The pH Sensitive Atram Peptide Hitchhikes on Human Serum Albumin En Route to Target Diseased Acidic Tissues

Abstract

Our lab developed the acidity triggered rational membrane (ATRAM) peptide to target the acidic extracellular environment of tumors. Biophysical and cellular experiments have shown that the membrane interaction of ATRAM is pH-dependent. Often rapid enzymatic degradation and renal clearance of peptides in vivo restricts their successful application as a drug delivery system. However, our previous mice studies demonstrated that ATRAM has an extended circulation half-life. We hypothesized that ATRAM might be interacting with a blood component that shields the peptide from degradation. Binding assays confirmed that ATRAM binds to human serum albumin (HSA), a plasma protein, with higher affinity than insulin detemir, a clinically used drug, suggesting that it might bind to this protein in the blood stream. Fluorescence studies established that ATRAM interacts reversibly with HSA, as the peptide partitioned to lipid membranes after pre-incubation with HSA. This result suggests that while that peptide can use albumin as a carrier in the blood stream, it will still target and transfer to the cell membrane. Understanding how ATRAM is able to avoid immediate degradation and renal clearance in vivo can broaden the design and application range of peptides as therapeutics.