Is receptor mediated active macrophage targeting of amphotericin B nanoformulations a promising approach?

We present an AmB-LIPOMER anchored with Acemannan (ACEM), a mannose ligand for active macrophage targeting, via mannose receptor mediated endocytosis (RME). The AmB-LIPOMER prepared by modified nanoprecipitation was anchored with ACEM by simple incubation. FITC was added to obtain fluorescent LIPOMERs. The LIPOMERs revealed a spherical morphology, an average size of 400–450 nm and a PDI < 0.3. Reduction in the zeta potential and FTIR confirmed ACEM anchoring. Flow cytometry demonstrated a >13-fold enhancement of the FITC-ACEM LIPOMER in vitro in RAW 264.7 macrophage cells, compared to the FITC-LIPOMER, ascribed to mannose receptor mediated endocytosis. This was confirmed by the decreased uptake of the FITC-ACEM LIPOMER in the mannose receptor blocking study. Nevertheless, we were surprised by an ∼2-fold decrease in the in vitro antileishmanial efficacy despite the augmented uptake of the ACEM LIPOMER. This poor efficacy was explained by the extensive localization of the FITC-ACEM LIPOMER in the lysosomal compartment, established by confocal microscopy, wherein AmB underwent rapid degradation. On the other hand phagocytic uptake and lipid mediated prolonged localization in the less harsh phagosome enabling lower degradation could have facilitated higher efficacy of the AmB-LIPOMER. The pharmacokinetic and biodistribution studies in rats revealed rapid and high reticuloendothelial system uptake. While the AmB-LIPOMER group exhibited no mortality, the mortality of 5 out of 6 animals in the AmB-ACEM LIPOMER group, within 15–30 minutes caused by lung necrosis was disturbing. While we propose an explanation for the toxicity, our study questions the rationale and safety of active targeting AmB using receptor mediated endocytosis.