Paradoxical role of C1561T glutamate carboxypeptidase II (GCPII) genetic polymorphism in altering disease susceptibility

Advances in PSMA theranostics

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PSMA is an appealing target for theranostic because it is a transmembrane protein with a known substrate that is overexpessed on prostate cancer cells and internalizes upon ligand binding.

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There are a number of PSMA theranostic ligands in clinical evaluation, clinical trial, or clinically approved.

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PSMA theranostic ligands increase progression-free survival, overall survival, and pain in patients with metastatic castration resistant prostate cancer.

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A major obstacle to PSMA-targeted radioligand therapy is off-target toxicity in salivary glands.

The validation of prostate specific membrane antigen (PSMA) as a molecular target in metastatic castration-resistant prostate cancer has stimulated the development of multiple classes of theranostic ligands that specifically target PSMA. Theranostic ligands are used to image disease or selectively deliver cytotoxic radioactivity to cells expressing PSMA according to the radioisotope conjugated to the ligand. PSMA theranostics is a rapidly advancing field that is now integrating into clinical management of prostate cancer patients. In this review we summarize published research describing the biological role(s) and activity of PSMA, highlight the most clinically advanced PSMA targeting molecules and biomacromolecules, and identify next generation PSMA ligands that aim to further improve treatment efficacy. The goal of this review is to provide a comprehensive assessment of the current state-of-play and a roadmap to achieving further advances in PSMA theranostics.

A meta-analysis and in silico analysis of polymorphic variants conferring breast cancer risk in the Indian subcontinent

Background: Genetic association studies on breast cancer on the Indian subcontinent have yielded conflicting results, and the precise effect of these variants on breast cancer pathogenesis is not known. Methods: Genomic variants, as obtained from selected studies from the Indian subcontinent, were subjected to random-effects and fixed-effect meta-analysis. Functional annotation of the relevant variants was done through a tried and tested in silico pipeline. Results: We found rs4646903/CYP1A1, rs1799814/CYP1A1, rs61886492/GCPII, del2/GSTM1, rs4680/COMT and rs1801394/MTRR to be associated with breast cancer. The del2/GSTM1 holds the association in premenopausal women. Conclusions: This is the first study of its kind from the Indian subcontinent analysing the extent of association of variants across populations followed by their functional annotation in the disease pathway.

Extracellular superoxide dismutase and its role in cancer

Reactive oxygen species (ROS) are increasingly recognized as critical determinants of cellular signaling and a strict balance of ROS levels must be maintained to ensure proper cellular function and survival. Notably, ROS is increased in cancer cells. The superoxide dismutase family plays an essential physiological role in mitigating deleterious effects of ROS. Due to the compartmentalization of ROS signaling, EcSOD, the only superoxide dismutase in the extracellular space, has unique characteristics and functions in cellular signal transduction. In comparison to the other two intracellular SODs, EcSOD is a relatively new comer in terms of its tumor suppressive role in cancer and the mechanisms involved are less well understood. Nevertheless, the degree of differential expression of this extracellular antioxidant in cancer versus normal cells/tissues is more pronounced and prevalent than the other SODs. A significant association of low EcSOD expression with reduced cancer patient survival further suggests that loss of extracellular redox regulation promotes a conducive microenvironment that favors cancer progression. The vast array of mechanisms reported in mediating deregulation of EcSOD expression, function, and cellular distribution also supports that loss of this extracellular antioxidant provides a selective advantage to cancer cells. Moreover, overexpression of EcSOD inhibits tumor growth and metastasis, indicating a role as a tumor suppressor. This review focuses on the current understanding of the mechanisms of deregulation and tumor suppressive function of EcSOD in cancer.

Clinical utility of genetic variants of glutamate carboxypeptidase II in predicting breast cancer and prostate cancer risk

In view of documented evidence showing glutamate carboxypeptidase II (GCPII) inhibitors as promising anti-cancer agents, certain variants of GCPII modulate breast and prostate cancer risk, and we developed an artificial neural network (ANN) model of GCPII variants and ascertained the risk associated with eight genetic variants of GCPII. In parallel, an in silico model was developed to substantiate the ANN simulations. The ANN model with modified sigmoid function was used for disease prediction, whereas the hyperbolic tangent function was used to predict folate hydrolase 1 (FOLH1) and prostate specific membrane antigen (PSMA) expression. PyMOL models of GCPII variants were developed, and their affinity toward the folylpolyglutamate (FPG) ligand was tested using glide score analysis. Of the eight genetic variants of GCPII, p.P160S alone conferred protection against both of the cancers. This variant exhibited higher affinity toward FPG compared with wild GCPII (-2.06 vs. -1.69); and positive correlation was observed between the P160S variant and circulating folate (r = 0.60). The ANN model for disease prediction showed significant predictability associated with GCPII variants toward breast cancer (area under the curve (AUC): 1.00) and prostate cancer (AUC: 0.97), with clear distinguishing ability of healthy controls (AUC: 0.96). The ANN models for the expression of FOLH1 and PSMA explained 60.5% and 86.7% of the variability, respectively. Thus, GCPII variants are potential contributors of risk toward breast cancer and prostate cancer. Risk modulation appeared to be mediated through changes in the expression of FOLH1 and PSMA.

Genetic Variation in Glutamate Carboxypeptidase II and Interaction with Dietary Natural Vitamin C May Predict Risk for Adenomatous Polyp Occurrence

BACKGROUND

The C1561T variant of the glutamate carboxypeptidase II (GCPII) gene is critical for natural methylfolylpolyglutamte (methylfolate) absorption, and has been associated with perturbations in folate metabolism and disease susceptibility. However, little is known on C1561T-GCPII as a risk factor for colorectal cancer. Therefore, this study examined whether C1561T-GCPII influences folate metabolism and adenomatous polyp occurrence.

MATERIALS AND METHODS

164 controls and 38 adenomatous polyp cases were analysed to determine blood folate and plasma homocysteine (Hcy) level, dietary intake of natural methylfolate, synthetic pteroylglutamic acid (PteGlu), vitamin C and C1561T-GCPII genotype.

RESULTS

In controls and cases, 7.3 and 18.4 percent of subjects respectively, were found to have the CT genotype, increasing the risk for adenomatous polyp occurrence 2.86 times (95% CI:1.37-8.0, p=0.035). Total dietary folate, methylfolate and PteGlu intake and the level of erythrocyte folate and plasma Hcy did not predict the occurrence of an adenomatous polyp. However, dietary natural vitamin C intake was associated with adenomatous polyp risk within C1561T-GCPII CT genotype subjects (p=0.037).

CONCLUSIONS

The findings suggest that C1561T-GCPII variation may be associated with risk for adenomatous polyp, and vitamin C may modify risk by interacting with the variant gene, its expression product and/or folate substrates.

Epigenetic modulation of RFC1, MHC2TA and HLA-DR in systemic lupus erythematosus: association with serological markers and six functional polymorphisms of one-carbon metabolic pathway

The current study was conducted to elucidate the effect of genetic variations in one-carbon metabolism on the epigenetic regulation of major histocompatibility complex II transactivator (MHC2TA), reduced folate carrier 1 (RFC1/SLC19A1) and human leukocyte antigen (HLA)-DR in systemic lupus erythematosus (SLE). PCR-RFLP/AFLP, bisulfite-sequencing and real-time PCR approaches were used for genetic, epigenetic and expression analysis respectively. SLE cases exhibited elevated plasma homocysteine levels compared to healthy controls (24.93 ± 1.3 vs. 11.67 ± 0.48 μmol/l), while plasma folate levels showed no association (7.10 ± 2.49 vs. 7.64 ± 2.09 ng/ml). The RFC1 80G>A polymorphism showed 1.32-fold risk (95% CI: 1.02-1.72) for SLE, while glutamate carboxypeptidase II (GCPII) 1561C>T showed reduced risk (OR: 0.47, 95% CI: 0.24-0.90). The expression of RFC1 (0.37 ± 0.09 vs. 0.60 ± 0.17) and HLA-DR (0.68 ± 0.17 vs. 0.98 ± 0.02) was down regulated in the SLE cases. The hypermethylation of RFC1 as observed in the current study may contribute for its down regulation. Plasma folate and thymidylate synthase (TYMS) 5'-UTR 28 bp tandem repeat showed an inverse association with methylation of RFC1 and MHC2TA. SLE cases with hypocomplementemia showed hypermethylation of RFC1, hypomethylation/up regulation of MHC2TA and down regulation of HLA-DR. The hypermethylation of MHC2TA and down regulation of RFC1, MHC2TA and HLA-DR were observed in anti-cardiolipin antibody positive SLE cases. The up regulation of RFC1 and HLA-DR was observed in anti-dsDNA antibody positive SLE cases. The hypomethylation/upregulation of RFC1 and MHC2TA was observed in anti-RNP antibody positive cases. To conclude, one-carbon genetic variants influence epigenetic of MHC2TA and RFC1, thus contributing to phenotypic heterogeneity of SLE.

GCPII modulates oxidative stress and prostate cancer susceptibility through changes in methylation of RASSF1, BNIP3, GSTP1 and Ec-SOD

Glutamate carboxypeptidase II (GCPII) haplotypes were found to influence susceptibility to prostate cancer. In the current study, we have elucidated the impact of these haplotypes on the expression of PSMA, BNIP3, Ec-SOD, GSTP1 and RASSF1 genes to understand the epigenetic basis of oxidative stress and prostate cancer risk. Expression analysis was carried out by RT-PCR. Bisulphite treated DNA was subjected to MS-PCR and COBRA for epigenetic studies. Plasma MDA and glutathione levels were measured. In prostate cancer, upregulation of BNIP3 (204.4 ± 23.77 vs. 143.9 ± 16.42 %, p = 0.03); and downregulation of Ec-SOD (105.8 ± 13.69 vs. 176.3 ± 21.1 %, p = 0.027) and RASSF1A (16.67 ± 16.0 vs. 90.8 ± 8.5 %, p = 0.0048) was observed. Hypomethylation of BNIP3 (31.25 ± 16.19 vs. 45.70 ± 2.42 %, p < 0.0001), hypermethylation of Ec-SOD (71.4 ± 6.75 vs. 10.0 ± 3.78 %, p < 0.0001) and RASSF1 (76.25 ± 12.53 vs. 30.0 ± 8.82 %, p = 0.0077) was observed in prostate cancer. The gene expression signature of PSMA, BNIP3, Ec-SOD, GSTP1, clearly demarcated cases and controls (AUC = 0.89 in the ROC curve). D191V variant of GCPII showed positive association with oxidative stress and inverse association with Ec-SOD expression. H475Y variant showed positive association with Ec-SOD expression and inverse association with oxidative stress. R190W variant was found to reduce oxidative stress by increasing glutathione levels. GCPII genetic variants contribute to increased oxidative stress and prostate cancer risk by modulating the CpG island methylation of Ec-SOD.

Association of glutamate carboxypeptidase II (GCPII) haplotypes with breast and prostate cancer risk

In view of the pivotal role of glutamate carboxypeptidase II (GCPII) in carcinogenesis, its expression as prostate specific membrane antigen (PSMA) and folate hydrolase (FOLH1) may be influenced by its haplotypes, contributing to the etiology of prostate and breast cancer. To test this hypothesis, breast and prostate cancer cases and controls were subjected to whole gene screening of GCPII and correlated with plasma folate levels and PSMA expression. The impact of variants on a 3-dimensional structure of GCPII was explored by in silico studies. Six novel variations i.e. V108A, P160S, Y176H, D191V, G206R and G245S; and two known variations i.e. R190W and H475Y were identified in GCPII. All-wild haplotype and a haplotype harbouring D191V showed association with breast cancer risk while haplotypes harbouring V108A and P160S reduced the risk. Haplotypes with V108A and G245S variants showed increased risk for prostate cancer due to high PSMA expression while P160S conferred protection against prostate cancer. In silico studies suggests that P160S and R190W variants result in relaxed substrate binding facilitating either rapid catalysis or exchange of substrates and products in the active site which was substantiated by high plasma folate levels associated with these variants. On the contrary, D191V was associated with very low plasma folate levels despite having a high PSMA expression. This is the first comprehensive study examining variations in GCPII in relation to breast and prostate cancer risk. Changes in the plasma folate levels and changes in PSMA expression are associated with breast and prostate cancer risk respectively.

Genetic variants of thiopurine and folate metabolic pathways determine 6-MP-mediated hematological toxicity in childhood ALL

Aim: The rationale of this study was to explore the contribution of genetic variants of the folate pathway to toxicity of 6-mercaptopurine (6-MP)-mediated hematological toxicity in children with acute lymphoblastic leukemia (ALL) and to explore the interaction of these variants with TPMT and ITPA haplotypes using multifactor dimensionality reduction analysis. Materials & methods: Children with ALL (n = 96) were screened for GCPII C1561T, RFC1 G80A, cSHMT C1420T, TYMS 5´-UTR 2R3R, TYMS 3´-UTR ins6/del6, MTHFR C677T, MTR A2756G polymorphisms using PCR-RFLP and PCR-amplified fragment length polymorphism techniques. Results: GCPII C1561T showed independent association with toxicity. The following synergetic interactions appeared to increase the toxicity of 6-mercaptopurine: TPMT*12 × RFC1 G80A; TPMT CTTAT haplotype × RFC1 G80A; TPMT CTTAT haplotype × RFC1 G80A × TYMS 2R3R. The genetic variants of thiopurine and folate pathway cumulatively appeared to increase the predictability of toxicity (r2 = 0.41) in a multiple linear regression model. For the observed toxicity grades of 1, 2, 3 and 4, the respective predicted toxicity grades were 1.65 ± 0.29, 1.68 ± 0.24, 2.56 ± 0.58 and 2.99 ± 1.03, ptrend < 0.0001. Conclusion: Gene–gene interaction between thiopurine and folate pathways inflate the 6-MP-mediated toxicity in Indian children with ALL illustrating the importance of ethnicity in the toxicity of 6-MP.

Original submitted 3 January 2012; Revision submitted 23 April 2012