Successful Shortening of Tuberculosis Treatment Using Adjuvant Host-Directed Therapy with FDA-Approved Phosphodiesterase Inhibitors in the Mouse Model

Global control of tuberculosis (TB), an infectious disease that claims nearly 2 million lives annually, is hindered by the long duration of chemotherapy required for curative treatment. Lack of adherence to this intense treatment regimen leads to poor patient outcomes, development of new or additional drug resistance, and continued spread of M.tb. within communities. Hence, shortening the duration of TB therapy could increase drug adherence and cure in TB patients. Here, we report that addition of the United Stated Food and Drug Administration-approved phosphodiesterase inhibitors (PDE-Is) cilostazol and sildenafil to the standard TB treatment regimen reduces tissue pathology, leads to faster bacterial clearance and shortens the time to lung sterilization by one month, compared to standard treatment alone, in a murine model of TB. Our data suggest that these PDE-Is could be repurposed for use as adjunctive drugs to shorten TB treatment in humans

Intracellular cAMP levels increase within <i>M.tb.</i>-infected THP-1 human monocytic cells upon exposure to PDE-Is.

<p>The treated infected cells received 100 uM of PDE inhibitors (PDE-I 3, and 5 class) for 2 h followed by infection. UI: uninfected cells; the PDE5-I was 4-{[3′,4′-(Methylenedioxy)benzyl]amino}-6-methoxyquinazoline (MBM); and the PDE3-I was trequinsin. Results shown (mean and SD) represent two biological replicates, each with 2 technical replicates.</p

Proportion of mice with no detectable CFUs during TB standard therapy with and without PDE-I.

<p>The proportions of mice with no detectable CFUs were determined by homogenizing and plating the entire lungs from 56 to 168 days of treatment. Treatment was terminated after 168 days, and groups of mice were kept for an additional 4 months (168+112). Shading indicates lung sterilization in all mice in the group. SD: standard drug therapy (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030749#pone-0030749-g004" target="_blank">Fig. 4</a> legend for details); S: 10 mg/kg sildenafil; C: 10 mg/kg cilostazol; CS: 10 mg/kg each of sildenafil and cilostazol.</p

Interaction of PDE-Is with Rifampin.

<p>BALB/c mice were infected with 3.6 log₁₀CFU <i>M.tb.</i> and were treated daily by oral gavage (starting the day after infection) with 10 or 30 mg/kg cilostazol (C10 and C30, respectively), 10 mg/kg rifampin (R10), C10 plus R10, or C30 plus R10. Lung CFU counts were determined on days 14 and 28 post-infection.</p

Addition of PDE-Is to standard TB therapy.

<p>The addition of PDE-Is to standard TB therapy reduces bacterial load, lung pathology and time to lung sterilization, and does not negatively interact with rifampin in <i>M.tb.</i>-infected mice. BALB/c mice were infected with 3.97 log₁₀CFU <i>M.tb</i> and treatment was started 14 days post-infection. The mice were treated daily by oral gavage with standard therapy (SD, which is 2 months 10 mg/kg rifampin (R), 25 mg/kg isoniazid H), and 150 mg/kg pyrazinamide (Z), followed by 4 months of R and H), SD plus 10 mg/kg sildenafil (S10), cilostazol (C10) or both (CS10). (<b>A</b>) CFU counts in mouse lungs. (<b>B</b>) Histopathology analyses of mouse lungs (hematoxylin and eosin stained lung sections).</p

Administration of PDE-I monotherapy to <i>M.tb.</i>-infected mice shows therapeutic benefits by several parameters.

<p>(<b>A</b>) Time-to-death analysis; BALB/c mice infected with 3.6 log₁₀CFU <i>M.tb.</i> were treated daily by oral gavage (starting the day after infection) with 10 or 30 mg/kg of cilostazol (C) or sildenafil (S). Isoniazid at 1 or 25 mg/kg (INH1 or INH25 respectively) and sham (PBS) were used as positive and negative controls, respectively. (<b>B–D</b>) BALB/c mice infected with 3.1 log₁₀CFU <i>M.tb.</i> were treated daily by oral gavage (starting the day after infection) with 10 mg/kg cilostazol (C10), sildenafil (S10) or sham. At day 28 post-infection, lung CFU counts (<b>B</b>), spleen CFU counts (<b>C</b>) and body weight (<b>D</b>) were determined.</p