© 2001 by Oxford University Press
Journal of the National Cancer Institute, Vol. 93, No. 16, 1234-1245,
August 15, 2001
© 2001 Oxford University Press
Effects of Orally Active Taxanes on P-Glycoprotein Modulation and Colon and Breast Carcinoma Drug Resistance
Affiliations of authors: M. R. Vredenburg, J. Veith, P. Pera, K. Kee, A. Sharma, P. Kanter, W. R. Greco, R. J. Bernacki, Department of Pharmacology and Therapeutics, Roswell Park Cancer Institute, Buffalo, NY; I. Ojima, State University at Stony Brook, NY; F. Cabral, The University of Texas Medical School, Houston.
Correspondence to: Ralph J. Bernacki, Ph.D., Department of Pharmacology and Therapeutics, Roswell Park Cancer Institute, Elm and Carlton Sts., Buffalo, NY 14263 (e-mail: Ralph.Bernacki{at}roswellpark.org).
Background: The taxane paclitaxel (Taxol) is often of limited efficacy in chemotherapeutic regimens because some cancer cells express high levels of the efflux pump, P-glycoprotein (Pgp), which removes the drug from the cells. The orally active paclitaxel analog IDN-5109 has been reported to overcome Pgp-mediated drug resistance. We tested whether IDN-5109 acts by modulating Pgp activity. Methods: Human MDA435/LCC6mdr1 and MDA435/LCC6 breast carcinoma cells, which express and do not express Pgp, respectively, were incubated with [3H]IDN-5109 and paclitaxel to determine intracellular drug accumulation. Flow cytometry was used to analyze intracellular retention of two Pgp substrates, rhodamine 123 (Rh-123) and doxorubicin, in both breast carcinoma cell lines and in human colon carcinoma cells (SW-620, DLD1, and HCT-15, whose Pgp levels vary) treated with different taxanes. The effects of IDN-5109 and paclitaxel on tumor growth in vivo were studied with the use of tumors established through xenografts of Pgp-expressing SW-620 and DLD1 cells in severe combined immunodeficiency mice. All statistical tests were two-sided. Results: Pgp-expressing cells treated with IDN-5109 or with the taxane-based drug resistance reversal agent tRA96023, which blocks Pgp activity, retained 8.1- and 9.4-fold more Rh-123 (P = .0001), respectively, and 1.7- and 1.9-fold more doxorubicin (P = .001), respectively, than cells treated with paclitaxel. Non-Pgp-expressing cells treated similarly demonstrated no increased retention of either substrate. MDA435/LCC6mdr1 cells retained 5.3-fold more [3H]IDN-5109 than [3H]paclitaxel after 2 hours (P = .01). IDN-5109 showed statistically significantly higher tumor growth inhibition than paclitaxel against the SW-620 xenograft (P = .003). Conclusions: IDN-5109 modulates Pgp activity, resulting in superior tumor growth inhibition against Pgp-expressing tumors as compared with paclitaxel. IDN-5109 may broaden the spectrum of taxane use to include colon tumors.
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