Table 2.

List of molecules or drugs tested as inhibitors of IDO1 and/or TDO2 in vitro, some of which are from the library of the National Institute of Cancer.

Target	Drug	Development Stage	Observations	Characteristics
IDO1, P38/MAPK pathway, JNK pathway	1-l-MT (1-methyl-l-tryptophan) [63,64,71]	in vitro, in vivo	delays tumor outgrowth when combined with chemotherapeutic agents	bioavailable
IDO1 inhibitor	MTH-TRP (methyl-thiohydantoin-trypt-ophan) [37]	in vitro, in vivo	delays tumor outgrowth when combined with chemotherapeutic agents	20-fold more potent than 1-MT, more rapidly cleared from serum, bioavailable
TDO2 inhibitor (mRNA level)	680C91 [72]	in vitro		poor bioavailability, poor solubility
TDO2 inhibitor	LM10 [73]	in vitro, in vivo		high bioavailability, high solubility
IDO1 and TDO2 inhibitor	NSC 26326 or β-lapachone [74]	in vitro	more potent inhibitor of TDO2 than IDO1	natural quinone isolated from lapacho tree; topoisomerase I inhibitor
IDO1/TDO2 inhibitor inhibits DNA synthesis JNK pathway inducing upregulation of death receptors	mitomycin C [74]	in vitro	8-fold more potent inhibitor of TDO2 than IDO1	active on 74 different tumor cell lines
TDO2 inhibitor	NSC 36398 (dihydroquercetin, taxifolin) [74]	in vitro	potent inhibitor of TDO2; no inhibition of IDO1	natural flavonoid with low toxicity
IDO1 and TDO2 inhibitor	NSC 267461 (nanaomycin A) [74]	in vitro	more potent inhibitor of TDO2 than IDO1	naphtoquinone based antibiotic; active on 59 cancer cell lines
IDO1 and TDO2 inhibitor	NSC 111041 [74]	in vitro	more potent inhibitor of TDO2 than IDO1	active on colon and breast cancer cell lines
IDO1 and TDO2 inhibitor	NSC 255109 [74]	in vitro	strong inhibitor of both IDO1 and TDO2	geldanamycin derivative; active on 65 different cell lines
IDO1 and TDO2 inhibitor	NSC 261726 (3-deazaguanine) [74]	in vitro	stronger inhibitor of TDO2 than IDO1	active on leukemia tumor cell lines