Luteinizing hormone-releasing hormone receptor targeted agents for prostate cancer

Nanomedicines in diagnosis and treatment of prostate cancers: an updated review

Prostate cancer (PC) is the third most common male cancer in the world, which occurs due to various mutations leading to the loss of chromatin structure. There are multiple treatments for this type of cancer, of which chemotherapy is one of the most important. Sometimes, a combination of different treatments, such as chemotherapy, radiotherapy, and surgery, are used to prevent tumor recurrence. Among other treatments, androgen deprivation therapy (ADT) can be mentioned, which has had promising results. One of the drawbacks of chemotherapy and ADT treatments is that they are not targeted to the tumor tissue. For this reason, their use can cause extensive side effects. Treatments based on nanomaterials, known as nanomedicine, have attracted much attention today. Nanoparticles (NPs) are one of the main branches of nanomedicine, and they can be made of different materials such as polymer, metal, and carbon, each of which has distinct characteristics. In addition to NPs, nanovesicles (NVs) also have therapeutic applications in PC. In treating PC, synthetic NVs (liposomes, micelles, and nanobubbles) or produced from cells (exosomes) can be used. In addition to the role that NPs and NVs have in treating PC, due to being targeted, they can be used to diagnose PC and check the treatment process. Knowing the characteristics of nanomedicine-based treatments can help design new treatments and improve researchers' understanding of tumor biology and its rapid diagnosis. In this study, we will discuss conventional and nanomedicine-based treatments. The results of these studies show that the use of NPs and NVs in combination with conventional treatments has higher efficacy in tumor treatment than the individual use of each of them.

About the Influence of PEG Spacers on the Cytotoxicity of Titanate Nanotubes-Docetaxel Nanohybrids against a Prostate Cancer Cell Line

The association between chemotherapeutic drugs and metal oxide nanoparticles has sparked a rapidly growing interest in cancer nanomedicine. The elaboration of new engineered docetaxel (DTX)-nanocarriers based on titanate nanotubes (TiONts) was reported. The idea was to maintain the drug inside cancer cells and avoid multidrug resistance mechanisms, which often limit drug efficacy by decreasing their intracellular concentrations in tumor cells. HS-PEGn-COOH (PEG: polyethylene glycol, n = 3000, 5000, 10,000) was conjugated, in an organic medium by covalent linkages, on TiONts surface. This study aimed to investigate the influence of different PEG derivatives chain lengths on the TiONts colloidal stability, on the PEGn density and conformation, as well as on the DTX biological activity in a prostate cancer model (human PC-3 prostate adenocarcinoma cells). In vitro tests highlighted significant cytotoxicities of the drug after loading DTX on PEGn-modified TiONts (TiONts-PEGn-DTX). Higher grafting densities for shorter PEGylated chains were most favorable on DTX cytotoxicity by promoting both colloidal stability in biological media and cells internalization. This promising strategy involves a better understanding of nanohybrid engineering, particularly on the PEGylated chain length influence, and can thus become a potent tool in nanomedicine to fight against cancer.

Gonadotropin-Releasing Hormone Receptors in Prostate Cancer: Molecular Aspects and Biological Functions

Pituitary Gonadotropin-Releasing Hormone receptors (GnRH-R) mediate the activity of the hypothalamic decapeptide GnRH, thus playing a key role in the regulation of the reproductive axis. Early-stage prostate cancer (PCa) is dependent on serum androgen levels, and androgen-deprivation therapy (ADT), based on GnRH agonists and antagonists, represents the standard therapeutic approach for PCa patients. Unfortunately, the tumor often progresses towards the more aggressive castration-resistant prostate cancer (CRPC) stage. GnRH receptors are also expressed in CRPC tissues, where their binding to both GnRH agonists and antagonists is associated with significant antiproliferative/proapoptotic, antimetastatic and antiangiogenic effects, mediated by the Gαi/cAMP signaling cascade. GnRH agonists and antagonists are now considered as an effective therapeutic strategy for CRPC patients with many clinical trials demonstrating that the combined use of these drugs with standard therapies (i.e., docetaxel, enzalutamide, abiraterone) significantly improves disease-free survival. In this context, GnRH-based bioconjugates (cytotoxic drugs covalently linked to a GnRH-based decapeptide) have been recently developed. The rationale of this treatment is that the GnRH peptide selectively binds to its receptors, delivering the cytotoxic drug to CRPC cells while sparing nontumor cells. Some of these compounds have already entered clinical trials.

Regulatory Actions of LH and Follicle-Stimulating Hormone on Breast Cancer Cells and Mammary Tumors in Rats

Gonadotrophins are mainly known to influence the body through the formation of gonadal steroids. However, receptors for luteinizing hormone (LH) and follicular-stimulating hormone (FSH) are present in a set of extra-gonadal tissues in humans and animals, but their functional relevance is uncertain. In this article, we present experimental evidence that, in T-47D breast cancer (BC) cells, FSH, and LH alter the expression of genes involved in adhesion, motility, and invasion through the activation of their receptors. Using miniarray technology we also found that LH influences the expression of a broad set of genes involved in cancer biology in T-47D cells. Interestingly, the regulatory actions of FSH and LH depend on the modality of exposure, with significant differences between pre-pubertal-like vs. post-menopausal-like amounts of gonadotrophins, but not after intermittent administration, representative of fertile life. We also studied the modulation of the circulating levels of gonadotrophins in an in vivo rat model of BC progression and observed a direct correlation with the extent of cancer growth. These results support the hypothesis that gonadotrophins may have direct effects on extra-gonadal tissues. They also highlight that gonadotrophins could potentially contribute to BC progression, particularly in post-menopausal women who typically have higher gonadotrophin levels. This research may ultimately lead to testing the use of gonadotrophin-modulating drugs in BC patients.

Taxane-Grafted Metal-Oxide Nanoparticles as a New Theranostic Tool against Cancer: The Promising Example of Docetaxel-Functionalized Titanate Nanotubes on Prostate Tumors

The combination of anticancer drugs and metal oxide nanoparticles is of great interest in cancer nanomedicine. Here, the development of a new nanohybrid, titanate nanotube-docetaxel (TiONts-DTX) is reported, the two parts of which are conjugated by covalent linkages. Unlike most nanoparticles currently being developed for biomedical purposes, TiONts present a needle-shaped morphology. The surface of TiONts is linked with 3-aminopropyl triethoxysilane and with a hetero-bifunctional polymer (polyethylene glycol) to create well-dispersed and biocompatible nanovectors. The prefunctionalized surface of this scaffold has valuable attachments to graft therapeutic agents (DTX in our case) as well as chelating agents (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) to monitor the nanohybrids. To evaluate drug efficacy, in vitro tests have demonstrated that the association between TiONts and DTX shows cytotoxic activity against a hormone-refractory prostate cancer cell line (22Rv1) whereas TiONts without DTX do not. Finally, the first in vivo tests with intratumoral injections show that more than 70% of TiONts nanovectors are retained within the tumor for at least 7 d. Moreover, tumor growth in mice receiving TiONts-DTX is significantly slower than that in mice receiving free DTX. This nanohybrid can thus become a promising new tool in biomedicine to fight against prostate cancer.

Antitumor effects of cecropin B-LHRH' on drug-resistant ovarian and endometrial cancer cells

Background

Luteinizing hormone-releasing hormone receptor (LHRHr) represents a promising therapeutic target for treating sex hormone-dependent tumors. We coupled cecropin B, an antimicrobial peptide, to LHRH’, a form of LHRH modified at carboxyl-terminal residues 4–10, which binds to LHRHr without interfering with luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion. This study aimed to assess the antitumor effects of cecropin B-LHRH’ (CB-LHRH’) in drug-resistant ovarian and endometrial cancers.

Methods

To evaluate the antitumor effects of CB-LHRH’, three drug resistant ovarian cancer cell lines (SKOV-3, ES-2, NIH:OVCAR-3) and an endometrial cancer cell line (HEC-1A) were treated with CB-LHRH’. Cell morphology changes were assessed using inverted and electron microscopes. In addition, cell growth and cell cytotoxicity were measured by MTT assay and LDH release, respectively. In addition, hemolysis was measured. Furthermore, radioligand receptor binding, hypersensitization and minimal inhibitory concentrations (against Staphylococcus aureus, Klebsiella pneumoniae, Escherichia coli, Enterobacter cloacae, Pseudomonas aeruginosa, and Acinetobacter baumannii) were determined. Finally, the impact on tumor growth in BALB/c-nu mice was assessed in an ES-2 xenograft model.

Results

CB-LHRH’ bound LHRHr with high-affinity (dissociation constant, Kd = 0.252 ± 0.061nM). Interestingly, CB-LHRH’ significantly inhibited the cell viability of SKOV-3, ES-2, NIH:OVCAR-3 and HEC-1A, but not that of normal eukaryotic cells. CB-LHRH’ was active against bacteria at micromolar concentrations, and caused no hypersensitivity in guinea pigs. Furthermore, CB-LHRH’ inhibited tumor growth with a 23.8 and 20.4 % reduction in tumor weight at 50 and 25 mg/kg.d, respectively.

Conclusions

CB-LHRH’ is a candidate for targeted chemotherapy against ovarian and endometrial cancers.

Cyclodextrin-based targeting strategies for tumor treatment

The efficacy and applicability of anticancer drugs are greatly restricted by severe systemic toxicities and drug resistance. Targeting drug delivery strategies have been developed to prevent the shortcomings of chemotherapy. Among various approaches to specifically target drug-loaded carrier systems to the required pathological sites, ligand-attached cyclodextrin-based targeting complexes are a promising drug delivery system, which is achieved mainly through specific molecular interactions between the drugs and cell surface receptors. The principal targeting tactics include conjugation of cyclodextrin with targeting moieties or encapsulation drugs in cyclodextrins. The cyclodextrin-based supramolecules, polymers, or nanoparticles bearing bioactive substances such as folate, estrogens, carbohydrates, peptides, etc. have been reviewed.

Targeted cytotoxic analog of luteinizing hormone-releasing hormone (LHRH), AEZS-108 (AN-152), inhibits the growth of DU-145 human castration-resistant prostate cancer in vivo and in vitro through elevating p21 and ROS levels

Management of castration-resistant prostate cancer (CRPC) is challenging due to lack of efficacious therapy. Luteinizing hormone-releasing hormone (LHRH) analogs appear to act directly on cells based on the LHRH receptors on human prostate adenocarcinoma cells. We explored anticancer activity of a cytotoxic analog of LHRH, AEZS-108, consisting of LHRH agonist linked to doxorubicin. Nude mice bearing DU-145 tumors were used to compare antitumor effects of AEZS-108 with its individual constituents or their unconjugated combination. The tumor growth inhibition of conjugate was greatest among treatment groups (90.5% inhibition vs. 41% by [D-Lys(6)]LHRH+DOX). The presence of LHRH receptors on DU-145 cells was confirmed by immunocytochemistry. In vitro, AEZS-108 significantly inhibited cell proliferation (61.2% inhibition) and elevated apoptosis rates (by 46%). By the detection of the inherent doxorubicin fluorescence, unconjugated doxorubicin was seen in the nucleus; the conjugate was perinuclear and at cell membrane. Autophagy, visualized by GFP-tagged p62 reporter, was increased by AEZS-108 (7.9-fold vs. 5.3-fold by DOX+[D-Lys(6)]LHRH. AEZS-108 more effectively increased reactive oxygen species (ROS, 2-fold vs. 1.4-fold by DOX+[D-Lys(6)]LHRH) and levels of the apoptotic regulator p21 in vivo and in vitro. We demonstrate robust inhibitory effects of the targeted cytotoxic LHRH analog, AEZS-108, on LHRHR positive castration-resistant prostate cancer cells.

Stability, permeability and growth-inhibitory properties of gonadotropin-releasing hormone liposaccharides

PURPOSE

In this study we aimed to address the poor drug-like properties of Gonadotropin-Releasing Hormone (GnRH) peptide through modification with lipids and carbohydrates.

METHODS

GnRH peptide was conjugated to 2-amino-D,L-octanoic acid (C8) and 2-amino-D,L-dodecanoic acid (C12) in monomer and dimer, along with (6-9) or without (2-5 and 11) a glucose moiety. Peptides were tested for their biological activity using different tumour cell lines. The toxicity of the constructs was evaluated in peripheral blood mononuclear cells (PBMC).

RESULTS

All (glyco)lipopeptides showed improved metabolic stability in Caco-2 cell homogenates. Those with single lipid moiety (2, 4 and 8) exhibited prodrug-like properties. Permeability across Caco-2 cell monolayers was enhanced in the dimer C8-modified (glyco)lipopeptide (3) and the lipopeptide with C12 inserted mid-sequence (11). Most of the constructs showed moderate-to-high antiproliferative activity against GnRH-receptor positive DU145 and OVCAR-3 cells (up to 60%). Compound 11 was the most effective with IC50 = 26.4 ± 1.07 μg.ml(-1), which was comparable to triptorelin (25.1 ± 1.14 μg.mL(-1)). The sensitivity of OVCAR-3 cells to the effect of all analogues except for 11 decreased significantly in estrogen-reconstituted media. Only compounds 2, 4, 5 and 8 showed a steroid-dependent effect in DU145 cells. No compounds exhibited significant toxicity on PBMCs.

CONCLUSION

These results indicated lipidation and glycosylation improves the druggability of GnRH and could lead to an increased direct antitumour activity in some hormone dependent and independent reproductive cancers.

Phase I, dose-escalation study of the targeted cytotoxic LHRH analog AEZS-108 in patients with castration- and taxane-resistant prostate cancer

PURPOSE

AEZS-108, formerly AN-152, is a cytotoxic hybrid molecule consisting of a luteinizing hormone-releasing hormone (LHRH) agonist moiety covalently coupled to doxorubicin, allowing it to deliver doxorubicin selectively to cells expressing LHRH receptors. LHRH receptors are expressed on the cell membrane of many tumors, including prostate cancer. This phase I study determined the maximum tolerated dose (MTD) of AEZS-108 in men with taxane- and castration-resistant prostate cancer (CRPC) while providing additional information on the safety profile and efficacy of this agent.

EXPERIMENTAL DESIGN

AEZS-108 was administered as an intravenous infusion every 21 days until progression or unacceptable toxicity in cohorts of 3 or 6 patients until the MTD was reached. Blood was collected for capture of circulating tumor cells (CTC) to visualize internalization of AEZS-108, an autofluorescent molecule.

RESULTS

The MTD of AEZS-108 in this cohort was 210 mg/m(2), which was lower than that seen in a phase I study conducted in women with endometrial or ovarian cancers. The dose-limiting toxicity was persistent neutropenia. Three patients had a PSA response with an additional 10 patients maintaining PSA stable disease. Of the 10 patients evaluable by RECIST criteria, 9 achieved stable disease. AEZS-108 internalization in CTCs was routinely visualized using its autofluorescence.

CONCLUSION

These findings show that AEZS-108 has an acceptable safety profile and a signal of efficacy, lowering PSA in heavily pretreated patients with prostate cancer, and that internalization of AEZS-108 in prostate cancer CTCs may be a viable pharmacodynamic marker. A phase II study in men with prostate cancer is ongoing.

Prostate cancer relevant antigens and enzymes for targeted drug delivery

Chemotherapy is one of the most widely used approaches in combating advanced prostate cancer, but its therapeutic efficacy is usually insufficient due to poor specificity and associated toxicity. Lack of targeted delivery to prostate cancer cells is also the primary obstacles in achieving feasible therapeutic effect of other promising agents including peptide, protein, and nucleic acid. Consequently, there remains a critical need for strategies to increase the selectivity of anti-prostate cancer agents. This review will focus on various prostate cancer-relevant antigens and enzymes that could be exploited for prostate cancer targeted drug delivery. Among various targeting strategies, active targeting is the most advanced approach to specifically deliver drugs to their designated cancer cells. In this approach, drug carriers are modified with targeting ligands that can specifically bind to prostate cancer-specific antigens. Moreover, there are several specific enzymes in the tumor microenvironment of prostate cancer that can be exploited for stimulus-responsive drug delivery systems. These systems can specifically release the active drug in the tumor microenvironment of prostate cancer, leading to enhanced tumor penetration efficiency.

Targeting alternative sites on the androgen receptor to treat castration-resistant prostate cancer

Recurrent, metastatic prostate cancer continues to be a leading cause of cancer-death in men. The androgen receptor (AR) is a modular, ligand-inducible transcription factor that regulates the expression of genes that can drive the progression of this disease, and as a consequence, this receptor is a key therapeutic target for controlling prostate cancer. The current drugs designed to directly inhibit the AR are called anti-androgens, and all act by competing with androgens for binding to the androgen/ligand binding site. Unfortunately, with the inevitable progression of the cancer to castration resistance, many of these drugs become ineffective. However, there are numerous other regulatory sites on this protein that have not been exploited therapeutically. The regulation of AR activity involves a cascade of complex interactions with numerous chaperones, co-factors and co-regulatory proteins, leading ultimately to direct binding of AR dimers to specific DNA androgen response elements within the promoter and enhancers of androgen-regulated genes. As part of the family of nuclear receptors, the AR is organized into modular structural and functional domains with specialized roles in facilitating their inter-molecular interactions. These regions of the AR present attractive, yet largely unexploited, drug target sites for reducing or eliminating androgen signaling in prostate cancers. The design of small molecule inhibitors targeting these specific AR domains is only now being realized and is the culmination of decades of work, including crystallographic and biochemistry approaches to map the shape and accessibility of the AR surfaces and cavities. Here, we review the structure of the AR protein and describe recent advancements in inhibiting its activity with small molecules specifically designed to target areas distinct from the receptor’s androgen binding site. It is anticipated that these new classes of anti-AR drugs will provide an additional arsenal to treat castration-resistant prostate cancer.

A review of the current status of siRNA nanomedicines in the treatment of cancer

RNA interference currently offers new opportunities for gene therapy by the specific extinction of targeted gene(s) in cancer diseases. However, the main challenge for nucleic acid delivery still remains its efficacy through intravenous administration. Over the last decade, many delivery systems have been developed and optimized to encapsulate siRNA and to specifically promote their delivery into tumor cells and improve their pharmacokinetics for anti-cancer purposes. This review aims to sum up the potential targets in numerous pathways and the properties of recently optimized siRNA synthetic nanomedicines with their preclinical applications and efficacy. Future perspectives in cancer treatment are discussed including promising concomitant treatment with chemotherapies or other siRNA. The outcomes in human clinical trials are also presented.

GnRH receptors in cancer: from cell biology to novel targeted therapeutic strategies

The crucial role of pituitary GnRH receptors (GnRH-R) in the control of reproductive functions is well established. These receptors are the target of GnRH agonists (through receptor desensitization) and antagonists (through receptor blockade) for the treatment of steroid-dependent pathologies, including hormone-dependent tumors. It has also become increasingly clear that GnRH-R are expressed in cancer tissues, either related (i.e. prostate, breast, endometrial, and ovarian cancers) or unrelated (i.e. melanoma, glioblastoma, lung, and pancreatic cancers) to the reproductive system. In hormone-related tumors, GnRH-R appear to be expressed even when the tumor has escaped steroid dependence (such as castration-resistant prostate cancer). These receptors are coupled to a G(αi)-mediated intracellular signaling pathway. Activation of tumor GnRH-R by means of GnRH agonists elicits a strong antiproliferative, antimetastatic, and antiangiogenic (more recently demonstrated) activity. Interestingly, GnRH antagonists have also been shown to elicit a direct antitumor effect; thus, these compounds behave as antagonists of GnRH-R at the pituitary level and as agonists of the same receptors expressed in tumors. According to the ligand-induced selective-signaling theory, GnRH-R might assume various conformations, endowed with different activities for GnRH analogs and with different intracellular signaling pathways, according to the cell context. Based on these consistent experimental observations, tumor GnRH-R are now considered a very interesting candidate for novel molecular, GnRH analog-based, targeted strategies for the treatment of tumors expressing these receptors. These agents include GnRH agonists and antagonists, GnRH analog-based cytotoxic (i.e. doxorubicin) or nutraceutic (i.e. curcumin) hybrids, and GnRH-R-targeted nanoparticles delivering anticancer compounds.

AEZS-108 : a targeted cytotoxic analog of LHRH for the treatment of cancers positive for LHRH receptors

INTRODUCTION

Receptors for the luteinizing hormone-releasing hormone [LHRH, also known as gonadotropin-releasing hormone (GnRH)] can be regarded as an ideal target for a personalized medicine approach in cancer therapy. LHRH receptors are expressed in about 80% of human endometrial and ovarian cancers, 86% of prostate cancer, and about 50% of breast cancers including triple-negative breast cancer, as well as bladder, colorectal, and pancreatic cancers, sarcomas, lymphomas, melanomas, and renal cell carcinomas. Apart from the pituitary and reproductive organs, other organs and hematopoietic stem cells express LHRH receptors. Thus, a targeted cytotoxic LHRH analog such as AEZS-108 (formerly known as AN-152), in which doxorubin is linked to the LHRH agonist [D-Lys(6)]LHRH, appears to be a suitable drug for targeted chemotherapy of cancers expressing receptors for LHRH, which would be more efficacious and less toxic than standard systemic chemotherapy.

AREAS COVERED

This review discusses the development of AEZS-108, its targeting mechanism, preclinical studies, and clinical trials in patients with endometrial, ovarian, prostatic, and bladder cancers. We emphasize its development as a personalized medicine approach. The studies reviewed demonstrate the effects of the cytotoxic LHRH analog, AEZS-108, mediated by LHRH receptors, in in vivo models of LHRH-receptor-positive human endometrial, ovarian, breast, prostatic, colorectal, pancreatic, and bladder cancers xenografted into nude mice. Intravenous administration of AEZS 108 inhibits the growth of LHRH-receptor-positive tumors better than equimolar doses of the cytotoxic agent doxorubicin and is far less toxic. AEZS 108 has no antitumor activity in cancers negative to LHRH receptor. This strongly supports the concept of targeting cytotoxic chemotherapy to tumor cells expressing LHRH receptors. Early clinical trials have demonstrated the efficacy of AEZS-108. A Phase I trial assessed the maximum tolerated dose and pharmacokinetics and pharmacodynamics of AEZS-108 given once every 3 weeks in patients with gynecological cancers. Two Phase II studies in heavily pretreated ovarian and recurrent endometrial cancers showed good clinical activity after a maximum of six courses of AEZS-108 as a single agent. Ongoing clinical studies with AEZS-108 in men with castration-resistant prostate cancer and patients with chemotherapy refractory bladder cancer had shown early signs of clinical efficacy. Side effects are moderate and easily manageable. In particular, no pituitary or cardiac toxicity is observed.

EXPERT OPINION

AEZS-108 is a cytotoxic analog designed for receptor-mediated targeted chemotherapy and consists of an LHRH carrier linked to doxorubicin. Preclinical studies demonstrate that the uptake of AEZS-108 is achieved by receptor-mediated endocytosis. Results of Phase I and II clinical trials in patients with gynecological cancers demonstrated anticancer activity without cardiotoxicity even in highly pretreated patients. Phase I/II studies in castration-resistant prostate cancer and chemotherapy refractory bladder cancer are in progress. Targeted chemotherapy with a cytotoxic analog of LHRH, such as AEZS-108, is therefore being considered for Phase III studies in advanced endometrial cancers positive for LHRH receptor. LHRH receptors are also present in human colon cancers, melanomas, lymphomas, and sarcomas, and treatment of these cancers with AEZS-108 should also be undertaken. Before such treatment with AEZS-108 is begun, the status of tumoral LHRH receptors of patients must be determined.

Endocrine control and physiology of the prostate

The endocrine control of prostatic physiology and anatomy is reviewed with emphasis on those factors in the hypothalamus and anterior adenohypophysis which affect the gland either directly or through the testes. The role of circulating estrogens and androgens and their binding to plasma proteins is presented, and the intracellular metabolism of testosterone, particularly in relation to specific receptors, is summarized. The possible significance of intracellular events in prostate cancer development is considered with particular emphasis on those parameters which may reside outside the endocrine effects on the prostatic cells.