TY - JOUR
T1 - Mechanisms of therapy resistance in patient-derived xenograft models of brca1-deficient breast cancer
AU - Ter Brugge, Petra
AU - Kristel, Petra
AU - Van Der Burg, Eline
AU - Boon, Ute
AU - De Maaker, Michiel
AU - Lips, Esther
AU - Mulder, Lennart
AU - De Ruiter, Julian
AU - Moutinho, Catia
AU - Gevensleben, Heidrun
AU - Marangoni, Elisabetta
AU - Majewski, Ian
AU - Jozwiak, Katarzyna
AU - Kloosterman, Wigard
AU - Van Roosmalen, Markus
AU - Duran, Karen
AU - Hogervorst, Frans
AU - Turner, Nick
AU - Esteller, Manel
AU - Cuppen, Edwin
AU - Wesseling, Jelle
AU - Jonkers, Jos
PY - 2016/11
Y1 - 2016/11
N2 - Background: Although BRCA1-deficient tumors are extremely sensitive to DNA-damaging drugs and poly(ADP-ribose) polymerase (PARP) inhibitors, recurrences do occur and, consequently, resistance to therapy remains a serious clinical problem. To study the underlying mechanisms, we induced therapy resistance in patient-derived xenograft (PDX) models of BRCA1- mutated and BRCA1-methylated triple-negative breast cancer. Methods: A cohort of 75 mice carrying BRCA1-deficient breast PDX tumors was treated with cisplatin, melphalan, nimustine, or olaparib, and treatment sensitivity was determined. In tumors that acquired therapy resistance, BRCA1 expression was investigated using quantitative real-time polymerase chain reaction and immunoblotting. Next-generation sequencing, methylation-specific multiplex ligation-dependent probe amplification (MLPA) and Target Locus Amplification (TLA)-based sequencing were used to determine mechanisms of BRCA1 re-expression in therapy-resistant tumors. Results: BRCA1 protein was not detected in therapy-sensitive tumors but was found in 31 out of 42 resistant cases. Apart from previously described mechanisms involving BRCA1-intragenic deletions and loss of BRCA1 promoter hypermethylation, a novel resistance mechanism was identified in four out of seven BRCA1-methylated PDX tumors that re-expressed BRCA1 but retained BRCA1 promoter hypermethylation. In these tumors, we found de novo gene fusions that placed BRCA1 under the transcriptional control of a heterologous promoter, resulting in re-expression of BRCA1 and acquisition of therapy resistance. Conclusions: In addition to previously described clinically relevant resistance mechanisms in BRCA1-deficient tumors, we describe a novel resistance mechanism in BRCA1-methylated PDX tumors involving de novo rearrangements at the BRCA1 locus, demonstrating that BRCA1-methylated breast cancers may acquire therapy resistance via both epigenetic and genetic mechanisms.
AB - Background: Although BRCA1-deficient tumors are extremely sensitive to DNA-damaging drugs and poly(ADP-ribose) polymerase (PARP) inhibitors, recurrences do occur and, consequently, resistance to therapy remains a serious clinical problem. To study the underlying mechanisms, we induced therapy resistance in patient-derived xenograft (PDX) models of BRCA1- mutated and BRCA1-methylated triple-negative breast cancer. Methods: A cohort of 75 mice carrying BRCA1-deficient breast PDX tumors was treated with cisplatin, melphalan, nimustine, or olaparib, and treatment sensitivity was determined. In tumors that acquired therapy resistance, BRCA1 expression was investigated using quantitative real-time polymerase chain reaction and immunoblotting. Next-generation sequencing, methylation-specific multiplex ligation-dependent probe amplification (MLPA) and Target Locus Amplification (TLA)-based sequencing were used to determine mechanisms of BRCA1 re-expression in therapy-resistant tumors. Results: BRCA1 protein was not detected in therapy-sensitive tumors but was found in 31 out of 42 resistant cases. Apart from previously described mechanisms involving BRCA1-intragenic deletions and loss of BRCA1 promoter hypermethylation, a novel resistance mechanism was identified in four out of seven BRCA1-methylated PDX tumors that re-expressed BRCA1 but retained BRCA1 promoter hypermethylation. In these tumors, we found de novo gene fusions that placed BRCA1 under the transcriptional control of a heterologous promoter, resulting in re-expression of BRCA1 and acquisition of therapy resistance. Conclusions: In addition to previously described clinically relevant resistance mechanisms in BRCA1-deficient tumors, we describe a novel resistance mechanism in BRCA1-methylated PDX tumors involving de novo rearrangements at the BRCA1 locus, demonstrating that BRCA1-methylated breast cancers may acquire therapy resistance via both epigenetic and genetic mechanisms.
UR - https://www.scopus.com/pages/publications/85014855146
U2 - 10.1093/jnci/djw148
DO - 10.1093/jnci/djw148
M3 - Article
C2 - 27381626
AN - SCOPUS:85014855146
SN - 0027-8874
VL - 108
JO - Journal of the National Cancer Institute
JF - Journal of the National Cancer Institute
IS - 11
M1 - djw148
ER -