Aerosolized protein delivery in asthma: gamma camera analysis of regional deposition and perfusion

Bioavailability of an aerosolized anti-inflammatory protein, soluble interleukin-4 receptor (IL-4R), was measured in patients with asthma using two different aerosol delivery systems, a prototype aerosol delivery system (AERx tethered model, Aradigm, Hayward, CA) and PARI LC STAR nebulizer (Pari, Richmond, VA). Regional distribution of the drug in the respiratory tract obtained by planar imaging using gamma camera scintigraphy was utilized to explain the differences in bioavailability. The drug, an experimental protein being developed for asthma, was mixed with radiolabel 99mTechnetium diethylene triaminepentaacetic acid (99mTc-DTPA). Aerosols were characterized in vitro using cascade impaction (mass median aerodynamic diameter [MMAD] and geometric standard deviation [GSD]); the AERx MMAD 2.0 microm (GSD 1.35), the PARI 3.5 microm (GSD 2.5). Four patients with asthma requiring maintenance aerosolized steroids were studied. First, regional volume was determined utilizing equilibrium 133Xe scanning. Then, after a brief period of instruction, patients inhaled four breaths of protein using AERx (0.45 mg in total) followed 1 week later by inhalation via PARI (3.0 mg nebulized until dry). Each deposition image was followed by a measurement of regional perfusion using injected 99mTc albumin macroaggregates. Deposition of 99mTc-DTPA in the subjects was determined by mass balance. Regional analysis was performed using computerized regions of interest. The regional distribution of deposited drug was normalized for regional volume and perfusion. Following each single inhalation, serial blood samples were drawn over a 7-day period to determine area under the curve (AUC) of protein concentration in the blood. Median AUC(AERx)/AUC(PARI) was 7.66/1, based on the amount of drug placed in each device, indicating that AERx was 7.66 times more efficient than PARI. When normalized for total lung deposition (AUC per mg deposited) the ratio decreased to 2.44, indicating that efficiencies of the drug delivery system and deposition were major factors. When normalized for sC/P and (pU/L)xe ratios (central to peripheral and upper to lower ratios are parameters of regional distribution of deposited particles and regional per- fusion ['p']), AUC(AER)x/AUC(PARI) further decreased to 1.35, demonstrating that peripheral sites of deposition with the AERx affected the final blood concentration of the drug. We conclude that inhaled bioavailability of aerosolized protein, as expressed by AUC, is a quantifiable function of lung dose and regional deposition as defined by planar scintigraphy.

Coarse spray delivery to a localized region of the pulmonary airways for gene therapy

Targeting adenoviral vectors for cystic fibrosis gene therapy to the human airways with minimal exposure to alveoli would avoid adverse reactions and maximize response. At present, to deliver gene therapy vectors, large volumes of fluid are instilled or nebulized as aerosols. Either approach would likely cause alveolar exposure and increases the potential for side effects. We describe a coarse spray delivery device that precisely and reproducibly delivers the viral vector to the human airways to treat a small region of the airways for clinical trials. An endoscopic washing pipe (Olympus) that can be inserted into the channel of a bronchoscope was used. To minimize the escape of the therapeutic material downstream from the site of administration, we restricted the volume delivered to <150 microl (to prevent bulk flow), and used large droplets. Their high velocity further enhanced the probability of impaction in the vicinity of the nozzle. A pneumatic dosing system (Kahnetics) was used to reproducibly deliver the spray. The droplet size distribution was determined by laser diffraction and confirmed by cascade impaction: 190-microm volume median diameter with 1% mass <10 microm. The localization of the spray was studied in hollow cast models of human airways. 99mTc-sulfur colloid was used as a radiolabeled marker for these studies. Localization of the deposited spray was determined by scintigraphy and by measuring the radioactivity exiting the terminal airways. In the lung casts the spray was localized to one or two generations over an approximately 2-cm2 area. We conclude that delivery of large droplet sprays limits exposure to a few generations and may be useful in topical gene delivery clinical trials.