A peptide comprising an amino acid sequence corresponding to a protein transduction domain (PTD) which has cell−penetrating capacity and a amino acid sequence corresponding to a variable part of the C−terminus of a Ras−like GTPase which has Ras−like GTPase signaling inhibiting capacity. Said peptide for use in a method to inhibit cellular functions mediated by the Ras−like GTPase. Pharmaceutical compositions comprising said peptide. A method for manufacturing an inhibitor of a Ras−like GTPase, comprising analyzing said Ras−like GTPase to determine the amino acid sequence located between the final alpha helix, counting from the N− to the C−terminus, and the CAAX−box or simular motif, if present, or the C−terminus itself when no CAAX−box or simular motif is present, selecting an amino acid sequence corresponding to a natural or artificial protein transduction domain (PTD), and producing a peptide comprising said selected amino acid sequence corresponding to a PTD, which has cell−penetrating capacity, said determined amino acid sequence corresponding to a variable part of the C−terminus of said Ras−like GTPase, which has capacity to inhibit signaling by said Ras−like GTPase, and optionally a spacer between both amino acid sequences.
