Bone marrow stromal cells reduce low-dose cytarabine-induced differentiation of acute myeloid leukemia.

Low-dose cytarabine (LDAC) is a standard therapy for elderly acute myeloid leukemia (AML) patients unfit for intensive chemotherapy. While high doses of cytarabine induce cytotoxicity, the precise mechanism of action of LDAC in AML remains elusive. In vitro studies have demonstrated LDAC-induced differentiation; however, such differentiation is seldom observed in vivo. We hypothesize that this discrepancy may be attributed to the influence of bone marrow (BM) stromal cells on AML cells. Thus, this study aimed to investigate the impact of BM stromal cells on LDAC-induced differentiation of AML cell lines and primary samples. Our results demonstrate that the presence of MS-5 stromal cells prevented LDAC-induced cell cycle arrest, DNA damage signaling and differentiation of U937 and MOLM-13 cell lines. Although transcriptomic analysis revealed that the stroma reduces the expression of genes involved in cytokine signaling and oxidative stress, data obtained with pharmacological inhibitors and neutralizing antibodies did not support the role for CXCL12, TGF-ß1 or reactive oxygen species. The presence of stromal cells reduces LDAC-induced differentiation in primary samples from AML-M4 and myelodysplastic syndrome/AML patients. In conclusion, our study demonstrates that BM stroma reduces differentiation of AML induced by LDAC. These findings provide insights into the limited occurrence of terminal differentiation observed in AML patients, and suggest a potential explanation for this observation.

Cytarabine-induced differentiation of AML cells depends on Chk1 activation and shares the mechanism with inhibitors of DHODH and pyrimidine synthesis.

Acute myeloid leukemia (AML) is characterized by arrested differentiation making differentiation therapy a promising treatment strategy. Recent success of inhibitors of mutated isocitrate dehydrogenase (IDH) invigorated interest in differentiation therapy of AML so that several new drugs have been proposed, including inhibitors of dihydroorotate dehydrogenase (DHODH), an enzyme in pyrimidine synthesis. Cytarabine, a backbone of standard AML therapy, is known to induce differentiation at low doses, but the mechanism is not completely elucidated. We have previously reported that 5-aminoimidazole-4-carboxamide ribonucleoside (AICAr) and brequinar, a DHODH inhibitor, induced differentiation of myeloid leukemia by activating the ataxia telangiectasia and Rad3-related (ATR)/checkpoint kinase 1 (Chk1) via pyrimidine depletion. In this study, using immunoblotting, flow cytometry analyses, pharmacologic inhibitors and genetic inactivation of Chk1 in myeloid leukemia cell lines, we show that low dose cytarabine induces differentiation by activating Chk1. In addition, cytarabine induces differentiation ex vivo in a subset of primary AML samples that are sensitive to AICAr and DHODH inhibitor. The results of our study suggest that leukemic cell differentiation stimulated by low doses of cytarabine depends on the activation of Chk1 and thus shares the same pathway as pyrimidine synthesis inhibitors.

Bendamustine: A review of pharmacology, clinical use and immunological effects (Review).

Bendamustine is an alkylating agent classified into the group of nitrogen mustard analogues, synthesized almost sixty years ago. It was registered in former East Germany in 1971 and approved by the US Food and Drug Administration in 2008 for treatment of chronic lymphocytic leukemia and indolent B­cell non­Hodgkin lymphoma. Considering its beneficial properties in the therapy of relapsed or refractory hematological malignancies, synergistic effects with other antineoplastic agents and increasing recent reports on its immunomodulatory effects, bendamustine has once again gained its justified attention. The uniqueness of bendamustine­mediated effects should be observed keeping in mind its distinctive structure with structural similarities to both alkylating agents and purine analogs. In the present review, the current knowledge on the use of bendamustine in oncology, its pharmacokinetics, mechanism of action and toxicity was summarized. In addition, its immune­modulating effects that have not been fully elucidated so far are emphasized, hoping to encourage further investigations of this unique drug.

All-trans retinoic acid induces differentiation in primary acute myeloid leukemia blasts carrying an inversion of chromosome 16.

All-trans retinoic acid (ATRA)-based therapy for acute promyelocytic leukemia (APL), a subtype of acute myeloid leukemia (AML), is the most successful example of differentiation therapy. Although ATRA can induce differentiation in some non-APL AML cell lines and primary blasts, clinical results of adding ATRA to standard therapy in non-APL AML patients have been inconsistent, probably due to use of different regimens and lack of diagnostic tools for identifying which patients may be sensitive to ATRA. In this study, we exposed primary blasts obtained from non-APL AML patients to ATRA to test for differentiation potential in vitro. We observed increased expression of differentiation markers, indicating a response to ATRA, in four out of fifteen primary AML samples. Three samples in which CD11b increased in response to ATRA had an inversion of chromosome 16 as well as the CBFB-MYH11 fusion gene, and the fourth sample was from a patient with KMT2A-rearranged, therapy-related AML. In conclusion, we identified a subgroup of non-APL AML patients with inv(16) and CBFB-MYH11 as the most sensitive to ATRA-mediated differentiation in vitro, and our results can help identify patients who may benefit from ATRA treatment.

AICAr, a Widely Used AMPK Activator with Important AMPK-Independent Effects: A Systematic Review.

5-Aminoimidazole-4-carboxamide ribonucleoside (AICAr) has been one of the most commonly used pharmacological modulators of AMPK activity. The majority of early studies on the role of AMPK, both in the physiological regulation of metabolism and in cancer pathogenesis, were based solely on the use of AICAr as an AMPK-activator. Even with more complex models of AMPK downregulation and knockout being introduced, AICAr remained a regular starting point for many studies focusing on AMPK biology. However, there is an increasing number of studies showing that numerous AICAr effects, previously attributed to AMPK activation, are in fact AMPK-independent. This review aims to give an overview of the present knowledge on AMPK-dependent and AMPK-independent effects of AICAr on metabolism, hypoxia, exercise, nucleotide synthesis, and cancer, calling for caution in the interpretation of AICAr-based studies in the context of understanding AMPK signaling pathway.

The Relationship between Autonomic Regulation of Cardiovascular Function and Body Composition.

BACKGROUND: We investigated whether the results of autonomic function tests correlate with body composition and shape in healthy young people. METHODS: We conducted cardiovascular reflex tests (heart rate [HR] and blood pressure [BP] responses to the Valsalva maneuver and HR response to deep breathing) and the tilt table test with 32 subjects (19 males; mean age, 22.1±1.9 years). Participants also completed an anthropometric measurement sequence (weight; height; upper arm, hips, and waist circumference; triceps and subscapular skinfold), bioelectric impedance testing, and hand grip strength measurements. RESULTS: Markers of obesity, other anthropometric measures, functional measures, and the basal metabolic rate (BMR) were significantly positively correlated with systolic BP (SBP) and diastolic BP (DBP) in both the supine and tilted positions. There was a positive correlation between the difference in HR (ΔHR) between the tilt and supine body positions and markers of obesity, the functional marker of dominant handgrip strength, and BMR. Participants with a body mass index (BMI) <25 kg/m2 had significantly lower median values of ΔHR, DBP in the tilt-test, SBP at rest, and SBP in the tilt-test than participants who had a BMI ≥25 kg/m2 (10.55 vs. 21.95 bpm, P=0.003; 77.55 vs. 90.05 mmHg, P=0.045; 113.45 vs. 140.55 mmHg, P=0.013; 117.00 vs. 135.25 mmHg, P=0.006, respectively). Body fat percentage was identified as an independent positive predictor (ß=0.993; 95% confidence interval [CI], 0.070 to 1.916; P=0.036) and body water percentage was an independent negative predictor of tilted SBP (ß=-1.370; 95% CI, -2.634 to 0.106; P=0.035). CONCLUSION: High sympathetic activity, as evaluated by cardiovascular regulation, correlates with a high share of adipose tissue in young healthy persons.

Autonomic symptom burden is an independent contributor to multiple sclerosis related fatigue.

OBJECTIVES: To investigate a possible association between autonomic dysfunction and fatigue in people with multiple sclerosis. METHODS: In 70 people with multiple sclerosis early in the disease course (51 females, mean age 33.8 ± 9.1), quantitative sudomotor axon reflex tests, cardiovascular reflex tests (heart rate and blood pressure responses to the Valsalva maneuver and heart rate response to deep breathing), and the tilt table test were performed. Participants completed the Composite Autonomic Symptom Score 31, the Modified Fatigue Impact Scale, and the Epworth Sleepiness Scale, as well as the Beck Depression Inventory. Cutoff scores of ≥ 38 or ≥ 45 on the Modified Fatigue Impact Scale were used to stratify patients into a fatigued subgroup (N = 17 or N = 9, respectively). RESULTS: We found clear associations between fatigue and scores in subjective tests of the autonomic nervous system: fatigued patients scored significantly worse on Composite Autonomic Symptom Score 31, and there was a strong correlation between the Modified Fatigue Impact Scale and the Composite Autonomic Symptom Score 31 (rs = 0.607, p < 0.001). On the other hand, we found only modest associations between fatigue and scores in objective tests of the autonomic nervous system: there was a clear trend for lower sweating outputs at all measured sites, which reached statistical significance for the distal leg and foot. We found weak correlations between the Modified Fatigue Impact Scale and the Valsalva ratio (rs = - 0.306, p = 0.011), as well as between the Modified Fatigue Impact Scale and quantitative sudomotor axon reflex tests of the forearm, proximal, and distal lower leg (rs = - 0.379, p = 0.003; rs = - 0.356, p = 0.005; and rs = - 0.345, p = 0.006, respectively). A multiple regression model showed that the Composite Autonomic Symptom Score 31, Beck Depression Inventory, and Epworth Sleepiness Scale were independent predictors of fatigue (p = 0.005, p = 0.019, and p = 0.010, respectively). CONCLUSION: These results suggest that-even early in the course of the disease-people with multiple sclerosis suffer from objective and subjective impairments of the autonomic nervous system. The results also point to an association between autonomic nervous system impairment and multiple sclerosis related fatigue.