Melphalan and other anticancer modalities up-regulate B7-1 gene expression in tumor cells

In this study, we show that administration of low-dose melphalan (L-PAM, L-phenylalanine mustard) to mice bearing a large MOPC-315 plasmacytoma led to a rapid up-regulation of B7-1 (CD80), but not B7-2 (CD86), expression on the surface of MOPC-315 tumor cells. This L-PAM-induced preferential up- regulation of B7-1 surface expression was due, at least in part, to a direct effect of L-PAM on the tumor cells, as in vitro exposure of MOPC-315 tumor cells to L-PAM led to the preferential up-regulation of B7-1 surface expression. Moreover, in vitro exposure of MOPC-315 tumor cells to two other anticancer modalities, γ-irradiation and mitomycin C, resulted in the preferential up-regulation of B7-1 surface expression. This effect was not restricted to MOPC-315 tumor cells, as preferential up-regulation of B7-1 surface expression was observed also following in vitro exposure of the P815 mastocytoma (that is negative for both B7-1 and B7-2 surface expression) to any of the three anticancer modalities. The up-regulation of B7-1 surface expression following in vitro exposure of tumor cells to L-PAM, γ- irradiation, or mitomycin C required de novo protein and RNA synthesis, and was associated with the accumulation of mRNA for B7-1 within 4-8 h, indicating that the regulation of B7-1 expression is at the RNA transcriptional level. These results have important implications for an additional immune-potentiating mechanism of these anticancer modalities in clinical setting.