Development of new potential antitumor drugs based on Ras protein inhibition

Because of their role in oncogenesis, inhibition of Ras proteins, particularly of their tumorigenic variants, represents today one of the principal strategies finalized to the obtainment of new antitumoral therapies. Among the different possible approaches, one of the most innovative and less explored is represented by the inhibition of this protein activation, key event for the explication of their biological activity, but also for the Ras-induced tumoral cell transformation. Objective of this thesis has been the development of new small molecules able to inhibit, at least partially (total inhibition in fact would result lethal for cell), Ras protein activation, in particular the GEFs-promoted GDP/GTP nucleotide exchange. Inhibitors able of inactivating Ras have been previously described by Schering-Plough. All these molecules contain a phenylhydroxylamino group that binds Ras in a region close to the nucleotide binding site and one aromatic group. Nevertheless, they present some negative characteristics that prevent their employment as potential drugs: (1) they are chemically unstable and (2) they are insoluble in water and in the most commonly used organic solvents. In order to obtain new more efficient inhibitors, we adopted the rational drug design strategy. Firstly, we studied the structure-activity relationship (SAR) of Schering-Plough compounds and of new molecules containing variants of their functional groups that we designed and synthesized. The data collected demonstrated that the phenylhydroxylamino group is an essential pharmacophore, while other positions are not so critical for the biological activity.Keeping in mind this, we prepared new compounds in which the phenylhydroxylamino moiety is supported on glycidic templates, in an attempt to try to take advantage of carbohydrate capability of orienting substituents in space, in this case in a suitable manner for the interaction with Ras proteins. In addition, the sugar portion can improve compound pharmacokinetic properties and decrease their toxicity. In this way, a new class of Ras inhibitors was obtained, their biological activity and the nature of their interaction with the molecular target were characterized.