Diffusion-weighted MR imaging after Near Infrared Photoimmunotherapy in an animal model

Authors

• Y Nakamura
• M Bernardo
• T Nagaya
• K Sato
• T Harada
• S Okuyama
• PL Choyke
• H Kobayashi

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 photoabsorbers after irradiation with NIR light. NIR-PIT induces nearly immediate necrotic cell death, rather than apoptotic cell death which is more typical of the majority of cancer treatments. The purpose of this study was to evaluate the changes in apparent diffusion coefficient (ADC) values in treated tumors shortly after NIR-PIT. A431 cells were injected subcutaneously in the right and left dorsi of 12 mice. Six days later, the mice were injected with a photoabsorber, IR700, conjugated to panitumumab, an antibody targeting epidermal growth factor receptor. One day later, only right sided tumors were exposed to NIR light (treated tumor). MRI was performed 1 day before and 1-2 hours after NIR-PIT. ADC values using the following combinations of b-values: 0-1000, 200-1000 and 500-1000 s/mm2 were compared before and after NIR-PIT using a two-sided paired t-test. For treated tumors 1-2 hours after NIR-PIT, all three ADC values decreased after NIR-PIT (p < 0.01). For non-treated tumors, for the b= 0 and 1000 s/mm2 pair, a decline in ADC was seen (p=0.04) but was not seen with the combinations of b=200 and 1000 or b=500 and 1000 s/mm2 (p=0.13 and 0.07). NIR-PIT results in early reductions in ADC. Unlike most cancer treatments NIR-PIT produces this early reductions of ADC values which could be a useful imaging biomarker for detecting therapeutic changes shortly after NIR-PIT.

Scientific Focus Area: Cancer Biology

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