RESPIRATORY SYNCYTIAL VIRUS EFFICACY STUDY IN AFRICAN GREEN MONKEYS

Tulane University Of Louisiana, New Orleans LA

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Abstract

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Two studies were conducted in African green monkeys (AGM) to test a proprietary compound (Cpd) formulated by Tibotec Pharmaceuticals against respiratory syncytial virus (RSV) in nonhuman primates. These studies were performed in collaboration with Bioqual, Inc. with animals and veterinary personnel at their facility. My laboratory was to provide not only virus challenge stock but performed all virological testing of samples taken from the animals. The first study was conducted to test the prophylactic and therapeutic efficacy of this compound by continuous intravenous infusion in RSV infected primates at a plasma level of 50 ng/mL. Fifteen AGMs were divided into three groups: 1) the prophylactic (Px50) arm, received 0.033 mg Cpd- 4% aqueous Captisol[unreadable] 24 hours before infection for 10 days, 2) the therapeutic (Tx50) arm, received the same dose at 24 hours post infection for eight days, and 3) the control arm, received vehicle - 4% aqueous Captisol[unreadable] 24 hours after infection for eight days. All fifteen AGMs were challenged with 104 plaque forming units (pfu) per mL RSV A2 intranasally and intratracheally. The AGMs were necropsied 14 days after challenge. Samples of the site of infusion, trachea, and lung were taken for histopathological evaluation. Viral load was determined by means of PCR and culture of nasal and throat swabs and bronchoalveolar lavages (BAL) taken before and during the infection. Blood samples were taken to confirm target exposure and to evaluate the effects of treatment on hematologic, immunological, and plasma chemistry parameters. Furthermore, the animals were observed daily, and their food consumption and body temperatures were monitored. The primary endpoint, RSV RNA viral loads, demonstrated that the prophylactic treatment with compound not only reduced the peak viral load by 1.5 log10 RNA copies per mL but also delayed the peak for two days. The therapeutic treatment only reduced the peak viral load by 1.5 log10 RNA copies per mL with no delay in the peak. From the secondary endpoints, the only difference observed was in the IL-6 levels, which were lower in the prophylactic and therapeutic groups than in the control groups. In conclusion, both prophylactic and therapeutic treatment at a continuous plasma level of 50 ng/mL for 10 and 8 days following infection, respectively, were effective in reducing the peak viral load, but not in preventing RSV infection. A third and final study was conducted to test the prophylactic efficacy of this same compound in RSV infected primates at plasma levels of 5 and 500 ng/mL. Twelve AGMs were divided into three groups: 1) Prophylactic 5 (Px5), received an intravenous infusion of 0.0033 mg / mL Cpd - 4% aqueous Captisol[unreadable] 72 hours before infection for 16 days, 2) Prophylactic 500 (Px500), received an intravenous infusion of 0.33 mg/ml Cpd - 4% aqueous Captisol[unreadable] 72 hours before infection for 16 days, 3) vehicle control group, received an intravenous infusion of 4% Captisol[unreadable] 72 hours before infection for 16 days. All twelve AGMs were challenged with 104 plaque forming units (pfu) per mL RSV A2 intranasally and intratracheally on day 0. The AGMs were necropsied 13 days after challenge. Clinical monitoring was as stated above for the earlier study. Viral loads as determined by PCR showed a similar kinetics in BAL and throat swabs for each of the groups. By culture and PCR, all Px500 animals had undetectable RNA viral loads in BAL and throat swabs rinses except AGM Y459, which showed positive PCR responses in the throat swab rinses and BAL shortly before euthanasia, which was probably due to insufficient distribution of the drug. The Px5 animals did not show a decrease but instead displayed a delayed viral load peak in the BAL and throat swab rinses. Interleukin- (IL-) 6 and IL-8 were suppressed only in the Px500 group, and slightly decreased in the Px5 group compared to the control group. White blood cell (WBC) counts in BAL appeared reduced in the Px500 group compared to the Px5 and vehicle control groups. Histological examination showed very pronounced changes predominantly of an inflammatory nature in the vehicle control group and Px5 group and much less pronounced changes in the Px500 group. In summary, prophylactic treatment of AGMs with a target plasma level of 500 ng/mL for 16 days resulted in the suppression of RSV replication to a level below the lower limit of detection, a clear treatment success. Prophylactic treatment of AGMs with a target plasma level of 5 ng/mL in the same manner did not show an antiviral effect, but demonstrated certain anti-inflammatory properties.