Iron-saturated Lactoferrin A Novel Adjuvant for Cancer Chemotherapy

Abstract

Lactoferrin (Lf), an iron-containing glycoprotein found in many bodily secretions, has previously been shown to exert anti-tumour activity. Bovine Lf (bLf) exists naturally in a form that contains ~15% iron, but can be treated with iron to generate a fully iron-saturated form, here designated Fe-Lf. Fe-Lf was demonstrated to augment cancer chemotherapy in mice, causing tumours to be completely and rapidly eradicated. In contrast, natural bLf was far less effective. The mechanisms responsible for the anti-tumour activity of Fe-Lf are poorly understood. Here I investigated whether bLf and Fe-Lf augment cancer chemotherapy against K562 cells, a human chronic myelogenous leukemia cell line. The ability of the bLfs to stimulate the antitumour cytotoxicity of peripheral blood mononuclear cells (PBMC) and lymphokineactivated killer cells (LAK) cells against K562 cells was also studied. Effector PBMC and LAK cells and target K562 cells were separately preincubated with or without 50 μg/ml of bLf or Fe-Lf for different time periods before measuring their anti-tumour cytotoxicity, and susceptibility to cytotoxicity and chemotherapy, respectively. Both forms of bLf failed to augment chemotherapy and had no effect on the spontaneous cytotoxicity of PBMC against K562 cells. In contrast, both forms of bLf increased the resistance of K562 cells to damage by chemotherapy. This property may explain why bLf prevents damage to the small intestine by protecting gut enterocytes against chemotherapy-induced damage. In contrast, Fe-Lf significantly increased the anti-tumour cytotoxicity of IL-2-activated LAK cells after a 2- week preincubation. Fe-Lf proved to be more effective than natural Lf at stimulating the antitumour cytotoxicity of LAK cells. The bLfs had no consistent effect on the ability of lymphocytes and monocytes to kill K562 cells. Immunohistochemistry studies revealed that iii both Lf and Fe-Lf influence the cellular composition of PBMC and LAK cells after a 2-week culture. In a parallel study ongoing in the laboratory, a colleague fed a control diet and the same diet containing Fe-Lf to mice bearing 4T1 breast tumours. Analysis here by immunohistochemical staining of tumour sections revealed that the Fe-Lf diet induced the infiltration of the tumours by immune cells. T, B cells and NK cells were readily detected in the tumours of mice fed Fe- Lf, but were absent from the tumours of mice fed the control diet. Many of the immune cells that infiltrated the tumours contained bLf, suggesting they had specifically migrated from the intestines of Fe-Lf-fed mice. In summary, the results described herein help to explain the antitumour activity of Fe-Lf by showing specific effects of Fe-Lf on the anti-tumour activity of LAK cells, and Fe-Lf-induced infiltration of tumours. They suggest that Fe-Lf is a potential adjuvant that could be used to augment IL-2-stimulated LAK therapy in the treatment of cancer.