Preclinical characterization of a novel diphenyl benzamide selective ERα agonist for hormone therapy in prostate cancer

Investigational luteinizing hormone releasing hormone (LHRH) agonists and other hormonal agents in early stage clinical trials for prostate cancer

INTRODUCTION

The treatment and management of prostate cancer continues to evolve; newer classes of agents and combination therapies are being developed and some are being investigated in early phase clinical trials.

AREAS COVERED

We discuss investigational hormonal agents for the treatment of prostate cancer and focus primarily on luteinizing hormone releasing hormone (LHRH) agonists in early stage trials. We look at agents that target the hormonal axis, including anti-androgens, gonadotropins, estrogenic agents and progestogenic agents and other non-hormonal agents often used in combination with LHRH agonists. We review these candidates in the specific clinical niche in which they might find utility.

EXPERT OPINION

Of all candidate compounds being evaluated in clinical trials, very few will receive FDA approval. Few, if any of the investigational agents discussed here will be used routinely in clinical practice for treating prostate cancer. Recognizing the reasons for the failure of agents to advance to later stage trials is important. Furthermore, a thorough understanding of the mechanisms underlying prostate cancer pathogenesis, including various points in the HGPA and parallel pathways, will help identify potentially actionable targets.

Selective estrogen receptor alpha agonist GTx-758 decreases testosterone with reduced side effects of androgen deprivation therapy in men with advanced prostate cancer

BACKGROUND

A need remains for new therapeutic approaches for men with advanced prostate cancer, particularly earlier in the disease course.

OBJECTIVE

To assess the ability of an oral selective estrogen receptor α agonist (GTx-758) to lower testosterone concentrations compared with leuprolide while minimizing estrogen deficiency-related side effects of androgen-deprivation therapy.

DESIGN, SETTING, AND PARTICIPANTS

Hormone-naive advanced prostate cancer patients were randomized to oral GTx-758 1000 mg/d, 2000 mg/d, or leuprolide depot.

INTERVENTION

GTx-758 and leuprolide.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

The primary end point was the proportion of patients achieving total testosterone ≤ 50 ng/dl by day 60. Secondary end points included serum free testosterone, prostate-specific antigen (PSA), sex hormone-binding globulin, hot flashes, bone turnover markers, and insulin-like growth factor (IGF)-1 levels.

RESULTS AND LIMITATIONS

Of 159 randomized patients, leuprolide reduced total testosterone to ≤ 50 ng/dl in a greater proportion of patients than GTx-758 by day 60 (43.4%, 63.6%, and 88.2% of subjects receiving GTx-758 1000 mg [p<0.001], GTx-758 2000 mg [p=0.004], and leuprolide, respectively). GTx-758 reduced free testosterone and PSA earlier and to a greater degree than leuprolide. GTx-758 led to fewer hot flashes, decreases in bone turnover markers, and alterations in IGF-1 compared with leuprolide. A higher incidence of venous thromboembolic events (VTEs) was seen with GTx-758 (4.1%) compared with leuprolide (0.0%).

CONCLUSIONS

Although leuprolide reduced total testosterone to ≤ 50 ng/dl in a greater proportion of patients compared with GTx-758, GTx-758 was superior in lowering free testosterone and PSA. GTx-758 reduced estrogen deficiency side effects of hot flashes, bone loss, and insulin resistance but with a higher incidence of VTEs.

PATIENT SUMMARY

This paper reports findings that leuprolide lowered total testosterone more than GTx-758 but that GTx-758 lowered free testosterone and prostate-specific antigen more than leuprolide. GTx-758 also reduced estrogen deficiency side effects, albeit at a higher rate of vascular events.

TRIAL REGISTRATION

Clinicaltrials.gov identifier NCT01615120.

Estrogen receptor ligands: a patent review update

INTRODUCTION

The role of estrogens is mostly mediated by two nuclear receptors (ERα and ERβ) and a membrane-associated G-protein (GPR30 or GPER), and it is not limited to reproduction, but it extends to the skeletal, cardiovascular and central nervous systems. Various pathologies such as cancer, inflammatory, neurodegenerative and metabolic diseases are often associated with dysfunctions of the estrogenic system. Therapeutic interventions by agents that affect the estrogenic signaling pathway might be useful in the treatment of many dissimilar diseases.

AREAS COVERED

The massive chemodiversity of ER ligands, limited to patented small molecules, is herein reviewed. The reported compounds are classified on the basis of their chemical structures. Non-steroidal derivatives, which mostly consist of diphenolic compounds, are further segregated into chemical classes based on their central scaffold.

EXPERT OPINION

Estrogens have been used for almost a century and their earlier applications have concerned interventions in the female reproductive functions, as well as the treatment of some estrogen-dependent cancers and osteoporosis. Since the discovery of ERβ in 1996, the patent literature has started to pay a progressively increasing attention to this newer receptor subtype, which holds promise as a target for new indications, most of which still need to be clinically validated.