Background: Multidrug resistance (MDR) is resistance of cancer cells to multiple
classes of chemotherapeutic drugs that can be structurally unrelated. MDR involves
altered membrane transport that results in a lower cell concentration of cytotoxic drugs
which plays an important role during cancer treatment. P-glycoprotein (Pgp) is localised
at the apical surface of epithelial cell in the intestine and it functions as a biological
barrier by extruding toxic substances and xenobiotics out of cells (Lin, 2003:54). The
ATP-binding-cassette superfamily is a rapidly growing group of membrane transport
proteins and are involved in diverse physiological processes which include antigen
presentation, drug efflux from cancer cells, bacterial nutrient uptake and cystic fibrosis
(Germann, 1996:928; Kerr, 2002:47). A number of drugs have been identified which are
able to reverse the effects of Pgp, multidrug resistance protein (MRPI) and their
associated proteins on multidrug resistance. The first MDR modulators discovered and
studied during clinical trials were associated with definite pharmacological actions, but
the doses required to overcome MDR were associated with the occurrence of
unacceptable side effects. As a consequence, more attention has been given to the
development of modulators with proper potency, selectivity and pharmacokinetic
characteristics that it can be used at a lower dose. Several novel MDR reversing agents
(also known as chemosensitisers) are currently undergoing clinical evaluation for the
treatment of resistant tumours (Teodori et al., 2002:385). Aim: The aim of this study was
to investigate the effect of selected flavonoids (morin, galangin, kaempferol and
quercetin) at two different concentrations (10 μM and 20 μM) on the transport of a known
Pgp substrate, Rhodamine 123 (Rho 123) across rat intestine (jejunum) and to
investigate structure activity relationships (SAR) of the selected flavonoids with
reference to the inhibition of Pgp. Methods: Morin, galangin, kaempferol and quercetin
were evaluated as potential modulators of Rho 123 transport, each at a concentration of
10 μM and 20 μM across rat jejunum using Sweetana-Grass diffusion cells. This study
was done bidirectionally, with two cells measuring transport in the apical to basolateral
direction (AP-BL) and two cells measuring transport in the basolateral to apical direction
(BL-AP). The rate of transport was expressed as the apparent permeability coefficient
(Pap,) and the extent of active transport was expressed by calculating the ratio of BL-AP
to AP-BL. Results: The BL-AP to AP-BL ratio calculated for Rho 123 with no
modulators added was 3.29. Morin decreased the BL-AP to AP-BL ratio to 1.88 at a
concentration of 10 μM and to 1.49 at a concentration of 20 μM. Galangin decreased
the BL-AP to AP-BL ratio to 1.60 at a concentration of 20 μM. These two flavonoids
showed statistically significant results and inhibition of active transport were clearly
demonstrated. However, the other flavonoids inhibited active transport of Rho 123 but
according to statistical analysis, the results were not significantly different. The two
different concentrations (10 μM and 20 μM) indicated that galangin, kaempferol and
quercetin showed practically significant differences according to the effect sizes. Morin,
however, did not show any practically significant differences at the different
concentrations. Regarding .the SAR, it was shown by Boumendjel and co-workers
(2002:512) that the presence of a 5-hydroxyl group and a 3-hydroxyl group as well as
the C2-C3 double bond are required for high potency binding to the nucleotide binding
domain (NBD) of Pgp. All the flavonoids tested had the above-mentioned
characteristics. Conclusion: All the selected flavonoids showed inhibition of active
transport of Rho 123 and should have an effect on the bioavailability of the substrates of
Pgp and other active transporters. This study described the inhibitory interaction of
selected flavonoids on Pgp activity. Practical significant differences between the same
modulator at different concentrations were also observed. Structure activity
relationships were identified describing the inhibitory potency of the flavonoids based on
hydroxyl group positioning / Thesis (M.Sc. (Pharmaceutics))--North-West University, Potchefstroom Campus, 2005.
| Identifer | oai:union.ndltd.org:NWUBOLOKA1/oai:dspace.nwu.ac.za:10394/792 |
| Date | January 2005 |
| Creators | Van Huyssteen, Stephanie |
| Publisher | North-West University |
| Source Sets | North-West University |
| Detected Language | English |
| Type | Thesis |
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