Anticancer activity of a thymidine quinoxaline conjugate is modulated by cytosolic thymidine pathways

Abstract

BackgroundHigh levels of thymidine kinase 1 (TK1) and thymidine phosphorylase (TYMP) are key molecular targets by thymidine therapeutics in cancer treatment. The dual roles of TYMP as a tumor growth factor and a key activation enzyme of anticancer metabolites resulted in a mixed outcome in cancer patients. In this study, we investigated the roles of TK1 and TYMP on a thymidine quinoxaline conjugate to evaluate an alternative to circumvent the contradictive role of TYMP.MethodsTK1 and TYMP levels in multiple liver cell lines were assessed along with the cytotoxicity of the thymidine conjugate. Cellular accumulation of the thymidine conjugate was determined with organelle-specific dyes. The impacts of TK1 and TYMP were evaluated with siRNA/shRNA suppression and pseudoviral overexpression. Immunohistochemical analysis was performed on both normal and tumor tissues. In vivo study was carried out with a subcutaneous liver tumor model.ResultsWe found that the thymidine conjugate had varied activities in liver cancer cells with different levels of TK1 and TYMP. The conjugate mainly accumulated at endothelial reticulum and was consistent with cytosolic pathways. TK1 was responsible for the cytotoxicity yet high levels of TYMP counteracted such activities. Levels of TYMP and TK1 in the liver tumor tissues were significantly higher than those of normal liver tissues. Induced TK1 overexpression decreased the selectivity of dT-QX due to the concurring cytotoxicity in normal cells. In contrast, shRNA suppression of TYMP significantly enhanced the selective of the conjugate in vitro and reduced the tumor growth in vivo.ConclusionsTK1 was responsible for anticancer activity of dT-QX while levels of TYMP counteracted such an activity. The counteraction by TYMP could be overcome with RNA silencing to significantly enhance the dT-QX selectivity in cancer cells.Electronic supplementary materialThe online version of this article (doi:10.1186/s12885-015-1149-5) contains supplementary material, which is available to authorized users.

Mendelian randomization identifies circulating proteins as biomarkers for age at menarche and age at natural menopause

“…(copine 1) may be involved in the DNA damage response 43 . In humans, DNER 44 has been associated with breast cancer, TYMP (thymidine phosphorylase) with liver tumours 45 , and PLXNA1 (plexin A1) with lung cancer 46 .…”

Chemistry and pharmacological diversity of quinoxaline motifs as anticancer agents

“…Degrees of dT-QX cytotoxicity, TYMP and TK1 proteins have been reported as good indicators of high anticancer activity of the thyme analogue of dT-QX, whose structure (32) is shown in Fig. 9 (6). The result of the cell viability 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay on four human liver cell lines was as shown in Fig.…”

“…Position C(3) is most often substituted by a short alkyl chain (e.g., CH 3 , CF 3 ) or phenyl. Substitution of C (6) or C(7) of QdNOs by Cl, F, CF 3 , or OCH 3 is also advantageous in antitumor diversity (81).…”

“…Thymidine kinase 1 (TK1) and thymidine phosphorylase (TYMP) are key molecular targets of thymidine therapeutics in cancer treatment. Hence, cytosolic thymidine pathways have been documented to be a highly effective tool in the modulation of anticancer activity of a thymidine quinoxaline conjugate (6). In view of the adverse effect of this global phenomenon, various researchers have synthesized numerous nitrogen containing heterocyclic compounds as agents of transformation in anticancer motifs in the chemotherapeutic world.…”