These findings implicate PSMA in both the metabolism of polyglutamated folates, and in the uptake of monoglutamated folates. Under conditions of LF or PF levels, PSMA gives cells expressing it a proliferative advantage.

In this review, we cover the evolution of knowledge on the biology of prostate-specific membrane antigen (PSMA) and its translation to therapy. The usual key to discovery is a realistic model for experimentation and for testing a hypothesis. A realistic model is especially needed in the case of the human prostate, which differs significantly from the prostate of species often used as research models. We will emphasize the genetic characterization of PSMA, the nature of the PSMA protein, and its role as a carboxypeptidase, with differing important substrates and products in different tissues. We give special prominence to the importance of PSMA as a target for imaging and therapy in prostate cancer and its underdeveloped role for imaging and targeting the neovasculature of tumors other than prostate cancer. Lastly, we bring attention to its importance in other nonprostatic tissues.

Glutamate carboxypeptidase II (GCPII, EC 3.14.17.21) is a membrane-bound enzyme found on the extracellular face of glia. The gene for this enzyme is designated FOLH1 in humans and Folh1 in mice. This enzyme has been proposed to be responsible for inactivation of the neurotransmitter N-acetylaspartylglutamate (NAAG) following synaptic release. Mice harboring a disruption of the gene for GCPII/Folh1 were generated by inserting into the genome a targeting cassette in which the intron-exon boundary sequences of exons 1 and 2 were removed and stop codons were inserted in exons 1 and 2. Messenger RNA for GCPII was not detected by northern blotting or RT-PCR analysis of RNA from the brains of -/-mutant mice nor was GCPII protein detected on western blots of this tissue. These GCPII null mutant mice developed normally to adulthood and exhibited a normal range of neurologic responses and behaviors including mating, open field activity and retention of position in rotorod tests. No significant differences were observed among responses of wild type, heterozygous mutant and homozygous mutant mice on tail flick and hot plate latency tests. Glutamate, NAAG and mRNA for metabotropic glutamate receptor type 3 levels were not significantly altered in response to the deletion of glutamate carboxypeptidase II. A novel membrane-bound NAAG peptidase activity was discovered in brain, spinal cord and kidney of the GCPII knock out mice. The kinetic values for brain NAAG peptidase activity in the wild type and GCPII null mutant were V max ¼ 45 and 3 pmol/mg/min and K m ¼ 2650 nM and 2494 nM, respectively. With the exception of magnesium and copper, this novel peptidase activity had a similar requirement for metal ions as GCPII. Two potent inhibitors of GCPII, 4,4¢-phosphinicobis-(butane-1,3 dicarboxilic acid) (FN6) and 2-(phosphonomethyl)pentanedioic acid (2-PMPA) 2 inhibited the residual activity. The IC 50 value for 2-PMPA was about 1 nM for wild-type brain membrane NAAG peptidase activity consistent with its activity against cloned rat and human GCPII, and 88 nM for the activity in brain membranes of the null mutants. Keywords: N-acetylaspartylglutamate (NAAG), N-acetylaspartylglutamate-peptidase (NAAG-peptidase), glutamate carboxypeptidase II metabotropic glutamate receptor. 3

Objective Despite a multitude of detection and treatment advances in the past two decades, prostate cancer remains the second leading cause of cancer death among men in the United States. Technological evolution and expanding knowledge of tumor biomarkers have invigorated exploration in prostate cancer therapeutics. Prostate-specific membrane antigen (PSMA) was one of the first prostate cancer biomarkers successfully cloned. Since that time, it has been characterized as the prototypical cell-surface marker for prostate cancer and has been the subject of intense clinical inquiry. We review the relevant research in PSMA on the 20th anniversary of its cloning. Methods and materials A PubMed® search using the keywords “prostate-specific membrane antigen” or “glutamate carboxypeptidase II” provided 1019 results. An additional 3 abstracts were included from scientific meetings. Articles were vetted by title and abstract with emphasis placed on those with clinically relevant findings. Results Sixty articles were selected for inclusion. PSMA was discovered and cloned in 1993. Its structure and function were further delineated in the ensuing decade. Consensus sites of expression in normal physiology are prostate, kidney, nervous system, and small intestine. PSMA has been implicated in the neovasculature of several tumors including urothelial and renal cell carcinomas. In prostate cancer, expression of PSMA is directly related to Gleason grade. PSMA has been tested both in imaging and therapeutics in a number of prostate cancer clinical trials. Several recent approaches to target PSMA include use of small molecule inhibitors, PSMA-based immunotherapy, RNA aptamer conjugates, and PSMA-targeted prodrug therapy. Future study of PSMA in prostate cancer might focus on its intracellular functions and possible role in tumor neurogenesis. Conclusions Twenty years from its discovery, PSMA represents a viable biomarker and treatment target in prostate cancer. Research to delineate its precise role in prostate carcinogenesis and within the therapeutic armamentarium for patients with prostate cancer remains encouraging.

Human Prostate Specific Membrane Antigen (PSMA), also known as folate hydrolase I (FOLH1), is a 750-amino acid type II membrane glycoprotein, which is primarily expressed in normal human prostate epithelium and is upregulated in prostate cancer, including metastatic disease. We have cloned and sequenced the mouse homolog of PSMA, which we have termed Folh1, and have found that it is not expressed in the mouse prostate, but primarily in the brain and kidney. We have demonstrated that Folh1, like its human counterpart, is a glutamate-preferring carboxypeptidase, which has at least two enzymatic activities: (1) N-acetylated alpha-linked L-amino dipeptidase (NAALADase), an enzyme involved in regulation of excitatory signaling in the brain, and (2) a gamma-glutamyl carboxypeptidase (folate hydrolase). The 2,256-nt open reading frame of Folh1 encodes for a 752-amino acid protein, with 86% identity and 91% similarity to the human PSMA amino acid sequence. Cells transfected with Folh1 gained both NAALADase and folate hydrolase activities. Examination of tissues for NAALADase activity correlated with the mRNA expression pattern for Folh1. Fluorescent in situ hybridization (FISH) revealed Folh1 maps to only one locus in the mouse genome, Chromosome 7D1-2.