SURFACTANT PROTEIN A-DIRECTED TOXIN GENE KILLS LUNG-CANCER CELLS IN-VITRO

Human surfactant protein A (SPA) expression is considered a marker of respiratory epithelial differentiation. Non-small cell lung cancers (N SCLC) are respiratory epithelial derivatives, and it was previously sh own that a minority of these cancers expressed SPA, presumably a conse quence of their respiratory epithelial origin. In the studies reported here, SPA-I gene transcriptional regulatory sequences were localized to a 2.75-kb genomic 5'-flanking region fragment obtained by screening a human genomic library. The 2.75-kb fragment was used to direct a lu ciferase coding sequence transcriptionally within a plasmid construct. In plasmid transduction experiments, the SPA-directed luciferase plas mid produced significant luciferase activity in the SPA-expressing NSC LC cell line, H441, but only background levels in the non-SPA-expressi ng A549 cells. Because Northern blot analysis of resected NSCLC showed that the majority expressed SPA, an SPA-transcriptional targeting str ategy was investigated using chimeric toxin genes comprising the codin g sequence for herpes simplex virus thymidine kinase (HSV-TK) under tr anscriptional control of SPA or SV40 regulatory sequences. As expected , transduction of the constitutive, SV40-directed plasmid followed by ganciclovir treatment reduced numbers of both the A549 and H441 cells. In contrast, the SPA-directed plasmid reduced only the SPA-expressing H441 cells and had no significant effect on the A549 cells. The resul ts of these in vivo experiments suggest the concept of transcriptional ly directing toxin genes with SPA can produce targeted toxicity in NSC LC.