Protease Responsive Nanogels for Transcytosis across the Blood-Brain Barrier and Intracellular Delivery of Radiopharmaceuticals to Brain Tumor Cells

Despite profound advances in treatment approaches, gliomas remain associated with very poor prognoses. The residual cells after incomplete resection often migrate and proliferate giving a seed for highly resistant gliomas. The efficacy of chemotherapeutic drugs is often strongly limited by their poor selectivity and the blood brain barrier (BBB). Therefore, the development of therapeutic carrier systems for efficient transport across the BBB and selective delivery to tumor cells remains one of the most complex problems facing molecular medicine and nano-biotechnology. To address this challenge, a stimuli sensitive nanogel is synthesized using pre-polymer approach for the effective delivery of nano-irradiation. The nanogels are cross-linked via matrix metalloproteinase (MMP-2,9) substrate and armed with Auger electron emitting drug 5-[¹²⁵ I]Iodo-4"-thio-2"-deoxyuridine ([¹²⁵ I]ITdU) which after release can be incorporated into the DNA of tumor cells. Functionalization with diphtheria toxin receptor ligand allows nanogel transcytosis across the BBB at tumor site. Functionalized nanogels efficiently and increasingly explore transcytosis via BBB co-cultured with glioblastoma cells. The subsequent nanogel degradation correlates with up-regulated MMP2/9. Released [¹²⁵ I]ITdU follows the thymidine salvage pathway ending in its incorporation into the DNA of tumor cells. With this concept, a highly efficient strategy for intracellular delivery of radiopharmaceuticals across the challenging BBB is presented.

Bacterial Growth Inhibition Screen (BGIS) identifies a loss-of-function mutant of the DEK oncogene, indicating DNA modulating activities of DEK in chromatin

The DEK oncoprotein regulates cellular chromatin function via a number of protein-protein interactions. However, the biological relevance of its unique pseudo-SAP/SAP-box domain, which transmits DNA modulating activities in vitro, remains largely speculative. As hypothesis-driven mutations failed to yield DNA-binding null (DBN) mutants, we combined random mutagenesis with the Bacterial Growth Inhibition Screen (BGIS) to overcome this bottleneck. Re-expression of a DEK-DBN mutant in newly established human DEK knockout cells failed to reduce the increase in nuclear size as compared to wild type, indicating roles for DEK-DNA interactions in cellular chromatin organization. Our results extend the functional roles of DEK in metazoan chromatin and highlight the predictive ability of recombinant protein toxicity in E. coli for unbiased studies of eukaryotic DNA modulating protein domains.

Bacterial Growth Inhibition Screen (BGIS): harnessing recombinant protein toxicity for rapid and unbiased interrogation of protein function

In two proof-of-concept studies, we established and validated the Bacterial Growth Inhibition Screen (BGIS), which explores recombinant protein toxicity in Escherichia coli as a largely overlooked and alternative means for basic characterization of functional eukaryotic protein domains. By applying BGIS, we identified an unrecognized RNA-interacting domain in the DEK oncoprotein (this study) and successfully combined BGIS with random mutagenesis as a screening tool for loss-of-function mutants of the DNA modulating domain of DEK [1]. Collectively, our findings shed new light on the phenomenon of recombinant protein toxicity in E. coli. Given the easy and rapid implementation and wide applicability, BGIS will extend the repertoire of basic methods for the identification, analysis and unbiased manipulation of proteins.

Impact of Glutathione Modulation on Stability and Pharmacokinetic Profile of Redox-Sensitive Nanogels

Nanoparticles degradable upon external stimuli combine pharmacokinetic features of both small molecules as well as large nanoparticles. However, despite promising preclinical results, several redox responsive disulphide-linked nanoparticles failed in clinical translation, mainly due to their unexpected in vivo behavior. Glutathione (GSH) is one of the most evaluated antioxidants responsible for disulfide degradation. Herein, the impact of GSH on the in vivo behavior of redox-sensitive nanogels under physiological and modulated conditions is investigated. Labelling of nanogels with a DNA-intercalating dye and a radioisotope allows visualization of the redox responsiveness at the cellular and the systemic levels, respectively. In vitro, efficient cleavage of disulphide bonds of nanogels is achieved by manipulation of intracellular GSH concentration. While in vivo, the redox-sensitive nanogels undergo, to a certain extent, premature degradation in circulation leading to rapid renal elimination. This instability is modulated by transient inhibition of GSH synthesis with buthioninsulfoximin. Altered GSH concentration significantly changes the in vivo pharmacokinetics. Lower GSH results in higher elimination half-life and altered biodistribution of the nanogels with a different metabolite profile. These data provide strong evidence that decreased nanogel degradation in blood circulation can limit the risk of premature drug release and enhance circulation half-life of the nanogel.