Influence of human alpha-interferon on four human osteosarcoma xenografts in nude mice.

Growth-inhibiting effects of human alpha-interferon (HuIFN-alpha) were investigated in four human osteosarcoma xenografts in nude mice. In addition to effects on growth, the HuIFN-alpha treatment was evaluated by histological examination and DNA flow cytometric analysis. Daily doses of 2 X 10(5) IU HuIFN-alpha completely arrested the growth of two osteosarcoma xenografts and partially inhibited one, whereas 1 X 10(6) IU/day were necessary to arrest the growth of the fourth. Growth inhibition was reversible and tumor size independent. The histological appearance, including mitotic indices, and S-phase proportions were unchanged in three xenografts. The mechanism of the HuIFN-alpha-induced growth inhibition of these three xenografts was therefore not considered to be a direct antiproliferative effect, but rather due to increased cell loss and/or increased cell cycle time. The modal DNA value of one xenograft was changed from aneuploid to diploid during HuIFN-alpha treatment. Histologically, these xenografts were partly replaced by normal appearing bone and bone marrow. The S-phase proportion was also reduced in these xenografts, implying that HuIFN-alpha can also have a direct antiproliferative effect.