Immunologic enhancement of experimental metastasis in the rat

Anti-tumor immunoglobulin M increases lung metastasis in an experimental model of malignant melanoma

Cancer metastasis involves distinct steps that depend on complicated tumor-host interactions. The hematogenous dissemination of tumor cells may be facilitated by factors that promote the arrest and adherence of cancer cells in capillaries. We examined whether anti-tumor monoclonal immunoglobulin M (IgM) antibodies promoted the hematogenous dissemination of B16 melanoma cells in syngeneic mice. IgM monoclonal antibodies were generated that selectively bind to B16 melanoma cells as compared to syngeneic fibroblasts, lymphocytes or Lewis lung carcinoma cells. Incubation of B16-BL6 or B16-F0 melanoma cells with these IgM anti-tumor antibodies significantly increased the number of lung colonies as compared with control antibodies. Moreover, intraperitoneal injection of specific antibody also significantly increased lung colonization. All anti-tumor antibodies promoted the aggregation of B16 melanoma cells. A chemically generated immunoglobulin G (IgG)-like fragment of an anti-tumor IgM antibody displayed greatly reduced tumor aggregation and, in contrast to intact IgM, did not significantly increase lung colonization of B16 melanoma cells. Neither intact IgM nor the IgG-like fragment enhanced the in vitro invasiveness of B16 melanoma cells across Matrigel-coated membranes. Our results, therefore, suggest that besides their beneficial anti-tumor effects, anti-tumor IgM antibodies may also promote the hematogenous dissemination of cancer cells.

The nature of tumor presentation in the animal changes the effects of levamisole treatment on metastasis

We have investigated the ability of levamisole (LMS) to modulate growth and metastasis of a rat hepatocarcinoma. LMS treatment decreased spontaneous metastasis to the lungs and lymph nodes, while it increased tumor lung colonization following intravenous tumor cell inoculation. Both serum immunoglobulin (Ig) and circulating immune complex (CIC) levels were higher than normal in tumor-bearing rats. LMS treatment did not alter these parameters in the lung colony assay, while a small decrease of serum IgG was noted for LMS treated animals in the spontaneous metastasis assay. We found no convincing evidence for CIC levels, immunoglobulin isotype shifts or induced changes in natural killer (NK) cell reactivity being involved in the observed LMS modulation of tumor metastasis. The nature of the presentation of the tumor in the animal, however, appeared to be critical in determining the metastatic response to LMS therapy.