Inhibition of human colon carcinoma development by lentinan from shiitake mushrooms (Lentinus edodes)

Objectives: Lentinan was extracted from shiitake mushrooms (Lentinus edodes) via a new cost-effective procedure that resulted in high purity (88%) and yield. Unlike previous reports whereby the lentinan was given parenterally, in this study the emphasis was on the oral administration of lentinan. The goal is to document whether the efficacy of the antitumor property is still expressed through this route of administration. Design: Initial study on the action of lentinan was conducted using murine lymphoma (K36) cells in a AKR mouse model. Further investigation on the effectiveness of the extracted lentinan was then performed using human colon-carcinoma cell lines in mice. Six established human colon-carcinoma cell lines segregated into three groups of different degrees of differentiation were used in this study. One group was not fed (control) and the second group was prefed with lentinan for 7 days prior to inoculations with the cancer cells. The size of the tumors that developed was rated after I month. Results: Significant regression in tumor formation was observed in prefed mice compared to control (unfod) mice when K36 or human colon-carcinoma cells were used. Significant reductions in the size of the tumors were observed in mice prefed with lentinan. Follow-up investigation proceeded with the use of nude mice (athymic). Lymphocytes extracted from AKR mice prefed with lentinan for 7 days were inoculated into the nude mice. This was then followed by inoculation of the human colon-carcinoma cell lines into these mice. Much smaller tumors were formed in nude mice inoculated with lymphocytes, in contrast to the larger tumor formed in nude mice without lymphocytes inoculation. Conclusion: This study showed that the antitumor property of lentinan was maintained with oral administration. In addition, primed lymphocytes, when given passively to immunodeficient mice, were able to retard the development of tumors in these mice.