Targeting Cancer by Using Nanoparticles to Modulate RHO GTPase Signaling.

Functionalized nanomaterials have recently been introduced as efficient vehicles for targeted delivery of drugs and other tailored molecules to cancer cells. They emerge as new opportunities for addressing particular challenging targets such as RHO guanosine triphosphatases (GTPases), a group of signaling molecules involved in the progression of a variety of tumor types. RHO GTPases comprise a subfamily of the Ras superfamily of small GTPases. They are best known for their role in cell migration through the remodeling of the actin cytoskeleton. However, they are also key regulators of a broad number of cellular functions, ranging from proliferation to cell adhesion and differentiation. Not surprisingly, their dysregulation has been implicated in the development and progression of many types of cancer. The RHO GTPase subfamily includes 20 members that can be further separated into typical and atypical RHO GTPases. The typical RHO family members include the classical RHOA, RAC1 and CDC42 proteins, which cycle between an active GTP-bound and inactive GDP-bound conformation, under the coordinated action of three types of regulators: GEFs, GAPs and GDIs. Atypical RHO family members have small changes in key residues that alter their regulatory mechanisms. Nevertheless, both typical and atypical RHO GTPases contribute to cancer progression but, in contrast to Ras proteins, very few mutations have been found in tumors. In most cancers, it is the expression level and/or activity of RHO GTPases that is dysregulated. RHO GTPase signaling has thus long been seen as an attractive target for cancer treatment but their ubiquity and the lack of isoform-specific drugs have posed significant obstacles to the development of viable therapeutic strategies. Based on the success of recent nanomedicine approaches, this chapter reviews representative studies of how functionalized nanoparticles can be designed to target tumor-specific molecules and directly or indirectly modulate the expression and/or activity of particular RHO GTPases in cancer cells.