The Nrf2 transcription factor contributes to resistance to cisplatin in bladder cancer.
OBJECTIVE
Cisplatin is the key systemic chemotherapeutic agent used for bladder cancer, but chemoresistance is a major clinical problem. The transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) regulates various critical cellular processes, including cellular antioxidant response, cellular detoxification, and drug uptake/efflux. These processes, and the expression of multiple Nrf2 target genes, have been found to be associated with bladder cancer prognosis and chemotherapy resistance. We, therefore, investigated whether Nrf2 might regulate cisplatin resistance in bladder cancer.


METHODS
We first used bladder cancer cell lines, including a cisplatin-resistant RT112 subline (RT112-CP), to investigate Nrf2 expression and activation and its association with cisplatin response. We then undertook immunohistochemical analysis of a tissue microarray of archival bladder cancer radical cystectomy specimens to test the relevance of clinical Nrf2 expression to outcomes following either neoadjuvant chemotherapy and cystectomy or cystectomy alone.


RESULTS
Bladder cancer cell lines showed variable Nrf2 expression. Nrf2 expression was greater in RT112-CP cisplatin-resistant cells compared with that in parental RT112 cells. Nrf2 overexpression was functional in this model as it was associated with increased antioxidant response element reporter construct activity, Nrf2 target gene expression (metallothionein and glutathione reductase), and basal glutathione levels. Cisplatin resistance was associated with Nrf2 expression, and in RT112-CP cells, its depletion partially restored cisplatin sensitivity. We demonstrated increased cytoplasmic or nuclear Nrf2 expression or both in 32% of clinical bladder cancer samples compared with that in normal tissue samples. Expression of Nrf2 in bladder cancer following radical cystectomy was associated with unfavorable overall (median = 0.65 vs. 2.11 y, P = 0.045), bladder cancer-specific, and recurrence-free survival in those patients who also received neoadjuvant cisplatin-based chemotherapy but not in those treated with cystectomy alone.


CONCLUSIONS
Nrf2 overexpression in bladder cancer is associated with clinically relevant cisplatin resistance that is reversible in experimental models and should now be tested in prospective studies.
Cancer Sciences Unit, University of Southampton Faculty of Medicine, Southampton General Hospital, Southampton, United Kingdom.
Annette
A
Hayden
Cancer Sciences Unit, University of Southampton Faculty of Medicine, Southampton General Hospital, Southampton, United Kingdom.
James
J
Douglas
Department of Histopathology, University Hospital Southampton NHS Foundation Trust, Southampton General Hospital, Southampton, United Kingdom.
Matthew
M
Sommerlad
Cancer Sciences Unit, University of Southampton Faculty of Medicine, Southampton General Hospital, Southampton, United Kingdom.
Lawrence
L
Andrews
Cancer Sciences Unit, University of Southampton Faculty of Medicine, Southampton General Hospital, Southampton, United Kingdom.
Katherine
K
Gould
Department of Molecular and Clinical Cancer Medicine, University of Liverpool, Liverpool, United Kingdom.
Syed
S
Hussain
Cancer Sciences Unit, University of Southampton Faculty of Medicine, Southampton General Hospital, Southampton, United Kingdom.
Gareth J
GJ
Thomas
Cancer Sciences Unit, University of Southampton Faculty of Medicine, Southampton General Hospital, Southampton, United Kingdom.
Graham
G
Packham
Cancer Sciences Unit, University of Southampton Faculty of Medicine, Southampton General Hospital, Southampton, United Kingdom. Electronic address: S.J.Crabb@southampton.ac.uk.
Simon J
SJ
Crabb
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000970:Antineoplastic Agents / Q000494:pharmacology / Q000627:therapeutic use; D045744:Cell Line, Tumor; D017024:Chemotherapy, Adjuvant; D002945:Cisplatin / Q000494:pharmacology* / Q000627:therapeutic use; D003131:Combined Modality Therapy; D015653:Cystectomy / Q000379:methods; D019008:Drug Resistance, Neoplasm; D005260:Female; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D053208:Kaplan-Meier Estimate; D008297:Male; D008856:Microscopy, Fluorescence; D008875:Middle Aged; D051267:NF-E2-Related Factor 2 / Q000235:genetics / Q000378:metabolism*; D020360:Neoadjuvant Therapy; D034622:RNA Interference; D046888:Tissue Array Analysis; D016896:Treatment Outcome; D001749:Urinary Bladder Neoplasms / Q000378:metabolism* / Q000473:pathology / Q000628:therapy
D000970:Antineoplastic Agents; D051267:NF-E2-Related Factor 2; C495635:NFE2L2 protein, human; D002945:Cisplatin
Bladder cancer; Chemotherapy; Cisplatin; Keap1; Nrf2; Resistance