In vivo modulation of N-myc expression by continuous perfusion with an antisense oligonucleotide.

In this study we investigated the in vivo efficacy of continuous subcutaneous perfusion of unmodified phosphodiester oligodeoxynucleotides. The in vitro sequelae of antisense inhibition of the target gene, N-myc, have been documented and include moderate growth inhibition without effects on myc expression, loss of secretogranin I expression, and morphologic alterations. We chose to use N-myc as a model target to determine if antisense effects observed in vitro can be reproduced in vivo. N-myc-expressing human neuroectodermal tumors were grown as subcutaneous xenografts in athymic mice. Antisense and sense oligodeoxynucleotides directed against N-myc were delivered to the vicinity of the tumor by a subcutaneously implanted microosmotic pump. Antisense treatment led to loss of N-myc protein from the tumor, as well as to the loss of the neuroendocrine differentiation marker protein secretogranin I. Myc protein expression remained unaffected. Mean tumor mass was reduced by 50% in antisense-treated animals, and antisense-treated tumors morphologically resembled antisense-transfected in vitro cell cultures. These results demonstrate that regional, in vivo perfusion of an unmodified oligonucleotide specifically downregulates gene expression in human tumor xenografts with concomitant effects on tumor phenotype and growth rate that correlate well with in vitro observations.