Androgen receptor mutations in prostate cancer

We analyzed the frequency and relevance of mutations in the coding region of the androgen receptor (AR) in genomic DNA extracted from 137 specimens of prostate cancer. The specimens were obtained from the primary tumors of patients affected by stage B disease [15 nonmicrodissected (group 1A) and 84 microdissected (group 1B)] and from the metastatic deposits of individuals with stage D1 disease [8 nonmicrodissected (group 2A) and 30 microdissected (group 2B)] who had not undergone androgen ablation therapy. The study was conducted by PCR-single strand conformational polymorphism (SSCP) analysis of exons 2-8 in the four groups and direct sequence analysis of exon 1 in group 1B. As positive and negative controls, we used genomic DNA extracted from genital skin fibroblasts of patients affected by various forms of androgen resistance with known mutations in the AR. To control for genetic instability, PCR-SSCP analysis of exon 2 of the human progesterone receptor was carried out on each specimen. The overall number of mutations detected was 11 (8%). No mutations were detected in any of the 99 patients with stage B disease. Eleven mutations were detected in exons 2-8 in 8 of the 38 patients with stage D1 disease (all in group 2B). Simultaneous analysis of exon 2 of the progesterone receptor was carried out, and no SSCP changes were identified. These data suggest that AR mutations are rare and presumably do not play a role in the initial phase of prostatic carcinogenesis. The presence of a significant number of AR mutations in metastatic disease indicates that mutations of this molecule may play a role in the most advanced phases of the natural history of this disease, either by facilitating growth or acquisition of the metastatic phenotype.     

Androgen receptor W741C and T877A mutations in AIDL cells,an androgen-independent subline of prostate cancer LNCaP cells

The androgen-independent LNCaP (AIDL) cell line was generated by maintaining prostate cancer LNCaP cells in a hormone-deprived medium. Notably, synthetic androgen R1881-related gene response is attenuated in AIDL cells as compared to the parental LNCaP cells. The aim of this study was to clarify the mechanisms underlying androgen sensitivity in AIDL cells. We first examined the expression of androgen receptor (AR) and its co-regulators. However, no significant difference in mRNA expression was found between LNCaP and AIDL cells. Remarkably, AR protein levels were induced by R1881 and DHT in LNCaP cells, but not in AIDL cells. We next performed the cDNA sequencing to detect mutations in the AR gene. The T877A mutation was detected both in LNCaP and AIDL cells. Furthermore, AIDL cells harbored a missense substitution (TGG → TGT) in the AR gene, which caused a point mutation at codon 741 (W741C). Double T877A and W741C AR mutants have been previously reported to exhibit reduced androgen sensitivity. Hence, the low-androgen-sensitive responses of AIDL cells may be explained, at least in part, by AR gene mutations.     

Androgen receptor signaling in androgen-refractory prostate cancer.

Prostate cancer is the second most prevalent cancer in males in the United States. Standard therapy relies on removing, or blocking the actions of, androgens. In most cases, this therapy results in a regression of the cancer because the prostate and most primary prostate tumors depend on androgens for growth and the avoidance of apoptosis. However, a portion of the cancers eventually relapse, at which point they are termed "androgen refractory" and can no longer be cured by conventional therapy of any type. The precise molecular events that lead from androgen-sensitive prostate cancer to androgen-refractory prostate cancer are, therefore, of great interest. This review seeks to identify specific molecular events that may be linked directly to the progression to androgen-refractory cancer. Some of the mechanisms appear to involve the androgen receptor (AR) directly and include mutations in, or amplification of, the AR gene in a manner that allows the AR to respond to low doses of androgens, other steroids, or antiandrogens. In a less direct manner, coactivators may increase the sensitivity of the AR to androgens and even other nonandrogenic substances through a number of mechanisms. Additional indirect mechanisms that do not result from mutation of the AR may involve activation of the AR by peptide growth factors or cytokines or may involve bypassing the AR entirely via other cellular pathways. Identification of the role of these mechanisms in the progression to androgen-refractory prostate cancer is critical for developing therapies capable of curing this disease.     

Androgen receptor mutations in patients with castration-resistant prostate cancer treated with apalutamide

BackgroundMutations in the androgen receptor (AR) ligand-binding domain (LBD), such as F877L and T878A, have been associated with resistance to next-generation AR-directed therapies. ARN-509-001 was a phase I/II study that evaluated apalutamide activity in castration-resistant prostate cancer (CRPC). Here, we evaluated the type and frequency of 11 relevant AR-LBD mutations in apalutamide-treated CRPC patients.Patients and methodsBlood samples from men with nonmetastatic CRPC (nmCRPC) and metastatic CRPC (mCRPC) pre- or post-abiraterone acetate and prednisone (AAP) treatment (≥6 months’ exposure) were evaluated at baseline and disease progression in trial ARN-509-001. Mutations were detected in circulating tumor DNA using a digital polymerase chain reaction-based method known as BEAMing (beads, emulsification, amplification and magnetics) (Sysmex Inostics’ GmbH).ResultsOf the 97 total patients, 51 had nmCRPC, 25 had AAP-naïve mCRPC, and 21 had post-AAP mCRPC. Ninety-three were assessable for the mutation analysis at baseline and 82 of the 93 at progression. The overall frequency of detected AR mutations at baseline was 7/93 (7.5%) and at progression was 6/82 (7.3%). Three of the 82 (3.7%) mCRPC patients (2 AAP-naïve and 1 post-AAP) acquired AR F877L during apalutamide treatment. At baseline, 3 of the 93 (3.2%) post-AAP patients had detectable AR T878A, which was lost after apalutamide treatment in 1 patient who continued apalutamide treatment for 12 months.ConclusionsThe overall frequency of detected mutations at baseline (7.5%) and progression (7.3%) using the sensitive BEAMing assay was low, suggesting that, based on this assay, AR-LBD mutations such as F877L and T878A are not common contributors to de novo or acquired resistance to apalutamide.ClinicalTrials.gov identifierNCT01171898.     

Androgen receptor and invasion in prostate cancer

Activation of androgen receptor (AR) stimulates the growth of not only androgen-dependent but also of androgen-refractory prostate cancer. However, neither the role of AR in invasion/metastasis nor the relationship between invasiveness and androgen-refractory status has been established. In this study, we used the androgen-dependent prostate cancer cell line MDA PCa 2b, derived from a human bone metastasis, to generate an invasive subline (MDA-I) using a Matrigel chamber. MDA-I cells expressed higher levels of AR and prostate-specific antigen than their less invasive parental cells. Blocking AR function or removal of androgen suppressed the invasion of MDA-I cells, whereas stimulating AR increased invasion. In addition, forced AR overexpression increased the invasiveness of MDA PCa 2b cells. Next, we showed that an androgen-refractory subline (MDA-hr) of MDA PCa 2b cells also expressed higher levels of AR and were more invasive than their parental androgen-dependent cells. Blocking AR function suppressed the invasiveness of MDA-hr cells. Gelatin zymography indicated that matrix metalloproteinase 2 (MMP-2) and MMP-9 activities were regulated by AR signaling and closely correlated with the invasiveness of the androgen-dependent and androgen-refractory prostate cancer cells. These data suggest that AR promotes the invasiveness of both androgen-dependent and androgen-refractory prostate cancer and that a more invasive phenotype might develop through AR activation during cancer progression. These findings potentially support the use of adjuvant hormonal therapy and the future development of more potent androgen blockade therapy.     

Androgen receptor binding activity in human prostate cancer

Androgen binding (cytosol and nucleus) was measured in tissue obtained from 223 untreated patients with proven prostate cancer (199 primary tumor, 24 malignant lymph nodes), 19 patients with hormone refractory cancer, and 46 patients with benign prostatic hyperplasia (BPH). The mean binding in both the cytosol and nucleus was significantly higher for patients with cancer than for those with BPH. Binding appeared to correlate with tumor stage. Androgen binding in malignant nodes can differ from that in the primary tissue and can vary from node to node in the same patient. Results obtained from an assay using a single saturating concentration of R1881 correlated well with those calculated from a full six-point Scatchard analysis when an adequate amount (500 mg) of tissue was available. However, binding results obtained from a single-point analysis performed on needle biopsy specimens (about 50 mg) obtained before complete surgical removal of the prostate correlated poorly with those derived from a full six-point analysis performed on tissue (500-1000 mg) removed from the center of the malignancy. Androgen binding in nuclear extracts of histologically benign tissue adjacent to the malignancy was significantly higher than in nuclear extracts of BPH tissue. Cytosolic androgen binding in tissue removed from patients who were refractory to hormonal therapy was higher than in tissue from untreated cancer patients. The binding of estradiol by extracts of benign and malignant prostate tissue was low or absent and, thus, did not appear to be a significant phenomenon.     

Androgen receptor: role and novel therapeutic prospects in prostate cancer

Androgen receptor (AR) signaling is necessary for the development of prostate cancer. Androgen-deprivation therapy (ADT) for prostate cancer was described over 50 years ago and ADT remains the mainstay of systemic therapy. AR signaling remains intact as the disease evolves to castration-resistant prostate cancer (CRPC). Through cellular adaptations, CRPC continues to rely on androgens and AR growth signaling, and thus AR remains an important therapeutic target. CRPC cells upregulate enzymes used in androgen synthesis, thus providing an intracellular source of androgen despite systemic castration. Compounds in development, such as antiandrogens, lyase inhibitors, heat-shock protein-90 inhibitors, histone deacetylase inhibitors and others, will provide new tools to more effectively reduce ligand, inhibit AR and/or inhibit costimulatory pathways and result in improved clinical outcomes.     

Androgen receptor-dependent PSA expression in androgen-independent prostate cancer cells does not involve androgen receptor occupancy of the PSA locus

It is widely suspected that androgen-independent prostate cancer growth depends on androgen receptor signaling via ill-defined mechanisms. Prostate-specific antigen (PSA) expression is often used to measure androgen receptor activity in cells and prostate cancer progression in patients. In the present study, we have compared androgen receptor activity using PSA and human male germ cell-associated kinase (hMAK), as read-outs in androgen-dependent LNCaP and androgen-independent C4-2B cells. As expected, very little PSA and hMAK expression were detected in LNCaP cells in the absence of androgens, whereas substantial expression of PSA was observed only in C4-2B cells under the same conditions. The addition of dihydrotestosterone to the culture medium increased the expression of both genes in both cell types. Comprehensive chromatin immunoprecipitation analysis of the entire PSA locus and an androgen-response element in hMAK unexpectedly revealed that androgen receptor was not occupying any site in the absence of dihydrotestosterone in either cell type. In line with the expression data, and in the absence of dihydrotestosterone, histone acetylation and RNA polymerase II occupancy was substantial at the PSA locus in C4-2B but not in LNCaP cells. In the presence of dihydrotestosterone, androgen receptor was found to occupy mainly the enhancer region of PSA in both cell types, accompanied with increases in histone acetylation and RNA polymerase II occupancy. Although the androgen receptor was not directly involved in the androgen-independent expression of PSA in C4-2B cells, small interfering RNA knock-down of androgen receptor significantly reduced PSA expression in both the presence and absence of dihydrotestosterone. In contrast, hMAK expression was decreased only in the presence of dihydrotestosterone after androgen receptor knock-down. We conclude that androgen-independent expression of PSA in C4-2B cells does not rely on the direct occupancy of the androgen receptor at the PSA locus, but is nevertheless affected indirectly via unknown androgen receptor-dependent mechanism(s) that influence the expression from some but not all androgen receptor target genes.     

Predictors of prostate cancer tissue acquisition by an undirected core bone marrow biopsy in metastatic castration-resistant prostate cancer--a Cancer and Leukemia Group B study.

PURPOSE: Analyzing metastatic prostate cancer tissue is of considerable importance in evaluating new targeted agents, yet acquiring such tissue presents a challenge due to the predominance of bone metastases. We assessed factors predicting a successful tumor harvest from bone marrow biopsies (BMBx) in castration-resistant metastatic prostate cancer patients. MATERIAL AND METHODS: Data from Cancer and Leukemia Group B study 9663 were reviewed. Bone marrow biopsies were obtained from 184 patients who underwent an office-based, unguided bone marrow biopsy of the posterior iliac crest. RESULTS: Forty-seven of the 184 patients (25.5%) had a positive bone marrow biopsy. When considered in a multivariate logistic regression analysis, lower hemoglobin levels, higher alkaline phosphatase, and higher lactate dehydrogenase levels were associated with a higher likelihood of a positive BMBx. The median survival time was 11 months (95% confidence interval, 8.0-14) among patients with a positive BMBx compared with 23 months (95% confidence interval, 19-27) with a negative BMBx. The median time to progression and time to prostate-specific antigen progression-free survival were also significantly decreased among positive BMBx patients. No patients with a positive BMBx survived beyond 3 years, whereas 11 of the 137 patients with a negative BMBx survived beyond 5 years. DISCUSSION: Using common laboratory values, a specific patient cohort can be defined from whom the yield of a nonguided BMBx would be high enough to justify this approach. For studies that require broader entry criteria, a more directed approach with image guidance is recommended.     

Androgen receptor: role and novel therapeutic prospects in prostate cancer

Androgen receptor (AR) signaling is necessary for the development of prostate cancer. Androgen-deprivation therapy (ADT) for prostate cancer was described over 50 years ago and ADT remains the mainstay of systemic therapy. AR signaling remains intact as the disease evolves to castration-resistant prostate cancer (CRPC). Through cellular adaptations, CRPC continues to rely on androgens and AR growth signaling, and thus AR remains an important therapeutic target. CRPC cells upregulate enzymes used in androgen synthesis, thus providing an intracellular source of androgen despite systemic castration. Compounds in development, such as antiandrogens, lyase inhibitors, heat-shock protein-90 inhibitors, histone deacetylase inhibitors and others, will provide new tools to more effectively reduce ligand, inhibit AR and/or inhibit costimulatory pathways and result in improved clinical outcomes.     

Phase II trial of topotecan in advanced breast cancer: a Cancer and Leukemia Group B study.

The topoisomerase I inhibitor topotecan had demonstrated good antitumor activity in several murine tumor systems and in human clonogenic assays by 1993. In that year, the Cancer and Leukemia Group B (CALGB) began a phase II trial to determine its activity in patients with breast cancer who had previously received one course of chemotherapy for advanced breast cancer. Between April 1993 and June 1994, 53 patients of performance status 0-2 entered the study, of whom 47 were eligible and 40 were evaluable. Topotecan was given at a dose of 1.5 mg/m2 over 30 minutes daily for 5 days every 21 days. In the absence of progression or withdrawal of consent, therapy was continued indefinitely. The median age was 58 years (range 30-79). There were no complete responses and four partial responses, resulting in an objective response rate of 10% (95% CI: 3-24%). Responses were noted in lymph nodes, liver, and skin. The median duration of response was 5 months. The median survival was 12 months. Life-threatening toxicities were almost exclusively hematologic. However, myelosuppression was not cumulative. It was concluded that topotecan has only modest activity among women with advanced breast cancer who have previously received one course of chemotherapy. Given its modest activity and predominant hematologic toxicity, it does not appear to be a promising drug for either single-agent or combination chemotherapy in the salvage setting of advanced breast cancer.     

Androgen receptor and vitamin D receptor gene polymorphisms and prostate cancer risk

We study the CAG repeat region in exon 1 of the androgen receptor (AR) and the TaqI polymorphism in exon 9 of the vitamin D receptor (VDR) and the association with prostate cancer. 137 incidentally discovered, histologically verified prostate cancers were analysed for CAG repeat length in AR and genotype at the TaqI site of the VDR. 124 control subjects were analysed to determine the CAG repeat length and TaqI genotype determined for 176 control subjects. An unpaired t-test shows that the mean CAG repeat length was significantly (p<0.001) shorter among cases (20.1 repeats) compared with controls (22.5 repeats). Dividing the prostate cohort and controls into tertiles (< or = 19, 20-22, > or = 23 repeats) shows that short repeats are significantly more common among cases (odds ratio (OR) 4.45, p=0.00003). Genotype frequencies for the TaqI polymorphism reveals no significant differences between cases and controls. We conclude that men with a short CAG repeat in the androgen receptor gene have an increased risk of developing prostate cancer.     

Prognostic significance of plasma vascular endothelial growth factor levels in patients with hormone-refractory prostate cancer treated on Cancer and Leukemia Group B 9480.

PURPOSE: Plasma vascular endothelial growth factor (VEGF) levels are significantly elevated in patients with hormone-refractory prostate cancer (HRPC) compared with patients with localized disease and have been associated with disease progression in other cancer patient populations. Therefore, we measured VEGF levels in plasma prospectively collected from patients enrolled in Cancer and Leukemia Group B 9480, an intergroup study of suramin in patients with HRPC, to determine whether these levels had prognostic significance. EXPERIMENTAL DESIGN: Pretreatment plasma was collected from patients with HRPC enrolled in Cancer and Leukemia Group B 9480. In a subset of samples representative of the entire cohort, plasma VEGF levels were determined in duplicate using a Quantiglo chemiluminescent ELISA kit (R&D Systems, Minneapolis, MN). Statistical analyses were performed to determine the correlation between pretreatment plasma VEGF levels and time of overall survival. The proportional hazards model was used to assess the prognostic significance of various cut points in multivariate models. RESULTS: Plasma VEGF levels in this population ranged from 4-885 pg/ml, with a median level of 83 pg/ml. As a continuous variable, plasma VEGF levels inversely correlated with survival time (P = 0.002). Using various exploratory cut points, plasma VEGF levels appeared to correlate with survival. In multivariate models in which other prognostic factors (serum prostate-specific antigen, alkaline phosphatase, evidence of measurable disease, and hemoglobin) were included, plasma VEGF levels were significant at various cut points tested. CONCLUSION: Although these data are exploratory and need to be confirmed in an independent data set, they suggest that VEGF may have clinical significance in patients with HRPC.     

Higher doses of mitoxantrone among men with hormone-refractory prostate carcinoma: a Cancer and Leukemia Group B study

BACKGROUND: Mitoxantrone in combination with a low-dose glucocorticoid has been shown to produce more favorable outcomes among men with hormone-refractory prostate carcinoma than glucocorticoid alone. Therefore, the authors sought to determine the safety and activity of higher doses of mitoxantrone in combination with granulocyte-macrophage colony-stimulating factor (GM-CSF) and a glucocorticoid in preparation for a possible Phase III trial comparing standard to dose-escalated mitoxantrone. METHODS: This Phase II trial enrolled 45 patients from October 1996 to March 1998. Twenty-one patients without pelvic irradiation (Arm I) received 21 mg/m(2) of mitoxantrone every 3 weeks, and 24 patients who had received pelvic irradiation (Arm II) were given 17 mg/m(2) on the same schedule. All patients received 40 mg of hydrocortisone in divided doses daily and GM-CSF at 500 microg/daily for a minimum of 10 days per cycle beginning on the third day of the cycle. RESULTS: In Arm I, 33% of assessable patients achieved a partial response, 50% had a > or = 50% decline in their PSA, and 35% had a > or = 75% decline in PSA values. The comparable numbers in Arm II were 24%, 48%, and 35%, respectively. The median survival times were 12 months in Arm I and 14 months in Arm II. Treatment had to be discontinued in 13% of patients because of thrombocytopenia. No other significant toxicities were encountered. CONCLUSIONS: Higher doses of mitoxantrone (17 and 21 mg/m(2)) were associated with activity comparable to many estramustine combinations and generally were well tolerated. However, because the degree and frequency of thrombocytopenia were greater than that observed with standard dose mitoxantrone (12-14 mg/m(2)), and because the median survival is apparently comparable to standard dose mitoxantrone, this approach to HRPC cannot be recommended for Phase III testing.     

Treatment options in androgen-independent prostate cancer

Metastatic prostate cancer is a leading cause of cancer-related death in men. Although most patients will respond to androgen ablation as initial systemic therapy, nearly all patients will develop androgen-independent prostate cancer (AI CaP) and will succumb to the disease. Advances in molecular biology have demonstrated mutations in and persistent expression of the human androgen receptor in metastatic disease. Furthermore, recent evidence indicates that an apoptotic block through p53 mutations or bcl-2 overexpression may have a potential role in the poor responses seen with standard chemotherapy. Presently, the six general treatment options available for AI CaP are best supportive care, radiation therapy, radioisotopes, secondline hormonal therapy, chemotherapy (single agent or combination), and investigational therapies such as monoclonal antibodies, cyclin-dependent kinase inhibitors, matrix metalloproteinase inhibitors, and antiangiogenesis agents, among others. None of these modalities have produced durable remissions, although some have demonstrated palliative benefit. The next generation of clinical trials should not consist of futile hormonal manipulations or repetitive chemotherapy. Therapeutic strategies aimed at circumventing molecular blocks to cell death or targeting unique cancer molecules and genes will be more likely to improve quality of life and longevity. Furthermore, the aggressive use of palliative care will ensure effective caring for patients and the healing of families in the absence of cure.     

Collocation of androgen receptor gene mutations in prostate cancer.

Consistent with both the development of the normal prostate gland and prostate tumorigenesis being dependent on testicular androgens, targeting the androgen-signaling axis (i.e., androgen ablation therapy) remains the predominant treatment regime for patients with metastatic prostate cancer. Although there is a very good initial response to androgen ablation, these treatments are essentially palliative. Recent evidence suggests that treatment failure may not result from a loss of androgen signaling but, rather, from the acquisition of genetic changes that lead to aberrant activation of the androgen-signaling axis. A consistent finding is that androgen receptor (AR) gene mutations, present in metastatic prostate cancer and in human prostate cancer cell lines as well as in xenograft and other animal models, result in decreased specificity of ligand-binding and inappropriate receptor activation by estrogens, progestins, adrenal androgens, glucocorticoids and/or AR antagonists. Because a significant proportion of missense mutations in the AR gene reported in prostate cancer collocate to the signature sequence and AF-2, two discrete regions of the ligand-binding domain critical for androgen signaling, we recently proposed that collocation of mutations identified in prostate cancer would identify additional regions of the AR important in receptor function. This approach led to the identification of a four-amino acid region at the boundary of the hinge and ligand-binding domains of the receptor that forms half of a potential protein-protein binding site. AR gene mutations have also been identified that collocate to areas in the DNA-binding domain, to the NH(2)-terminal transactivation domain, and to the hinge region in prostate tumors. In nearly every case, missense mutations in the AR gene identified in prostate cancer that collocate to discrete regions of the receptor contribute to altered androgen signaling and provide a potential mechanism to explain the reemergence of tumor growth during the course of hormone ablation therapies.