Antisense oligonucleotides targeted to the p53 gene modulate liver regeneration in vivo

The rapidly proliferating cells of the regenerating liver after partial hep atectomy (PH) present a reproducible in vivo model to study the functional role of the tumor suppressor gene p53. The present study uses the rat 70% P H model along with systemic administration of three different structural ty pes of antisense oligonucleotides (ODNs) designed to suppress p53 expressio n. We tested the hypothesis that antisense ODNs can inhibit the expression of p53, resulting in the loss of the G(1)-S cell cycle checkpoint and an al tered pattern of liver regeneration. Intraperitoneal administration of 5 mg /kg/day antisense phosphorothioate ODN after 70% PH resulted in reduced exp ression of the p53 protein in the regenerating liver. There were concomitan t increases in weight gain of remnant-regenerating liver and expression of proliferating cell nuclear antigen and p21(waf-1) compared with either sali ne or 5 mg/kg/day mispaired phosphorothioate ODN treatment. Flow cytometric analysis of DNA content of isolated hepatocytes revealed a reduction in th e G(0)/G(1) cell population and accumulation of cells with more than 4n DNA in antisense-treated rats. The regenerating livers had significantly dimin ished cytochrome P-450 (CYP) enzyme activities. Rats treated with p53 antis ense ODNs, but not saline or mispair ODN controls, had significantly elevat ed CYP activities. These observations functionally link the expression of p 53 with diminished expression of several CYP isoforms in the liver regenera tion model.