Molecular expression of PSMA mRNA and protein in primary renal tumors

Dependence of Renal Uptake on Kidney Function in [68Ga]Ga-PSMA-11 PET/CT Imaging

(1) Background: PSMA ligand PET/CT is increasingly important for diagnostics of prostate cancer and other tumor diseases. In particular, the radiopharmaceutical [68Ga]Ga-PSMA-11 is widely used. Besides its tumor-specific binding, the uptake within the kidneys is dominant and seems to visualize the renal cortex specifically. Kidney diseases may alter the uptake of radiopharmaceuticals. Therefore, the correlation between renal uptake in PET/CT imaging and renal function should be investigated. (2) Methods: A group of 103 male patients were retrospectively evaluated for eGFR according to the CKD-EPI equation, tracer uptake intensity (SUVmax, SUVpeak, SUVmean), the molecular volume of the renal cortex, morphological kidney size, and total renal uptake. Manual and three different computer-assisted contouring methods (thresholds at 50% of SUVmax, 30% of SUVmax, and absolute SUV of 20) were used for measurements. Correlations between parameters were calculated using linear regression models. (3) Results: Renal SUVmax, SUVpeak, and SUVmean do not correlate with eGFR for manual or computer-assisted measurements. In contrast, molecular cortex volume shows a moderate correlation with eGFR (R2 = 0.231, p < 0.001), superior to morphological kidney size. A contouring threshold of 30% of SUVmax outperformed the other settings for renal cortex volume and total renal uptake. (4) Conclusions: Renal uptake of [68Ga]Ga-PSMA-11 cannot predict eGFR, but the functional renal cortex can be quantified by PET/CT imaging.

Dynamic 68Ga-PSMA-11 PET/CT for the Primary Evaluation of Localized Renal Mass: A Prospective Study

The potential role of prostate-specific membrane antigen (PSMA) PET/CT in non-prostate cancer tumors has shown promising results. We examined the performance of dynamic ⁶⁸Ga-PSMA-11 PET/CT (DPSMA) for the evaluation of localized renal mass. Methods: A prospective case series of patients with a newly diagnosed renal mass who were referred for surgery was examined. DPSMA was performed in a standardized manner before surgery. The final surgical histology served as the standard of reference. PSMA expression in the tumor vasculature was assessed and staining intensity was scored. Tracer uptake and PSMA expression were compared between benign and malignant tissue. Results: Of 29 enhancing renal masses evaluated in 27 patients, 24 (83%) were malignant lesions. The median SUV_mean of benign and malignant lesions was 2.3 (interquartile range [IQR], 2.2-2.7) and 6.8 (IQR, 4.2-10.1), respectively (P = 0.009). Median SUV_max of benign and malignant lesions was 3.8 (IQR, 3.3-4.5) and 9.4 (IQR, 5.4-15.8), respectively (P = 0.015). The median washout coefficient (K ₂) was significantly lower in malignant lesions than in benign lesions (0.17 vs. 0.70, P = 0.02). Positive PSMA staining was found in 20 of 24 malignant lesions and in 2 of 5 benign lesions (P = 0.04). Conclusion: This pilot study demonstrated DPSMA uptake and kinetics in localized renal masses. Increased ⁶⁸Ga-PSMA-11 tracer uptake and intratumoral retention correlate with PSMA expression in malignant renal tumors compared with benign renal masses, supporting further assessment of DPSMA as a potential tool for evaluating localized renal masses.

A Review of Prostate-Specific Membrane Antigen (PSMA) Positron Emission Tomography (PET) in Renal Cell Carcinoma (RCC)

Metastatic renal cell carcinoma (mRCC) is a disease that portends poor prognosis despite an increasing number of novel systemic treatment options including new targeted therapies and immunotherapy. Ablative intervention directed at oligometastatic RCC has demonstrated survival benefit. Consequently, developing techniques for improved staging of mRCC on contemporary imaging modalities including X-ray computed tomography (CT), magnetic resonance imaging (MRI) and/or bone scan (BS) is a clinical priority. This is relevant for metastatic deposits too small to characterize or lymph nodes within physiological normality. Prostate-specific membrane antigen (PSMA) is a type II transmembrane glycoprotein highly expressed on prostate cancer epithelial cells. Recently, small molecules targeting the PSMA receptor, linked to radioactive isotopes have been developed for use with positron emission tomography (PET). Despite its nomenclature, PSMA has also been found to be expressed in the neovasculature of non-prostate cancers such as renal cell carcinoma (RCC) and hence PSMA PET/CT imaging has been proposed as an alternative staging modality. Preliminary small studies involving the use of PSMA PET/CT imaging in mRCC have been encouraging with evidence of improved staging sensitivity which has directly led to change in management in some cases. Given these early encouraging reports, we performed a comprehensive narrative review on the available evidence, including the scientific basis for PSMA expression in RCC, the role of PSMA PET/CT imaging with potential clinical implications in mRCC, its limitations and future opportunities.

Prostate-specific membrane antigen for the surgical oncologist: interpreting expression beyond the prostate

The use of prostate-specific membrane antigen (PSMA) radiotracer in positron emission tomography (PET) has been successfully incorporated into the clinical management of prostate cancer. However, PSMA tracer uptake is not limited to prostate cancer tissue. We reviewed studies exploring PSMA expression beyond the prostate gland using techniques of ⁶⁸ Ga-PSMA PET imaging and immunohistochemistry. PSMA expression has been associated with a variety of solid tumours, and the vasculature associated with neoplastic disease, suggesting that this trans-membrane glycoprotein may be involved in the neovascularisation process in malignancy. These studies demonstrate the need for more research into the potential utility for ⁶⁸ Ga-PSMA PET imaging in patients with non-prostatic cancers.

Diagnostic and prognostic biomarker potential of kallikrein family genes in different cancer types

Purpose

The aim of this study was to compare and contrast the expression of all members of the Kallikrein (KLK) family of genes across 15 cancer types and to evaluate their utility as diagnostic and prognostic biomarkers.

Results

Severe alterations were found in the expression of different Kallikrein genes across various cancers. Interestingly, renal clear cell and papillary carcinomas have similar kallikrein expression profiles, whereas, chromophobe renal cell carcinoma has a unique expression profile. Several KLK genes have excellent biomarker potential (AUC > 0.90) for chromophobe renal cell carcinoma (KLK2, KLK3, KLK4, KLK7, KLK15), renal papillary carcinoma (KLK1, KLK6, KLK7), clear cell renal cell carcinoma (KLK1, KLK6), thyroid carcinoma (KLK2, KLK4, KLK13, KLK15) and colon adenocarcinoma (KLK6, KLK7, KLK8, KLK10). Several KLK genes were significantly associated with mortality in clear cell renal cell carcinoma (KLK2: HR = 1.69; KLK4: HR = 1.63; KLK8: HR = 1.71; KLK10: HR = 2.12; KLK11: HR = 1.76; KLK14: HR = 1.86), papillary renal cell carcinoma (KLK6: HR = 3.38, KLK7: HR = 2.50), urothelial bladder carcinoma (KLK5: HR = 1.89, KLK6: HR = 1.71, KLK8: HR = 1.60), and hepatocellular carcinoma (KLK13: HR = 1.75).

Methods

The RNA-seq gene expression data were downloaded from The Cancer Genome Atlas (TCGA). Statistical analyses, including differential expression analysis, receiver operating characteristic curves and survival analysis (Cox proportional-hazards regression models) were performed.

Conclusions

A comprehensive analysis revealed the changes in the expression of different KLK genes associated with specific cancers and highlighted their potential as a diagnostic and prognostic tool.

Comprehensive Evaluation of Prostate Specific Membrane Antigen Expression in the Vasculature of Renal Tumors: Implications for Imaging Studies and Prognostic Role

PURPOSE

Prostate specific membrane antigen is expressed by the endothelium of many tumors. The aim of the study was to find a rationale for prostate specific membrane antigen based imaging and investigate the prognostic role of vascular prostate specific membrane antigen expression in patients with renal cell carcinoma.

MATERIALS AND METHODS

A total of 257 patients with renal cell carcinoma were included in study with a median followup exceeding 10.0 years. Prostate specific membrane antigen expression on tumor vessels was detected by immunohistochemistry. Vascular expression of FOLH1 gene (prostate specific membrane antigen) mRNA was investigated in clear cell carcinoma and papillary renal cell carcinoma using TCGA (The Cancer Genome Atlas) data.

RESULTS

Endothelial prostate specific membrane antigen protein expression was higher in clear cell than in papillary and chromophobe renal cell carcinoma. Higher grade and stage, metastatic and lethal clear cell renal cell carcinoma showed higher prostate specific membrane antigen expression in tumor vessels. On univariate and multivariate analysis the intensity of positive vs negative endothelial prostate specific membrane antigen protein expression was significantly associated with overall survival. TCGA based analyses confirmed the prognostic role of vascular expression of FOLH1 mRNA. The analyses also supported the usefulness of prostate specific membrane antigen based imaging in cases of clear cell but not papillary renal cell carcinoma.

CONCLUSIONS

We provide a rationale for further development of prostate specific membrane antigen targeted imaging in patients with clear cell renal cell carcinoma. The prognostic role of prostate specific membrane antigen was determined at the protein level in clear cell renal cell carcinoma and at the mRNA level in clear cell and papillary renal cell carcinoma.

The prognostic value of BAP1, PBRM1, pS6, PTEN, TGase2, PD-L1, CA9, PSMA, and Ki-67 tissue markers in localized renal cell carcinoma: A retrospective study of tissue microarrays using immunohistochemistry

OBJECTIVE

To assess the prognostic roles of BAP1, PBRM1, pS6, PTEN, TGase2, PD-L1, CA9, PSMA, and Ki-67 tissue biomarkers in localized renal cell carcinoma (RCC).

METHODS

Patients who underwent a nephrectomy during 1992-2015 and had a primary specimen of their kidney tumor were included. The nine tissue biomarkers were immunohistochemically stained on tissue microarrays of RCC, and the semi-quantitative H-score, including intensity score, was used to grade the sample. The Cox proportional hazards model was used to evaluate tissue markers significant for overall survival (OS), cancer-specific survival (CSS), and recurrence-free survival (RFS) after adjusting for significant clinicopathological parameters.

RESULTS

Samples from 351 RCC patients were included. The mean age of the patients was 53.9 years; the rates of pathologic T1-2/≥T3 stage, Fuhrman 1+2/3+4 grade, recurrence, and death were 269/65(80.5/19.5%), 222/107 (67.5/32.5%), 6.6%, and 10.5%, respectively. Median OS, CSS, and RFS were 220.6, 220.6, and 147.1 months, respectively. The multivariable analysis showed that pathologic T stage and Fuhrman nuclear grade were significantly associated with OS and CSS. Pathologic T stage and tumor size were associated with RFS. After adjusting for these significant prognostic clinicopathological factors, Ki-67 was significantly associated with OS (hazard ratio [HR], 2.7), CSS (HR, 3.82), and RFS (HR, 4.85) and pS6 was associated with CSS (HR, 8.63) and RFS (HR, 8.51) in the multivariable model (p<0.05).

CONCLUSION

pS6 and Ki-67 are significant prognostic factors of RCC; however, BAP1, PBRM1, TGase 2, PD-L1, CA9, PTEN loss, and PSMA markers did not show this association.

99mTc-labeling and evaluation of a HYNIC modified small-molecular inhibitor of prostate-specific membrane antigen

INTRODUCTION

Prostate-specific membrane antigen (PSMA) is a well-established target in the development of radiopharmaceuticals for the diagnosis and therapy of prostate cancer (PCa). In this study, we evaluated a novel ^99mTc-labeled small molecular inhibitor of PSMA.

METHODS

This new small-molecular inhibitor of PSMA, 6-hydrazinonicotinate-Aminocaproic acid-Lysine-Urea-Glutamate (HYNIC-ALUG) was radiolabeled by ^99mTc and was evaluated both in vitro and in vivo using PCa models (PC-3 and LNCaP). Radiation dosimetry was assessed in mice.

RESULTS

^99mTc-HYNIC-ALUG showed excellent stability in different media. A cell assay preliminarily displayed its specificity for PSMA. The inhibitor showed good pharmacokinetics making it suitable for in vivo imaging. PC-3-derived tumors showed no obvious radioactive uptake; however, the LNCaP-derived tumors showed very high radioactive uptake which was significantly decreased by the selective PSMA inhibitor 2-PMPA. Biodistribution in LNCaP xenografts showed an optimum tumor-to-blood ratio of 24.23±3.54 at 2h. Tumor uptake was also decreased in the inhibition experiment with 2-PMPA (19.45±2.14%ID/g versus 1.42±0.15%ID/g at 2h). The effective dose of the ^99mTc-HYNIC-ALUG was 8.4E-04mSv/MBq.

CONCLUSIONS

A new ^99mTc-labeled PSMA inhibitor with specific accumulation in PSMA-positive tumors and low background in other organs was synthesized. The radiopharmaceutical also showed very low radiation dosimetry. This agent may significantly improve the diagnosis, staging, and subsequent monitoring of therapeutic effects in PCa patients.

A Novel Prostate-Specific Membrane-Antigen (PSMA) Targeted Micelle-Encapsulating Wogonin Inhibits Prostate Cancer Cell Proliferation via Inducing Intrinsic Apoptotic Pathway

Prostate cancer (PCa) is a malignant tumor for which there are no effective treatment strategies. In this study, we developed a targeted strategy for prostate-specific membrane-antigen (PSMA)-positive PCa in vitro based on 2-(3-((S)-5-amino-1-carboxypentyl)ureido) pentanedioic acid (ACUPA) modified polyethylene glycol (PEG)-Cholesterol micelles containing wogonin (WOG), which was named ACUPA-M-WOG. ACUPA-M-WOG was conventionally prepared using a self-assembling method, which produced stable particle size and ζ potential. Moreover, ACUPA-M-WOG showed good drug encapsulating capacity and drug release profiles. Fluorescence activated cell sorting (FACS) results suggested that ACUPA modified PEG-Cholesterol micelles could effectively enhance the drug uptake on PSMA(+) PCa cells, and the cytotoxicity of ACUPA-M-WOG was stronger than other controls according to in vitro cellular proliferation and apoptosis assays, separately through methyl thiazolyl tetrazolium (MTT) and Annexin V/Propidium Iodide (PI) staining. Finally, the molecular mechanisms of ACUPA-M-WOG’s effects on human PSMA(+) PCa were investigated, and were mainly the intrinsic or extrinsic apoptosis signaling pathways. The Western blot results suggested that ACUPA-M-WOG could enhance the WOG-induced apoptosis, which was mainly via the intrinsic signaling pathway rather than the extrinsic signaling pathway. In conclusion, ACUPA-M-WOG was successfully developed for WOG-selective delivery to PSMA(+) PCa cells and had stronger inhibition than free drugs, which might make it an effective strategy for PSMA(+) PCa.

Prostate-specific membrane antigen: a new potential prognostic marker of osteosarcoma

Previous studies have demonstrated that the expression of prostate-specific membrane antigen (PSMA) is restricted to endothelium from tumor-associated neovasculature. But the expression of PSMA in osteosarcoma and its clinical significance are unknown. Using immunohistochemical analysis and quantum dot probes, we found that 46.7% (21/45) of the osteosarcoma showed positive staining for PSMA while no PSMA staining in osteofibrous dysplasia. The expression and localization of PSMA was confirmed by CD34 staining. More importantly, the expression of PSMA is correlated with tumor size, pulmonary metastasis and worse survival (survival rate 63.2% in the PSMA-negative group versus 36.6% in the PSMA-positive group). Thus, PSMA could be used as an independent prognostic marker for the osteosarcoma patients, and PSMA staining in tumor-associated neovasculature may be a potential target for antineovasculature-based therapy in osteosarcoma.

Efficacy of large doses of IL-2-activated human leukocyte antigen haploidentical peripheral blood stem cells on refractory metastatic renal cell carcinoma

Traditional immunotherapy for patients with refractory metastatic renal cell carcinoma (RCC) is limited because the tumors themselves induce immunosuppression. The aim of this article was to evaluate the clinical efficacy of the infusion of a high dose of interleukin (IL)-2-activated allogeneic haploidentical peripheral blood stem cells (haplo-PBSCs) in patients with advanced intractable RCC. Ten advanced RCC patients and their haploidentical relatives, who were haplo-PBSC donors, were enrolled in this study. All patients accepted one cycle of activated haplo-PBSCs. The clinical and immunologic responses were evaluated. A range from 2.3 to 5.5×10(10) of activated haplo-PBSCs were harvested after exposure to recombinant human IL-2 (rhIL-2), along with a significant increase in the proportion of natural killer cells and activated lymphocytes (CD69+ and CD25+). Enhanced cytotoxicity of haplo-PBSCs for RCC was also observed. After treatment, 2 (2/10) cases of partial remission, 6 (6/10) cases of stable disease, and 2 (2/10) cases of progressive disease were identified in these 10 patients. The median progression-free survival of the 10 patients was 5.5 months (3-14 months). The adoptive transfusion of IL-2-activated haplo-PBSCs can induce sustained antitumor effects for advanced intractable RCC patients who have had no response to conventional immunotherapy.

Broad antigenic coverage induced by vaccination with virus-based cDNA libraries cures established tumors

Effective cancer immunotherapy requires the release of a broad spectrum of tumor antigens in the context of potent immune activation. We show here that a cDNA library of normal tissue, expressed from a highly immunogenic viral platform, cures established tumors of the same histological type from which the cDNA library was derived. Immune escape occurred with suboptimal vaccination, but tumor cells that escaped the immune pressure were readily treated by second-line virus-based immunotherapy. This approach has several major advantages. Use of the cDNA library leads to presentation of a broad repertoire of (undefined) tumor-associated antigens, which reduces emergence of treatment-resistant variants and also permits rational, combined-modality approaches in the clinic. Finally, the viral vectors can be delivered systemically, without the need for tumor targeting, and are amenable to clinical-grade production. Therefore, virus-expressed cDNA libraries represent a novel paradigm for cancer treatment addressing many of the key issues that have undermined the efficacy of immuno- and virotherapy to date.

2-5A ligands--a new concept for the treatment of prostate cancer

Several potent prostate specific membrane antigen (PSMA) inhibitors have been described recently. We generated a PSMA-specific 2-5A ligand called RBI 1033 by linking 2-5A to the N-acetylaspartylglutamate (NAAG)-based inhibitor ZJ-24. We measured the inhibitory activity of RBI 1033 to the folate hydrolase activity of PSMA. Amazingly, we found that compared to ZJ-24 (IC50 = 53.9 nM), RBI 1033 was more than 10 times more potent (IC50 = 4.78 nM) as a folate hydrolase inhibitor, while SMCC 2-5A lacking the ZJ-24 part, did not show much activity (IC50 = 1974 nM). Also, RBI 1033's affinity to PSMA was found to be 10 times higher than ZJ-24 itself.

Mapping of the active site of glutamate carboxypeptidase II by site-directed mutagenesis

Human glutamate carboxypeptidase II [GCPII (EC 3.4.17.21)] is recognized as a promising pharmacological target for the treatment and imaging of various pathologies, including neurological disorders and prostate cancer. Recently reported crystal structures of GCPII provide structural insight into the organization of the substrate binding cavity and highlight residues implicated in substrate/inhibitor binding in the S1' site of the enzyme. To complement and extend the structural studies, we constructed a model of GCPII in complex with its substrate, N-acetyl-l-aspartyl-l-glutamate, which enabled us to predict additional amino acid residues interacting with the bound substrate, and used site-directed mutagenesis to assess the contribution of individual residues for substrate/inhibitor binding and enzymatic activity of GCPII. We prepared and characterized 12 GCPII mutants targeting the amino acids in the vicinity of substrate/inhibitor binding pockets. The experimental results, together with the molecular modeling, suggest that the amino acid residues delineating the S1' pocket of the enzyme (namely Arg210) contribute primarily to the high affinity binding of GCPII substrates/inhibitors, whereas the residues forming the S1 pocket might be more important for the 'fine-tuning' of GCPII substrate specificity.

Expression of Prostate-Specific Membrane Antigen in Tumor-Associated Neovasculature of Renal Neoplasms

OBJECTIVES

Prostate-specific membrane antigen (PSMA) is highly expressed in prostate cancer cells. Recently, PSMA has been found in the neovasculature in association with other solid malignant tumors, including clear cell renal carcinoma (RCC). We studied the expression of PSMA in different primary renal tumors.

METHODS

A tissue microarray was constructed from 60 normal kidney, 21 clear cell RCC (CCRCC), 20 papillary RCC (PRCC), 16 chromophobe RCC, 19 oncocytoma, 14 transitional cell carcinoma, and 19 angiomyolipoma (AML) specimens. This tissue microarray was then immunostained for a vascular endothelial marker CD34 and PSMA. PSMA expression in CD34-positive tumor-associated neovasculature was scored according to the staining intensity and the percentage of vessels. Only diffuse strong or weak, or focal strong PSMA staining was graded as positive.

RESULTS

PSMA was expressed in the proximal tubules of the normal kidney and in the tumor-associated vasculature in the renal tumors. Positive PSMA staining was detected in 76.2% of CCRCC, 31.2% of chromophobe RCC, 52.6% of oncocytoma, 21.4% of transitional cell carcinoma, and 0% of PRCC and AML specimens. Its expression was greater in CCRCC than PRCC, chromophobe RCC, transitional cell carcinoma, and AML (P <0.001), but was not significantly different from the expression in oncocytoma (P = 0.79). PSMA expression did not correlate with the pathologic stage in CCRCC.

CONCLUSIONS

PSMA is differentially expressed in the tumor-associated neovasculature in different renal tumors. It is most commonly detected in CCRCC and rarely detectable in PRCC and AML. This finding suggests that antibodies against PSMA may potentially be used as a diagnostic marker and therapeutic target for renal neoplasms.

Prostate-specific membrane antigen (PSMA) protein expression in normal and neoplastic tissues and its sensitivity and specificity in prostate adenocarcinoma: an immunohistochemical study using mutiple tumour tissue microarray technique

AIMS

To determine prostate-specific membrane antigen (PSMA) expression in normal tissues and in 3161 benign and malignant tumours and subsequently to define its sensitivity and specificity in prostatic adenocarcinoma (PaC).

METHODS AND RESULTS

Multiple tissue microarray sections were stained with a monoclonal antibody to PSMA. PaC was positive in 93/141 cases (66.0%) with various staining patterns including cytoplasmic, apical, apical/cytoplasmic and cytoplasmic with membranous accentuation. Of 2174 various tumour types, 154 expressed PSMA, including 59/346 (17.0%) urothelial carcinomas of the bladder (UBC). In those tumours, the staining pattern was always cytoplasmic. All 846 benign tumours were negative for PSMA. The sensitivity and specificity of PSMA in distinguishing PaC from any other type of malignancy is 65.9% and 94.5%, respectively. Furthermore, its sensitivity and specificity in differentiating PaC from urothelial cancer is 65.9% and 82.9%, respectively.

CONCLUSIONS

Despite its expression by subsets of various types of malignancies, PSMA is still considered to be fairly sensitive and highly specific for PaC.

Expression of prostate-specific membrane antigen in normal and malignant human tissues

BACKGROUND

Prostate-specific membrane antigen (PSMA) is upregulated in androgen-dependent prostate carcinoma and it has been targeted for immunotherapy and diagnosis of this cancer. However, this protein is also expressed in other tissues. The objective of this study is to investigate its expression in normal and malignant human tissues.

METHODS

Using monoclonal antibodies 24.4E6 (specific for residues 638-657) and 7E11.C5 (specific for the transmembrane domain of PSMA), immunohistochemical detection of PSMA was performed in surgical specimens.

RESULTS

Prostate-specific membrane antigen was detected in the epithelium of prostate, urinary bladder, proximal tubules of kidney, liver, esophagus, stomach, small intestine, colon, breast, fallopian tubes and testicular seminiferous tubules, hippocampal neurons and astrocytes, ependyma, cortex and medulla of the adrenal gland, and ovary stroma. It was also detected in neoplasms of the prostate, kidney, urinary bladder, stomach, small intestine, colon, lung, adrenal gland, and testis. It was not detected in normal seminal vesicles or the lung.

CONCLUSIONS

These findings demonstrate that PSMA is widely distributed in normal tissues, and, depending on the tumors, its expression is up- or down-regulated, or unchanged. The broad distribution of PSMA may make it suitable for the diagnosis and therapy of a wide variety of tumors.

A Dimeric Peptide That Binds Selectively to Prostate-Specific Membrane Antigen and Inhibits its Enzymatic Activity

Prostate-specific membrane antigen (PSMA) is highly expressed by both normal and malignant prostate epithelial cells and by the neovasculature of many tumor types; however, it is not expressed by normal endothelial cells or other normal tissues. PSMA, therefore, represents an attractive candidate for selectively targeted therapies for prostate and/or other solid tumors. As an alternative approach to antibody-based anti-PSMA therapies, small peptides that bind selectively to PSMA-producing cells can be used to deliver cytotoxic drugs, protein toxins, and viruses selectively to malignant sites while minimizing systemic toxicity to normal tissues. Small peptides are relatively inexpensive to produce, not immunogenic, and easily coupled to cytotoxic agents. In the present study, a random phage library consisting of linear 12 amino acid peptides was used to identify peptides that bound selectively to PSMA. From a series of monomeric peptides, one with the sequence WQPDTAHHWATL was used to show binding of soluble peptide to PSMA. A dimeric version of this peptide showed markedly enhanced binding to soluble PSMA and an IC50 of 2.2 micromol/L for inhibition of PSMA enzymatic activity. Fluorescently labeled dimeric peptide bound selectively to PSMA-producing prostate cancer cells in vitro with no significant binding to non-PSMA-producing cells. Molecular modeling of the dimeric peptide revealed that histidine residues in close vicinity can efficiently coordinate a divalent ion and hold the peptide in a favorable configuration for binding and subsequent inhibition. These dimeric peptides, therefore, represent putative PSMA-selective targeting agents that are currently being evaluated for selective binding in vivo.

Recombinant glutamate carboxypeptidase II (prostate specific membrane antigen--PSMA)--cellular localization and bioactivity analyses

Glutamate Carboxypeptidase II (also known as Prostate Specific Membrane Antigen-PSMA) is an important marker in the diagnosis of prostate cancer, however, relatively little is known about its biochemical and structure-function characteristics. We have expressed mutant forms of PSMA and have started to address the roles of three putative domains of PSMA in its cellular localization and peptidase activity. Three mutants, a full-length recombinant PSMA (rPSMA-FL), one expressing only the proposed extracellular domain of PSMA (rPSMA-ECD) and one form omitting the proposed transmembrane domain (rPSMA-deltaTMD) have been produced in human cells via a mammalian expression vector system. We show that rPSMA-FL is associated with the cell surface membrane; so too is rPSMA-deltaTMD even though it lacks the proposed transmembrane domain, whereas rPSMA-ECD has a cytosolic localization. Only rPSMA-FL retains functional hydrolytic activity and is similarly glycosylated to PSMA found in the cultured prostate cancer cell line LNCaP.

Detection of clinically significant, occult prostate cancer metastases in lymph nodes using a splice variant-specific rt-PCR assay for human glandular kallikrein

PURPOSE

To compare the detection of human glandular kallikrein 2 (hK2) mRNA expression in archival lymph nodes with disease progression, the development of prostate cancer metastases, and mortality in patients undergoing radical prostatectomy for locally advanced nonmetastatic prostate cancer.

PATIENTS AND METHODS

We evaluated total RNA extracted from fixed, paraffin-embedded, histopathologically normal pelvic lymph nodes, removed at radical prostatectomy, from 199 pT3N0 prostate cancer patients (150 extraprostatic extension only; 49 seminal vesicle involvement) for hK2-expressing cells using a novel reverse transcriptase polymerase chain reaction (RT-PCR)/hK2 assay. Cumulative incidence functions and Cox proportional hazards analyses were performed.

RESULTS

Forty patients (20%) had positive results, 80 patients (40%) had negative results, and 79 patients (40%) had equivocal results. RT-PCR/hK2 status was not associated with any pathologic characteristics (P >.05). In postoperative multivariable models, the RT-PCR/hK2 result was associated with prostate cancer progression (P =.001), development of distant metastases (P =.001), and prostate cancer-specific survival (P =.005). In patients experiencing biochemical progression (n = 33), RT-PCR/hK2 status was a predictor of failure to respond to salvage radiotherapy (P =.002).

CONCLUSION

RT-PCR/hK2 can detect biologically and clinically significant occult prostate cancer metastases in histopathologically normal lymph nodes. In patients with locally advanced prostate cancer, RT-PCR/hK2 is strongly associated with prostate cancer progression, failure following salvage radiation therapy, development of clinically evident metastases, and prostate cancer-specific mortality after surgery.

Allogeneic dendritic cells fused with tumor cells: preclinical results and outcome of a clinical phase I/II trial in patients with metastatic renal cell carcinoma

Therapeutic vaccination with dendritic cells (DC) can lead to tumor regression in animal models and has shown promising results in the first clinical trials of metastatic renal cell carcinoma and malignant melanoma. In vitro data and results of a clinical phase I/II trial using DC tumor fusions in patients with progressive metastatic renal cell carcinoma are presented here. In addition to toxicity and feasibility, complex immune monitoring was a point of interest. DC precursor cells were obtained from the peripheral blood mononuclear cells (PBMCs) of healthy donors and were fused with either allogeneic (8 patients) or autologous (4 patients) renal tumor cells. In total, 12 patients with progressive metastatic renal cell carcinoma were treated with an average of 2.8 x 10(7) tumor cells fused with 1.8 x 10(7) DC each administered on days 0, 28, and 56 intradermally. Fusion efficacy for the tumor cells used was 14.3% +/- 7.8%. Cell viability was 59.8% +/- 6.8% after fusion and irradiation. We observed no adverse effects and no difference in clinical outcome between the allogeneic and the autologous treatment. Eight patients remained in a progressive disease state and four patients in a stable disease state. T-cell immunity was carefully monitored before, during, and after treatment. Delayed-type hypersensitivity (DTH) reaction using tumor cells was positive after treatment in 7 of 12 patients, 2 of whom were found to have stable disease. An increase in the reactivity against recall antigens was seen in most patients. Interestingly, cytotoxicity of peripheral blood lymphocytes (PBLs) against renal cell carcinoma cells increased during treatment as well as the percentage of interferon-gamma-secreting cells. This effect was significantly enhanced within the group that had stable disease. The lack of adverse effects together with positive immunologic signs justifies further investigation of this novel therapeutic approach. Further studies are necessary to test for clinical effectiveness in patients with tumors, especially those with less advanced disease.

Upregulation of prostate specific membrane antigen/folate hydrolase transcription by an enhancer

Prostate specific membrane antigen (PSMA), also known as folate hydrolase (FOLH1), is a 100 kDa glycoprotein with elevated expression in prostate epithelial tissue. Expression of PSMA is upregulated as prostate tumor grade increases and is found in the vasculature of many tumors, with no presence in benign tissues. Due to the potential of the regulatory elements of the PSMA promoter and enhancer to be used in gene therapy and as biomarkers for prostate cancer under conditions of androgen ablation during treatment, we sequenced and analyzed the ability of 5.5 kb of PSMA promoter/leader region to promote transcription. A recently discovered enhancer, found in the third intron of the PSMA gene, FOLH1, was also studied. The promoter/leader region sequence provided basal expression in transcription assays, while addition of the enhancer activated transcription 41-fold in transient transfections and 144-fold in stable transfections of the LNCaP prostate cell line. This enhancement of transcription was not found in nonprostate cell lines or prostate cell lines that do not express PSMA. An analysis of the ability of androgens to act via the PSMA promoter/leader region and enhancer to activate transcription in transiently transfected LNCaP cells revealed no significant androgen response using the FOLH1 promoter/leader region and a downregulation of 42% with addition of the enhancer. In stably transfected LNCaP cells, the FOLH1 promoter/leader region produced a 21% downregulation in response to androgens, while addition of the enhancer resulted in a 45% downregulation. These results demonstrate significant upregulation of transcription by the PSMA promoter/enhancer, with specificity for the LNCaP prostate cell line, and downregulation of transcription in response to physiological levels of androgen.

Optimization of the reverse transcriptase polymerase chain reaction for the detection of circulating prostate cells

The reverse transcriptase polymerase chain reaction (RT-PCR) is a sensitive technique that can detect prostate-specific messenger RNA in circulating blood. Many authors have studied the potential of RT-PCR as a staging technique in prostate cancer (PC). Clinical sensitivity and in some cases specificity has been disappointing. Few authors have been able to correlate RT-PCR result with patient stage. We have compared the results of using two different RT-PCR protocols with different sensitivities on blood samples from prostate cancer patients. An 80-amplification-cycle nested primer RT-PCR assay had a detection limit of 10 prostate cells and a 50-cycle RT-PCR could detect 20 cells in 5 ml blood. The 80-cycle assay detected prostate mRNA in four of 10 female samples, whereas the 50-cycle assay detected it in none. There was little difference in the assays' ability to detect prostate mRNA in advanced PC patients. The 50-cycle assay could differentiate between hormone-escaped, stable hormone-treated and untreated localized PC patients, whereas the 80-cycle assay could not. Each blood sample must be assayed several times with RT-PCR to avoid false-negative results and, if this is done, assay specificity can be increased with little effect on clinical sensitivity.

Regression of metastatic renal-cell carcinoma after nonmyeloablative allogeneic peripheral-blood stem-cell transplantation

BACKGROUND

Since allogeneic stem-cell transplantation can induce curative graft-versus-leukemia reactions in patients with hematologic cancers, we sought to induce analogous graft-versus-tumor effects in patients with metastatic renal-cell carcinoma by means of nonmyeloablative allogeneic peripheral-blood stem-cell transplantation.

METHODS

Nineteen consecutive patients with refractory metastatic renal-cell carcinoma who had suitable donors received a preparative regimen of cyclophosphamide and fludarabine, followed by an infusion of a peripheral-blood stem-cell allograft from an HLA-identical sibling or a sibling with a mismatch of a single HLA antigen. Cyclosporine, used to prevent graft-versus-host disease, was withdrawn early in patients with mixed T-cell chimerism or disease progression. Patients with no response received up to three infusions of donor lymphocytes.

RESULTS

At the time of the last follow-up, 9 of the 19 patients were alive 287 to 831 days after transplantation (median follow-up, 402 days). Two had died of transplantation-related causes, and eight from progressive disease. In 10 patients (53 percent) metastatic disease regressed; 3 had a complete response, and 7 had a partial response. The patients who had a complete response remained in remission 27, 25, and 16 months after transplantation. Regression of metastases was delayed, occurring a median of 129 days after transplantation, and often followed the withdrawal of cyclosporine and the establishment of complete donor-T-cell chimerism. These results are consistent with a graft-versus-tumor effect.

CONCLUSIONS

Nonmyeloablative allogeneic stem-cell transplantation can induce sustained regression of metastatic renal-cell carcinoma in patients who have had no response to conventional immunotherapy.