The purpose of this study is to evaluate the cell interactions of a new class of compounds composed of phosphodiester oligonucleotides linked to the cholesterol group at position 3, 7, or 22 of the steroid structure. The resulting conjugates were assessed for their capacity to bind, penetrate and partition in the cytoplasmic compartment of murine macrophages. The results showed that lipophilic conjugates bind to cells much faster (t(1/2) < or = 10 min) than do underivatized oligomers. Oligomers tethered to the cholesterol at positions 3 and 7 (PO-GEM-3-Chol and PO-GEM-7-Chol) interacted more efficiently with cell membranes and were better internalized than oligomers attached to the cholesterol moiety at position 22 (PO-GEM-22-Chol). The cytosolic fraction of internalized oligomers was studied by a digitonin-based membrane permeabilization method. The recovered fraction of oligomers that can freely diffuse from the cytosol was comparable for GEM-91, a phosphorothioate congener, and for PO-GEM-7-Chol (50-60% of the internalized oligomers), while that of PO-GEM-3-Chol was less (30% of the internalized oligomers) indicating a higher membrane affinity of the latter derivative as compared to the other investigated compounds. Membrane binding and cell internalization correlated well with the hydrophobicity of the conjugates as characterized by their partition coefficients in a water-octanol system. Due to their capacity of rapid binding and cytosolic partition in cells, cholesterol-derivatized oligonucleotides at position 3 or 7 of the steroid molecule appeared as good candidates for systemic delivery of anti-HIV antisense compounds.