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Inhibition of endosomal sequestration of basic anticancer drugs: influence on cytotoxicity and tissue penetration.

Lee CM, Tannock IF - Br. J. Cancer (2006)

Bottom Line: Chloroquine, omeprazole and bafilomycin A showed concentration-dependent effects to raise endosomal pH, and to inhibit sequestration of doxorubicin in endosomes.Chloroquine and omeprazole but not bafilomycin A decreased the net uptake of doxorubicin into cells, but there was no significant effect on uptake of mitoxantrone.We conclude that modifiers of endosomal pH might increase therapeutic effectiveness of basic drugs by increasing their toxicity and/or tissue penetration in solid tumours.

View Article: PubMed Central - PubMed

Affiliation: Division of Applied Molecular Oncology, Princess Margaret Hospital/University of Toronto, 610 University Avenue, Toronto, Ontario, Canada M5G 2M9.

ABSTRACT
The basic drugs doxorubicin and mitoxantrone are known to be concentrated in acidic endosomes of cells. Here, we address the hypotheses that raising endosomal pH with the modifying agents chloroquine, omeprazole or bafilomycin A might decrease sequestration of anticancer drugs in endosomes, thereby increasing their cytotoxicity and availability for tissue penetration. Chloroquine, omeprazole and bafilomycin A showed concentration-dependent effects to raise endosomal pH, and to inhibit sequestration of doxorubicin in endosomes. Chloroquine and omeprazole but not bafilomycin A decreased the net uptake of doxorubicin into cells, but there was no significant effect on uptake of mitoxantrone. Omeprazole and bafilomycin A increased the cytotoxicity of the anticancer drugs for cultured cells, as measured in a clonogenic assay, whereas chloroquine had minimal effects on cytotoxicity despite reduced uptake of doxorubicin. Omeprazole but not chloroquine or bafilomycin A increased the penetration of anticancer drugs through multicellular layers of tumour tissue. We conclude that modifiers of endosomal pH might increase therapeutic effectiveness of basic drugs by increasing their toxicity and/or tissue penetration in solid tumours.

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Related in: MedlinePlus

Time-dependent uptake of radiolabelled doxorubicin (A and C) and mitoxantrone (B and D) into EMT-6 cells (A and B) and MCF-7 cells (C and D). Doxorubicin alone (•), mitoxantrone alone (▪), drug plus chloroquine 100 μM (▴) or omeprazole 100 μM (▾). Mean and s.e.m. are shown for three independent experiments. Significant effects (P<0.001, Student's t-test) are seen for both modifiers in Figure 3A. (c.p.m.=counts per minute in cell pellet).
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fig3: Time-dependent uptake of radiolabelled doxorubicin (A and C) and mitoxantrone (B and D) into EMT-6 cells (A and B) and MCF-7 cells (C and D). Doxorubicin alone (•), mitoxantrone alone (▪), drug plus chloroquine 100 μM (▴) or omeprazole 100 μM (▾). Mean and s.e.m. are shown for three independent experiments. Significant effects (P<0.001, Student's t-test) are seen for both modifiers in Figure 3A. (c.p.m.=counts per minute in cell pellet).

Mentions: There were inconsistent effects of chloroquine or omeprazole to influence the total cellular uptake of the radiolabelled anticancer drugs (Figure 3). The total cellular accumulation of doxorubicin in EMT-6 cells was reduced by coadministration of chloroquine and by omeprazole at 100 μM (Figure 3A), but (surprisingly) not at 1 mM (data not shown). Both modifiers reduced uptake of doxorubicin into MCF-7 cells, but there was no difference in the magnitude of the effect for concentrations of 100 μM (Figure 3B) and 1 mM (not shown). There was no consistent effect for omeprazole or chloroquine (at either concentration) to influence the net uptake of mitoxantrone (Figure 3B and D). Bafilomycin A (100 nM) did not influence the uptake of doxorubicin into EMT-6 cells.


Inhibition of endosomal sequestration of basic anticancer drugs: influence on cytotoxicity and tissue penetration.

Lee CM, Tannock IF - Br. J. Cancer (2006)

Time-dependent uptake of radiolabelled doxorubicin (A and C) and mitoxantrone (B and D) into EMT-6 cells (A and B) and MCF-7 cells (C and D). Doxorubicin alone (•), mitoxantrone alone (▪), drug plus chloroquine 100 μM (▴) or omeprazole 100 μM (▾). Mean and s.e.m. are shown for three independent experiments. Significant effects (P<0.001, Student's t-test) are seen for both modifiers in Figure 3A. (c.p.m.=counts per minute in cell pellet).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2361369&req=5

fig3: Time-dependent uptake of radiolabelled doxorubicin (A and C) and mitoxantrone (B and D) into EMT-6 cells (A and B) and MCF-7 cells (C and D). Doxorubicin alone (•), mitoxantrone alone (▪), drug plus chloroquine 100 μM (▴) or omeprazole 100 μM (▾). Mean and s.e.m. are shown for three independent experiments. Significant effects (P<0.001, Student's t-test) are seen for both modifiers in Figure 3A. (c.p.m.=counts per minute in cell pellet).
Mentions: There were inconsistent effects of chloroquine or omeprazole to influence the total cellular uptake of the radiolabelled anticancer drugs (Figure 3). The total cellular accumulation of doxorubicin in EMT-6 cells was reduced by coadministration of chloroquine and by omeprazole at 100 μM (Figure 3A), but (surprisingly) not at 1 mM (data not shown). Both modifiers reduced uptake of doxorubicin into MCF-7 cells, but there was no difference in the magnitude of the effect for concentrations of 100 μM (Figure 3B) and 1 mM (not shown). There was no consistent effect for omeprazole or chloroquine (at either concentration) to influence the net uptake of mitoxantrone (Figure 3B and D). Bafilomycin A (100 nM) did not influence the uptake of doxorubicin into EMT-6 cells.

Bottom Line: Chloroquine, omeprazole and bafilomycin A showed concentration-dependent effects to raise endosomal pH, and to inhibit sequestration of doxorubicin in endosomes.Chloroquine and omeprazole but not bafilomycin A decreased the net uptake of doxorubicin into cells, but there was no significant effect on uptake of mitoxantrone.We conclude that modifiers of endosomal pH might increase therapeutic effectiveness of basic drugs by increasing their toxicity and/or tissue penetration in solid tumours.

View Article: PubMed Central - PubMed

Affiliation: Division of Applied Molecular Oncology, Princess Margaret Hospital/University of Toronto, 610 University Avenue, Toronto, Ontario, Canada M5G 2M9.

ABSTRACT
The basic drugs doxorubicin and mitoxantrone are known to be concentrated in acidic endosomes of cells. Here, we address the hypotheses that raising endosomal pH with the modifying agents chloroquine, omeprazole or bafilomycin A might decrease sequestration of anticancer drugs in endosomes, thereby increasing their cytotoxicity and availability for tissue penetration. Chloroquine, omeprazole and bafilomycin A showed concentration-dependent effects to raise endosomal pH, and to inhibit sequestration of doxorubicin in endosomes. Chloroquine and omeprazole but not bafilomycin A decreased the net uptake of doxorubicin into cells, but there was no significant effect on uptake of mitoxantrone. Omeprazole and bafilomycin A increased the cytotoxicity of the anticancer drugs for cultured cells, as measured in a clonogenic assay, whereas chloroquine had minimal effects on cytotoxicity despite reduced uptake of doxorubicin. Omeprazole but not chloroquine or bafilomycin A increased the penetration of anticancer drugs through multicellular layers of tumour tissue. We conclude that modifiers of endosomal pH might increase therapeutic effectiveness of basic drugs by increasing their toxicity and/or tissue penetration in solid tumours.

Show MeSH
Related in: MedlinePlus