Semiquinone free radical formation by daunorubicin aglycone incorporated into the cellular membranes of intact Chinese hamster ovary cells

A computational study of Anthracyclines interacting with lipid bilayers: Correlation of membrane insertion rates, orientation effects and localisation with cytotoxicity

Anthracyclines interact with DNA and topoisomerase II as well as with cell membranes, and it is these latter interactions that can cause an increase in their cytotoxic activity. In the present study a detailed computational analysis of the initial insertion, orientation and nature of the interaction occurring between Anthracyclines and two different lipid bilayers (unsaturated POPC and saturated DMPC) is explored through molecular dynamics (MD) simulations; four Anthracyclines: Doxorubicin (DOX), Epirubicin (EPI), Idarubicin (IDA) and Daunorubicin (DAU) were examined. The results indicate that the increased cytotoxicity of DOX, in comparison to the other three analogues, is correlated with its ability to diffuse at a faster rate into the bilayers. Additionally, DOX exhibited considerably different orientational behaviour once incorporated into the bilayer and exhibited a higher propensity to interact with the hydrocarbon tails in both lipids indicating a higher probability of transport to the other leaflet of the bilayer.

Doxorubicin-conjugated dexamethasone induced MCF-7 apoptosis without entering the nucleus and able to overcome MDR-1-induced resistance

Background

Doxorubicin (DOX) is the most widely used chemotherapeutic agent that has multimodal cytotoxicity. The main cytotoxic actions of DOX occur in the nucleus. The emergence of drug-resistant cancer cells that have the ability to actively efflux DOX out of the nucleus, and the cytoplasm has led to the search for a more effective derivative of this drug.

Materials and methods

We created a new derivative of DOX that was derived via simple conjugation of the 3' amino group of DOX to the dexamethasone molecule.

Results

Despite having a lower cytotoxic activity in MCF-7 cells, the conjugated product, DexDOX, exerted its actions in a manner that was different to that of DOX. DexDOX rapidly induced MCF-7 cell apoptosis without entering the nucleus. Further analysis showed that Dex-DOX increased cytosolic oxidative stress and did not interfere with the cell cycle. In addition, the conjugated product retained its cytotoxicity in multidrug resistance-1-overexpressing MCF-7 cells that had an approximately 16-fold higher resistance to DOX.

Conclusion

We have synthesized a new derivative of DOX, which has the ability to overcome multidrug resistance-1-induced resistance. This molecule may have potential as a future chemotherapeutic agent.

Prevention of pulmonary metastasis from subcutaneous tumors by binary system-based sustained delivery of catalase

Catalase delivery can be effective in inhibiting reactive oxygen species (ROS)-mediated acceleration of tumor metastasis. Our previous studies have demonstrated that increasing the plasma half-life of catalase by pegylation (PEG-catalase) significantly increases its potency of inhibiting experimental pulmonary metastasis in mice. In the present study, a biodegradable gelatin hydrogel formulation was used to further increase the circulation time of PEG-catalase. Implantation of (111)In-PEG-catalase/hydrogel into subcutaneous tissues maintained the radioactivity in plasma for more than 14 days. Then, the effect of the PEG-catalase/hydrogel on spontaneous pulmonary metastasis of tumor cells was evaluated in mice with subcutaneous tumor of B16-BL6/Luc cells, a murine melanoma cell line stably expressing luciferase. Measuring luciferase activity in the lung revealed that the PEG-catalase/hydrogel significantly (P<0.05) inhibited the pulmonary metastasis compared with PEG-catalase solution. These findings indicate that sustaining catalase activity in the blood circulation achieved by the use of pegylation and gelatin hydrogel can reduce the incidence of tumor cell metastasis.

Anthracycline-induced phospholipase A2 inhibition

The purpose of this essay is to overview our findings that membrane-associated calcium-independent phospholipase A2 is markedly inhibited by low, clinically relevant concentrations of anthracyclines. Our studies suggest that due to the essential role of this enzyme in membrane homeostasis, its inhibition can be one of the early culprits leading to anthracycline-induced cardiac dysfunction. The clinical importance and potential pharmaceutical use of this new phenomenon await further studies.

Inhibition of Metastatic Tumor Growth in Mouse Lung by Repeated Administration of Polyethylene Glycol-Conjugated Catalase

PURPOSE

To develop a novel and effective approach to inhibit tumor metastasis based on controlled delivery of catalase, we first evaluated the characteristics of the disposition and proliferation of tumor cells. Then, we examined the effects of polyethylene glycol-conjugated catalase (PEG-catalase) on tumor metastasis. On the basis of the results obtained, PEG-catalase was repetitively administered to completely suppress the growth of tumor cells.

EXPERIMENTAL DESIGN

Murine melanoma B16-BL6 cells were stably transfected with firefly luciferase gene to obtain B16-BL6/Luc cells. These cells were injected intravenously into syngeneic C57BL/6 mice. PEG-catalase was injected intravenously, and the effect was evaluated by measuring the luciferase activity as the indicator of the number of tumor cells.

RESULTS

At 1 hour after injection of B16-BL6/Luc cells, 60 to 90% of the injected cells were recovered in the lung. The numbers decreased to 2 to 4% at 24 hours, then increased. An injection of PEG-catalase just before inoculation significantly reduced the number of tumor cells at 24 hours. Injection of PEG-catalase at 1 or 3 days after inoculation was also effective in reducing the cell numbers. Daily dosing of PEG-catalase greatly inhibited the proliferation and the number assayed at 14 days after inoculation was not significantly different from the minimal number observed at 1 day, suggesting that the growth had been markedly suppressed by the treatment.

CONCLUSIONS

These findings indicate that sustained catalase activity in the blood circulation can prevent the multiple processes of tumor metastasis in the lung, which could lead to a state of tumor dormancy.

Changes in phospholipid content and myocardial calcium-independent phospholipase A2 activity during chronic anthracycline administration

Despite numerous investigations, the causes underlying anthracycline cardiomyopathy are yet to be established. We have recently reported that acute treatment with anthracyclines inhibits membrane-associated calcium-independent phospholipase A(2) (iPLA(2)) activity both in vitro and in vivo. This study presents data that iPLA(2) activity is also suppressed during chronic drug administration. Adult Sprague-Dawley rats were given weekly 1 mg/kg i.v. injections of doxorubicin for a total of 8 weeks. One week after the last injection, the animals were sacrificed, and heart tissue was assessed for phospholipid content and iPLA(2) activity. Membrane-associated iPLA(2) activity in the myocardium of doxorubicin-treated animals was 40% lower than that in control hearts. In addition, doxorubicin treatment resulted in significant alterations in the distribution of fatty acyl moieties esterified to the sn-2 position of choline glycerophospholipids. The ethanolamine species remained unaffected. Elevation in the amount of arachidonate and linoleate esterified to the sn-2 position of choline plasmalogens was consistent with the hypothesis that iPLA(2) displays selectivity for plasmalogen phospholipids; therefore, enzyme inhibition may affect hydrolysis of these phospholipid subclasses. Notably, the changes in phospholipid content occurred at a low cumulative dose of 8 mg/kg at which appearance of structural lesions was minimal. Therefore, these alterations seem to be both specific and early signs of cardiomyocyte pathology. The results support our hypothesis that myocardial iPLA(2) inhibition may be one of the steps that leads to the functional and structural changes associated with chronic anthracycline treatment.

Interactions between cancer cells and the endothelium in metastasis

The haematogenous phase of cancer metastasis facilitates the transport of metastatic cells within the blood and incorporates a sequence of interactions between circulating intravascular cancer cells and the endothelium of blood vessels at the sites of tumour cell arrest. Initial interactions involve mechanical contact and transient adhesion, mediated by endothelial selectins and their ligands on the neoplastic cells. This contact initiates a sequence of activation pathways that involves cytokines, growth factors, bioactive lipids, and reactive oxygen species produced by either the cancer cell or the endothelium. These molecules elicit expression of integrin adhesion molecules in cancer cells and the endothelium, matrix metalloproteinases, and chemotactic factors that promote the attachment of tumour cells to the vessel wall and/or transvascular penetration. Induction of endothelial free radicals can be cytotoxic to cancer cells. Collectively, the sum of these interactions constitutes an interdependent relationship, the outcome of which determines the fate of the metastatic process.