Glutathione S-transferase P1-1 as a target for mesothelioma treatment.

Malignant pleural mesothelioma is a poorly responsive tumor known to overexpress the phase II detoxification enzyme glutathione-S-transferase, which catalyzes the conjugation between glutathione and platinum(II)-containing drugs. Therefore, we evaluated the effect of the strong glutathione S-transferase inhibitor NBDHEX on human mesothelioma cell lines (MSTO-211H, MPP89, MM-B1 and Mero 48a) featuring the most common mesothelioma phenotypes: epithelioid and biphasic. Even though a different response to NBDHEX was observed, the molecule was very effective on all cell lines tested, triggering a sustained activation of both JNK and p38, followed by caspase activation and apoptosis. NBDHEX also caused severe oxidative stress in the MPP89 cells and, to a lesser extent, in the MMB1 cells, while it did not cause a significant redox imbalance in the other cell lines. The efficacy of the drug was found to be comparable or even higher than that of cisplatin. Moreover, it showed synergistic or additive effects when used in combination with cisplatin. In conclusion, NBDHEX was effective on mesothelioma cell lines, with IC(50) values in the low micromolar range (IC(50) between 1 and 4 µM). These findings indicate that NBDHEX, alone or in combination with cisplatin, is a promising new strategy for treating this rare and aggressive malignancy.

Glutathione transferases and development of new principles to overcome drug resistance.

Chemoresistance is a multifactorial phenomenon and many studies clearly show that a coordinated expression of efflux transporter proteins and phase II conjugating enzymes in tumor cells is linked to the development of the multidrug resistance phenotype. In particular, the overexpression of glutathione S-transferases and efflux pumps in tumors may reduce the reactivity of various anticancer drugs. In recent years it has become evident that glutathione S-transferases are also involved in the control of apoptosis through the inhibition of the JNK signaling pathway. As such, the glutathione S-transferase superfamily has become the focus of extensive pharmaceutical research in attempt to generate more efficient anticancer agents. Here we present an overview of the GST inhibitors and the GST-activated pro-drugs utilized to date to overcome drug resistance.

In vitro and in vivo efficacy of 6-(7-nitro-2,1,3-benzoxadiazol-4-ylthio)hexanol (NBDHEX) on human melanoma.

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.

The glutathione S-transferase inhibitor 6-(7-nitro-2,1,3-benzoxadiazol-4-ylthio)hexanol overcomes the MDR1-P-glycoprotein and MRP1-mediated multidrug resistance in acute myeloid leukemia cells.

PURPOSE: There has been an ever growing interest in the search for new anti-tumor compounds that do not interact with MDR1-Pgp and MRP1 drug transporters and so circumvent the effect of these proteins conferring multidrug resistance (MDR) and poor prognosis in AML patients. We have investigated the cytotoxic activity of the strong glutathione S-transferase (GST) inhibitor 6-(7-nitro-2,1,3-benzoxadiazol-4-ylthio)hexanol (NBDHEX) on AML (HL60) cell lines. METHODS: Functional drug efflux studies and cell proliferation assays were performed on both sensitive and MDR AML (HL60) cells after incubation with NBDHEX. Moreover, the mode of cell death (apoptosis vs. necrosis) as well as the correlation between NBDHEX susceptibility and GST activity or Bcl-2 expression was investigated. RESULTS: NBDHEX is not a substrate of either MDR1-Pgp or MRP1 efflux pumps; in fact, it is not only cytotoxic toward the parental HL60 cell line, but also overcomes the MDR phenotype of its HL60/DNR and HL60/ADR variants. CONCLUSIONS: The data herein reported show that NBDHEX mediates efficient killing of both MDR1-Pgp and MRP1 over-expressing AML cells. Therefore, this drug can potentially be used as an effective agent for treating MDR in AML patients.