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

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

Expression Analysis of miR-29b in Malignant and Benign Breast Tumors: A Promising Prognostic Biomarker for Invasive Ductal Carcinoma With a Possible Histotype-Related Expression Status

The transcript levels of miR-29b, which has been claimed to be involved in breast cancer molecular pathology, were evaluated with regard to their clinical utility by analyzing miR-29b expression in 177 breast tissue samples of either benign or malignant characterization. Our data showed that miR-29b might constitute a promising prognostic marker for invasive ductal carcinoma. Background: Aberrations in microRNA levels seem to provide valuable information regarding breast cancer prognosis and therapy. In this study, we sought to analyze miR-29b expression in breast tumors and thus explore its clinical value. Materials and Methods: One hundred twenty-one malignant and 56 benign breast tissue specimens were collected and subjected to extraction of total RNA, which was polyadenylated and reverse transcribed to cDNA. Subsequently, a highly sensitive quantitative real-time polymerase chain reaction protocol was developed and miR-29b levels, estimated via the comparative C T method, were finally subjected to comprehensive statistical analysis. Results: MiR-29b levels did not differ between the analyzed benign and malignant breast tissue specimens, but were found to be significantly (P =.010) decreased in invasive ductal adenocarcinomas compared with their lobular counterparts, albeit receiver operating characteristics curve analysis did not verify the latter correlation. Additionally, miR-29b expression was elevated in samples with positive estrogen receptor status (P =.021) in the overall population, whereas it was negatively correlated (P =.035) with primary tumor staging in the ductal subset and increased in poorly-differentiated tumors of lobular origin (P =.041). Furthermore, Kaplan–Meier and Cox regression analyses showed that patients with ductal carcinoma and elevated miR-29b levels had a significantly longer disease-free survival (P =.010) and a lower risk to relapse (hazard ratio = 0.35, 95% confidence interval, 0.15-0.81; P =.014). Conclusion: Our results provide evidence that miR-29b levels constitute a promising biomarker of favorable prognosis for patients with invasive ductal breast carcinoma and imply that its expression status might be affected by the histological origin of breast malignancy. © 2017 Elsevier Inc

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 & Sons A/S. Published by John Wiley & Sons Lt