Using siRNA in Prophylactic and Therapeutic Regimens Against SARS Coronavirus in Rhesus Macaque

Bao-jian Li; Qingquan Tang; Du Cheng; Chuan Qin; Frank Y Xie; Qiang Wei; Jun Xu; Yijia Liu; Bo-jian Zheng; Martin C Woodle; Nanshan Zhong; Patrick Y Lu

Disclosures

Nat Med. 2005;11(9):944-951. 

In This Article

Abstract and Introduction

Development of therapeutic agents for severe acute respiratory syndrome (SARS) viral infection using short interfering RNA (siRNA) inhibitors exemplifies a powerful new means to combat emerging infectious diseases. Potent siRNA inhibitors of SARS coronavirus (SCV) in vitro were further evaluated for efficacy and safety in a rhesus macaque (Macaca mulatta) SARS model using clinically viable delivery while comparing three dosing regimens. Observations of SARS-like symptoms, measurements of SCV RNA presence and lung histopathology and immunohistochemistry consistently showed siRNA-mediated anti-SARS efficacy by either prophylactic or therapeutic regimens. The siRNAs used provided relief from SCV infection-induced fever, diminished SCV viral levels and reduced acute diffuse alveoli damage. The 10-40 mg/kg accumulated dosages of siRNA did not show any sign of siRNA-induced toxicity. These results suggest that a clinical investigation is warranted and illustrate the prospects for siRNA to enable a massive reduction in development time for new targeted therapeutic agents.

The outbreak of SARS has posed an urgent need to understand its disease pathogenesis[1,2,3] and the biology of its causative agent, now identified as SCV.[4,5,6,7,8] Individuals with SARS usually develop a high fever followed by severe clinical symptoms including acute respiratory distress syndrome with a diffuse alveolar damage (DAD) at autopsy.[2,4,9] The containment of SARS has been achieved largely through traditional quarantine and sanitation measures.[9,10] Because SARS is a newly emerging disease, a safe and effective vaccine is not yet available,[11] although some candidate vaccines have been advanced to monkey models and clinical testing.[12,13,14,15] To treat individuals with SARS, combinations of existing drugs, including ribavirin, antibiotics, anti-inflammatory steroids and immune stimulators, have achieved some clinical success.[16,17,18] Many ongoing efforts to develop SARS-specific drugs, such as screening of small-molecule inhibitors and current biologic approaches, will clarify the strengths and weaknesses of each approach, based on the ultimate success rate and the time and cost incurred.[19,20]

The identification of SCV as the causative pathogen of SARS was achieved mainly by demonstration that exposure of cynomolgus macaques to SCV resulted in symptoms similar to those of individuals with SARS.[1,2] Meanwhile, development of macaque models became important not only for understanding SARS pathogenesis but also for evaluation of potential vaccines and therapeutics.[11,12,13,16,19,20] Recently, a Rhesus macaque SARS model was established with intranasal instillation of SCV strain PUMC01, showing many elements of pathology similar to those of individuals with SARS.[21,22] The pathogenesis includes elevated body temperature, low appetite and acute DAD clearly visible at 7 d after infection (d.p.i.), but with somewhat worse severity than other macaque SARS models,[19,20] offering an ideal model for evaluation of therapeutic candidates.

The search for developing antiviral agents directly from viral genome sequences has led to short interfering RNA (siRNA), the mediator of a sequence-selective inhibition known as RNA interference (RNAi).[23] We reported a screen of 48 siRNA candidates targeting elements throughout the entire SCV genome and identified several siRNAs active in SCV-infected fatal Rhesus monkey kidney (FRhK-4) cells,[24] distinct from other active siRNA reported by other labs.[25,26,27,28] However, translation of in vitro siRNA activity into clinically useful therapeutics depends on a clinically acceptable means for administration. Therefore, siRNAs showing prominent prophylactic and therapeutic activity in cell culture,[24] referred to as siSC2 and siSC5, were further evaluated in vivo, first using a reporter gene assay in mice and subsequently using a clinically acceptable intranasal administration in the recently established Rhesus macaque SARS model.[21,22] The study provided strong evidence that these siRNA agents are potent both for prophylactic and therapeutic treatment of SARS infection, and they lack toxicity in this nonhuman primate model. The results support the growing expectation that siRNA can fulfill the need for moving rapidly from gene sequence to targeted therapeutic agents for many previously intractable disease targets.

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