PT  - JOURNAL ARTICLE
AU  - Kohei Sano
AU  - Makoto Mitsunaga
AU  - Takahito Nakajima
AU  - Peter L. Choyke
AU  - Hisataka Kobayashi
TI  - Acute Cytotoxic Effects of Photoimmunotherapy Assessed by <sup>18</sup>F-FDG PET
AID  - 10.2967/jnumed.112.112110
DP  - 2013 May 01
TA  - Journal of Nuclear Medicine
PG  - 770--775
VI  - 54
IP  - 5
4099  - http://jnm.snmjournals.org/content/54/5/770.short
4100  - http://jnm.snmjournals.org/content/54/5/770.full
SO  - J Nucl Med2013 May 01; 54
AB  - We have recently developed a cancer-specific therapy, photoimmunotherapy, which uses an antibody-IR700 (phototoxic phthalocyanine dye) conjugate to bind to the cell membrane and near-infrared light to induce immediate and highly specific tumor killing in vivo. For monitoring the acute cytotoxic effects of photoimmunotherapy before the tumor begins to shrink, we used 18F-FDG PET before and after this intervention in mice. Methods: Photoimmunotherapy was performed by binding panitumumab (anti-HER1)-IR700 to HER1-positive tumor cells (A431), followed by near-infrared light irradiation in vitro and in vivo. The uptake of 18F-FDG in the tumor after photoimmunotherapy was evaluated in cellular uptake studies and PET imaging studies. Serial histologic analyses were conducted after photoimmunotherapy. Results: The in vitro cellular uptake of 18F-FDG was reduced as the dose of light increased, and at high light dose (2 J/cm2) the uptake was reduced by more than 99% within 1 h after photoimmunotherapy. In vivo 18F-FDG PET imaging showed that the accumulation of radioactivity in the treated tumors decreased 76% at 75 min after photoimmunotherapy and did not change for 24 h. In contrast, no significant changes were demonstrated in nontreated tumors. None of tumors changed size within 24 h after photoimmunotherapy, although diffuse necrosis was observed in photoimmunotherapy-treated tumors. Conclusion: Immediate cytotoxic effects induced by photoimmunotherapy were clearly detected by decreased glucose uptake using 18F-FDG PET even before changes in tumor size became evident. 18F-FDG allows the clinical assessment of the therapeutic effects of photoimmunotherapy earlier than anatomic methods that rely on tumor size.