EXPERIMENTAL GENE-THERAPY OF HUMAN COLON-CANCER

Background. Gastrin regulates growth of human colon cancer cells by ac tivation of the cyclic adenosine monophosphate (cAMP)-dependent protei n kinase A (PKA). Gastrin and 8-Br-cAMP, a membrane-permeable cAMP ana log, inhibit growth of HCT116 cells; both stimulate growth of LoVo cel ls. This dual effect on growth may be explained by relative amounts of the regulatory subunit (R(I alpha) or R(II beta)) of PKA within the c ancer cells. Antisense oligodeoxynucleotides (ASO) to either R(I alpha ) or R(II beta) inhibit protein translation of the target mRNA by sequ ence-specific binding; subsequently, cellular PKA content and the cAMP -mediated growth may be altered. We determined whether ASO to either t he R(I alpha) or R(II beta) subunit altered the cAMP-mediated growth o f HCT116 and LoVo human colon cancer cells. Methods. HCT116 cells were treated with R(II beta) ASO (15 mu mol/L, 4 days) and then treated wi th 8-Br-cAMP (25 mu mol/L); tritiated thymidine incorporation was meas ured after 24 hours, and the cell number was determined on alternate d ays. Protein and mRNA levels of the R(II beta) subunit were determined by Western and Northern blotting, respectively. Similar studies with an ASO against the R(I alpha) subunit were performed on LoVo cells. Re sults R(II beta) ASO reversed the cAMP-mediated inhibition of growth o f HCT116 cells, and R(II beta) ASO decreased the protein level of the R(II beta) subunit. R(II beta) ASO did not alter the basal growth of H CT116 cells. R(I alpha) ASO reversed the cAMP-mediated stimulation of the growth of LoVo cells. Conclusions. The regulatory subunits of PKA are potential targets to alter growth of human colon cancer cells. Gen e therapy directed to alter specific steps in signal transduction path ways may provide new therapeutic strategies.