Phosphodiesterase-4 Inhibition Alters Gene Expression and Improves Isoniazid – Mediated Clearance of Mycobacterium tuberculosis in Rabbit Lungs

Abstract

Tuberculosis (TB) treatment is hampered by the long duration of antibiotic therapy required to achieve cure. This indolent response has been partly attributed to the ability of subpopulations of less metabolically active Mycobacterium tuberculosis (Mtb) to withstand killing by current anti-TB drugs. We have used immune modulation with a phosphodiesterase-4 (PDE4) inhibitor, CC-3052, that reduces tumor necrosis factor alpha (TNF-α) production by increasing intracellular cAMP in macrophages, to examine the crosstalk between host and pathogen in rabbits with pulmonary TB during treatment with isoniazid (INH). Based on DNA microarray, changes in host gene expression during CC-3052 treatment of Mtb infected rabbits support a link between PDE4 inhibition and specific down-regulation of the innate immune response. The overall pattern of host gene expression in the lungs of infected rabbits treated with CC-3052, compared to untreated rabbits, was similar to that described in vitro in resting Mtb infected macrophages, suggesting suboptimal macrophage activation. These alterations in host immunity were associated with corresponding down-regulation of a number of Mtb genes that have been associated with a metabolic shift towards dormancy. Moreover, treatment with CC-3052 and INH resulted in reduced expression of those genes associated with the bacterial response to INH. Importantly, CC-3052 treatment of infected rabbits was associated with reduced ability of Mtb to withstand INH killing, shown by improved bacillary clearance, from the lungs of co-treated animals compared to rabbits treated with INH alone. The results of our study suggest that changes in Mtb gene expression, in response to changes in the host immune response, can alter the responsiveness of the bacteria to antimicrobial agents. These findings provide a basis for exploring the potential use of adjunctive immune modulation with PDE4 inhibitors to enhance the efficacy of existing anti-TB treatment.

Roflumilast, a Type 4 Phosphodiesterase Inhibitor, Shows Promising Adjunctive, Host-Directed Therapeutic Activity in a Mouse Model of Tuberculosis

“…Hematoxylin and eosin (H&E) staining of lung sec-tions showed marginal differences in cellularity upon treatment with roflumilast (see the supplemental material). Consistent with previous observations that monotherapy of TB-infected animals with a PDE4-I had no effect on bacterial burden (5,14), roflumilast monotherapy showed no antibacterial properties in vivo (Fig. 1C).…”

“…The bacterium-derived intramacrophage cAMP delivered by this adenylate cyclase results in reductions of TNF-␣ production via protein kinase A and the cAMP response elementbinding protein pathway, leading to decreased immunopathology and bacterial survival (15). Although not all PDE4-Is are beneficial as adjunctive agents for tuberculosis treatment (2), roflumilast has an effect similar to that of CC-3052 in combination therapy with isoniazid (5,14). The roflumilast effect appears between weeks 4 and 8 of treatment, when rapidly dividing cells have been eliminated by INH and the remaining bacilli are found in a persistent state and are phenotypically resistant to isoniazid killing.…”

Host-Directed Therapeutics for Tuberculosis: Can We Harness the Host?

“…PDE4 hydrolyzes cAMP and is expressed in monocytes and macrophages but not in T cells. Mice and rabbits treated with the PDE4 inhibitor CC-3052, in combination with INH, had improved resolution of lung pathology and a lower burden of M. tuberculosis compared to mice treated with INH alone (148)(149)(150). However, a separate study found that administration of the PDE4 inhibitors rolipram and cilomilast decreased survival time of M. tuberculosis-infected mice and that addition of rolipram to the standard TB treatment resulted in a higher bacterial burden than with the standard treatment alone (151).…”

Sharpening nature's tools for efficient tuberculosis control: A review of the potential role and development of host-directed therapies and strategies for targeted respiratory delivery

“…Phospohdiesterase (PDE) inhibitors, including agents currently licensed for other clinical uses such as cilostazol and sildenafil, also regulate TNF-α production through decreasing cAMP activation and have shown promising results in preclinical murine and rabbit studies [166][167][168][169][170].…”