Targeted cytotoxic analogue of luteinizing hormone-releasing hormone (LH-RH) only transiently decreases the gene expression of pituitary receptors for LH-RH

Epigenetic repression of gonadotropin gene expression via a GnRH-mediated DNA delivery system

The reproductive axis is activated by gonadotropin-releasing hormone (GnRH), which stimulates the pituitary gonadotropes to secrete hormones that drive gonadal function and steroidogenesis. Thus repression of this axis, which is conserved across mammals and sexes, can reduce steroid levels and/or prevent reproduction. Steroid-dependent pathologies, including various cancers, are commonly treated with GnRH super-analogs which have long-term side-effects, while humane solutions for controlling reproduction in domestic and wild animal populations are lacking. GnRH-conjugated toxins are undergoing clinical trials for GnRHR-expressing cancer cells, and have been examined for gonadotrope ablation in animals, but showed low and/or transient effects and administration of toxins has many potential complications. Here we exploit GnRH targeting to gonadotropes to deliver DNA encoding an effector that induces gonadotropin gene repressive epigenetic modifications which are perpetuated over time. Several layers of specificity are endowed through targeting to GnRHR-expressing cells and due to local cleavage of the peptide packaging the DNA; the DNA-encoded effector is expressed and directed to the target genes by the DNA binding domain of a highly specific transcription factor. This design has multiple advantages over existing methods of shutting down the reproductive axis, and its modular design should allow adaptation for broad applications.

Characterization of luteinizing hormone-releasing hormone receptor type I (LH-RH-I) as a potential molecular target in OCM-1 and OCM-3 human uveal melanoma cell lines

Introduction

Uveal melanoma (UM) is the most common primary intraocular malignancy with very poor prognosis. Conventional chemotherapy only rarely prolongs the survival, therefore patients require novel treatment modalities. The discovery of specific receptors for hypothalamic hormones on cancer cells has led to the development of radiolabeled and cytotoxic hormone analogs.

Materials and methods

In the present study, our aim was to investigate the expression of mRNA for receptors of luteinizing hormone-releasing hormone type I (LH-RH-I) and LH-RH ligand in OCM-1 and OCM-3 human uveal melanoma cell lines. The presence and binding characteristics of LH-RH-I receptor protein was further studied by Western blot, immunocytochemistry and ligand competition assay. The expression of mRNA and protein for LH-RH-I receptors has been also studied using tumor samples originating from nude mice xenografted with OCM-1 or OCM-3 cells.

Results

The mRNA for LH-RH-I receptor has been detected in OCM-1 and OCM-3 cell lines and was found markedly higher in OCM-3 cells. The mRNA for LH-RH-I receptors was also observed in both UM xenograft models in vivo with higher levels in OCM-3. The presence of LH-RH-I receptor protein was found in both cell lines in vitro by immunocytochemistry and Western blot, and also in tumor tissue samples grown in nude mice by Western blot. Both human uveal melanoma models investigated showed specific high affinity receptors for LH-RH-I using ligand competition assay. The mRNA for LH-RH ligand has also been detected in OCM-1 and OCM-3 cell lines and cancer tissues.

Conclusion

The demonstration of the expression of LH-RH-I receptors in OCM-1 and OCM-3 human UM cell lines suggests that they could serve as potential molecular target for therapy. Our findings support the development of new therapeutic approaches based on cytotoxic LH-RH analogs or modern powerful antagonistic analogs of LH-RH targeting LH-RH-I receptors in UM.

Human Malignant Melanomas Express Receptors for Luteinizing Hormone Releasing Hormone Allowing Targeted Therapy with Cytotoxic Luteinizing Hormone Releasing Hormone Analogue

Cytotoxic analogue of luteinizing hormone releasing hormone (LHRH), AN-207, binds with high affinity to LHRH receptors and can be targeted to tumors expressing these receptors. We investigated the expression of LHRH receptors in surgical specimens of human malignant melanoma and evaluated the effects of AN-207 in models of human melanoma. Human melanoma specimens derived from primary tumors or metastases were examined for LHRH receptor expression by immunohistochemistry. Binding assays, Western immunoblotting, and reverse transcription-PCR analyses were used to investigate LHRH receptors in MRI-H255 and MRI-H187 transplantable human melanoma tumor lines. Antitumor effects of AN-207 and its components were evaluated in vivo in nude mice bearing xenografts of either melanoma tumor line. All 19 human melanoma specimens examined showed positive staining for LHRH receptors. The mRNA for LHRH receptors, receptor protein and binding sites for LHRH were detected in both transplantable melanoma tumor lines. AN-207 significantly inhibited the growth of MRI-H255 and MRI-H187 xenografts in vivo, reducing tumor volume by 59.9% to 79.2% and tumor weight by 61.0% to 76.9% (all P < 0.05). The components of AN-207 (LH-RH analogue carrier and cytotoxic radical AN-201 as single drugs or as an unconjugated mixture) had no significant effects. Blockade of LHRH receptors by an excess of LHRH agonist Decapeptyl suppressed the effects of AN-207. LHRH receptors are expressed in a very high percentage of human malignant melanoma specimens and can be used for targeted chemotherapy with cytotoxic LHRH analogue AN-207.

New approaches to treatment of various cancers based on cytotoxic analogs of LHRH, somatostatin and bombesin

The development of targeted cytotoxic analogs of hypothalamic peptides for the therapy of various cancers is reviewed and various oncological studies on experimental tumors are summarized. Novel therapeutic modalities for breast, prostate and ovarian cancer consist of the use of targeted cytotoxic analogs of LH-RH containing doxorubicin (DOX) or 2-pyrrolino-DOX. The same radicals have been incorporated into cytotoxic analogs of somatostatin which can be also targeted to receptors for this peptide in prostatic, mammary, ovarian, renal and lung cancers, brain tumors and their metastases. A targeted cytotoxic analog of bombesin containing 2-pyrrolino-DOX has also been synthesized and successfully tried in experimental models of prostate cancer, small cell lung carcinoma and brain tumors. The development of these new classes of peptide analogs should lead to a more effective treatment for various cancers.