Ribonucleotide reductase inhibitors suppress SAMHD1 ara‐CTPase activity enhancing cytarabine efficacy

The deoxycytidine analogue cytarabine (ara‐C) remains the backbone treatment of acute myeloid leukaemia (AML) as well as other haematological and lymphoid malignancies, but must be combined with other chemotherapeutics to achieve cure. Yet, the underlying mechanism dictating synergistic efficacy of combination chemotherapy remains largely unknown. The dNTPase SAMHD1, which regulates dNTP homoeostasis antagonistically to ribonucleotide reductase (RNR), limits ara‐C efficacy by hydrolysing the active triphosphate metabolite ara‐CTP. Here, we report that clinically used inhibitors of RNR, such as gemcitabine and hydroxyurea, overcome the SAMHD1‐mediated barrier to ara‐C efficacy in primary blasts and mouse models of AML, displaying SAMHD1‐dependent synergy with ara‐C. We present evidence that this is mediated by dNTP pool imbalances leading to allosteric reduction of SAMHD1 ara‐CTPase activity. Thus, SAMHD1 constitutes a novel biomarker for combination therapies of ara‐C and RNR inhibitors with immediate consequences for clinical practice to improve treatment of AML

Genome-Wide Local Ancestry Approach Identifies Genes and Variants Associated with Chemotherapeutic Susceptibility in African Americans

Chemotherapeutic agents are used in the treatment of many cancers, yet variable resistance and toxicities among individuals limit successful outcomes. Several studies have indicated outcome differences associated with ancestry among patients with various cancer types. Using both traditional SNP-based and newly developed gene-based genome-wide approaches, we investigated the genetics of chemotherapeutic susceptibility in lymphoblastoid cell lines derived from 83 African Americans, a population for which there is a disparity in the number of genome-wide studies performed. To account for population structure in this admixed population, we incorporated local ancestry information into our association model. We tested over 2 million SNPs and identified 325, 176, 240, and 190 SNPs that were suggestively associated with cytarabine-, 5′-deoxyfluorouridine (5′-DFUR)-, carboplatin-, and cisplatin-induced cytotoxicity, respectively (p≤10−4). Importantly, some of these variants are found only in populations of African descent. We also show that cisplatin-susceptibility SNPs are enriched for carboplatin-susceptibility SNPs. Using a gene-based genome-wide association approach, we identified 26, 11, 20, and 41 suggestive candidate genes for association with cytarabine-, 5′-DFUR-, carboplatin-, and cisplatin-induced cytotoxicity, respectively (p≤10−3). Fourteen of these genes showed evidence of association with their respective chemotherapeutic phenotypes in the Yoruba from Ibadan, Nigeria (p<0.05), including TP53I11, COPS5 and GAS8, which are known to be involved in tumorigenesis. Although our results require further study, we have identified variants and genes associated with chemotherapeutic susceptibility in African Americans by using an approach that incorporates local ancestry information

JNK1/2 expression and modulation of STAT3 signaling in oral cancer

Mitogen-activated protein kinases (MAPKs) are a family of protein kinases that link extracellular stimuli with intracellular responses and participate in numerous cellular processes such as growth, proliferation, differentiation, inflammation and apoptosis. Persistent activation of signal transducer and activator of transcription 3 (STAT3), which is accompanied by increases in STAT3 tyrosine phosphorylation, is associated with cell proliferation, differentiation and apoptosis in oral squamous cell carcinoma (OSCC). The role and significance of the activation of MAPKs, particularly of c-Jun N-terminal kinase (JNK), on STAT3 signaling in OSCC have not been thoroughly investigated. The present study examines the effects of JNK1/2 modulation on STAT3 signaling and cellular activities in OSCC cells. The expression levels of STAT3 [total, tyrosine phosphorylated (p-Tyr) and serine phosphorylated (p-Ser)], JNK, c-Jun and cyclin D1 were assessed in the OSCC cell lines SCC25 and SCC9. Inhibition of JNK1/2 was achieved by pharmacological agents (SP600125) and by small interfering RNA (siRNA) silencing, while JNK1/2 was induced by active MAPK kinase 7. Cell proliferation and viability rates were also evaluated. Inhibition of JNK1/2 with either SP600125 treatment or specific siRNA silencing resulted in decreased levels of p-Ser STAT3 and increased levels of p-Tyr STAT3 and cyclin D1 in both cell lines. Furthermore, JNK1/2 inhibition resulted in a dose-dependent increase in cell growth and viability in both cell lines. Opposite results were observed with JNK1/2 induction in both cell lines. The present results are supportive of a potential tumor suppressive role of JNK1/2 signaling in OSCC, which may be mediated through negative crosstalk with the oncogenic STAT3 signaling pathway. The possible therapeutic implications of JNK1/2 inhibition for patients with OSCC require to be investigated. © 2016, Spandidos Publications. All rights reserved

Immunohistochemical evaluation of the mTOR pathway in intra-oral minor salivary gland neoplasms

Objectives: The aim of this study was to investigate the expression of upstream and downstream molecules of the oncogenic mTOR signaling pathway in intra-oral minor salivary gland tumors (SGTs). Materials and Methods: Tissue samples consisted of 39 malignant and 13 benign minor SGTs, and 8 controls of normal minor salivary glands (NMSG). An immunohistochemical analysis for phosphorylated Akt, 4EBP1 and S6 (total and phosphorylated), and eIF4E was performed. Results: Expression of pAkt and 4EBP1 was observed in all SGTs and in most NMSG. p4EBP1 was detected in almost all SGT cases, NMSG being negative. S6 immunoreactivity was observed in 37.5% of NMSG, 92.3% of benign and 100% of malignant SGTs, while pS6 expression was observed in 77% of benign and 95% of malignant SGTs, but not in NMSG. Finally, eIF4E was expressed in 12.5% of NMSG, 69.2% of benign, and 76.9% of malignant tumors. All molecules studied had statistically significantly lower expression in NMSG compared with SGTs. Moreover, malignant neoplasms received higher scores compared with benign tumors for all molecules with the exception of eIF4E. Conclusion: The mTOR signaling pathway is activated in SGTs, especially in malignancies. Therefore, the possible therapeutic role of targeting the mTOR pathway by rapamycin analogs in SGTs needs further investigation. © 2016 John Wiley &amp; Sons A/S. Published by John Wiley &amp; Sons Lt

ERK1/2, JNK and STAT3 activation and correlation with tumor differentiation in oral SCC

Signal transducer and activator of transcription 3 (STAT3) and mitogen activated protein kinases (MAPKs), including ERK and JNK, have been implicated in oral squamous cell carcinoma (OSCC) development and progression. Our purpose was to evaluate the levels of activated STAT3, ERK1/2 and JNK by immunohistochemistry in OSCC and to investigate possible correlations of these molecules with each other as well as with the degree of tumor differentiation. Immunohistochemical assessment of the phosphorylated levels of STAT3(tyrosine/ serine), ERK1/2 and JNK was performed in 60 OSCC, including well, moderately and poorly differentiated tumors. Semiquantitative scoring system was used, by calculating intensity of immunostaining, percentage of positive cells and combined scores. Statistics included Fisher’s test, Student’s T-Test and Kruskal-Wallis analysis, Spearman’s correlation coefficient and multivariate logistic regression analyses. Immunohistochemical levels of both pSTAT3(tyr) and pERK1/2 showed statistically significant differences between well and poorly differentiated tumors with the latter receiving higher mean percentage, intensity and total scores. On the other hand, pJNK showed statistically significantly higher intensity levels in moderately compared to poorly differentiated tumors. pSTAT3(ser) immunoexpression did not appear to correlate with tumor differentiation. Between different molecules, more pronounced, pERK1/2 levels exhibited statistically significant positive correlation with pSTAT3(ser), pSTAT3(tyr) and pJNK expression. ERK1/2 and STAT3 activation (as assessed by tyrosine but not serine phosphorylation) could contribute to a less differentiated phenotype in OSCC, while JNK activation may have an opposite, although possibly less pronounced, effect. Positive correlations between MAPK and STAT3 levels may indicate a direct crosstalk and/or regulation by common upstream pathways