Effects of flutamide as a second-line agent for maximum androgen blockade of hormone refractory prostate cancer

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.

Novel combination therapy of prostate cancer cells with arsenic trioxide and flutamide: An in-vitro study

OBJECTIVE

The study objective was to assess the therapeutic potential of Arsenic Trioxide (ATO) and Flutamide combination for metastatic prostate cancer (PCa) treatment.

MATERIAL AND METHOD

LNCaP and PC3 cell lines were treated with different concentrations of ATO and PCa conventional drug Flutamide alone and/or in combination to find effective doses and IC₅₀ values. Percentages of apoptotic cells were evaluated by Annexin/PI staining and the proliferative inhibitory effect was assessed by Micro Culture Tetrazolium Test (MTT). Expression of SNAIL, KLK2, E-cadherin, and angiogenesis genes (VEGFA and VEGFC), and apoptosis genes (Bcl₂, and P53) were examined by real-time PCR.

RESULTS

The combination of Flutamide and ATO significantly increased the percentage of apoptotic cells and inhibited PCa cells proliferation compared with each drug alone in LNCaP and PC3 cell lines. Generally, both cell lines treated with the combination of Flutamide and ATO showed a decrease in expression of KLK2, angiogenesis genes (VEGFA and VEGFC), and apoptosis gene (Bcl₂), and an increase in expression of E-cadherin and P53 genes; however, contradictory findings were found regarding SNAIL expression in LNCaP and PC3 cells.

CONCLUSION

The combination therapy with ATO and flutamide has augmented the anti-tumor effect on LNCaP and PC3 cells, which probably originates from their potential to induce apoptosis and inhibit the proliferation of PCa cells simultaneously.

Enzalutamide + androgen deprivation therapy (ADT) versus flutamide + ADT in Japanese men with castration‐resistant prostate cancer: AFTERCAB study

Objectives

The objective of the study is to compare the efficacy and safety of alternative androgen therapy (AAT) with enzalutamide + androgen deprivation therapy (ADT) and flutamide + ADT in the treatment of Japanese men with metastatic or nonmetastatic castration‐resistant prostate cancer (CRPC) who progressed despite combined androgen blockade (CAB) with bicalutamide + ADT. AAT treatment sequence was also investigated.

Materials and methods

The open‐label, Phase 4 AFTERCAB study (NCT02918968) was conducted from November 2016 to March 2020 in Japanese men aged ≥20 years with asymptomatic or mildly symptomatic CRPC. Patients were initially randomized to enzalutamide (160 mg/day) + ADT (enzalutamide first) or flutamide (375mg/day [125mg three times daily]) + ADT (flutamide first) as first‐line therapy. Following prostate‐specific antigen (PSA) progression, other disease progression, or discontinuation of first‐line therapy due to an adverse event (AE), patients switched to the other treatment as second‐line therapy. The primary endpoint was time to PSA progression with first‐line therapy (TTPP1). Secondary endpoints included TTPP2 (TTPP1 + time to PSA progression with second‐line therapy). AEs were monitored to assess safety.

Results

Overall, 206 men were randomized (enzalutamide first, n = 102; flutamide first, n = 104) and stratified by study site and disease stage; 133 patients transitioned to second‐line therapy (enzalutamide first, n = 48; flutamide first, n = 85). TTPP1 was significantly improved with enzalutamide first versus flutamide first (median 21.4 months vs. 5.8 months; hazard ratio [HR] 0.42; 95% confidence interval [CI] [0.29, 0.61]). TTPP2 was numerically improved with enzalutamide first versus flutamide first (median not reached vs. 21.2 months; HR 0.76; 95% CI [0.48, 1.19]). Both treatments were generally well tolerated, with AEs consistent with their known safety profiles.

Conclusion

First‐line AAT with enzalutamide + ADT provided a significant improvement in time to PSA progression versus flutamide + ADT. Enzalutamide + ADT may therefore be the preferred first‐line AAT option in Japanese men with metastatic or nonmetastatic CRPC who progress despite CAB with bicalutamide + ADT.

Predictors of poor response to first-generation anti-androgens as criteria for alternate treatments for patients with non-metastatic castration-resistant prostate cancer

PURPOSE

There are no criteria for administering first- or second-generation anti-androgens (FGA and SGA, respectively) to patients with non-metastatic castration-resistant prostate cancer (nmCRPC). This study aimed to assess the efficacy of alternative FGA therapy in nmCRPC patients and the prognosis of these patients and to identify factors for predicting patients potentially responsive to FGA.

METHODS

Data from 63 men with nmCRPC who underwent alternative FGA therapy (bicalutamide, flutamide, or chlormadinone acetate) as first-line therapy after failure of primary androgen-deprivation therapy (PADT) between 2004 and 2017 at Hiroshima University Hospital and affiliated hospitals were retrospectively investigated. The associations of clinicopathological parameters with overall survival (OS) and prostate-specific antigen (PSA) progression-free survival (PFS) of alternative FGA-treated patients were analyzed.

RESULTS

Time to CRPC [p = 0.007, hazard ratio (HR) = 4.77], regional lymph node involvement at the diagnosis of CRPC (p = 0.022, HR = 2.42), and PSA-PFS of alternative FGA therapy ≤ 6 months (p = 0.020, HR = 2.39) were identified as prognostic factors using a multivariate analysis. Additionally, Cox proportional hazard models revealed that PSA nadir value > 1 ng/mL during PADT (p = 0.034, HR = 2.40) and time from starting PADT to PSA nadir ≤ 1 year (p = 0.047, HR = 1.85) were predictive factors for worse PSA-PFS in alternative FGA therapy.

CONCLUSIONS

Shorter time to CRPC, regional lymph node involvement, PSA nadir during PADT > 1 ng/mL, and time from starting PADT to PSA nadir ≤ 1 year might suggest the potential benefit of immediate commencement of SGA, compared to FGA administration after nmCRPC diagnosis.

Enzalutamide versus flutamide for castration-resistant prostate cancer after combined androgen blockade therapy with bicalutamide: study protocol for a multicenter randomized phase II trial (the OCUU-CRPC study)

Background

Enzalutamide is an oral androgen receptor targeted agent that has been shown to improve survival in PREVAIL trials and has been approved for patients with chemo-naïve metastatic castration-resistant prostate cancer (CRPC). Meanwhile, flutamide is a non-steroidal oral anti-androgen that was commonly used before the approval of bicalutamide. The objective of the OCUU-CRPC study is to compare the efficacy and safety between second-line hormonal therapy of enzalutamide and flutamide as alternative anti-androgen therapy (AAT) after combined androgen blockade (CAB) therapy that included bicalutamide in patients with CRPC.

Methods

A total of 100 patients with CRPC with or without distant metastases after disease progression who received CAB therapy with bicalutamide were randomly assigned at a 1:1 ratio according to distant metastases to the enzalutamide (160 mg/day, 4 × 40 mg capsules once daily) and flutamide (375 mg/day; 3 × 125 mg tablets thrice daily) groups. The primary endpoint for the drug efficacy is the response rate of prostate-specific antigen (PSA) (i.e., the ratio of patients whose PSA declined by ≥50% from baseline) at 3 months. Meanwhile, the secondary endpoints are PSA progression rate at 3 and 6 months, PSA response rate at 6 months, change in quality of life, PSA progression-free survival, and safety. The patient registration started in January 2015 and will end in March 2018, and the follow-up period is 6 months after the last patient registration. The main result will be reported in March 2019.

Discussion

In the OCUU-CRPC study, we compare the efficacy and safety of enzalutamide or alternative AAT with flutamide in participants with CRPC who were previously treated with a CAB therapy with bicalutamide. The expected results of this study will be that enzalutamide is superior to flutamide in terms of PSA response. A longer time to disease progression with enzalutamide over flutamide may translate to better overall survival. However, flutamide may be more accessible for patients owing to its lower cost than enzalutamide.

Trial registration

The OCUU-CRPC study was prospectively registered at clinicaltrials.gov (NCT02346578, January 2015) and University Hospital Medical Information Network (UMIN000016301, January 2015).

Management of nonmetastatic castration-resistant prostate cancer

PURPOSE OF REVIEW

The widespread use of prostate-specific antigen (PSA) resulted in stage migration of prostate cancer where androgen deprivation therapy (ADT) is administered for biochemical recurrence in patients following primary treatment. A proportion of these patients progress to a disease state termed nonmetastatic castration-resistant prostate cancer (nmCRPC), with a rising PSA despite ADT and without evidence of metastases on conventional imaging. We will review the treatment options in nmCRPC, especially in light of recent trials showing significant improvement in metastasis-free survival with newer agents.

RECENT FINDINGS

Historically, nmCRPC patients were followed-up if PSA doubling-time (PSADT) exceeded 10 months. Treatment options for patients with shorter PSADT included hormonal manipulations that often resulted in transient PSA decline. Denosumab was found to delay the onset of bone metastasis but did not impact survival. Recently, phase 3 trials showed that second-generation antiandrogens resulted in a significant delay in metastasis and a trend toward survival improvement in a select group of nmCRPC patients.

SUMMARY

The importance of reducing mortality and morbidity associated with metastasis has led to the acceptance of new primary endpoints in the design of trials for nmCRPC and might result in widespread approval of new agents for this disease state.

Effectiveness of Deferred Combined Androgen Blockade Therapy Predicts Efficacy in Abiraterone Acetate Treated Metastatic Castration-Resistant Prostate Cancer Patients after Docetaxel

Introduction: Conventional anti-androgen regimens were widely used as an initiation or combined androgen blockade (CAB) therapy in advanced prostate cancer patients. Currently, new androgen pathway inhibitors such as abiraterone acetate (AA) and enzalutamide had been proven effective in metastatic castration resistant prostate cancer. In this study, we attempt to analyze the role of conventional anti-androgen drugs as deferred CAB therapy in castration-resistant prostate cancer patients.

Materials and Methods: From 2012 to 2017, 48 metastatic castration-resistant prostate cancer (CRPC) patients who received sequential treatments with primary androgen blockade, oral anti-androgen regimens, and docetaxel followed by AA treatment were included. We defined effective deferred CAB as any decline of PSA after add-on antiandrogen after CRPC. Patients were separated into effective and ineffective deferred CAB. Comparison between two groups in the first line androgen deprivation therapy duration, CRPC PSA level, pre-AA PSA level, chemotherapy dosages, duration, and patients progression free survival and overall survival after AA treatment were analyzed.

Results: Twenty-three patients (47.9%) achieved PSA decline after deferred CAB. Among total 48 patients, 24 patients experienced PSA decline more than 50% after AA treatment. The median PSA progression-free survival and overall survival after AA treatment in the total cohort of 48 patients were 4.4 and 24.3 months, respectively. The effective deferred CAB group showed significantly lower PSA level, lower percentage of PSA progression, higher total follow-up duration, higher percentage of surviving patients, better progression free survival, and overall survival estimate after AA treatment. Of the eight variables analyzed, effectiveness in deferred CAB showed positive association to progression free survival (HR 0.29, 95% CI 0.12–0.67, p = 0.004) and overall survival (HR 0.24, 95% CI 0.07–0.81, p = 0.022). First line androgen deprivation therapy (ADT) duration also showed positive association to overall survival (HR 0.95, 95% CI 0.91–0.99, p = 0.023).

Conclusions: Effectiveness of deferred CAB therapy was positively associated with progression free survival and overall survival of AA treatment after docetaxel. It can be used as a pre-treatment predictor.

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.

Targeting the relaxin hormonal pathway in prostate cancer

Targeting the androgen signalling pathway has long been the hallmark of anti-hormonal therapy for prostate cancer. However, development of androgen-independent prostate cancer is an inevitable outcome to therapies targeting this pathway, in part, owing to the shift from cancer dependence on androgen signalling for growth in favor of augmentation of other cellular pathways that provide proliferation-, survival- and angiogenesis-promoting signals. This review focuses on the role of the hormone relaxin in the development and progression of prostate cancer, prior to and after the onset of androgen independence, as well as its role in cancers of other reproductive tissues. As the body of literature expands, examining relaxin expression in cancerous tissues and its role in a growing number of in vitro and in vivo cancer models, our understanding of the important involvement of this hormone in cancer biology is becoming clearer. Specifically, the pleiotropic functions of relaxin affecting cell growth, angiogenesis, blood flow, cell migration and extracellular matrix remodeling are examined in the context of cancer progression. The interactions and intercepts of the intracellular signalling pathways of relaxin with the androgen pathway are explored in the context of progression of castration-resistant and androgen-independent prostate cancers. We provide an overview of current anti-hormonal therapeutic treatment options for prostate cancer and delve into therapeutic approaches and development of agents aimed at specifically antagonizing relaxin signalling to curb tumor growth. We also discuss the rationale and challenges utilizing such agents as novel anti-hormonals in the clinic, and their potential to supplement current therapeutic modalities.

Castration-resistant prostate cancer: AUA Guideline

PURPOSE

This Guideline is intended to provide a rational basis for the management of patients with castration-resistant prostate cancer based on currently available published data.

MATERIALS AND METHODS

A systematic review and meta-analysis of the published literature was conducted using controlled vocabulary supplemented with keywords relating to the relevant concepts of prostate cancer and castration resistance. The search strategy was developed and executed by reference librarians and methodologists to create an evidence report limited to English-language, published peer-reviewed literature. This review yielded 303 articles published from 1996 through 2013 that were used to form a majority of the guideline statements. Clinical Principles and Expert Opinions were used for guideline statements lacking sufficient evidence-based data.

RESULTS

Guideline statements were created to inform clinicians on the appropriate use of observation, androgen-deprivation and antiandrogen therapy, androgen synthesis inhibitors, immunotherapy, radionuclide therapy, systemic chemotherapy, palliative care and bone health. These were based on six index patients developed to represent the most common scenarios encountered in clinical practice.

CONCLUSIONS

As a direct result of the significant increase in FDA-approved therapeutic agents for use in patients with metastatic CRPC, clinicians are challenged with a multitude of treatment options and potential sequencing of these agents that, consequently, make clinical decision-making more complex. Given the rapidly evolving nature of this field, this guideline should be used in conjunction with recent systematic literature reviews and an understanding of the individual patient's treatment goals. In all cases, patients' preferences and personal goals should be considered when choosing management strategies.

Biological properties of androgen receptor pure antagonist for treatment of castration-resistant prostate cancer: optimization from lead compound to CH5137291

BACKGROUND

Castration-resistant prostate cancer (CRPC) is still dependent on androgen receptor (AR) signaling. We previously reported that a novel nonsteroidal AR pure antagonist, CH4933468, which is a thiohydantoin derivative with a sulfonamide side chain, provided in vitro proof of concept but did not in vivo.

METHODS

We developed other derivatives, CH5137291, CH5138514, and CH5166623, and their pharmacological properties were compared with CH4933468 and bicalutamide. Agonist/antagonist activities in AR-mediated transactivation, cell proliferation against LNCaP and LNCaP-BC2, and AR translocation were evaluated. Agonist metabolite was monitored in liver microsomes and in pharmacokinetics experiments. Antitumor activities in CRPC xenograft models were examined using LNCaP-BC2 and VCaP-CRPC.

RESULTS

All CH compounds completely inhibited AR-mediated transactivation and proliferation of LNCaP and LNCaP-BC2. In contrast bicalutamide showed a partial inhibition of AR-mediated transactivation and a proliferation of LNCaP-BC2. AR translocation to nucleus was inhibited by CH compounds, but stimulated by bicalutamide. In the LNCaP-BC2 xenograft model, however, only CH5137291 showed significant inhibition of plasma PSA level and antitumor activity. The other three CH compounds were metabolized to their core structure which had agonist activity. CH5137291 also exhibited antitumor activity in a VCaP-CRPC xenograft model, but bicalutamide did not.

CONCLUSIONS

The molecular mechanism of the CH compounds, inhibition of AR translocation, was different from bicalutamide and this action could contribute to AR pure antagonist activity. Agonist metabolite diminished the antitumor activity of AR pure antagonist. CH5137291 exhibited antitumor activity in LNCaP-BC2 and VCaP-CRPC xenograft models, suggesting that the compound has potential for the treatment of CRPC.

Role of maximum androgen blockade in advanced prostate cancer

Androgen ablation is the mainstay treatment for advanced prostate cancer (PC). Researchers proposed that maximum androgen blockade (MAB) therapy with antiandrogen agent in combination with castration might result in a better outcome among patients with advanced PC. In the last two decades, numerous trials and pooled data analyses were conducted to optimize the role of MAB in the treatment of metastatic PC. Non-steroidal antiandrogens administered as part of MAB proved to have a small (3%) survival benefit, however, the magnitude of this difference is of questionable clinical significance. Available evidence suggests that MAB should not be routinely offered to patients with metastatic PC, however, it should remain a reasonable option when discussing management. The standard first line treatment should be a monotherapy, consisting of orchiectomy or LHRH agonist. MAB still has a role as a short-term therapy (2-4 weeks). The ongoing large sample population based prospective studies may add new dimensions in the use of MAB in treatment of the prostate cancer in future.

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.

Efficacy of alternative antiandrogen therapy for prostate cancer that relapsed after initial maximum androgen blockade

PURPOSE

We evaluated the effectiveness of second-line maximum androgen blockade (MAB) with an alternative antiandrogen in patients who relapsed after initial MAB.

MATERIALS AND METHODS

We retrospectively analyzed 47 patients with prostate cancer who relapsed after initial MAB, including surgical or medical castration combined with antiandrogens, from January 1998 to December 2009. When the serum prostate-specific antigen (PSA) level was increased on three consecutive occasions, we discontinued the antiandrogen and then administered an alternative antiandrogen. Seven patients were assessed for antiandrogen withdrawal syndrome (AWS). The effect of the second-line MAB was evaluated by the serum PSA level, and response was subdivided into ≥50% and <50% PSA reductions from the baseline PSA at the start of second-line MAB.

RESULTS

PSA reduction was observed in 32 patients (68.1%). Among them, 23 (48.9%) achieved ≥50% PSA reductions with a mean response duration of 13.4±5.4 months. Nine (19.2%) patients reached <50% PSA reductions with a mean response duration of 12.2±6.2 months. The time to nadir PSA level after first-line MAB in the ≥50% PSA reduction group, <50% PSA reduction group, and PSA elevation group was 15.6±12.9 months, 11.8±6.0 months, and 8±6.5 months, respectively. That is to say, it was significantly longer in the responder groups (p=0.038).

CONCLUSIONS

Second-line MAB using an alternative antiandrogen is an effective treatment option before cytotoxic chemotherapy in patients who relapse after initial MAB.

Alternative antiandrogen therapy in patients with castration-resistant prostate cancer: a single-center experience

Outcomes of alternative (second-line) antiandrogen therapy in 112 patients with relapsing prostate cancer after first-line hormonal therapy were analyzed. A good response (prostate-specific antigen [PSA] decrease 50%) and a partial response (PSA decrease of 0–50%) by switching from bicalutamide (BCL) to flutamide (FLT) and from FLT to BCL were achieved in 35.4% (28/79) and 30.4% (24/79), and in 45.0% (9/20) and 20.0% (4/20) of cases, respectively. A good response and a partial response with the change from chlormadinone acetate (CMA) to a non-steroidal antiandrogen (FLT or BCL)and from a non-steroidal antiandrogen to CMA were obtained in 25.0% (2/8) and 37.5% (3/8), and in 20.0% (1/5) and 0% (0/5)of cases, respectively. In multivariate analyses, a second-line good response was significantly predictive of cause-specific survival from first therapy relapse to cancer death in all patients. Patients (52/112, 46.4%) with 30% decrease in PSA levels were associated with significantly better cause-specific survival as measured from the start of first-line treatment and first-line relapse.

Complete androgen blockade safely allows for delay of cytotoxic chemotherapy in castration refractory prostate cancer

PURPOSE

Complete androgen blockade (CAB) does not prolong overall survival (OS) in patients with castration refractory prostate cancer (CRPC). Although there is variable clinical benefit with second-line hormone manipulation, we do not know which patients might benefit the most.

OBJECTIVES

To identify clinical predictors of benefit of complete androgen blockade.

MATERIALS AND METHODS

We reviewed the records for 54 patients who received treatment with CAB in the setting of disease progression despite castration. We evaluated progression-free survival (PFS) and OS according to PSA at diagnosis, Gleason scores, age, testosterone level, and duration of prior disease control during castration in first line treatment.

RESULTS

Among 54 patients who received CAB, the median PFS was 9 months (CI 4.3-13.7) and OS was 36 months (CI 24-48). We did not find an effect of PSA at diagnosis (p = 0.32), Gleason score (p = 0.91), age (p = 0.69) or disease control during castration (p = 0.87) on PFS or OS. Thirty-four patients subsequently received chemotherapy, with a mean OS of 21 months (CI 16.4-25.5, median not reached).

CONCLUSION

Age, Gleason score, PSA at diagnosis and length of disease control with castration did not affect PFS or OS. In the absence of predictors of benefit, CAB should still be considered in CRPC.

Adrenal androgen levels as predictors of outcome in castration-resistant prostate cancer patients treated with combined androgen blockade using flutamide as a second-line anti-androgen

OBJECTIVES

To analyze the clinical effects of flutamide as a second-line anti-androgen for combined androgen blockade in patients with castration-resistant prostate cancer (CRPC) initially treated with bicalutamide as a first-line anti-androgen.

METHODS

Our study population consisted of 16 patients with CRPC who were treated with flutamide (375 mg daily) as second-line hormonal therapy. Dehydroepiandrosterone (DHEA), androstenedione, androstenediol, testosterone and dihydrotestosterone were measured to investigate the relationship between plasma androgens and outcome following treatment. Furthermore, adrenal androgen levels in a medium of adrenal cancer cell line were also measured.

RESULTS

Second-line hormonal therapy using flutamide resulted in a reduction of the prostate-specific antigen (PSA) level in 14 (87.5%) of 16 patients. A PSA decline greater than 50% was observed in 8 (50%) of the 16 patients. The duration of median responsiveness was 6.25 months. PSA elevation of baseline androstenediol level was a predictive factor of PSA responsiveness. The lower DHEA group improved the duration of responsiveness to flutamide. In vitro, 3 micromol/L flutamide suppressed DHEA, androstenedione and androstenediol synthesis compared with bicalutamide in a medium of adrenal cancer cell line.

CONCLUSIONS

Our data show that flutamide suppresses the adrenal androgens in comparison with bicalutamide. The responsiveness and response duration of flutamide can be predicted in patients with a higher baseline androstenediol level and a lower DHEA level. Metabolites from adrenal androgens contribute to the progression of prostate cancer.

Antiandrogen withdrawal syndrome and alternative antiandrogen therapy associated with the W741C mutant androgen receptor in a novel prostate cancer xenograft

BACKGROUND

The mechanisms underlying antiandrogen withdrawal syndrome (AWS) and alternative antiandrogen therapy (AAT) effectiveness were assumed to be mutations in the androgen receptor (AR), which resulted in an altered response to antiandrogens. The aim of the present study was to test this assumption using the novel prostate cancer xenograft model KUCaP-1 harboring the W741C mutant AR (Yoshida et al., Cancer Res 2005; 65(21): 9611-9616).

METHODS

Mice bearing xenograft tumors were castrated, and the long-term sequential changes in tumor volume were observed. To determine whether AWS was observed in this model, bicalutamide (BCL) was orally administered to the castrated mice and then withdrawn. The effect of flutamide (FLT) on the W741C mutant AR was examined with transactivation assays in vitro and with the oral administration of FLT to non-castrated mice harboring KUCaP-1 in vivo. The AAT efficacy against KUCaP-1 was evaluated by changing BCL with FLT.

RESULTS

KUCaP-1 regressed significantly after castration and did not re-grow. KUCaP-1 treated with BCL continued to grow even after castration and started regressing 2 months after BCL withdrawal, replicating clinically recognized AWS. The antagonistic effect of FLT against the W741C mutant AR was revealed in vitro and in vivo. AAT with FLT suppressed tumor growth after BCL withdrawal.

CONCLUSIONS

KUCaP-1 was an entirely androgen-dependent xenograft and mimicked the clinical phenomena of AWS and AAT caused by the agonistic and antagonistic activity of BCL and FLT, respectively. KUCaP-1 could be an in vivo model for screening novel antiandrogens for the treatment of BCL resistant prostate cancer harboring the W741C mutation in the AR.

Inhibition of prostate cancer cell growth by second-site androgen receptor antagonists

The impact of ligand binding on nuclear receptor (NR) structure and the ability of target cells to distinguish between different receptor-ligand complexes are key determinants of the pharmacological activity of NR ligands. However, until relatively recently, these mechanistic insights have not been used in a prospective manner to develop screens for NR modulators with specific therapeutic activities. Driven by the need for unique androgen receptor (AR) antagonists that retain activity in hormone-refractory prostate cancer, we developed and applied a conformation-based screen to identify AR antagonists that were mechanistically distinct from existing drugs of this class. Two molecules were identified by using this approach, D36 and D80, which interact with AR in a unique manner and allosterically inhibit AR agonist activity. Unlike the clinically important antiandrogens, casodex and hydroxyflutamide, both D36 and D80 block androgen action in cellular models of hormone-refractory prostate cancer. Mechanistically, these compounds further distinguish themselves from classical AR antagonists in that they do not promote AR nuclear translocation and quantitatively inhibit the association of AR with DNA even under conditions of overexpression. Although the therapeutic potential of these antiandrogens is apparent, it is the demonstration that it is possible, to modulate the interaction of cofactors with agonist-activated AR, using second-site modulators, that has the greatest potential with respect to the therapeutic exploitation of AR and other NRs.

Tyrosine 687 Phosphorylated Alzheimer’s Amyloid Precursor Protein Is Retained Intracellularly and Exhibits a Decreased Turnover Rate

Tyrosine 687 (Y687) of the Alzheimer's amyloid precursor protein (APP) was shown to be phosphorylated in the brains of Alzheimer's disease patients. This residue lies within a typical endocytosis consensus motif commonly found in molecules with receptor functions, strongly suggesting a potential role for APP in signal transduction. Consequently, the work here described addressed how phosphorylation of Y687 may be affecting APP in terms of its proteolytic cleavage and subcellular distribution. Our data show that the APP mutant mimicking constitutive dephosphorylation of Y687 had a faster turnover rate, both in terms of maturation and metabolism, when compared to Wt-APP-GFP and even more so when compared to the mutant mimicking constitutive phosphorylation. Thus, the mutant mimicking constitutively phosphorylated Y687 had a much higher t(1/2) and was significantly retained both in the ER and TGN. Additionally, this mutant was not incorporated into visible vesicular structures, with a concomitant dramatic decrease in Abeta production. Our findings point to the direct phosphorylation of APP on Y687 as an important regulatory mechanism in terms of determining the subcellular localization of APP and modulating its processing via different proteolytic pathways.