c-myc antisense limits rat liver regeneration and indicates role for c-mycin regulating cytochrome P-450 3A activity

Expression of c-myc protein is associated with cell proliferation. The pres ent study uses antisense oligomers to inhibit c-myc expression in the regen erating rat liver after 70% partial hepatectomy (PH). Antisense phosphorodi amidate morpholino oligomers (novel DNA analogs) were administered i.p. imm ediately after surgery to block expression of c-myc within the first 24 h a fter PH. A 20-mer PMO complimentary to the c-myc mRNA at the translation st art site was an effective sequence (AVI-4126, 5'-ACGTTGAGGGGCATCGTCGC-3'). A single i.p. dose of 0.5 mg/kg AVI-4126 caused reduction of the regenerati ng liver c-myc protein in a sequence-specific and dose-dependent manner. In hibition of c-myc expression resulted in reduction of proliferating cell nu clear antigen and arrested cells in the G(0)/G(1) phase of the cell cycle. The ratio of G(2):G(0) cell populations in the regenerating liver 24 h afte r PH dropped from 29.1 in saline vehicle-treated rats to 18.0 in rats treat ed with 2.5 mg/kg AVI-4126. The expression of cell cycle checkpoint protein p53 was inhibited with increasing doses of AVI-4126, but expression of p21 (waf-1) was unaffected. The activity of cytochrome P-450 3A2 (CYP3A2) was e valuated by immunoblot analysis and erythromycin N-demethylation. AVI-4126 did not alter CYP3A activity in nonhepatectamized animals but showed a dose -dependent decrease in PH rats. We conclude that AVI-4126, antisense oligom er to c-myc, can reduce cell proliferation in the regenerating rat liver. F urthermore, inhibition of c-myc may indirectly influence the expression of CYP3A.