Monitoring of the interaction between U937 cells and electroactive daunomycin with an arginine-rich peptide

Daunomycin penetrates the membrane of a U937 cell, which is a human histiocyte-related lymphoma cell. Several arginine-rich peptides have also exhibited a high degree of permeability with these cells. Therefore, we attempted to improve the membrane permeability of daunomycin by coupling it with an arginine-rich peptide. The cell membrane permeability of daunomycin was monitored using voltammetry, because daunomycin is an electroactive compound. First, daunomycin was combined with N-(6-maleimidocaproyloxy)sulfosuccinimide. Second, the cross-linking agent with daunomycin was bound to the cysteine residue of RRRRRRRRGC (peptide-1). The two-step synthesis suppressed the formation of by-products that might have conjugated with the amino groups of peptide-1. After the quinone moieties of daunomycin were reduced using an electrode, an oxidation peak appeared due to the moieties. The peak current of daunomycin with U937 cells had decreased. For the mixture of the daunomycin/peptide-1 probe and cells, the electrode response was smaller than that of daunomycin with the cells. Thus, the membrane penetration of the daunomycin/peptide-1 probe was improved compared with the use of only daunomycin. In addition, the membrane penetration of the probe was measured using fluorescence spectroscopy. The sensitivity of the electrochemical procedure was 100-fold that was obtained by fluorescence spectrometry.