Saiko Hosokawa

Antitumor effect of MCC-465, pegylated liposomal doxorubicin tagged with newly developed monoclonal antibody GAH, in colorectal cancer xenografts.

MCC‐465 is an immunoliposome‐encapsulated doxorubicin. The liposome is tagged with polyethylene glycol and the F(ab)2 of a monoclonal antibody named GAH, a human antibody obtained by the hybridoma technique. The epitope recognized by GAH is not well characterized, but human gastric, colorectal, and mammary cancer cells were GAH‐positive, while the normal counterparts were GAH‐negative. Pegylated liposome doxorubicin (PLD) and MCC‐465 did not show significant antitumor activity against GAH‐negative Caco‐2 xenografts. On the other hand, MCC‐465 exhibited significantly superior antitumor effects against GAH‐positive WiDr‐Tc and SW837 xenografts, compared with PLD. Immunohis‐tochemistry with GAH revealed that 94% (100 of 106) of surgical specimens of colorectal cancer were GAH‐positive. These results warrant a phase I clinical trial of MCC‐465 for patients with metastatic colorectal cancer.

Establishment and Evaluation of Cancer-Specific Human Monoclonal Antibody GAH for Targeting Chemotherapy Using Immunoliposomes

To establish human monoclonal antibodies suitable for targeting chemotherapy, we prepared a panel of human-mouse hybridomas, using mouse myelomas and lymphocytes of regional lymph nodes excised from cancer patients, and selected antibodies on the basis of their specificity of binding to the surface of viable cancer cells derived from fresh cancer tissues. A selected antibody, named GAH, was found to react with viable cancer cells from 21/22 stomach and 13/20 colon cancer tissues. As for further analysis, complementary DNAs encoding GAH were cloned and recombinant GAH (rGAH) was obtained from established CHO cells transfected with GAH expression vectors. rGAH selectively stained cancer cells in human tissue sections from 13/14 stomach, 4/11 colon, 5/11 mammary, and 0/7 lung cancers, while no positive staining was observed in those of non-tumor and various normal specimens. Notably, using confocal fluorescence microscopy, rGAH was not only bound to the surface of cancer cells, but was also internalized by the cells. The potential of rGAH for intracellular drug delivery was subsequently evaluated using rGAH-conjugated, doxorubicin (DXR)-encapsulated immunoliposomes. The immunoliposomes were also internalized into the cancer cells and finally DXR was delivered to the cell nucleus. Furthermore, the immunoliposomes could inhibit the growth of DXR-insensitive stomach cancer cells (B37) in an in vivo model. These results suggest that a GAH-utilized liposome-targeting technique will provide a potent and useful cancer chemotherapy with broad applications for cancer patients.

Effect of Alpha-Interferon on Anti-Alpha-Fetoprotein-Monoclonal-Antibody Targeting of Hepatoma

We studied the potential of alpha-interferon (IFN-alpha) to enhance alpha-fetoprotein (AFP) and thus alter the localization of 125I-labeled antibody to the human hepatoma xenograft in athymic mice using monoclonal antibody (MAb) 19F12, which recognized AFP on the surface of human hepatoma cells. Treatment of the human hepatoma cell NuE with IFN-alpha increased the surface expression of AFP 2.4-fold in an IFN-dose-dependent manner. The IFN-alpha treatment substantially increased (2.7-fold) the localization of 125I-labeled 19F12 to NuE xenografts in athymic mice. The increase in localization of 125I-labeled 19F12 was dependent on the circulating plasma IFN levels. Our experimental results suggested that IFN-alpha could act as a potent modulator of the cellular antigen AFP, and be used to enhance the targeting of a conjugated MAb to hepatoma cell populations.