Novel chemical tools for Cancer therapy and imaging: from targeted photoactivatable Pt(IV) complexes to coumarin-based fluorophores and caging groups

Abstract

In the present Thesis, it has been carried out the development of new chemical tools for the diagnosis and treatment of cancer through the use of light as an external factor. On the one hand, light can be used to control, with high spatiotemporal precision, the activation of a molecule (either the release of cytotoxic species from an inactive pro-drug or the removal of a photocleavable protecting group from a key functionality), as well as to visualize biological events in vivo by using suitable fluorophores. On the other hand, the conjugation of photoactivatable cytotoxic drugs and/or fluorescent probes to targeting ligands can be used to develop novel highly selective anticancer drugs and imaging agents.

First, owing to the potential of photoactivatable Pt(IV) complexes as an alternative to current cisplatin-based anticancer drugs, one of the main objectives of this Thesis was to explore the conjugation of trans,trans,trans-[Pt(N3)2(OH)2(py)2] to targeting ligands (c(RGDfK) and folic acid) whose receptors are overexpressed on tumor cells, with the aim of developing novel anticancer agents with dual selectivity. In addition, we explored the photoactivation of the Pt(IV)-peptide/folate conjugates under visible light irradiation and the biological properties of the Pt(IV)-RGD conjugate (photoxicity and cellular uptake).

The approach of using photocleavable protecting groups to regulate the activity of a given molecule has found widespread applications when caging biologically-relevant compounds, from small organic drugs and metal complexes to large biomolecules such as peptides, proteins and oligonucleotides. In such a context, in this Thesis was related with dicyanocoumarins, specifically we design and synthesize a series of 7-N,N-diethylamino-dicyanocoumarinylmethyl (DEAdcCM) and 7-N,N-diethylamino-dicyanocoumarinylethyl (DEAdcCE) caged model compounds and we studied the photophysical and photochemical properties of DEAdcCM- and DEAdcCE-caged model compounds.

Moreover, we synthesized a dicyanocoumarin-caged cyclic RGD peptide and its conjugate to ruthenocene and study the photolysis of the dicyanocoumarin-caged peptide and its ruthenocenoyl conjugate.

Finally, the need for understanding essential recognition events in Chemical Biology has directed considerable efforts in recent years towards the development of novel fluorescent dyes based on small organic molecules. In addition, owing to their potential applications in medical diagnoses and in fluorescence-guided surgery, the availability of ligand-targeted fluorescent probes operating in the far-red and near- infrared region is a priority challenge for combating cancer disease. Hence, in the present Thesis was to red-shift absorption and emission maxima of the conventional coumarin scaffold, for this reason we design, synthesize and characterize a new family of coumarin-based scaffolds with an extended pi-conjugation system through position 2, and novel push-pull fluorophores (COUPYs) through N-alkylation of the pyridine heterocycle incorporated at position 2 of the coumarin scaffold. Finally, we explored its conjugation to targeting ligands based on octreotide, a FDA-approved synthetic cyclooctapeptide with high affinity and selectivity for somatostatin subtype-2 receptor (SSTR2).

En esta tesis doctoral, se han desarrollado nuevas herramientas químicas basadas en el empleo de la luz como elemento regulatorio y de diagnóstico. En primer lugar, se exploró la conjugación de un complejo de Pt(IV) fotoactivable a vehículos selectivos de ciertas células tumorales, como el péptido cíclico c(RGDfK), selectivo de ciertas integrinas, y un derivado de ácido fólico que presenta afinidad por los receptores folato. Posteriormente, se abordaron los estudios de fotoactivación del pro-fármaco con luz visible y su evaluación biológica en diferentes líneas celulares.

Por otro lado, se diseñó y sintetizó una nueva familia de grupos protectores fotolábiles basados en el esqueleto de cumarina, los cuales pueden ser eliminados con luz verde. Ello permitió sintetizar un derivado del péptido c(RGDfK) protegido con un derivado de dicianocumarina, así como su conjugado a un metalofármaco modelo, rutenoceno.

Finalmente, se desarrolló una nueva familia de fluoróforos basados en cumarina, denominados COUPY, que operan en la región que va del rojo lejano al infrarrojo cercano (NIR). Dichos marcadores fluorescentes permitieron marcar selectivamente el péptido octreotide en fase sólida y visualizar células tumorales que sobre-expresan su receptor.