Synthesis and biological evaluation of Cyclin G-associated Kinase inhibitors

Promovendus/a: Randy Wouters

Promotor(en): Prof. dr. Piet Herdewyn (promotor), De heer Steven De Jonghe (co-promotor)

Dengue virus is the causative agent of dengue, one of the world’s most neglected tropical diseases. Dengue’s incidence has increased >30-fold in the last 50 years with recent estimates suggesting up to 390 million infections every year counting up to 21.000 deaths As there is currently no treatment for dengue, there is an unmet need for strategies to combat the disease.

Cyclin G-associated kinase (GAK), a cellular regulator of the clathrin-associated host adaptor proteins AP1 and AP2, was reported to regulate intracellular trafficking of multiple unrelated RNA viruses, including dengue virus, during early and late stages of the viral lifecycle. The lab of medicinal chemistry at KU Leuven reported the discovery of potent and selective GAK inhibitors based on an isothiazolo[4,3-b]pyridine scaffold, albeit with moderate antiviral activity

In this PhD thesis we describe the extensive exploration of the SAR of isothiazolo[4,3-b]pyridines in order to maintain potent GAK affinity and selectivity, and also improve the antiviral activity.

In a first part, efforts leading to the discovery of novel isothiazolo[4,3-b]pyridines that maintain high GAK affinity and selectivity are described. These compounds demonstrate improved in vitro activity against dengue virus, and they show efficacy against the unrelated Ebola and chikungunya viruses. Moreover, inhibition of GAK activity was validated as an important mechanism of antiviral action of these compounds. These findings demonstrate the potential utility of a GAK-targeted broad-spectrum approach for combating currently untreatable emerging viral infections.

In a second part, the influence of carbon linked substituents at position 3 of the isothiazolo[4,3-b]pyridine scaffold on GAK affinity and dengue virus activity is explored. Here, the regioselective introduction of aryl and alkynyl moieties (at position 3 of the scaffold) by Suzuki and Sonogashira coupling reactions, respectively, is described. One of the synthesized compounds is endowed with low nanomolar binding affinity for GAK, demonstrating that appropriate substitution of a phenyl moiety at position 3 of the scaffold allows to improve GAK binding affinity. The last part of this thesis describes a scaffold hopping approach. Scaffold hopping is a widely applied medicinal chemistry strategy in which the core skeleton of lead molecules is subjected to bioisosteric replacements. Based on the original isothiazolo[4,3-b]pyridine scaffold, a number of 5,6- and 6,6- fused bicyclic heteroaromatic scaffolds were synthesized. From the 13 novel scaffolds, four of them displayed GAK affinity with Kd values in the low micromolar range. Only one derivative was endowed with potent antiviral activity for dengue virus, despite it having rather weak GAK inhibition. This chapter also describes the synthesis of new scaffolds that are underrepresented in organic/medicinal chemistry.