d Lt n 1. Introduction io 2. LH-RHK antagonistst versus U u , a ib ad tr lo 3.m LH-RHagonists antagonists n r is ow . fo D d se Luteinizing hormone-releasing 4. LH-RH antagonists an for l u In l c a a rs on 9 i e rs hormone antagonists 0 fertilizationrc us e 0 5. LH-RH antagonistsd r p in tumor e e fo 2 m ris y Ga ´ © ho op † bor Mezo 6.m Cetrorelixtherapyt (CET) c E€ t Au e otv h o . gl 1117 Budapest,os€ Lora Pa 7.C Abarelixd in ig ite s in vitro † r r ib a ´ o8. Ganirelixh t Background: nd University,& Marilena Hungarian Manea Academy of Sciences, Research Group of Peptide Chemistry, y ro rin p le p p role in the vertebrate reproduction by regulating gonadal activity. Based on o a 9.se LH-RHnd antagonists: new C S u a its binding to pituitary´zma LH-RH receptors, as well as to LH-RH receptors ed w ´ r is ie ny P. stny. 1/A, Hungary o or , vcandidates for clinical expressed on cancerLuteinizing cells, LH-RH hormone-releasing agonists and antagonists hormone have (LH-RH) been plays devel- a central f th ay t u 10.pl Orallyapplications active non-peptidic oped for different therapeutic applications. o na is N U d an overview of the most relevant LH-RH antagonists and their therapeutic Review applications. Recently patented compounds as well as drug formulations and 11. Expertantagonists opinion of LH-RH receptors dosage are presented. applications in osis and in the treatment of hormone-dependent tumors. Work in progress is focused on further development of both peptidic and orally active non-peptidic LH-RH antagonists. in vitro Keywords: Conclusion: luteinizing hormone-releasing hormone, LH-RHfertilization, antagonists, non-peptidic benign prostatic LH-RH hyperplasia, antagonists, endometri- tumor therapy gonadotropin-releasing hormone, hormone-dependent tumors, Objective/method: LH-RH antagonists have found clinical Expert Opin. Ther. Patents (2009) 1. Introduction Here we give The hypothalamic decapeptide luteinizing hormone-releasing hormone (LH-RH; Glp-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH ing hormone (GnRH), was discovered in 1971 by Andrew V. Schally and his colleagues 19 structure and synthesis.) The primary biological function(12):1771-1785 of LH-RH is the regulation of the gonadal activity by releasing gonadotropic hormones, luteinizing hormone [1] (LH) and follicle stimulating. (Schally’s hormone group was (FSH), the first from to the accomplish anteriorpituitary its isolation, gland, elucidation that of act on the female and male gonads to trigger the gametogenesis, as well as the synthesis in vitro and release of sex-steroids. Therefore, this neurohormone plays a central role in vertebrate reproduction fertilization, thalamic neurons exposure to LH-RH results in the suppression of gonadotropin and sex-steroid secretion due to the desensitization of gonadotropic cells and the downregulation of pituitary LH-RH receptors (LH-RH-Rs) 2 ), also called gonadotropin-releas- medical approach to therapy[3] of hormone-dependent tumors such as prostate and [2] breast tumors, benign prostatic hyperplasia,and it has. LH-RH a endometriosisshort half-life is secreted and in female a pulsatile infertility fashion by the hypo- Since the discovery of LH-RH, 23 natural isoforms have been identified thousand synthetic agonists and antagonists have been developed and some of them have found therapeutic applications (e.g., buserelin, goserelin, triptorelin and leuprolide as superagonists; cetrorelix, abarelix and ganirelix as antagonists) in vivo 2. LH-RH antagonists versus agonists [5] of 2 – 5 min By modifying the Gly . The observed chemical castration is a derivatives can be produced. Gly [4] . Continuous 6 and Gly 10 6 in mammalian LH-RH (LH-RH-I), superagonist is replaced by D-amino acid derivatives with bulky [7] , several[6] . [8] . 1771 Luteinizing hormone-releasing hormone antagonists A. LH-RH agonist B. LH-RH antagonist IVF Endometriosis and BPH Cancer Castration level Serum hormone level Serum hormone level 10 20 Days 4 8 12 24 Hours Figure 1. Effect of LH-RH agonists (A) and antagonists (B) on serum hormone levels (e.g., LH, FSH, testosterone, estradiol levels). BPH: Benign prostatic hyperplasia; IVF: In vitro fertilization; LH-RH: Luteinizing hormone-releasing hormone. apolaric side chain (Leu, Trp, Ser(tBu), His(Bzl)), while Pro9- variety of amino acid derivatives have been substituted 10 Gly -NH2 is modified as Pro-NHEt or Pro-Azgly-NH2 [9]. (Figure 2). At present, cetrorelix (Æterna Zentaris), abarelix Compared to the natural LH-RH, five or more substitutions (Preacis) and ganirelix (Organon, Inc.) are on the market, of the amino acids in positions 1 – 3, 6, 10, (5, 8) are required while antarelix/teverelix (Ardana), degarelix (Ferring Pharma- for the preparation of antagonists [10]. ceutical), ozarelix (Æterna Zentaris), ornirelix (Oakwood Lab- The main difference between LH-RH antagonists and oratories), iturelix (Ares Serono), azaline B and acyline agonists is represented by their mode of action on the release (NICHD/Salk Institute) are in clinical trials (Table 1) [15-26]. of gonadotropins. After an initial stimulatory effect, the The main areas where LH-RH antagonists are or could be agonists lead to the desensitization of gonadotropic cells recommended are the in vitro fertilization (IVF), benign and to a decrease in the number of LH-RH-R on the cell prostatic hyperplasia (BPH), endometriosis and cancer ther- membrane (downregulation), followed by the reduction of LH apy [10,26-28]. The administration of LH-RH antagonists leads and FSH release [10,11]. The blockade of the production of to a reduction of serum hormone levels in a dose-dependent gonadotropins results in the inhibition of sex-steroid produc- manner. Since the hormone level required for various ther- tion. The complete inhibition can be reached in 15 – 20 days, apeutic applications is different (Figure 1B), the dose of LH- causing a subsequent delay in the therapeutic benefit RH antagonists must be carefully chosen. In the case of IVF, (Figure 1A) [12]. The temporary increase of sex-steroids (e.g., the complete hormonal withdrawal should be avoided, while testosterone surge) can exacerbate the hormone-sensitive can- chemical castration is needed for efficient tumor therapy. The cers and may cause catastrophic flare events such as spinal-cord attainment of a low, but not completely reduced hormone compression and urinary-tract obstruction. This clinical flare level in BPH and endometriosis is also recommended [12]. should be avoided especially in the case of cancer metasta- Some of the LH-RH antagonists such as cetrorelix and sis [13]. The application of LH-RH antagonists results in an ganirelix are efficient in IVF and employed for assisted immediate decrease of LH and FSH levels by a rapid, but reproduction technology (ART) treatment [11]. However, reversible blockade of LH-RH-Rs without any flare abarelix is not suitable for this application, but it is effective (Figure 1B). However, many of the first and second generation in tumor therapy [29]. At present, abarelix is the only LH-RH antagonists showed anaphylactic reactions due to the hista- antagonist clinically used as an antineoplastic agent. The mine release, which prevented their application in clinical studies with cetrorelix indicate that the dosage of the LH- trials [10,14]. This side effect was greatly reduced in the third RH antagonist might influence the therapeutic application [12]. generation LH-RH antagonists (e.g., cetrorelix, ganirelix). A low dose for IVF (clinical application) [11,12], a medium dose Some of these antagonists are currently on the market and for BPH (Phase III clinical trial) [12,29] and a high dose for the others are in clinical trials. prostate cancer treatment (Phase I clinical trial) are neces- sary [12]. However, the high dose might cause unwanted side 3. LH-RH antagonists effects due to the fact that cetrorelix has higher histamine- releasing properties than other LH-RH antagonists such as The most promising third and fourth generation LH-RH abarelix, ganirelix and degarelix [30]. Therefore, in addition to antagonists contain Ac-D-Nal-D-Cpa-D-Pal in the N-terminal new compounds (e.g., degarelix [31], ozarelix [32], non-peptidic part and D-Ala in position 10. In positions 5, 6 and 8, a large antagonists [33]), most of the recent patents are focused on the 1772 Mezo & Manea Cl O OH O O R1 O R3 O R5 H H HN N N N O N N N N H H H H O R O O R2 O 4 N N NH H 2 N O R1 = H (Tyr), CH3 (N-Me-Tyr) O N OH HN NH H R2 = N HN O O O Tyr Aph(Hor) Lys(Pic) N HN N H N H NH N 2 N HN O O O Lys(Nic) Aph(Ac) Aph(Atz) Figure 2. Chemical structures of LH-RH antagonists. 6Anic: 6-Aminonicotinoyl; Aph: 4-Aminophenylalanine; Atz: 5¢-(3¢-Amino-1H-1¢,2¢,4¢-triazolyl); Cit: Citruline; Cba: Carbamoyl; Cpa: 4-Chlorophenylalanine; Et: Ethyl; hArg: Homoarginine; hCit: Homocitruline; Hor: L-Hydroorotyl; iPr: Isopropyl; LH-RH: Luteinizing hormone-releasing hormone; Nal: 2-Naphtylalanine; Nic: Nicotinoyl; Nle: Norleucine; Pal: 3-Pyridylalanine; Pic: Picoloyl. development of drug formulations [34,35], dosage [36] and a patients [39,40]. Both LH-RH agonists and antagonists are more convenient route of administration [37,38]. used in ovarian stimulation for IVF. Due to their different mechanisms of action, the antagonists have several advantages 4. LH-RH antagonists for in vitro fertilization in comparison with the agonists [10,41]. In contrast to LH-RH agonists, the increase of the premature LH can be prevented The in vitro fertilization process involves controlled ovarian easier and faster by antagonists (within a few hours instead of stimulation (COS) to stimulate the follicular growth.