LAC REPRESSOR INDUCIBLE GENE-EXPRESSION IN HUMAN BREAST-CANCER CELLS IN-VITRO AND IN A XENOGRAFT TUMOR

We have studied the lac repressor (lacR) system in two breast cancer c ell lines, MCF-7 and MDA-MB-231, in vitro and in vivo. Breast cancer c ell lines were stably transfected with lacR and tested for inducibilit y by transient transfection with a lac operator/luciferase reporter pl asmid. The level expression of lacR did not appear to correlate with t he basal or maximal activation of induction by isopropyl beta-D-thioga lactoside (IPTG). Stable transfection with tile same reporter gene res ulted in Icp to 40-fold (MDA-MB-231) and 50-fold (MCF7) induction. In the absence of IPTG, a low level of basal reporter gene expression was seen in all clones. Detailed analysis showed that induction was rapid (maximal at 24 h), reversible (a return to basal expression by 24 hi and dose-dependent. To test if this system was also inducible in vivo, cells were grown as a xenograft tumor in nude mice. Mice were gir en IPTG (0.53 mmol) by intraperitoneal injection, and the tumors were bio psied at several time points following administration. IPTG caused a 1 0-fold increase in luciferase activity after 8 h, which persisted for 24 h. Thus, this system allows tightly controlled inducible in vivo an d in vitro gene expression with low basal expression, and it may provi de an important tool for the study of lethal genes in human breast can cer cells.