Simvastatin and downstream inhibitors circumvent constitutive and stromal cell-induced resistance to doxorubicin in IGHV unmutated CLL cells

The immunoglobulin heavy-chain variable region (IGHV) mutational status is a strong determinant of remission duration in chronic lymphocytic leukemia (CLL). The aim of this work was to compare the multidrug resistance (MDR) signature of IGHV mutated and unmutated CLL cells, identifying biochemical and molecular targets potentially amenable to therapeutic intervention.We found that the mevalonate pathway-dependent Ras/ERK1-2 and RhoA/RhoA kinase signaling cascades, and the downstream HIF-1\u3b1/P-glycoprotein axis were more active in IGHV unmutated than in mutated cells, leading to a constitutive protection from doxorubicin-induced cytotoxicity. The constitutive MDR phenotype of IGHV unmutated cells was partially dependent on B cell receptor signaling, as shown by the inhibitory effect exerted by ibrutinib. Stromal cells further protected IGHV unmutated cells from doxorubicin by upregulating Ras/ERK1-2, RhoA/RhoA kinase, Akt, HIF-1\u3b1 and P-glycoprotein activities. Mevalonate pathway inhibition with simvastatin abrogated these signaling pathways and reversed the resistance of IGHV unmutated cells to doxorubicin, also counteracting the protective effect exerted by stromal cells. Similar results were obtained via the targeted inhibition of the downstream molecules ERK1-2, RhoA kinase and HIF-1\u3b1.Therefore, targeting the mevalonate pathway and its downstream signaling cascades is a promising strategy to circumvent the MDR signature of IGHV unmutated CLL cells

Temozolomide down-regulates P-glycoprotein in human blood-brain barrier cells by disrupting Wnt3-signalling.

Low delivery of many anticancer drugs across the blood-brain barrier (BBB) is a limitation to the success of chemotherapy in glioblastoma. This is because of the high levels of ATP-binding cassette transporters like P-glycoprotein (Pgp/ABCB1), which effluxes drugs back to the bloodstream. Temozolomide is one of the few agents able to cross the BBB; its effects on BBB cells permeability and Pgp activity are not known. We found that temozolomide, at therapeutic concentration, increased the transport of Pgp substrates across human brain microvascular endothelial cells and decreased the expression of Pgp. By methylating the promoter of Wnt3 gene, temozolomide lowers the endogenous synthesis of Wnt3 in BBB cells, disrupts the Wnt3/glycogen synthase kinase 3/?-catenin signaling, and reduces the binding of ?-catenin on the promoter of mdr1 gene, which encodes for Pgp. In co-culture models of BBB cells and human glioblastoma cells, pre-treatment with temozolomide increases the delivery, cytotoxicity, and antiproliferative effects of doxorubicin, vinblastine, and topotecan, three substrates of Pgp that are usually poorly delivered across BBB. Our work suggests that temozolomide increases the BBB permeability of drugs that are normally effluxed by Pgp back to the bloodstream. These findings may pave the way to new combinatorial chemotherapy schemes in glioblastoma. © 2013 Springer Basel

Temozolomide down-regulates P-glycoprotein in human blood-brain barrier cells by disrupting Wnt3 signaling

Low delivery of many anticancer drugs across the blood-brain barrier (BBB) is a limitation to the success of chemotherapy in glioblastoma. This is because of the high levels of ATP-binding cassette transporters like P-glycoprotein (Pgp/ABCB1), which effluxes drugs back to the bloodstream. Temozolomide is one of the few agents able to cross the BBB; its effects on BBB cells permeability and Pgp activity are not known. We found that temozolomide, at therapeutic concentration, increased the transport of Pgp substrates across human brain microvascular endothelial cells and decreased the expression of Pgp. By methylating the promoter of Wnt3 gene, temozolomide lowers the endogenous synthesis of Wnt3 in BBB cells, disrupts the Wnt3/glycogen synthase kinase 3/?-catenin signaling, and reduces the binding of ?-catenin on the promoter of mdr1 gene, which encodes for Pgp. In co-culture models of BBB cells and human glioblastoma cells, pre-treatment with temozolomide increases the delivery, cytotoxicity, and antiproliferative effects of doxorubicin, vinblastine, and topotecan, three substrates of Pgp that are usually poorly delivered across BBB. Our work suggests that temozolomide increases the BBB permeability of drugs that are normally effluxed by Pgp back to the bloodstream. These findings may pave the way to new combinatorial chemotherapy schemes in glioblastoma. © 2013 Springer Basel