Increased Doxorubicin Uptake Research Articles

Guiding mechanism of platycodin D in treatment of mouse lung cancer with doxorubicin

This study is to observe whether platycodin D has the guiding role in treatment of mouse lung cancer with doxorubicin and explore its guiding mechanism. In vitro, platycodin D and doxorubicin(alone or in combination) were added into Lewis lung cancer(LLC) cells to detect the cell proliferation and doxorubicin uptake. Cell morphological changes were analyzed by cell holographic analysis system; cell gap junctional intercellular communication(GJIC) was tested by fluorescent yellow tracer; lyso-tracker red was used to examine lysosomal function; LC-3 B(Light chain 3 beta)and P62(heat shock 90-like protein)staining were used to test auto-phagy and autophagic degradation respectively; and P-glycoprotein(P-gp) expression was examined by Western blot. In vivo, lung solid tumor was formed in mouse LLC cells via intravenous injection. Platycodin D and doxorubicin(alone or in combination) were used to treat tumor-bearing mice for four weeks, and then the tumor size was examined, mouse survival time was recorded, doxorubicin uptake in lung tissues was tested, and lung tissues were stained for observation by HE(hematoxylin-eosin) and immunohistochemistry. The results showed that platycodin D at the experimental concentration had no effect on LLC cell proliferation but decreased LLC cell volume, promoted the cells to uptake doxorubicin and enhanced the inhibitory action of doxorubicin on cell proliferation. Platycodin D could promote GJIC and lysosomal function, increase autophagy and autophagic degradation and suppress P-gp expression. Platycodin D at the experimental dose in this study had no effect on LLC lung solid tumors in mice, increased doxorubicin uptake in lung tissues and enhanced the therapeutic efficacy of doxorubicin on lung solid tumors. Platycodin D could improve the extracellular matrix deposition in lung solid tumors, decreased the lung mucin 5 AC secretion and pulmonary vessel permeability. In summary, platycodin D had the guiding role in treating mouse lung cancer with doxorubicin, and its guiding mechanism may be associated with the promotion of cell communication, lysosomal function, and improvement of extracellular environment.

Abstract 1729: Novel liposomal topotecan formulation has a lower IC50 than the free form on neuroblastoma cells

Abstract Introduction: Neuroblastomas (NB) are the most common solid tumor in children and infants, and are frequently resistant to all standard therapies. Patients are accordingly vulnerable to acute and long-term systemic effects of toxic chemotherapy. These drugs target rapidly dividing cells throughout the body, leading to severe side effects. One strategy to reduce off-target toxicities is to selectively increase drug uptake in the tumor. In pilot studies, we found that microbubbles containing liposomal doxorubicin, an agent that is effective against NB, and focused ultrasound (sonoporation) increased doxorubicin uptake in NB xenografts. However, NB is typically treated with multidrug chemotherapy, raising the importance of testing additional agents. In these studies, we evaluated a novel liposomal formulation of topotecan, an agent used in NB treatment which is both effective and associated with significant systemic toxicities. In vitro studies are needed to determine the IC50 (concentration of the drug needed to reduce the number of live cells by half). A required esterase cleavage at the delivery site can inhibit liposome encapsulated drug release. Therefore, we hypothesized that liposomal topotecan (2T-T) would have a higher IC50 than free topotecan. Methods: We tested the effect of 2T-T on nine different NB cell lines:LA1-55n, LA-1-5S, LAN-5, NGP, SK-N-AS, BE2, SHEP, NBL-WN, and SH-SY5Y;five N-type (invasive), three S-type (noninvasive), seven MYCN-amplified (poor prognosis). We have tested free topotecan in 3 of these (LA-1-5S, NBL-WN, SH-SY5Y). Cells were plated in full RPMI at 80% confluence. 2T-T or topotecan (0 to 50 uM) were added to cells 24 hours later for 72 hours. Viable cells were estimated using a WST cell counting kit. 50uM empty liposomes and lysis buffer were used as controls. Experiments were performed in triplicate, with p≥0.05deemed significant (student t-test or ratio-paired t-test using PRISM). Results: 2T-T had a mean IC50 of 0.37±0.58uM(mean R2=0.9±0.07).Empty liposomes caused no cytotoxicity in any cell line. We found no difference in IC50 according to S or N type (0.50±0.65vs 0.35±0.58(p=ns)). The mean IC50 of MYCN-amplified cells was 0.47±0.63,while that of non-MYCN-amplified was 0.031±0.029(n=2), suggesting no difference in cytotoxicity based on MYCN status. 2T-T had a 2 fold lower IC50 than free topotecan (1.14±1.19vs 0.48±0.82,p=0.046), suggesting liposomes did not inhibit topotecan release. Conclusion: These findings suggest that liposomal topotecan (T2-T) has a lower IC50 than free topotecan in NB, and that MYCN amplification and phenotype do not modify 2T-T cytotoxicity. Our results suggest that liposomal encapsulation does not inhibit topotecan release, but could increase its cytotoxicity by increasing topotecan half-life. We predict that, in vivo 2T-T could reduce toxicities and side effects, warranting the investigation of 2T-T sonoporation in NB xenografts. Citation Format: Paula Viza Gomes, Stephanie Shen, Meghan Hill, Kilkee Flynn, Mendi Marquez, Liliya Frolova, Jessica J. Kandel, Michaelann Tartis, Sonia L. Hernandez. Novel liposomal topotecan formulation has a lower IC50 than the free form on neuroblastoma cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1729.

Arctigenin Enhances the Cytotoxic Effect of Doxorubicin in MDA-MB-231 Breast Cancer Cells.

Several reports have described the anti-cancer activity of arctigenin, a lignan extracted from Arctium lappa L. Here, we investigated the effect of arctigenin (ATG) on doxorubicin (DOX)-induced cell death using MDA-MB-231 human breast cancer cells. The results showed that DOX-induced cell death was enhanced by ATG/DOX co-treatment in a concentration-dependent manner and that this was associated with increased DOX uptake and the suppression of multidrug resistance-associated protein 1 (MRP1) gene expression in MDA-MB-231 cells. ATG enhanced DOX-induced DNA damage and decreased the phosphorylation of signal transducer and activator of transcription 3 (STAT3) and the expressions of RAD51 and survivin. Cell death caused by ATG/DOX co-treatment was mediated by the nuclear translocation of apoptosis inducing factor (AIF), reductions in cellular and mitochondrial Bcl-2 and Bcl-xL, and increases in mitochondrial BAX levels. However, caspase-3 and -7 did not participate in DOX/ATG-induced cell death. We also found that DOX/ATG-induced cell death was linked with activation of the p38 signaling pathway and suppressions of the phosphorylations and expressions of Akt and c-Jun N-terminal kinase. Taken together, these results show that ATG enhances the cytotoxic activity of DOX in MDA-MB-231 human breast cancer cells by inducing prolonged p21 expression and p38-mediated AIF-dependent cell death. In conclusion, our findings suggest that ATG might alleviate the side effects and improve the therapeutic efficacy of DOX.

Uptake and release profiles of PEGylated liposomal doxorubicin nanoparticles: A comprehensive picture based on separate determination of encapsulated and total drug concentrations in tissues of tumor-bearing mice

The PEGylated liposomal nanoparticle has been widely used as a carrier in drug delivery system. To become biologically active, the encapsulated drug must be released from the nanoparticle vehicle. However, due to limitations of current bioanalytical methods, the characterization of this release process has been restricted to determination of total drug in tissues and tumor. As a result, the fate of liposomal nanoparticles including their uptake into target tissue has not been fully characterized. In this study, we developed a novel two-step solid phase extraction on two separated columns procedure to separate liposomes from tissues and tumors without liposomal leakage. This allowed us to determine encapsulated drug, total drug and, by difference, released drug and compare the release and uptake profiles of PEGylated liposomal doxorubicin in tissues and tumor of tumor-bearing mice with corresponding profiles for free doxorubicin. The liposomal nanoparticles released doxorubicin into tumor efficiently and, compared with administration of free drug, increased doxorubicin uptake into tumor by 1.8-fold. It also decreased doxorubicin uptake into heart (0.78-fold lower) with the potential to reduce doxorubicin cardiotoxicity. Drug release reached constant levels in tissues and tumor after 12 h with released doxorubicin concentration remaining at 70–80% of total doxorubicin concentration and in tumor at 86% of total drug concentration. The assay also included determination of the main doxorubicin metabolites. Determination of the metabolites showed that liposomal entrapment delays and decreases the metabolism of doxorubicin but does not alter the metabolic pathway. These results provide a clear and comprehensive picture of the biodistribution of doxorubicin administered in liposomal nanoparticles which may assist in the rational design of other liposomal nanoparticles.

Validation of Thiosemicarbazone Compounds as P-Glycoprotein Inhibitors in Human Primary Brain-Blood Barrier and Glioblastoma Stem Cells.

P-glycoprotein (Pgp) is highly expressed on blood-brain barrier (BBB) and glioblastoma (GB) cells, particularly on cancer stem cells (SC). Pgp recognizes a broad spectrum of substrates, limiting the therapeutic efficacy of several chemotherapeutic drugs in eradicating GB SC. Finding effective and safe inhibitors of Pgp that improve drug delivery across the BBB and target GB SC is open to investigation. We previously identified a series of thiosemicarbazone compounds that inhibit Pgp with an EC50 in the nanomolar range, and herein, we investigate the efficacy of three of them in bypassing Pgp-mediated drug efflux in primary human BBB and GB cells. At 10 nM, the compounds were not cytotoxic for the brain microvascular endothelial hCMEC/D3 cell line, but they markedly enhanced the permeability of the Pgp-substrate doxorubicin through the BBB. Thiosemicarbazone derivatives increased doxorubicin uptake in GB, with greater effects in the Pgp-rich SC clones than in the differentiated clones derived from the same tumor. All compounds increased intratumor doxorubicin accumulation and consequent toxicity in GB growing under competent BBB, producing significant killing of GB SC. The compounds crossed the BBB monolayer. The most stable derivative, 10a, had a half-life in serum of 4.2 h. The coadministration of doxorubicin plus 10a significantly reduced the growth of orthotopic GB-SC xenografts, without eliciting toxic side effects. Our work suggests that the thiosemicarbazone compounds are able to transform doxorubicin, a prototype BBB-impermeable drug, into a BBB-permeable drug. Bypassing Pgp-mediated drug efflux in both BBB and GB SC, thiosemicarbazones might increase the success of chemotherapy in targeting GB SC, which represent the most aggressive and difficult components to eradicate.

Effects of ethanol on the anticancer function of doxorubicin in JJ012 cells.

Chondrosarcoma is difficult to treat because of resistance to conventional chemotherapy and radiotherapy. This study evaluated the effects of ethanol in combination with doxorubicin in chondrosarcoma cells. JJ012, was treated with doxorubicin alone or in combination with ethanol. Effects on cellular proliferation, migration, invasion, apoptosis, and the cell cycle were evaluated. Treatment of JJ012 cells with 100mM ethanol and doxorubicin resulted in reduced cell growth, invasion, and migration. In addition, doxorubicin uptake into the nucleus was enhanced and p53 mRNA expression was upregulated in JJ012 cells. Ethanol combined with doxorubicin increased doxorubicin uptake in the nucleus and enhanced the effects of doxorubicin in JJ012 cells.

Formulation and Optimization of Doxorubicin and Biochanin A Combinational Liposomes for Reversal of Chemoresistance.

Circumvention of drug resistance still remains a challenge in the development of anticancer therapeutics. Combinational nano-formulations provide many avenues for effective cancer therapy and reversal of drug resistance. In the current study, combination of biochanin A (BioA) and doxorubicin (DOX) in liposomes were prepared and studied for its potential to reverse DOX resistance in COLO205 cells. After development and validation of DOX resistant cells of COLO205 (ColoR), dosing ratio of DOX and BioA for reversal of DOX resistance was determined by co-treatment in ColoR cells. As limited solubility and analytical data available for BioA, therefore solubility was studied for BioA and analytical method was developed for the combination. Combinational liposomes were prepared and optimized for both lipid content and surface charge by evaluating size, polydispersity index, zeta potential, and encapsulation efficiency. The optimized formulation had a size about 125nm; zeta potential of -19.5mV and 70% encapsulation efficiency (EE) for BioA. Thus, prepared combinational liposomes of DOX and BioA were evaluated for its cellular uptake and efficacy to reverse DOX resistance. From the study, increased DOX uptake and promising effect for reversal of DOX resistance was observed.

Modulation of P-glycoprotein activity by novel synthetic curcumin derivatives in sensitive and multidrug-resistant T-cell acute lymphoblastic leukemia cell lines

BackgroundMultidrug resistance (MDR) and drug transporter P-glycoprotein (P-gp) represent major obstacles in cancer chemotherapy. We investigated 19 synthetic curcumin derivatives in drug-sensitive acute lymphoblastic CCRF–CEM leukemia cells and their multidrug-resistant P-gp-overexpressing subline, CEM/ADR5000. Material and methodsCytotoxicity was tested by resazurin assays. Doxorubicin uptake was assessed by flow cytometry. Binding modes of compounds to P-gp were analyzed by molecular docking. Chemical features responsible for bioactivity were studied by quantitative structure activity relationship (QSAR) analyses. A 7-descriptor QSAR model was correlated with doxorubicin uptake values, IC50 values and binding energies. ResultsThe compounds displayed IC50 values between 0.7±0.03 and 20.2±0.25μM. CEM/ADR5000 cells exhibited cross-resistance to 10 compounds, collateral sensitivity to three compounds and regular sensitivity to the remaining six curcumins. Molecular docking studies at the intra-channel transmembrane domain of human P-gp resulted in lowest binding energies ranging from −9.00±0.10 to −6.20±0.02kcal/mol and pKi values from 0.24±0.04 to 29.17±0.88μM. At the ATP-binding site of P-gp, lowest binding energies ranged from −9.78±0.17 to −6.79±0.01kcal/mol and pKi values from 0.07±0.02 to 0.03±0.03μM. CEM/ADR5000 cells accumulated approximately 4-fold less doxorubicin than CCRF–CEM cells. The control P-gp inhibitor, verapamil, partially increased doxorubicin uptake in CEM/ADR5000 cells. Six curcumins increased doxorubicin uptake in resistant cells or even exceeded uptake levels compared to sensitive one. QSAR yielded good activity prediction (R=0.797 and R=0.794 for training and test sets). ConclusionSelected derivatives may serve to guide future design of novel P-gp inhibitors and collateral sensitive drugs to combat MDR.

Opioid receptor activation triggering downregulation of cAMP improves effectiveness of anti-cancer drugs in treatment of glioblastoma

Glioblastoma are the most frequent and malignant human brain tumors, having a very poor prognosis. The enhanced radio- and chemoresistance of glioblastoma and the glioblastoma stem cells might be the main reason why conventional therapies fail. The second messenger cyclic AMP (cAMP) controls cell proliferation, differentiation, and apoptosis. Downregulation of cAMP sensitizes tumor cells for anti-cancer treatment. Opioid receptor agonists triggering opioid receptors can activate inhibitory Gi proteins, which, in turn, block adenylyl cyclase activity reducing cAMP. In this study, we show that downregulation of cAMP by opioid receptor activation improves the effectiveness of anti-cancer drugs in treatment of glioblastoma. The µ-opioid receptor agonist D,L-methadone sensitizes glioblastoma as well as the untreatable glioblastoma stem cells for doxorubicin-induced apoptosis and activation of apoptosis pathways by reversing deficient caspase activation and deficient downregulation of XIAP and Bcl-xL, playing critical roles in glioblastomas’ resistance. Blocking opioid receptors using the opioid receptor antagonist naloxone or increasing intracellular cAMP by 3-isobutyl-1-methylxanthine (IBMX) strongly reduced opioid receptor agonist-induced sensitization for doxorubicin. In addition, the opioid receptor agonist D,L-methadone increased doxorubicin uptake and decreased doxorubicin efflux, whereas doxorubicin increased opioid receptor expression in glioblastomas. Furthermore, opioid receptor activation using D,L-methadone inhibited tumor growth significantly in vivo. Our findings suggest that opioid receptor activation triggering downregulation of cAMP is a promising strategy to inhibit tumor growth and to improve the effectiveness of anti-cancer drugs in treatment of glioblastoma and in killing glioblastoma stem cells.

In vivo disposition of doxorubicin is affected by mouse Oatp1a/1b and human OATP1A/1B transporters

Organic anion-transporting polypeptides (OATPs) are important drug uptake transporters, mediating distribution of substrates to several pharmacokinetically relevant organs. Doxorubicin is a widely used anti-cancer drug extensively studied for its interactions with various drug transporters, but not OATPs. Here, we investigated the role of OATP1A/1B proteins in the distribution of doxorubicin. In vitro, we observed ∼ 2-fold increased doxorubicin uptake in HEK293 cells overexpressing human OATP1A2, but not OATP1B1 or OATP1B3. In mice, absence of Oatp1a/1b transporters led to up to 2-fold higher doxorubicin plasma concentrations and 1.3-fold higher plasma AUC. Conversely, liver AUC and liver-to-plasma ratios of Oatp1a/1b(-/-) mice were 1.4-fold and up to 4.1-fold lower than in wild-type mice, respectively. Decreased doxorubicin levels in the small intestinal content reflected those in the liver, indicating a reduced biliary excretion of doxorubicin in Oatp1a/1b(-/-) mice. These results demonstrate important control of doxorubicin plasma clearance and hepatic uptake by mouse Oatp1a/1b transporters. This is unexpected, as the fairly hydrophobic weak base doxorubicin is an atypical OATP1A/1B substrate. Interestingly, transgenic liver-specific expression of human OATP1A2, OATP1B1 or OATP1B3 could partially rescue the increased doxorubicin plasma levels of Oatp1a/1b(-/-) mice. Hepatic uptake and bile-derived intestinal excretion of doxorubicin were completely reverted to wild-type levels by OATP1A2, and partially by OATP1B1 and OATP1B3. Thus, doxorubicin is transported by hepatocyte-expressed OATP1A2, -1B1 and -1B3 in vivo, illustrating an unexpectedly wide substrate specificity. These findings have possible implications for the uptake, disposition, therapy response and toxicity of doxorubicin, also in human tumors and tissues expressing these transporters.

Doxorubicin-loaded cyclic peptide nanotube bundles overcome chemoresistance in breast cancer cells.

The purpose of this study was to design and fabricate a new cyclic peptide-based nanotube (CPNT) and to explore its potential application in cancer therapy. For such a purpose, the CPNT bundles with a diameter of -10 nm and a length of -50-80 nm, self-assembled in a micro-scaled aggregate, were first prepared using a glutamic acid and a cysteine residue-containing cyclic octapeptide. In order to explore the potential application of these supramolecular structures, the CPNTs were loaded with doxorubicin (DOX), and further modified using polyethylene glycol (PEG). The PEG-modified DOX-loaded CPNTs, showing high drug encapsulation ratio, were nano-scaled dispersions with a diameter of -50 nm and a length of -200-300 nm. More importantly, compared to free DOX, the PEG-modified DOX-loaded CPNT bundles demonstrated higher cytotoxicity, increased DOX uptake and altered intracellular distribution of DOX in human breast cancer MCF-7/ADR cells in vitro. In addition, an enhanced inhibition of P-gp activity was observed in MCF-7/ADR cells by the PEG-modified DOX-loaded CPNT bundles, which shows their potential to overcome the multidrug resistance in tumor therapy. These findings indicate that using cyclic peptide-based supramolecular structures as nanocarriers is a feasible and a potential solution for drug delivery to resistant tumor cells.

Cell death sensitization of leukemia cells by opioid receptor activation

Cyclic AMP (cAMP) regulates a number of cellular processes and modulates cell death induction. cAMP levels are altered upon stimulation of specific G-protein-coupled receptors inhibiting or activating adenylyl cyclases. Opioid receptor stimulation can activate inhibitory Gi-proteins which in turn block adenylyl cyclase activity reducing cAMP. Opioids such as D,L-methadone induce cell death in leukemia cells. However, the mechanism how opioids trigger apoptosis and activate caspases in leukemia cells is not understood. In this study, we demonstrate that downregulation of cAMP induced by opioid receptor activation using the opioid D,L-methadone kills and sensitizes leukemia cells for doxorubicin treatment. Enhancing cAMP levels by blocking opioid-receptor signaling strongly reduced D,L-methadone-induced apoptosis, caspase activation and doxorubicin-sensitivity. Induction of cell death in leukemia cells by activation of opioid receptors using the opioid D,L-methadone depends on critical levels of opioid receptor expression on the cell surface. Doxorubicin increased opioid receptor expression in leukemia cells. In addition, the opioid D,L-methadone increased doxorubicin uptake and decreased doxorubicin efflux in leukemia cells, suggesting that the opioid D,L-methadone as well as doxorubicin mutually increase their cytotoxic potential. Furthermore, we found that opioid receptor activation using D,L-methadone alone or in addition to doxorubicin inhibits tumor growth significantly in vivo. These results demonstrate that opioid receptor activation via triggering the downregulation of cAMP induces apoptosis, activates caspases and sensitizes leukemia cells for doxorubicin treatment. Hence, opioid receptor activation seems to be a promising strategy to improve anticancer therapies.

Epigenetic loss of CDH1 correlates with multidrug resistance in human hepatocellular carcinoma cells

Promoter CpG hypermethylation of tumor suppressor genes is an essential step in cancer progression but little is known about its effect on cancer multidrug resistance. In this study, we showed that CDH1 promoter was hypermethylated in drug resistance of a doxorubicin-induced multidrug resistant hepatocellular carcinoma cell line R-HepG2. Transfection of CDH1 cDNA into R-HepG2 cells led to increased amount of doxorubicin uptake, decreased cell viability, decreased P-glycoprotein expression and increased apoptotic population of cells exposed to doxorubicin. Proto-oncogene tyrosine-protein kinase FYN was over-expressed in R-HepG2 cells which displayed a negative correlation with the expression of CDH1. FYN was knocked down in R-HepG2 cells, leading to less drug resistance by increased cell viability, increased doxorubicin uptake and attenuated P-glycoprotein expression. Our findings identified epigenetic silencing of CDH1 in cancer cells might be a new molecular event of multidrug resistance.

Real-Time Visualization and Quantitation of Vascular Permeability In Vivo: Implications for Drug Delivery

The leaky, heterogeneous vasculature of human tumors prevents the even distribution of systemic drugs within cancer tissues. However, techniques for studying vascular delivery systems in vivo often require complex mammalian models and time-consuming, surgical protocols. The developing chicken embryo is a well-established model for human cancer that is easily accessible for tumor imaging. To assess this model for the in vivo analysis of tumor permeability, human tumors were grown on the chorioallantoic membrane (CAM), a thin vascular membrane which overlays the growing chick embryo. The real-time movement of small fluorescent dextrans through the tumor vasculature and surrounding tissues were used to measure vascular leak within tumor xenografts. Dextran extravasation within tumor sites was selectively enhanced an interleukin-2 (IL-2) peptide fragment or vascular endothelial growth factor (VEGF). VEGF treatment increased vascular leak in the tumor core relative to surrounding normal tissue and increased doxorubicin uptake in human tumor xenografts. This new system easily visualizes vascular permeability changes in vivo and suggests that vascular permeability may be manipulated to improve chemotherapeutic targeting to tumors.

A self-organized 3-diethylaminopropyl-bearing glycol chitosan nanogel for tumor acidic pH targeting: In vitro evaluation

In this study, a novel pH-responsive nanogel composed of glycol chitosan (GCS) grafted with functional 3-diethylaminopropyl (DEAP) groups (denoted as GCS- g-DEAP hereafter) was fabricated. The GCS- g-DEAP was designed to have a self-assembled arrangement consisting of hydrophilic block (GCS) and hydrophobic block (DEAP) at physiological pH. As the pH decreased to tumor extracellular pH (pH e), the nanogel was destabilized due to the protonation of DEAP. The pH-responsive property of the nanogel at tumor extracellular pH (pH e) was characterized in drug-release kinetic studies. The release of doxorubicin (DOX) from DOX-loaded nanogels was significantly accelerated at lower pH values, which allowed for increased DOX uptake by non-small lung carcinoma A546 cells under a slightly acidic pH condition, as in tumor pH e.

Paclitaxel and Docetaxel Stimulation of Doxorubicinol Formation in the Human Heart: Implications for Cardiotoxicity of Doxorubicin-Taxane Chemotherapies

Antitumor therapy with the anthracycline doxorubicin is limited by a dose-related cardiotoxicity that is aggravated by a concomitant administration of the taxane paclitaxel. Previous limited studies with isolated human heart cytosol showed that paclitaxel was able to stimulate an NADPH-dependent reduction of doxorubicin to its toxic secondary alcohol metabolite doxorubicinol. Here we characterized that 0.25 to 2.5 microM paclitaxel caused allosteric effects that increased doxorubicinol formation in human heart cytosol, whereas 5 to 10 microM paclitaxel decreased doxorubicinol formation. The closely related taxane docetaxel caused similar effects. Basal or taxane-stimulated doxorubicinol formation was blunted by 2,7-difluorospirofluorene-9,5'-imidazolidine-2',4'-dione (AL1576), a specific inhibitor of aldehyde reductases. Doxorubicinol was measured also in the cytosol of human myocardial strips incubated in plasma and exposed to doxorubicin in the absence or presence of paclitaxel or docetaxel and their clinical vehicles Cremophor EL or polysorbate 80. Low concentrations of taxanes stimulated doxorubicinol formation, whereas high concentrations decreased it. Doxorubicinol formation reached its maximum on adding plasma with 6 microM paclitaxel or docetaxel; this corresponded to the partitioning of 1.5 to 2.5 microM taxanes in the cytosol of the strips. Taxane-stimulated doxorubicinol formation was not mediated by vehicles, nor was it caused by increased doxorubicin uptake or de novo protein synthesis; however, doxorubicinol formation was blunted by AL1576. These results show that allosteric interactions with cytoplasmic aldehyde reductases enable paclitaxel or docetaxel to stimulate doxorubicinol formation in human heart. This information serves metabolic insights into the risk of cardiotoxicity induced by doxorubicin-taxane therapies.

Increased doxorubicin uptake and toxicity in multicellular tumour spheroids treated with DC electrical fields.

Electrochemotherapy (ECT) is a new approach to the treatment of tumours. In the present study, multicellular prostate tumour spheroids were treated with non-lethal direct current (DC) electrical fields, and uptake and toxicity of doxorubicin were investigated. An electrical field with a field strength of 500 Vm−1 applied for a duration of 90 s resulted in neither reversible nor irreversible membrane breakdown as revealed by fluid phase uptake studies of the membrane impermeant tracer Lucifer yellow. However, treated spheroids showed an increased uptake of doxorubicin and, consequently, an increased toxicity following electrical field exposure. The electrical field raised intracellular reactive oxygen species (ROS) as revealed using 2′,7′-dichlorofluorescein diacetate (H2DCFDA) as an indicator. ROS induced membrane lipid peroxidation since the lipid peroxidation end products malondialdehyde (MDA) and 4-hydroxy-2-(E)-nonenal (4-HNE) were detected after electrical field treatment. Moreover, lipid peroxidation decreased the lipid diffusion coefficient D from 4.2 × 10−10 cm2 s−1 to 2.7 × 10−10 cm2 s−1 in the control and treated sample, respectively, as revealed by fluorescence recovery after photobleaching (FRAP) experiments. The field effects could be mimicked by incubating spheroids with 100 nM hydrogen peroxide and were inhibited by the radical scavengers dehydroascorbate (DHA) and α-tocopherol (vitamin E), indicating that the increased uptake of doxorubicin after electrical field treatment is owing to lipid peroxidation and decreased membrane lipid mobility. Treatment of tumours with low intensity electrical fields may be useful to improve the cytotoxic capacity of anthracyclines. © 1999 Cancer Research Campaign