Dean J. Bacich

Expression of prostate-specific membrane antigen (PSMA), increases cell folate uptake and proliferation and suggests a novel role for PSMA in the uptake of the non-polyglutamated folate, folic acid.

Prostate specific membrane antigen (PSMA) is a unique folate hydrolase that is significantly upregulated in prostate cancer. In a mouse model, PSMA is able to facilitate prostate carcinogenesis, however, little is known about the mechanism by which this occurs. As PSMA is able to hydrolyze polyglutamated folates, and cancer cells proliferate directly in response to available folate, we examined if expression of human PSMA in PC‐3 cells confers a proliferative advantage in a microenvironment with physiologically relevant folate levels.

Mice lacking glutamate carboxypeptidase II are protected from peripheral neuropathy and ischemic brain injury.

Excessive glutamate release is associated with neuronal damage. A new strategy for the treatment of neuronal injury involves inhibition of the neuropeptidase glutamate carboxypeptidase II (GCP II), also known as N‐acetylated α‐linked acidic dipeptidase. GCP II is believed to mediate the hydrolysis of N‐acetyl‐aspartyl‐glutamate (NAAG) to glutamate and N‐acetyl‐aspartate, and inhibition of NAAG peptidase activity (by GCP II and other peptidases) is neuroprotective. Mice were generated in which the Folh1 gene encoding GCP II was disrupted (Folh1–/– mice). No overt behavioral differences were apparent between Folh1–/– mice and wild‐type littermates, with respect to their overall performance in locomotion, coordination, pain threshold, cognition and psychiatric behavioral paradigms. Morphological analysis of peripheral nerves, however, showed significantly smaller axons (reduced myelin sheaths and axon diameters) in sciatic nerves from Folh1–/– mice. Following sciatic nerve crush, Folh1–/– mice suffered less injury and recovered faster than wild‐type littermates. In a model of ischemic injury, the Folh1–/– mice exhibited a significant reduction (p < 0.05) in infarct volume compared with their wild‐type littermates when subjected to middle cerebral artery occlusion, a model of stroke. These findings support the hypothesis that GCP II inhibitors may represent a novel treatment for peripheral neuropathies as well as stroke.

Increased cancer cell proliferation in prostate cancer patients with high levels of serum folate.

A recent clinical trial revealed that folic acid supplementation is associated with an increased incidence of prostate cancer (Figueiredo et al., J Natl Cancer Inst 2009; 101(6): 432–435). As tumor cells in culture proliferate directly in response to available folic acid, the goal of our study was to determine if there is a similar relationship between patient folate status, and the proliferative capacity of tumors in men with prostate cancer.

Opposing Roles of Folate in Prostate Cancer

The US diet has been fortified with folic acid to prevent neural tube defects since 1998. The Physician Data Queries from the National Cancer Institute describe folate as protective against prostate cancer, whereas its synthetic analog, folic acid, is considered to increase prostate cancer risk when taken at levels easily achievable by eating fortified food or taking over-the-counter supplements. We review the present literature to examine the effects of folate and folic acid on prostate cancer, help interpret previous epidemiologic data, and provide clarification regarding the apparently opposing roles of folate for patients with prostate cancer. A literature search was conducted in Medline to identify studies investigating the effect of nutrition and specifically folate and folic acid on prostate carcinogenesis and progression. In addition, the National Health and Nutrition Examination Survey database was analyzed for trends in serum folate levels before and after mandatory fortification. Folate likely plays a dual role in prostate carcinogenesis. There remains conflicting epidemiologic evidence regarding folate and prostate cancer risk; however, there is growing experimental evidence that higher circulating folate levels can contribute to prostate cancer progression. Further research is needed to clarify these complex relationships.

NAAG peptidase inhibitors and deletion of NAAG peptidase gene enhance memory in novel object recognition test

The peptide neurotransmitter N-acetylaspartylglutamate (NAAG) is inactivated by the extracellular enzyme glutamate carboxypeptidase II. Inhibitors of this enzyme reverse dizocilpine (MK-801)-induced impairment of short-term memory in the novel object recognition test. The objective of this study was to test the hypothesis that NAAG peptidase inhibition enhances long-term (24h delay) memory of C57BL mice. These mice and mice in which glutamate carboxypeptidase II had been knocked out were presented with two identical objects to explore for 10min on day 1 and tested with one of these familiar objects and one novel object on day 2. Memory was assessed as the degree to which the mice recalled the familiar object and explored the novel object to a greater extent on day 2. Uninjected mice or mice injected with saline prior to the acquisition session on day 1 demonstrated a lack of memory of the acquisition experience by exploring the familiar and novel objects to the same extent on day 2. Mice treated with glutamate carboxypeptidase II inhibitors ZJ43 or 2-PMPA prior to the acquisition trial explored the novel object significantly more time than the familiar object on day 2. Consistent with these results, mice in which glutamate carboxypeptidase II had been knocked out distinguished the novel from the familiar object on day 2 while their heterozygous colony mates did not. Inhibition of glutamate carboxypeptidase II enhances recognition memory, a therapeutic action that might be useful in treatment of memory deficits related to age and neurological disorders.

Novel nuclear localization of fatty acid synthase correlates with prostate cancer aggressiveness.

Fatty acid synthase is up-regulated in a variety of cancers, including prostate cancer. Up-regulation of fatty acid synthase not only increases production of fatty acids in tumors but also contributes to the transformed phenotype by conferring growth and survival advantages. In addition, increased fatty acid synthase expression in prostate cancer correlates with poor prognosis, although the mechanism(s) by which this occurs are not completely understood. Because fatty acid synthase is expressed at low levels in normal cells, it is currently a major target for anticancer drug design. Fatty acid synthase is normally found in the cytosol; however, we have discovered that it also localizes to the nucleus in a subset of prostate cancer cells. Analysis of the fatty acid synthase protein sequence indicated the presence of a nuclear localization signal, and subcellular fractionation of LNCaP prostate cancer cells, as well as immunofluorescent confocal microscopy of patient prostate tumor tissue and LNCaPs confirmed nuclear localization of this protein. Finally, immunohistochemical analysis of prostate cancer tissue indicated that nuclear localization of fatty acid synthase correlates with Gleason grade, implicating a potentially novel role in prostate cancer progression. Possible clinical implications include improving the accuracy of prostate biopsies in the diagnosis of low- versus intermediate-risk prostate cancer and the uncovering of novel metabolic pathways for the therapeutic targeting of androgen-independent prostate cancer.

Deficiency of DNA repair nuclease ERCC1‐XPF promotes prostate cancer progression in a tissue recombination model

The excision repair cross complementing (ERCC1) gene product plays a vital role in the nucleotide excision repair (NER) and DNA interstrand crosslink repair pathways, which protect the genome from mutations and chromosomal aberrations, respectively. Genetic deletion of Ercc1 in the mouse causes dramatically accelerated aging. We examined the effect of Ercc1 deletion in the development of prostate cancer in a prostate recapitulation model as Ercc1 deficient mice die within four weeks of birth.

Contrasting roles of the ABCG2 Q141K variant in prostate cancer

ABSTRACT ABCG2 is a membrane transport protein that effluxes growth‐promoting molecules, such as folates and dihydrotestosterone, as well as chemotherapeutic agents. Therefore it is important to determine how variants of ABCG2 affect the transporter function in order to determine whether modified treatment regimens may be necessary for patients harboring ABCG2 variants. Previous studies have demonstrated an association between the ABCG2 Q141K variant and overall survival after a prostate cancer diagnosis. We report here that in patients with recurrent prostate cancer, those who carry the ABCG2 Q141K variant had a significantly shorter time to PSA recurrence post‐prostatectomy than patients homozygous for wild‐type ABCG2 (P=0.01). Transport studies showed that wild‐type ABCG2 was able to efflux more folic acid than the Q141K variant (P<0.002), suggesting that retained tumoral folate contributes to the decreased time to PSA recurrence in the Q141K variant patients. In a seemingly conflicting study, it was previously reported that docetaxel‐treated Q141K variant prostate cancer patients have a longer survival time. We found this may be due to less efficient docetaxel efflux in cells with the Q141K variant versus wild‐type ABCG2. In human prostate cancer tissues, confocal microscopy revealed that all genotypes had a mixture of cytoplasmic and plasma membrane staining, with noticeably less staining in the two homozygous KK patients. In conclusion, the Q141K variant plays contrasting roles in prostate cancer: 1) by decreasing folate efflux, increased intracellular folate levels result in enhanced tumor cell proliferation and therefore time to recurrence decreases; and 2) in patients treated with docetaxel, by decreasing its efflux, intratumoral docetaxel levels and tumor cell drug sensitivity increase and therefore patient survival time increases. Taken together, these data suggest that a patients ABCG2 genotype may be important when determining a personalized treatment plan. HighlightsThe presence of ABCG2 Q141K variant decreases time to PSA recurrence.Cells expressing the Q141K variant retain more folic acid than wild type.Cells expressing the Q141K variant are more sensitive to docetaxel.ABCG2 protein is repressed miR‐519c and/or miR‐520h in prostate cancer cell lines.