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Review

What Makes Tumors Multidrug Resistant?

Piet Borst, Jos Jonkers and Sven Rottenberg

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Tumors arising “spontaneously” in genetically modified mice now make it possible to study mechanisms of drug resistance in animal tumors resembling their human counterparts. We have studied mouse mammary tumors induced by conditional deletion of Brca1 and p53. These tumors respond to monotherapy with the maximal tolerable dose of doxorubicin, or docetaxel, but eventually always become resistant to the drugs. Resistance in most tumors is caused by upregulation of drug transporters and not by interference with apoptosis/senescence. The tumors also respond to cisplatin, but do not become resistant, even after repeated treatments at the maximum tolerable dose. We conclude that resistance due to interference with cell death effector pathways (apoptosis/senescence) is not an option in these tumors, re-emphasizing doubts that such mechanisms play a role in epithelial tumors. Tumors responding to drug may shrink to less than 5% of their volume before relapsing. We argue that this resistant remnant fraction may provide a test for the tumor stem cell hypothesis and, more generally, that “spontaneous” mouse tumors resembling their human counterparts provide a useful new tool for drug development and for improving treatment regimens.

Authors

Piet Borst

The Netherlands Cancer Institute; Amsterdam, The Netherlands

Jos Jonkers

The Netherlands Cancer Institute; Amsterdam, The Netherlands

Sven Rottenberg

The Netherlands Cancer Institute; Amsterdam, The Netherlands

This is an open-access article

 Download PDF

If the document does not open, please right-click on the link (control-click on a Macintosh) and select the option to save the file to disk.