Transdermal use of phosphorodiamidate morpholino oligomer AVI-4472 inhibits cytochrome P450 3A2 activity in male rats

Purpose. To determine if dermal absorption of an antisense phosphorodiamidate Morpholino oligomers (PMO) can inhibit target gene expression in the liver in vivo. Method. Antisense PMO targeted to cytochrome P450 (CYP) 3A2 was applied topically to adult male rats at doses of 0.03, 0.3, and 3.0 mg. CYP3A enzyme activity in the underlying skin and liver was evaluated 24 h following application. Results. Systemic PMO bioavailability was determined by detection of full-length PMO in liver and fluorescence micrography in underlying skin. CYP3A enzyme activity were measured by hydroxylation of 7-benzyloxy-4-(trifluoromethyl)-coumarin and data were expressed as nanomoles of product/100 mug S9 protein/h. A topical dose of 0.03 mg inhibited enzyme levels from 576 +/- 17 (vehicle) and 564 +/- 20 (control PMO) to 432 +/- 20 in the antisense-treated liver (p < 0.05). Increasing the dose to 0.3 mg further inhibited enzyme level to 278 +/- 13 (p < 0.005). The inhibition did not increase further when the dose was increased to 3 mg. In the skin, starting enzyme levels were approximately one third of the liver (171 +/- 9) and maximum inhibition was reached at a lower dose. Topical delivery of 0.03 mg led reduced skin enzyme levels in half to 89 +/- 32 (p < 0.05). Increasing the dose to 0.3 mg and 3.0 mg did not produce any further inhibition, at 73 +/- 8 and 72 +/- 17 respectively. Conclusion. Topical application of antisense PMO in rats is a feasible delivery strategy for gene targets in liver and underlying skin.