Polymyxins Facilitate Entry into Mammalian Cells.

Area of Science:

• Biochemistry
• Cell Biology
• Drug Delivery

Background:

• Polymyxin B is a critical antibiotic for treating multi-resistant Gram-negative infections.
• Nephrotoxicity is a significant limitation of Polymyxin B therapy.
• Understanding Polymyxin B's cellular uptake is key to developing safer, more effective analogs.

Purpose of the Study:

• To synthesize functionalized Polymyxin B derivatives and a per-guanidinylated derivative.
• To explore the structural requirements for enhanced mammalian cell uptake.
• To investigate the potential of these novel scaffolds as molecular transporters for intracellular delivery.

Main Methods:

• Synthesis of functionalized polymyxin derivatives.
• Cellular uptake studies using nanomolar concentrations and large cargo (>300 kDa).
• Investigating uptake mechanisms via heparan sulfate dependence, caveolae-mediated endocytosis, and lysosomal colocalization.
• Assessing cytosolic delivery using a ribosome-inactivating toxin.
• Incorporating the polymyxin scaffold into liposomes to enhance uptake.

Main Results:

• Functionalized polymyxin derivatives efficiently deliver large cargo (>300 kDa) into living cells at nanomolar concentrations.
• Cellular uptake is exclusively dependent on cell surface heparan sulfate.
• Internalization occurs via caveolae-mediated pathways, with cargo localizing to lysosomes.
• Polymyxin-based transporters achieve cytosolic delivery of a toxin.
• Incorporation into liposomes enhances the intracellular uptake of the polymyxin scaffold.

Conclusions:

• The polymyxin scaffold can be modified to facilitate efficient internalization into mammalian cells.
• These novel polymyxin derivatives show significant potential as molecular transporters for intracellular drug delivery.
• Polymyxin and guanidinopolymyxin scaffolds offer promising avenues for targeted intracellular delivery applications.