Elastin-based protein polymer nanoparticles carrying drug at both corona and core suppress tumor growth in vivo

Abstract

Numerous nanocarriers of small molecules depend on either non-specific physical encapsulation or direct covalent linkage. In contrast, this manuscript explores an alternative encapsulation strategy based on high-specificity avidity between a small molecule drug and its cognate protein target fused to the corona of protein polymer nanoparticles. With the new strategy, the drug associates tightly to the carrier and releases slowly, which may decrease toxicity and promote tumor accumulation via the enhanced permeability and retention effect. To test this hypothesis, the drug Rapamycin (Rapa) was selected for its potent anti-proliferative properties, which give it immunosuppressant and anti-tumor activity. Despite its potency, Rapa has low solubility, low oral bioavailability, and rapid systemic clearance, which make it an excellent candidate for nanoparticulate drug delivery. To explore this approach, genetically engineered diblock copolymers were constructed from elastin-like polypeptides (ELPs) that assemble small (<100 nm) nanoparticles. ELPs are protein polymers of the sequence (Val-Pro-Gly-Xaa-Gly)n, where the identity of Xaa and n determine their assembly properties. Initially, a screening assay for model drug encapsulation in ELP nanoparticles was developed, which showed that Rose Bengal and Rapa have high non-specific encapsulation in the core of ELP nanoparticles with a sequence where Xaa = Ile or Phe. While excellent at entrapping these drugs, their release was relatively fast (2.2 h half-life) compared to their intended mean residence time in the human body. Having determined that Rapa can be non-specifically entrapped in the core of ELP nanoparticles, FK506 binding protein 12 (FKBP), which is the cognate protein target of Rapa, was genetically fused to the surface of these nanoparticles (FSI) to enhance their avidity towards Rapa. The fusion of FKBP to these nanoparticles slowed the terminal half-life of drug release to 57.8 h. To determine if this class of drug carriers has potential applications in vivo, FSI/Rapa was administered to mice carrying a human breast cancer model (MDA-MB-468). Compared to free drug, FSI encapsulation significantly decreased gross toxicity and enhanced the anti-cancer activity. In conclusion, protein polymer nanoparticles decorated with the cognate receptor of a high potency, low solubility drug (Rapa) efficiently improved drug loading capacity and its release. This approach has applications to the delivery of Rapa and its analogues; furthermore, this strategy has broader applications in the encapsulation, targeting, and release of other potent small molecules.

Nanotechnological Approaches to Therapeutic Delivery Using Elastin-Like Recombinamers

“…This system was tested in vitro in a breast cancer model cell line and was found to increase the loading capacity and release, and therefore the anti-cancer activity, of the drug. 60 Additionally, ELR diblocks were designed with the knob protein domain from adenovirus to improve the cellular internalization of the complex. The knob domain binds to the overexpressed adenovirus receptor (CAR), which is widely located in hepatocytes and acinar cells.…”

Genetically engineered nanocarriers for drug delivery

“…In the last 2-3 years, multiple articles have been published focusing on these nanocarriers in the delivery of genes and drugs. 6,26,27,29,31,[41][42][43] …”

“…6 Moreover, FKBP (FK506-binding protein), the cognate receptor of an antiproliferative drug rapamycin (Rapa) has also been genetically fused onto the corona of micelles assembled from the ELP block copolymer ( Figure 3A). 41,42 Because of high-avidity binding of the drug to the receptor, the new fusion protein (FKBP-ELP [FSI]) slowed the terminal half-life of drug release to 57.8 hours ( Figure 3B). 42 The in vivo antitumor and immunosuppressant applications of the new Rapa formulation (FSI-Rapa) were respectively examined in a MDA-MB-468 breast cancer xenograft nude mouse model …”

“…41,42 Because of high-avidity binding of the drug to the receptor, the new fusion protein (FKBP-ELP [FSI]) slowed the terminal half-life of drug release to 57.8 hours ( Figure 3B). 42 The in vivo antitumor and immunosuppressant applications of the new Rapa formulation (FSI-Rapa) were respectively examined in a MDA-MB-468 breast cancer xenograft nude mouse model …”

Elastin-like polypeptides and their applications in anticancer drug delivery systems: a review

“…Shi et al (2013) have investigated the application of a biosynthesized ELP as a nanocarrier. They developed an encapsulation strategy in which Rapamycin associates tightly to an ELP.…”