LSD1 inhibition suppresses ASCL1 and de-represses YAP1 to drive potent activity against neuroendocrine prostate cancer

Lysine-specific demethylase 1 (LSD1 or KDM1A ) has emerged as a critical mediator of tumor progression in metastatic castration-resistant prostate cancer (mCRPC). Among mCRPC subtypes, neuroendocrine prostate cancer (NEPC) is an exceptionally aggressive variant driven by lineage plasticity, an adaptive resistance mechanism to androgen receptor axis-targeted therapies. Our study shows that LSD1 expression is elevated in NEPC and associated with unfavorable clinical outcomes. Using genetic approaches, we validated the on-target effects of LSD1 inhibition across various models. We investigated the therapeutic potential of bomedemstat, an orally bioavailable, irreversible LSD1 inhibitor with low nanomolar potency. Our findings demonstrate potent antitumor activity against CRPC models, including tumor regressions in NEPC patient-derived xenografts. Mechanistically, our study uncovers that LSD1 inhibition suppresses the neuronal transcriptional program by downregulating ASCL1 through disrupting LSD1:INSM1 interactions and de-repressing YAP1 silencing. Our data support the clinical development of LSD1 inhibitors for treating CRPC - especially the aggressive NE phenotype.

Statement of Significance

Neuroendocrine prostate cancer presents a clinical challenge due to the lack of effective treatments. Our research demonstrates that bomedemstat, a potent and selective LSD1 inhibitor, effectively combats neuroendocrine prostate cancer by downregulating the ASCL1- dependent NE transcriptional program and re-expressing YAP1.

Comparative analysis of monoclonal antibodies against prostate-specific membrane antigen (PSMA)

BACKGROUND

Prostate-specific membrane antigen (PSMA), also known as glutamate carboxypeptidase II (GCPII), is generally recognized as a diagnostic and therapeutic cancer antigen and a molecular address for targeted imaging and drug delivery studies. Due to its significance in cancer research, numerous monoclonal antibodies (mAbs) against GCPII have been described and marketed in the past decades. Unfortunately, some of these mAbs are poorly characterized, which might lead to their inappropriate use and misinterpretation of the acquired results.

METHODS

We collected the 13 most frequently used mAbs against GCPII and quantitatively characterized their binding to GCPII by enzyme-linked immunosorbent assay (ELISA) and surface plasmon resonance (SPR). Using a peptide library, we mapped epitopes recognized by a given mAb. Finally, we assessed the applicability of these mAbs to routine experimental setups, including Western blotting, immunohistochemistry, and flow cytometry.

RESULTS

ELISA and SPR analyses revealed that mAbs J591, J415, D2B, 107-1A4, GCP-05, and 2G7 bind preferentially to GCPII in native form, while mAbs YPSMA-1, YPSMA-2, GCP-02, GCP-04, and 3E6 bind solely to denatured GCPII. mAbs 24.4E6 and 7E11-C5.3 recognize both forms of GCPII. Additionally, we determined that GCP-02 and 3E6 cross-react with mouse GCPII, while GCP-04 recognizes GCPII and GCPIII proteins from both human and mouse.

CONCLUSION

This comparative analysis provides the first detailed quantitative characterization of the most commonly used mAbs against GCPII and can serve as a guideline for the scientific community to use them in a proper and efficient way.

An inhibitor of Na(+)/Ca(2+) exchange blocks activation of insect olfactory receptors

Earlier we showed that the Na(+)/Ca(2+) exchanger inhibitor, KB-R7943, potently blocks the odor-evoked activity of lobster olfactory receptor neurons. Here we extend that finding to recombinant mosquito olfactory receptors stably expressed in HEK cells. Using whole-cell and outside-out patch clamping and calcium imaging, we demonstrate that KB-R7943 blocks both the odorant-gated current and the odorant-evoked calcium signal from two different OR complexes from the malaria vector mosquito, Anopheles gambiae, AgOr48+AgOrco and AgOr65+AgOrco. Both heteromeric and homomeric (Orco alone) OR complexes were susceptible to KB-R7943 blockade when activated by VUAA1, an agonist that targets the Orco channel subunit, suggesting the Orco subunit may be the target of the drug's action. KB-R7943 represents a valuable tool to further investigate the functional properties of arthropod olfactory receptors and raises the interesting specter that activation of these ionotropic receptors is directly or indirectly linked to a Na(+)/Ca(2+) exchanger, thereby providing a template for drug design potentially allowing improved control of insect pests and disease vectors.

PITX2 and non-canonical Wnt pathway interaction in metastatic prostate cancer

The non-canonical Wnt pathway, a regulator of cellular motility and morphology, is increasingly implicated in cancer metastasis. In a quantitative PCR array analysis of 84 Wnt pathway associated genes, both non-canonical and canonical pathways were activated in primary and metastatic tumors relative to normal prostate. Expression of the Wnt target gene PITX2 in a prostate cancer (PCa) bone metastasis was strikingly elevated over normal prostate (over 2,000-fold) and primary prostate cancer (over 200-fold). The elevation of PITX2 protein was also evident on tissue microarrays, with strong PITX2 immunostaining in PCa skeletal and, to a lesser degree, soft tissue metastases. PITX2 is associated with cell migration during normal tissue morphogenesis. In our studies, overexpression of individual PITX2A/B/C isoforms stimulated PC-3 PCa cell motility, with the PITX2A isoform imparting a specific motility advantage in the presence of non-canonical Wnt5a stimulation. Furthermore, PITX2 specific shRNA inhibited PC-3 cell migration toward bone cell derived chemoattractant. These experimental results support a pivotal role of PITX2A and non-canonical Wnt signaling in enhancement of PCa cell motility, suggest PITX2 involvement in homing of PCa to the skeleton, and are consistent with a role for PITX2 in PCa metastasis to soft and bone tissues. Our findings, which significantly expand previous evidence that PITX2 is associated with risk of PCa biochemical recurrence, indicate that variation in PITX2 expression accompanies and may promote prostate tumor progression and metastasis.

Inhibition of androstenediol-dependent LNCaP tumour growth by 17alpha-ethynyl-5alpha-androstane-3alpha, 17beta-diol (HE3235)

Androst-5-ene-3β, 17β-diol (AED) is an adrenal hormone that has been reported to sustain prostate cancer growth after androgen deprivation therapy (ADT). LNCaP cells express a mutated androgen receptor that confers the ability to respond not only to androgen but also to oestrogen and adrenal hormones such as AED, and thus provide a cell line useful for identifying compounds capable of inhibiting AED-stimulated cell growth. We sought to determine whether structurally related steroids could inhibit AED-stimulated LNCaP cell growth in vitro and tumour growth in vivo. We report here the identification of a novel androstane steroid, HE3235 (17α-ethynyl-5α-androstan-3α, 17β-diol), with significant inhibitory activity for AED-stimulated LNCaP proliferation. This inhibitory activity is accompanied by an increase in the number of apoptotic cells. Animal studies have confirmed the cytoreductive activity of HE3235 on LNCaP tumours. The results suggest that this compound may be of clinical use in castration-resistant prostate cancer.

Single nucleotide polymorphisms refine QTL intervals for hip joint laxity in dogs

Hip laxity is one characteristic of canine hip dysplasia (CHD), an inheritable disease that leads to hip osteoarthritis. Using a genome-wide screen with 250 microsatellites in a crossbreed pedigree of 159 dysplastic Labrador retrievers and unaffected greyhounds, we previously identified putative (P < 0.01) QTL on canine chromosomes 11 and 29 (CFA11 and CFA29). To refine these QTL locations, we have genotyped 257 dogs including 105 Labrador retrievers, seven greyhounds, four generations of their crossbreed offspring and three German shepherds for 111 and 171 SNPs on CFA11 and CFA29 respectively. The distraction index (DI, a measure of maximum hip laxity) was used as an intermediate phenotype that predicts whether a hip joint will or will not develop osteoarthritis. Using a multipoint linkage analysis, significant evidence (95% posterior probability) was found for QTL contributing to hip laxity in the 16.2-21 cM region on CFA11 that explained 15-18% of the total variance in DI. Evidence for an independent QTL on CFA29 was weaker than that on CFA11. Identification of the causative mutation(s) will lead to better understanding of biochemical pathways in both dogs and humans with hip laxity and dysplasia.

A new mechanism of estrogen action in prostate cancer: Inhibition of tissue androgen production and prostate cancer growth by Estradiol in androgen independent prostate cancer xenografts

15509

Background: Estrogens are effective agents in treating prostate cancer in patients in which serum androgens are already at ‘castrate‘ or anorchid levels. The mechanisms whereby estrogens inhibit ‘androgen-independent‘ prostate cancer are unclear. Methods: The androgen-independent human prostate cancer xenograft LuCaP 35V was implanted into orchiectomized male SCID mice and established tumors were treated with placebo pellets, 17β-estradiol (E2) slow-release pellets or E2 with the estrogen receptor antagonist ICI 182,780 as previously described (Clin Cancer Res 8:1003). Effects of E2 on tumor growth and tissue testosterone (T) and dihydrotestosterone (DHT) levels were evaluated by radioimmunoassay. Results: E2 significantly inhibited growth of androgen-independent LuCaP35V ( ∼35% inhibition at 4 weeks, p=0.0047, and increased survival of tumor bearing animals, (p trend =0.03) . The estrogen receptor antagonist ICI 182,780 did not block E2 inhibition of tumor growth, suggesting a receptor independent mechanism of tumor suppression. We then examined the effect of E2 on tissue T and DHT. E2 suppressed levels of tumor T and DHT in treated tumors. Tissue androgens in placebo treated LuCaP35V xenografts were; T=1.21 (± 0.18) pg/mg and DHT=3.54 (±1.07) pg/mg, and in E2-treated LuCaP35V T=0.23 (±0.09) pg/mg and DHT =0.44 (±0.14) pg/mg, (p<0.001). Levels of T and DHT in control liver tissue from both placebo and E2-treated animals were equivalent, at less than 0.2 pg/mg. Conclusions: We have shown that E2 inhibits growth of the androgen- independent human prostate cancer xenograft LuCaP35V, and that this inhibition is estrogen receptor independent. E2 significantly suppressed tumor tissue T and DHT suggesting a new mechanism of E2 mediated growth inhibition of androgen independent prostate cancer, potentially through inhibition of tumoral steroidogenesis. This model of ‘intracrine‘ tumor androgen production can be used to evaluate other inhibitors of tissue steroidogenesis.

No significant financial relationships to disclose.

Comparison of Fc-osteoprotegerin and zoledronic acid activities suggests that zoledronic acid inhibits prostate cancer in bone by indirect mechanisms

Zoledronic acid (ZA) has been shown to inhibit prostate tumor growth in vitro and have beneficial effects in patients with advanced prostate cancer (CaP). The aim of this study was to determine whether ZA exhibits direct anti-tumor effects on CaP cells in vivo. To distinguish the effects of inhibition of osteolysis and direct anti-tumor activity of ZA in vivo, we compared the results of treatment with ZA and osteoprotegerin (Fc-OPG), which inhibits osteolysis, but without significant direct anti-tumor effects. In vitro Fc-OPG had no significant effects on C4-2 proliferation, whereas ZA decreased proliferation. However, both agents decreased tumor growth in bone. Moreover, both increased bone volume and prevented the overall decreases in BMD associated with growth of C4-2 cells in bone. Our study provides novel and significant observations that the in vivo effects of ZA are consistent with indirect effects mediated by osteoclasts.

The effect of osteoprotegerin administration on the intra-tibial growth of the osteoblastic LuCaP 23.1 prostate cancer xenograft

Osteoprotegerin (OPG) plays a central role in controlling bone resorption. Exogenous administration of OPG has been shown to be effective in preventing osteolysis and limiting the growth of osteolytic metastasis. The objective of this study was to investigate the effects of OPG on osteoblastic prostate cancer (CaP) metastases in an animal model. LuCaP 23.1 cells were injected intra-tibially and Fc-OPG (6.0 mg/kg) was administered subcutaneously three times a week starting either 24 hours prior to cell injection (prevention regimen) or at 4 weeks post-injection (treatment regimen). Changes in bone mineral density at the tumor site were determined by dual x-ray absorptiometry. Tumor growth was monitored by evaluating serum prostate specific antigen (PSA). Fc-OPG did not inhibit establishment of osteoblastic bone lesions of LuCaP 23.1, but it decreased growth of the tumor cells, as determined by decreases in serum PSA levels of 73.0 +/- 44.3% (P < 0.001) and 78.3 +/- 25.3% (P < 0.001) under the treatment and prevention regimens, respectively, compared to the untreated tumor-bearing animals. Administration of Fc-OPG decreased the proliferative index by 35.0% (P = 0.1838) in the treatment group, and 75.2% (P = 0.0358) in the prevention group. The results of this study suggest a potential role for OPG in the treatment of established osteoblastic CaP bone metastases.

Cathepsin K mRNA and protein expression in prostate cancer progression

Prostate cancer (CaP) is the most commonly diagnosed malignancy in men and is often associated with bone metastases, which cause much of the morbidity associated with CaP. Lesions associated with CaP generally exhibit increased bone formation and resorption. Increased bone resorption may release factors from the extracellular matrix that contribute to tumor growth. Cathepsin K (cat K) is a cysteine protease that exhibits strong degradative activity against the extracellular matrix and is involved in osteoclast-mediated bone destruction. In this study, we analyzed the expression of cat K in CaP cell lines and patient samples. Cat K message was detected in CaP cell lines by reverse transcription-polymerase chain reaction (RT-PCR) and in primary CaP and metastases by in situ hybridization. Immunohistochemistry revealed variable expression of cat K in primary CaP samples, as well as nonosseous metastases, whereas expression in bone metastases was significantly higher than in primary CaP, and normal prostate tissues were negative. Cat K protein was detected in CaP cell lines by Western blotting after immunoprecipitation. Cat K enzymatic activity was also detected in CaP cell lines by a fluorogenic assay and by an assay for degradation of collagen type I. Increased levels of NTx, a marker of bone matrix degradation mediated primarily by cat K, were also detected in sera of patients with CaP bone metastases. We hypothesize that CaP-expressed cat K may contribute to the invasive potential of CaP, while increased expression in bone metastases is consistent with a role in matrix degradation.

Bone morphogenetic protein signaling in prostate cancer cell lines

Prostate cancer is the most commonly diagnosed malignancy in men and is often associated with bone metastases. Prostate cancer bone lesions can be lytic or schlerotic, with the latter predominating. Bone morphogenetic proteins (BMPs) are a family of growth factors, which may play a role in the formation of prostate cancer osteoblastic bone metastases. This study evaluated the effects of BMPs on prostate cancer cell lines. We observed growth inhibitory effects of BMP-2 and -4 on LNCaP, while PC-3 was unaffected. Flow cytometric analysis determined that LNCaP cell growth was arrested in G(1) after bone morphogenetic protein-2 treatment. Treatment of LNCaP and PC-3 with BMP-2 and -4 activated downstream signaling pathways involving SMAD-1, up-regulation of p21(CIP1/WAF1) and changes in retinoblastoma (Rb) phosphorylation. Interestingly, bone morphogenetic protein-2 treatment stimulated a 2.7-fold increase in osteoprotegerin (OPG), a molecule, which inhibits osteoclastogenesis, production in PC-3.

Serum osteoprotegerin levels are increased in patients with advanced prostate cancer

PURPOSE

Osteoprotegerin (OPG) is a soluble osteoclastogenesis inhibitor that regulates bone turnover. We reported recently that OPG protein expression is significantly increased in prostate cancer (CaP) cells present in bone metastases. The aim of this study was to determine serum OPG levels in patients at different stages of CaP and correlate the results with disease status.

EXPERIMENTAL DESIGN

OPG levels were examined in patients with benign prostatic hyperplasia, clinically localized CaP, early recurrence of CaP, and advanced CaP and evidence of bone metastases. Serum OPG levels were measured by sandwich ELISA assays. The serum Crosslaps (sCTX) assay was used to quantify bone resorption in the advanced CaP group.

RESULTS

Serum OPG levels were increased significantly in the advanced CaP group versus all other groups. There was no significant correlation between serum OPG levels and PSA levels either in the advanced CaP group or within any of three treatment subclasses of this group: no Tx, those not treated; Tx, those treated; and R, those treated with resorption blockers. Levels of OPG were negatively correlated with sCTX levels only in the advanced CaP Tx group. sCTX levels correlated with prostate-specific antigen levels in the advanced CaP Tx and R groups but not in the no-Tx group.

CONCLUSIONS

Our data show that serum OPG levels are increased with advanced CaP. We hypothesize that OPG levels are related to CaP progression and suggest that further studies of the biological effects of OPG on CaP metastases are warranted.

Osteoprotegerin and rank ligand expression in prostate cancer

OBJECTIVES

To investigate the expression of osteoprotegerin (OPG) and RANK ligand (RANKL) in human prostatic tissues. The factors regulating the increased turnover associated with prostate cancer (CaP) bone metastasis are unknown. OPG and RANKL are recently identified regulators of bone resorption and bone remodeling.

METHODS

Tissues from 28 patients with CaP and from 4 normal organ donors were analyzed by reverse transcriptase-polymerase chain reaction and immunohistochemistry for the expression of OPG and RANKL.

RESULTS

OPG and RANKL messages were detected in both normal and cancerous prostate samples. In the normal prostate, OPG protein was detected in luminal epithelial and stromal cells (5% to 65% and 15% to 70%, respectively) and RANKL immunoreactivity was observed in 15% to 50% of basal epithelial cells, 40% to 90% of luminal epithelial cells, and 70% to 100% of stromal cells. OPG was not detected in 8 of 10 primary CaP specimens; RANKL was heterogeneously expressed in 10 of 11 CaP specimens. The percentage of tumor cells expressing OPG and RANKL was significantly increased in all CaP bone metastases compared with nonosseous metastases or primary CaP.

CONCLUSIONS

CaP bone metastases were consistently immunoreactive for both OPG and RANKL compared with nonosseous metastases or primary CaP. The presence of these crucial bone resorption regulators in CaP bone metastases suggests a mechanism whereby CaP cells may modulate bone turnover and has profound implications for the establishment and development of CaP bone metastases in advanced disease.

Study of free and complexed prostate-specific antigen in mice bearing human prostate cancer xenografts

BACKGROUND

Our objective was to evaluate five preclinical prostate cancer (CaP) xenograft models to determine whether (1) prostate-specific antigen (PSA) formed complexes in murine serum, (2) the percentage of free PSA (f-PSA) was characteristic of a given xenograft line, and (3) the percentage of f-PSA was similar to that in the patient at time of tumor harvest. Our fourth objective was to identify which murine serpin(s) bind(s) to PSA in vivo.

METHODS

Xenografts were established from metastatic foci. The percentage of f-PSA, and total PSA (t-PSA) in serum of animals bearing CaP xenografts was determined by immunoassay. Size exclusion high-performance liquid chromatography and Western blots were used to evaluate the presence of PSA complexes in murine serum. Edman degradation was used to determine the N-terminal sequence of complexed proteins.

RESULTS

PSA was detected as both free and complexed forms in murine serum from all mice bearing the CaP xenografts. Three xenografts (related sublines) produced PSA that resulted in low mean percentages of f-PSA (1.9-6.4%). In sera from the other two xenografts, the mean percentages of f-PSA were high (>25%); patient sera, where available at time of tumor acquisition, were in agreement. Western blots showed that murine protease inhibitors formed complexes with PSA. Edman degradation yielded a sequence with 80% homology over 15 amino acids with that of murine alpha1-protease inhibitor (alpha1-PI).

CONCLUSIONS

Our data have shown that the majority of PSA secreted by these CaP xenografts complexes in murine serum with a protease inhibitor with high homology to murine alpha1-PI and that the percentage of f-PSA is a characteristic of each xenograft line tested, which is in agreement with patient values at time of tumor harvest. These CaP xenografts offer opportunities for study of human PSA biology and phenomenology.

LNCaP produces both putative zymogen and inactive, free form of prostate-specific antigen

BACKGROUND

Our objective was to investigate the presence of prostate specific antigen (PSA) and alpha-1-antichymotrypsin (ACT) mRNA and protein in prostate cancer cell lines, and the complexing characteristics of expressed PSA.

METHODS

RT-PCR, immunohistochemistry, and Western blots were employed. Trypsin treatment of PSA was performed to establish the possible presence of an activatable form of PSA.

RESULTS

ACT mRNA and protein were detected in LNCaP, PC-3, and DU 145 by RT-PCR and by immunohistochemistry, respectively. Only LNCaP cells were positive for PSA mRNA and protein. LNCaP expressed approximately 30% active PSA, approximately 40% putative zymogen form of PSA, and approximately 30% stably inactive PSA.

CONCLUSIONS

We have shown that the majority of PSA expressed by LNCaP cells is present in free, noncomplexed forms in the conditioned media. A portion (40%) can be activated by trypsin, while the rest is stably inactive PSA. LNCaP cells may serve as a source of the "unreactive" PSA present in prostate cancer patients' serum.

The value of a reverse transcriptase polymerase chain reaction assay in preoperative staging and followup of patients with prostate cancer

PURPOSE

The reverse transcriptase polymerase chain reaction (RT-PCR) assay is an extremely sensitive technique of detecting cells expressing prostate specific antigen (PSA). Controversy exists regarding the ability of peripheral blood PSA RT-PCR testing to reflect pathological staging or treatment outcome. We examine the phenomenology of RT-PCR results in patients with prostate cancer, with particular emphasis on the RT-PCR test before and after radical prostatectomy, and correlations with pathological staging and treatment outcome.

MATERIALS AND METHODS

Peripheral blood was obtained from a wide variety of patients with and without prostate cancer, including before and after radical prostatectomy. After ribonucleic acid isolation, complementary deoxyribonucleic acid was generated and amplified with a hot-start technique. RT-PCR results were compared with pathological stage, Gleason score, tumor volume and disease-free status. Correlations between preoperative and postoperative RT-PCR tests were also made.

RESULTS

The RT-PCR test was positive in 1 of 56 controls (1.8%) without suspicion of prostate cancer. A positive test was obtained in 12 of 65 men (18.5%) with a suspicion of prostate cancer but a negative biopsy. Before radical prostatectomy a positive test was obtained in 13 of 75 men (17.3%) with pT2 disease versus 10 of 46 (21.7%) with pT3 disease. There was no significant difference in serum PSA, Gleason score or tumor volume between the men with positive or negative results. With repetitive testing an increasing percentage of men had at least 1 positive test preoperatively. With a median followup of 8 months 6 of the 7 patients in whom radical prostatectomy failed had had negative RT-PCR before treatment. Of patients with known metastatic disease or failed primary treatment a positive test was obtained in 32 to 75%. Radical prostatectomy and prostate needle biopsy appeared to have a negligible effect on RT-PCR tests immediately following these procedures. Following radical prostatectomy results were variable but many men who are RT-PCR positive preoperatively become RT-PCR negative postoperatively.

CONCLUSIONS

The PSA RT-PCR test in our laboratory cannot be used preoperatively to predict pathological stage of prostate cancer or treatment failure. Most cases that are positive preoperatively become negative postoperatively. While increasing tumor burden increases the likelihood of positive tests, there appears to be significant sampling error associated with the use of this test in the peripheral blood.

Cross-reactivity of ten anti-prostate-specific antigen monoclonal antibodies with human glandular kallikrein

OBJECTIVES

Prostate-specific antigen (PSA) is commonly used as a marker for prostate disease. Prostate epithelium expresses both PSA and human glandular kallikrein (hK2) proteins, which share 80% sequence homology. The immunologic cross-reactivity of these two proteins could potentially interfere with determination of PSA levels in diagnoses of prostate cancer. We set out to determine the extent of this cross-reactivity for a panel of 10 anti-PSA monoclonal antibodies (mAbs).

METHODS

Enzyme-linked immunosorbent assay (ELISA), sandwich assays, and western transfer techniques were used to assess the PSA/hK2 cross-reactivity of the anti-PSA mAbs.

RESULTS

We did not detect the hK2 protein with any of the 10 anti-PSA mAbs under western transfer conditions. In ELISA experiments, 8 of 10 mAbs exhibited hK2 cross-reactivity under certain conditions. However, no combination of mAbs tested in sandwich assays exhibited a signal in hK2 cross-reactivity experiments greater than 0.1% of the PSA signal.

CONCLUSIONS

We have evaluated 10 anti-PSA mAbs and determined that despite the 80% homology between PSA and hK2 proteins, cross-reactivity with hK2 by these antibodies would not significantly affect the determination of PSA levels by means of sandwich assays.

Detection of circulating prostate cells by reverse transcriptase-polymerase chain reaction of human glandular kallikrein (hK2) and prostate-specific antigen (PSA) messages

OBJECTIVES

To investigate the clinical value of human glandular kallikrein (hK2) reverse transcriptase-polymerase chain reaction (RT-PCR) for detection of prostate cells in circulation and to compare the results with those obtained from prostate-specific antigen (PSA) RT-PCR.

METHODS

We examined peripheral blood (PB) and bone marrow (BM) samples of 13 patients with advanced-stage prostate cancer and 63 patients with clinically localized disease for the presence of circulating prostate cells. An RT-PCR protocol with a two-step amplification cycle and hot-start conditions was used.

RESULTS

The limit of detection of the PCR portion is similar for PSA and hK2 (5 to 10 copies of the plasmid containing the cDNA). The RT-PCR limit of detection is one LNCaP cell in 10(8) peripheral blood mononuclear cells (PMBC) for PSA, and one LNCaP cell in 10(7) PMBC for hK2. Of the BM samples obtained prior to radical prostatectomy, 71.4% were positive for PSA mRNA and 41.3% were positive for hK2 mRNA. In PB, the PSA positivity was 19% and hK2 positivity 12.7%. In advanced-stage patients, there were 76.9% PSA-positive samples in BM versus 38.5% hK2-positive samples; 46.2% of patients were positive in PB for PSA versus 30.8% for hK2.

CONCLUSIONS

We have developed a sensitive RT-PCR protocol for detection of hK2 mRNA and evaluated the suitability of hK2 mRNA in comparison with PSA mRNA as an additional marker for detection of prostate cells in circulation. Combining results of these two tests increased the sensitivity of detection.

Characterization of 10 new monoclonal antibodies against prostate-specific antigen by analysis of affinity, specificity and function in sandwich assays

While prostate-specific antigen (PSA) is already an invaluable marker for prostate cancer, there is continuing demand for new anti-PSA antibodies with specific characteristics, e.g., high sensitivity and specificity and equimolar binding to free PSA (f-PSA) and the PSA-alpha-1-antichymotrypsin complex (PSA-ACT), as well as the ability to distinguish between these 2 immunoreactive forms of PSA. We have therefore generated and characterized 10 anti-PSA monoclonal antibodies (MAbs). Apparent dissociation constants (Kd) of MAbs were determined by direct ELISA yielding Kd-0.2-164.0 nM. Western blots suggested that 3 of the MAbs (60-1A2, 60-8A2 and 17-1A2) bind to linear epitopes. Sandwich assays identified 5 major antigenic regions as binding targets of the MAbs. Three combinations of MAbs recognize f-PSA and PSA-ACT in equimolar fashion with high sensitivity. Two of the MAb combinations are specific for f-PSA. Physical analysis of the new antibodies has allowed us to assign the MAbs to binding classes (based on their sandwiching capabilities) and to determine accurate apparent dissociation constants.

Prostate-specific antigen: characterization of epitopes by synthetic peptide mapping and inhibition studies

To improve our understanding of the prostate-specific antigen (PSA) antigenic regions, we studied the association targets of one anti-PSA polyclonal antibody and 10 anti-PSA monoclonal antibodies (mAbs). We also examined the ability of the mAbs to inhibit PSA enzymatic activity and block the association of PSA with alpha 1-antichymotrypsin (ACT). Linear epitope mapping with a polyclonal antibody indicated the presence of six major antigenic regions in PSA. Examination of the panel of mAbs established that three of them bind to linear epitopes. Five of the mAbs inhibited > 90% of PSA enzymatic activity. However, inhibition of PSA enzymatic activity and hindrance of PSA-ACT association by mAbs cannot be used to predict whether the mAbs bind to free PSA, the PSA-ACT complex, or both. Some of the mAbs may block PSA-ACT association through peripheral occlusion of the binding site, or through induction of conformational changes in PSA.

High-affinity peptide ligands to prostate-specific antigen identified by polysome selection

We have used the polysome-selection method to isolate peptide ligands that bind with high affinity to Prostate-Specific Antigen (PSA), an important prostate-cancer marker. Two random libraries, each encoding approximately 10(12) random peptides, were transcribed into RNA and translated in vitro. Polysomes were panned by affinity selection of the nascent peptides against immobilized PSA. Over 30% of the selected species had significant affinity for PSA; the dissociation constant of the complex formed by the best isolate with PSA was < 10(-9) M. Formation of streptavidin conjugates of selected peptides improved their affinities and, in one case, virtually eliminated non-specific binding. The polysome-selection method can be used to produce high-affinity peptide ligands of potential use in diagnostic and therapeutic procedures.

Improved reverse transcriptase-polymerase chain reaction protocol with exogenous internal competitive control for prostate-specific antigen mRNA in blood and bone marrow

The possibility of improving diagnosis of micrometastases from prostate cancer by further enhancing the detection of prostate-specific antigen-producing cells in circulation is being evaluated. We have developed a reverse transcriptase-PCR protocol with the desirable characteristics of low limit of detection, high specificity, reproducibility of response, and ease of performance. Among the procedural alterations that have contributed to these improvements are longer PCR primers, a two-step amplification cycle, and hot-start PCR. We have lowered the limit of detection to one LNCaP prostate-cancer cell in 10(8) peripheral blood mononuclear cells, and samples of blood and bone marrow from healthy donors have yielded no false positives. Because PCR procedures frequently exhibit tube-to-tube variability, we have incorporated a set of internal and external controls into the protocol-a significant advance in assuring assay reliability.

Identification of differentially expressed prostate genes: increased expression of transcription factor ETS-2 in prostate cancer

BACKGROUND

Little is known about the genetic events in the malignant transformation of prostatic cells. This is due in large measure to the cellular heterogeneity of the prostate.

METHODS

An amplification method was devised to synthesize cDNA from small samples of cancer and benign tissues of the same resected glands. Differential gene expression of candidate informative markers between cancer and benign was screened by the polymerase chain reaction with gene-specific oligonucleotide primers.

RESULTS

The expression of a transcription factor, ETS-2, was shown to be elevated in some cancer specimens. Elevated expression was also noted for neuron-specific enolase (NSE) and another transcription factor, SEF2.

CONCLUSIONS

Our method can be used to identify quickly genes that are differentially expressed between benign and cancerous prostate cells. Transcription factors, such as ETS-2, may play a significant role in cancer progression.

Early tumor cell dissemination in patients with clinically localized carcinoma of the prostate

Because a significant number of patients with pathologically organ-confined carcinoma of the prostate subsequently develop recurrent disease, metastasis may occur much earlier than previously believed. We have used a reverse transcription-PCR assay for prostate-specific antigen mRNA and an immunocytochemical staining method for cytokeratins to test this hypothesis in paired peripheral blood (PB) and bone marrow (BM) specimens from 71 patients with clinically localized disease before radical prostatectomy, 14 patients with advanced-stage carcinoma of the prostate, and 30 controls (young healthy volunteers, patients without prostate disease, and patients with benign prostatic hyperplasia). Controls were negative in BM and PB. Fifty-six% of patients with organ-confined tumors (pT2) and 73% of those with extracapsular extension (pT3) were positive in the BM versus 16% of those with pT2 tumors and 27% of those with pT3 tumors in the PB. Patients with advanced-stage disease were positive in 86% of BM versus 71% of PB. The sensitivity of the immunocytochemistry assay to detect tumor cells was lower as compared with the reverse transcription-PCR assay. The results suggest that tumor cell dissemination occurs early during disease progression. Prostate cells seem to preferentially concentrate in the BM rather than the PB, which may be due to sequestration there by homing mechanisms. As the rate of detection in the BM exceeds the proportion of patients with subsequently progressing disease, we hypothesize that only a subset of these cells can survive in the BM and evolve to clinically apparent disease.

On the failure of de novo-designed peptides as biocatalysts

While the elegance and efficiency of enzymatic catalysis have long tempted chemists and biochemists with reductionist leanings to try to mimic the functions of natural enzymes in much smaller peptides, such efforts have only rarely produced catalysts with biologically interesting properties. However, the advent of genetic engineering and hybridoma technology and the discovery of catalytic RNA have led to new and very promising alternative means of biocatalyst development. Synthetic chemists have also had some success in creating nonpeptide catalysts with certain enzyme-like characteristics, although their rates and specificities are generally much poorer than those exhibited by the best novel biocatalysts based on natural structures. A comparison of the various approaches from theoretical and practical viewpoints is presented. It is suggested that, given our current level of understanding, the most fruitful methods may incorporate both iterative selection strategies and rationally chosen small perturbations, superimposed on frameworks designed by nature.

Prostatic cell lineage markers: emergence of BCL2+ cells of human prostate cancer xenograft LuCaP 23 following castration

A model of prostate cancer progression based on the expression pattern of informative genes in the human prostate cancer xenograft LuCaP 23.1 is presented. Apparently, there are at least 2 tumor cell populations of LuCaP 23.1, representing 2 different phenotypes. One is NSE (neuron-specific enolase)-positive and the other NSE-negative. NSE-positive tumors were recovered after hormone-independent growth in castrated mice. These hormone-independent tumors also expressed BCL2, a gene product shown to inhibit apoptosis. With NSE, BCL2 and PSA (prostate-specific antigen) as identifying markers, the model specifies a putative progression sequence of the prostate cancer cell types. We also show a proposed lineage relationship among the 3 principal normal cell types found in the prostatic epithelium.

IgE-mediated release of leukotriene C4, chondroitin sulfate E proteoglycan, beta-hexosaminidase, and histamine from cultured bone marrow-derived mouse mast cells

Mouse bone marrow-derived mast cells differentiated in vitro and sensitized with monoclonal IgE respond to antigen-initiated activation with the release of histamine, beta-hexosaminidase, chondroitin sulfate E proteoglycan, and leukotriene C4 (LTC4). The chondroitin sulfate E nature of the glycosaminoglycan side chain was established by demonstrating that the chondroitinase ABC disaccharide digestion products were composed of equal quantities of 4-sulfated and 4,6-disulfated N-acetyl-galactosamine. The single immunoreactive sulfidopeptide leukotriene, released and quantitated with a class-specific antibody, was identified as LTC4 by its retention time on reverse-phase high-performance liquid chromatography and by its specific spasmogenic activity on the guinea pig ileum. The release of the preformed mediators, as well as of LTC4, was related in a dose-response fashion to the concentration of monoclonal IgE used during the sensitization step and to the concentration of specific antigen used to initiate the activation-secretion response. The optimal concentrations of IgE for sensitization and of antigen for challenge were the same for the release of preformed mediators and of LTC4. In addition, the time courses of their release were superimposable, with a plateau at 5 min after antigen challenge. The release of three preformed mediators and of LTC4 after fixation of IgE, washing of the sensitized cells, and antigen challenge unequivocally indicates a bone marrow-derived mast cell origin for these products. Linear regression analyses of the net percent release of beta-hexosaminidase to histamine and of 35S-chondroitin sulfate E to beta-hexosaminidase yielded straight lines that intersected at the origin, which indicates that the three preformed mediators are localized in the secretory granules of the bone marrow-derived mast cells. The concomitant generation of 23 ng of LTC4/10(6) sensitized bone marrow-derived mast cells represents the first example of IgE-dependent release of substantial amounts of LTC4, a component of slow reacting substance of anaphylaxis, from a mast cell population of greater than 95% purity. The IgE-dependent generation of LTC4, rather than prostaglandin D2, by the chondroitin sulfate E proteoglycan-containing bone marrow-derived mast cells contrasts with the predominant generation of prostaglandin D2 by heparin proteoglycan-containing mast cells. These differences together support the existence of two phenotypically different mast cell subclasses.