Low-dose aerosol infection model for testing drugs for efficacy against Mycobacterium tuberculosis

Abstract

As a paradigm for chronic infectious diseases, tuberculosis exhibits a variety of clinical presentations, ranging from primary pulmonary tuberculosis to reactivation tuberculosis and cavitary disease. To date, the animal models used in evaluating chemotherapy of tuberculosis have been high-dose intravenous models that mimic the disseminated forms of the disease. In the present study, we have used a low-dose aerosol exposure model which we feel better reflects newly diagnosed tuberculosis in patients converting to tuberculin positivity. As appropriate examples of chemotherapy, four rifamycins (rifampin, rifabutin, rifapentine, and KRM-1648) were tested, first in an in vitro murine macrophage model and then in the low-dose aerosol infection model, for their activity against Mycobacterium tuberculosis. In both models, KRM-1648 had the highest level of activity of the four compounds. In the infected-lung model, rifabutin, rifapentine, and KRM-1648 all had sterilizing activity when given orally at 5 mg/kg of body weight per day. When given at 2.5 mg/kg/day, KRM-1648 had the highest level of activity of the four drugs, reducing the bacterial load by 2.7 logs over 35 days of therapy.

Significant increases in the levels of liver enzymes in mice treated with anti-tuberculosis drugs

“…This elevation in serum levels is not surprising given the knowledge that the bacterial infection in the low-dose aerosol infection model in mice becomes systemic within a few weeks of infection and induces granuloma formation [8]. At 7 weeks post infection, the infection itself gave rise to more fluctuations in ALT results within the untreated mouse group.…”

“…The virulent M. tuberculosis strain Erdman (TMCC 107) has been used as the standard strain for drug testing in animal models in our laboratory [8,9]. Bacteria were grown to mid-log phase in Proskauer-Beck medium containing 0.01% Tween-80 (Sigma Chemical Co., St Louis, MO).…”

“…Mice were exposed to a low-dose aerosol infection with M. tuberculosis as previously described [8]. Mice were sacrificed by CO 2 inhalation.…”

Current perspectives in drug discovery against tuberculosis from natural products

“…Mice are usually infected via aerosol exposure to virulent strains of MTB, resulting in the deposition of low numbers of tubercle bacilli in the lungs [46]. Following multiplication of tubercle bacilli and host immune response, therapy is commenced either during the phase of rapid multiplication (up to 1 month) [135,136], or during the non-replicating/dormancy phase [119], which can last for months. Recently, long-term models evaluating the sterilizing ability of novel compounds have been described [137].…”

Prospects for development of new antimycobacterial drugs

“…87,121,[131][132][133][134][135][136][137][138] KRM had much greater in-vivo therapeutic efficacy than RFP and RBT against MTB infection induced in mice. 121,[133][134][135][136] Although clinical isolates of MTB exhibited cross-resistance to KRM and either RFP or RBT, KRM still exhibited significantly stronger in-vivo activity against moderately RFP-resistant MTB strains than did RFP. 121 KRM may therefore be useful for the clinical treatment of patients with MTB infection caused by strains with moderate levels of RFP resistance.…”