Unravelling the Secrets of Mycobacterial Cidality through the Lens of Antisense

PLoS One. 2016 May 4;11(5):e0154513. doi: 10.1371/journal.pone.0154513. eCollection 2016.

Abstract

One of the major impediments in anti-tubercular drug discovery is the lack of a robust grammar that governs the in-vitro to the in-vivo translation of efficacy. Mycobacterium tuberculosis (Mtb) is capable of growing both extracellular as well as intracellular; encountering various hostile conditions like acidic milieu, free radicals, starvation, oxygen deprivation, and immune effector mechanisms. Unique survival strategies of Mtb have prompted researchers to develop in-vitro equivalents to simulate in-vivo physiologies and exploited to find efficacious inhibitors against various phenotypes. Conventionally, the inhibitors are screened on Mtb under the conditions that are unrelated to the in-vivo disease environments. The present study was aimed to (1). Investigate cidality of Mtb targets using a non-chemical inhibitor antisense-RNA (AS-RNA) under in-vivo simulated in-vitro conditions.(2). Confirm the cidality of the targets under in-vivo in experimental tuberculosis. (3). Correlate in-vitro vs. in-vivo cidality data to identify the in-vitro condition that best predicts in-vivo cidality potential of the targets. Using cidality as a metric for efficacy, and AS-RNA as a target-specific inhibitor, we delineated the cidality potential of five target genes under six different physiological conditions (replicating, hypoxia, low pH, nutrient starvation, nitrogen depletion, and nitric oxide).In-vitro cidality confirmed in experimental tuberculosis in BALB/c mice using the AS-RNA allowed us to identify cidal targets in the rank order of rpoB>aroK>ppk>rpoC>ilvB. RpoB was used as the cidality control. In-vitro and in-vivo studies feature aroK (encoding shikimate kinase) as an in-vivo mycobactericidal target suitable for anti-TB drug discovery. In-vitro to in-vivo cidality correlations suggested the low pH (R = 0.9856) in-vitro model as best predictor of in-vivo cidality; however, similar correlation studies in pathologically relevant (Kramnik) mice are warranted. In the acute infection phase for the high fidelity translation, the compound efficacy may also be evaluated in the low pH, in addition to the standard replication condition.

MeSH terms

  • Animals
  • Antitubercular Agents / pharmacology
  • Bacterial Load / drug effects
  • Drug Discovery
  • Gene Silencing
  • Genome, Bacterial
  • Host-Pathogen Interactions
  • Humans
  • Male
  • Mice
  • Mice, Inbred BALB C
  • Mycobacterium tuberculosis / drug effects*
  • Mycobacterium tuberculosis / genetics*
  • Mycobacterium tuberculosis / physiology
  • RNA, Antisense / genetics
  • RNA, Antisense / pharmacology
  • Tuberculosis, Pulmonary / drug therapy
  • Tuberculosis, Pulmonary / microbiology

Substances

  • Antitubercular Agents
  • RNA, Antisense

Grants and funding

The authors have no support or funding to report. AstraZeneca India Pvt. Ltd. provided support in the form of salaries for authors PK, RKS, NK, NR, SG, and SN but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section.