Rationally designed cyclic analogues of luteinizing hormone-releasing hormone: enhanced enzymatic stability and biological properties

Rational Design, Synthesis and Binding Affinity Studies of Anthraquinone Derivatives Conjugated to Gonadotropin-Releasing Hormone (GnRH) Analogues towards Selective Immunosuppression of Hormone-Dependent Cancer

Gonadotropin-releasing hormone (GnRH) is pivotal in regulating human reproduction and fertility through its specific receptors. Among these, gonadotropin-releasing hormone receptor type I (GnRHR I), which is a member of the G-protein-coupled receptor family, is expressed on the surface of both healthy and malignant cells. Its presence in cancer cells has positioned this receptor as a primary target for the development of novel anti-cancer agents. Moreover, the extensive regulatory functions of GnRH have underscored decapeptide as a prominent vehicle for targeted drug delivery, which is accomplished through the design of appropriate conjugates. On this basis, a rationally designed series of anthraquinone/mitoxantrone-GnRH conjugates (con1-con8) has been synthesized herein. Their in vitro binding affinities range from 0.06 to 3.42 nM, with six of them (con2-con7) demonstrating higher affinities for GnRH than the established drug leuprolide (0.64 nM). Among the mitoxantrone based GnRH conjugates, con3 and con7 show the highest affinities at 0.07 and 0.06 nM, respectively, while the disulfide bond present in the conjugates is found to be readily reduced by the thioredoxin (Trx) system. These findings are promising for further pharmacological evaluation of the synthesized conjugates with the prospect of performing future clinical studies.

Discovery of a stable tripeptide targeting the N-domain of CRF1 receptor

The corticotropin-releasing factor (CRF) and its CRF1 receptor (CRF₁R) play a central role in the maintenance of homeostasis. Malfunctioning of the CRF/CRF₁R unit is associated with several disorders, such as anxiety and depression. Non-peptide CRF₁R-selective antagonists have been shown to exert anxiolytic and antidepressant effects on experimental animals. However, none of them is in clinical use today because of several side effects, thus demonstrating the need for the development of other more suitable CRF₁R antagonists. In an effort to develop novel CRF₁R antagonists we designed, synthesized and chemically characterized two tripeptide analogues of CRF, namely (R)-LMI and (S)-LMI, having their Leu either in R (or D) or in S (or L) configuration, respectively. Their design was based on the crystal structure of the N-extracellular domain (N-domain) of CRF₁R/CRF complex, using a relevant array of computational methods. Experimental evaluation of the stability of synthetic peptides in human plasma has revealed that (R)-LMI is proteolytically more stable than (S)-LMI. Based on this finding, (R)-LMI was selected for pharmacological characterization. We have found that (R)-LMI is a CRF antagonist, inhibiting (1) the CRF-stimulated accumulation of cAMP in HEK 293 cells expressing the CRF₁R, (2) the production of interleukins by adipocytes and (3) the proliferation rate of RAW 264.7 cells. (R)-LMI likely blocked agonist actions by interacting with the N-domain of CRF₁R as suggested by data using a constitutively active chimera of CRF₁R. We propose that (R)-LMI can be used as an optimal lead compound in the rational design of novel CRF antagonists.

Gonadotropin-releasing hormone-Cu complex (Cu-GnRH) transcriptional activity in vivo in the female rat anterior pituitary gland

Unlike gonadotropin-releasing hormone (GnRH) analogues characterized by amino acid replacement in decapeptide primary structure, Cu-GnRH molecule preserves the native sequence but contains a Cu²⁺ ion stably bound to the nitrogen atoms including that of the imidazole ring of His². Cu-GnRH can operate via cAMP/PKA signalling in anterior pituitary cells, suggesting that it may affect selected gonadotropic network gene transcription in vivo. We analysed pituitary mRNA expression of Egr-1, Nr5a1, and Lhb based on their role in luteinizing hormone (LH) synthesis; and Nos1, Adcyap1, and Prkaca due to their dependence on cAMP/PKA activity. In two independent experiments, ovariectomized rats received intracerebroventricular pulsatile (one pulse/h or two pulses/h over 5 h) microinjections of 2 nM Cu-GnRH; 2 nM antide (GnRH antagonist) + 2 nM Cu-GnRH; 100 nM PACAP_6-38 (PACAP receptor antagonist) + 2 nM Cu-GnRH. Relative expression of selected mRNAs was determined by qRT-PCR. LH serum concentration was examined according to RIA. All examined genes responded to Cu-GnRH stimulation with increased transcriptional activity in a manner dependent on pulse frequency pattern. Increased expression of Nr5a1, Lhb, Nos1, Adcyap1, and Prkaca mRNA was observed solely in rats receiving the complex with frequency of two pulses/h over 5 h. Egr-1 transcription was up-regulated for both applied Cu-GnRH pulsatile patterns. The stimulatory effect of Cu-GnRH on gene transcription was dependent on both GnRH receptor and PAC-1 activation. In conclusion, obtained results indicate that Cu-GnRH complex is a GnRH analogue able to induce both IP₃/PKC and cAMP/PKA-dependent gonadotrope network gene transcription in vivo.

On the design principles of peptide-drug conjugates for targeted drug delivery to the malignant tumor site

Cancer is the second leading cause of death affecting nearly one in two people, and the appearance of new cases is projected to rise by >70% by 2030. To effectively combat the menace of cancer, a variety of strategies have been exploited. Among them, the development of peptide–drug conjugates (PDCs) is considered as an inextricable part of this armamentarium and is continuously explored as a viable approach to target malignant tumors. The general architecture of PDCs consists of three building blocks: the tumor-homing peptide, the cytotoxic agent and the biodegradable connecting linker. The aim of the current review is to provide a spherical perspective on the basic principles governing PDCs, as also the methodology to construct them. We aim to offer basic and integral knowledge on the rational design towards the construction of PDCs through analyzing each building block, as also to highlight the overall progress of this rapidly growing field. Therefore, we focus on several intriguing examples from the recent literature, including important PDCs that have progressed to phase III clinical trials. Last, we address possible difficulties that may emerge during the synthesis of PDCs, as also report ways to overcome them.

Novel peptidomimetics related to gonadotropin-releasing hormone (GnRH)

Novel GnRH I and II analogues were designed and synthesized by Solid Phase Peptides Synthesis (SPPS), since GnRH has antiproliferative properties, but poor metabolic stability.