Antitumor effect of preparation for colon cancer cells with hyperthermia and/or Hsp70 inducer, geranylgeranylacetone in pulmonary metastasis models of colon cancer and subcutaneous tumor model in mice

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Aim: The transcription factor-kB(NF-kB)is activated in many human cancers, and induces the expression of multiple genes including CyclinD1, COX-2, VEGF, Bcl-2, and IAP. Therefore, the blocking of NF-kB activity may be associated with the suppression of proliferation, angiogenesis, and induction of apoptosis.

Recently, we confirmed heat treatment inhibited activation of NF-kB through the expression of heat shock proteins in a human colon cancer cell line.

In clinically, it is known that chemotherapy for cancer growing at several local areas induces remote metastasis. The part of the reason is thought that NF-kB is activated by chemotherapy. We reported previously that hyperthermia and induction of Hsp70 inhibited continuous activation of NF-kB of cancer cells. In this study, we examined whether hyperthermia attenuated the metastatic potential of colon cancer through the induction of Hsp70.

Method: Colon26 cell, a mouse colon adenocarcinoma cell line, were separated four groups. 1) no treatment, 2) treatment with hyperthermia at 42 degree Celsius in the CO₂ incubator for one hour, 3) treatment with Hsp inducer, geranylgeranylacetone (GGA, 10^-6M) for two hours, 4) treatment with hyperthermia after GGA treatment. We measured the viability of each-treated colon26 cells by WST-8 and the content of Hsp 70 in each-treated cell by Western blotting.

For in vivo study, colon26 cells in four groups were injected via the tail vein or into the subcutaneous zone of male BALB/c mice and numbers of pulmonary metastases or size of subcutaneous tumors were assessed 14 days later.

Results: Cell viability is almost equal in four groups. About the induction of Hsp70 in colon26 cells, GGA and hyperthermia induced Hsp70 as compared with untreated colon26. The combination of GGA and hyperthermia further induced Hsp70. In pulmonary metastasis models, the combination of GGA and hyperthermia is less pulmonary metastases than other cell groups. In subcutaneous tumor models, all cell groups were developing as same.

Conculusion: It is suggested that the metastatic potential but not the proliferation potency of cancer cells is inhibited by transient induced Hsp70.