Longer Hydroxyurea Administration Prior to Imatinib Mesylate is Risk Factor for Unsuccessful Major Molecular Response in Chronic-Phase Chronic Myeloid Leukemia: Possibility of P-Glycoprotein Role

A strategy for the investigation of toxic mechanisms and protection by efflux pumps using Schizosaccharomyces pombe strains: Application to rotenone

Effects not related with the inhibition of complex I of the mitochondrial electron transport chain are studied in S. pombe, which lacks it. This study aims: First, the use of a strategy with S. pombe strains to investigate the toxicity, mechanisms of action, interactions and detoxication by efflux pumps. Second, to investigate the mechanisms of toxic action of rotenone. In the dose-response assessment, the yeast presented a good correlation with the toxicity in Daphnia magna for 15 chemicals. In the mechanistic study, the mph1Δ strain presented marked specificity to the interaction with microtubules by carbendazim. DNA damage caused by hydroxyurea, an inhibitor of deoxynucleotide synthesis, was identified with marked specificity with the rad3Δ strain. The sty1Δ strain was very sensitive to the oxidative and osmotic stress induced by hydrogen peroxide and potassium chloride, respectively, being more sensitive to oxidative stress than the pap1Δ strain. The protection by exclusion pumps was also evaluated. Rotenone presented low toxicity in S. pombe due to the lack of its main target, and the marked protection by the exclusion transporters Bfr1, Pmd1, Caf5 and Mfs1. Marked cellular stress was detected. Finally, the toxicity of rotenone could be potentiated by the fungicide carbendazim and the antimetabolite hydroxyurea. In conclusion, the use of S. pombe strains is a valid strategy to: a) assess global toxicity; b) investigate the main mechanisms of toxic action, particularly spindle and DNA interferences, and osmotic and oxidative stress not related to complex I inhibition; c) explore the detoxication by efflux pumps; and d) evaluate possible chemical interactions. Therefore, it should be useful for the investigation of adverse outcome pathways.

HIF2-α Expression in CML Patients Receiving Hydroxyurea Prior to Imatinib That Achieved Major Molecular Response (MMR) versus in Those Not Achieving MMR

Introduction

Currently, Imatinib (IM) which is a Tyrosine Kinase Inhibitor (TKI), is the main treatment for patients with chronic myeloid leukemia (CML). Major molecular response (MMR) is used as therapeutic response. Resistance to IM may be caused by hypoxia which is regulated by hypoxia inducible factor (HIF) 2-α. The role of HIF2-α is currently not researched extensively. This study aimed to analyse the differences in HIF-2α expression between chronic phase CML patients that achieved MMR and those that did not achieve MMR.

Methods

This study used a cross-sectional method which analysed secondary data from whole blood samples in chronic phase CML patients aged 18-60 years that received hydroxyurea (HU) before IM, aged 18-60 years, received IM therapy for more than 12 months, and were willing to participate in the study. The exclusion criteria for this study were patients who were receiving IM at a dose of more than 400 mg/day. HIF-2α protein expression was examined using the enzyme-linked immunosorbent assay (ELISA) method. Differences between HIF-2α protein expression in groups that achieved MMR versus not achieving MMR was analysed using the Mann-Whitney test.

Results

A total of 79 subjects were obtained. The median HIF-2α was 90.56 pg/mg protein (3.01-4628.74). There was no statistically significant difference in expression of HIF-2α in the group that reached MMR and did not reach MMR, namely 123.45 pg/mg protein and 89.25 pg/mg protein respectively (p 0.718).

Conclusion

This study found no statistically significant difference between HIF-2α expression level and MMR achievement of chronic phase CML patients who received HU before IM therapy.

High STAT5A Expression is Associated with Major Molecular Response Achievement Failure of Chronic Phase Chronic Myeloid Leukemia Patients Receiving Hydroxyurea before Imatinib: A Cross-sectional Study

BACKGROUND: STAT5 is a transcriptional factor which when highly expressed in chronic myeloid leukemia (CML) cells stimulate proliferation and mediate resistance from tyrosine kinase inhibitors, resulting in major molecular response (MMR) failure. STAT5 has two isoforms, STAT5A and STAT5B. However, prolonged use of imatinib appears to only upregulate STAT5A pathway. In addition, the resistance conferred by STAT5A does not extend to other drugs such as hydroxyurea. Hence, STAT5A and STAT5B might have different functions in CML cells. AIM: The objective of the study was to determine the association of STAT5A and STAT5B expression with MMR failure in CML patients. METHODS: This was a cross-sectional study of CML patients in chronic phase with age ≥ 18 years old, receiving IM therapy ≥ 12 months, and previously given hydroxyurea. MMR status was evaluated and patients were categorized as achieved or failed to achieve MMR. Expression levels of STAT5A and STAT5B were conducted using RT-PCR methods. Associations between STAT5A expression, STAT5B expression, hydroxyurea duration, and imatinib duration with MMR achievement were calculated using logistic regression. RESULTS: A total of 118 patients were analyzed; 71.1% failed to achieve MMR. Multivariate logistic regression analysis showed statistically significant association between high STAT5A expression (odds ratio [OR]: 3.852; 95% confidence interval [CI]: 1.420–10.452; p = 0.008), STAT5A/STAT5B interaction (OR: 0.150; 95% CI: 0.038–0.593; p = 0.007), longer hydroxyurea administration (OR: 3.882; 95% CI: 1.023–14.733; p = 0.046), and shorter imatinib administration (OR: 0.333; 95% CI: 0.132–0.840; p = 0.020) with MMR achievement failure. After adjusting STAT5A expression with STAT5A/STAT5B interaction, high STAT5A expression independently increased the likelihood of MMR achievement failure only in high expression STAT5B patients (OR: 3.852; 95% CI: 1.420–10.452; p = 0.008). CONCLUSION: High STAT5A expression which is induced by high STAT5B is associated with MMR achievement failure of chronic phase CML patients who received hydroxyurea before imatinib. Longer duration of hydroxyurea and shorter duration of IM confound of STAT5A expression to MMR achievement failure.