We could show for the first time in our studies that lobeline can moderately inhibit P-gp mediated efflux and reverse P-gp dependent resistance at non-toxic concentrations.
Lobeline, verapamil, doxorubicin, MTT, rhodamine 123, G418, mitoxantrone, and other chemicals were from Sigma Aldrich.
Lobeline was applied at different concentrations into wells 20min after 1[micro]g/ml rhodamine 123 had been added.
Cells were washed and incubated with 20[micro]M lobeline at 37 [degrees]C for 120 min.
Different concentration of lobeline or different concentration of doxorubicin and 10[micro]M lobeline were added into three triplicate wells after cells were incubated for 24 h at 37 [degrees]C and 5% [CO.sub.2].
Inhibition efficiency was defined as (fluorescence intensity of lobeline treated cells minus fluorescence of untreated control)/(fluorescence intensity of verapamil treated minus fluorescence of untreated control).
2, the rhodamine fluorescence of Caco-2 cells is positively correlated with an increase of lobeline concentration.
In order to corroborate the findings from Caco-2 cells, the P-gp overexpressing and doxorubicin resistant cell line, CEM ADR5000 cells was loaded with rhodamine 123, and then treated with 20[micro]M lobeline. The dot plot of flow cytometry in Fig.
In order to test if P-gp mediated MDR can be overcome by lobeline a reversal assay was conducted.
A mitoxantrone accumulation assay was performed to test if lobeline can inhibit BCRP.
It could be shown for the first time in our experiments that the piperidine alkaloid lobeline can enhance rhodamine 123 retention in Caco-2 cells and in a P-gp overexpressing cell line, CEM ADR5000 (Table 1, Figs.
Furthermore, we could show that lobeline can reduce insensitivity to the otherwise cytotoxic doxorubicin in Caco-2 and CEM ADR5000 cells, which are quite resistant to doxorubicin.