Biomedical subjects

Gabor Halmos

Publications and source records attributed to Gabor Halmos.

44 records · Page 3Linked to original sources

PubMed2003

Effective treatment of H838 human non-small cell lung carcinoma with a targeted cytotoxic somatostatin analog, AN-238.

The accumulation of radioactive somatostatin analog [111In]pentetreotide in non-small cell lung cancer (non-SCLC) during scintigraphy of patients provides a rationale for investigating the efficacy of somatostatin receptor-based chemotherapy in non-SCLC. Consequently, in this study, we evaluated the antitumor effects of cytotoxic somatostatin analog AN-238 on H838 human non-SCLC xenografted into nude mice in comparison with its cytotoxic radical, 2-pyrrolinodoxorubicin (AN-201). The expression of messenger RNA (mRNA) for human somatostatin receptor subtypes 2 (hsst2) and 5 (hsst5) in H838 cells, and tumors was also investigated using reverse-transcription polymerase chain reaction (RT-PCR). Somatostatin receptors on H838 tumors were characterized by ligand competition assay using radiolabeled somatostatin analog, RC-160. Three i.v. injections of AN-238 at 150 nmol/kg, given on days 1, 7 and 21, resulted in a significant (p<0.05) tumor growth inhibition, the final tumor volume being 60% smaller than in the controls. The tumor doubling time was also extended significantly (p<0.05) from 9.65+/-0.56 days in the controls to 17.52+/-3.3 days. Only one of 8 mice died due to toxicity. In contrast, cytotoxic radical AN-201 was ineffective and more toxic, killing 2 of 7 animals. mRNA for hsst2 was found in H838 xenografts, but not in H838 cells from which the xenografts originated. Interestingly, H838 cells grown in a special, serum-free medium did express mRNA for hsst2. mRNA for hsst5 was not found in any samples tested. Binding studies demonstrated the presence of high affinity (K(d) = 7.3+/-1.2 nM) binding sites for RC-160 with a mean maximal binding capacity (B(max)) of 953.3+/-45.3 fmol/mg protein. AN-238 at 3.14+/-0.93 nM concentration displaced 50% of radiolabeled RC-160 binding to somatostatin receptors in H838 tumors. Our results indicate that patients with inoperable non-SCLC may benefit from chemotherapy targeted to somatostatin receptors based on AN-238.

Animals↗

PubMed2002

Inhibition of PC-3 human prostate cancers by analogs of growth hormone-releasing hormone (GH-RH) endowed with vasoactive intestinal peptide (VIP) antagonistic activity.

Vasoactive intestinal peptide (VIP) stimulates the proliferation and invasiveness of malignant prostatic cells. Receptors for VIP and the closely related growth hormone-releasing hormone (GH-RH) show considerable homology and are found in prostatic and other carcinomas. Among various analogs of GH-RH synthesized, JV-1-52 is a non-selective VIP/GH-RH antagonist, whereas JV-1-53 is a VIP antagonist devoid of GH-RH antagonistic effect. In our study, nude mice bearing PC-3 human androgen-independent prostate carcinomas were treated with JV-1-52 or JV-1-53 (20 microg/day, s.c.) for 28 days. Both antagonists produced a similar reduction in tumor volume (62-67%, p < 0.01) and tumor weight (59-62%; p < 0.05) vs. controls and extended tumor doubling-time from 9.1 to about 16 days (p < 0.05). To investigate the mechanisms involved, in another study we compared the effects of JV-1-53 with those of somatostatin analog RC-160. VIP antagonist JV-1-53 reduced tumor weight by 67% (p < 0.01) and suppressed the expression of mRNA for c-fos and c-jun oncogenes by about 34% (p < 0.05), without affecting serum levels of insulin-like growth factor-I (IGF-I). In contrast, RC-160 (50 microg/day) reduced serum IGF-I by 19% (p < 0.05), but did not significantly decrease tumor weight. mRNA for VIP and high affinity receptors for VIP were detected on PC-3 tumors. Our results suggest that VIP/GH-RH antagonists can inhibit the growth of androgen-independent prostate cancer by abrogating the autocrine/paracrine mitogenic stimuli of VIP. The ability of GH-RH antagonists to block tumoral VIP receptors, in addition to GH-RH receptors, could be potentially beneficial for prostate cancer therapy.

Animals↗

PubMed2002

Targeted cytotoxic somatostatin analogue AN-238 inhibits somatostatin receptor-positive experimental colon cancers independently of their p53 status.

The resistance of advanced colorectal cancers to therapy is often related to mutations in the p53 tumor suppressor gene. Because somatostatin (SRIF) receptors (ssts) are present in colorectal carcinomas, the treatment with targeted cytotoxic SRIF analogue AN-238, consisting of 2-pyrrolinodoxorubicin (AN-201) linked to octapeptide SRIF carrier RC-121, may overcome this resistance by producing a higher concentration of the cytotoxic agent in the tumors. Four colon cancer cell lines, HCT-116 and LoVo expressing wild-type p53, and HCT-15 and HT-29 with mutated p53, were investigated. HCT-116, HCT-15, and HT-29, but not LoVo possess functional ssts. We analyzed changes in p53, p21, and proliferating cell nuclear antigen (PCNA) concentrations in these cells in vitro by immunoblotting after exposure to AN-238, its radical AN-201, or doxorubicin (DOX). Equitoxic doses of AN-238, AN-201, or DOX affected p53, p21, and PCNA differently. Analysis of the p21:p53 ratios revealed that DOX increased p53 levels, but most of p53 was mutated and inactive, whereas AN-238 produced smaller changes in p53 concentrations but enhanced its activity. In HCT-15 cells, PCNA:p21 ratios, which are indicators of proliferation and repair processes, remained unchanged after exposure to AN-238 but were increased by DOX. In vivo studies in nude mice demonstrated that AN-238, AN-201, and DOX were equally effective on HCT-116 tumors that express wild-type p53. However, AN-238 also inhibited the growth of HCT-15 and HT-29 cancers that express mutant p53, whereas AN-201 and DOX showed no effect. None of the compounds could suppress the proliferation of LoVo tumors that lack functional ssts. In conclusion, cytotoxic SRIF analogue AN-238 inhibits the growth of experimental colon cancers that express ssts, regardless of their p53 status.

Animals↗

PubMed2002

Changes in subcellular distribution of pituitary receptors for luteinizing hormone-releasing hormone (LH-RH) after treatment with the LH-RH antagonist cetrorelix.

Treatment with antagonists of luteinizing hormone-releasing hormone (LH-RH) leads to down-regulation of pituitary LH-RH receptors. Thus, the effect of LH-RH antagonists is similar to that of the LH-RH agonists, but the mode of action of antagonists is not completely understood. The aim of this study was to investigate the effects of LH-RH antagonist cetrorelix on the binding characteristics and subcellular localization of receptors for LH-RH in rat pituitaries. Radioligand binding studies, performed after in vitro desaturation, revealed that a single s.c. injection of cetrorelix at a dose of 100 microg per rat significantly decreased the number of pituitary membrane receptors for LH-RH in a time-dependent manner with the nadir occurring at 6 h. In contrast, 2-6 h after cetrorelix treatment, the concentration of binding sites for LH-RH in the nuclei of rat pituitaries was significantly higher (P < 0.01) than in controls. Chronic administration of cetrorelix also decreased the level of membrane receptors for LH-RH by 83% (P < 0.01) after 7 days, and 86% (P < 0.01) after 14 days. The number of LH-RH binding sites in the nuclear pellet was increased 3-fold (P < 0.01) by days 7 and 14 after the initiation of treatment with cetrorelix. A single injection or prolonged treatment with LH-RH antagonist also decreased the mRNA expression of pituitary receptors for LH-RH. Our results demonstrate that the down-regulation of LH-RH receptors on the cell membranes of rat pituitaries after therapy with antagonist cetrorelix is associated with an increase in receptor concentration in the nuclei. These phenomena could be related to the internalization and subcellular translocation of LH-RH receptors.

Animals↗

PubMed2002

Expression of a splice variant of the receptor for GHRH in 3T3 fibroblasts activates cell proliferation responses to GHRH analogs.

The stimulatory effects of growth hormone-releasing hormone (GHRH) and the antiproliferative action of GHRH antagonists have been demonstrated in various cancers, but the receptors that mediate these responses are not clearly identified. Recently, we reported that human cancer cell lines express splice variants (SVs) of the receptors for GHRH. SV1 exhibits the greatest similarity to the pituitary GHRH receptor and is most likely to be functional. To ascertain whether SV1 mediates mitogenic effects on nonpituitary tissues, we expressed SV1 in 3T3 mouse fibroblasts and studied the properties of the transfected cells. Radioligand binding assays with (125)I-labeled GHRH antagonist JV-1-42 detected high affinity (K(d) = 0.58 +/- 0.17 nM) binding sites for GHRH with a maximal binding capacity (B(max)) of 103 +/- 17.4 fmol/mg of membrane protein in 3T3 cells transfected with pcDNA3-SV1, whereas the control cells transfected with the empty vector did not show any GHRH binding. Cell proliferation studies showed that cells expressing SV1 are much more sensitive to GHRH analogs than the pcDNA3 controls. Thus, the expression of SV1 augments the stimulatory responses to GHRH(1-29)NH(2) or GHRH agonist JI-38 and inhibitory responses to GHRH antagonist JV-1-38 as compared with pcDNA3 controls. The stimulation of SV1-expressing cells by GHRH or JI-38 is followed by an increase in cAMP production, but no GH release occurs. Vasoactive intestinal peptide had no effect, and its antagonist JV-1-53 did not inhibit the proliferation of SV1-expressing cells stimulated by GHRH. Our results suggest that SV1 could mediate responses of nonpituitary cells and various tumors to GHRH and GHRH antagonists. The presence of SV1 in several human cancer cell lines provides a rationale for antitumor therapy based on the blockade of this receptor by specific GHRH antagonists.

3T3 Cells↗

PubMed2002

Expression of growth hormone-releasing hormone (GHRH) and splice variants of GHRH receptors in human experimental prostate cancers.

The expression of mRNA for GHRH and splice variants (SVs) of GHRH receptors in LNCaP, MDA-PCa-2b and PC-3 human prostate cancers grown in nude mice was investigated by RT-PCR. The expression of mRNA for GHRH was detected in LNCaP and PC-3, but not in MDA-PCa-2b prostatic carcinoma. RT-PCR analyses of mRNA isolated from LNCaP, MDA-PCa-2b and PC-3 cancers, revealed the presence of 720 and 566 bp products, corresponding to SV(1) and SV(2) isoforms of GHRH receptors. In PC-3 tumor membranes a radiolabeled GHRH antagonist [125I]-JV-1-42 was bound to one class of high-affinity binding sites (K(d)=1.81+/-0.47 nM) and maximum binding capacity of 332.7+/-27.8 fmol/mg membrane protein. The in vivo uptake of [125I]-JV-1-42 was observed in all xenografts of human prostate cancer, the tracer accumulation being the highest in PC-3 tumors. These results indicate that GHRH and SVs of its receptors, different from those found in the pituitary, are present in experimental human prostate cancers and may form a local mitogenic loop. The antiproliferative effects of GHRH antagonists on growth of prostate cancer could be exerted in part by an interference with this local GHRH system.

Alternative Splicing↗

PubMed2002

Expression of growth hormone-releasing hormone and its receptor splice variants in human prostate cancer.

Antagonists of GHRH inhibit the growth of various human tumors, including prostate cancer, but the tumoral receptors mediating the antiproliferative effect of GHRH antagonists have not been clearly identified. Recently, we demonstrated that human cancer cell lines express splice variants (SVs) of receptors for GHRH, of which SV1 exhibits the greatest similarity to the pituitary GHRH receptors. In this study we investigated the expression of GHRH and SVs of GHRH receptor and the binding characteristics of the GHRH receptor isoform in 20 surgical specimens of organ-confined and locally advanced human prostatic adenocarcinomas. The mRNA expression of GHRH and SVs of GHRH receptor was investigated by RT-PCR. The affinity and density of receptors for GHRH were determined by ligand competition assays based on binding of (125)I-labeled GHRH antagonist JV-1-42 to tumor membranes. Twelve of 20 tumors (60%) exhibited specific, high affinity binding for JV-1-42, with a mean dissociation constant (K(d)) of 0.81 nmol/liter and a mean maximal binding capacity of 185.2 fmol/mg membrane protein. The mRNA of SV1 was detected in 13 of 20 (65%) prostate cancer specimens and was consistent with the presence of GHRH binding. RT-PCR analyses also revealed the expression of mRNA for GHRH in 13 of 15 (86%) prostatic carcinoma specimens examined. The presence of GHRH and its tumoral receptor SVs in prostate cancers suggests the possible existence of an autocrine mitogenic loop. The antitumor effects of GHRH antagonists in prostate cancer could be exerted in part by interference with this local GHRH system.

Adenocarcinoma↗

PubMed2002

Effective treatment of experimental DU-145 prostate cancers with targeted cytotoxic somatostatin analog AN-238.

We evaluated the effectiveness of targeted cytotoxic analog of somatostatin (SST) AN-238, consisting of 2-pyrrolinodoxorubicin (AN-201) linked covalently to SST octapeptide carrier RC-121 in DU-145 human androgen-independent prostate cancers xenografted into nude mice. We also investigated the expression of mRNAs for SST receptor subtypes 2A and 5 (sst2A and sst5) in DU-145 tumors. After 8 weeks of treatment, AN-238 practically arrested the proliferation of DU-145 cancers. The tumor volume in nude mice that received 4 injections of AN-238 at the dose of 150 nmol/kg was 63.4+/-6.7 mm3, nearly 4 times smaller than that in controls which measured 249.1+/-36.3 mm3 (p<0.001). Treatment with AN-238 lowered tumor weight by 68% (p<0.01) compared with the control group and extended the tumor volume doubling time to 184.1+/-69.4 days, versus 32.1+/-6.6 days in controls (p<0.05). No toxicity-related deaths occurred during treatment with AN-238. Cytotoxic radical AN-201 administered alone or in an unconjugated mixture with carrier RC-121 inhibited the growth of DU-145 tumors only after the third and fourth injection and was toxic. The expression of mRNA for sst2A and sst5 was detected in all specimens of control DU-145 tumors and in tumors treated with AN-238. The present study demonstrates the high efficacy of SST-receptor-targeted chemotherapy in a model of human androgen-independent prostatic carcinoma.

Animals↗