Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.6.3.44 (P-glycoprotein)
 13,344 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Multicellular prostate tumor spheroids develop intrinsic P-glycoprotein (Pgp)-mediated multidrug resistance with the appearance of quiescent cell areas. We have investigated the effect of intracellular reactive oxygen species (ROS) on Pgp expression in large, quiescent and drug-resistant multicellular spheroids (diameter 250 +/- 50microm). Using the ROS-sensitive fluorescence dye 2;7;-dichlorodihydrofluorescein diacetate (H(2)DCFDA), we demonstrated that these tumor spheroids are characterized by reduced intracellular ROS compared with drug-sensitive small spheroids (diameter 60 +/- 20microm) consisting predominantly of proliferating cells. The prooxidants hydrogen peroxide, menadione and glyceraldehyde raised ROS in large tumor spheroids and significantly down-regulated Pgp within 24 hr. Comparable effects were achieved with the known Pgp-reversing agents sodium orthovanadate, quinidine and cyclosporin A but not with verapamil. Consequently, the retention and toxicity of the anthracycline doxorubicin was increased in tumor spheroids treated with prooxidants. Co-administration of prooxidants and the free radical scavenger ebselen did not alter Pgp levels, indicating that down-regulation of Pgp is mediated via ROS. Down-regulation of Pgp by H(2)O(2) was abolished when either forskolin, 8-Br-cAMP or IBMX, which raise intracellular cAMP levels, was co-administered, indicating that Pgp expression is regulated by protein kinase A (PKA). Furthermore, Pgp was down-regulated by the PKA inhibitors Rp-cAMPs and H89. Since prooxidants stimulated the growth of multicellular spheroids and down-regulated the cyclin-dependent kinase inhibitor p27(kip1), we conclude that ROS-mediated Pgp down-regulation may be paralleled by recruitment of drug-resistant quiescent cells in the depth of the tumor tissue for cell-cycle activity.
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PMID:Redox regulation of P-glycoprotein-mediated multidrug resistance in multicellular prostate tumor spheroids. 1062 88

Osteosarcoma is the most frequently occurring bone cancer in children and adolescents. Unfortunately, treatment failures are common. Eribulin is a synthetic microtubule inhibitor that has demonstrated activity in preclinical osteosarcoma models. The effects of eribulin were evaluated in two human osteosarcoma cell lines as well as in eribulin-sensitive and -resistant osteosarcoma xenograft tumors of the Pediatric Preclinical Testing Program (PPTP) by characterizing cell viability, microtubule destabilization, mitotic arrest and mechanism of cell death. Eribulin demonstrated cytotoxic activity in vitro, through promotion of microtubule dynamic instability, arrest of cells in the G2/M phase, mitotic catastrophe and cell death. The microtubule-destabilizing protein stathmin-1 (STMN1) was coimmunoprecipitated with the cyclin-dependent kinase inhibitor p27 indicating that these cytoplasmic complexes can protect cells from the microtubule destabilizing effect of eribulin. Increased tumoral expression of P-glycoprotein (P-gp) and TUBB3 were also associated with lower drug sensitivity. In summary, eribulin successfully blocked cells in G2/M phase but interfered with mitochondria activity to inhibit proteins involved in apoptosis. Understanding the complex and inter-related mechanisms involved in the overall drug response to eribulin may help in the design of therapeutic strategies that enhance drug activity and improve benefits of eribulin in pediatric patients with osteosarcoma.
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PMID:Integrating mechanisms of response and resistance against the tubulin binding agent Eribulin in preclinical models of osteosarcoma. 2786 9