Glutathione S-transferases

The effect of the glutathione transferase P1-1 (GSTP1-1) targeting has been investigated in both sensitive (U-2OS) and cisplatin-resistant (U-2OS/CDDP4 mg) human osteosarcoma cell lines. Despite the different enzyme's content, inhibition of GSTP1-1 by 6-(7-nitro-2,1,3-benzoxadiazol-4-ylthio)hexanol (NBDHEX) causes the activation of c-Jun N-terminal kinase (JNK) and apoptosis in both cell lines. However, different time courses of JNK activation and cell responses are observed. Whereas in the U-2OS/CDDP4 mg cell line drug treatment results in an early increase of caspase activity and secondary necrosis, in the U-2OS cells it mainly causes an early cell cycle arrest followed by apoptosis. In order to elucidate the action mechanism of NBDHEX we performed a proteomic investigation by label-free nLC-MS E . The high-throughput analysis associated with a bioinformatic tool suggested the involvement of the TNF receptor associated factor (TRAF) family in the cellular response to the drug treatment. We report experimental evidence of the interaction between GSTP1-1 and TRAF2 and we demonstrate that NBDHEX is able to dissociate the GSTP1-1 : TRAF2 complex. This restores the TRAF2 : ASK1 signaling, thereby leading to the simultaneous and prolonged activation of JNK and p38. These mitogenactivated protein kinases (MAPKs) mediate different effects: JNK is crucial for apoptosis, whereas p38 causes an increase in the p21 level and a concomitant cell cycle arrest. Our study shows that GSTP1-1 plays an important regulatory role in TRAF signaling of osteosarcoma and discloses new features of the action mechanism of NBDHEX that suggest potentially practical consequences of these findings.

In the present work,

6-(7-Nitro-2,1,3-benzoxadiazol-4-ylthio)hexanol (NBDHEX) is a powerful inhibitor of the glutathione transferase P1-1 (GSTP1-1) and causes the disruption of the complex between GSTP1-1 and c-Jun N-terminal Kinase (JNK). This induces JNK activation and apoptosis in tumour cells. In the present work we assess the in vitro and in vivo effectiveness of NBDHEX on two human melanoma cell lines, Me501 and A375. NBDHEX shows IC(50) values in the low micromolar range (IC(50) of 1.2+/-0.1microM and 2.0+/-0.2 microM for Me501 and A375, respectively) and is over 100 times more cytotoxic to these cell lines than temozolomide. Apoptosis is observed in Me501 cells within 3h of the addition of NBDHEX, while in A375 cells the apoptotic event is rather late, and is preceded by a G2/M phase arrest. In both melanoma cell lines, JNK activity is required for the ability of NBDHEX to trigger apoptosis, confirming that the JNK pathway is an important therapeutic target for this tumour. NBDHEX is also both effective and well tolerated in in vivo tumour models. A tumour inhibition of 70% is observed in vivo against Me501 human melanoma and a similar result is obtained on A375 model, with 63% of tumour inhibition. These findings indicate that the activation of the JNK pathway, through a selective GSTP1-1 targeting, could prove to be a promising new strategy for treating melanoma, which responds poorly to conventional therapies.

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