The uptake and efflux of doxorubicin by a sensitive human bladder cancer cell line and its doxorubicin-resistant subline

Contribution of membrane transporters to chemotherapy-induced cardiotoxicity

Membrane transporters play a key role in determining the pharmacokinetic profile, therapeutic safety, and efficacy of many chemotherapeutic drugs by regulating cellular influx and efflux. Rapidly emerging evidence has shown that tissue-specific expression of transporters contributes to local drug accumulation and drug-drug interactions and that functional alterations in these transporters can directly influence an individual's susceptibility to drug-induced toxicity. Comprehending the complex mechanism of transporter function in regulating drug distribution in tissues, such as the heart, is necessary in order to acquire novel therapeutic strategies aimed at evading unwanted drug accumulation and toxicities and to ameliorate the safety of current therapeutic regimens. Here, we provide an overview of membrane transporters with a role in chemotherapy-induced cardiotoxicity and discuss novel strategies to improve therapeutic outcomes.

Targeting OCT3 attenuates doxorubicin-induced cardiac injury

Doxorubicin is a commonly used anticancer agent that can cause debilitating and irreversible cardiac injury. The initiating mechanisms contributing to this side effect remain unknown, and current preventative strategies offer only modest protection. Using stem-cell-derived cardiomyocytes from patients receiving doxorubicin, we probed the transcriptomic landscape of solute carriers and identified organic cation transporter 3 (OCT3) (SLC22A3) as a critical transporter regulating the cardiac accumulation of doxorubicin. Functional validation studies in heterologous overexpression models confirmed that doxorubicin is transported into cardiomyocytes by OCT3 and that deficiency of OCT3 protected mice from acute and chronic doxorubicin-related changes in cardiovascular function and genetic pathways associated with cardiac damage. To provide proof-of-principle and demonstrate translational relevance of this transport mechanism, we identified several pharmacological inhibitors of OCT3, including nilotinib, and found that pharmacological targeting of OCT3 can also preserve cardiovascular function following treatment with doxorubicin without affecting its plasma levels or antitumor effects in multiple models of leukemia and breast cancer. Finally, we identified a previously unrecognized, OCT3-dependent pathway of doxorubicin-induced cardiotoxicity that results in a downstream signaling cascade involving the calcium-binding proteins S100A8 and S100A9. These collective findings not only shed light on the etiology of doxorubicin-induced cardiotoxicity, but also are of potential translational relevance and provide a rationale for the implementation of a targeted intervention strategy to prevent this debilitating side effect.

Next generation risk assessment (NGRA): Bridging in vitro points-of-departure to human safety assessment using physiologically-based kinetic (PBK) modelling - A case study of doxorubicin with dose metrics considerations

Using the chemical doxorubicin (DOX), the objective of the present study was to evaluate the impact of dose metrics selection in the new approach method of integrating physiologically-based kinetic (PBK) modelling and relevant human cell-based assays to inform a priori the point of departure for human health risk. We reviewed the literature on the clinical consequences of DOX treatment to identify dosing scenarios with no or mild cardiotoxicity observed. Key concentrations of DOX that induced cardiomyocyte toxicity in vitro were derived from studies of our own and others. A human population-based PBK model of DOX was developed and verified against pharmacokinetic data. The model was then used to predict plasma and extracellular and intracellular heart concentrations of DOX under selected clinical settings and compared with in vitro outcomes, based on several dose metrics: C_max (maximum concentration) or AUC (area under concentration-time curve) in free or total form of DOX. We found when using in vitro assays to predict cardiotoxicity for DOX, AUC is a better indicator. Our study illustrates that when appropriate dose metrics are used, it is possible to combine PBK modelling with in vitro-derived toxicity information to define margins of safety and predict low-risk human exposure levels.

Anthracycline-induced cardiomyopathy: cellular and molecular mechanisms

Despite the known risk of cardiotoxicity, anthracyclines are widely prescribed chemotherapeutic agents. They are broadly characterized as being a robust effector of cellular apoptosis in rapidly proliferating cells through its actions in the nucleus and formation of reactive oxygen species (ROS). And, despite the early use of dexrazoxane, no effective treatment strategy has emerged to prevent the development of cardiomyopathy, despite decades of study, suggesting that much more insight into the underlying mechanism of the development of cardiomyopathy is needed. In this review, we detail the specific intracellular activities of anthracyclines, from the cell membrane to the sarcoplasmic reticulum, and highlight potential therapeutic windows that represent the forefront of research into the underlying causes of anthracycline-induced cardiomyopathy.

Oncoprotein 18 is necessary for malignant cell proliferation in bladder cancer cells and serves as a G3-specific non-invasive diagnostic marker candidate in urinary RNA

Background

Urine-based diagnostics indicated involvement of oncoprotein 18 (OP18) in bladder cancer. In cell culture models we investigated the role of OP18 for malignant cell growth.

Methods

We analyzed 113 urine samples and investigated two human BCa cell lines as a dual model: RT-4 and ECV-304, which represented differentiated (G1) and poorly differentiated (G3) BCa. We designed specific siRNA for down-regulation of OP18 in both cell lines. Phenotypes were characterized by cell viability, proliferation, and expression of apoptosis-related genes. Besides, sensitivity to cisplatin treatment was evaluated.

Results

Analysis of urine samples from patients with urothelial BCa revealed a significant correlation of the RNA-ratio OP18:uroplakin 1A with bladder cancer. High urinary ratios were mainly found in moderately to poorly differentiated tumors (grade G2-3) that were muscle invasive (stage T2-3), whereas samples from patients with more differentiated non-invasive BCa (G1) showed low OP18:UPK1A RNA ratios. Down-regulation of OP18 expression in ECV-304 shifted its phenotype towards G1 state. Further, OP18-directed siRNA induced apoptosis and increased chemo-sensitivity to cisplatin.

Conclusions

This study provides conclusive experimental evidence for the link between OP18-derived RNA as a diagnostic marker for molecular staging of BCa in non-invasive urine-based diagnostics and the patho-mechanistic role of OP18 suggesting this gene as a therapeutic target.

Drug transporters and anthracycline-induced cardiotoxicity

The solute carrier superfamily comprises of uptake transporters that can contribute to the absorption and elimination of a broad array of clinically important drugs. Recent studies have suggested that the tissue-specific expression of these transporters may have important consequences for an individual's susceptibility to drug-induced organ damage or to drug–drug interactions. Polymorphic variants have been identified in genes encoded by this family, and some of these have been associated with functional changes in transport function and response to anthracycline-induced toxicity and efficacy. Here, we review recent advances in the role solute carrier transporters play in anthracycline-induced cardiotoxicity, highlight potential implications of genetic variants that may contribute to drug response and discuss novel technologies to study mechanisms of anthracycline transport.

P-glycoprotein inhibitors enhance saturable uptake of idarubicin in rat heart: pharmacokinetic/pharmacodynamic modeling

Little is known about cardiac uptake kinetics of idarubicin, including a possible protective role of P-glycoprotein (Pgp)-mediated transport. This study therefore investigated uptake and negative inotropic action of idarubicin in the single-pass isolated perfused rat heart by using a pharmacokinetic/pharmacodynamic modeling approach. Idarubicin was administered as a 10-min constant infusion of 0.5 mg followed by a 70-min washout period in the absence and presence of the Pgp antagonists verapamil or amiodarone. Outflow concentration and left ventricular developed pressure were measured and the model parameters were estimated by simultaneous nonlinear regression. The results indicate the existence of a saturable, Michaelis-Menten type uptake process into the heart (K(m) = 3.06 microM, V(max) = 46.0 microM/min). Verapamil and amiodarone significantly enhanced the influx rate (V(max) increased 1.8-fold), suggesting that idarubicin is transported by Pgp directly out of the membrane before it gets into the cell. Verapamil and amiodarone attenuated the negative inotropic action of idarubicin, which was linked to the intracellular concentration of idarubicin.

MMAC1/PTEN inhibits cell growth and induces chemosensitivity to doxorubicin in human bladder cancer cells

The development and progression of bladder cancer is associated with multiple alterations in the genome, including loss of chromosome 10. Recently, MMAC1/PTEN, a phosphatidylinositol phosphatase, has been mapped to chromosome 10q23. We previously demonstrated that MMAC1/PTEN has tumor suppressive properties in glioblastoma and prostate cancer. To investigate the efficacy of gene therapy with MMAC1/PTEN, we examined whether the exogenous introduction of MMAC1/PTEN via an adenoviral vector (Ad-MMAC) can inhibit tumor growth and reverse drug resistance to doxorubicin in human bladder cancer cells. Human bladder cancer cell lines UM-UC-3 and T24 were infected with Ad-MMAC to induce exogenous expression of MMAC1/PTEN. The cells were then analysed for cell growth and expression of phosphorylated protein kinase B (Akt/PKB) and MMAC1/PTEN. UM-UC-6dox, a doxorubicin resistant subline, was infected with Ad-MMAC to evaluate its role in reversing drug resistance to doxorubicin. We found that MMAC1/PTEN suppressed tumor growth in UM-UC-3 and T24 cells with arrest in the G1 phase of the cell cycle. We also showed that gene therapy with MMAC1/PTEN abrogated phosphorylated Akt/PKB expression in UM-UC-3, T24 and UMUC-6dox cells, and restored doxorubicin sensitivity in UM-UC-6dox. These data demonstrate that MMAC1/PTEN can induce growth suppression and increase sensitivity to doxorubicin in bladder cancer cells and suggest that the MMAC1/PTEN gene and its pathways can be therapeutic targets for bladder cancer.