3)H]dopamine from the lateral olivocochlear efferent bundle of guinea pig in response to accumulation of [Na(+)](i), under condition characteristics of ischemia. Veratridine, that acts only on excitable membranes as a specific activator of voltage-sensitive sodium channels, significantly increased the electrically evoked release of [(3)H]dopamine, which was completely inhibited by tetrodotoxin. Dizocilpine (MK-801), a non-competitive NMDA-receptor antagonist, and GYKI-52466, a selective non-NMDA-receptor antagonist, had no effect on veratridine-induced [(3)H]dopamine release. Our data provide further evidence that the cochlear release of dopamine is of neural origin and possibly independent on a local effect of glutamate. The veratridine-induced transmitter release in the cochlea will be a very useful method in studying the effect of drugs on ischemic injury.

Animals↗

PubMed2000

Antagonists of growth hormone-releasing hormone (GH-RH) inhibit in vivo proliferation of experimental pancreatic cancers and decrease IGF-II levels in tumours.

Insulin-like growth factors (IGF-I and IGF-II) are implicated in the pathogenesis of pancreatic carcinoma. Antagonists of growth hormone-releasing hormone (GH-RH) suppress the GH-RH-GH-IGF-I axis and also act directly on tumours to reduce production of IGF-I or II. The aim of this study was to investigate the effects of two potent GH-RH antagonists in two experimental models of pancreatic cancer. Syrian golden hamsters with nitrosamine-induced pancreatic tumours were treated with 10 micrograms/day of GH-RH antagonist MZ-4-71 for 60 days. The therapy reduced the number of tumorous animals, decreased the weight of tumorous pancreata by 55%, and lowered AgNOR numbers in tumour cells. In two other experiments, GH-RH antagonists MZ-4-71 and MZ-5-156 significantly inhibited growth of SW-1990 human pancreatic cancers xenografted into nude mice, as shown by a reduction in tumour volume and tumour weights, and a decrease in AgNORs in cancer cells. IGF-I levels in serum and in pancreatic cancer tissue remained unchanged after therapy, suggesting that an effect on IGF-I is not involved in tumour inhibition. In contrast, IGF-II concentrations in tumours were significantly reduced by 50-60% after treatment with the GH-RH antagonists as compared with controls. In vitro studies showed that the concentration of IGF-II in the culture medium was increased after seeding of SW-1990 cells, indicating that this pancreatic cancer cell line produced and released IGF-II. This finding was also supported by the expression of IGF-II mRNA in the SW-1990 cells. Addition of 3 x 10(-6) M of GH-RH antagonist MZ-5-156 to the reduced-serum medium decreased cell proliferation, IGF-II mRNA expression in the cells and IGF-II concentration in the medium. Our findings indicate that inhibitory effects of GH-RH antagonists on the growth of experimental pancreatic cancers, may result from a decrease in the production and concentration of IGF-II in the tumours.

Animals↗

PubMed2000

Administration of a targeted cytotoxic analog of luteinizing hormone-releasing hormone inhibits growth of estrogen-independent MDA-MB-231 human breast cancers in nude mice.

Receptor targeted chemotherapy is less toxic and more effective than conventional chemotherapy. Receptors for luteinizing hormone-releasing hormone (LH-RH) are found in about 50% of human breast cancers. Highly potent cytotoxic radical 2-pyrrolinodoxorubicin (AN-201) was linked to the agonistic analog [D-Lys6]LH-RH to form cytotoxic LH-RH analog AN-207. We evaluated whether AN-207 could be targeted to the hormone-independent MDA-MB-231 human breast cancers. Nude mice bearing MDA-MB-231 tumors were injected i.v. with 250 nmol/kg doses of cytotoxic radical AN-201, cytotoxic LH-RH analog AN-207, the unconjugated mixture of AN-201 and carrier [D-Lys6]LH-RH, [D-Lys6]LH-RH alone and vehicle (control). The growth of MDA-MB-231 tumors in animals given a single dose of AN-207 was inhibited significantly (p = 0.01) for 3 weeks after injection, whereas tumors in all the other groups grew steadily. All cytotoxic compounds produced leukopenia, but the strongest lymphocyte suppression was caused by cytotoxic radical AN-201. Three weeks after treatment, the presence of mRNA for LH-RH receptors was demonstrated by RT-PCR in all the groups and radioreceptor assays demonstrated high-affinity binding sites for LH-RH on tumor cell membranes of control animals and those treated with AN-201, the carrier peptide alone or in combination with AN-201. At this time point binding assays did not reveal the expression of membrane proteins in tumors treated with AN-207, but 60 days after administration of AN-207, high affinity LH-RH binding sites were found again in MDA-MB-231 tumors. These results indicate that cytotoxic LH-RH analog AN-207 could be utilized for receptor targeted chemotherapy of breast cancers expressing receptors for LH-RH.

Animals↗

PubMed2000

Antagonists of growth hormone-releasing hormone arrest the growth of MDA-MB-468 estrogen-independent human breast cancers in nude mice.

Since antagonists of growth hormone-releasing hormone (GH-RH) inhibit proliferation of various tumors, in this study we investigated the effects of GH-RH antagonists MZ-5-156 or JV-1-36 on growth of estrogen-independent MDA-MB-468 human breast cancers xenografted into nude mice. Both GH-RH antagonists administered at a dose of 20 microg/day induced regression of some and growth-arrest of other tumors, while control tumors continued to grow. After 5 weeks of therapy with MZ-5-156 or JV-1-36, final volume and weight of MDA-MB-468 tumors were significantly decreased (all p values < 0.001) and serum IGF-I levels as well as tumor IGF-I mRNA expression were reduced as compared with controls. High affinity binding sites for IGF-I were detected by the ligand binding method. Gene expression of human IGF-I receptors, as measured by the RT-PCR, was not significantly different in control and treated MDA-MB-468 tumors. In cell culture, IGF-I did not stimulate, GH-RH slightly stimulated, while MZ-5-156 and JV-1-36 inhibited proliferation of MDA-MB-468 cells known to possess defective insulin and IGF-I receptor signaling. The expression of mRNA for human GH-RH was found in five of 8 tumors treated with GH-RH antagonists, and in one of the five control tumors. These results suggest that GH-RH antagonists inhibit MDA-MB-468 breast cancers possibly through mechanisms involving interference with locally produced GH-RH.

Animals↗

PubMed2000

Antagonists of growth hormone-releasing hormone (GH-RH) inhibit IGF-II production and growth of HT-29 human colon cancers.

Insulin-like growth factors (IGFs) I and II are implicated in progression of various tumours including colorectal carcinomas. To interfere with the production of IGFs, we treated male nude mice bearing xenografts of HT-29 human colon cancer with various potent growth hormone-releasing hormone (GH-RH) antagonists. Twice daily injections of antagonist MZ-4-71, 10 microg intraperitoneally or 5 microg subcutaneously (s.c.) resulted in a significant 43-45% inhibition of tumour growth. Longer acting GH-RH antagonists, MZ-5-156 and JV-1-36 given once daily at doses of 20 microg s.c. produced a 43-58% decrease in volume and weight of cancers. Histological analyses of HT-29 cancers demonstrated that both a decreased cell proliferation and an increased apoptosis contributed to tumour inhibition. GH-RH antagonists did not change serum IGF-I or IGF-II levels, but significantly decreased IGF-II concentration and reduced mRNA expression for IGF-II in tumours. In vitro studies showed that HT-29 cells produced and secreted IGF-II into the medium, and addition of MZ-5-156 dose-dependently decreased IGF-II production by about 40% as well as proliferation of HT-29 cells. Our studies demonstrate that GH-RH antagonists inhibit growth of HT-29 human colon cancers in vivo and in vitro. The effect of GH-RH antagonists may be mediated through a reduced production and secretion of IGF-II by cancer cells.

Animals↗

PubMed2000

Antagonists of growth hormone-releasing hormone and vasoactive intestinal peptide inhibit tumor proliferation by different mechanisms: evidence from in vitro studies on human prostatic and pancreatic cancers.

Antagonists of GH-releasing hormone (GHRH) and vasoactive intestinal peptide (VIP) inhibit the proliferation of various tumors in vitro and in vivo, but a comparison of their antitumor effects and mechanisms of action has not been reported to date. We recently synthesized and characterized a series of analogs, some of which are primarily GHRH antagonists (JV-1-36, JV-1-38, and JV-1-42), whereas others are more selective for VIP receptors (VPAC-R; JV-1-50, JV-1-51, JV-1-52, and JV-1-53). LNCaP human prostatic cancer cells express VPAC-R, with predominant subtype 1 determined by RT-PCR. Our studies show that GHRH antagonists significantly inhibit the proliferation of both VPAC-R positive LNCaP cells (P < 0.001) and VPAC-R negative MiaPaCa-2 human pancreatic cancer cells cultured in vitro (P < 0.05 to P < 0.001). Growth inhibition of LNCaP cells is accompanied by a proportional reduction in prostate-specific antigen (PSA) secretion (P < 0.001). In a superfusion system, the inhibitory activities of the analogs on the rate of VIP and GHRH-induced PSA secretion correlate well with their VPAC-R binding affinities to LNCaP cell membranes. Antagonists more selective for VPAC-R display a stronger inhibition of inducible PSA release than GHRH antagonists, but have smaller effects or no effects on proliferation and PSA secretion in culture. Collectively, our findings demonstrate that the antiproliferative activity of the analogs on cancer cells is not correlated to their VPAC-R antagonistic potencies. Because GHRH antagonists inhibit the proliferation of LNCaP cells more powerfully than VPAC-R antagonists and also suppress the growth ofVPAC-R-negative MiaPaCa-2 cells, it can be concluded that their antiproliferative effect is exerted through a mechanism independent of VPAC-R.

Antineoplastic Agents↗

PubMed2000

Human ovarian cancers express somatostatin receptors.

Characteristics of receptors for somatostatin (SST) analog RC-160 on 17 surgical specimens of human epithelial ovarian cancer and two human ovarian cancer lines were determined by ligand competition assays. The expression of mRNA for four SST receptor subtypes (sst1, sst2A, sst3 and sst5) was investigated by RT-PCR. Thirteen of 17 specimens (76%) exhibited high affinity binding sites for RC-160 with Kd = 6.55 nmol/L and a Bmax = 575.4 fmol/mg membrane protein. Specific receptors for RC-160 were also found in xenografts of OV-1063 and UCI-107 human ovarian cancer lines. The mRNA for sst1 was detected in 65% of the ovarian cancer specimens, while the incidence of sst2A, sst3 and sst5 was 65%, 41% and 24%, respectively. Both ovarian cancer cell lines also expressed mRNA for these four subtypes. The presence of these SST receptor subtypes in human ovarian cancers allows the use of SST analogs and their radionuclide and cytotoxic derivatives for the diagnosis and treatment of this malignancy.

Adult↗

PubMed2000

High expression of somatostatin receptors and messenger ribonucleic acid for its receptor subtypes in organ-confined and locally advanced human prostate cancers.

To evaluate the potential application of somatostatin (SST) analogs as an adjuvant treatment for prostate cancer, we characterized the binding sites for SST octapeptide analogs on prostate cancers in patients treated with radical prostatectomy. The affinity and density of binding sites for SST analog RC-160 on 80 surgical specimens of prostate cancers were determined by ligand competition assays. The expression of messenger ribonucleic acid (mRNA) for SST receptor subtype 1 (SSTR1), subtype 2 (SSTR2), and subtype 5 (SSTR5) was also investigated in 22 samples by RT-PCR. Fifty-two of 80 specimens (65%), showed a single class of specific binding sites for RC-160 with a mean dissociation constant (K(d)) of 9.44 nmol/L and a mean maximal binding capacity of 754.8 fmol/mg membrane protein. The mRNA for SSTR1 was detected in 86% of samples, whereas the incidences of mRNA for SSTR2 and SSTR5 were 14% and 64%, respectively. The expression of SSTR2 and/or SSTR5 was 100%, consistent with the presence of RC-160 binding. In patients at high risk of cancer recurrence (stage pT3 and/or Gleason score of 8-10), the incidence of RC-160 binding (65.7%) was similar to that observed in the low risk group (64.3%). The demonstration of the high incidence of octapeptide-preferring SSTRs in organ-confined and locally advanced prostate cancers supports the merit of further investigations of the application of SST analogs and their radionuclide and cytotoxic derivatives for adjuvant treatment of patients at high risk of cancer recurrence after radical prostatectomy. Such approaches could be also considered for patients with advanced prostate cancer at the time of relapse.

Aged↗

PubMed2000

Down-regulation and change in subcellular distribution of receptors for luteinizing hormone-releasing hormone in OV-1063 human epithelial ovarian cancers during therapy with LH-RH antagonist Cetrorelix.

The inhibition of growth of various hormone-dependent cancers by analogs of luteinizing hormone-releasing hormone (LH-RH) may be exerted in part through receptors for LH-RH present on tumor cells, but the direct mode of action of LH-RH agonists and antagonists is still not completely understood. The aim of this study was to investigate the effects of agonist [D-Trp6]LH-RH and antagonist Cetrorelix, administered s.c. at a dose of 100 microg/day for 3 weeks on the binding characteristics and subcellular localization of receptors for LH-RH in OV-1063 human epithelial ovarian cancers xenografted into nude mice. Using radioligand binding studies, following in vitro desaturation, we demonstrated the presence of specific, high affinity binding sites for LH-RH in both cell membrane and nuclear fraction of OV-1063 tumors. Treatment with Cetrorelix, but not [D-Trp6]LH-RH, caused about 60% reduction (p<0. 01) in tumor volume and weight. [D-Trp6]LH-RH decreased the number of LH-RH receptors on OV-1063 tumor membranes by 44% after 14 days (p<0.01), and the concentration of receptors remained at that level on day 21. The maximal binding capacity of receptors for LH-RH in the nuclei was significantly higher (p<0.05) after 3 weeks of treatment with [D-Trp6]LH-RH. Cetrorelix decreased the concentration of membrane receptors for LH-RH by 53% (p<0.01) after 14 days and the levels on day 21 were even lower, showing a 70% reduction (p<0. 01). In contrast, the number of LH-RH binding sites in the nuclear pellet was significantly increased (p<0.01) by Cetrorelix at that time. Our results demonstrate for the first time that the down-regulation of LH-RH receptors on the cell membranes of OV-1063 human ovarian cancers after therapy with antagonist Cetrorelix or agonist [D-Trp6]LH-RH is associated with an increase in receptor concentration in the nuclei. These phenomena could be related to the internalization and subcellular translocation of receptors in these tumor cells.

Adenocarcinoma, Papillary↗

PubMed2000

High incidence of receptors for luteinizing hormone-releasing hormone (LHRH) and LHRH receptor gene expression in human prostate cancers.

PURPOSE: Agonistic analogs of luteinizing hormone-releasing hormone (LHRH) are widely used for therapy of advanced prostate cancer based upon their ability to suppress testosterone secretion in patients. Various studies also indicate that LHRH analogs might have direct inhibitory effects on prostate tumors mediated by specific LHRH receptors. In this study we investigated the presence and characteristics of receptors for LHRH and their messenger (m) ribonucleic acid (RNA) expression in specimens of human prostate adenocarcinomas and benign prostatic tissue. MATERIALS AND METHODS: In vitro ligand competition assays as well as reverse transcriptase polymerase chain reaction (RT-PCR) were performed to investigate the expression of receptors for LHRH in surgical specimens of human prostate cancers and benign prostatic tissue. RESULTS: Sixty-nine of 80 (86%) cancers exhibited specific, medium to high-affinity binding for [D-Trp6]LHRH with a dissociation constant (Kd) of 6.55+/-0.4 nM and a maximal binding capacity (Bmax) of 483.6+/-25.4 fmol./mg. membrane protein. Two prostate cancer patients who were treated with the LHRH agonist goserelin prior to prostatectomy did not show tumor LHRH receptors. The expression of mRNA for LHRH receptors was observed in 19 of 22 (86%) prostate cancers. Benign prostatic tissue also displayed LHRH receptor gene expression, but exhibited lower Bmax value. There was a negative correlation (p <0.001) between LHRH receptor binding capacity and cancer grade (Gleason score); higher Gleason scores were associated with significantly lower binding capacity but an increased binding affinity. CONCLUSIONS: The expression of specific receptor proteins for LHRH in human prostate cancer provides a rationale for the improvement in methods for therapy of this malignancy based on LHRH analogs.

Aged↗

PubMed2000

Regression of U-87 MG human glioblastomas in nude mice after treatment with a cytotoxic somatostatin analog AN-238.

Receptors for somatostatin (SST) found on brain tumors could be used for targeting of chemotherapeutic agents. This study was conducted to investigate the effects of targeted cytotoxic SST analogue AN-238, consisting of 2-pyrrolinodoxorubicin (AN-201), a potent derivative of doxorubicin (DOX) linked to somatostatin analogue RC-121, on the growth of SST receptor-positive U-87 MG human glioblastomas. Nude mice bearing U-87 MG xenografts received i.v. saline or equimolar doses of AN-238 or AN-201 (150 nmol/kg). Experiments also included groups that were administered RC-121 prior to the injection of AN-238, and groups injected with AN-162, a cytotoxic SST analogue similar to AN-238 but containing DOX instead of AN-201. Tumor volume, weight, and burden were determined. The effect of AN-238 and AN-201 on the survival time of nude mice bearing orthotopically implanted U-87 MG tumors was also evaluated. The binding of AN-238 to U-87 MG tumors was determined by radioreceptor assay and SST receptor (SSTR) subtype by reverse transcription-PCR. Nineteen days after a single administration of AN-238 the growth of U-87 MG tumors in nude mice was significantly inhibited (P = 0.00168), whereas two injections of AN-238 produced the regression of tumors (P = 0.0046). AN-201 was toxic and ineffective at the same dose. The antitumor effect on AN-238 could be blocked by pretreatment of the tumor-bearing mice with RC-121. The mean survival time of nude mice inoculated orthotopically with U-87 MG cells into the brain was significantly prolonged by treatment with AN-238 (P = 0.0099). AN-162 failed to inhibit significantly the growth of U-87 MG xenografts. High affinity binding sites for SST and mRNA for SST-2 receptor subtype were detected in U-87 MG tumors. Cytotoxic SST analogue AN-238 can be targeted to SST receptors on U-87 MG human glioblastomas to produce powerful inhibition of growth.

Animals↗

PubMed2000

Effective treatment of metastatic MDA-MB-435 human estrogen-independent breast carcinomas with a targeted cytotoxic analogue of luteinizing hormone-releasing hormone AN-207.

A highly potent derivative of doxorubicin, 2-pyrrolinodoxorubicin (AN-201), was linked to [D-Lys6]luteinizing hormone-releasing hormone (LH-RH) to form a cytotoxic analogue, AN-207, that can be targeted to LH-RH receptors. The effects of AN-207 were investigated in MDA-MB-435 human estrogen-independent breast carcinomas, which express LH-RH receptors. In experiment 1, nude mice bearing orthotopically implanted tumors received a single i.v. injection of AN-207, AN-201, or the carrier at 250 nmol/kg. Five weeks after administration of AN-207, tumor volume was significantly decreased by 66% (P < 0.001) and tumor burden by 71% (P < 0.05) as compared with controls, but no significant effects occurred in other groups. Six of eight (75%) control animals and 37.5% of mice treated with AN-201 developed metastases in the lymph nodes, whereas no lymphatic spread was found in any of the mice that received injections of AN-207. The antitumor effect of AN-207 could be partially blocked by pretreatment of the tumor-bearing mice with high doses of agonist [D-Trp6]LH-RH, which suggests that AN-207 acts on LH-RH receptors on tumors. The mortality due to toxicity was 25% in the group receiving AN-201 and 12.5% in the AN-207-treated group. Radioligand binding assays revealed the presence of high-affinity binding sites for LH-RH on tumor membranes, and mRNA for LH-RH receptors was demonstrated by reverse transcription-PCR. In experiment 2, two i.v. injections of AN-207 or AN-201 at 150 nmol/kg were given on days 0 and 28 to mice bearing orthotopic xenografts of MDA-MB-435. The outcome of the treatment was similar to that observed in experiment 1, but without any toxicity-related deaths. Tumor growth inhibition and prevention of metastatic disease suggest that cytotoxic LH-RH analogue AN-207 could be considered for the treatment of human estrogen-independent breast cancers expressing receptors for LH-RH.

Animals↗

PubMed1999

Inhibition of growth of MX-1, MCF-7-MIII and MDA-MB-231 human breast cancer xenografts after administration of a targeted cytotoxic analog of somatostatin, AN-238.

Since somatostatin (sst) receptors are expressed in a high percentage of human breast cancers, we studied the effects of a targeted cytotoxic somatostatin analog (AN-238) formed by linking the highly active doxorubicin (DOX) derivative 2-pyrrolino-DOX (AN-201) to octapeptide RC-121 (D-Phe-Cys-Tyr-D-Trp-Lys-Val-Cys-Thr-NH(2)) in 3 human breast cancer models. The models included estrogen-independent MDA-MB-231 and MX-1 and estrogen-sensitive MCF-7-MIII tumors. Nude mice bearing xenografts of these cancers were injected i.v. with 250 nmol/kg doses of cytotoxic radical AN-201, cytotoxic analog AN-238 or the unconjugated mixture of AN-201 and sst analog RC-121. Significant inhibition of growth of MDA-MB-231, MX-1 and MCF-7-MIII tumors was observed 1 week after injection of a single dose of cytotoxic analog AN-238. The volume of MDA-MB-231 tumors remained significantly decreased 3 weeks after treatment. The volumes and weights of MCF-7-MIII tumors continued to be significantly reduced 60 days after therapy with AN-238. AN-238 also caused complete regression of MX-1 tumors in 5 of 10 animals, which remained tumor-free 60 days after treatment. In contrast, after treatment with cytotoxic radical AN-201, MDA-MB-231 and MCF-7-MIII tumors grew steadily and the regression of MX-1 tumors was only transitory in most animals. Toxicity of AN-201 was much greater than that of AN-238, as measured by animal deaths, loss of body weight and leukopenia. High-affinity sst receptors and mRNA for both sst(2) and sst(5) subtypes were found in all 3 tumor lines. Expression of sst receptors was not significantly affected by treatment with AN-238. Our results indicate that the cytotoxic somatostatin analog AN-238 efficaciously inhibits growth of human breast cancers expressing sst receptor subtypes 2 and 5.

Animals↗