Nucleosome-releasing treatment makes surviving tumor cells better targets for nucleosome-specific anticancer antibodies.

Monoclonal antibody (MoAb) 2C5, a nucleosome-specific antinuclear autoantibody (ANA) from the repertoire of aged mice, was recently reported to recognize the surface of various tumor cells but not normal cells. Surface-bound nucleosomes (NSs) were previously proven to be MoAb 2C5's target on the outer membrane of tumor cells. Furthermore, MoAb 2C5 was found to have a strong antitumor effect during the early stages of tumor development. In an attempt to further increase antitumor effect of nucleosome-specific tumorocidal monoclonal antibody against established tumors, we investigated a possible way to enhance antibody association with tumor cells. Evidence is presented here demonstrating that the in vitro treatment of tumor cells (S49 T lymphoma) resulting in a partial cell death and massive liberation of intact NSs from dead tumor cells into the culture medium was accompanied by a 50-fold increase of MoAb 2C5 binding to the surface of surviving tumor cells. Massive NS release was observed in the case of S49 T-cell treatment with dexamethasone and vincristine. However, a partial cell killing that was not accompanied with NS release (EL4 lymphoma treatment with doxorubicin) did not result in the enhanced binding of MoAb 2C5 to the surface of surviving tumor cells. The use of NS-specific tumorocidal antibodies, such as MoAb 2C5, in combination with another NS release-inducing tumor therapy, should provide an enhanced antibody-tumor binding.