Polymorphisms in methotrexate transporters and their relationship to plasma methotrexate levels, toxicity of high-dose methotrexate, and outcome of pediatric acute lymphoblastic leukemia Polymorphisms in methotrexate transporters and their relationship to plasma methotrexate levels, toxicity of high-dose methotrexate, and outcome of pediatric acute lymphoblastic leukemia

Background: Acute lymphoblastic leukemia (ALL) is the most frequently-occurring malignant neoplasm in children, but the pathogenesis of the disease remains unclear. In a microarray assay using samples from 100 children with ALL, SFRS1 was found to be up-regulated. Serine/arginine-rich splicing factor 1 (SRSF1, also termed SF2/ASF), encoded by the SFRS1 gene, had been shown to be a pro-oncoprotein. Our previous study indicated that SRSF1 can be methylated by protein arginine methyltransferase 1 (PRMT1) in vitro; however, the biological function of SRSF1 and PRMT1 in pediatric ALL are presently unknown. Methods: Matched, newly diagnosed (ND), complete remission (CR) and relapse (RE) bone marrow samples from 57 patients were collected in order to evaluate the expression patterns of SRSF1 and PRMT1. The potential oncogenic mechanism of SRSF1 and PRMT1 in leukemogenesis was also investigated. Results: We identified significant up-regulation of SRSF1 and PRMT1 in the ND samples. Importantly, the expression of SRSF1 and PRMT1 returned to normal levels after CR, but rebounded in the RE samples. Our observation that SRSF1 could predict disease relapse was of particular interest, although the expression patterns of SRSF1 and PRMT1 were independent of the cytogenetic subtypes. In pre-B-cell lines, both SRSF1 and PRMT1 expression could be efficiently attenuated by the clinical chemotherapy agents arabinoside cytosine (Ara-c) or vincristine (VCR). Moreover, SRSF1 and PRMT1 were associated with each other in leukemia cells in vivo. Knock-down of SRSF1 resulted in an increase in early apoptosis, which could be further induced by chemotherapeutics. Conclusions: Our results indicate that SRSF1 serves as an anti-apoptotic factor and potentially contributes to leukemogenesis in pediatric ALL patients by cooperating with PRMT1.

Pediatric acute lymphoblastic leukemia (ALL) contains cytogenetically distinct subtypes that respond differently to cytotoxic drugs. Subtype classification can be also achieved through gene expression profiling. However, how to apply such classifiers to a single patient and correctly diagnose the disease subtype in an independent patient group has not been addressed. Furthermore, the underlying regulatory mechanisms responsible for the subtype-specific gene expression patterns are still largely unknown. Here, by combining 3 published microarray datasets on 535 mostly white children's samples and generating a new dataset on 100 Chinese children's ALL samples, we were able to (1) identify a 62-gene classifier with 97.6% accuracy from the white children's samples and validated it on the completely independent set of 100 Chinese samples, and (2) uncover potential regulatory networks of ALL subtypes. The classifier we identified was, thus far, the only one that could be applied directly to a single sample and that sustained validation in a large independent patient group. Our results also suggest that the etiology of ALL is largely the same among different ethnic groups, and that the transcription factor hubs in the predicted regulatory network might play important roles in regulating gene expression and development of ALL.

Currently, O6-methylguanine-DNA methyltransferase(MGMT) promoter methylation is the most convincing predictive biomarker for temozolomide (TMZ) response in patients with glioblastoma multiforme (GBM). However, technical obstacles prevent this biomarker from being applied widely. On the other hand, microRNAs (miRNAs) are easily investigated in the clinical setting using quantitative real-time polymerase chain reactions. This study aimed to identify miRNAs that could serve as predictive biomarkers for TMZ response. The Cancer Genome Atlas (TCGA) and the Chinese Glioma Genome Atlas (CGGA) databases were used to investigate the significance of associations between miRNA expression and overall survival (OS) in TMZ-treated patients with GBM. Cytotoxicity assays were used to validate the miRNAs’ roles in the response of glioma cells to TMZ. Biological insights concerning the miRNAs were explored using gene set enrichment analysis (GSEA) and gene ontology (GO) analysis. miR-130a was found to be significantly associated with OS in TMZ-treated patients from TCGA and the CGGA. In contrast, miR-130a appeared to be unassociated with OS in patients who only received radiotherapy. The TMZ cytotoxicity assay showed that miR-130a over-expression could sensitize response to TMZ in glioma cells. GSEA and GO analysis indicated that lower miR-130a could generate a more extensive response to oxidative stress, which in turn could elevate Ape1 and mediate resistance to TMZ. In vitro experiment verified that cells with lower miR-130a express higher Ape1 under oxidative stress. Our data suggested that miR-130a could be a predictive marker for TMZ response in patients with GBM, independently of the mechanism by which MGMT acts as a biomarker. miR-130a could serve as a guide for treatment strategy selection in cases of GBM.

MicroRNAs (miRNAs) expression profiles were screened in plasma samples from pediatric patients with acute lymphoblastic leukemia (ALL) and healthy controls, using qRT-PCR-based TaqMan low-density miRNA arrays. MiR-652-3p (a circulating miRNA) was downregulated in new diagnosis (ND) patients compared with healthy controls. The levels of miR652-3p were restored in complete remission (CR) but were downregulated again in disease relapse (RE). The expression pattern of miR-652-3p was validated in bone marrow (BM) samples from other pediatric ALL patients. MiR-652-3p was significantly upregulated in BM when the patients (n=86) achieved CR, as compared with the matched ND samples (p<0.001). Moreover, the miR-652-3p levels in BM decreased again in two patients at RE. In addition, the lymphoblastic leukemia cell lines Reh and RS4:11 were found to have lower levels of miR-625-3p than the normal B-cell line. Overexpression of miR-652-3p using agomir increased the sensitivity to vincristine and cytarabine (all p<0.05) and promoted apoptosis (both p<0.05) in Reh and RS4:11 cells. In conclusion, the results suggested that a low level of miR-652-3p might be involved in the pathogenesis of pediatric ALL. Overexpression of miR-652-3p might suppress lymphoblastic leukemia cells, promoting apoptosis and increasing sensitivity to chemotherapeutic drugs.

Folypolyglutamate synthase (FPGS) catalyzes the polyglutamation of folates and antifolates, such as methotrexate (MTX), to produce highly active metabolites. FPGS tag SNP rs1544105C > T is located in the gene promoter. The aim of the present study was to investigate the impact of rs1544105 polymorphism on the treatment outcome in pediatric B-cell precursor acute lymphoblastic leukemia (BCP-ALL).