title: Mitomycin C induces multidrug resistance in glaucoma surgery.
abstract: BACKGROUND
  Despite the adjuvant use of mitomycin C during trabeculectomy, failures still occur. We investigated whether cultured human Tenon fibroblasts exposed to low-dose mitomycin C developed a multidrug resistance phenotype in vitro, and whether mitomycin C treatment during previous filtration surgery induces P-glycoprotein expression in vivo.
  
  
  METHODS
  Cultured human Tenon fibroblasts treated with low-dose 0.01 nM mitomycin C for 2 weeks were subsequently treated with 0.1 to 100 microM mitomycin C in the absence or presence of 4 microM verapamil, and allowed to recover for 24 hours. Low-dose mitomycin C-treated fibroblasts were analysed for P-glycoprotein expression using flow cytometry, immunoblotting, and RT-PCR for mdr-1 mRNA. In addition, fibroblasts were treated with low dose 0.1 nM 5-fluorouracil for 2 weeks and analysed for P-glycoprotein expression using flow cytometry. Expression of P-glycoprotein was analysed in surgically removed Tenon tissue (n = 30) using immunohistochemistry. Of the 30 patients, 20 had a previous trabeculectomy, of which nine had previous adjuvant therapy with mitomycin C during trabeculectomy.
  
  
  RESULTS
  Partial resistance to mitomycin C after low-dose mitomycin C pre-treatment was significantly neutralised by the addition of verapamil. Low-dose mitomycin C up-regulated P-glycoprotein expression, but not mdr-1 mRNA expression. 5-Fluorouracil did not induce P-glycoprotein expression. P-glycoprotein expression was detected in all nine patients exposed to mitomycin C during previous trabeculectomies. Only six of 21 specimens from patients not previously exposed to mitomycin C showed faint P-glycoprotein expression.
  
  
  CONCLUSIONS
  The induction of P-glycoprotein by mitomycin C could explain some failures that occur after repeated use of mitomycin C during trabeculectomy. The concomitant use of verapamil or the use of 5-fluorouracil alone could increase the success rate of repeat trabeculectomies.
authors.affiliation: Centre of Ophthalmology, University of Cologne, Cologne, Germany. arno.hueber@uni-koeln.de
authors.forename: Arno
authors.initials: A
authors.lastname: Hueber
authors.forename: Johannes M
authors.initials: JM
authors.lastname: Esser
authors.forename: Norbert
authors.initials: N
authors.lastname: Kociok
authors.forename: Gerhard
authors.initials: G
authors.lastname: Welsandt
authors.forename: Christoph
authors.initials: C
authors.lastname: Lüke
authors.forename: Sigrid
authors.initials: S
authors.lastname: Roters
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Esser
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000477:Alkylating Agents / Q000008:administration & dosage*; D002478:Cells, Cultured; D002648:Child; D003239:Connective Tissue Cells; D018432:Drug Resistance, Multiple / Q000187:drug effects*; D005260:Female; D005347:Fibroblasts / Q000187:drug effects* / Q000378:metabolism; D005434:Flow Cytometry; D005472:Fluorouracil / Q000494:pharmacology; D005902:Glaucoma, Open-Angle / Q000473:pathology / Q000601:surgery*; D006801:Humans; D007124:Immunoenzyme Techniques; D008297:Male; D008875:Middle Aged; D016685:Mitomycin / Q000008:administration & dosage*; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014130:Trabeculectomy; D014700:Verapamil / Q000494:pharmacology
chemical_list: C513055:ABCB1 protein, human; D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000477:Alkylating Agents; D012333:RNA, Messenger; D016685:Mitomycin; D014700:Verapamil; D005472:Fluorouracil