Liposome‐Encapsulated Hemoglobin Enhances Chemotherapy to Suppress Metastasis in Mice

Liposome‐encapsulated hemoglobin with high O 2 ‐affinity ( P 50 O 2  = 10 mm  Hg , h ‐ LEH ) was reported to enhance tumor radiosensitivity. We hypothesize that targeted O 2 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 C 57 BL /6 N mice inoculated with L ewis L ung C arcinoma ( 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.