Riboflavin-targeted nanomedicines for cancer imaging and drug delivery

  • Riboflavin-funktionalisierte Nanotherapeutika zur bildgebenden Darstellung von Krebs und für den Wirkstofftransport

Tsvetkova, Yoanna; Kießling, Fabian (Thesis advisor); Stahl, Wolfgang (Thesis advisor)

Aachen (2018, 2019)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2018

Abstract

The development of nanomaterials and their physicochemical, in vitro, and in vivo evaluation in preclinical settings have a great impact on the improvement of cancer diagnosis and treatment. Nanomaterials can be used as contrast agents and/or drug delivery systems, and their efficiency in cancer therapy may be improved by their conjugation to a targeting ligand, which specifically binds to cellular receptors overexpressed in the tumor lesion. Riboflavin Transporters (RFT) and Riboflavin Carrier Protein (RCP) are overexpressed by many tumor cells and cells of the malignant stroma. This is why this thesis involves two studies focused on the preclinical evaluation of riboflavin (vitamin B2) as a tumor targeting ligand for nanomaterials. In the first study, flavin mononucleotide (a riboflavin derivative) was grafted on the surface of ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles, used as contrast agents for magnetic resonance imaging (MRI). The riboflavin-targeted USPIOs were further stabilized with different small biomolecules that influenced the size and functionality of the magnetic nanoparticles. The nanoparticles’ uptake by endothelial and numerous cancer cells was evaluated photometricaly and with MRI. The results showed that the surface modification of the contrast agents had a significant influence on the cellular internalization: riboflavin faciliated a receptor-mediated endocytosis of the magnetic nanoparticles by cancer cells, and the amount of targeting ligand on the particles’ surface regulated the degree of cellular uptake. In the second study, the targeting efficiency of riboflavin-functionalized polymers was evaluated in vivo - in mice bearing prostate and epidermoid tumors - using fluorescent molecular and computed tomography. The polymers had different molecular weights and hydrodynamic sizes (10 kDa, DH~6 nm and 40 kDa, DH~14 nm) and, therefore, displayed different pharmacokinetic profiles in terms of plasma residence and volume of distribution. The results led to the hypothesis that targeted drug delivery systems should have the size of diagnostic antibodies (DH~12 nm) in order to display an ideal balance between EPR-based accumulation, sufficient tumor penetration, active binding, and cellular internalization. Riboflavin targeting with drug carriers exhibiting rapid compartmental exchange and fast tissue clearance significantly improved tumor accumulation and cellular uptake in the cancer lesion. On the other hand, riboflavin targeting with long circulating drug carriers improved only their cellular internalization in the malignant lesion and hardly increased their tumor accumulation. In addition, the results showed that already small differences in probe size could influence drug carrier uptake in targeted cell populations in tumors.