P-glycoprotein (P-gp) and multidrug resistance-associated protein 1 (MRP1) are induced by arsenic trioxide (As(2)O(3)), but are not the main mechanism of As(2)O(3)-resistance in acute promyelocytic leukemia cells

Enhancing the stability, BBB permeability and neuroprotective activity of verbascoside in vitro using lipid nanocapsules in combination with menthol

Verbascoside (VER) shows promising neuroprotective activity. However, the instability and low permeability in crossing the blood-brain barrier (BBB) greatly hinder its application. In the present study, verbascoside was encapsulated into lipid nanocapsules (LNC) by reverse micelle (RM) to increase its stability. Besides, we used VER-RM-LNC combined with an envoy drug, menthol, to improve its BBB permeability and neuroprotective activity. VER-RM-LNC was prepared by the phase inversion temperature method, resulting in an encapsulation efficiency of nearly 85 %. The formulated VER-RM-LNC was stable for 6 months at 4 °C. VER encapsulated into LNC possessed enhanced stability and a reduced release profile. Menthol increased the cellular uptake and the permeability of VER-RM-LNC in the BBB model in vitro. In addition, the improved neuroprotective activity of VER through incubation with menthol and VER-RM-LNC was verified in the neurotoxic human brain microvascular endothelial cells model induced by Aβ_25-35.

Poly(ADP-Ribose) Polymerase Inhibitors for Arsenic Trioxide-Resistant Acute Promyelocytic Leukemia: Synergistic In Vitro Antitumor Effects with Hypomethylating Agents or High-Dose Vitamin C

Arsenic trioxide (ATO) is an anticancer agent used for the treatment ofacute promyelocytic leukemia (APL). However, 5%-10% of patients fail to respond or experience disease relapse. Based on poly(ADP-ribose) polymerase (PARP) 1 involvement in the processing of DNA demethylation, here we have tested the in vitro susceptibility of ATO-resistant clones (derived from the human APL cell line NB4) to PARP inhibitors (PARPi) in combination with hypomethylating agents (azacitidine and decitabine) or high-dose vitamin C (ascorbate), which induces 5-hydroxymethylcytosine (5hmC)-mediated DNA demethylation. ATO-sensitive and -resistant APL cell clones were generated and initially analyzed for their susceptibility to five clinically used PARPi (olaparib, niraparib, rucaparib, veliparib, and talazoparib). The obtained PARPi IC50 values were far below (olaparib and niraparib), within the range (talazoparib), or above (rucaparib and veliparib) the C max reported in patients, likely as a result of differences in the mechanisms of their cytotoxic activity. ATO-resistant APL cells were also susceptible to clinically relevant concentrations of azacitidine and decitabine and to high-dose ascorbate. Interestingly, the combination of these agents with olaparib, niraparib, or talazoparib resulted in synergistic antitumor activity. In combination with ascorbate, PARPi increased the ascorbate-mediated induction of 5hmC, which likely resulted in stalled DNA repair and cytotoxicity. Talazoparib was the most effective PARPi in synergizing with ascorbate, in accordance with its marked ability to trap PARP1 at damaged DNA. These findings suggest that ATO and PARPi have nonoverlapping resistance mechanisms and support further investigation on PARPi combination with hypomethylating agents or high-dose ascorbate for relapsed/ATO-refractory APL, especially in frail patients. SIGNIFICANCE STATEMENT: This study found that poly(ADP-ribose) inhibitors (PARPi) show activity as single agents against human acute promyelocytic leukemia cells resistant to arsenic trioxide at clinically relevant concentrations. Furthermore, PARPi enhance the in vitro efficacy of azacitidine, decitabine, and high-dose vitamin C, all agents that alter DNA methylation. In combination with vitamin C, PARPi increase the levels of 5-hydroxymethylcytosine, likely as a result of altered processing of the oxidized intermediates associated with DNA demethylation.

Acute Promyelocytic Leukemia: Update on the Mechanisms of Leukemogenesis, Resistance and on Innovative Treatment Strategies

This review highlights new findings that have deepened our understanding of the mechanisms of leukemogenesis, therapy and resistance in acute promyelocytic leukemia (APL). Promyelocytic leukemia-retinoic acid receptor α (PML-RARa) sets the cellular landscape of acute promyelocytic leukemia (APL) by repressing the transcription of RARa target genes and disrupting PML-NBs. The RAR receptors control the homeostasis of tissue growth, modeling and regeneration, and PML-NBs are involved in self-renewal of normal and cancer stem cells, DNA damage response, senescence and stress response. The additional somatic mutations in APL mainly involve FLT3, WT1, NRAS, KRAS, ARID1B and ARID1A genes. The treatment outcomes in patients with newly diagnosed APL improved dramatically since the advent of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO). ATRA activates the transcription of blocked genes and degrades PML-RARα, while ATO degrades PML-RARa by promoting apoptosis and has a pro-oxidant effect. The resistance to ATRA and ATO may derive from the mutations in the RARa ligand binding domain (LBD) and in the PML-B2 domain of PML-RARa, but such mutations cannot explain the majority of resistances experienced in the clinic, globally accounting for 5-10% of cases. Several studies are ongoing to unravel clonal evolution and resistance, suggesting the therapeutic potential of new retinoid molecules and combinatorial treatments of ATRA or ATO with different drugs acting through alternative mechanisms of action, which may lead to synergistic effects on growth control or the induction of apoptosis in APL cells.

Factors determining sensitivity and resistance of tumor cells to arsenic trioxide

Previously, arsenic trioxide showed impressive regression rates of acute promyelocytic leukemia. Here, we investigated molecular determinants of sensitivity and resistance of cell lines of different tumor types towards arsenic trioxide. Arsenic trioxide was the most cytotoxic compound among 8 arsenicals investigated in the NCI cell line panel. We correlated transcriptome-wide microarray-based mRNA expression to the IC(50) values for arsenic trioxide by bioinformatic approaches (COMPARE and hierarchical cluster analyses, Ingenuity signaling pathway analysis). Among the identified pathways were signaling routes for p53, integrin-linked kinase, and actin cytoskeleton. Genes from these pathways significantly predicted cellular response to arsenic trioxide. Then, we analyzed whether classical drug resistance factors may also play a role for arsenic trioxide. Cell lines transfected with cDNAs for catalase, thioredoxin, or the anti-apoptotic bcl-2 gene were more resistant to arsenic trioxide than mock vector transfected cells. Multidrug-resistant cells overexpressing the MDR1, MRP1 or BCRP genes were not cross-resistant to arsenic trioxide. Our approach revealed that response of tumor cells towards arsenic trioxide is multi-factorial.

Elevation of cellular BPDE uptake by human cells: a possible factor contributing to co-carcinogenicity by arsenite

BACKGROUND

Arsenite (iAsIII) can promote mutagenicity and carcinogenicity of other carcinogens. Considerable attention has focused on interference with DNA repair by inorganic arsenic, especially the nucleotide excision repair (NER) pathway, whereas less is known about the effect of arsenic on the induction of DNA damage by other agents.

OBJECTIVES

We examined how arsenic modulates DNA damage by other chemicals.

METHODS

We used an NER-deficient cell line to dissect DNA damage induction from DNA repair and to examine the effects of iAsIII on the formation of benzo[a]pyrene diol epoxide (BPDE)-DNA adducts.

RESULTS

We found that pretreatment with iAsIII at subtoxic concentrations (10 microM) led to enhanced formation of BPDE-DNA adducts. Reduced glutathione levels, glutathione S-transferase activity and chromatin accessibility were also measured after iAsIII treatment, but none of these factors appeared to account for the enhanced formation of DNA adducts. However, we found that pretreatment with iAsIII increased the cellular uptake of BPDE in a dose-dependent manner.

CONCLUSIONS

Our results suggest that iAsIII enhanced the formation of BPDE-DNA adducts by increasing the cellular uptake of BPDE. Therefore, the ability of arsenic to increase the bioavailability of other carcinogens may contribute to arsenic co-carcinogenicity.

Arsenic trioxide in the treatment of haematological malignancies

Arsenic trioxide (As(2)O(3)) for leukaemia treatment was described a century ago. Recent resurgence in the use of arsenic trioxide is related to its high efficacy in acute promyelocytic leukaemia (APL). Most arsenic trioxide preparations are intravenous, although an oral formulation is similarly efficacious. Side effects of arsenic trioxide are usually minor, including skin reactions, gastrointestinal upset, and reversible increases in transaminases. During therapy, a leukocytosis occasionally occurs, which may be complicated by fluid accumulation and pulmonary infiltration. Arsenic trioxide causes an asymptomatic QT prolongation in most patients. However, if concomitant cardiopulmonary diseases or electrolyte disturbances are present, more sinister arrhythmias may develop. Therefore, before commencement of arsenic trioxide therapy, a full cardiac assessment and avoidance of drugs that prolong QT interval should be instituted. Arsenic trioxide is partly renally excreted and, therefore, dose adjustment is required when renal function is impaired. In addition to its use in APL, arsenic trioxide is now tested in other malignancies, notably multiple myeloma.

Efficacy of gemtuzumab ozogamicin on ATRA- and arsenic-resistant acute promyelocytic leukemia (APL) cells

Acute promyelocytic leukemia (APL) cells express a considerable level of CD33, which is a target of gemtuzumab ozogamicin (GO), and a significantly lower level of P-glycoprotein (P-gp). In this study, we examined whether GO was effective on all-trans retinoic acid (ATRA)- or arsenic trioxide (ATO)-resistant APL cells. Cells used were an APL cell line in which P-gp was undetectable (NB4), ATRA-resistant NB4 (NB4/RA), NB4 and NB4/RA that had been transfected with MDR-1 cDNA (NB4/MDR and NB4/RA/MDR, respectively), ATO-resistant NB4 (NB4/As) and blast cells from eight patients with clinically ATRA-resistant APL including two patients with ATRA- and ATO-resistant APL. The efficacy of GO was analyzed by (3)H-thymidine incorporation, the dye exclusion test and cell cycle distribution. GO suppressed the growth of NB4, NB4/RA and NB4/As cells in a dose-dependent manner. GO increased the percentage of hypodiploid cells significantly in NB4, NB4/RA and NB4/As cells, and by a limited degree in NB4/MDR and NB4/RA/MDR cells. Similar results were obtained using blast cells from the patients with APL. GO is effective against ATRA- or ATO-resistant APL cells that do not express P-gp, and the mechanism of resistance to GO is not related to the mechanism of resistance to ATRA or ATO in APL cells. Leukemia (2005) 19, 1306-1311. doi:10.1038/sj.leu.2403807; published online 26 May 2005.

MRP-1 expression levels determine strain-specific susceptibility to sodium arsenic-induced renal injury between C57BL/6 and BALB/c mice

To clarify the pathophysiological mechanism underlying acute renal injury caused by acute exposure to arsenic, we subcutaneously injected both BALB/c and C57BL/6 mice with sodium arsenite (NaAs; 13.5 mg/kg). BALB/c mice exhibited exaggerated elevation of serum blood urea nitrogen (BUN) and creatinine (CRE) levels, compared with C57BL/6 mice. Moreover, half of BALB/c mice died by 24 h, whereas all C57BL/6 mice survived. Histopathological examination on kidney revealed severe hemorrhages, acute tubular necrosis, neutrophil infiltration, cast formation, and disappearance of PAS-positive brush borders in BALB/c mice, later than 10 h. These pathological changes were remarkably attenuated in C57BL/6 mice, accompanied with lower intrarenal arsenic concentrations, compared with BALB/c mice. Among heavy metal inducible proteins including multidrug resistance-associated protein (MRP)-1, multidrug resistance gene (MDR)-1, metallothionein (MT)-1, and arsenite inducible, cysteine- and histidine-rich RNA-associated protein (AIRAP), intrarenal MDR-1, MT-1, and AIRAP gene expression was enhanced to a similar extent in both strains, whereas NaAs challenge augmented intrarenal MRP-1 mRNA and protein expression levels in C57BL/6 but not BALB/c mice. Moreover, the administration of a specific inhibitor of MRP-1, MK-571, significantly exaggerated acute renal injury in C57BL/6 mice. Thus, MRP-1 is crucially involved in arsenic efflux and eventually prevention of acute renal injury upon acute exposure to NaAs.

Phosphoinositide 3-kinase/Akt involvement in arsenic trioxide resistance of human leukemia cells

The purpose of this study was to evaluate the possible involvement of the phosphoinositide 3-kinase (PI3K)/Akt survival pathway in determining resistance to arsenic trioxide (As2O3)-induced apoptosis. We employed a HL60 cell clone (HL60AR) with a constitutively active PI3K/Akt survival pathway, as well as U937 and K562 cells. In addition, we used parental (PT) HL60 cells overexpressing a constitutively active Akt. Selective pharmacological inhibitors of the PI3K/Akt axis (LY294002, wortmannin) were employed to influence the sensitivity to As2O3. While HL60PT cells were sensitive to 2.5 microM As2O3 and died of apoptosis, HL60AR cells were resistant up to 5 microM As2O3. Treatment with either LY294002 or wortmannin lowered resistance of HL60AR cells to As2O3. Also in U937 and K562 cells, inhibitors of the PI3K/Akt axis caused a decrease in As2O3 resistance. Overexpression of constitutively active Akt in HL60PT cells caused the induction of resistance to 2.5 microM As2O3. Conversely, forced expression of a dominant negative Akt in HL60AR cells resulted in a decrease in As2O3 resistance. Moreover, HL60 cell resistance to 2.5 microM As2O3 could be significantly reduced by incubation with SN50, a peptide inhibitor selective for the NF-kappaB transcription factor. Taken together our findings suggest that a constitutive activation of the PI3K/Akt pathway, which is increasingly detected in some types of acute myeloid leukemia, may contribute to As2O3 resistance, most likely through NF-kappaB activation. Selective pharmacological inhibitors of this survival pathway, as well as of NF-kappaB, might be usefully employed in the future to reverse resistance to this treatment.