Nilutamide as second line hormone therapy for prostate cancer after androgen ablation fails

Synthesis, Absolute Configuration, Biological Profile and Antiproliferative Activity of New 3,5-Disubstituted Hydantoins

Hydantoins, a class of five-membered heterocyclic compounds, exhibit diverse biological activities. The aim of this study was to synthesize and characterize a series of novel 3,5-disubstituted hydantoins and to investigate their antiproliferative activity against human cancer cell lines. The new hydantoin derivatives 5a-i were prepared as racemic mixtures of syn- and anti-isomers via a base-assisted intramolecular amidolysis of C-3 functionalized β-lactams. The enantiomers of syn-5a and anti-hydantoins 5b were separated by preparative high-performance liquid chromatography (HPLC) using n-hexane/2-propanol (90/10, v/v) as the mobile phase. The absolute configuration of the four allyl hydantoin enantiomers 5a was assigned based on a comparison of the experimental electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) spectra with those calculated using density functional theory (DFT). The antiproliferative activity evaluated in vitro against three different human cancer cell lines: HepG2 (liver hepatocellular carcinoma), A2780 (ovarian carcinoma), and MCF7 (breast adenocarcinoma), and on the non-tumor cell line HFF1 (normal human foreskin fibroblasts) using the MTT cell proliferation assay. In silico drug-like properties and ADMET profiles were estimated using the ADMET Predictor ver. 9.5 and the online server admetSAR. Eighteen new 3,5-disubstituted hydantoins were synthesized and characterized. The compound anti-5c showed potent cytotoxic activity against the human tumor cell line MCF7 (IC50 = 4.5 µmol/L) and the non-tumor cell line HFF1 (IC50 = 12.0 µmol/L). In silico analyzes revealed that the compounds exhibited moderate water solubility and membrane permeability and are likely substrates for CYP3A4 and P-glycoprotein and have a high probability of antiarthritic activity.

Therapeutic potential of targeting AKR1C2 in the treatment of prostate cancer

Prostate cancer development and progression are driven by androgens, and changes in androgen metabolic pathways can lead to prostate cancer progression or remission. AKR1C2 is a member of the aldo-keto reductase superfamily and plays an important role in the metabolism of steroids and prostaglandins. Alterations in the expression and activity of AKR1C2 affect the homeostasis of active androgens, which in turn affects the progression of prostate cancer. AKR1C2 reduces the highly active dihydrotestosterone to the less active 3α-diol in the prostate, resulting in lower androgen levels. Whereas the expression of AKR1C2 is significantly reduced in prostate cancer tissues relative to normal prostate tissues, this results in a weakening of the dihydrotestosterone metabolic inactivation pathway, leading to the retention of dihydrotestosterone in the prostate cancer cells, which promotes the progress of prostate cancer. Given the critical role of AKR1C2 in prostate cancer cells, targeting AKR1C2 for the treatment of prostate cancer may be an effective strategy. It has been demonstrated that curcumin and neem leaf extract effectively inhibit prostate cancer in vitro and in vivo by modulating AKR1C2.

Updates on Overcoming Bicalutamide Resistance: A Glimpse into Resistance to a Novel Antiandrogen

The standard androgen deprivation therapy for advanced prostate cancer includes the use of bicalutamide, which is a well-known antagonist of androgen receptors. Despite numerous benefits of the drugs in prostate cancer treatment, there is always a risk of developing a resistant phenotype, which paves the way for a more aggressive and low-survival type of prostate cancer. Over the years, many studies have investigated the candidate mechanisms of such resistance and have managed to find possible therapeutic solutions. In this Review, we shed light on the heterogeneous dynamics of progression to resistance against bicalutamide treatment, referring to the most recent studies and the approaches that have been so far discussed. This Review tries to offer a deep and comprehensive understanding about how the resistant cells become sensitive to the drug and what corresponding pathways lead to an appropriate solution for the antiandrogen resistance challenge.

Two dimensional architectures of graphitic carbon nitride with the substitution of heteroatoms for bifunctional electrochemical detection of nilutamide

The exploration of graphitic carbon nitride (g-C₃N₄), a two-dimensional (2D) metal-free polymer semiconducting material, is largely discussed due to its large specific surface area, high electrical conductivity, thermal stability, and adaptable electronic structure. The adaption of sulfur (S) and phosphorous (P) atoms into the layers of g-C₃N₄ increases the electrochemical performance of detecting nilutamide (NT). The aggregation severity can be decreased by integrating S/P into g-C₃N₄, thereby improving surface area and electrical conductance. The g-C₃N₄, S/gC₃N₄, P/g-C₃N₄, and S/P/g-C₃N₄ were studied with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), Fourier transform infrared (FTIR), Ultraviolet visible spectroscopy (UV), Thermogravimetric analysis (TGA), and Brunauer-Emmett-Teller (BET). The well-assigned S/P/g-C₃N₄ exhibited a good crystalline structure with more active sites for improved electron transfer toward NT detection. Both differential pulse voltammetry (DPV) and amperometry (IT) was studied for NT detection. The electrochemical studies were done with a linear range of 0.019-1.17 μM to 5.36-1891.98 μM in DPV and 0.01 μM-158.3 μM in IT technique. The attained limit of detection in DPV analysis was 3.2 nM and with IT analysis 2.4 nM. The nanocomposite S/P/g-C₃N₄ shows good selectivity towards NT. The fabricated electrode showed excellent repeatability, reproducibility, and stability, with a significant recovery range in real sample analysis.

Synthesis of new 5-benzylidene-hydantoin esters

Compounds containing a hydantoin moiety are found in several medicines in clinical use. In this research, ethyl- and methyl-[2-(5-benzylidene)-2,4-dioxoimidazolidin-3-yl]acetyl esters are successfully synthesized over four reaction steps using conventional methods. The synthesis begins by subjecting hydantoin to a Knoevenagel condensation reaction with three different benzaldehydes to afford the penultimate products, which are further reacted with ethyl or methyl (bromoacetyl)alaninates, butanoates, valinates, and norvalinates to give the desired products as esters in low to moderate yields.

Targeting signaling pathways in prostate cancer: mechanisms and clinical trials

Prostate cancer (PCa) affects millions of men globally. Due to advances in understanding genomic landscapes and biological functions, the treatment of PCa continues to improve. Recently, various new classes of agents, which include next-generation androgen receptor (AR) signaling inhibitors (abiraterone, enzalutamide, apalutamide, and darolutamide), bone-targeting agents (radium-223 chloride, zoledronic acid), and poly(ADP-ribose) polymerase (PARP) inhibitors (olaparib, rucaparib, and talazoparib) have been developed to treat PCa. Agents targeting other signaling pathways, including cyclin-dependent kinase (CDK)4/6, Ak strain transforming (AKT), wingless-type protein (WNT), and epigenetic marks, have successively entered clinical trials. Furthermore, prostate-specific membrane antigen (PSMA) targeting agents such as ¹⁷⁷Lu-PSMA-617 are promising theranostics that could improve both diagnostic accuracy and therapeutic efficacy. Advanced clinical studies with immune checkpoint inhibitors (ICIs) have shown limited benefits in PCa, whereas subgroups of PCa with mismatch repair (MMR) or CDK12 inactivation may benefit from ICIs treatment. In this review, we summarized the targeted agents of PCa in clinical trials and their underlying mechanisms, and further discussed their limitations and future directions.

Enantioseparation of syn- and anti-3,5-Disubstituted Hydantoins by HPLC and SFC on Immobilized Polysaccharides-Based Chiral Stationary Phases

The enantioseparation of syn- and anti-3,5-disubstituted hydantoins 5a–i was investigated on three immobilized polysaccharide-based columns (CHIRAL ART Amylose-SA, CHIRAL ART Cellulose-SB, CHIRAL ART Cellulose-SC) by high performance liquid chromatography (HPLC) using n-hexane/2-PrOH (90/10, v/v) or 100% dimethyl carbonate (DMC) as mobile phases, respectively, and by supercritical fluid chromatography (SFC) using CO2/alcohol (MeOH, EtOH, 2-PrOH; 80/20, v/v) as a mobile phase. The chromatographic parameters, such as separation and resolution factors, have indicated that Amylose-SA is more suitable for enantioseparation of the most analyzed syn- and anti-3,5-disubstituted hydantoins than Celullose-SB and Cellulose-SC in both HPLC and SFC modalities. All three tested columns showed better enantiorecognition ability toward anti-hydantoins compared to syn-hydantoins, both in HPLC and SFC modes. We have demonstrated that environmentally friendly solvent DMC can be efficiently used as the mobile phase in HPLC mode for enantioseparation of hydantoins on the immobilized polysaccharide-based chiral stationary phases.

The Bucherer-Bergs Multicomponent Synthesis of Hydantoins-Excellence in Simplicity

Hydantoins and their hybrids with other molecules represent a very important group of heterocycles because they exhibit diverse biological and pharmacological activities in medicinal and agrochemical applications. They also serve as key precursors in the chemical or enzymatic synthesis of significant nonnatural α-amino acids and their conjugates with medical potential. This review provides a comprehensive treatment of the synthesis of hydantoins via the Bucherer-Bergs reaction including the Hoyer modification but limited to free carbonyl compounds or carbonyl compounds protected as acetals (ketals) and cyanohydrins used as starting reaction components. In this respect, the Bucherer-Bergs reaction provides an efficient and simple method in the synthesis of important natural products as well as for the preparation of new organic compounds applicable as potential therapeutics. The scope and limitations, as well as a comparison with some other methods for preparing hydantoins, are also discussed.

Analysis of the binding modes of the first- and second-generation antiandrogens with respect to F876L mutation

Androgen receptor (AR) is an important target for the treatment of prostate cancer, and mutations in the AR have an important impact on the resistance of existing drugs. In this work, we performed molecular dynamics simulations of the existing marketed antiandrogens flutamide, nilutamide, bicalutamide, enzalutamide, apalutamide, darolutamide, and its main metabolite ORM15341 in complex with the wild-type and F876L mutant AR. We calculated the residue-specific binding free energy contribution of the wild-type and mutant ARs with the AS-IE method and analyzed the hotspot residues and the binding free energy contributions of specific residues before and after the mutation. In addition, we analyzed the total binding obtained by adding residue binding energy contributions and compared the results with experimental values. The obtained residue-specific binding information should be very helpful in understanding the mechanism of drug resistance with respect to specific mutations and in the design of new generation drugs against possible new mutations.

Polymorphic forms of antiandrogenic drug nilutamide: structural and thermodynamic aspects

Attempts to obtain new cocrystals of nonsteroidal antiandrogenic drug nilutamide produced alternative polymorphic forms of the compound (Form II and Form III) and their crystal structures were elucidated by single-crystal X-ray diffraction. Apart from the cocrystallization technique, lyophilization was found to be an effective strategy for achieving polymorph control of nilutamide, which was difficult to obtain by other methods. The physicochemical properties and relative stability of the commercial Form I and newly obtained Form II were comprehensively investigated by a variety of analytical methods (thermal analysis, solution calorimetry, solubility, and sublimation), whereas for Form III, only a handful of experimental parameters were obtained due to the elusive nature of the polymorph. Form I and Form II were found to be monotropically related, with Form I being confirmed as the thermodynamically most stable solid phase. In addition, the performance of different DFT-D and semi-empirical schemes for lattice energy calculation and polymorph energy ranking was compared and analysed. Lattice energy calculations using periodic DFT at B3LYP-D3/6-31(F+)G(d,p) and PBEh-3c/def2-mSVP levels of theory were found to provide the most accurate lattice energy values for Form I against experimental data, while PIXEL and PBEh-3c/def2-mSVP were the only methods that predicted the correct order of stability of Forms I and II.

Computational Analysis of Residue-Specific Binding Free Energies of Androgen Receptor to Ligands

Androgen receptor (AR) is an important therapeutic target for the treatment of diseases such as prostate cancer, hypogonadism, muscle wasting, etc. In this study, the complex structures of the AR ligand-binding domain (LBD) with fifteen ligands were analyzed by molecular dynamics simulations combined with the alanine-scanning-interaction-entropy method (ASIE). The quantitative free energy contributions of the pocket residues were obtained and hotspot residues are quantitatively identified. Our calculation shows that that these hotspot residues are predominantly hydrophobic and their interactions with binding ligands are mainly van der Waals interactions. The total binding free energies obtained by summing over binding contributions by individual residues are in good correlation with the experimental binding data. The current quantitative analysis of binding mechanism of AR to ligands provides important insight on the design of future inhibitors.

Synthesis and Evaluation of 5-imino-4-thioxoimidazolidin-2-one Derivatives as Antibacterial and Antifungal Agents

OBJECTIVE

It was interesting to synthesize some new 5-imino-4-thioxoimidazolidin-2- one derivatives with different halogenated and alkylated aromatic substituents at N-(1) and N-(3) and evaluation of their expected antibacterial and antifungal activities.

METHODS

New 5-imino-4-thioxoimidazolidin-2-one derivatives were synthesized through the reaction of different halogenated and alkylated N-arylcyanothioformamides with halogenated and alkylated aryl isocyanates.

RESULTS

5-Imino-4-thioxoimidazolidin-2-ones were obtained in high yields with excellent purity. The activities of imidazolidines as antibacterial and antifungal agents were studied. Some of the imidazolidine derivatives displayed significant antibacterial and antifungal activities.

CONCLUSION

5-Imino-4-thioxoimidazolidin-2-ones were obtained in 77-90% yields with excellent purity. The antibacterial and antifungal activities suggest that some of the imidazole derivatives possess significant antimicrobial activity against B. subtilis, K. pneumonia and C. albicans and moderate activity against S. aureus.

Asymmetric Synthesis of Adjacent Tri- and Tetrasubstituted Carbon Stereocenters: Organocatalytic Aldol Reaction of an Hydantoin Surrogate with Azaarene 2-Carbaldehydes

A bifunctional amine/squaramide catalyst promoted direct aldol addition of an hydantoin surrogate to pyridine 2-carbaldehyde N-oxides to afford adducts bearing two vicinal tertiary/quaternary carbons in high diastereo- and enantioselectivity (d.r. up to >20:1; ee up to 98 %) is reported. Acid hydrolysis of adducts followed by reduction of the N-oxide group yields enantiopure carbinol-tethered quaternary hydantoin-azaarene conjugates with densely functionalized skeletons. DFT studies of the potential energy surface (B3LYP/6-31+G(d)+CPCM (dichloromethane)) of the reaction correlate the activity of different catalysts and support an intramolecular hydrogen-bond-assisted activation of the squaramide moiety in the transition state of the catalytic reaction.

Connective synthesis of 5,5-disubstituted hydantoins by tandem α-amination and α-arylation of silyl ketene acetals

Amination of a silylated ester generates an intermediate urea that transfers an aryl ring to the aminated centre and cyclises to a hydantoin.

5,5-Disubstituted hydantoins, formally the cyclisation products of quaternary amino acids, were formed connectively from simple ester-derived starting materials by a one-pot tandem method. Amination of the silyl ketene acetal derivative of a methyl ester takes place by silver-catalysed addition to the N Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> N bond of an azocarboxamide, generating a N-amino-N′-aryl urea derivative of a substituted aminoester. Treatment with a base forms an ester enolate which undergoes arylation by intramolecular migration of an aryl ring to the α-position of the ester. The product undergoes ring closure to a hydantoin, which may itself be deprotected and functionalised. Aryl migration is successful with rings of various electronic character and with esters bearing functionalised and unfunctionalised chains, and the products have features in common with several bioactive compounds.

Efficacy and Safety of Nilutamide in Patients with Metastatic Prostate Cancer who Underwent Orchiectomy: A Systematic Review and Metaanalysis

BACKGROUND

Prostate cancer is the sixth leading cause of death, among all cancer deaths By 2030, this burden is expected to increase with 1.7 million new cases and 499,000 new deaths. We aimed to evaluate the efficacy and safety of Nilutamide in metastatic prostate cancer (mPCa) patients who underwent orchiectomy.

METHODS

A comprehensive search was conducted in the Medline/PubMed and Cochrane Library. References from included studies and studies from clinicaltrials.gov were explored without language and date restrictions. We included only randomized controlled trials, comparing the safety and efficacy of Nilutamide in Metastatic Prostate Cancer (mPCa) patients who underwent orchiectomy with placebo. The outcomes of concerns were survival and the response of drug and safety.. Quality of the included studies was assessed using the Cochrane Risk of Bias Tool. Two authors were independently involved in the study selection, data extraction and quality assessment. Disagreements between the two reviewers were resolved by consulting a third reviewer.

RESULTS

A total of five out of 244 studies were included in meta-analysis involving1637 participants. Nilutamide group showed improved response rate (RR=1.77, 95%CI 1.46-2.14, p<0.00001), disease progression (RR=0.59, 95%CI 0.47-0.73, p<0.00001), complete response (RR=2.13, 95%CI 1.40-3.23, p=0.003) and clinical benefit (RR=1.23, 95%CI 1.13-1.34, p<0.00001) when compared to placebo; however, stable disease favored the control group (RR=0.80, 95%CI 0.68-0.94, p=0.007). In addition, patients on Nilutamide showed prolonged progression-free survival and overall survival. Nausea and vomiting were the most common adverse events reported in Nilutamide group.

CONCLUSION

Evidence suggests that patients with mPCa who underwent orchiectomy receiving Nilutamide showed significant improvement in progression-free survival and overall survival response rate and clinical benefits in comparison with the placebo group.

Enzalutamide and blocking androgen receptor in advanced prostate cancer: lessons learnt from the history of drug development of antiandrogens

Enzalutamide is a nonsteroidal antiandrogen for the treatment of metastatic castration-resistant prostate cancer (mCRPC) both before and after chemotherapy. Enzalutamide is more effective than its predecessor bicalutamide, which was analyzed in head-to-head studies of patients with CRPC. This family of nonsteroidal antiandrogens is now comprised of four drugs approved by the US Food and Drug Administration with two investigational drugs in clinical trials. Antiandrogens have been employed clinically for more than five decades to provide a rich resource of information. Steady-state concentration minimums (C_min or trough) in the range of ~1–13 μg/mL are measured in patients at therapeutic doses. Interestingly, enzalutamide which is considered to have strong affinity for the androgen receptor (AR) requires C_min levels >10 μg/mL. The sequence of antiandrogens and the clinical order of application in regard to other drugs that target the androgen axis remain of high interest. One novel first-in-class drug, called ralaniten, which binds to a unique region in the N-terminus domain of both the full-length and the truncated constitutively active splice variants of the AR, is currently in clinical trials for patients who previously received abiraterone, enzalutamide, or both. This highlights the trend to develop drugs with novel mechanisms of action and potentially differing mechanisms of resistance compared with antiandrogens. Better and more complete inhibition of the transcriptional activity of the AR appears to continue to provide improvements in the clinical management of mCRPC.

Efficacy of Immediate Switching from Bicalutamide to Flutamide as Second-Line Combined Androgen Blockade

We determined whether prostate specific antigen (PSA) would decrease with immediate antiandrogen switching from bicalutamide (BCL) to flutamide (FLT) in patients receiving combined androgen blockade for advanced prostate cancer. From 2002 to 2006, 20 patients who showed PSA failure after first-line hormonal therapy with a luteinizing hormone-release hormone (LH-RH) agonist and BCL were enrolled. All patients were immediately switched from BCL to FLT, administered with an LH-RH agonist, as second-line combined androgen blockade (CAB). We evaluated the PSA response to second-line CAB. Eight patients (40%) were responsive, showing PSA decreases of at least 50%. The median (range) duration of the PSA response was 18.4 (3–26) months. Second-line CAB using FLT was effective in 40% of patients who received first-line CAB using BCL. The lower Gleason scores at the initial prostate biopsy probably reflect the response to second-line CAB. Responders showed significantly better OS and CSS in the determination of any PSA decline and 40% PSA decline. The median OS duration in nonresponders and responders (40% PSA decline) was 1433 days versus 3617 days. It is concluded that an immediate switch from BCL to FLT is effective for some CRPC patients after first-line CAB using BCL.

Clinical outcomes of anti-androgen withdrawal and subsequent alternative anti-androgen therapy for advanced prostate cancer following failure of initial maximum androgen blockade

The present study aimed to investigate the significance of anti-androgen withdrawal and/or subsequent alternative anti-androgen therapy in patients with advanced prostate cancer (PC) who relapsed after initial maximum androgen blockade (MAB). The present study evaluated the clinical outcomes of 272 consecutive advanced PC patients undergoing anti-androgen withdrawal and/or subsequent alternative anti-androgen therapy with flutamide following the failure of initial MAB using bicalutamide. With the exception of 41 patients (15.1%) who did not undergo anti-androgen withdrawal due to the characteristics of PC suggesting aggressive diseases, prostate-specific antigen (PSA) declined from the baseline value in 83 patients (35.9%), including 18 (7.8%) with PSA decline >50%, but not in the remaining 148 (64.1%). No significant difference in the overall survival (OS) or cancer-specific survival (CSS) among the three groups was observed based on the response to anti-androgen withdrawal. Following the introduction of alternative anti-androgen therapy with flutamide, PSA decline was observed in 185 patients (68.0%), including 103 (37.9%) who achieved a PSA reduction of >50%; however, the PSA level continued to elevate in the remaining 87 (32.0%). Furthermore, of the numerous factors examined, only the duration of the initial MAB therapy was shown to be significantly correlated with the PSA decline following alternative anti-androgen therapy. Multivariate analysis of several factors identified revealed that only PSA decline following alternative anti-androgen therapy was an independent predictor of CSS and OS. If initial MAB is effective, the introduction of alternative anti-androgen therapy may be considered; however, anti-androgen withdrawal should be omitted, irrespective of the characteristics of advanced PC.

Sequencing current therapies in the treatment of metastatic prostate cancer

The standard treatment for metastatic prostate cancer is androgen deprivation therapy. However, progressive, metastatic disease usually develops, giving rise to metastatic castration-resistant prostate cancer (mCRPC). Great improvements have been made recently in the management of mCRPC, with current approved treatments including chemotherapy, androgen receptor-targeted agents, immunotherapies and radiopharmaceuticals. While the emergence of multiple effective therapies is encouraging, devising a treatment strategy can be difficult and it is becoming increasingly important, and challenging, to identify factors that influence the ideal timing of specific therapies. Considering where to place these agents in the treatment schedule of mCRPC, or whether these agents should be sequenced or combined to derive the optimal benefit for the patient, is not yet clear. Furthermore, cross-resistance may exist between these agents, which may ultimately influence treatment decisions and sequence choices. Preliminary data are emerging regarding the safety and activity for sequential treatment regimens, but there are currently no prospective studies. As prostate cancer is highly heterogeneous clinically, it is likely that no single treatment sequence will be optimal for all patients. However, at present, there are no validated biomarkers to guide individualized treatment for mCRPC. Here we review available data for the different mCRPC treatments, discussing potential sequencing of agents and possible cross-resistance or synergy among the recently approved and emerging therapies.

Advancement in methodologies for reduction of nitroarenes

Recent advancement in reduction methods of nitroarenes are reviewed. The different methods are classified based on the source of hydrogen utilized during reduction and the mechanism involved in the reduction process.

Recent discoveries and developments of androgen receptor based therapy for prostate cancer

The main focus of this review is to discuss the discoveries and developments of various therapies for prostate cancer.

Metastatic castration resistant prostate cancer: current strategies of management in the Middle East

Although most patients with prostate cancer respond to initial androgen-deprivation therapy, progression to castration-resistant prostate cancer (CRPC) is almost inevitable. In 2004, the docetaxel/prednisone regimen was approved for the management of patients with metastatic CRPC, becoming the standard first-line therapy. Recent advances have also led to an unprecedented number of approved new drugs; thus, providing several treatment options for patients with metastatic CRPC. Five new drugs have received US Food and Drug Administration-approval between 2010 and 2012: sipuleucel-T, an immunotherapeutic agent; cabazitaxel, a novel microtubule inhibitor; abiraterone acetate, a new androgen biosynthesis inhibitor; enzalutamide, a novel androgen receptor inhibitor; and denosumab, a bone-targeting agent. Such drugs are either already marketed or about to be marketed in the Middle East. Data supporting the approval of each of these agents are described in this review, as are recent approaches to the treatment of metastatic CRPC.

Recent advances revolutionize treatment of metastatic prostate cancer

In 2004, the chemotherapy agent docetaxel was approved for the treatment of metastatic prostate cancer. Although it has taken almost a decade, significant new advances have been made in this area, including the clinical development of modern hormonal therapies, such as abiraterone and enzalutamide, and immunotherapies, such as sipuleucel-T, all of which have improved survival in metastatic prostate cancer. These agents have not only provided new therapeutic options for patients with advanced disease, they have also spurred research in both androgen receptor-targeting therapy and immunotherapy. Future trials will focus on the optimal sequence of these and other emerging therapies, with the aim of using these treatments earlier in the disease course (including the adjuvant setting) to enhance clinical benefit and potentially increase the cure rate for prostate cancer.

Non-metastatic CRPC and asymptomatic metastatic CRPC: which treatment for which patient?

The introduction of early PSa-based diagnosis has profoundly impacted the epidemiology of castration-resistant prostate cancer (CRPC). Many patients enter the disease at an early stage when the only sign of resistance to androgen deprivation therapy (ADT) is a progressive elevation of prostate-specific antigen (PSA). This created a very heterogeneous population of non-metastatic (M0) CRPC. PSa kinetics is the most powerful indicator of aggressiveness in that population and can be used to trigger imaging investigation and enrollment in clinical trials. Several registered and near to come treatments have not been tested in that population but in men with more advanced metastatic and often symptomatic disease. Several agents have been investigated to delay the onset of the first bone metastasis but only one, denosumab, has reached its end-point. Because CRPC remains largely driven by the androgen receptor (AR), physicians have relied on second-line hormonal manipulations to delay the progression of the disease, including first generation antiandrogens, adrenal synthesis inhibitors, steroids and estrogens. The data however are mostly limited to phase II trials.

Spongian diterpenoids inhibit androgen receptor activity

Androgen receptor is a ligand-activated transcription factor and a validated drug target for all stages of prostate cancer. Antiandrogens compete with physiologic ligands for androgen receptor ligand-binding domain (LBD). High-throughput screening of a marine natural product library for small molecules that inhibit androgen receptor transcriptional activity yielded the furanoditerpenoid spongia-13(16),-14-dien-19-oic acid, designated terpene 1 (T1). Characterization of T1 and the structurally related semisynthetic analogues (T2 and T3) revealed that these diterpenoids have antiandrogen properties that include inhibition of both androgen-dependent proliferation and androgen receptor transcriptional activity by a mechanism that involved competing with androgen for androgen receptor LBD and blocking essential N/C interactions required for androgen-induced androgen receptor transcriptional activity. Structure-activity relationship analyses revealed some chemical features of T1 that are associated with activity and yielded T3 as the most potent analogue. In vivo, T3 significantly reduced the weight of seminal vesicles, which are an androgen-dependent tissue, thereby confirming the on-target activity of T3. The ability to create analogues of diterpenoids that have varying antiandrogen activity represents a novel class of chemical compounds for the analysis of androgen receptor ligand-binding properties and therapeutic development.

Castration-resistant prostate cancer: mechanisms, targets, and treatment

Patients with castration-resistant prostate cancer (CRPC), who progress after docetaxel therapy, had until very recently, only a few therapeutic options. Recent advances in this field brought about new perspectives in the treatment of this disease. Molecular, basic, and translational research has given us a better understanding on the mechanisms of CRPC. This great investment has turned into a more rational approach to the development of new drugs. Some of the new treatments are already available to our patients outside clinical trials and may include inhibitors of androgen biosynthesis; new chemotherapy agents; bone-targeted therapy; and immunotherapy. This paper aims to review the mechanisms of prostate cancer resistance, possible therapeutic targets, as well as new options to treat CRPC.

Novel, potent anti-androgens of therapeutic potential: recent advances and promising developments

The beneficial effect of androgen ablation has been well established in prostate cancer therapy. Despite the initial response, patients typically relapse with a more aggressive form described as castration-resistant prostate cancer (CRCP), driven by continued androgen receptor (AR) signaling. This review details the current state of anti-androgen therapy, mainly for CRPC, with major emphasis on the most potent and promising compounds under development. Anti-androgen failure has been linked to elevated AR expression, increased expression of coactivator proteins, AR mutations, ligand-independent AR activation and persistent intraprostatic androgens. MDV3100, BMS-641988 and VN/124-1 were developed to overcome these mechanisms. In CRCP, prostate cancer cells still rely on intracellular androgens and, to a greater extent, on active AR for growth and survival. Therefore, potent anti-androgens that efficiently disrupt the functions (signaling) of AR are envisioned to be effective drugs for all types of prostate cancers.

Sipuleucel-T for therapy of asymptomatic or minimally symptomatic, castrate-refractory prostate cancer: an update and perspective among other treatments

Sipuleucel-T is an autologous cell immunotherapy for castrate-refractory prostate cancer, with US Food and Drug Administration (FDA) approval in asymptomatic or minimally symptomatic prostate cancer. In this review we address the background of prostate cancer incidence and other available therapy onto which sipuleucel-T treatment has been added, with discussion of hormone-therapy, chemotherapy, and other investigational immunotherapies. The sipuleucel-T manufacturing process, toxicity and clinical benefit are reviewed, along with an examination of the issue of clinical benefit to survival, independent of apparent changes of prostate-specific antigen (PSA) levels. Sipuleucel-T therapy is appraised from clinician, patient and immunotherapeutic perspectives, with reference to the clinical data from the pivotal trial, the mechanism of action, and the treatment process.

Current treatment strategies for castration-resistant prostate cancer

Prostate cancer is the most common cancer in men in United States and the fifth most common cancer in men in Korea. Although the majority of patients with metastatic prostate cancer initially respond to androgen deprivation therapy, almost all patients will eventually progress to develop castration-resistant prostate cancer (CRPC). Treatment options for CRPC remain limited. Prostate cancer was considered unresponsive to chemotherapy until the mid-1990s, when mitoxantrone combined with prednisone was shown to play a role in the palliative treatment of patients with CRPC. In 2004, two large randomized clinical trials demonstrated for the first time a small but significant survival advantage of docetaxel-based chemotherapy compared with mitoxantrone in patients with metastatic CRPC. Recently, cabazitaxel was shown to improve survival in patients with metastatic CRPC who progressed after docetaxel-based chemotherapy. Sipuleucel-T was also demonstrated to improve overall survival in patients with asymptomatic or minimally symptomatic metastatic CRPC. Along with mitoxantrone and docetaxel, cabazitaxel and sipuleucel-T are now approved for use in metastatic CRPC by the US Food and Drug Administration. There have been multiple early-phase clinical trials of various agents for the treatment of CRPC, and some are in phase III development. This review focuses on the key clinical trials of various treatment options of CRPC currently in use and under investigation.

Novel therapeutic strategies for castration resistant prostate cancer: inhibition of persistent androgen production and androgen receptor mediated signaling

PURPOSE

Androgen receptor signaling remains essential for many prostate cancers that have progressed despite androgen deprivation therapy. After medical or surgical castration persistent though not insignificant low levels of androgens are produced from nongonadal sources, such as the adrenal glands. Some castration resistant prostate cancers acquire the ability to convert adrenal steroids to androgens, maintaining levels sufficient to activate androgen receptor. Inhibition of persistent androgen production and androgen receptor mediated signaling are relevant therapeutic strategies for castration resistant prostate cancer.

MATERIALS AND METHODS

The scientific foundation of and clinical experience with secondary hormonal therapy as well as the development of new investigational agents for castration resistant prostate cancer, specifically selective cytochrome p450 17 inhibitors and second generation antiandrogens, are discussed.

RESULTS

Selective inhibition of cytochrome p450 17 has emerged as an important therapeutic pathway for castration resistant prostate cancer. The selective cytochrome p450 17 inhibitor abiraterone acetate showed promising activity and tolerability in phase I-II trials. Phase III studies are underway in men with chemotherapy naïve castration resistant prostate cancer as well as those with progression after docetaxel based chemotherapy. TAK-700 and TOK-001 (formerly VN124-1) are novel selective cytochrome p450 17 inhibitors that recently entered phase I/II evaluation. MDV3100 is a second generation antiandrogen that blocks androgen receptor signaling by inhibiting nuclear translocation of the ligand-receptor complex. Clinical data on MDV3100 are encouraging and support continued phase III study.

CONCLUSIONS

Novel therapies for castration resistant prostate cancer that target persistent androgen production and androgen receptor mediated signaling have demonstrated promising activity in many men with castration resistant prostate cancer and may redefine the clinical management of these patients.

[Management of metastatic androgeno-independent prostate cancer]

After first line hormonal therapy (agonist LHRH), metastasic prostate cancer becomes androgen independent in a period of 18 months on average. After this period and after having verified the castration by blood testosterone level, a few options are possible: either inhibit adrenal androgens by maximum androgen blockage (+anti androgens) or by specific adrenal androgen inhibitors. It is also possible to use estrogen or, in a few cases, to propose chemotherapy.

Maximal androgen blockade for advanced prostate cancer

Maximal androgen blockade (MAB) refers to the combination of medical (gonadotrophin-releasing hormone agonist) or surgical castration with an anti-androgen for the treatment of advanced prostate cancer. A substantial body of basic research has improved our understanding of the interactions between the anti-androgens, the androgen receptor, and androgen response elements in the genome. Anti-androgens act by two primary mechanisms: inhibition of ligand (androgen) binding to the androgen receptor, and inhibition of androgen-independent activation of the receptor. The latter mechanism occurs via several pathways, including inhibiting nuclear co-activators, activating co-suppressors, and inhibiting transcription of a variety of androgen-regulated genes. It is more accurate to refer to these compounds as androgen-receptor antagonists, since they inhibit activation whether this is androgen-mediated or not. Within the class of non-steroidal anti-androgens, there is variation in the degree to which ligand-independent activation is inhibited. Over the last 25 years, approximately 30 clinical trials have addressed the benefit of MAB versus monotherapy. Most of these trials have evaluated flutamide or nilutamide. Several meta-analyses suggest a modest survival benefit of these drugs, amounting to an 8% mortality reduction at 5 years. Preclinical data and two randomized trials -- one historic and one current -- suggest that bicalutamide may be a more effective drug in this respect. This requires confirmation pending further maturity of the current trial, which is the only one directly comparing bicalutamide plus castration to castration alone. In prostate cancer patients at high risk for mortality (based on extent of disease or prostate-specific antigen kinetics), combination therapy with bicalutamide should be considered in preference to monotherapy.

Phase II study of ketoconazole plus granulocyte-macrophage colony-stimulating factor for prostate cancer: effect of extent of disease on outcome

PURPOSE

The efficacy of ketoconazole plus the immunostimulatory cytokine granulocyte-macrophage colony-stimulating factor was prospectively evaluated in patients with castration resistant prostate cancer with and without metastases.

MATERIALS AND METHODS

Eligible patients had progressive castration resistant prostate cancer by consensus criteria and had received no prior immunotherapy, chemotherapy or ketoconazole. Patients received 400 mg ketoconazole orally 3 times daily, and 20 mg hydrocortisone orally each morning and 10 mg hydrocortisone orally each evening. Granulocyte-macrophage colony-stimulating factor (250 microg/m2) was administered subcutaneously on days 15 to 28 of each 28-day cycle. Progression was defined as disease progression or toxicity.

RESULTS

A total of 49 patients were enrolled, including 37 with radiographically evident metastases and 12 with prostate specific antigen only disease. Median patient age was 68 years (range 52 to 84) and median prostate specific antigen was 23.1 ng/ml (range 5.4 to 306.5). Time to progression, which was the primary study end point, was 9.7 months for all patients. Ten of the 30 treatment failures showed radiographic progression and 6 were due to toxicity, while treatment failure in 14 of 30 patients (47%) consisted only of increasing prostate specific antigen. Median time to progression was 6.9 and 15.4 months in patients with and without metastases, respectively (p = 0.01). Of 48 patients 36 (75%, 95% CI 60-86) experienced a 50% or greater decrease in prostate specific antigen. Four grade 4 events occurred that were unrelated to the study drug. Grade 3 events related to study therapy in more than 1 patient consisted of fatigue in 7 (14%).

CONCLUSIONS

Combined ketoconazole and granulocyte-macrophage colony-stimulating factor yields a high response rate and it is an option for patients with castration resistant prostate cancer. Time to progression in patients without metastases is significantly longer than in those without metastases.

Rising prostate-specific antigen after primary treatment of prostate cancer: sequential hormone manipulation

OBJECTIVE

To evaluate systematically the current endocrine treatment options for patients with biochemical recurrence after radical prostatectomy or radiation therapy for localized prostate cancer.

METHODS

Literature search of PubMed documented publications and abstracts from international meetings. Key items included timing and type of salvage hormone therapy, length of its application and handling of side effects.

RESULTS

The majority of patients with isolated prostate-specific antigen (PSA) relapse are not candidates for salvage treatment with curative intent. The PSA threshold that triggers initiation of hormonal therapy is debatable and should be based also on pretreatment risk assessment. Intermittent androgen suppression is an emerging concept to circumvent the unresolved controversy of early versus deferred endocrine therapy. Since the tumor load at time of recurrence is low, peripheral androgen blockade with an antiandrogen and a 5alpha-reductase inhibitor is an acceptable first choice. In case of progression, addition of a LHRH analogue would be the next step. Antiandrogen withdrawal and second-line antiandrogens are clinically of limited value.

CONCLUSIONS

Biochemical-only progression after definitive treatment in curative intent is different from objective or even symptomatic relapse and allows for sequential hormonal therapy with a variety of compounds.

Castration resistant, taxane naïve metastatic prostate cancer: current clinical approaches and future directions

PURPOSE

With the wide use of prostate specific antigen to detect response and disease progression resistance to androgen deprivation is being detected at an increasingly earlier stage. We focused on the current management and novel investigational strategies for the chemonaïve patient population with castration resistant metastatic disease.

MATERIALS AND METHODS

We reviewed standard and investigational hormonal, chemotherapeutic, biological and immune based strategies for patients with castration resistant metastatic prostate cancer who have not yet received taxane based chemotherapy.

RESULTS

Our understanding of the natural history of this group of patients is evolving. A variety of standard and experimental treatment options are available for this group of patients. Manipulating the androgen receptor signaling axis, targeting antiapoptotic pathways, using antiangiogenic strategies, harnessing the immune system and optimizing docetaxel based regimens and novel cytotoxic agents are under investigation.

CONCLUSIONS

Multiple agents currently under development offer a promise of palliation and prolongation of survival above and beyond that of docetaxel. In the absence of guidance from randomized trials with regard to chemotherapy timing, and considering the modest effects of docetaxel on survival, decisions regarding choice of therapy (standard chemotherapy or experimental therapies) must be based on careful consideration of the functional status of each individual, presence of symptoms, comorbidities and overall therapeutic objectives.