title: Molecular mechanisms underlying IFN-gamma-mediated tumor growth inhibition induced during tumor immunotherapy with rIL-12.
abstract: The present study investigates the molecular mechanisms by which IFN-gamma produced as a result of in vivo IL-12 administration exerts its anti-tumor effects. rIL-12 was administered three or five times into mice bearing CSA1M fibrosarcoma, OV-HM ovarian carcinoma or MCH-1-A1 fibrosarcoma. This regimen induced complete regression of CSA1M and OV-HM tumors but only transient growth inhibition of MCH-1-A1 tumors. The anti-tumor effects of IL-12 were associated with enhanced induction of IFN-gamma because these effects were abrogated by pretreatment of hosts with anti-IFN-gamma antibody. Exposure in vitro of the three types of tumor cells to rRFN-gamma resulted in moderate to potent inhibition of tumor cell growth. IFN-gamma stimulated the expression of mRNAs for an inducible type of NO synthase (iNOS) in CSA1M cells and indoleamine 2,3-dioxygenase (IDO), an enzyme capable of degrading tryptophan, in OH-HM cells, but induced only marginal levels of these mRNAs in MCH-1-A1 cells. In association with iNOS gene expression, IFN-gamma-stimulated CSA1M cells produced a large amount of NO which functioned to inhibit their own growth in vitro. Although OV-HM and MCH-1A1 cells did not produce NO, they also exhibited NO susceptibility. Whereas the tumor masses from IL-12-treated CSA1M-bearing or OV-HM-bearing mice induced higher levels of iNOS (for CSA1M) or IDO and iNOS (for OV-HM) mRNAs, the MCH-1-A1 tumor mass expressed lower levels of iNOS mRNA alone. Moreover, massive infiltration of CD4(+) and CD8(+) T cells and Mac-1(+) cells was seen only in the CSA1M and OV-HM tumors. Thus, these results indicate that IFN-gamma produced after IL-12 treatment induces the expression of various genes with potential to modulate tumor cell growth by acting directly on tumor cells or stimulating tumor-infiltrating lymphoid cells and that the effectiveness of IL-12 therapy is associated with the operation of these mechanisms.
authors.affiliation: Biomedical Research Center, Osaka University, Medical School, 2-2, Yamada-oka, Suita, Osaka 565, Japan.
authors.forename: W G
authors.initials: WG
authors.lastname: Yu
authors.forename: N
authors.initials: N
authors.lastname: Yamamoto
authors.forename: H
authors.initials: H
authors.lastname: Takenaka
authors.forename: J
authors.initials: J
authors.lastname: Mu
authors.forename: X G
authors.initials: XG
authors.lastname: Tai
authors.forename: J P
authors.initials: JP
authors.lastname: Zou
authors.forename: M
authors.initials: M
authors.lastname: Ogawa
authors.forename: T
authors.initials: T
authors.lastname: Tsutsui
authors.forename: R
authors.initials: R
authors.lastname: Wijesuriya
authors.forename: R
authors.initials: R
authors.lastname: Yoshida
authors.forename: S
authors.initials: S
authors.lastname: Herrmann
authors.forename: H
authors.initials: H
authors.lastname: Fujiwara
authors.forename: T
authors.initials: T
authors.lastname: Hamaoka
mesh_terms: D000818:Animals; D002277:Carcinoma / Q000188:drug therapy / Q000201:enzymology; D002634:Chemotaxis, Leukocyte; D005260:Female; D005354:Fibrosarcoma / Q000188:drug therapy / Q000201:enzymology; D005786:Gene Expression Regulation / Q000276:immunology; D006084:Graft Rejection; D006131:Growth Inhibitors / Q000494:pharmacology*; D016233:Immunotherapy, Active; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase; D007371:Interferon-gamma / Q000494:pharmacology*; D018664:Interleukin-12 / Q000494:pharmacology* / Q000627:therapeutic use*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D009569:Nitric Oxide / Q000502:physiology; D019001:Nitric Oxide Synthase / Q000032:analysis; D010051:Ovarian Neoplasms / Q000188:drug therapy / Q000201:enzymology; D012333:RNA, Messenger / Q000032:analysis; D011994:Recombinant Proteins / Q000494:pharmacology; D014366:Tryptophan Oxygenase / Q000032:analysis; D014407:Tumor Cells, Cultured
chemical_list: D006131:Growth Inhibitors; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase; D012333:RNA, Messenger; D011994:Recombinant Proteins; D018664:Interleukin-12; D009569:Nitric Oxide; D007371:Interferon-gamma; D014366:Tryptophan Oxygenase; D019001:Nitric Oxide Synthase