Targeting TGFβ superfamily ligand accessory proteins as novel therapeutics for chronic lung disorders

Dysregulation of the transforming growth factor β (TGFβ) pathway has been implicated to underlie a number of disease indications including chronic lung disorders such as asthma, chronic obstructive pulmonary disease (COPD), interstitial pneumonias, and pulmonary arterial hypertension (PAH). Consequently, the pharmaceutical industry has devoted significant resources in the pursuit of TGFβ pathway inhibitors that target the cognate type I and II receptors and respective ligands. The progress of these approaches has been painfully slow, due in part to dose-limiting safety issues that result from the antagonism of a pathway that is responsible for regulating many fundamental biological processes including immune surveillance and cardiovascular responses. These disappointments have led many in the field to conclude that modulating the TGFβ pathway for chronic indications with a sufficient safety window using conventional approaches may be extremely difficult to achieve. Here we review the rationale and limitations of the use of TGFβ pathway inhibitors in chronic lung disorders and the possibility of targeting TGFβ superfamily ligand accessory proteins to allow rheostatic regulation of signaling to achieve efficacy while maintaining a sufficient therapeutic index.