Research

Optimization of nitroxoline-based inhibitors of cathepsin B as potential drugs for the treatment of cancer

Code:

Z1-7181

Range:

01. January 2016 - 31. December 2017

Range:

1,00 FTE

Leader:

Izidor Sosič

Field:

1-09 Natural sciences and Mathematics - Pharmacy

Abstract:

Human cathepsin B is a lysosomal cysteine protease that has many house-keeping functions, such as intracellular proteolysis. It can act as both an endopeptidase and an exopeptidase, a characteristic that is attributed to a 21-amino-acid insertion above the active site. Dysregulation of cathepsin B activity is associated with many pathological states. The most thoroughly studied is its involvement in cancer, where its essential role in the proteolytic processes that lead to tumour invasion and metastasis has been established. Metastatic progression still remains the biggest challenge in the development of effective therapies for the treatment of cancer. With respect to the important pharmacological relevance of cathepsin B, the discovery of new small-molecule inhibitors that can bind selectively and reversibly into its active site needs to be given substantial emphasis. However, none of the currently identified cathepsin B inhibitors are in clinical use, due to poor bioavailability, off-target effects, and high toxicity. The reasons for this are associated with the chemical nature of these compounds, as they contain a peptide backbone and a highly reactive electrophilic functional group that interacts with the catalytic cysteine and irreversibly inactivates the enzyme. Recently, we discovered that nitroxoline (5-nitro-8-hydroxyquinoline) is a non-covalent, reversible, low-micromolar inhibitor of cathepsin B. Its applicability was demonstrated in cell-based assays and in in vivo models. The new mechanism of cysteine protease inhibition and the resolved nitroxoline-cathepsin B co-crystal structure represent a template for the rational structure-based improvement of the inhibitory activities of novel cathepsin B inhibitors. It is known that more potent lead compounds in vitro have greater potential to be successfully developed into clinical candidates, and subsequently into drugs that achieve their therapeutic effects at the correct doses. The ultimate goals of the Project are: (i) to design, develop and synthesise nitroxoline derivatives with optimised pharmacodynamic properties; (ii) to optimise the pharmacokinetic (ADME) properties of new inhibitors; and (iii) to determine the effects of cathepsin B inhibition on the reduction of tumour progression processes in in vitro and in vivo models. To achieve these goals, the PI will initially use computer-aided structure-based design. Using this approach, the essential structural elements required for enhanced biological activity will be predicted (i.e., appropriate side chains, functional groups). Special focus will be addressed to a correctly positioned functional group in the molecule that can form reversible covalent interactions with the catalytic cysteine in the cathepsin B active site. As it is known that the ADME (i.e., absorption, distribution, metabolism, excretion) parameters are equally relevant to potency in lead compound optimisation, the appropriate physico-chemical properties of new compounds will be continually monitored during the design process. Based on all assembled information, the appropriate nitroxoline derivatives will be synthesised. Selective cathepsin B inhibitors developed within the Project will be optimised in terms of their pharmacodynamic and pharmacokinetic properties. Finally, the influence of efficient cathepsin B inhibition by the prepared compounds on in vitro and in vivo anti-tumour activity will be experimentally established through comprehensive biochemical and biological evaluations. In this way, we will be able to determine the full therapeutic potential of cathepsin B inhibition as a cancer treatment approach. Therefore, these advanced lead compounds or clinical candidates will be of paramount scientific, economical and healthcare importance, as they will serve as a valuable contribution in the permanent battle against cancer.