TY - JOUR
T1 - MSH6 haploinsufficiency at relapse contributes to the development of thiopurine resistance in pediatric B-lymphoblastic leukemia
AU - Evensen, Nikki A.
AU - Madhusoodhan, P. Pallavi
AU - Meyer, Julia
AU - Saliba, Jason
AU - Chowdhury, Ashfiyah
AU - Araten, David J.
AU - Nersting, Jacob
AU - Bhatla, Teena
AU - Vincent, Tiffaney L.
AU - Teachey, David
AU - Hunger, Stephen P.
AU - Yang, Jun
AU - Schmiegelow, Kjeld
AU - Carroll, William L.
N1 - Funding Information:
We gratefully acknowledge the Children’s Oncology Group (COG) Specimen Bank for samples. Support for flow cytometry was provided by NYU School of Medicine’s Cytometry and Cell Sorting Laboratory, which is supported in part by grant P30CA016087 from the NIH/NCI, and the CHOP Flow Cytometry Core. We acknowledge the VA-Mertid award 1I01BX-000670, which helped support this work.
Funding Information:
This work was supported by the Leukemia and Lymphoma Society SCOR grant: 7010-14 (WLC, JY, DT, SPH), the US National Institutes of Health (NIH) funded grant RO1 CA140729 (WLC), and the Perlmutter Cancer Center Support Grant: P30 DA016087.
Funding Information:
This work was supported by the Leukemia and Lymphoma Society SCOR grant: 7010-14 (WLC, JY, DT, SPH), the US National Institutes of Health (NIH) funded grant RO1 CA140729 (WLC), and the Perlmutter Cancer Center Support Grant: P30 DA016087.We gratefully acknowledge the Children’s Oncology Group (COG) Specimen Bank for samples. Support for flow cytometry was provided by NYU School of Medicine’s Cytometry and Cell Sorting Laboratory, which is supported in part by grant P30CA016087 from the NIH/NCI, and the CHOP Flow Cytometry Core. We acknowledge the VA-Mertid award 1I01BX-000670, which helped support this work.
Publisher Copyright:
© 2018 Ferrata Storti Foundation.
PY - 2018/4/30
Y1 - 2018/4/30
N2 - Survival of children with relapsed acute lymphoblastic leukemia is poor, and understanding mechanisms underlying resistance is essential to developing new therapy. Relapse-specific heterozygous deletions in MSH6, a crucial part of DNA mismatch repair, are frequently detected. Our aim was to determine whether MSH6 deletion results in a hypermutator phenotype associated with generation of secondary mutations involved in drug resistance, or if it leads to a failure to initiate apoptosis directly in response to chemotherapeutic agents. We knocked down MSH6 in mismatch repair proficient cell lines (697 and UOCB1) and showed significant increases in IC50s to 6-thioguanine and 6-mercaptopurine (697: 26- and 9-fold; UOCB1: 5- and 8-fold) in vitro, as well as increased resistance to 6-mercaptopurine treatment in vivo. No shift in IC50 was observed in deficient cells (Reh and RS4;11). 697 MSH6 knockdown resulted in increased DNA thioguanine nucleotide levels compared to non-targeted cells (3070 vs. 1722 fmol/μg DNA) with no difference observed in mismatch repair deficient cells. Loss of MSH6 did not give rise to microsatellite instability in cell lines or clinical samples, nor did it significantly increase mutation rate, but rather resulted in a defect in cell cycle arrest upon thiopurine exposure. MSH6 knockdown cells showed minimal activation of checkpoint regulator CHK1, γH2AX (DNA damage marker) and p53 levels upon treatment with thiopurines, consistent with intrinsic chemoresistance due to failure to recognize thioguanine nucleotide mismatching and initiate mismatch repair. Aberrant MSH6 adds to the list of alterations/mutations associated with acquired resistance to purine analogs emphasizing the importance of thiopurine therapy.
AB - Survival of children with relapsed acute lymphoblastic leukemia is poor, and understanding mechanisms underlying resistance is essential to developing new therapy. Relapse-specific heterozygous deletions in MSH6, a crucial part of DNA mismatch repair, are frequently detected. Our aim was to determine whether MSH6 deletion results in a hypermutator phenotype associated with generation of secondary mutations involved in drug resistance, or if it leads to a failure to initiate apoptosis directly in response to chemotherapeutic agents. We knocked down MSH6 in mismatch repair proficient cell lines (697 and UOCB1) and showed significant increases in IC50s to 6-thioguanine and 6-mercaptopurine (697: 26- and 9-fold; UOCB1: 5- and 8-fold) in vitro, as well as increased resistance to 6-mercaptopurine treatment in vivo. No shift in IC50 was observed in deficient cells (Reh and RS4;11). 697 MSH6 knockdown resulted in increased DNA thioguanine nucleotide levels compared to non-targeted cells (3070 vs. 1722 fmol/μg DNA) with no difference observed in mismatch repair deficient cells. Loss of MSH6 did not give rise to microsatellite instability in cell lines or clinical samples, nor did it significantly increase mutation rate, but rather resulted in a defect in cell cycle arrest upon thiopurine exposure. MSH6 knockdown cells showed minimal activation of checkpoint regulator CHK1, γH2AX (DNA damage marker) and p53 levels upon treatment with thiopurines, consistent with intrinsic chemoresistance due to failure to recognize thioguanine nucleotide mismatching and initiate mismatch repair. Aberrant MSH6 adds to the list of alterations/mutations associated with acquired resistance to purine analogs emphasizing the importance of thiopurine therapy.
UR - http://www.scopus.com/inward/record.url?scp=85046358433&partnerID=8YFLogxK
U2 - 10.3324/haematol.2017.176362
DO - 10.3324/haematol.2017.176362
M3 - Article
C2 - 29449434
AN - SCOPUS:85046358433
SN - 0390-6078
VL - 103
SP - 830
EP - 839
JO - Haematologica
JF - Haematologica
IS - 5
ER -