Near Infrared Photoimmunotherapy in a Transgenic Mouse Model of Spontaneous Epidermal Growth Factor Receptor (EGFR)-expressing Lung Cancer

Abstract

Near infrared photoimmunotherapy (NIR-PIT) is a new cancer treatment that combines the specificity of antibodies for targeting tumors with the toxicity induced by a sensitive photoabsorber following exposure to NIR light. Most studies of NIR-PIT have been performed in xenograft models of cancer. The purpose of this study was to evaluate the therapeutic effects of NIR-PIT in a transgenic model of spontaneous lung cancer expressing human EGFR (hEGFR-TL). Mice were separated into 3 groups for the following treatments: (1) no treatment (control); (2) 150 μg of photoabsorber, IR700, conjugated to panitumumab, an antibody targeting EGFR [antibody-photoabsorber conjugate (APC)] intravenously (i.v.) only; (3) 150 μg of APC i.v. with NIR light administration. Each treatment was performed every week up to three weeks. MRI was performed 1 day before and 3, 6, 13, 20, 27, and 34 days after first NIR-PIT. The relative volume of lung tumors was calculated from the tumor volume at each MRI time point divided by the initial volume. Steel test for multiple comparisons was used to compare the tumor volume ratio with that of control. Tumor volume ratio was inhibited significantly in the NIR-PIT group compared with control group (P < 0.01 at all time points). In conclusion, NIR-PIT effectively treated a spontaneous lung cancer in a hEGFR-TL transgenic mouse model. MRI successfully monitored the therapeutic effects of NIR-PIT. Mol Cancer Ther; 16(2); 408-14. ©2016 AACR.

Conflict of interest statement

DISCLOSURE OF POTENTIAL CONFLICTS OF INTEREST

Choyke P. L. and Kobayashi H. appear as inventers of the patent of PIT, but do not receive any royalties as the patent is owned by the US government.

©2016 American Association for Cancer Research.

Figures

Figure 1

In vivo effect of NIR-PIT on lung tumor. (A) NIR-PIT regimen of APC administration and NIR light exposure is shown (n = 6, 6, and 8 mice in control, APC i.v. and NIR-PIT group, respectively). MR images were obtained at each time point as indicated. (B) MR imaging of lung tumor bearing mice. In control and APC i.v. only animals the size of the lung tumor increased rapidly, while in the NIR-PIT group of the lung tumors increased only gradually demonstrating an effect on tumor growth rates. (C) Tumor volume ratio was inhibited significantly in the NIR-PIT group compared with control group (p < 0.01 at all time points), while no significant difference in tumor volume ratio in APC i.v. only group compared to control group was observed. (D) There was no significant difference in survival among three groups (p = 0.50).

Figure 2

Ex vivo fluorescence imaging and histological fluorescence distribution of lung tumor. (A) The regimen for ex vivo imaging is shown. (B) IR700 fluorescence image of extracted lungs. Lung tumors show high fluorescence signal. (C) Differential interference contrast (DIC) and fluorescence microscopy images of lung tumors. High fluorescence intensity is shown in a lung tumor 24 hours after injection of pan-IR700. Scale bars = 200 μm. (D) Flow cytometric analysis. Mean fluorescence intensity was 109.1 and 31.0 for A431 cells and lung cancer cells, respectively.

Figure 3

Resected lung tumors stained with hematoxylin and eosin are shown. Tumors in control and APC only groups contain healthy, typical adenocarcinoma cells with dark nuclei and eosinophilic cytoplasm in ×400 images. A tumor after NIR-PIT therapy contains large numbers of necrotic cells that are shown typically less dark nuclei and eosinophilic cytoplasm with some vacuolar degeneration than healthy cancer cells with micro-hemorrhage and infiltration of inflammatory mononuclear cells in the ×400 image. These damaged cancer cells were widely seen in light red color in the ×100 image (left panel) of a tumor after NIR-PIT, while no such damaged cell was observed in both ×100 and ×400 images of APC i.v. alone without NIR light as well as no treatment control. These histopathological changes were consistent in all tumors examined in each group.