Exploratory Clinical Study of Neutrophil Activation Probe (NAP) for Optical Molecular Imaging in Human Lungs

Acute lung injury (ALI)/adult respiratory distress syndrome (ARDS) is clinically important (16% of mechanically ventilated patients acquire ALI, of whom one third die), yet no pharmacological therapy has been shown to impact significantly on outcome. This is in part due to inadequate stratification of patients with neutrophil predominant ALI/ARDS and the inability to determine disease activity and hence target therapy.

Molecular Imaging (MI) offers a potential strategy to visualize neutrophil activity in vivo in situ. Indeed FDG PET has been used to image neutrophil activity but it is not a bedside modality, and moving critically ill patients to remote scanners is dangerous and expensive and there there are currently no bedside 'smart' MI solutions that can guide, at the cellular/functional level, the diagnostic or therapeutic pathway in patients with inflammatory lung disease. Indeed, in ICU, there is a specific need to rapidly diagnose patients with deteriorating gas exchange, particularly those with chest X-ray (CXR) shadowing. Such CXR infiltrates result from numerous causes including cardiac failure, fluid overload, secondary pneumonia and ALI/ARDS. All require different treatments but, at present, options to distinguish these conditions are severely limited, resulting in empirical 'blunderbuss' antimicrobial therapy and non-correction of the primary condition. There is now a pressing need to rapidly stratify such patients to inform focused implementation of specific targeted therapies.

Activated neutrophils and their histotoxic products, particularly human neutrophil elastase (HNE), have been specifically implicated in the pathogenesis of ALI/ARDS, and there is considerable clinical interest in new drugs in this area. However, there is currently no way of rapidly determining whether new therapeutic candidates are exerting their predicted effects in situ in the human lung prior to embarking upon major clinical trials. Such a solution would inevitably accelerate the pathway of new drugs to clinical application.

The Proposed Solution: probe-based confocal laser endomicroscopy (pCLE) combined with direct intra-pulmonary instillation of microdoses (pharmacologically-inactive and non-toxic) of a highly specific and sensitive 'smartprobe' (NAP) will detect neutrophil activity and the presence of active HNE in the lungs of ventilated ICU patients.

pCLE itself safely provides high-resolution, real-time images of the human lung at cellular resolution in situ. Alone, however, it provides no functional or molecular information. The investigators have therefore embarked on a discovery programme to synthesise highly sensitive smartprobes, detectable by pCLE and specifically directed against key inflammatory events. This provides a new dimension of clinical application for this cutting-edge technology. NAP, the prototype has now been validated in vitro and in vivo where it is effective at a dose of < 10µg and generates a powerful fluorescent signal in < 30 sec. Our pilot study aims are to apply the combined utility of pCLE and NAP in healthy volunteers and patients with inflammatory lung disease. The study will also provide a prototypic foundation that can be applied to future smartprobes, not only in the lung but in any organ accessible to endoscopy.

The primary end-point will be a proof of concept demonstration that this technique can be used to visualise activated neutrophils over background autofluorescence. Other end points include safety. The investigators shall also assess alveolar (by bronchoscopy) neutrophil activation and elastase activity in patients. Demonstration of activated neutrophils by pCLE in ICU would be expected to lead directly to clinical trials in patients with ALI/ARDS.