An update on emerging drugs for the treatment of erectile dysfunction.

Introduction: Erectile dysfunction is an extremely frequent and extensively studied condition, currently affecting the lives of tens of millions of men around the globe. The extensive knowledge of its pathophysiology has led to the development of phosphodiesterase 5-inhibitors, which can facilitate sexual intercourse in a large number of patients. However, an ever-increasing number of patients is unresponsive to these drugs due to underlying comorbidities or previous surgery. Different molecular pathways need to be addressed to provide treatment for a larger patient population. Areas covered: In this paper, we will review the underlying molecular pathways, discuss already available treatment options and their limitations and provide an overview of the newest therapeutics in development. Centrally and peripherally acting agents will be discussed separately. Additionally, newest advances in regenerative medicine options will be discussed. Expert opinion: Even though novel drugs have not been tested in a phase III setting, several phase II clinical trial results are eagerly awaited. These newest therapeutics could be applied as monotherapy or combination therapy in the subset of patients unresponsive to traditional treatment options.

C3 Transferase Gene Therapy for Continuous RhoA Inhibition.

The identification of RhoA inhibition as a therapeutic target in neurodegenerative diseases and traumatic central nervous system (CNS) injuries has introduced a need to develop tools that effectively modulate intracellular RhoA-dependent signaling. In neurons, the bacterial exoenzyme C3 transferase irreversibly inactivates RhoA GTPase signaling to promote neuritogenesis and axon regeneration following an injury. Thus, we have adopted a gene therapy approach for the targeted inhibition of RhoA activity in the CNS by expressing C3 transferase. Herein we describe the construction of adeno-associated viral vectors for the expression of cell-permeable-C3 transferase and their functional characterization in vitro.

C3 transferase gene therapy for continuous conditional RhoA inhibition.

Regrowth inhibitory molecules prevent axon regeneration in the adult mammalian central nervous system (CNS). RhoA, a small GTPase in the Rho family, is a key intracellular switch that mediates the effects of these extracellular regrowth inhibitors. The bacterial enzyme C3-ADP ribosyltransferase (C3) selectively and irreversibly inhibits the activation of RhoA and stimulates axon outgrowth and regeneration. However, effective intracellular delivery of the C3 protein in vivo is limited by poor cell permeability and a short duration of action. To address this, we have developed a gene therapy approach using viral vectors to introduce the C3 gene into neurons or neuronal progenitors. Our vectors deliver C3 in a cell-autonomous (endogenous) or a cell-nonautonomous (secretable/permeable) fashion and promote in vitro process outgrowth on inhibitory chondroitin sulfate proteoglycan substrate. Further conditional control of our vectors was achieved via the addition of a Tet-On system, which allows for transcriptional control with doxycycline administration. These vectors will be crucial tools for promoting continued axonal regeneration after CNS injuries or neurodegenerative diseases.