This study demonstrates that conjugation of CPP to PMO enhances the PMO pharmacokinetic profile, tissue uptake, and subsequent retention. Therefore, when dosed at < or = 15 mg/kg, CPP is a promising transporter for enhancing PMO delivery in therapeutic settings.

ABSTRACT:Antisense phosphorodiamidate morpholino oligomers (PMO) inhibit targeted gene expression by preventing ribosomal assembly, thus preventing translation. Inhibition of cytochrome P450 (P450) 3A4 expression was examined in primary human hepatocytes from 11 donors and in Caco-2 cells (stably transfected with CYP3A4 cDNA on an extrachromosomal vector) by evaluating the metabolism of substrate 7-benzyloxy-4-[trifluoromethyl]-coumarin and Western immunoblot analysis. Cellular uptake of PMO was confirmed in both cell systems using fluorescein-labeled PMOs. Three antisense PMO sequences and two control PMO sequences were tested. AVI-4557, a 20-mer PMO with the sequence 5-CTGGGAT-GAGAGCCATCACT-3 was selected as the optimal agent. AVI-4557 inhibited expression of CYP3A4 in Caco-2/h3A4 cells by 64% at 24 h following administration of 2.8 M by an assisted delivery protocol. Inhibition of CYP3A activity was observed in primary human hepatocytes after 24 h exposure to AVI-4557 by an average of 32 ؎ 11%. Furthermore, AVI-4557 exposure resulted in a sequence-dependent inhibition of cyclophosphamide-related cytocidal activity and a sequence-dependent induction of paclitaxelrelated cytocidal activity in both cell types. Finally, the cytocidal activity of cisplatin was not affected with AVI-4557 treatment in either cell type. These studies indicate AVI-4557 is an effective and specific inhibitor of CYP3A4 expression.

Tamoxifen (TAM) is widely used in the treatment and prevention of breast cancer. There is clear evidence that cytochrome P450 (CYP) 3A enzymes play an important role in TAM metabolism, resulting in metabolites that lead to formation of TAM-DNA adducts. We have investigated the effect of CYP3A2 antisense (AVI-4472) exposure on CYP3A2 transcription, enzyme activity, translation, and TAM-DNA adducts, in livers of rats administered TAM (50 mg/kg body weight [bw]/day) for 7 days. The study design included administration of 0, 0.5, 2.5, or 12.5 mg AVI-4472/kg bw/day for 8 days, beginning 1 day before TAM exposure. The specific activity of CYP3A2 was increased after TAM administration, and decreased significantly (approximately 70%) in the presence of 12.5 mg AVI-4472. CYP3A2 protein levels, determined by immunoblot analysis, showed a similar pattern. Hepatic TAM-DNA adduct levels were measurable in all TAM-exposed groups. However, when rats were co-treated with 2.5 and 12.5 mg AVI-4472/kg bw/day, statistically significant (approximately 50%) reductions in TAM-DNA adduct levels (2.0-2.8 adducts/10(8) nucleotides) were observed compared to rats treated with TAM alone (5.1 adducts/10(8) nucleotides). Rat toxicology U34 arrays (Affymetrix) were used to investigate the modulation of gene expression patterns on co-administration of TAM with AVI-4472. Results indicated that several CYP genes were down regulated although no significant induction of CYP3A2 was observed in the TAM-exposed rats co-treated with AVI-4472. Overall the data suggest the utility of antisense technology in the redirection of TAM metabolism thereby lowering TAM genotoxicity in rat liver.