Multifunctionality of Prostatic Acid Phosphatase in Prostate Cancer Pathogenesis

The role of human prostatic acid phosphatase (PAcP, P15309|PPAP_HUMAN) in prostate cancer was investigated using a new proteomic tool termed signal sequence swapping (replacement of domains from the native cleaved amino terminal signal sequence of secretory/membrane proteins with corresponding regions of functionally distinct signal sequence subtypes). This manipulation preferentially redirects proteins to different pathways of biogenesis at the endoplasmic reticulum, magnifying normally difficult to detect subsets of the protein of interest. For PAcP this technique reveals three forms identical in amino acid sequence but profoundly different in physiological functions, subcellular location, and biochemical properties. These three forms of PAcP can also occur with the wild-type PAcP signal sequence. Clinical specimens from patients with prostate cancer demonstrate that one form, termed PLPAcP, correlates with early prostate cancer. These findings confirm the analytical power of this method, implicate PLPAcP in prostate cancer pathogenesis, and suggest novel anticancer therapeutic strategies.

ARC-6: A phase 1b/2, open-label, randomized platform study to evaluate efficacy and safety of etrumadenant (AB928)-based treatment combinations in patients with metastatic castrate-resistant prostate cancer (mCRPC).

5039 Background: Standard-of-care (SOC) chemotherapy may contribute to immunosuppression by elevating intratumoral levels of adenosine, activating the A2a and A2b receptors on immune cells. Extracellular adenosine is primarily produced by the enzyme CD73; in prostate cancer, additional adenosine is also produced by the highly expressed protein, prostatic acid phosphatase (PAP). Etrumadenant (etruma) is an orally bioavailable, small-molecule, selective dual adenosine receptor antagonist and has been well tolerated in dose escalation studies as monotherapy or combined with chemo/immunotherapy. Adenosine axis inhibition combined with SOC regimens and/or immunotherapy may have a synergistic effect on the induction of sustained antitumor immunity against mCRPC. Initial results from the etruma + zimberelimab (zim; anti–PD-1 mAb) + docetaxel (doc) arm are presented herein. Methods: ARC-6 (NCT04381832) is an ongoing, phase 1b/2, open-label, multicohort platform study to evaluate efficacy and safety of etruma combination therapy. All eligible patients (pts) have mCRPC that has progressed on androgen deprivation therapy and are checkpoint inhibitor-naive; additionally, for this arm, pts must be androgen signaling inhibitor (ASI)-experienced and taxane-naive. Study pts receive 150 mg etruma orally once daily + 360 mg zim IV every 3 weeks + SOC doc (EZD). The primary objectives are to evaluate safety and antitumor activity (prostate-specific antigen [PSA], radiographic, and composite response rates) of EZD. PSA levels are assessed every 3 weeks, and radiographic scans are performed every 12 weeks. PSA response-evaluable pts have baseline (BL) + ≥2 consecutive post-BL PSA assessments; radiographic response-evaluable pts have RECIST measurable or non-measurable disease per BL imaging + ≥1 post-BL radiographic assessment. Results: As of 22Jan2021, 17 pts have received EZD in phase 1b; 14 are PSA response-evaluable and 8 are radiographic response-evaluable. 15 (88%) pts reported treatment emergent adverse events (TEAEs); the most common ( > 30%) were lymphocyte count decreased and neutrophil count decreased (7 pts each; 41%), and hyponatremia and alopecia (6 pts each; 35%). Grade ≥3 treatment-related TEAEs were reported by 9 pts (53%). As of 22Jan2021, 16 pts were continuing treatment; median time on EZD for all pts was 9.9 weeks (0.1–27.4+ weeks). In response-evaluable pts, PSA response rate was 36% (5/14), radiographic response rate was 38% (3/8; 1 CR), and the composite response rate was 43% (6/14). Conclusions: Phase 1b results indicate that EZD treatment in pts with mCRPC had a manageable safety profile and was associated with clinical benefit. Having met phase 2 advancement criteria, randomized pt enrollment to EZD vs. doc is ongoing. Clinical trial information: NCT04381832.

Prostatic Acid Phosphatase Is a Progenitor Cell Marker That Persists After Androgen Ablation

Introduction: Prostatic Acid Phosphatase (PAP), a protein phosphatase and 5’ecto-nucleotidase, is expressed in prostate cancer (PCa) bone metastases and correlates with poor survival. Growing evidence suggests that PAP is not regulated by androgens, but rather by factors in the tumor microenvironment. Hypothesis: We hypothesized that PAP is a marker for a more progenitor type PCa cell and its expression is androgen-independent, persisting in castration-resistant disease. Methods: Protein expression of PAP and three androgen-regulated proteins, the Androgen Receptor (AR), Prostate-Specific Antigen (PSA), and ETS-related gene (ERG) protein, was assessed with immunohistochemistry in human fetal prostate (9.5 - 20 weeks of gestational age), archival human PCa bone metastases, and human PCa cell lines. VCaP cells were treated in vitro with dihydrotestosterone (DHT) and the effects on AR and PAP protein expression determined with Western Blotting. PAP-expressing PCa cell lines (LNCaP, C42B, and VCaP) were inoculated subcutaneously (s.c.) into SCID mice. To model tumor-bone interaction, LNCaP and MC3T3 osteoblast cells were co-inoculated s.c. into SCID mice. A VCaP castration study with surgical or sham castration was performed after tumors were palpable and effects of castration on tumor growth and protein expression determined. Results: PAP expression was observed in the fetal prostate as early as 11.5 weeks of gestational age prior to PSA and AR expression. Strong PAP expression was noted in all human PCa bone metastases examined, both treatment-naive and castrate-resistant (n=10). In vitro, VCaP cells expressed high levels of AR and PAP protein and DHT treatment increased AR and decreased PAP protein expression. In vivo, PAP expression was observed in all tumor models; LNCaP (low PAP expression), C42B (moderate PAP expression) and VCaP (high PAP expression). Castrated VCaP tumors underwent tumor stasis, were significantly smaller compared to intact mice, had decreased AR, PSA and ERG expression but persistent expression of PAP. Double staining of tumors for PAP and AR demonstrated a population of cells that were positive for PAP but negative for AR expression in hypoxic areas near necrosis. Inoculation of LNCaP cells with MC3T3 osteoblastic cells increased PAP expression in vivo. Conclusions: PAP is expressed early in human fetal prostate development prior to the secretion of significant androgens or expression of AR. In mouse xenograft tumors and human PCa bone metastases, androgens did not significantly regulate PAP expression. Both hypoxia and stroma increased PAP expression. These data demonstrate that PAP is a marker of early progenitor cells, is persistently expressed after castration and is upregulated by tumor microenvironmental factors. PAP may be a suitable target for the treatment of castration-resistant metastatic disease.

How to turn up the heat on the cold immune microenvironment of metastatic prostate cancer

Background Advanced prostate cancer remains one of the most common and deadly cancers, despite advances in treatment options. Immunotherapy has provided little benefit to a majority of patients, largely due to the immunosuppressive tumor microenvironment that gives rise to inherently “cold tumors”. In this review, we discuss the immunopathology of the prostate tumor microenvironment, strategies for treating prostate cancer with immunotherapies, and a perspective on potential approaches to enhancing the efficacy of immunotherapies. Methods Databases, including PubMed, Google Scholar, and Cochrane, were searched for articles relevant to the immunology of prostate cancer. We discuss the impact of different types of treatments on the immune system, and potential mechanisms through which prostate cancer evades the immune system. Results The tumor microenvironment associated with prostate cancer is highly immunosuppressive due to (1) the function of regulatory T cells, tumor-associated macrophages, and myeloid-derived suppressor cells (MDSCs), (2) the cytokine milieu secreted by tumor stromal cells and fibroblasts, and (3) the production of adenosine via prostatic acid phosphatase. Both adenosine and tumor growth factor beta (TGF-beta) serve as potent immunosuppressive molecules that could also represent potential therapeutic targets. While there have been many immunotherapy trials in prostate cancer, the majority of these trials have targeted a single immunosuppressive mechanism resulting in limited clinical efficacy. Future approaches will require the integration of improved patient selection as well as use of combination therapies to address multiple mechanisms of resistance. Conclusion Prostate cancer inherently gives rise to multiple immunosuppressive mechanisms that have been difficult to overcome with any one immunotherapeutic approach. Enhancing the clinical activity of immunotherapies will require strategic combinations of multiple therapies to address the emerging mechanisms of tumor immune resistance.

Dual concentration-dependent effect of Ascorbic acid on PAP(248-286) amyloid formation and SEVI-mediated HIV infection

Human semen contains various amyloidogenic peptides derived from Prostatic Acid Phosphatase (PAP) and Semenogelin proteins that are capable of enhancing HIV-1 infection when assembled into fibrils. The best characterized among...

Prostate Specific Antigen (PSA): The Historical Perspective

In 1970, shortly after joining Roswell Park Memorial Institute, the New York State institute for the study of malignant diseases, the author initiated investigations on the use of tumor cell products for diagnosis and therapy of cancer. Immunochemical approaches were used primarily to differentiate quantitatively or qualitatively normal cells from tumor cells. Prostate cancer was a major area of endeavor, with the goal to identify and characterize prostate tumor specific and associated antigens, and eventually to develop a simple but reliable blood test for prostate cancer. Prostate cancer research had not received much attention at the time this work was begun. The early studies focused upon, among others, prostatic acid phosphatase, alkaline phosphatase, and new prostate tumor markers. By the mid 1970s, three able investigators--Dr. Ching-Li Lee, Dr. Carl S. Killian, and Dr. Ming C. Wang--had joined the prostate cancer research team, and were invited to take charge of these three research projects, respectively.

Antibody profiling of patients with prostate cancer reveals differences in antibody signatures among disease stages

BackgroundPrevious studies of prostate cancer autoantibodies have largely focused on diagnostic applications. So far, there have been no reports attempting to more comprehensively profile the landscape of prostate cancer-associated antibodies. Specifically, it is unknown whether the quantity of antibodies or the types of proteins recognized change with disease progression.MethodsA peptide microarray spanning the amino acid sequences of the gene products of 1611 prostate cancer-associated genes was synthesized. Serum samples from healthy male volunteers (n=15) and patients with prostate cancer (n=85) were used to probe the array. These samples included patients with various clinical stages of disease: newly diagnosed localized prostate cancer (n=15), castration-sensitive non-metastatic prostate cancer (nmCSPC, n=40), castration-resistant non-metastatic prostate cancer (n=15) and castration-resistant metastatic disease (n=15). The patients with nmCSPC received treatment with either standard androgen deprivation therapy (ADT) or an antitumor DNA vaccine encoding prostatic acid phosphatase. Serial sera samples from these individuals were also used to probe the array, to secondarily determine whether this approach could be used to detect treatment-related changes.ResultsWe demonstrated that this peptide array yielded highly reproducible measurements of serum IgG levels. We found that the overall number of antibody responses did not increase with disease burden. However, the composition of recognized proteins shifted with clinical stage of disease. Our analysis revealed that the largest difference was between patients with castration-sensitive and castration-resistant disease. Patients with castration-resistant disease recognized more proteins associated with nucleic acid binding and gene regulation compared with men in other groups. Our longitudinal data showed that treatments can elicit antibodies detectable by this array, and notably vaccine-treated patients developed increased responses to more proteins over the course of treatment than did ADT-treated patients.ConclusionsThis study represents the largest survey of prostate cancer-associated antibodies to date. We have been able to characterize the classes of proteins recognized by patients and determine how they change with disease burden. Our findings further demonstrate the potential of this platform for measuring antigen spread and studying responses to immunomodulatory therapies.

External quality assessment program for biochemical assays of human seminal plasma: a French 6-years experience

Background In 1999, despite a longstanding use, the WHO manual for the examination of human semen finally proposed to assay several biochemical components of the seminal plasma for a functional exploration of the male accessory glands. At the same time, an international effort was made to standardize laboratory tests and to increase their performance through ISO 15189 accreditation. In this setting, participation to relevant external quality assessment (EQA) schemes is an essential requirement for laboratories. To fulfil this injunction, we have organized an EQA program for seminal biochemistry using presumed commutable samples. In this study, we aimed to report an overview of the French laboratory offer, the kinds of assays used, their performance as well as their likelihood of satisfying ISO15189 requirements for EQA. Results Between 2014 and 2019, we performed seven surveys. A median of six laboratories participated to each survey giving a ratio of one laboratory per 11.2 million inhabitants. Seven biomarkers are routinely assayed but the core set shared by all laboratories comprised citrate and zinc (prostate), fructose (seminal vesicles) and α-1, 4 glucosidase (epididymis). The use of CE-IVD marked methods concerned between 0 to 75% of overall assays. According to analytical specifications, 100% of laboratories results were compliant for zinc, 75% for citrate and α-1,4 glucosidase and 67% for fructose. By combining overall data in an empirical scoring system, we identified several types of seminal biomarkers: citrate, fructose and zinc appear as good candidates for a full accreditation, α-1,4 glucosidase still presents an analytical weakness, but prostatic acid phosphatase, free L-carnitine and glycerophosphocholine cannot be accredited in the current state. Conclusions We organized the first French EQA program for seminal biochemistry to help local laboratories to face their legal requirement to be fully accredited by 2020. It could be improved still further but it gave us an oversight on the analytic landscape. Effective methods are available for a confident biochemical exploration of prostate and seminal vesicles. However, that of epididymis appeared unexpectedly fragile. This andrological issue should be addressed by dedicated recommendations from health authorities and scientific societies.

Effects of combined ethanol extract of Funtumia africana and Abutilon mauritianum leaves on prostate biomarkers and serum mineral levels in prostatic hyperplasia induced male rats

Introduction: Benign prostatic hyperplasia (BPH) is a prostate disorder in ageing males that negatively affects the quality of life and requires multidimensional approaches to ameliorate its adverse health effects. Objectives: This study evaluated the effects of combined ethanol extract of Funtumia africana and Abutilon mauritianum leaves on the prostate biomarkers, serum mineral levels and prostate histomorphology of BPH induced rats. Materials and Methods: Thirty-six male Wistar albino rats randomly distributed into 5 groups containing 6 rats each was used for this study. Group 1 served as the normal control rats without BPH induction while groups 2–5 were BPH induced rats that served as BPH control (untreated), finasteride control, and BPH induced treated with 200 and 600 mg/kg/d of the combined ethanol extract of F. africana and A. mauritianum leaves respectively. BPH was induced in the rats by subcutaneous injection of 5 mg/kg/d of testosterone propionate injection and treatment followed 1h after the induction for 28 consecutive days. All the biochemical analyses and prostate histological examinations were carried out using standard methods. Results: BPH induction significantly elevated serum prostatic acid phosphatase activities and serum prostate-specific antigen (PSA) concentrations in the BPH control rats relative to the normal control. The BPH induction caused significant (P<0.05) reductions in the serum levels of calcium and selenium levels and significantly increased the serum inorganic phosphate concentration in the BPH control when compared with the normal control. Treatment with the combined extract significantly (P<0.05) increased the serum zinc, calcium, copper, iron and inorganic phosphate and significantly reduced serum selenium level when compared with the BPH control. The combined extract further significant (P<0.0) reduced the serum prostatic acid phosphatase activities and PSA level relative to the BPH control. The BPH control showed severe prostate histomorphological alterations consistent with BPH which were largely reduced to mild alterations in combined extract-treated BPH induced rats. Conclusion: This study revealed that the combined ethanol extract of F. africana and A. mauritianum leaves positively regulate the serum mineral levels, serum prostatic acid phosphatase activities, PSA levels and improves prostate histomorphology BPH induced rats.

Decreased Equilibrative Nucleoside Transporter 1 (ENT1) Activity Contributes to the High Extracellular Adenosine Levels in Mesenchymal Glioblastoma Stem-Like Cells

Glioblastoma multiforme is one of the most malignant types of cancer. This is mainly due to a cell subpopulation with an extremely aggressive potential, called glioblastoma stem-like cells (GSCs). These cells produce high levels of extracellular adenosine which has been associated with increased chemoresistance, migration, and invasion in glioblastoma. In this study, we attempted to elucidate the mechanisms that control extracellular adenosine levels in GSC subtypes. By using primary and U87MG-derived GSCs, we associated increased extracellular adenosine with the mesenchymal phenotype. [3H]-adenosine uptake occurred mainly through the equilibrative nucleoside transporters (ENTs) in GSCs, but mesenchymal GSCs have lower expression and ENT1-mediated uptake activity than proneural GSCs. By analyzing expression and enzymatic activity, we determined that ecto-5′-nucleotidase (CD73) is predominantly expressed in proneural GSCs, driving AMPase activity. While in mesenchymal GSCs, both CD73 and Prostatic Acid Phosphatase (PAP) contribute to the AMP (adenosine monophosphate) hydrolysis. We did not observe significant differences between the expression of proteins involved in the metabolization of adenosine among the GCSs subtypes. In conclusion, the lower expression and activity of the ENT1 transporter in mesenchymal GSCs contributes to the high level of extracellular adenosine that these GSCs present.