Stimulation of non-specific resistance to tumors in the mouse using a poly(maleic-acid-styrene)-conjugated neocarzinostatin

The development of non-specific resistance to tumors following stimulation with poly(maleic-acid-styrene)-conjugated neocarzinostatin (SMANCS), a polymer-conjugated derivative of neocarzinostatin, was investigated in mice. The growth of syngeneic solid tumors (Meth-A fibrosarcoma and RL ♂ 1 leukemia) inoculated into BALB/c mice was suppressed after one treatment with SMANCS at doses ranging from 0.14 mg/kg to 3.4 mg/kg i.v. 24 h before tumor implantation. Since previously observations concerning SMANCS have shown that it disappeared within 1.5 h after i.v. administration in mice and that it was inactivated quickly in plasma, SMANCS evidently inhibited tumor growth by mediating non-specific resistance. In addition, the non-specific resistance to tumors stimulated by SMANCS could be passively transferred to untreated mice by serum which was shown to contain interferon (IFN) from 12 h to 20 h after SMANCS administration. However, the resistance was not produced by serum prepared from mice at 8 h or 32 h after administration presumably because of the observation that the interferon activity was only demonstrated from 12 h to 28 h after SMANCS stimulation. When the serum specimens were treated with anti-IFN-γ antiserum, the antitumor activity of the sera was abrogated. However, no significant change was detected in the antitumor activity of the specimens following treatment with anti-IFN-α/β antiserum. Treatment of mice with SMANCS and anti-IFN-γ antiserum together resulted in the elimination of the non-specific resistance to tumors. The IFN induced in the sera of mice by SMANCS was shown to be 57% IFN-γ and 41% IFN-α/β. Half of the interferon produced in SMANCS-stimulated mice could be eliminated by treatment with anti-IFN-γ, and treatment of SMANCS-stimulated mice with both anti-IFN-γ and anti-IFN-α/β antisera resulted in a total absence of detectable interferon. These findings suggest that while the administration of SMANCS induces both IFN-γ and IFN-α/β production, in this case, it is only the former which mediates the non-specific resistance to tumors.