Binding with Serum Components Favorably Affects Cellular Uptake of 111 In-Oligonucleotide in a Leukemia Cell Line

Purpose: The influence of serum components on the intracellular uptake of an ¹¹¹In-oligonucleotide (ODN) against mdr1 mRNA was investigated in the murine leukemia cell line, P388/S, and its mdr1-overexpressed P388/R. Methods: ¹¹¹In-ODNs naked and vectorized with lipids were analyzed for binding with serum components using high-performance liquid chromatography (HPLC). ¹¹¹In-ODN was incubated in albumin and transferrin solutions. ¹¹¹In-DTPA and ¹¹¹In-mononucleotide were incubated in serum. Degradation of naked ¹¹¹In-ODN was detected in phosphate buffered saline (PBS) and serum containing endonuclease S1. Cellular uptakes of naked and vectorized ¹¹¹In-ODN in the above cells were examined with and without fetal calf serum (FCS). Results: Time-dependent binding of naked and vectorized ¹¹¹In- ODN with serum components was observed throughout 24 hours. Transchelation of ¹¹¹In to transferrin was not detected. HPLC profiles of ¹¹¹In-DTPA and ¹¹¹In-mononucleotide did not change in serum. Degradation of ¹¹¹In-ODN by S1 was less remarkable in serum than in PBS. Specific accumulation of vectorized¹¹¹In-ODN in P388/R cells was achieved in culture with and without 10% FCS. Conclusions: This study verified the intense binding of ODN with serum components, leading to no inhibition on ODN intracellular specific uptake. Binding with serum components protects ¹¹¹In-ODN from degradation by endonuclease and thus may facilitate ODN transmembrane delivery.