Genotyping and Expression Analysis of IDO2 in Human Pancreatic Cancer: A Novel, Active Target

Abstract

Background We recently discovered that the enzyme indoleamine 2,3-dioxygenase (IDO) is overexpressed in primary pancreatic ductal adenocarcinomas (PDA) and in lymph node metastases (J Am Coll Surg. 5:849-54: 2008). IDO2 is a recently discovered relative of IDO that has unique signaling properties (Cancer Res. 67:7082-7087: 2007). Notably, the IDO2 gene has two functional polymorphisms commonly found in human populations that abolish its enzymatic activity (R235W and Y359STOP). Both IDO and IDO2 repress the immune system and we hypothesize that expression of these enzymes in PDA may help cancer cells evade immune detection. Methods Based on evidence that the IDO2 may be a preferential target of D-1-methyl-tryptophan (1-MT), a clinical lead inhibitor of IDO currently being evaluated in Phase I trials, we sequenced IDO2 in 36 resected PDAs and evaluated its expression in relation to the two known genetic polymorphisms. Results In our patient cohort, we found that 58% (21/36) of the cases were heterozygous for the R235W polymorphism; 28% (10/36) were homozygous wild-type; and only 14% (5/36) were homozygous for the functionally inactive polymorphism. Interestingly, IDO2 had a homozygous wild-type configuration in two pancreatic cancer cell lines whereas one cell line (MiaPaCa2 cells) was homozygous for the R235W polymorphism. As for the Y359STOP polymorphism (seen in the cell line Hs766T), we found that 27% (10/36) of the cases were heterozygous, 62% (22/36) were homozygous wild-type, and only 11% (4/36) were homozygous for this functionally inactive allele. Ruling out the possibility of compound polymorphic variants, we estimated 75% of our resected patient cohort had an active IDO2 enzyme with a conservative estimate that 58% of the patients had at least one functional allele. In immunohistochemical analyses, we found that IDO2 was equally overexpressed in pancreatic cancer tissue from each genetially polymorphic subgroup. We also detected IDO2 protein expression in the genetically distinct pancreatic cancer cell lines after exposure with IFN-γ, establishing that even functionally polymorphic IDO2 sequences can generate IDO2 protein. Conclusions These are the first data to report IDO2 expression in PDA and indicate that IDO2 genetic polymorphisms do not negate IFN-γ-inducible protein expression. IDO2 genotyping and expression analysis of our PDA patient tissue bank and cell lines show that IDO2 is active and expressed in a majority of PDA patients. Taken together, these data strongly suggest that the clinical lead compound D-1-MT acting through IDO2 might be useful in treatment of PDA, either alone or in combination with other anti-tumor modalities.

Prognostic Significance of Tryptophan Catabolism in Adult T-cell Leukemia/Lymphoma

“…Therefore, the Kyn/Trp ratio is merely one surrogate marker of IDO activity, and does not directly exclusively reflect IDO activity. Indeed, IDO2 was reported to be expressed in some cancers including pancreatic tumors (47,48). Thus, although we confirmed IDO production by ATL cells in some patients, and lack of TDO production by ATL cells in all patients, further investigation of IDO2 expression in ATL cells is warranted.…”

Indoleamine 2,3-Dioxygenase Expression in Human Cancers: Clinical and Immunologic Perspectives

“…Moreover, patients with pancreatic adenocarcinoma were more densely infiltrated by T reg in metastatic lymph nodes compared with nonmetastatic lymph nodes (22). Also, in all the cases, those metastatic lymph nodes were expressing IDO at different levels.…”

Spontaneous Cytotoxic T-Cell Reactivity against Indoleamine 2,3-Dioxygenase-2

“…In this respect, IDO2 expression has been found in human tumors, including gastric, colon, renal, and pancreatic tumors. Immunohistochemical analysis done in pancreatic tumors reveals IDO2 expression both at the level of the tumor cell as well as immune cells in tumor-draining lymph nodes (10).…”