Evolutionary trade-offs associated with loss of PmrB function in host-adapted Pseudomonas aeruginosa.

Pseudomonas aeruginosa colonises the upper airway of cystic fibrosis (CF) patients, providing a reservoir of host-adapted genotypes that subsequently establish chronic lung infection. We previously experimentally-evolved P. aeruginosa in a murine model of respiratory tract infection and observed early-acquired mutations in pmrB, encoding the sensor kinase of a two-component system that promoted establishment and persistence of infection. Here, using proteomics, we show downregulation of proteins involved in LPS biosynthesis, antimicrobial resistance and phenazine production in pmrB mutants, and upregulation of proteins involved in adherence, lysozyme resistance and inhibition of the chloride ion channel CFTR, relative to wild-type strain LESB65. Accordingly, pmrB mutants are susceptible to antibiotic treatment but show enhanced adherence to airway epithelial cells, resistance to lysozyme treatment, and downregulate host CFTR expression. We propose that P. aeruginosa pmrB mutations in CF patients are subject to an evolutionary trade-off, leading to enhanced colonisation potential, CFTR inhibition, and resistance to host defences, but also to increased susceptibility to antibiotics.

Orally Bioavailable and Blood-Brain Barrier-Penetrating ATM Inhibitor (AZ32) Radiosensitizes Intracranial Gliomas in Mice.

Inhibition of ataxia-telangiectasia mutated (ATM) during radiotherapy of glioblastoma multiforme (GBM) may improve tumor control by short-circuiting the response to radiation-induced DNA damage. A major impediment for clinical implementation is that current inhibitors have limited central nervous system (CNS) bioavailability; thus, the goal was to identify ATM inhibitors (ATMi) with improved CNS penetration. Drug screens and refinement of lead compounds identified AZ31 and AZ32. The compounds were then tested in vivo for efficacy and impact on tumor and healthy brain. Both AZ31 and AZ32 blocked the DNA damage response and radiosensitized GBM cells in vitro AZ32, with enhanced blood-brain barrier (BBB) penetration, was highly efficient in vivo as radiosensitizer in syngeneic and human, orthotopic mouse glioma model compared with AZ31. Furthermore, human glioma cell lines expressing mutant p53 or having checkpoint-defective mutations were particularly sensitive to ATMi radiosensitization. The mechanism for this p53 effect involves a propensity to undergo mitotic catastrophe relative to cells with wild-type p53. In vivo, apoptosis was >6-fold higher in tumor relative to healthy brain after exposure to AZ32 and low-dose radiation. AZ32 is the first ATMi with oral bioavailability shown to radiosensitize glioma and improve survival in orthotopic mouse models. These findings support the development of a clinical-grade, BBB-penetrating ATMi for the treatment of GBM. Importantly, because many GBMs have defective p53 signaling, the use of an ATMi concurrent with standard radiotherapy is expected to be cancer-specific, increase the therapeutic ratio, and maintain full therapeutic effect at lower radiation doses. Mol Cancer Ther; 17(8); 1637-47. ©2018 AACR.

A shutoff and exonuclease mutant of murine gammaherpesvirus-68 yields infectious virus and causes RNA loss in type I interferon receptor knockout cells.

Significant loss of RNA followed by severely reduced cellular protein pool, a phenomenon termed host shutoff, is associated with a number of lytic virus infections and is a critical player in viral pathogenesis. Until recently, viral DNA exonucleases were associated only with processing of viral genomic DNA and its encapsidation. However, recent observations have identified host shutoff and exonuclease function for the highly conserved viral exonucleases in γ-herpesviruses, which include Kaposi's sarcoma-associated herpesvirus, Epstein-Barr virus and the mouse model murine gammaherpesvirus-68, also referred to as MHV-68. In this study, we show that although ablation of the MHV-68 exonuclease ORF37 caused a restrictive phenotype in WT IFN-α/ß receptor-positive cells such as NIH 3T3, lack of ORF37 was tolerated in cells lacking the IFN-α/ß receptor: the ORF37Stop virus was capable of forming infectious particles and caused loss of mRNA in IFN-α/ß receptor knockout cells. Moreover, ORF37Stop virus was able to establish lytic infection in the lungs of mice lacking the IFN-α/ß receptor. These observations provide evidence that lytic MHV-68 infection and subsequent loss of mRNA can take place independently of ORF37. Moreover, efficient growth of ORF37Stop virus also identifies a role for this family of viral nucleases in providing a window of opportunity for virus growth by overcoming type I IFN-dependent responses.