Improving the Stability of EGFR Inhibitor Cobalt(III) Prodrugs.

Marlene Mathuber,Éva A. Enyedy,Petra Heffeter,Hemma Schueffl,Orsolya Dömötör,Claudia Karnthaler,Christian R. Kowol,Bernhard K. Keppler

doi:10.1021/acs.inorgchem.0c03083

Marlene Mathuber, Éva A. Enyedy + Show 6 more

Open Access

https://doi.org/10.1021/acs.inorgchem.0c03083

Copy DOI

Abstract

Although tyrosine kinase inhibitors (TKIs) have revolutionized cancer therapy in the past two decades, severe drawbacks such as strong adverse effects and drug resistance limit their clinical application. Prodrugs represent a valuable approach to overcoming these disadvantages by administration of an inactive drug with tumor-specific activation. We have recently shown that hypoxic prodrug activation is a promising strategy for a cobalt(III) complex bearing a TKI of the epidermal growth factor receptor (EGFR). The aim of this study was the optimization of the physicochemical properties and enhancement of the stability of this compound class. Therefore, we synthesized a series of novel derivatives to investigate the influence of the electron-donating properties of methyl substituents at the metal-chelating moiety of the EGFR inhibitor and/or the ancillary acetylacetonate (acac) ligand. To understand the effect of the different methylations on the redox properties, the newly synthesized complexes were analyzed by cyclic voltammetry and their behavior was studied in the presence of natural low-molecular weight reducing agents. Furthermore, it was proven that reduction to cobalt(II) resulted in a lower stability of the complexes and subsequent release of the coordinated TKI ligand. Moreover, the stability of the cobalt(III) prodrugs was investigated in blood serum as well as in cell culture by diverse cell and molecular biological methods. These analyses revealed that the complexes bearing the methylated acac ligand are characterized by distinctly enhanced stability. Finally, the cytotoxic activity of all new compounds was tested in cell culture under normoxic and various hypoxic conditions, and their prodrug nature could be correlated convincingly with the stability data. In summary, the performed chemical modifications resulted in new cobalt(III) prodrugs with strongly improved stabilities together with retained hypoxia-activatable properties.

Highlights

The epidermal growth factor receptor (EGFR) belongs to the family of receptor tyrosine kinases, a group of proteins that are responsible for numerous signal transduction processes in the human body.[1]
To design an EGFR inhibitor that can coordinate to cobalt(III), we used in our previous study the typical quinazoline ring of most approved EGFR inhibitors but modified the 6 position by introducing an ethylenediamine (“en”) type metal-binding moiety [L (Scheme 1)]
The cobalt(III) complexes were synthesized by reaction of Na[Co(acac)2(NO2)2] or Na[Co(Meacac)2(NO2)2] with L or MeL in a water/methanol mixture in the presence of activated charcoal following a procedure described by Denny et al.[21] (Scheme 1)

Summary

Introduction

The epidermal growth factor receptor (EGFR) belongs to the family of receptor tyrosine kinases, a group of proteins that are responsible for numerous signal transduction processes in the human body (e.g., cell growth, differentiation, and metabolism).[1]. As a result of this intensive research, several small-molecule or antibody inhibitors targeting the EGFR have been clinically developed mainly for NSCLC treatment.[6] The mode of action of low-molecular weight EGFR tyrosine kinase inhibitors (TKIs) is the (ir)reversible binding into the ATP-binding pocket, which hampers the activation of the downstream signaling [e.g., phosphorylation of extracellular signal-regulated kinases (ERKs)].7. Erlotinib (in combination with gemcitabine) is approved for advanced and metastatic pancreatic cancer.[8]

Objectives

Results

Conclusion