Cyclophilin Inhibitors

A novel role for the peptidyl-prolyl cis-trans isomerase Cyclophilin A in DNA-repair following replication fork stalling via the MRE11-RAD50-NBS1 complex

Cyclosporin A (CsA) induces DNA double-strand breaks in LIG4 syndrome fibroblasts, specifically upon transit through S-phase. The basis underlying this has not been described. CsA-induced genomic instability may reflect a direct role of Cyclophilin A (CYPA) in DNA repair. CYPA is a peptidyl-prolyl cis-trans isomerase (PPI). CsA inhibits the PPI activity of CYPA. Using an integrated approach involving CRISPR/Cas9-engineering, siRNA, BioID, co-immunoprecipitation, pathway-specific DNA repair investigations as well as protein expression interaction analysis, we describe novel impacts of CYPA loss and inhibition on DNA repair. We characterise a direct CYPA interaction with the NBS1 component of the MRE11-RAD50-NBS1 complex, providing evidence that CYPA influences DNA repair at the level of DNA end resection. We define a set of genetic vulnerabilities associated with CYPA loss and inhibition, identifying DNA replication fork protection as an important determinant of viability. We explore examples of how CYPA inhibition may be exploited to selectively kill cancers sharing characteristic genomic instability profiles, including MYCN-driven Neuroblastoma, Multiple Myeloma and Chronic Myelogenous Leukaemia. These findings propose a repurposing strategy for Cyclophilin inhibitors.

Emerging treatments for hepatitis C

INTRODUCTION

About 2.35% of the world population can be infected with hepatitis C virus (HCV) responsible for chronic hepatitis, liver cirrhosis and hepatocellular carcinoma. Currently available interferon-based medication is successful in up to 75% of the patients infected with HCV genotypes 1, 2 or 3 and lower efficacy in other genotypes. Unfortunately sustained virologic response (SVR) rate in genotype 1 infected non-responders to previous therapy with advanced hepatic fibrosis even after retreatment with the first generation direct acting antivirals (DAA) is about 40% only.

AREAS COVERED

The second generation DAA, which have recently been submitted for registration (Sofosbuvir and Simeprevir) still need combination with PegIFNα and RBV in patients infected with HCV genotype 1. There is a need for more effective antiviral therapy for difficult to treat patients who are interferon intolerant, developed liver cirrhosis or non-responders to previous therapies. Therefore, IFN-free regimens are step for future therapies consisting of combinations of novel investigational DAA and host targeting agents.

EXPERT OPINION

The introduction of novel DAA with a good safety profile and high barrier to resistance can lead to SVR rates exceeding 90% in treatment naïve patients and non-responders to previous therapy infected with different genotypes.

Cyclophilin inhibitors for hepatitis C therapy

This article highlights a unique time in the history of hepatitis C therapy. In the last few years new families of direct-acting antivirals have emerged, that block different viral proteins to interrupt viral replication, such as protease, NS5A inhibitors, and NS5B inhibitors. There are few host-targeted agents in development; currently cyclophilin inhibitors are the only host-targeted agents in advanced development. One of these new agents has now progressed to phase 3 clinical trials; in this review article their potential role as a future therapy to cure hepatitis C is discussed.