(Glyco)-protein drug carriers with an intrinsic therapeutic activity: The concept of dual targeting

Dual targeting can in principle be achieved by using intrinsically active carriers that not only deliver the conjugated drug but also otherwise influence the pathological process. Potential carriers of this kind are monoclonal antibodies, certain interferons and interleukins, as well as certain enzymes, peptide hormones and antivirally active (glyco)-proteins. The low molecular weight protein lysozyme, that is easily filtered and reabsorbed in kidney tubular cells, was used as a carrier for renal delivery of various drugs including anti-bacterial agents. The carrier itself can add to the anti-infective effect through its lysing effect on bacterial cell walls. Albumins derivatized with various sugars were used for delivery of the anti-inflammatory drug naproxen to hepatocytes, endothelial cells and Kupffer cells. Naproxen-albumin exhibited a potent hepatoprotective effect if delivered to sinusoidal cell types. Negatively charged and enzymatically active protein carriers can contribute to therapeutic effects, among others, through receptor antagonism and detoxification of endotoxins. Some (glyco)-proteins, designed as a drug carrier for anti-HIV agents, exhibited an intrinsic antiviral activity even without coupling of antiviral drugs. This activity was caused by an increased negative charge of the particular (glyco)-proteins. The in vitro IC50 values of some of these polyanionic proteins were in the nanomolar concentration range. The mechanism of action was found to be inhibition of a post binding virus/cell fusion event. The particular negatively charged albumins (NCAs) showed, in the therapeutic dose range, favorable pharmacokinetics with regard to lymphatic distribution and residence time in the blood stream. They have little acute toxicity and, in contrast to other polyanionic compounds, such as dextran sulfate are readily biodegradable. The NCAs lack an anticoagulant activity and exhibit low immunogenicity. Importantly, a high activity against primary clinical HIV isolates was observed. We detected a high affinity binding to the V3 loop of the envelope glycoprotein gp120, explaining the potent effect on virus/cell fusion and HIV-1 replication as well as the significant activity on syncytium-inducing HIV variants. The particular antiviral proteins can in principle be applied as intrinsically active drug carriers for the targeting of nucleoside analogues such as AZT, protease inhibitors and glycosidase inhibitors. A major advantage would be the concomitant blocking of sequential steps in the viral replication process with the aims to obtain synergism and prevention of drug resistance.