Interaction of nilotinib, dasatinib and bosutinib with ABCB1 and ABCG2: implications for altered anti-cancer effects and pharmacological properties

BACKGROUND AND PURPOSE

ABC multidrug transporters (MDR-ABC proteins) cause multiple drug resistance in cancer and may be involved in the decreased anti-cancer efficiency and modified pharmacological properties of novel specifically targeted agents. It has been documented that ABCB1 and ABCG2 interact with several first-generation, small-molecule, tyrosine kinase inhibitors (TKIs), including the Bcr-Abl fusion kinase inhibitor imatinib, used for the treatment of chronic myeloid leukaemia. Here, we have investigated the specific interaction of these transporters with nilotinib, dasatinib and bosutinib, three clinically used, second-generation inhibitors of the Bcr-Abl tyrosine kinase activity.

EXPERIMENTAL APPROACH

MDR-ABC transporter function was screened in both membrane- and cell-based (K562 cells) systems. Cytotoxicity measurements in Bcr-Abl-positive model cells were coupled with direct determination of intracellular TKI concentrations by high-pressure liquid chromatography-mass spectrometry and analysis of the pattern of Bcr-Abl phosphorylation. Transporter function in membranes was assessed by ATPase activity.

KEY RESULTS

Nilotinib and dasatinib were high-affinity substrates of ABCG2, and this protein mediated an effective resistance in cancer cells against these compounds. Nilotinib and dasatinib also interacted with ABCB1, but this transporter provided resistance only against dasatinib. Neither ABCB1 nor ABCG2 induced resistance to bosutinib. At relatively higher concentrations, however, each TKI inhibited both transporters.

CONCLUSIONS AND IMPLICATIONS

A combination of in vitro assays may provide valuable preclinical information for the applicability of novel targeted anti-cancer TKIs, even in multidrug-resistant cancer. The pattern of MDR-ABC transporter-TKI interactions may also help to understand the general pharmacokinetics and toxicities of new TKIs.

Reduction of Bcr-Abl function leads to erythroid differentiation of K562 cells via downregulation of ERK

The chimeric bcr-abl gene encodes a constitutively active tyrosine kinase that leads to abnormal transduction of growth and survival signals leading to chronic myeloid leukemia (CML). According to our previous observations, in vitro differentiation of several erythroid cell lines is accompanied by the downregulation of extracellular signal-regulated kinases (ERK)1/2 mitogen-activated protein kinase (MAPK) activities. In this work we investigated whether ERKs have a decisive role in either the erythroid differentiation process or apoptosis of bcr-abl+ K562 cells by means of direct (MEK1/2 inhibitor UO126) and indirect (reduced Bcr-Abl function) inhibition of their activities. We found that both Gleevec and UO126 induced hemoglobin expression. Gleevec treatment reduced the phosphorylation of Bcr-Abl, ERK and STAT-5 for up to 24 h, decreased Bcl-XL levels, and induced caspase-3-dependent apoptosis. In contrast, UO126 treatment resulted in only a transient decrease of ERK activity and did not induce cell death. For studying the effect of reduced Bcr-Abl function on erythroid differentiation at the level of the bcr-abl transcript, we applied the siRNA approach. Stable degradation of bcr-abl mRNA was achieved by using a retroviral vector with enhanced green fluorescent protein (EGFP) reporter. Despite a high (>90%) transduction efficiency we detected only a transient decrease in Bcr-Abl protein and in phosphorylated ERK1/2 levels. This transient change in Bcr-Abl signaling was sufficient to induce hemoglobin expression without significant cell death. These results suggest that by transiently reducing Bcr-Abl function it is possible to overcome the differentiation blockade without evoking apoptosis in CML cells and that reduced ERK activity may have a crucial role in this process.

Fibrous myopathy as a complication of repeated intramuscular injections for chronic headache

Two cases of fibrous myopathy associated with repeated, long-term intramuscular injections for treatment of chronic temporomandibular joint pain and chronic headache, respectively, are described. Both patients developed severe, function-limiting contractures in upper and lower extremity muscles used as injection sites. In one of the cases, the contractures were painful. Electrophysiological testing, magnetic resonance imaging and muscle biopsy results were all consistent with myopathy and replacement of skeletal muscle with noncontractile fibrous tissue. These cases are presented to increase awareness of fibrous myopathy and to promote surveillance for this serious potential complication of long-term intramuscular injections in chronic headache and other pain patients.

Comparative microstructural study of the diffusion zone between NiCr alloy and different dental ceramics

Our knowledge on the bonding mechanisms between the metal and ceramic parts of dental systems is very limited. This work tested the hypothesis that the details of the interface processes can be described in the framework of a chemical diffusion model. The development of interfacial phases was investigated by cross-sectional analytical transmission electron microscopy between a NiCr (Wiron 99) alloy and three different dental ceramics (Carat, Vita VMK 95, and Vision). All systems were investigated at normal firing conditions (suggested by the manufacturer) and at increased firing times as well. The conclusions are based on the results that the formation of a nanocrystalline Cr(2)O(3) layer and amorphous silicon oxide inclusions were detected in the early stage of the firing process in all investigated systems, and that, in the case of Carat and Vision ceramics, formation of complex NiCr and NiCrTi oxides was also observed at longer annealing times.

3D reconstruction based on hard tissue microtome cross-section pictures in dentistry

The aim of this study was to examine the accuracy of the computerized 3D surface analyzing and volume measuring method in dentistry. Two different types of test objects were used in the first part of the measurements. Each sample of the two groups was cross-sectioned using a hard tissue microtome. The sections were photographed on both sides and were projected on a graphical tablet and analyzed using a computer program. The measured and calculated parameters were compared. In the second part, 200 microm thick horizontal sections were prepared from 11 human incisor roots using the hard tissue microtome. This way, five sections were prepared from the apical 2 mm of each root. The effects of section thickness and number were modeled by decreasing the inclusion rate of the obtained number of sections from 10 to 2 and its influence on the calculated results was determined. This method was suitable for the approximation and analysis of 3D parameters. The results indicated that using 200-300 microm section thickness, the measured values were approximately 8-21% lower than the real parameters.

The role of reactive oxygen intermediates in the pathogenesis of chronic apical periodontitis

The level of malondialdehyde, a stable end product of lipid peroxidation induced by reactive oxygen intermediates and the activity of two potent antioxidant enzymes, superoxide dismutase and glutathione peroxidase, was investigated in tissue homogenates of 22 surgical periapical granuloma specimens. Malondialdehyde levels were significantly higher and glutathione peroxidase activity was significantly lower in periapical granuloma samples than in healthy gingival tissue homogenates, which were used as controls. The activity of superoxide dismutase was similar in periapical granuloma and in control samples. Our results indicate an altered balance between the production and the elimination of toxic oxygen metabolites in chronic apical periodontitis. We hypothesize that reactive oxygen intermediates, which are being produced by activated phagocytic cells abundantly present in periapical granulomas, can contribute to periapical tissue injury and bone loss in this disease.

Mammary Paget's disease and intraductal carcinoma. Histologic, histochemical, and immunocytochemical comparison

This study of mammary Paget's disease was carried out with the objects of clarifying its histogenesis and of determining optimal diagnostic measures. Ten consecutive cases of mammary Paget's disease with their underlying ductal carcinomas were compared. Histologic, histochemical, and immunocytochemical examination mainly supported the hypothesis that mammary Paget's disease is an extension of mammary ductal carcinoma into the overlying nipple epithelium. However, two of our ductal carcinomas stained strongly with S-100 protein, while Paget's disease was uniformly negative with this antibody. The significance of this finding is not known. Optimal diagnostic accuracy is obtained by using a combination of routinely stained sections along with a panel of immunocytochemical stains. Nipple wedge biopsy may demonstrate both intraduct carcinoma and Paget's disease, and is thus a superior biopsy technique.

Malignant peritoneal mesothelioma after remote abdominal radiation

Peritoneal mesothelioma in a 61-year-old man, occurred 26 years after abdominal radiotherapy for a testicular seminoma. The patient had no history of asbestos exposure. After asbestos, radiation is the second most frequent defined cause of mesothelioma in North America, but the number of well-documented cases is small; this case represents only the fifth example of peritoneal mesothelioma after therapeutic irradiation of the abdomen.