Potentiation of in vivo antitumor effects of recombinant interleukin-1 alpha by gelatin conjugation.

Chemical conjugation of a recombinant human interleukin-1 alpha (IL-1) with gelatin was conducted using a water-soluble carbodiimide in an attempt to augment the indirect effect of IL-1 on in vivo tumor cell growth in mice. Chromatographic studies of the IL-1-gelatin conjugate demonstrated that the apparent molecular weight of IL-1 was increased by the gelatin conjugation and about 60% of IL-1 activity was retained in the prepared conjugate. Intraperitoneal (i.p.) injection of the conjugate significantly suppressed the intraperitoneal growth of a subline of Meth A fibrosarcoma cells (RR1 cells), compared with the effect of free IL-1 at the same dose, although the cells per se were resistant not only to free IL-1 but also to gelatin-conjugated IL-1. Simple mixing of gelatin with free IL-1 did not augment the in vivo antitumor effect as compared with that of free IL-1. Gelatin conjugation improved the in vivo stability of IL-1. Prolonged retention of IL-1 activity in the peritoneal cavity as well as the circulation of mice was observed after i.p. injection of the IL-1-gelatin conjugate in comparison with free IL-1 injection, irrespective of the presence of tumor cells. Gelatin conjugation was effective in augmenting the in vivo antitumor effects of IL-1 to activate host cells, e.g. macrophages (M phi). The i.p. injection of the conjugate enhanced M phi infiltration into the peritoneal cavity of tumor-bearing mice and peritoneal M phi were strongly activated to inhibit the in vitro growth of RR1 cells. Thus, gelatin conjugation was effective in augmenting the indirect effect of IL-1 via host cells, leading to a high suppressive effect on in vivo growth of tumor cells.