Tumor-Targeted, Cytoplasmic Delivery of Large, Polar Molecules Using a pH-Low Insertion Peptide

Abstract

Tumor-targeted drug delivery systems offer not only the advantage of an enhanced therapeutic index, but also the possibility of overcoming the limitations that have largely restricted drug design to small, hydrophobic, "drug-like" molecules. Here, we explore the ability of a tumor-targeted delivery system centered on the use of pH-low insertion peptide (pHLIP) to directly deliver moderately polar, multi-kDa molecules into tumor cells. A pHLIP is a short, pH-responsive peptide capable of inserting across a cell membrane to form a transmembrane helix at acidic pH. pHLIP targets the acidic tumor microenvironment with high specificity, and a drug attached to the inserting end of pHLIP can be translocated across the cell membrane during the insertion process.

Pharmacokinetic modeling reveals parameters that govern tumor targeting and delivery by a pH-Low Insertion Peptide (pHLIP)

“…This reduction is accompanied by a reduction in the tumor state 3 AUC, which is indicative of the total drug dose delivered by pHLIP. Depending on the amount of cargo needed for a desired effect, the model suggests that there is a practical limit to the useful cargoes that pHLIP is capable of delivering, in agreement with previous results ( 25 ).…”

“…That said, it should be noted that the model’s predicted values assume that the cargo molecule does not affect targeting and delivery. In the majority of cases, this assumption most likely will not hold true, especially with C terminus-linked cargoes, which are known to significantly slow transmembrane insertion ( 24 , 25 ) and also may affect the p K a and cooperativity of insertion and exit. In addition, the cargo molecule may affect serum protein and cell binding, as well as the routes of elimination.…”

“…Cargo molecules on the C terminus of pHLIP can result in a dramatic slowing of transmembrane insertion time ( 24 , 25 ). In addition, many variants of pHLIP have far more rapid transmembrane insertion times than wild-type pHLIP, up to ∼1,000-fold more rapid ( 28 ).…”

“…Nevertheless, when the insertion time is slowed to rates below ∼10 h −1 , as may be the case when a cargo molecule is attached to the C terminus of pHLIP ( 24 , 25 ), a significant effect can be observed. The tumor state 3 concentration of pHLIP is significantly reduced throughout early to mid time points for insertion/exit rates on the order of ≤1 h −1 .…”

Peptide Nucleic Acids and Gene Editing: Perspectives on Structure and Repair

“…In addition to traditional CPPs, recent work has described a strategy to deliver PNAs using a peptide which preferentially accumulates in acidic microenvironments [73,74]. Under physiologic pH, pHLIP (pH (low) insertion peptide)), weakly associates with the cellular membrane [75].…”