DT-0111: a novel drug-candidate for the treatment of COPD and chronic cough

Abstract

Background: Extracellular adenosine 5'-triphosphate (ATP) plays important mechanistic roles in pulmonary disorders in general and chronic obstructive pulmonary disease (COPD) and cough in particular. The effects of ATP in the lungs are mediated to a large extent by P2X2/3 receptors (P2X2/3R) localized on vagal sensory nerve terminals (both C and Aδ fibers). The activation of these receptors by ATP triggers a pulmonary-pulmonary central reflex, which results in bronchoconstriction and cough, and is also proinflammatory due to the release of neuropeptides from these nerve terminals via the axon reflex. These actions of ATP in the lungs constitute a strong rationale for the development of a new class of drugs targeting P2X2/3R. DT-0111 is a novel, small, water-soluble molecule that acts as an antagonist at P2X2/3R sites.

Methods: Experiments using receptor-binding functional assays, rat nodose ganglionic cells, perfused innervated guinea pig lung preparation ex vivo, and anesthetized and conscious guinea pigs in vivo were performed.

Results: DT-0111 acted as a selective and effective antagonist at P2X2/3R, that is, it did not activate or block P2YR; markedly inhibited the activation by ATP of nodose pulmonary vagal afferents in vitro; and, given as an aerosol, inhibited aerosolized ATP-induced bronchoconstriction and cough in vivo.

Conclusions: These results indicate that DT-0111 is an attractive drug-candidate for the treatment of COPD and chronic cough, both of which still constitute major unmet clinical needs. The reviews of this paper are available via the supplementary material section.

Keywords: ATP; COPD; asthma; bronchoconstriction; pulmonary inflammation; pulmonary-pulmonary reflex.

Figure 1.

Diagram showing the exposure chamber and setup of cough recording system. Arrows indicate flow direction. The signals generated by video camera, microphone, and pressure transducer were amplified, digitized, and recorded continuously through a PowerLab system (ADInstruments Inc.) and LabChart Pro software (ADInstruments).

Figure 2.

DT-0111 (1.5 µM) abolished ATP-induced inward current in isolated rat nodose ganglionic cells. Upper panel tracings: Left, control effect of ATP; Middle, lack of effect of ATP in the presence of DT-0111; Right, recovery of ATP effect upon washout. Lower panel: Dose response of the attenuation of ATP effect to increasing doses of DT-0111. IC₅₀ = 0.3 µM, n = 3.

Figure 3.

DT-0111 antagonized the effect of ATP (10 µM) on nodose ganglion vagal sensory nerve terminals in the innervated guinea pig lung preparation in vitro. Upper panel: a typical example of neural AP recordings: Left, a burst of APs induced by ATP (Control); Middle, DT-0111 markedly suppressed the effect of ATP; Right, recovery of ATP effect after 30 min of DT-0111 washout. Lower panel: Number of APs recorded in the absence (ATP), presence of DT-0111 (1 mM) (ATP + DT), and after washout (ATP + washout). Blue arrows mark the administration of ATP, n = 3. AP, action potential.

Figure 4.

The peak AP discharge HZ in response to ATP in the absence (black bar) and presence (white bar) of DT-0111 (1 mM). Data are presented as mean ± SEM, n = 10, *denotes p < 0.05, Student’s t test for paired data. AP, action potential; SEM, standard error of the mean.

Figure 5.

Aerosolized ATP generally induced elevation of Ptr in a dose-dependent manner. (a) Effect of ATP on Ptr in eight individual guinea pigs. (b) Correlation between Ptr response and ATP concentration using linear and dose response (curved) models, with adjusted R² 0.85 and 0.71, respectively (both p < 0.001), n = 8. Ptr, tracheal pressure.

Figure 6.

DT-0111 effects on tracheal pressure (Ptr). Left panel: Ptr responses to different ATP doses were significantly suppressed by pretreatment of aerosolized DT-0111. Ptr responses to middle and high ATP concentration were higher than those induced by low ATP dose. Right panel: The averaged percentage of the inhibition of Ptr responses to the three groups of ATP doses by aerosolized DT-0111 are similar in individual guinea pigs. n = 7 for L, M, and H ATP dose, respectively. Data are mean ± SEM. *p < 0.01, compared with baseline Ptr, and to ATP at a given concentration prior to DT-0111; ^†p < 0.01, compared with L ATP dose; and ^‡p < 0.01, compared with before DT-0111 pretreatment. Aerosolized DT-0111 (6 mg/ml for 2 min) alone failed to change baseline Ptr (not shown). H, high dose; L, low dose; M, medium dose; Ptr, tracheal pressure; SE, standard error of the mean.

Figure 7.

Bronchoconstrictive effect of inhaled increasing doses of aerosolized ATP before and after aerosolized DT-0111 inhalation (DT-0111) in conscious guinea pigs expressed as % change in airways pressure (sRaw). n = 6; *p < 0.05, versus ATP 0.0 mg/ml; ^†p < 0.05, DT-0111 versus Ctrl at the same ATP dose.

Figure 8.

Effects of DT aerosol inhalation on aerosolized ATP-induced cough response in guinea pigs. Upper panel: typical burst of coughs occurred during exposure to aerosolized ATP (48 mg/ml) for 5 min (left panel), and immediately after the administration of aerosolized DT-0111 (DT, 12 mg/ml; right). The dashed line under the sound trace indicates a bout of coughs, while arrow heads point to individual coughs. In most cases, the sound signal of a cough in bouts of coughs is mainly composed of low audio frequency component (100 Hz or lower) resulting from the body-movement or deep breathing and hardly heard. Lower panel: Number of coughing bouts and number of coughs induced by aerosolized ATP before and after aerosolized DT-0111, n = 5, 6 (ATP and ATP+DT, respectively).