Erschienen in:
01.11.2011 | Original Article
Accumulation and distribution of doxorubicin in tumour spheroids: the influence of acidity and expression of P-glycoprotein
verfasst von:
Howard R. Mellor, Richard Callaghan
Erschienen in:
Cancer Chemotherapy and Pharmacology
|
Ausgabe 5/2011
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Abstract
Purpose
The intra-tumour distribution of anticancer drugs remains an important, but often under-estimated, influence on drug efficacy. Tumour acidity and the presence of efflux pumps were examined for their influence on the distribution of doxorubicin in a solid tumour model.
Methods
Anticancer drug distribution and overall accumulation was measured in tumour spheroids (TS) of varying sizes. The distribution profiles were examined in normoxic and hypoxic TS, the latter generating metabolic acidosis. Finally, the drug distribution profiles were related to efficacy using radial outgrowth assays.
Results
In large tumour spheroids (TS) (d ~500 μm), intracellular accumulation of doxorubicin was restricted to cells in the outermost layers and failed to accumulate within the viable cells in the ‘intermediate’ hypoxic zone. A similar profile was obtained for another protonatable amine, 7-AAD. In contrast, the distribution of the non-ionisable drug (at physiological pH) BODIPY-Taxol was uniform throughout the TS. In order to independently model the hypoxic and normoxic zones of TS, we compared drug accumulation in small entirely normoxic TS (d ~200 μm) with equivalent sized ones exposed to hypoxia in an anaerobic chamber. Exposure of TS to hypoxia caused a considerable reduction in the pH of the bathing medium and lower tissue accumulation of doxorubicin. Interstitial acidity reduces the proportion of doxorubicin in the non-ionised form.
Conclusions
In TS, the accumulation and distribution of doxorubicin was influenced by both the expression of P-glycoprotein and hypoxia-induced acidity. Therefore, optimisation of doxorubicin chemotherapy for hypoxic tumours will require circumvention of both of these crucial pharmacokinetic determinants.