Redox regulation of P-glycoprotein-mediated multidrug resistance in multicellular prostate tumor spheroids

✍ Scribed by Maria Wartenberg; Kerstin Fischer; Jürgen Hescheler; Heinrich Sauer

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: French
• Weight: 374 KB
• Volume: 85
• Category: Article
• ISSN: 0020-7136
• DOI: 10.1002/(sici)1097-0215(20000115)85:2<267::aid-ijc19>3.0.co;2-h

✦ Synopsis

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 ؎ 50m). Using the ROSsensitive fluorescence dye 2Ј7Ј-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 ؎ 20m) 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 downregulation may be paralleled by recruitment of drug-resistant quiescent cells in the depth of the tumor tissue for cell-cycle activity.