Role of P-glycoprotein in accumulation and cytotoxicity of amrubicin and amrubicinol in MDR1 gene-transfected LLC-PK1 cells and human A549 lung adenocarcinoma cells

Metabolic carbonyl reduction of anthracyclines - role in cardiotoxicity and cancer resistance. Reducing enzymes as putative targets for novel cardioprotective and chemosensitizing agents

Anthracycline antibiotics (ANT), such as doxorubicin or daunorubicin, are a class of anticancer drugs that are widely used in oncology. Although highly effective in cancer therapy, their usefulness is greatly limited by their cardiotoxicity. Possible mechanisms of ANT cardiotoxicity include their conversion to secondary alcohol metabolites (i.e. doxorubicinol, daunorubicinol) catalyzed by carbonyl reductases (CBR) and aldo-keto reductases (AKR). These metabolites are suspected to be more cardiotoxic than their parent compounds. Moreover, overexpression of ANT-reducing enzymes (CBR and AKR) are found in many ANT-resistant cancers. The secondary metabolites show decreased cytotoxic properties and are more susceptible to ABC-mediated efflux than their parent compounds; thus, metabolite formation is considered one of the mechanisms of cancer resistance. Inhibitors of CBR and AKR were found to reduce the cardiotoxicity of ANT and the resistance of cancer cells, and therefore are being investigated as prospective cardioprotective and chemosensitizing drug candidates. In this review, the significance of a two-electron reduction of ANT, including daunorubicin, epirubicin, idarubicin, valrubicin, amrubicin, aclarubicin, and especially doxorubicin, is described with respect to toxicity and efficacy of therapy. Additionally, CBR and AKR inhibitors, including monoHER, curcumin, (−)-epigallocatechin gallate, resveratrol, berberine or pixantrone, and their modulating effect on the activity of ANT is characterized and discussed as potential mechanism of action for novel therapeutics in cancer treatment.

The connection between the toxicity of anthracyclines and their ability to modulate the P-glycoprotein-mediated transport in A549, HepG2, and MCF-7 cells

Multidrug resistance (MDR) is a major obstacle to the successful chemotherapy of solid tumors. We compared the resistance of the most popular solid tumors, breast adenocarcinoma (MCF-7 cell line) and nonsmall cell lung (A549 cell line) hepatocellular liver carcinoma (HepG2 cells), to aclarubicin (ACL) and doxorubicin (DOX). This research aimed at determining the relation between the toxicity of ACL and DOX, their cell accumulation, and then effect on P-glycoprotein functionality. ACL is more cytotoxic for tumor cells compared to DOX. The intracellular concentration of drugs in cancer cells was dependent on the dose of the drugs and the time of incubation. The P-gp inhibitor Verapamil (V) increased DOX accumulation in all tested cell lines. By contrast, the intracellular level of ACL was not affected by this modifying agent. The assessment of the uptake of 5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethylbenzimidazolocarbocyanine iodide (JC-1) or Rhodamine 123 (R123) allows the evaluation of the different influence of drugs on P-gp activity which is in agreement with the estimation of expression measured by MDR-1 shift assay. These data suggest that ACL is less P-gp dependent than DOX and consequently may be used in a clinical setting to increase treatment efficacy in resistant human tumors.

Primary porcine proximal tubular cells as an alternative to human primary renal cells in vitro: an initial characterization

Background

A good in vitro model should approximate an in vivo-like behavior as closely as possible in order to reflect most likely the in vivo situation. Regarding renal physiology of different species, humans are more closely related to pigs than to rodents, therefore primary porcine kidney cells (PKC) and their subsequent cell strain could be a valid alternative to primary human cells for renal in vitro toxicology. For this PKC must display inherent characteristics (e.g. structural organization) and functions (e.g. transepithelial transport) as observed under in vivo conditions within the respective part of the kidney.

Results

We carried out a comprehensive characterization of PKC and their subsequent cell strain, including morphology and growth as well as transporter expression and functionality. The data presented here demonstrate that PKC express various transporters including pMrp1 (abcc1), pMrp2 (abcc2), pOat1 (slc22a6) and pOat3 (slc22a8), whereas pMdr1 (abcb1) and pOatp1a2 (slco1a2) mRNA could not be detected in either the PKCs or in the porcine cortical tissue. Functionality of the transporters was demonstrated by determining the specific PAH transport kinetics.

Conclusions

On the basis of the presented results it can be concluded that PKC and to some extent their subsequent cell strain represent a valuable model for in vitro toxicology, which might be used as an alternative to human primary cells.

Pluronic mixed micelles overcoming methotrexate multidrug resistance: in vitro and in vivo evaluation

A Pluronic polymeric mixed micelle delivery system was developed in this study by using Pluronic P105 and F127 block copolymers to encapsulate the antitumor compound, methotrexate (MTX). The MTX-loaded Pluronic P105/F127 mixed micelle exhibited the spherical shape with about 22 nm in diameter, high encapsulation efficiency (about 85%) and pH-dependent in vitro drug release. In this study, A-549 and KBv cell lines were selected as multidrug resistance tumor cell models, while H-460 and KB cell lines were chosen as sensitive tumor cells. The MTX-loaded Pluronic P105/F127 mixed micelle exhibited significant higher in vitro cytotoxicity in multidrug resistant tumor cells than that of control (MTX injection) mainly because of higher cellular uptake of MTX. The pharmacokinetic studies indicated that the Pluronic micelles significantly prolonged systemic circulation time of MTX compared to MTX injection. Moreover, a much stronger antitumor efficacy in KBv tumor xenografts nude mice was observed in the MTX-loaded Pluronic P105/F127 mixed micelle group, than MTX. Collectively, Pluronic P105/F127 mixed micelles could significantly enhance the antitumor activity of MTX and might be a promising drug delivery platform for multidrug resistance modulation.

Combination of TRAIL and actinomycin D liposomes enhances antitumor effect in non-small cell lung cancer

The intractability of non-small cell lung cancer (NSCLC) to multimodality treatments plays a large part in its extremely poor prognosis. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising cytokine for selective induction of apoptosis in cancer cells; however, many NSCLC cell lines are resistant to TRAIL-induced apoptosis. The therapeutic effect can be restored by treatments combining TRAIL with chemotherapeutic agents. Actinomycin D (ActD) can sensitize NSCLC cells to TRAIL-induced apoptosis by upregulation of death receptor 4 (DR4) or 5 (DR5). However, the use of ActD has significant drawbacks due to the side effects that result from its nonspecific biodistribution in vivo. In addition, the short half-life of TRAIL in serum also limits the antitumor effect of treatments combining TRAIL and ActD. In this study, we designed a combination treatment of long-circulating TRAIL liposomes and ActD liposomes with the aim of resolving these problems. The combination of TRAIL liposomes and ActD liposomes had a synergistic cytotoxic effect against A-549 cells. The mechanism behind this combination treatment includes both increased expression of DR5 and caspase activation. Moreover, systemic administration of the combination of TRAIL liposomes and ActD liposomes suppressed both tumor formation and growth of established subcutaneous NSCLC xenografts in nude mice, inducing apoptosis without causing significant general toxicity. These results provide preclinical proof-of-principle for a novel therapeutic strategy in which TRAIL liposomes are safely combined with ActD liposomes.

Amrubicin for the treatment of neuroendocrine carcinoma of the gastrointestinal tract: a retrospective analysis of five cases

PURPOSE

A standard chemotherapy regimen for neuroendocrine carcinoma of the gastrointestinal tract (GI-NEC) has not been established. Treatment usually consists of platinum doublets, consistent with the standard treatment for small-cell lung cancer (SCLC), with which it shares clinicopathological similarities. Here, we retrospectively examined responses of five GI-NEC patients treated with amrubicin chloride (AMR) which has shown activity against SCLC as salvage therapy.

METHODS

Five patients with histologically proven unresectable GI-NEC in whom previous chemotherapy regimens had failed were treated with AMR, a synthetic anthracycline with potent topoisomerase II inhibition.

RESULTS

Primary tumors were located in the esophagus in three patients, anus in one, and colon in one. AMR was administered intravenously at 35-40 mg/m(2) on days 1-3 every 3 weeks for a median of six treatment cycles (range, 2-8). Although all patients had received one to four previous chemotherapy regimens, including cisplatin doublets, three of five achieved objective responses to AMR. All three had esophageal NEC in relapse following combination treatment with irinotecan plus cisplatin. The most common adverse events of ≥ grade 3 were neutropenia (75%), anemia (60%), thrombocytopenia (20%), and febrile neutropenia (20%).

CONCLUSIONS

Single-agent AMR achieved objective responses in three of five patients with GI-NEC. This compound may be a candidate for prospective evaluation in a larger series.

Over-expression of MDR1 in amrubicinol-resistant lung cancer cells

PURPOSE

Amrubicin, a totally synthetic 9-aminoanthracycline anticancer drug, has shown promising activity for lung cancer, but little is known about the mechanism of resistance for this agent. This study was aimed to clarify the role of P-glycoprotein (P-gp) in amrubicinol, an active metabolite of amrubicin, resistance in lung cancer cells.

METHODS

Amrubicinol-resistant cell line PC-6/AMR-OH was developed by continuously exposing the small-cell lung cancer cell line PC-6 to amrubicinol. Gene expression level of MDR1, which encodes P-gp, and intracellular accumulation of amrubicinol were evaluated by PC-6 and PC-6/AMR-OH cells. The involvement of MDR1 in amrubicinol resistance was evaluated by treatment with P-gp inhibitor verapamil and small interfering RNA (siRNA) against MDR1. Also, expression levels and single-nucleotide polymorphisms (SNPs) of MDR1 in 22 lung cancer cell lines were examined, and the relationships between these factors and sensitivity to amrubicinol were evaluated.

RESULTS

The MDR1 gene was increased approximately 4,500-fold in PC-6/AMR-OH cells compared with PC-6 cells, and intracellular accumulation of amrubicinol in PC-6/AMR-OH cells was decreased to about 15 percent of that in PC-6 cells. Treatment with verapamil and siRNA against MDR1 significantly increased the sensitivity to amrubicinol in PC-6/AMR-OH cells with increased cellular accumulation of amrubicinol. Meanwhile, neither MDR1 gene expression levels nor SNPs of the gene were associated with amrubicinol sensitivity.

CONCLUSIONS

Results of this study indicate that increased MDR1 expression and P-gp activity confer acquired resistance to amrubicinol. In contrast, neither expression level nor SNPs of MDR1 are likely to be predictive markers for amrubicin activity.

Paclitaxel-loaded Pluronic P123/F127 mixed polymeric micelles: formulation, optimization and in vitro characterization

The objective of this study was to optimize and characterize a novel polymeric mixed micelle composed of Pluronic P123 and F127 loaded with paclitaxel (PTX). A Doehlert matrix design was utilized to investigate the effect of four variables, namely P123 mass fraction, amount of water, feeding of PTX and hydration temperature on the responses including drug-loading coefficient (DL %), encapsulation ratio (ER %) and the percentage of PTX precipitated from the drug-loaded mixed micelles after 48 h at 37 (PTX precipitated %) for improvement of drug solubilization efficiency and micelle stability. PTX-loaded P123/F127 mixed micelles were prepared by thin-film hydration method. The optimized formulation showed a particle size of about 25 nm with ER %>90%, and a sustained release behavior compared to Taxol. Micelle formation was confirmed by NMR spectroscopy. The mixed micelles had a low CMC of 0.0059% in water. In addition, micelle stability studies implied that introduction of Pluronic F127 (33 wt%) into P123 micelle system significantly increased the stability of PTX-loaded micelles. More importantly, in vitro cytotoxicity was assessed using human lung adenocarcinoma cell lines SPC-A1 and A-549 and was compared to Taxol and the free drug. The cell viability assay against A-549 cells exhibited the 50% inhibition concentration (IC50) of PTX-loaded P123/F127 mixed micelles (0.1 microg/ml) was much lower than those of Taxol injection (0.4 microg/ml) and the free PTX (1.7 microg/ml). Therefore, PTX-loaded P123/F127 mixed micelles may be considered as an effective anticancer drug delivery system for cancer chemotherapy.

Next-generation anthracycline for the management of small cell lung cancer: focus on amrubicin

Amrubicin is a totally synthetic anthracycline anticancer agent that acts as a potent topoisomerase II inhibitor. Amrubicin has been approved in Japan for the treatment of lung cancer, and the results from clinical studies of amrubicin as a single agent or as part of combination regimens for lung cancer, particularly for small cell lung cancer, conducted in Japan and overseas have been promising. Amrubicin should be included among new treatment strategies especially for chemoresistant patients. Here, preclinical, pharmacological, and clinical data on the use of amrubicin for the treatment of small cell lung cancer are reviewed.