Pulmonary exacerbations are one of the most common manifestations of cystic fibrosis (CF), a life-limiting, multisystem disease that affects 30,000 Americans. These exacerbations are often caused by highly drug- resistant Gram-negative bacteria that colonize the lungs of people with CF. Among such organisms, the most feared is the Burkholderia cepacia complex (Bcc). Bcc have extensive intrinsic antibiotic resistance and readily acquire further resistance mechanisms under selective pressure during antibiotic treatment; pan-resistant strains can emerge following repeated antibiotic courses. Bcc infection is associated with frequent hospitalizations and increased mortality in people with CF, but there are no new antibiotics with activity against BCC in the development pipeline, and alternative treatment strategies are urgently needed. The goal of the proposed research is to identify known bioactive compounds that have activity against Bcc either alone or in combination with antibiotics. This work will be carried out through two aims.
In Aim 1, we will test 14,000 known bioactive small molecules, including all FDA-approved drugs, both alone and in combination with six antibiotics commonly used to treat Bcc (meropenem, ceftazidime, minocycline, levofloxacin, trimethoprim-sulfamethoxazole, and tobramycin, each at an individually ineffective concentration), to identify compounds and compound/antibacterial combinations that inhibit growth of a representative Bcc isolate.
In Aim 2, we will further characterize the activity of promising compounds identified in the screen using several complementary in vitro models. First, we will perform spectrum-of-activity and dose-response testing of compounds and combinations against a collection of 30 Bcc isolates using inkjet printer-assisted checkerboard array synergy studies as well as time-kill synergy studies. We will also evaluate the capacity of compounds to prevent the emergence of antibiotic resistance during treatment. Then, in order to better approximate the environment in which bacteria live in the lungs of people with CF, which is characterized by increased viscosity, high concentrations of mucin, albumin, amino acids, and free DNA, and lower oxygen tension relative to standard in vitro antimicrobial susceptibility testing conditions, we will test compounds and combinations using an artificial sputum medium in a microaerophilic environment. With this approach, we will assess whether activity is maintained under conditions more closely resembling those in which they would be used in clinical practice. When the project is completed, we expect to have identified a collection of molecules with previously unrecognized activity against Bcc and to have determined which of these are most likely to be clinically effective in people with CF. Identification of well-characterized compounds that have potential therapeutic activity against Bcc will facilitate future evaluation in animal models and human trials in order to develop desperately needed new therapeutic options for Bcc.
Lung infection with Burkholderia cepacia complex (Bcc) bacteria causes increased mortality in people with cystic fibrosis, a multisystem disease that affects 30,000 people in the United States, yet there are very few treatment options available for this intrinsically multidrug-resistant pathogen, and no new drugs in the development pipeline. The proposed research project will screen 14,000 known bioactive compounds for activity against Bcc, either alone or as potentiators of antibiotics. Compounds identified in the screen will be further evaluated using a variety of techniques designed to determine which are most likely to be clinically effective for patients with cystic fibrosis.
