Monitoring Mitochondrial Complex-I Activity Using Novel PET Probe 18F-BCPP-EF Allows Early Detection of Radiotherapy Effect in Murine Squamous Cell Carcinoma.

OBJECTIVES: Aerobic glycolysis, the main pathway of energy production in tumors (Warburg effect) allows detection of tumors by positron emission tomography (PET) using 18F-fluoro-2-deoxy-D-glucose (18F-FDG). Since ionizing radiation (IR) is reported to switch aerobic glycolysis to mitochondrial oxidative phosphorylation, radiotherapeutic efficacy was monitored by the activity of mitochondrial complex I (MC-I), using a new PET probe 18F-BCPP-EF, 18F-2-tert-butyl-4-chloro-5-{6-[2-(2-fluoro-ethoxy)-ethoxy] -pyridine-3-ylmethoxy}-2H-pyridazin-3-one, compared with 18F-FDG uptake and the apoptosis index. METHODS: Tumor uptake of 18F-BCPP-EF or 18F-FDG was examined in C3H/HeN mice inoculated with murine squamous cell carcinoma SCCVII at various time points after a single dose of x-ray irradiation at 0, 6, 15, or 30 Gy. Apoptosis incidence was determined by TUNEL staining in excised tumor tissue. RESULTS: Tumor growth suppression was dose-dependent; tumor grew 10-fold (0 Gy), 5-fold (6 Gy), 2-fold (15 Gy), and reduced to half in its volume (30 Gy) 14 days after treatment. 18F-BCPP-EF uptake was significantly increased as early as 3 days after 15 Gy or 30 Gy, when tumor size and apoptosis index showed no difference among radiation doses. In contrast, 18F-FDG uptake was initially increased dose-dependently, remained elevated up to 7 days, and eventually decreased 10 days after 30 Gy and also 14 days after 15 Gy when tumor size was already reduced. Apoptosis index was increased after irradiation but failed to correlate with tumor response. CONCLUSION: Tumor uptake of 18F-BCPP-EF was increased dose-dependently early after effective doses of IR when 18F-FDG uptake as well as apoptosis incidence were not indicative of tumor response. The results suggest that 18F-BCPP-EF is a promising "positive" MC-I imaging PET probe for early detection of efficacy of tumor radiotherapy.

Liposome-encapsulated hemoglobin enhances chemotherapy to suppress metastasis in mice.

Liposome-encapsulated hemoglobin with high O2 -affinity (P50 O2 = 10 mm Hg, h-LEH) was reported to enhance tumor radiosensitivity. We hypothesize that targeted O2 delivery to tumor hypoxia by h-LEH may also enhance chemotherapy to suppress tumor growth and metastasis in mice. Doxorubicin (DXR; 0.5 or 2 mg/kg i.p.) or S-1 (4 or 8 mg/kg orally) alone or in combination with h-LEH (5 mL/kg i.v.) was administered for 2 weeks to C57BL/6N mice inoculated with Lewis Lung Carcinoma (LLC) in the leg. After the 2-week therapy in six treatment groups, mice were sacrificed for quantitative assessment of tumor growth and lung metastasis. The tumor was then evaluated for its expression of hypoxia-inducible factor-1α (HIF-1α) and matrix metallopoteinase-2 (MMP-2) activity. Combined use of h-LEH and chemotherapeutic agents (DXR or S-1) showed no additional enhancement on suppression of the tumor growth over the chemotherapeutic agent alone. However, the combination use of h-LEH significantly suppressed the number and total area of metastatic colonies in the lung compared with each chemotherapeutic agent alone. Although HIF-1α expression and MMP-2 activity in the original tumor was significantly suppressed in the groups of mice treated with either DXR or S-1 alone, the addition of h-LEH to either agent showed further enhancement of oxygen-mediated degradation of HIF-1α and suppression of MMP-2 activity. Although the addition of h-LEH to DXR or S-1 had little effect on original LLC tumor growth, it significantly enhanced suppression of lung metastasis in mice.