Critical role of indoleamine 2,3-dioxygenase in tumor resistance to repeated treatments with targeted IFNγ

Abstract

Targeted delivery of IFN; to tumors has been achieved by fusing this cytokine with GCNGRC, a tumor neovasculature homing peptide. Although the therapeutic efficacy of this protein (called IFN;-NGR) in animal models is greater than that of IFN;, frequent administrations of IFN;-NGR may result in lower efficacy and tumor resistance. We investigated the role of indoleamine 2,3-dioxygenase (IDO), an IFN;-inducible enzyme that may down-regulate T cells by affecting local tryptophan catabolism in tumor resistance to repeated treatments with IFN;-NGR. The study was carried out in immunocompetent mice and in nu/nu mice bearing RMA lymphoma, B16F melanoma, or WEHI-164 fibrosarcoma and in vitro using cultured tumor cells. IDO activity was increased in lymphoma homogenates after multiple treatments with IFN;-NGR but not after a single treatment. Coadministration of 1-methyltryptophan, an inhibitor of IDO, increased tumor responses to multiple treatments in the lymphoma, melanoma, and fibrosarcoma models. No synergism between IFN;-NGR and 1-methyl-tryptophan was observed in vitro in tumor cell proliferation assays or in nu/nu tumor-bearing mice, suggesting that the antitumor effect was host mediated. We conclude that IDO is critically involved in tumor resistance to repeated treatments with IFN;-NGR, likely causing excessive stimulation of tryptophan catabolism and inhibiting antitumor immune mechanisms. Coadministration of IFN;-NGR with IDO inhibitors could represent a new strategy for increasing its antitumor activity. [Mol Cancer Ther 2008;7(12):3859 -66]

Critical Role of Flanking Residues in NGR-to-isoDGR Transition and CD13/Integrin Receptor Switching

“…The molecular mass of each peptide was checked by MALDI-TOF mass spectrometry (MS) analysis. NGR-Qdot, ARAQdot, and isoDGR-Qdot conjugates (consisting of ac-NGR-2C-TNF [1][2][3][4][5][6][7][8][9][10][11] , ac-ARA-2C-TNF [1][2][3][4][5][6][7][8][9][10][11] and acisoDGR-2C-TNF 1-11 chemically coupled to amine-modified quantum dots) were prepared as described (36).…”

“…The product were then analyzed by reverse-phase HPLC (RP-HPLC) and MALDI-TOF MS. RP-HPLC was performed using a C18 column (PepMap C18, 250 ϫ 4.6 mm, PerSeptive Biosystem, Framingham, MA) (5 g) and NGR-2G-TNF [1][2][3][4][5][6][7][8][9][10][11] (5 g) after incubation at 37°C in PBS. Dotted line, untreated peptide.…”

“…Dotted line, untreated peptide. Peak 1 corresponds to NGR-2C-TNF [1][2][3][4][5][6][7][8][9][10][11] ; peak height was proportional to the loaded material within the range of 1-50 g. B, RP-HPLC of NGR-2C after incubation at 37°C in human serum. The peptide was added to human serum (500 g/ml, final concentration) and incubated for the indicated time.…”

“…Peak 1 corresponds to NGR-2C. C, stability of NGR-2C-TNF 1-11 , NGR-2G-TNF [1][2][3][4][5][6][7][8][9][10][11] , and NGR-2C after incubation at 37°C or at 4°C in PBS, HEPES buffer, water, or human serum, as determined by RP-HPLC. D and E, MALDI-TOF MS analysis of non-acetylated and acetylated NGR-2G, NGR-2C, isoDGR-2G, and isoDGR-2C after incubation at 37°C for 0 and 8 days in PBS.…”

“…To this aim we compared the stability of CNGRCGVRSSSRTPSDKY (NGR-2C-TNF [1][2][3][4][5][6][7][8][9][10][11] ) with that of linear GNGRGGVRSSSRTPSDKY (NGR-2G-TNF 1-11 ), i.e. two peptides currently used for targeted delivery of TNF and liposomes to tumors (5,11).…”