Antitumor effects of human recombinant interleukin-1 alpha and etoposide against human tumor cells: mechanism for synergism in vitro and activity in vivo.
Recombinant human interleukin 1 alpha (rh IL-1 alpha) and etoposide (VP-16) synergize for direct growth inhibition of several human tumor cell lines in vitro. Our previous studies demonstrated that VP-16 increased the number of membrane-associated IL-1 receptors (IL-1Rs) and also enhanced the internalization of receptor-bound rh IL-1 alpha. The purposes of this study were to test our hypotheses that these events were critical to the synergy between rhIL-1 alpha and VP-16, to determine whether rhIL- 1 alpha and VP-16 synergize to increase superoxide (SO) anion radical production in vitro since SO anion has been implicated in the toxic effects of IL-1, and to investigate the antitumor efficacy of the combination against tumors in vivo. A375/C6 melanoma cells and OVCAR-3 ovarian carcinoma cells were tested with IL-1 receptor antagonist (IL-1 ra) before exposure to rhIL-1 alpha, VP-16 and rhIL-1 alpha plus VP-16. The synergistic or antagonistic effects were assessed by MTT assay. SO production was measured by reduction of cytochrome C. Athymic female mice bearing the A375/C6 melanoma were treated by rhIL-1 alpha, VP-16, and rhIL- 1 alpha+VP-16. The antitumor effects were evaluated by quantitating tumor growth and survival time. Pretreatment with the IL-1ra abrogated the synergistic effects of rhIL-1 alpha and VP-16. The production of SO radical by A375/C6 cells was increased 2.5 fold by the combination of rhIL-1 alpha and VP-16, and the addition of exogenous SOD blocked the synergy between rhIL-1 alpha and VP-16. However, when A375/SOD15 cells which over-expressed manganese superoxide dismutase (MnSOD) after MnSOD cDNA transfection were exposed to rhIL-1 alpha and VP-16, in vitro antagonism was observed. In vivo studies demonstrated that the combination of rhIL-1 alpha and VP-16 delayed tumor growth better than either agent alone, although long-term survival was not improved because of substantial toxicity. Our results suggest that the synergistic antitumor effects of IL-1 alpha and VP-16 may be due to IL-1R modulation and increased internalization of IL-1-IL-1R complex by VP-16 treatment, as well as to a subsequent increase in SO anion radical production from the tumor cells exposed to both drugs. Thus, the combination of IL-1 alpha and VP-16 might prove useful for the treatment of malignant disease in vivo, if the increased toxicity can be reduced or managed.
Usui
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Laboratory of Experimental Immunology, National Cancer Institute, FCRDC, Maryland 21702-1201, USA.
Matsushima
K
K
Pilaro
A M
AM
Longo
D L
DL
Wiltrout
R H
RH
D000818:Animals; D000970:Antineoplastic Agents / Q000008:administration & dosage*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use; D004357:Drug Synergism; D005047:Etoposide / Q000008:administration & dosage*; D005260:Female; D006801:Humans; D053590:Interleukin 1 Receptor Antagonist Protein; D007375:Interleukin-1 / Q000008:administration & dosage*; D051379:Mice; D008807:Mice, Inbred BALB C; D009374:Neoplasms, Experimental / Q000188:drug therapy; D011994:Recombinant Proteins / Q000008:administration & dosage; D012795:Sialoglycoproteins / Q000494:pharmacology; D013482:Superoxide Dismutase / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; C507763:IL1RN protein, human; C507764:Il1rn protein, mouse; D053590:Interleukin 1 Receptor Antagonist Protein; D007375:Interleukin-1; D011994:Recombinant Proteins; D012795:Sialoglycoproteins; D013481:Superoxides; D005047:Etoposide; D013482:Superoxide Dismutase