Use of a modified ornithine decarboxylase promoter to achieve efficient c-MYC- or N-MYC-regulated protein expression

One of the advantages of viral-directed enzyme prodrug therapy (VDEPT) is i ts potential for tumor-specific cytotoxicity. However, the viruses used to deliver cDNAs encoding prodrug-activating enzymes transduce normal cells as well as tumor cells, and several approaches to achieve tumor-specific expr ession of the delivered cDNAs are being investigated. One such approach is to regulate transcription of the prodrug-activating enzyme with a promoter that is preferentially activated by tumor cells. Published data suggest tha t the most promising transcription factor/promoter/enhancer combinations ar e those activated by a tumor-specific transcription factor to retain tumor cell specificity but that are equal in strength to nonspecific viral promot ers in their ability to upregulate target cDNAs, This report identifies MYC -responsive, modified ornithine decarboxylase (ODC) promoter/enhancer seque nces that upregulate target protein expression in tumor cells overexpressin g either N-MYC or c-MYC protein. The most efficient of the four constructs assessed contained six additional CACGTG MYC binding sites 5' to the endoge nous ODC promoter (R60DC), Reporter assays with this chimeric promoter/enha ncer regulating expression of chloramphenicol acetyltransferase demonstrate d 50-250-fold more activity in MYC-expressing cells compared with similar a ssays with promoterless plasmids, The R60DC regulatory sequence was approxi mately equivalent to the CMV promoter in inducing expression of the neomyci n resistance gene in c-MYC-expressing SW480 and HT-29 colon carcinoma cells and in N-MYC-expressing NB-1691 neuroblastoma cells, The modified ODC prom oter may, therefore, be useful in achieving tissue-specific expression of t arget proteins in tumor cells that overexpress c- or N-MYC.