Passive Pulmonary Targeting: Preliminary Assessment of the Effects of Microparticle Deposition in the Lungs

Abstract

IntroductionThe lung possesses many functions including gas (O2, CO2) exchange, and filtration of natural or foreign debris resulting in their removal from the blood circulation. It is this filtration capability that we exploited for the delivery of MPs to the lung since the lung is the first capillary filter encountered by IV administered MPs. By engineering MPs to be larger than the diameter of lung capillaries we can effectively deliver drugs (loaded in MPs) directly to the organ. This is a passively targeted drug delivery approach that can be used to deliver drugs to treat a number of lung diseases, including lung cancer.MethodsWe conducted a small study to assess the effects of microparticle deposition in the lung. Rhodamine‐labeled gelatin MPs, with a mean particle size of 11 μm and a standard deviation of 4 μm, were prepared by a water‐in‐oil emulsification method. MPs were suspended in sterile saline containing 0.1% Tween 80, briefly sonicated and injected IV into the tail veins of healthy male CD‐1 mice. There were three treatment groups in our study: Group 1 (n=1) = 0.5 mg dose, Group 2 (n=2) = 1.0 mg dose, Group 3 (n=2) = 1.5 mg dose, and a control (no dose; n=1). In all three treatment groups the volume of vehicle used was kept constant, i.e., 100 μl of 0.1% Tween 80‐saline. Following MP administration, animals were observed each day for signs of stress, weight loss, etc., for the duration of the study (7 days). Control and 0.5 mg dose animals were sacrificed at 2 days. One animal from each of the 1.0 mg & 1.5 mg dose groups was also sacrificed at 2 days, while the remaining animals were sacrificed at day 7. The following organs were excised from all sacrificed animals for fluorescence imaging: lung, heart, liver, kidneys and spleen. The lungs were inflated using saline solution for imaging, cryo‐sectioning and histology. Lung samples from each animal were embedded in paraffin, sectioned at 4 μm thickness and stained with hematoxylin and eosin (H&E) for histology.ResultsBoth histology and fluorescence imaging showed MPs (single and/or multiple) entrapped in the lung vasculature at day 2 and day 7, for both the 1.0 mg and 1.5 mg dose groups. The low (0.5 mg) dose group results did not show presence of MPs in the histology images, and there was no fluorescence signal indicating presence of MPs in this group. All lung samples from injected mice displayed normal morphology that was similar to the control group. Neither hemorrhage nor neutrophil infiltration was observed in the lung tissues at any time in any of the dose groups, throughout the duration of the study (2 days or 7 days).ConclusionVascularly localized MPs showed dose and time dependent retention. At 48 h, significant pulmonary retention of gelatin MPs was found in the 1.5 mg and 1.0 mg groups, with more of the 1.5 mg retained than of the 1.0 mg cohort. At day 7, much reduced retention was observed. Neither hemorrhage nor neutrophil infiltration in the lung tissues was observed in any dose group at any time, suggesting that gelatin MPs present a low risk of acute pulmonary toxicity. A more comprehensive study will be conducted to further assess the pulmonary retention and rate of clearance of gelatin MPs from the lungs.Support or Funding InformationThis study was supported by NIH grants: 1R01CA155061 (NCI/NIH) & U54AR055073 (NIAMS/NIH).The authors acknowledge The Rutgers University Molecular Imaging Center and Derek Adler.