Inhibition of growth of human small cell and non-small cell lung carcinomas by antagonists of growth hormone-releasing hormone (GH-RH)

Insulin-like growth factors-I and-II (IGF-I and IGF-II) may be involved in the proliferation of human lung carcinomas. The purpose of this study was to investigate the effects of two potent antagonists of growth hormone-releasing hormone (GH-RH), MZ-4-71 and MZ-5-156 on the growth of the H69 human small cell lung cancer (SCLC) and H157 non-SCLC (NSCLC) lines transplanted into nude mice or cultured in vitro. Nude mice bearing H69 and H157 tumors were treated for 3-5 weeks with MZ-4-71 or MZ-5-156 injected s.c. twice a day at a dose of 20 mu g/animal. Growth of H69 and H157 tumors in nude mice was significantly inhibited by MZ-4-71 and MZ-5-156 as shown by a reduction in tumor volume and weight. In animals bearing H157 NSCLC, treatment with MZ-4-71 decreased IGF-I and IGF-II levels in tumor tissue. Levels of IGF-I, but not of IGF-II in serum and liver tissue of H157 tumor-bearing nude mice treated with MZ-4-71 were decreased. High affinity binding sites for ICF-I were demonstrated on membranes of H69 and H157 tumors. In cell cultures, the proliferation rate of H69 SCLC cells was suppressed by 10(-7)-10(-5) M MZ-4-71, but H157 NSCLC line was only inhibited by 10(-5) M antagonist. Our findings demonstrate that the GHRH antagonists MZ-4-71 and MZ-5-156 can inhibit the growth of SCLC and NSCLC. This new approach to the management of lung cancer merits further investigation.

Inhibitory effects of antagonistic analogs of GHRH on GH3 pituitary cells overexpressing the human GHRH receptor

GH3 rat pituitary tumor cells produce GH and prolactin (PRL), but lack the GHRH receptor (GHRH-R). We expressed human GHRH-R (hGHRH-R) in GH3 cells using recombinant adenoviral vectors and studied the effects of GHRH antagonists. The mRNA expression of the GHRH-R gene in the cells was demonstrated by RT-PCR. An exposure of the GH3 cells infected with hGHRH-R to 10(-10), 10(-9) and 10(-8) m hGHRH for 1 or 2 h in culture caused a dose-dependent elevation of the intracellular cAMP concentration and the cAMP efflux. Exposure to hGHRH also elicited dose-dependent increases in GH and PRL secretion from these cells. Neither the uninfected nor the antisense hGHRH-R-infected control cells exhibited cAMP, GH and PRL responses to GHRH stimulation. GHRH antagonists JV-1-38 and jv-1-36 applied at 3x10(-8) m for 3 h, together with 10(-9) m GHRH, significantly inhibited the GHRH-stimulated cAMP efflux from the hGHRH-R-infected cells by 36 and 80% respectively. The more potent antagonist JV-1-36 also decreased the intracellular cAMP levels in these cells by 55%. Exposure to JV-1-36 for 1 h nullified the stimulatory effect of GHRH on GH secretion and significantly inhibited it by 64 and 77% after 2 and 3 h respectively. In a superfusion system, GHRH at 10(-10), 10(-9) and 10(-8) m concentrations induced prompt and dose-related high cAMP responses and smaller increases in the spontaneous GH secretion of the hGHRH-R-infected cells. Antagonists JV-1-36 and JV-1-38 applied at 3x10(-8) m for 15 min, together with 10(-9) m GHRH, inhibited the GHRH-stimulated cAMP response by 59 and 35% respectively. This work demonstrates that GHRH antagonists can effectively inhibit the actions of GHRH on the hGHRH-R. Our results support the view that this class of compounds would be active clinically.

Expression of mRNA for growth hormone-releasing hormone and splice variants of GHRH receptors in human malignant bone tumors

Splice variants (SV) of receptors for growth hormone-releasing hormone (GHRH) have been found in several human cancer cell lines. GHRH antagonists inhibit growth of various human cancers, including osteosarcomas and Ewing's sarcoma, xenografted into nude mice or cultured in vitro and their antiproliferative action could be mediated, in part, through these SV of GHRH receptors. In this study, we found mRNA for the SV(1) isoform of GHRH receptors in human osteosarcoma line MNNG/HOS and SK-ES-1 Ewing's sarcoma line. We also detected mRNA for GHRH, which is apparently translated into the GHRH peptide and secreted by the cells, as shown by the presence of GHRH-like immunoreactivity in the conditioned media of cell cultures. In proliferation studies in vitro, the growth of SK-ES-1 and MNNG/HOS cells was dose-dependently inhibited by GHRH antagonist JV-1-38 and an antiserum against human GHRH. Our study indicates the presence of an autocrine stimulatory loop based on GHRH and SV(1) of GHRH receptors in human sarcomas. The direct antiproliferative effects of GHRH antagonists on malignant bone tumors appear to be exerted through the SV(1) of GHRH receptors on tumoral cells.

Inhibition of growth and reduction in tumorigenicity of UCI-107 ovarian cancer by antagonists of growth hormone-releasing hormone and vasoactive intestinal peptide

PURPOSE

To evaluate the tumor inhibitory activities of antagonists of growth hormone-releasing hormone (GH-RH) and vasoactive intestinal peptide (VIP) in UCI-107 human ovarian cancer model, and to investigate the role of the insulin-like growth factor (IGF) system in the response.

METHODS

In the present study we investigated the effects of GH-RH antagonist JV-1-36 and VIP antagonist JV-1-52, on the growth and tumorigenicity of UCI-107 ovarian cell carcinoma xenografted into nude mice. Studies on the effects of hGH-RH(1-29)NH2, IGF-I, IGF-II, JV-1-36, and JV-1-52 on the proliferation of UCI-107 cells cultured in vitro were also performed.

RESULTS

After 22 days of therapy with JV-1-36 or JV-1-52 at the dose of 20 microg/day, the final volume of UCI-107 tumors was significantly (P<0.05) decreased by 50.5% and 56%, respectively, compared to controls. The concentration of IGF-II in tumors was reduced by 66% in the JV-1-36-treated group and by 62% in the group given JV-1-52 (both P < 0.05). Exposure in vitro to 1 microM concentrations of JV-1-36 or JV-1-52 for 24 h decreased the tumorigenicity of UCI-107 cells in nude mice. All ten mice injected with cells treated with medium alone developed tumors within 23 days after cell inoculation, while only eight of ten and four of ten mice injected with cells exposed to JV-1-36 or JV-1-52, respectively, had tumors. In vitro exposure of UCI-107 cells to 5-35 ng/ml IGF-II produced a significant suppression in the rate of cell proliferation (P < 0.01).

CONCLUSION

Our results suggest that GH-RH and VIP antagonists inhibit the growth of UCI-107 ovarian cell carcinoma by mechanisms that appear to involve direct effects on the cancer cells.

Antagonists of GHRH decrease production of GH and IGF-I in MXT mouse mammary cancers and inhibit tumor growth

The involvement of IGF-I in mammary carcinogenesis is well established, but the role of GH, as an autocrine growth factor for breast cancers is poorly understood. The goal of our study was to investigate whether antagonists of GHRH can interfere with the effects of GH and IGF-I in MXT mouse mammary cancers. GHRH antagonists JV-1-36 and JV-1-38 inhibited growth of estrogen-independent MXT mouse mammary cancers in vivo, producing about 50% reduction in tumor volume (P < 0.05). This growth inhibition was associated with a decrease in cell proliferation and an increase in apoptosis in MXT cancers. RIA and RT- PCR analyses showed that the concentrations of GH and IGF-I and the levels of mRNA for GH and IGF-I in MXT tumors were reduced by the therapy with GHRH antagonists. Messenger RNA for GH receptors was also decreased. In vitro, the proliferation of MXT cancer cells was strongly stimulated by GH and less effectively by IGF-I, indicating that both GH and IGF-I may act as growth factors for this mammary carcinoma. GHRH antagonist JV-1-38 inhibited the autonomous growth of MXT cells and the proliferation induced by IGF-I or GH and diminished (3)H-thymidine-incorporation stimulated by IGF-I and GH. These findings and a sustained increase in cyclin B2 concentrations in the cells shown by immunoblotting indicate that JV-1-38 causes a block at the end of the G(2) phase of cell cycle. Our results demonstrate that GHRH antagonists decrease the local production of both GH and IGF-I in MXT mouse mammary cancers, the resulting growth inhibition being the consequence of reduced cell proliferation and increased apoptosis.

Inhibition of growth and metastases of MDA-MB-435 human estrogen-independent breast cancers by an antagonist of growth hormone-releasing hormone

Antagonists of growth hormone-releasing hormone (GH-RH) inhibit the growth of various cancers by mechanism(s) that include the suppression of the insulin-like growth factors (IGF)-I and/or -II. In this study, nude mice bearing orthotopic implants of MDA-MB-435 human estrogen-independent breast carcinoma received 39 days of therapy with GH-RH antagonist JV-1-36 (20 microg/day). The treatment significantly inhibited tumor growth by 71.1% (p<0.01) and nullified the metastatic potential of MDA-MB-435 cells. Four of eight control mice (50%) developed metastases in the lymph nodes and one (12.5%) in the lung, but none of the animals receiving JV-1-36 showed metastatic spread. GH-RH antagonist JV-1-36 inhibited the growth of MDA-MB-435 cells in vitro, while IGF-I stimulated it. However, mRNA for IGF-I or -II was not detected in MDA-MB-435 cells, indicating that the suppression of autocrine IGFs may not be involved in the antiproliferative mechanism. Using ligand competition assays with (125)I-labeled GH-RH antagonist JV-1-42, specific high-affinity binding sites for GH-RH were found on tumor membranes. Reverse transcription-polymerase chain reaction revealed the expression of mRNA for GH-RH receptor splice variant-1 in MDA-MB-435 tumors. Our results suggest that the antitumorigenic action of GH-RH antagonists on MDA-MB-435 breast cancer could be direct and mediated by tumoral GH-RH receptors.

Antiproliferative actions of growth hormone-releasing hormone antagonists on MiaPaCa-2 human pancreatic cancer cells involve cAMP independent pathways

We evaluated the effects of GHRH antagonists on the proliferation of MiaPaCa-2 human pancreatic cancer cells and cAMP signaling in vitro. GHRH antagonists inhibited the proliferation of MiaPaCa-2 cells in vitro in a dose-dependent way and caused a significant elevation in cAMP production. In a superfusion system, short-term exposure of the cells to GHRH antagonists evoked an acute, dose-dependent release of cAMP into the medium. Native GHRH, which stimulates cAMP efflux from pituitary at nanomolar doses, did not influence cAMP release from cultured or superfused MiaPaCa-2 cells even at 10-30 microM. VIP, PACAP, secretin and glucagon also did not influence cell proliferation or cAMP production. Adenylate cyclase activator forskolin (FSK) caused a greater cAMP response, but a smaller antiproliferative effect than GHRH antagonists. Combined treatment with FSK and GHRH antagonist JV-1-38 potentiated the cAMP-inducing effect of FSK, but did not produce a greater inhibition of cell proliferation than JV-1-38 alone. A selective accumulation of radiolabeled GHRH antagonist [(125)I]JV-1-42 in vivo in MiaPaCa-2 carcinoma xenografted into nude mice was also observed. In conclusion, second messengers other than cAMP participate in the signal transduction pathways of GHRH analogs mediated by tumoral GHRH receptors.

Antagonists of growth hormone-releasing hormone and somatostatin analog RC-160 inhibit the growth of the OV-1063 human epithelial ovarian cancer cell line xenografted into nude mice

The effects of antagonists of GHRH and the somatostatin analog RC-160 on the growth of OV-1063 human epithelial ovarian cancer cells xenografted into nude mice were investigated. Treatment with 20 microg/day of the GHRH antagonist JV-1-36 or MZ-5-156 and 60 microg/day of the somatostatin analog RC-160 for 25 days decreased tumor volume by 70.9% (P < 0.01), 58.3% (P < 0.05), and 60.6% (P < 0.01), respectively, vs. the control value. The levels of GH in serum were decreased in all of the treated groups, but only RC-160 significantly reduced serum insulin-like growth factor I (IGF-I). The levels of messenger ribonucleic acid (mRNA) for IGF-I and -II and for their receptors in OV-1063 tumors were investigated by multiplex RT-PCR. No expression of mRNA for IGF-I was detected, but treatment with JV-1-136 caused a 51.8% decrease (P < 0.05) in the level of mRNA for IGF-II in tumors. Exposure of OV-1063 cells cultured in vitro to GHRH, IGF-I, or IGF-II significantly (P < 0.05) stimulated cell growth, but 10(-5) mol/L JV-1-36 nearly completely inhibited (P < 0.001) OV-1063 cell proliferation. OV-1063 tumors expressed mRNA for GHRH receptors and showed the presence of binding sites for GHRH. Our results indicate that antagonistic analogs of GHRH and the somatostatin analog RC-160 inhibit the growth of epithelial ovarian cancers. The effects of RC-160 seem to be exerted more on the pituitary GH-hepatic IGF-I axis, whereas GHRH antagonists appear to reduce IGF-II production and interfere with the autocrine regulatory pathway. The antitumorigenic action of GHRH antagonists appears to be mediated by GHRH receptors found in OV-1063 tumors.

Direct action of growth hormone-releasing hormone agonist JI-38 on normal human fibroblasts: evidence from studies on cell proliferation and c-myc proto-oncogene expression

Growth hormone-releasing hormone (GHRH) is secreted by the hypothalamus and stimulates the release of growth hormone from the pituitary. Recent studies also indicate that in addition to its neuroendocrine function, GHRH may play a direct role in the proliferation of cancer cells, acting as growth factor for various human tumors. In the present study we investigated the effects of JI-38, an agonistic analog of GHRH, on the rate of proliferation of normal human diploid dermal fibroblasts (NHF) cultured in vitro. The effects of JI-38 on the levels of mRNA for c-myc proto-oncogene were also tested. Exposure to 10(-7) M JI-38 stimulated the rate of proliferation of early passage NHF by about 100%. Exposure of NHF cells to 10(-8)-5x10(-6) M JI-38 for 24 h resulted in about 0.5-3.5 fold increase in the levels of mRNA for c-myc proto-oncogene. The ability of JI-38 to stimulate the proliferation of NHF cells was abolished in cells cultured at late passage. Continuous exposure to 10(-7) M JI-38, over 6-7 passages (15-20 population doublings), progressively reduced the rate of proliferation of NHF compared with cells exposed to medium alone, indicating that GHRH agonist acted as a growth inhibitor. Our results suggest that at certain developmental stages, GHRH may act on various tissues, stimulating cell proliferation.

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.

Inhibition of growth of OV-1063 human epithelial ovarian cancers and c- jun and c- fos oncogene expression by bombesin antagonists

Receptors for bombesin are present on human ovarian cancers and bombesin-like peptides could function as growth factors in this carcinoma. Therefore, we investigated the effects of bombesin/gastrin-releasing peptide (GRP) antagonists RC-3940-II and RC-3095 on the growth of human ovarian carcinoma cell line OV-1063, xenografted into nude mice. Treatment with RC-3940-II at doses of 10 microg and 20 microg per day s.c. decreased tumour volume by 60.9% (P< 0.05) and 73.5% (P< 0.05) respectively, after 25 days, compared to controls. RC-3095 at a dose of 20 microg per day reduced the volume of OV-1063 tumours by 47.7% (P = 0.15). In comparison, luteinizing hormone-releasing hormone (LH-RH) antagonist Cetrorelix at a dose of 100 microg per day caused a 64.2% inhibition (P< 0.05). RT-PCR analysis showed that OV-1063 tumours expressed mRNA for bombesin receptor subtypes BRS-1, BRS-2, and BRS-3. In OV-1063 cells cultured in vitro, GRP(14-27) induced the expression of mRNA for c- jun and c- fos oncogenes in a time-dependent manner. Antagonist RC-3940-II inhibited the stimulatory effect of GRP(14-27) on c- jun and c- fos in vitro. In vivo, the levels of c- jun and c- fos mRNA in OV-1063 tumours were decreased by 43% (P< 0.05) and 45% (P = 0. 05) respectively, after treatment with RC-3940-II at 20 microg per day. Exposure of OV-1063, UCI-107 and ES-2 ovarian carcinoma cells to RC-3940-II at 1 microM concentration for 24 h in vitro, extended the latency period for the development of palpable tumours in nude mice. Our results indicate that antagonists of bombesin/GRP inhibit the growth of OV-1063 ovarian cancers by mechanisms that probably involve the downregulation of c- jun and c- fos proto-oncogenes.

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.

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.

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.

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.

Growth hormone-releasing hormone: an autocrine growth factor for small cell lung carcinoma

Antagonists of growth hormone-releasing hormone (GHRH) inhibit the growth of various cancers in vivo. This effect is thought to be exerted through suppression of the pituitary growth hormone-hepatic insulin-like growth factor I (IGF-I) axis and direct inhibition of autocrine/paracrine production of IGF-I and -II in tumors. However, other evidence points to a direct effect of GHRH antagonists on tumor growth that may not implicate IGFs, although an involvement of GHRH in the proliferation of cancer cells has not yet been established. In the present study we investigated whether GHRH can function as an autocrine/paracrine growth factor in small cell lung carcinoma (SCLC). H-69 and H-510A SCLC lines cultured in vitro express mRNA for GHRH, which apparently is translated into peptide GHRH and then secreted by the cells, as shown by the detection of GHRH-like immunoreactivity in conditioned media from the cells cultured in vitro. In addition, the levels of GHRH-like immunoreactivity in serum from nude mice bearing H-69 xenografts were higher than in tumor-free mice. GHRH(1-29)NH(2) stimulated the proliferation of H-69 and H-510A SCLCs in vitro, and GHRH antagonist JV-1-36 inhibited it. JV-1-36 administered s.c. into nude mice bearing xenografts of H-69 SCLC reduced significantly (P < 0.05) tumor volume and weight, after 31 days of therapy, as compared with controls. Collectively, our results suggest that GHRH can function as an autocrine growth factor in SCLCs. Treatment with antagonistic analogs of GHRH may offer a new approach to the treatment of SCLC and other cancers.

Inhibition of growth of human malignant glioblastoma in nude mice by antagonists of bombesin/gastrin-releasing peptide

The effects of antagonists of bombesin/gastrin-releasing peptide (GRP) on the growth of human malignant glioblastoma cell line U-87MG xenografted into nude mice were evaluated. Nude mice bearing s.c. implanted U-87MG tumors were treated with bombesin/GRP antagonists RC-3095 and RC-3940-II. RC-3095 and RC-3940-II administered s.c. at a dose of 20 micrograms/day for 4 weeks decreased the volume of U-87MG xenografts by 60 and 74%, respectively, compared with controls. RT-PCR analysis showed that U-87MG xenografts expressed mRNA for bombesin receptor subtype (BRS)-1 (GRP receptor) and BRS-2 (neuromedin-B receptor), but the mRNA for GRP ligand was not detected in U-87MG cells suggesting that GRP may stimulate the growth of U-87MG glioblastomas by a paracrine mechanism. The levels of mRNA for c-fos oncogene were decreased by 30-40% in U-87MG tumors treated with RC-3095 or RC-3940-II. In U-373MG glioblastoma cells, which also express BRS-1, and U-87MG cells, cultured in vitro, GRP(14-27) induced the expression of c-fos mRNA, and some c-jun mRNA, in a time-dependent manner with the maximal effect occurring 2 h after the stimulation and a return to basal levels after 8 h. Antagonist RC-3940-II inhibited the stimulation of c-fos by GRP(14-27). Our results indicate that antagonists of bombesin/GRP inhibit the growth of U-87MG glioblastomas by a mechanism that may involve the downregulation of c-fos oncogene.

Targeted cytotoxic analogue of bombesin/gastrin-releasing peptide inhibits the growth of H-69 human small-cell lung carcinoma in nude mice

Recently, we developed a powerful cytotoxic analogue of bombesin AN-215, in which the bombesin-like carrier peptide Gln-Trp-Ala-Val-Gly-His-Leu-psi(CH2-NH)-Leu-NH2 (RC-3094) is conjugated to a potent derivative of doxorubicin, 2-pyrrolinodoxorubicin (AN-201). Small-cell lung carcinomas (SCLCs) are known to express high levels of bombesin receptors. We evaluated whether these receptors could be used for targeting cytotoxic bombesin analogue to H-69 SCLC cells. H-69 cells were xenografted into male nude mice, which then received an intravenous injection of AN-215, cytotoxic radical AN-201, the carrier peptide RC-3094 alone or unconjugated mixture of RC-3094 and AN-201. The levels of mRNA for bombesin receptor subtypes were evaluated by reverse transcription-polymerase chain reaction. In vitro, both the analogue AN-215 and the radical AN-201 showed strong antiproliferative effects on H-69 cells, AN-215 requiring more time to exert its action at 10(-8) M concentration than AN-201. In vivo, the growth of H-69 SCLC tumours was significantly inhibited by the treatment with 200 nmol kg(-1) of AN-215, while equimolar doses of the cytotoxic radical AN-201 or the mixture of AN-201 and the carrier peptide were toxic and produced only a minor tumour inhibition as compared with control groups. mRNA for bombesin receptor subtypes 2 (BRS-2) and 3 (BRS-3) was detected in H-69 tumours. The mRNA levels for BRS-3, but not for BRS-2, were lower in the AN-215-treated tumours as compared with controls. Our results demonstrate that the cytotoxic bombesin analogue AN-215 could be considered for targeted therapy of tumours, such as SCLC, that express bombesin receptors.

Targeted cytotoxic analog of luteinizing hormone-releasing hormone AN-207 inhibits growth of OV-1063 human epithelial ovarian cancers in nude mice

OBJECTIVE

The aim of the study was to investigate the effects of the cytotoxic analog of luteinizing hormone-releasing hormone AN-207 on the growth of the OV-1063 human epithelial ovarian cancers, which express luteinizing hormone-releasing hormone receptor. AN-207 consists of doxorubicin derivative 2-pyrrolinodoxorubicin (AN-201) linked with the carrier [D-lysine6 ]luteinizing hormone-releasing hormone.

STUDY DESIGN

Female nude mice bearing xenografts of OV-1063 ovarian cancers were treated with analog AN-207, cytotoxic radical AN-201, or agonist [D-lysine6 ]luteinizing hormone-releasing hormone. The levels and expression of messenger ribonucleic acid of receptors for luteinizing hormone-releasing hormone and epidermal growth factor were evaluated.

RESULTS

The growth of OV-1063 tumor was significantly inhibited by 3 to 5 nmol AN- 207 but not by [D-lysine6 ]luteinizing hormone-releasing hormone. Cytotoxic radical AN-201 was toxic at these doses. After treatment with AN-207 receptors for luteinizing hormone-releasing hormone were not detectable, epidermal growth factor receptor levels declined, and expressions of their respective messenger ribonucleic acids were decreased.

CONCLUSIONS

Targeted cytotoxic luteinizing hormone-releasing hormone analog AN-207 is less toxic than equimolar doses of its radical 2-pyrrolinodoxorubicin and effectively inhibits ovarian tumor growth. Targeted chemotherapy may improve management of ovarian cancer.

Inhibition of growth, production of insulin-like growth factor-II (IGF-II), and expression of IGF-II mRNA of human cancer cell lines by antagonistic analogs of growth hormone-releasing hormone in vitro

Antagonistic analogs of growth hormone-releasing hormone (GHRH) suppress growth of various tumors in vivo. This effect is exerted in part through inhibition of the GHRH-GH-insulin-like growth factor (IGF)-I axis. Nevertheless, because autocrine/paracrine control of proliferation by IGF-II also is a major factor in many tumors, the interference with this growth-stimulating pathway would offer another approach to tumor control. We thus investigated whether GHRH antagonists MZ-4-71 and MZ-5-156 also act on the tumor cells directly by blocking the production of IGF-II. An increase in the IGF-II concentration in the media during culture was found in 13 of 26 human cancer cell lines tested. Reverse transcription-PCR studies on 8 of these cell lines showed that they also expressed IGF-II mRNA. Antagonists of GHRH significantly inhibited the rate of proliferation of mammary (MDA-MB-468 and ZR-75-1), prostatic (PC-3 and DU-145), and pancreatic (MiaPaCa-2, SW-1990, and Capan-2) cancer cell lines as shown by colorimetric and [3H]thymidine incorporation tests and reduced the expression of IGF-II mRNA in the cells and the concentration of IGF-II secreted into the culture medium. Growth and IGF-II production of lung (H-23 and H-69) and ovarian (OV-1063) cancer cells that express mRNA for IGF-II and excrete large quantities of IGF-II also was marginally suppressed by the antagonists. These findings suggest that antagonistic analogs of GHRH can inhibit growth of certain tumors not only by inhibiting the GHRH-GH-IGF-I axis, but also by reducing the IGF-II production and by interfering with the autocrine regulatory pathway.

Inhibition of the growth of Caki-I human renal adenocarcinoma in vivo by luteinizing hormone-releasing hormone antagonist Cetrorelix, somatostatin analog RC-160, and bombesin antagonist RC-3940-II

BACKGROUND

Metastatic or recurrent renal cell carcinoma (RCC) is a therapeutic challenge because it is resistant to chemotherapy and external radiotherapy. No uniformly effective therapeutic agents are available for the management of patients with RCC. Hormones and growth factors may play a role in promoting the transformation and/or proliferation of kidney neoplasms.

METHODS

Luteinizing hormone-releasing hormone (LH-RH) antagonist Cetrorelix (SB-75), somatostatin analog RC-160, and bombesin antagonist RC-3940-II were tested for their effects on the growth of the Caki-I renal adenocarcinoma cell line xenografted into nude mice.

RESULTS

After 4 weeks of treatment, tumor volume was significantly (P < 0.01) decreased in animals receiving RC-160, to 167.5 +/- 34.2 mm3, compared with the control group (485.7 +/- 77.2 mm3). LH-RH antagonist SB-75 and bombesin antagonist RC-3940-II also significantly reduced the volume of Caki-I tumors, to 159.9 +/- 18.1 and 234.7 +/- 81.8 mm3, respectively. Somatostatin analog RC-160 decreased serum levels for growth hormone (GH) and insulin-like growth factor-I compared with controls. Treatment with RC-160, Cetrorelix, and RC-3940-II significantly reduced the number of high-affinity receptors for epidermal growth factor on Caki-I tumors.

CONCLUSIONS

LH-RH antagonist Cetrorelix, somatostatin analog RC-160, and bombesin antagonist RC-3940-II effectively inhibit the growth of human Caki-I renal adenocarcinomas in nude mice. These peptide analogs should be considered for the therapy of patients with metastatic or recurrent RCC.

Expression of mRNA for luteinizing hormone-releasing hormone receptors and epidermal growth factor receptors in human cancer cell lines

Conventional chemotherapy produces varying degrees of response in patients with many advanced cancers and has significant side effects. Receptors for luteinizing hormone-releasing hormone (LH-RH) are present in a high percentage of human ovarian, prostatic, breast and endometrial tumors and targeted chemotherapy based on cytotoxic analogs of LH-RH might yield better results. The present study was undertaken to determine whether human cancer cell lines express mRNA for LH-RH receptors and epidermal growth factor (EGF) receptors. Using radioligand binding studies, we showed the presence of high-affinity binding sites for LH-RH and EGF in the membranes of human ovarian, prostatic, breast and endometrial cancer cell lines as well as in the JAR choriocarcinoma cell line. The expression of the mRNA for LH-RH receptors and EGF receptors in these cell lines was demonstrated by RT-PCR using specific primers and by subsequent Southern blot analysis. The PCR products obtained were of the expected size, 319 bp for LH-RH receptors and 400 bp for EGF receptors. These findings support the view that cytotoxic analogs of LH-RH could be used for targeted chemotherapy of these cancers. Moreover, the results suggest that these human cancer cell lines might have local regulatory systems for their proliferation based on LH-RH and EGF. Further investigations are required to elucidate the signal transduction pathways involved in the effects of cytotoxic LH-RH analogs on human tumors.

Synthesis and biological evaluation of cytotoxic analogs of somatostatin containing doxorubicin or its intensely potent derivative, 2-pyrrolinodoxorubicin

To create cytotoxic hybrid analogs of somatostatin (SST), octapeptides RC-160 (D-Phe-Cys-Tyr-D-Trp- Lys-Val-Cys-Trp-NH2) and RC-121 (D-Phe-Cys-Tyr-D-Trp- Lys-Val-Cys-Thr-NH2) were linked to doxorubicin (DOX) or its superactive derivative, 2-pyrrolino-DOX (AN-201). The conjugation was performed by coupling N-9-fluorenylmethoxycarbonyl (N-Fmoc)-DOX-14-O-hemiglutarate or 2-pyrrolino-DOX-14-O-hemiglutarate to the amino terminus of [Lys(Fmoc)5]RC-160 yielding AN-163 and AN-258, respectively, after deprotection. The respective cytotoxic conjugates of RC-121 (AN-162 and AN-238) were prepared similarly. In vitro tests on human cancer cell lines-MKN-45 gastric cancer, MDA-MB-231 breast cancer, PC-3 prostate cancer, and MIA PaCa-2 pancreatic cancer-demonstrated that the antiproliferative activity of the cytotoxic radicals in these conjugates was virtually retained. In H-345 human small cell lung carcinoma cell line, conjugates of RC-121 preserved the cytotoxic activity of their radicals, but the hybrids with RC-160 showed approximately 10 times lower activity. The ability of the carriers and the hybrids to inhibit the binding of 125I-labeled RC-160 to receptors for SST on rat pituitary membrane preparation was also determined. The cytotoxic conjugates inhibited 50% of the specific binding of the radioligand in the nanomolar concentration range (IC50 < 80 nM). When SST-like activities of AN-238 and its carrier, RC-121, were compared in the rat pituitary superfusion system, both compounds were found to suppress a stimulated growth hormone release at nanomolar concentrations. Preliminary studies in animal models of breast and prostate cancers showed that AN-238 is less toxic than AN-201 and more potent in inhibiting tumor growth. These highly active cytotoxic analogs of SST have been designed as targeted antitumor agents for the treatment of various cancers expressing receptors for SST octapeptides.

Growth inhibition of human ovarian cancers by cytotoxic analogues of luteinizing hormone-releasing hormone

BACKGROUND

Receptors for luteinizing hormone-releasing hormone (LH-RH) are found in nearly 80% of human ovarian cancers. The chemotherapeutic agent doxorubicin can be linked to [D-lysine6]LH-RH to form a cytotoxic analogue (AN-152) that may have greater specificity for tumor cells. This study was conducted to investigate the effects of AN-152 on the growth of LH-RH receptor-positive OV-1063 human epithelial ovarian cancers.

METHODS

Nude mice bearing human ovarian tumors, OV-1063 or UCI-107 (LH-RH receptor negative), were injected intraperitoneally with saline (control) or with equimolar doses of AN-152 or doxorubicin; experiments involving mice with OV-1063 tumors also included groups that were administered [D-lysine6]LH-RH either alone or in combination with doxorubicin. Tumor volume, weight, doubling time, and burden (i.e., tumor weight/body weight) as well as tumor apoptotic and mitotic indices were determined. The levels of receptors for LH-RH and epidermal growth factor (EGF) and their messenger RNAs were measured by use of radioreceptor and reverse transcription-polymerase chain reaction assays, respectively.

RESULTS

The growth of OV-1063 ovarian tumors in nude mice, as based on reduction in tumor volume, was inhibited significantly (all P<.05, two-sided) 4 weeks after treatment with AN-152, even at the lowest dose tested (413 nmol/20 g weight); the toxic effects of an equivalent dose of doxorubicin caused substantial mortality. High-affinity receptors for LH-RH and EGF were found on cell membranes of OV-1063 cancers; however, after in vivo treatment with AN-152, LH-RH receptor-binding sites were not detectable and EGF receptors were reduced in number. The growth of UCI-107 ovarian cancers was not inhibited by AN-152.

CONCLUSIONS

In nude mice bearing LH-RH receptor positive OV-1063 epithelial ovarian cancers, systemic administration of AN-152 is less toxic and inhibits tumor growth better than equimolar doses of doxorubicin.

Growth hormone-releasing hormone antagonist MZ-4-71 inhibits in vivo proliferation of Caki-I renal adenocarcinoma

In view of evidence that growth hormone (GH) and insulin-like growth factors (IGF) may play a role in the development of renal cell carcinoma (RCC), we investigated the effects of growth hormone-releasing hormone (GH-RH) antagonist MZ-4-71 on the proliferation of the human renal adenocarcinoma cell line Caki-I in vitro and in vivo. Male nude mice bearing xenografts of human Caki-I RCC were treated for 4 weeks with MZ-4-71 injected s.c. twice daily at a dose of 20 microg per animal. Tumor growth, serum, liver, and tumor IGF levels and IGF-I receptor concentrations in Caki-I cell membranes were measured. After 4 weeks of therapy, the final volume of Caki-I tumors in nude mice treated with MZ-4-71 was significantly (P < 0.01) decreased to 52.6 +/- 12.3 mm3 as compared with controls that measured 504.2 +/- 104.1 mm3. Treatment with GH-RH antagonist also significantly reduced tumor weight, serum levels of GH and IGF-I, liver concentrations of IGF-I, and tumor levels of IGF-I and IGF-II. High-affinity binding sites for IGF-I were detected in the cell membranes of Caki-I tumors. IGF-I and IGF-II stimulated the proliferation of Caki-I cells in tissue cultures. Antagonist MZ-4-71 could inhibit in vitro growth of Caki-I cells, but only at high concentrations. Our findings demonstrate that GH-RH antagonist MZ-4-71 can significantly inhibit the growth of Caki-I RCC. MZ-4-71 may exert its suppressive effect on tumor growth through a reduction in GH release from the pituitary and the subsequent decrease in the production of IGF-I in the liver and IGF-I and II by the tumors. The efficacy of MZ-4-71 suggests that this compound could be considered for the therapy of recurrent or metastatic RCC.

Design, synthesis, and in vitro evaluation of cytotoxic analogs of bombesin-like peptides containing doxorubicin or its intensely potent derivative, 2-pyrrolinodoxorubicin

Five peptide fragments, based on the C-terminal sequence of bombesin (BN)-(6-14) or BN-(7-14), were selected as carriers for radicals doxorubicin (DOX) and 2-pyrrolino-DOX to create hybrid cytotoxic analogs. All these compounds had a reduced peptide bond (CH2-NH or CH2-N) between positions 13 (Phe or Leu) and 14 (Phe, Leu, or Tac) (Tac = thiazolidine-4-carboxylic acid). Three pseudononapeptide carriers contained N-terminal D-Phe or D-Tpi at position 6 (Tpi = 2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole-3-carboxylic acid). Two pseudooctapeptides had Gln7 at the N terminus. The conjugation of N-(9-fluorenylmethoxycarbonyl) doxorubicin (N-Fmoc-DOX)-14-O-hemiglutarate to the peptide carriers at the N terminus resulted in cytotoxic hybrids of BN-like peptides containing DOX. These hybrids could then be converted to analogs with 2-pyrrolino-DOX by a reaction with 4-iodobutyraldehyde. The ability of the carriers and the conjugates to inhibit the binding of 125I-labeled [Tyr4]BN to receptors for BN/gastrin releasing peptide (GRP) on Swiss 3T3 cells was determined. Cytotoxic conjugates of pseudooctapeptide carrier analogs displayed the highest binding affinity (KD approximately 1 nM). The cytotoxic BN analogs and their corresponding cytotoxic radicals exerted similar inhibitory effects on the in vitro growth of CFPAC-1 human pancreatic cancer, DMS-53 human lung cancer, PC-3 human prostate cancer, and MKN-45 human gastric cancer cell lines that have receptors for BN/GRP. In DMS-53 cells, the activity of 2-pyrrolino-DOX and its conjugates was approximately 2500 times higher than that of DOX and its hybrids. These highly potent cytotoxic analogs of BN have been designed as targeted anti-tumor agents for the treatment of various cancers that possess receptors for BN/GRP.

Inhibition of in vivo proliferation of androgen-independent prostate cancers by an antagonist of growth hormone-releasing hormone

Tumour-inhibitory effects of a new antagonist of growth hormone-releasing hormone (GH-RH), MZ-4-71, were evaluated in nude mice bearing androgen-independent human prostate cancer cell lines DU-145 and PC-3 and in Copenhagen rats implanted with Dunning R-3327 AT-1 prostatic adenocarcinoma. After 6 weeks of therapy, the tumour volume in nude mice with DU-145 prostate cancers treated with 40 microg day(-1) MZ-4-71 was significantly decreased to 37 +/- 13 mm3 (P < 0.01) compared with controls that measured 194 +/- 35 mm3. A similar inhibition of tumour growth was obtained in nude mice bearing PC-3 cancers, in which the treatment with MZ-4-71 for 4 weeks diminished the tumour volume to 119 +/- 35 mm3 compared with 397 +/- 115 mm3 for control animals. Therapy with MZ-4-71 also significantly decreased weights of PC-3 and DU-145 tumours and increased tumour doubling time. Serum levels of GH and IGF-I were significantly decreased in animals treated with GH-RH antagonist. In PC-3 tumour tissue, the levels of IGF-I and IGF-II were reduced to non-detectable values after therapy with MZ-4-71. The growth of Dunning R-3327 AT-1 tumours in rats was also significantly inhibited after 3 weeks of treatment with 100 microg of MZ-4-71 day(-1) i.p. as shown by a reduction in tumour volume and weight (both P-values < 0.05). Specific high-affinity binding sites for IGF-I were found on the membranes of DU-145, PC-3 and Dunning R-3327 AT-1 tumours. Our results indicate that GH-RH antagonist MZ-4-71 suppresses growth of PC-3, DU-145 and Dunning AT-1 androgen-independent prostate cancers, through diminution of GH release and the resulting decrease in the secretion of hepatic IGF-I, or through mechanisms involving a lowering of tumour IGF-I levels and possibly an inhibition of tumour IGF-I and IGF-II production. GH-RH antagonists could be considered for further development for the therapy of prostate cancer, especially after the relapse.

Cytotoxic analogs of luteinizing hormone-releasing hormone containing doxorubicin or 2-pyrrolinodoxorubicin, a derivative 500-1000 times more potent

Doxorubicin (DOX) and its daunosamine-modified derivative, 2-pyrrolino-DOX, which is 500-1000 times more active than DOX, were incorporated into agonistic and antagonistic analogs of luteinizing hormone-releasing hormone (LH-RH). The conjugation of DOX with LH-RH analogs was performed by using N-(9-fluorenylmethoxycarbonyl)-DOX-14-O-hemiglutarate, a dicarboxylic acid ester derivative of DOX. Coupling this derivative covalently to the epsilon-amino group of the D-Lys side chain of agonist [D-Lys6]LH-RH or antagonistic analog AC-D-Nal(2)-D-Phe(4Cl)-D-Pal(3)-Ser-Tyr-D-Lys-Leu-Arg-Pro-D-Ala-NH 2 [where Nal(2) = 3-(2-naphthyl)alanine, Pal(3) = 3-(3-pyridyl)alanine, and Phe(4CI) = 4-chlorophenylalanine] was followed by the removal of the 9-fluorenylmethoxycarbonyl protective group to yield cytotoxic derivatives of LH-RH analogs containing DOX. From these DOX containing LH-RH hybrids, intensely potent analogs with daunosamine-modified derivatives of DOX can be readily formed. Thus, cytotoxic LH-RH agonist containing DOX (AN-152) can be converted in a 66% yield by a reaction with a 30-fold excess of 4-iodobutyraldehyde in N,N-dimethylformamide into a derivative having 2-pyrrolino-DOX (AN-207). Hybrid molecules AN-152 and AN-207 fully preserve the cytotoxic activity of their radicals, DOX or 2-pyrrolino-DOX, respectively, in vitro, and also retain the high binding affinity of the peptide hormone portion of the conjugates to rat pituitary receptors for LH-RH. These highly potent cytotoxic analogs of LH-RH were designed as targeted anti-cancer agents for the treatment of various tumors that possess receptors for the carrier peptide. Initial in vivo studies show that the hybrid molecules are much less toxic than the respective cytotoxic radicals incorporated and significantly more active in inhibiting tumor growth.

High yield conversion of doxorubicin to 2-pyrrolinodoxorubicin, an analog 500-1000 times more potent: structure-activity relationship of daunosamine-modified derivatives of doxorubicin

A convenient, high yield conversion of doxorubicin to 3'-deamino-3'-(2''-pyrroline-1''-yl)doxorubicin is described. This daunosamine-modified analog of doxorubicin is 500-1000 times more active in vitro than doxorubicin. The conversion is effected by using a 30-fold excess of 4-iodobutyraldehyde in anhydrous dimethylformamide. The yield is higher than 85%. A homolog of this compound, 3'-deamino-3'-(1'',3''-tetrahydropyridine-1''-yl)doxorubicin, was also synthesized by using 5-iodovaleraldehyde. In this homolog, the daunosamine nitrogen is incorporated into a six- instead of a five-membered ring. This analog was 30-50 times less active than its counterpart with a five-membered ring. A similar structure-activity relationship was found when 3'-deamino-3'-(3''-pyrrolidone-1''-yl)doxorubicin (containing a five-membered ring) and 3'-deamino-3'-(3''-piperidone-1''-yl)doxorubicin (with a six-membered ring) were tested in vitro, the former being 5 times more potent than the latter. To further elucidate structure-activity relationships, 3'-deamino-3'-(pyrrolidine-1''-yl)doxorubicin, 3'-deamino-3'-(isoindoline-2''-yl)doxorubicin, 3'-deamino-3'-(2''-methyl-2''-pyrroline-1''-yl)doxorubicin, and 3'-deamino-3'-(3''-pyrroline-1''-yl)doxorubicin were also synthesized and tested. All the analogs were prepared by using reactive halogen compounds for incorporating the daunosamine nitrogen of doxorubicin into a five- or six-membered ring. These highly active antineoplastic agents can be used for incorporation into targeted cytotoxic analogs of luteinizing hormone-releasing hormone intended for cancer therapy.

Inhibition of growth of human osteosarcomas by antagonists of growth hormone-releasing hormone

BACKGROUND

Insulin-like growth factor I (IGF-I) may be involved in the proliferation of human osteosarcomas. Most of the IGF-I found in blood is produced in the liver, where transcription of the IGF-I gene is regulated by growth hormone (GH). Recently, we synthesized various potent antagonists of GH-releasing hormone (GH-RH), including [Ibu0, D-Arg2, Phe(4-Cl)6, Abu15, Nle27]hGH-RH(1-28)Agm, which is also called MZ-4-71.

PURPOSE

We investigated the effects of this antagonist on the growth of the human osteosarcoma cell lines SK-ES-1 and MNNG/HOS, transplanted into nude mice or cultured in vitro.

METHODS

Nude male mice bearing SK-ES-1 and MNNG/HOS tumors were treated for 4 and 3 weeks, respectively, with MZ-4-71 administered from osmotic minipumps at a dose of 40 micrograms per animal per day. Tumor volume, tumor weight, and levels of receptors for IGF-I were determined. IGF-I levels in serum, tumor, and liver tissue were measured by radioimmunoassay. In other experiments, tumor-bearing nude mice were treated subcutaneously for 3 weeks with the GH-RH agonist hGH-RH(1-29)NH2 or with MZ-4-71 for 13 days at doses of 50 micrograms per animal per day. Effects of MZ-4-71, hGH-RH(1-29)NH2, and human GH (hGH) on cell proliferation and on the production of IGF-I and cyclic adenosine monophosphate were also evaluated in SK-ES-1 and MNNG/HOS cells in vitro.

RESULTS

The growth of SK-ES-1 and MNNG/HOS tumors in nude mice was significantly inhibited by MZ-4-71, as measured by a reduction in tumor volume and weight (all P values < .05). MZ-4-71 treatment of either SK-ES-1 or MNNG/HOS tumor-bearing animals decreased tumor tissue IGF-I levels. The growth of MNNG/HOS xenografts was stimulated by hGH-RH(1-29)NH2 (P < .01). IGF-I levels in serum of tumor-bearing nude mice treated subcutaneously for 13 days with MZ-4-71 were decreased (both P values < .01). High-affinity binding sites for IGF-I were demonstrated on cell membranes of SK-ES-1 and MNNG/HOS tumors. In cell cultures of both osteosarcomas, IGF-I production was stimulated by 25 ng/mL hGH but was not changed by 10 ng/mL hGH-RH(1-29)NH2 or 5 microM MZ-4-71. Incorporation of [3H]thymidine into DNA in SK-ES-1 (but not MNNG/HOS) cells was increased by 25 ng/mL IGF-I (P < .01). The proliferation rate of the two cell lines was not affected by 5-50 ng/mL hGH-RH(1-29)NH2 or 1-80 ng/mL hGH but was suppressed by 10(-6)-10(-5) M MZ-4-71.

CONCLUSIONS

Our findings demonstrate that the GH-RH antagonist MZ-4-71 can significantly inhibit the growth of SK-ES-1 and MNNG/HOS osteosarcomas in mice.

Potent bombesin antagonists with C-terminal Leu-psi(CH2-N)-Tac-NH2 or its derivatives

Various pseudononapeptide bombesin (BN)-(6-14) antagonists with a reduced peptide bond (CH2-NH) between positions 13 and 14 can suppress the mitogenic activity of BN or gastrin-releasing peptide in 3T3 fibroblast cells and small cell lung carcinoma. In the search for more potent BN antagonists, 10 modified nonapeptide BN antagonists containing N-terminal D-Phe, D-Cpa, and D- or L-Tpi and C-terminal Leu-psi(CH2-N)-Tac-NH2, Leu-psi(CH2-N)-MeTac-NH2, or Leu-psi(CH2-N)-Me2Tac-NH2 have been synthesized by incubating [13 psi 14,CH2-NH,Cys14]BN-(6-14) or [13 psi 14-CH2-NH,Pen14]BN-(6-14) with formaldehyde or acetaldehyde (Cpa = 4-chlorophenylalanine, Tac = thiazolidine-4-carboxylic acid, Tpi = 2,3,4,9-tetrahydro-1H- pyrido[3,4-b]indol-3-carboxylic acid, and Pen = penicillamine). The biological activities of these compounds were then evaluated. [D-Phe6,13 psi 14,CH2-N,Tac14]BN-(6-14) (RC-3950-II) and [D-Phe6,13 psi 14,CH2-N,Me2Tac14]BN-(6-14) (RC-3985-II) exhibited greater potency in inhibition of 125I-labeled [Tyr4]BN binding to Swiss 3T3 cells than their parent compounds [D-Phe6,13 psi 14,CH2-NH,Cys14]BN-(6-14) (RC-3950-I) and [D-Phe6,13 psi 14,CH2-NH,Pen14]BN-(6-14) (RC-3985-I). The order of binding affinities of these compounds was as follows: [13 psi 14,CH2-N,Tac14]BN-(6-14) > [13 psi 14,CH2-N,Me2Tac14]BN-(6-14) > [13 psi 14,CH2-N,MeTac14]BN-(6-14). In most cases, the analogs with C-terminal Leu-psi(CH2-N)-Tac-NH2 were also more potent growth inhibitors of 3T3 cells than compounds containing C-terminal Leu-psi(CH2-N)-Me2Tac-NH2 or Leu-psi(CH2-N)-MeTac-NH2. The best BN antagonists of this series, RC-3950-II and [D-Cpa6,13 psi 14,CH2-N,Tac14]BN- (6-14) (RC-3925-II), inhibited gastrin-releasing peptide-stimulated growth of Swiss 3T3 cells with IC50 values of 1 nM and 6 nM, respectively. Since antagonists of this class inhibit growth of various tumors in animal cancer models, some of them may have clinical applications.

Enhanced frequency of spontaneous B cell lines from Epstein-Barr virus (EBV) seropositive donors 80 years and older

Based on the well-recognized decline in immunocompetence which develops with advancing age, we have evaluated the effect of age on the frequency of development of spontaneous Epstein-Barr virus (EBV)-infected B cell lines. Blood mononuclear cells were isolated from 38 clinically healthy seropositive donors. The cells were maintained in vitro according to routine culture conditions for lymphocytes. Eight spontaneously EBV-infected B lymphoblastoid cell lines (LCL) were isolated. The LCL developed in 12.5, 14.3, or 6.3% of the samples derived from donors in the three age groups 20-39, 40-59, 60-79, respectively. In contrast, samples from five of seven (71%) donors 80 years and older yielded LCL. Although the reason(s) for the increased frequency of occurrence of spontaneous LCL from the older adults is yet to be explored, the possible role of the virus-specific T lymphocytes as a contributing factor is discussed.