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Carcinogenesis Advance Access published online on November 21, 2003
Carcinogenesis, doi:10.1093/carcin/bgh018
© 2003 by Oxford University Press
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© 2003 Oxford University Press

CARCINOGENESIS

Effect of PSC 833, an inhibitor of P-glycoprotein on N-methyl-N-nitrosourea induced mammary carcinogenesis in rats

Janarthanan Kankesan 1, Ramesh Vanama 1, Aroon Yusuf 1, Jake J. Thiessen 2, Victor Ling 3, Prema M. Rao 1, Srinivasan Rajalakshmi 1, and Dittakavi S. R. Sarma 1*

1 Departments of Laboratory Medicine & Pathobiology, University of Toronto, Toronto, ON
2 Department of Pharmacy, University of Toronto, Toronto, ON
3 BC Cancer Agency and University of British Columbia, Vancouver, BC, Canada

* Corresponding author. E-mail: sarma.dittakavi{at}utoronto.ca.

Received 19 June 2003 ; revised 21 October 2003 ; accepted 28 October 2003

Abstract

Studies in our laboratory on the role of P-glycoprotein (Pgp, coded by mdr1 gene) have led to the hypothesis that over-expression of Pgp is closely associated with the development of cancer. It was conceived therefore that inhibitors of Pgp should inhibit the development of cancer. We have reported that PSC833 (PSC), a potent inhibitor of Pgp, inhibits the development of liver cancer in rats. Similarly, based on the intrinsic over-expression of Pgp in experimental mammary carcinogenesis, we studied the effect of PSC on N-methyl-N-nitrosourea induced mammary cancer in female Sprague Dawley rats. The study indicates that PSC at daily dietary doses of 15mg/kg (PSC15) and 30mg/kg (PSC30) body weight resulted in dose-dependent inhibition of the incidence as well as the growth of mammary tumors. Compared to controls, PSC15 and PSC30 inhibited (i) mean tumor multiplicity by 32% and 67%, (iii) median tumor burden by 46% and 93%, and (iv) incidence of ulcerated tumors by 40% and 82% respectively. Most remarkably, PSC delayed median tumor incidence by 8 weeks, and exerted a 100% inhibitory effect on the incidence of large tumors, 4 cubic cm and greater. In all the cases, although the inhibitory effect of PSC was evident at both doses, only PSC30 exhibited statistical significance. A possible compounding effect that was also observed in PSC30 treated rats was a decrease in body weight gain not attributed to diminished food consumption. All in all, consistent with recent reports which have demonstrated inhibition of cancer development by compromising Pgp function, this study introduces a novel role for Pgp in breast cancer and potentially an unexplored therapeutic approach in treating the disease.

P-glycoprotein, PSC 833, mammary cancer
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