BRCA1 modulates sensitivity to 5F-203 by regulating xenobiotic stress-inducible protein levels and EROD activity.
OBJECTIVE
We have investigated the effects of BRCA1 over-expression and knockdown on 5F-203-induced gene expression and cytotoxicity in human breast cancer cells. 5F-203 is a chemotherapeutic prodrug that both induces a p450 enzyme, CYP1A1, and is metabolically activated by CYP1A1.


METHODS
We used several molecular biological techniques to confirm our findings. BRCA1 regulates sensitivity to 5F-203 by regulating the expression of CYP1A1 mRNA and its EROD activity. XRE-Luc reporter assays, semi-quantitative RT-PCR, Western blot analysis, EROD activity measurements, gene knockdown and MTT cell survival assays were used for this study.


RESULTS
Our results show that the ability of 5F-203 treatments to increase CYP1A1 mRNA level and CYP1A1 enzymatic activity (EROD activity) are affected by BRCA1 protein levels. In addition, the ability of 5F-203 treatments to induce proteins, P53 and P53 target genes such as P21, is significantly decreased in BRCA1 knockdown cells, suggesting that BRCA1-related effects could at least partially explain why BRCA1 knockdown increases resistance to 5F-203-mediated cytotoxicity. We also observed altered expression of the two major transcription factors (AhR and ARNT) that affect CYP1A1 expression when BRCA1 protein levels are altered.


CONCLUSIONS
BRCA1 is an important protein, which affects 5F-203-mediated cytotoxicity. Our findings are potentially clinically significant; they suggest that those patients most likely to respond to this new prodrug will have tumors containing normal amounts of BRCA1.
Kang
Hyo Jin
HJ
Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, 3970 Reservoir Road, NW, Washington DC, 20057-1469, USA.
Kim
Hee Jeong
HJ
Kwon
Sang Hoon
SH
Kang
Brian Donghoon
BD
Eling
Thomas E
TE
Lee
Sang Han
SH
Bae
Insoo
I
D000970:Antineoplastic Agents / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism; D019363:Cytochrome P-450 CYP1A1 / Q000096:biosynthesis* / Q000235:genetics; D004305:Dose-Response Relationship, Drug; D004354:Drug Screening Assays, Antitumor; D004790:Enzyme Induction / Q000187:drug effects; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D020868:Gene Silencing; D006801:Humans; D011355:Prodrugs / Q000494:pharmacology*; D034741:RNA, Small Interfering / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000235:genetics* / Q000378:metabolism
C425784:2-(4-amino-3-methylphenyl)-5-fluorobenzothiazole; D000970:Antineoplastic Agents; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D011355:Prodrugs; D034741:RNA, Small Interfering; D013844:Thiazoles; D016159:Tumor Suppressor Protein p53; D019363:Cytochrome P-450 CYP1A1; C111164:BRAP protein, human; D044767:Ubiquitin-Protein Ligases