Published online Dec 28, 2018. doi: 10.3748/wjg.v24.i48.5491
Peer-review started: October 2, 2018
First decision: November 1, 2018
Revised: November 7, 2018
Accepted: November 16, 2018
Article in press: November 16, 2018
Published online: December 28, 2018
Pancreatic cancer is still one of major life-threatening diseases. Therefore, there is an urgent need to explore early diagnostic and new therapeutic options. Near infrared photoimmunotherapy (NIR-PIT) is a highly selective tumor treatment that utilizes antibody-photosensitizer conjugate systemic administration, accompanied by subsequent NIR light exposure. Tissue factor (TF) is a transmembrane protein and its overexpression is associated with increased tumor growth, tumor angiogenesis and metastatic potential in many malignancies, including pancreatic cancer.
Previously, we suggested that TF may be a promising target for cancer diagnostic imaging probe and have already reported the usefulness of anti-TF monoclonal antibody (anti-TF mAb) in cancer imaging and therapy. However, NIR-PIT using anti-TF mAb has not been attempted.
In this study, we aim to investigate the photoimmunotherapeutic effect induced by a rat IgG2b anti-TF monoclonal antibody 1849 (anti-TF 1849), conjugated to the NIR photosensitizer, indocyanine green (ICG), in a TF-expressing BxPC-3 pancreatic cancer model.
An ICG-labeled antibody conjugate (1849-ICG) was generated by labeling an anti-TF 1849 with ICG. The expression levels of TF in two human pancreatic cancer cell lines were examined by western blotting. Specific binding of the 1849-ICG to BxPC-3 cells was examined by fluorescence microscopy. NIR-PIT-induced cell death was determined by cell viability imaging assay. In vivo longitudinal fluorescence imaging was used to explore the accumulation of 1849-ICG conjugate in xenograft tumors. To determine the effect of NIR-PIT, tumor-bearing mice were divided into 5 groups: (1) 100 μg of 1849-ICG i.v. administration followed by NIR light exposure (50 J/cm2) on two consecutive days (Days 1 and 2); (2) NIR light exposure (50 J/cm2) only on two consecutive days (Days 1 and 2); (3) 100 μg of 1849-ICG i.v. administration; (4) 100 μg of unlabeled anti-TF 1849 i.v. administration; and (5) the untreated control. Semiweekly tumor volume measurements, accompanied with histological and immunohistochemical (IHC) analyses of tumors, were performed 3 d after the 2nd irradiation with NIR light to monitor the effect of treatments.
High TF expression in BxPC-3 cells was observed via western blot analysis, concordant with the observed preferential binding with intracellular localization of 1849-ICG via fluorescence microscopy. NIR-PIT-induced cell death was observed by performing cell viability imaging assay. In contrast to the other test groups, tumor growth was significantly inhibited by NIR-PIT with a statistically significant difference in relative tumor volumes (P < 0.05). Tumors that received NIR-PIT showed evidence of necrotic cell death-associated features upon hematoxylin-eosin staining accompanied by a decrease in Ki-67-positive cells (a cell proliferation marker) by IHC examination.
The TF-targeted NIR-PIT with the 1849-ICG conjugate can potentially open a new platform for treatment of TF-expressing pancreatic cancer.
Because TF-targeted NIR-PIT is a promising new treatment modality with a useful contemporaneous diagnostic utility, we will approach to apply it in clinical use. In addition, the association of PIT and immune response is an interesting topic and we will explore it in the future study.