pH-Responsive Liposomes for Targeted Detection of Pancreatic Adenocarcinoma Using MSOT

Pancreatic ductal adenocarcinoma (PDAC) diagnosis and treatment are limited due to the insufficient availability of contrast agents that can detect tumors with high sensitivity and specificity. Nanocontrast agents can be actively targeted toward the highly acidic tumor microenvironment to facilitate the detection of tumor cells during intraoperative imaging using an advanced imaging modality: multispectral optoacoustic tomography (MSOT). We developed IR780 dye encapsulated liposomes (Lipo-780) as a nanocontrast agent and actively targeted them using the pH low insertion peptide (pHLIP) V7 (V7-lipo-780) toward the extremely acidic pH tumor microenvironment of pancreatic cancer. Tumor-specific uptake of liposomes were evaluated in vitro in aggressive metastatic pancreatic cancer cells (S2VP10, S2013) and in vivo in orthotopic human pancreatic cancer xenograft murine model. Lipo-780 (110 nm, polydispersity index (PDI) of 0.13) were conjugated with V7 peptide using SMCC NH2-maleimide linker and the conjugation was confirmed with zeta potential measurements. The uptake of V7-lipo-780 increased by 3.5-fold in comparison to Lipo-780 in S2013 cells (p < 0.001), and by 2.4-fold (p < 0.001) at pH 6.6 in S2VP10 cells. Propidium iodide encapsulated liposomes (Lipo-PI) with a size of 118 nm validated the internalization of liposomes. In S2VP10 cells, V7-lipo-PI demonstrated higher uptake with the mean red fluorescence of 5535 counts in comparison to 334 counts for Lipo-PI at pH 6.6 (p < 0.001). Biodistribution analysis indicated 40× higher tumor accumulation of V7-lipo-780 in comparison to the liver (p < 0.001), and 4× higher tumor accumulation than the kidney (p < 0.001) post 6 h of intravenous administration. Histological analysis of kidney, liver, and spleen confirmed the nontoxic nature of liposomes. Tumor-specific liposome accumulation and IR780 contrast agent release prevent off-target toxicity with maximum contrast signal at the tumor site, further expanding the potential of MSOT for clinical applications.