Evaluation of RGD-Targeted Albumin Carriers for Specific Delivery of Auristatin E to Tumor Blood Vessels

Abstract

Induction of apoptosis in endothelial cells is considered an attractive strategy to therapeutically interfere with a solid tumor's blood supply. In the present paper, we constructed cytotoxic conjugates that specifically target angiogenic endothelial cells, thus preventing typical side effects of apoptosis-inducing drugs. For this purpose, we conjugated the potent antimitotic agent monomethyl-auristatin-E (MMAE) via a lysosomal cleavable linker to human serum albumin (HSA) and further equipped this drug-albumin conjugate with cyclic c(RGDfK) peptides for multivalent interaction with alphavbeta3-integrin. The RGD-peptides were conjugated via either an extended poly(ethylene glycol) linker or a short alkyl linker. The resulting drug-targeting conjugates RGDPEG-MMAE-HSA and RGD-MMAE-HSA demonstrated high binding affinity and specificity for alphavbeta3-integrin expressing human umbilical vein endothelial cells (HUVEC). Both types of conjugates were internalized by endothelial cells and killed the target cells at low nM concentrations. Furthermore, we observed RGD-dependent binding of the conjugates to C26 carcinoma. Upon i.v. administration to C26-tumor bearing mice, both drug-targeting conjugates displayed excellent tumor homing properties. Our results demonstrate that RGD-modified albumins are suitable carriers for cell selective intracellular delivery of cytotoxic compounds, and further studies will be conducted to assess the antivascular and tumor inhibitory potential of RGDPEG-MMAE-HSA and RGD-MMAE-HSA.

Preparation, characterization, and in vitro targeted delivery of folate-decorated paclitaxel-loaded bovine serum albumin nanoparticles

“…Recent applications of serum albumin (human and bovine) have demonstrated some advantages as a natural and therefore biocompatible and biodegradable carrier for drugs. [12][13][14] The albumin-based drug delivery system has increased the disease tissue/normal tissue drug concentration ratio. Nanoparticles of human serum albumin-bound paclitaxel (Abraxane, an example of nab TM [nanometer albumin-bound] technology), have been approved by the Food and Drug Administration and a Phase III trial of a variety of cancer.…”

Angiogenic endothelium shows lactadherin-dependent phagocytosis of aged erythrocytes and apoptotic cells

“…Polyclonal rabbit anti-RGD antiserum (1:1000) followed by goat anti-rabbit HRP (1:250; Dako) were used for immunostaining of the blotted membranes. 18,19 Scanning electron microscopy HUVECs were fixed with Karnovsky fixative directly after sample incubation and washing. Next, cells were washed with 0.1 M cacodylate buffer followed by OsO4 2%, tanine 1%, and OsO4 1% incubation.…”

Rational Design of RGD–Albumin Conjugates for Targeted Delivery of the VEGF‐R Kinase Inhibitor PTK787 to Angiogenic Endothelium

“…[11,12] We therefore optimized the attachment of the targeting ligand followed by subsequent conjugation of the drug. RGD coupling was carried out with a 22-fold molar excess of N-hydroxysuccinimide ester (SIA) or a 50-fold molar excess of vinylsulfone polyethylene glycol-N-hydroxysuccinimide ester (VS-PEG-NHS, 3.5 kDa) over HSA.…”

“…[7,15] The drug-targeting conjugates demonstrated less inhibition of gene expression compared with free PTK787, which can be explained by different mechanisms of uptake and the required processing of the conjugates by target cells. While the RGD-equipped macromolecular prodrugs require receptor-mediated endocytosis and lysosomal processing for drug release, [12,16] free PTK787 can readily enter any cell by passive diffusion. This difference favors the activity of the free drug in vitro, but at the same time is disadvantageous in vivo relative to targeted drugs that are target-cell specific.…”