Development of a Negative-Biased Zwitterionic Polypeptide-Based Nanodrug Vehicle for pH-Triggered Cellular Uptake and Accelerated Drug Release

Abstract

Albumin mimics could be an attractive platform for nanodrug carriers through systematic administration because of high safety and plentiful properties to be adjusted for a high drug efficacy, such as pH-triggered targeting cellular uptake and drug release. In this work, negative-biased zwitterionic nanodrug carriers based on zwitterionic polypeptide chains that mimic albumin were prepared, which have an outermost layer of zwitterionic glutamic acid (E) and lysine (K) pairs with a small amount of aspartic acid (D) to adjust the overall ζ potential. On the other hand, doxorubicin (Dox) was encapsulated in a hydrophobic core by 11-maleimidoundecanoic acid covalently linked with additional cysteine (C) residues on the polypeptide. The results show that the negative-biased zwitterionic nanodrug carriers can sensitively enhance the cellular uptake in responding to a pH change from 7.4 to 6.7 without reversing the ζ potential to a positive charge, leading to accelerating the Dox release rate in a slightly acidic environment through the polypeptide secondary structure change. Moreover, the anionic nanodrug carrier can also be easily enzymatically digested by trypsin for quick drug release. In short, this negative-biased zwitterionic nanodrug delivery vector could be an ideal candidate for a safer tumor inhibition with a high efficacy than conventional synthetic polymer-based ones.

Development of an Integrated High Serum Stability Zwitterionic Polypeptide-Based Nanodrug with Both Rapid Internalization and Endocellular Drug Releasing for Efficient Targeted Chemotherapy

“…The composition of D and C in the product was slightly higher than the feeding composition since smaller D and C monomers have higher reactivity than EK units in a polymerization process. The additional 15% (mol/mol) D of EK was introduced in the polypeptide for enhancing the drug loading efficiency of the positively charged DOX and stabilizing the final nanodrug in blood …”

“…Moreover, after lowering the pH to 5.5, the reduction of charge attractions due to the protonation of carboxyl groups and the full protonation of amino groups on DOX accelerates the release of DOX. The further destabilization of the hydrophobic core by the cleavage of the MAs from P­(EK-D-C) peptide chains after adding 10 mM GSH also accelerates the release rate, which might be the reason for the much quicker release than similar systems with noncleavable long-chain alkanoic acid …”

“…The additional 15% (mol/mol) D of EK was introduced in the polypeptide for enhancing the drug loading efficiency of the positively charged DOX and stabilizing the final nanodrug in blood. 32 The deprotection of -Trt and -Z groups was carried out in harsh acidic conditions using a cocktail solution of 33 wt % HBr/HOAc and TFA in a 2:1 ratio. The additional PyS-SPy in the deprotection solution can convert the -S-Trt on Cs to -S- SPy, which was confirmed from the 1 H NMR analysis (Figure S2).…”

“…In this work, the zwitterionic polypeptide-based nanodrugs (P­(EK-D-CMA)-DOX) were prepared from the peptides containing glutamyl lysine (EK dimer) with a definite amount of aspartic acid (D) and cysteine (C) residues to address the challenge mentioned above. The portion of D is designed to tune the negative charge of the nanodrugs to improve resistance to nonspecific protein adsorption at physiological pH 7.4 and enhance the cellular uptake and pH-triggered tumor targeting in slightly acidic tumor microenvironments. , The reductive disulfide bond conjugation between thiol groups of the C residue and long alkyl chain n -mercaptoalkanoic acid (MA) is designed to form a hydrophobic core for the encapsulation of hydrophobic DOX, as well as accelerate DOX release when exposed to the high GSH concentration of the tumor cell cytoplasm . In this way, the DOX can be quickly released in tumor cells when the nanodrugs internalized through either an endosome/lysosome pathway or direct penetration of the plasma membrane due to the pH-sensitive release of DOX caused by its protonation and the destabilization of micelle caused by the digestion of peptide bonds in the endosome/lysosome or reduction of disulfide bonds between the P­(EK-D-C) and MA, respectively.…”

Zwitterionic Polypeptide-Based Nanodrug Augments pH-Triggered Tumor Targeting via Prolonging Circulation Time and Accelerating Cellular Internalization

“…The reason for the additional sulfo groups was to balance the positive charge accumulation caused by the conjugated Dox, as well as make the nanodrug vehicles sensitive to targeting the PSA on the tumor cell membranes in the slightly acidic microenvironment of solid tumor . The enzymatically digestible polypeptide chain can not only accelerate the loaded Dox release in tumor cells to improve inhibition efficacy but also lower the safety concern about the accumulation of polymers in health cells. Moreover, glutamatyl-lysine dimers with benzyloxycarbonyl (Z)-protected side chain groups were used in copolymerization to ensure homogenous distribution of both glutamic acid and lysine residues to mimic the feature surface structure of plasma proteins .…”