Evaluation of Aminolevulinic Acid-Derived Tumor Fluorescence Yields Disparate Results in Murine and Spontaneous Large Animal Models of Lung Cancer

Abstract

Fluorescence guided surgery is an emerging technology that may improve accuracy of pulmonary resection for non-small cell lung cancer (NSCLC). Herein we explore optical imaging for NSCLC surgery using the well-studied protoporphyrin IX (PPIX)/5-aminiolevulinic acid (5-ALA) system. More specifically, we evaluate fluorescent patterns observed when using (1) commonly utilized in vitro and murine NSCLC models and with (2) spontaneous canine NSCLCs, which closely mimic human disease. Using flow cytometry and fluorescent microscopy, we confirmed that NSCLC models fluoresce after exposure to 5-ALA in vitro . High levels of fluorescence were similarly observed in murine tumors within 2 hours of systemic 5-ALA delivery. When evaluating this approach in spontaneous canine NSCLC, tumor fluorescence was observed in 6 of 7 canines. Tumor fluorescence, however, was heterogenous owing to intratumoral variations in cellularity and necrosis. Margin and lymph node detection was inaccurate. These data demonstrate the importance of incorporating reliable cancer models into preclinical evaluations of optical agents. Utilization of spontaneous large animal models of cancer may further provide an important intermediate in the path to human translation of optical contrast agents.

Near-Infrared Fluorescence Tumor-Targeted Imaging in Lung Cancer: A Systematic Review

“…In this review, three studies that examined non-specific fluorophores were included [ 36 , 37 , 38 ].…”

“…5-ALA induces the synthesis and accumulation of fluorescent protoporphyrin IX (PpIX) in various epithelia and neoplastic tissues and is mostly clinically applied in glioma patients for fluorescence-guided surgery [ 80 ]. 5-ALA was tested preclinically as a fluorescent agent in seven dogs with primary lung tumors [ 38 ]. Two to four hours prior to surgery, dogs were orally administered 20 mg/kg 5-ALA.…”

Advanced Cancer Imaging Applied in the Comparative Setting

“…For example, the real-time intraoperative assessment of the completeness of surgical margins, sentinel node and distant regional metastasis at the time of tumor resection would be advantageous to waiting for time and labor intense ex vivo assessments and may abrogate the need for revision surgery. Examples where companion species have been involved in evaluating intraoperative surgical margins include optical coherence tomography (OCT) in dogs and cats with soft tissue sarcoma (STS) and fluorescence-guided surgical and sentinel node assessment for a variety of solid tumors (e.g., primary lung tumors, carcinomas, and STS) (71)(72)(73)(74)(75)(76)(77)(78). Fluorescent probes used in these studies include agents with preferential/differential avidity for tumor cells such as protoporphyrins, lipid nanoparticles, integrintargeting compounds (α v β 3 ), folate-targeting agents, modified chlorotoxins these technologies have also been used to assess surgical wound beds for residual tumor cells after tumor extirpation (72).…”

Clinically useful tumor fluorescence greater than 24 hours after 5-aminolevulinic acid administration

“…5-ALA is a prodrug with selective intracellular conversion to protoporphyrin IX, the fluorescent downstream metabolite of 5-ALA that preferentially accumulates in high-grade tumor cells to glow under blue-light illumination. [ 8 , 12 , 16 , 23 ] In vivo animal studies report peak fluorescence between 1.5 and 4 h after administration,[ 19 , 23 ] yet, clinical experience has demonstrated visually discernible tumor fluorescence even 12–16 h after initial dosing. [ 7 , 13 , 28 ] While those instances of prolonged fluorescence have been informally described, we present the first reported case of clinically useful intraoperative tumor fluorescence >24 h after 5-ALA administration, without redosing.…”