DEREGULATION OF MAJOR DNA REPAIR MECHANISMS CORRELATES WITH CLINICAL OUTCOME OF ANTI-MYELOMA THERAPY. THE BENEFICIAL EFFECT OF DNA REPAIR INHIBITION
(Abstract release date: 05/19/16)
EHA Library. Gkotzamanidou M. 06/09/16; 132787; E1238
Dr. Maria Gkotzamanidou
Contributions
Contributions
Abstract
Abstract: E1238
Type: Eposter Presentation
Background
Deregulation of DNA repair pathways in malignant plasma cells mediates onset of disease and survival. The precise nature of dysregulated DNA repair and how it improves multiple myeloma (MM) cells survival or is co-opted during antitumor therapy is as yet unexplored and requires extensive study. If fully understood, DNA repair dysregulations could be exploited to selectively kill MM cells by targeting the remaining repair pathways that are critical for their survival.
Aims
We investigated the mechanistic basis for the link between DNA repair efficiency and response to anti-myeloma therapy.
Methods
We evaluated major DNA repair mechanisms [nucleotide excision repair (NER), interstrand cross-links repair (ICL/R), double-strand breaks repair (DSB/R)] in MM cell lines (melphalan-sensitive, RPMI8226; melphalan-resistant, LR5), peripheral blood mononuclear cells (PBMCs) from 25 healthy controls (HC; 14M/11F, median age 58 years), as well as bone marrow plasma cells (BMPCs) and PBMCs from 15 newly diagnosed MM patients (8M/7F; median age 61 years), responders (≥PR, n=9) and non-responders (
Results
Following ex vivo melphalan treatment, responders’ primary cells (both BMPCs and PBMCs) showed significantly slower rates of NER and DSB/R compared to non-responders (P=0.0015). Similar rates of ICL/R were found in primary cells from all individuals. Moreover, apoptotic rates of the primary cells were inversely correlated with individual DNA repair efficiencies, being significantly higher in responders’ cells compared to non-responders ones (P=0.0015). In line with these data, RPMI8226 cells showed slower rates of NER and DSB/R, but not ICL/R, and higher apoptotic rates than LR5 cells. Interestingly, co-treatment of all types of cells with DSB/R inhibitors significantly reduced the rates of DSB/R and increased melphalan sensitivity of the cells. Moreover, in untreated PBMCs from MM patients, we found an inverse correlation between the local chromatin condensation and the repair capacity of the cells. Particularly, we observed a progressive, significant increase in the looseness of the local chromatin structure, from HC to MM patients, with responders showing more condensed chromatin structure compared to non-responders (all P<0.05). Finally, microarray analyses of untreated PBMCs from MM patients consistently point to an altered expression of several DNA damage response-related genes in MM patients compared to HC. Particularly, responders’ PBMCs showed upregulation of ATR, CHEK2, XPA, XRCC1 and CHEK2 genes and downregulation of ATM, MPG, UNG, CDKN1A and CDC25C compared to non-responders (in all cases, fold changes between groups were >2, P<0.001), suggesting that perturbation in the molecular components of DDR/R pathways also plays an important role in the therapeutic action of genotoxic drugs.
Conclusion
Responders to melphalan therapy are characterized by lower efficiencies of NER and DSB/R mechanisms resulting in higher accumulation of the extremely cytotoxic ICLs and DSBs lesions which in turn, triggers the induction of the apoptotic pathway. Moreover, the potentiation of melphalan cytotoxicity by DSB/R inhibition offers a promising strategy toward improvement of existing regimens.
Session topic: E-poster
Keyword(s): DNA repair, Melphalan, Myeloma
Type: Eposter Presentation
Background
Deregulation of DNA repair pathways in malignant plasma cells mediates onset of disease and survival. The precise nature of dysregulated DNA repair and how it improves multiple myeloma (MM) cells survival or is co-opted during antitumor therapy is as yet unexplored and requires extensive study. If fully understood, DNA repair dysregulations could be exploited to selectively kill MM cells by targeting the remaining repair pathways that are critical for their survival.
Aims
We investigated the mechanistic basis for the link between DNA repair efficiency and response to anti-myeloma therapy.
Methods
We evaluated major DNA repair mechanisms [nucleotide excision repair (NER), interstrand cross-links repair (ICL/R), double-strand breaks repair (DSB/R)] in MM cell lines (melphalan-sensitive, RPMI8226; melphalan-resistant, LR5), peripheral blood mononuclear cells (PBMCs) from 25 healthy controls (HC; 14M/11F, median age 58 years), as well as bone marrow plasma cells (BMPCs) and PBMCs from 15 newly diagnosed MM patients (8M/7F; median age 61 years), responders (≥PR, n=9) and non-responders (
Results
Following ex vivo melphalan treatment, responders’ primary cells (both BMPCs and PBMCs) showed significantly slower rates of NER and DSB/R compared to non-responders (P=0.0015). Similar rates of ICL/R were found in primary cells from all individuals. Moreover, apoptotic rates of the primary cells were inversely correlated with individual DNA repair efficiencies, being significantly higher in responders’ cells compared to non-responders ones (P=0.0015). In line with these data, RPMI8226 cells showed slower rates of NER and DSB/R, but not ICL/R, and higher apoptotic rates than LR5 cells. Interestingly, co-treatment of all types of cells with DSB/R inhibitors significantly reduced the rates of DSB/R and increased melphalan sensitivity of the cells. Moreover, in untreated PBMCs from MM patients, we found an inverse correlation between the local chromatin condensation and the repair capacity of the cells. Particularly, we observed a progressive, significant increase in the looseness of the local chromatin structure, from HC to MM patients, with responders showing more condensed chromatin structure compared to non-responders (all P<0.05). Finally, microarray analyses of untreated PBMCs from MM patients consistently point to an altered expression of several DNA damage response-related genes in MM patients compared to HC. Particularly, responders’ PBMCs showed upregulation of ATR, CHEK2, XPA, XRCC1 and CHEK2 genes and downregulation of ATM, MPG, UNG, CDKN1A and CDC25C compared to non-responders (in all cases, fold changes between groups were >2, P<0.001), suggesting that perturbation in the molecular components of DDR/R pathways also plays an important role in the therapeutic action of genotoxic drugs.
Conclusion
Responders to melphalan therapy are characterized by lower efficiencies of NER and DSB/R mechanisms resulting in higher accumulation of the extremely cytotoxic ICLs and DSBs lesions which in turn, triggers the induction of the apoptotic pathway. Moreover, the potentiation of melphalan cytotoxicity by DSB/R inhibition offers a promising strategy toward improvement of existing regimens.
Session topic: E-poster
Keyword(s): DNA repair, Melphalan, Myeloma
Abstract: E1238
Type: Eposter Presentation
Background
Deregulation of DNA repair pathways in malignant plasma cells mediates onset of disease and survival. The precise nature of dysregulated DNA repair and how it improves multiple myeloma (MM) cells survival or is co-opted during antitumor therapy is as yet unexplored and requires extensive study. If fully understood, DNA repair dysregulations could be exploited to selectively kill MM cells by targeting the remaining repair pathways that are critical for their survival.
Aims
We investigated the mechanistic basis for the link between DNA repair efficiency and response to anti-myeloma therapy.
Methods
We evaluated major DNA repair mechanisms [nucleotide excision repair (NER), interstrand cross-links repair (ICL/R), double-strand breaks repair (DSB/R)] in MM cell lines (melphalan-sensitive, RPMI8226; melphalan-resistant, LR5), peripheral blood mononuclear cells (PBMCs) from 25 healthy controls (HC; 14M/11F, median age 58 years), as well as bone marrow plasma cells (BMPCs) and PBMCs from 15 newly diagnosed MM patients (8M/7F; median age 61 years), responders (≥PR, n=9) and non-responders (
Results
Following ex vivo melphalan treatment, responders’ primary cells (both BMPCs and PBMCs) showed significantly slower rates of NER and DSB/R compared to non-responders (P=0.0015). Similar rates of ICL/R were found in primary cells from all individuals. Moreover, apoptotic rates of the primary cells were inversely correlated with individual DNA repair efficiencies, being significantly higher in responders’ cells compared to non-responders ones (P=0.0015). In line with these data, RPMI8226 cells showed slower rates of NER and DSB/R, but not ICL/R, and higher apoptotic rates than LR5 cells. Interestingly, co-treatment of all types of cells with DSB/R inhibitors significantly reduced the rates of DSB/R and increased melphalan sensitivity of the cells. Moreover, in untreated PBMCs from MM patients, we found an inverse correlation between the local chromatin condensation and the repair capacity of the cells. Particularly, we observed a progressive, significant increase in the looseness of the local chromatin structure, from HC to MM patients, with responders showing more condensed chromatin structure compared to non-responders (all P<0.05). Finally, microarray analyses of untreated PBMCs from MM patients consistently point to an altered expression of several DNA damage response-related genes in MM patients compared to HC. Particularly, responders’ PBMCs showed upregulation of ATR, CHEK2, XPA, XRCC1 and CHEK2 genes and downregulation of ATM, MPG, UNG, CDKN1A and CDC25C compared to non-responders (in all cases, fold changes between groups were >2, P<0.001), suggesting that perturbation in the molecular components of DDR/R pathways also plays an important role in the therapeutic action of genotoxic drugs.
Conclusion
Responders to melphalan therapy are characterized by lower efficiencies of NER and DSB/R mechanisms resulting in higher accumulation of the extremely cytotoxic ICLs and DSBs lesions which in turn, triggers the induction of the apoptotic pathway. Moreover, the potentiation of melphalan cytotoxicity by DSB/R inhibition offers a promising strategy toward improvement of existing regimens.
Session topic: E-poster
Keyword(s): DNA repair, Melphalan, Myeloma
Type: Eposter Presentation
Background
Deregulation of DNA repair pathways in malignant plasma cells mediates onset of disease and survival. The precise nature of dysregulated DNA repair and how it improves multiple myeloma (MM) cells survival or is co-opted during antitumor therapy is as yet unexplored and requires extensive study. If fully understood, DNA repair dysregulations could be exploited to selectively kill MM cells by targeting the remaining repair pathways that are critical for their survival.
Aims
We investigated the mechanistic basis for the link between DNA repair efficiency and response to anti-myeloma therapy.
Methods
We evaluated major DNA repair mechanisms [nucleotide excision repair (NER), interstrand cross-links repair (ICL/R), double-strand breaks repair (DSB/R)] in MM cell lines (melphalan-sensitive, RPMI8226; melphalan-resistant, LR5), peripheral blood mononuclear cells (PBMCs) from 25 healthy controls (HC; 14M/11F, median age 58 years), as well as bone marrow plasma cells (BMPCs) and PBMCs from 15 newly diagnosed MM patients (8M/7F; median age 61 years), responders (≥PR, n=9) and non-responders (
Results
Following ex vivo melphalan treatment, responders’ primary cells (both BMPCs and PBMCs) showed significantly slower rates of NER and DSB/R compared to non-responders (P=0.0015). Similar rates of ICL/R were found in primary cells from all individuals. Moreover, apoptotic rates of the primary cells were inversely correlated with individual DNA repair efficiencies, being significantly higher in responders’ cells compared to non-responders ones (P=0.0015). In line with these data, RPMI8226 cells showed slower rates of NER and DSB/R, but not ICL/R, and higher apoptotic rates than LR5 cells. Interestingly, co-treatment of all types of cells with DSB/R inhibitors significantly reduced the rates of DSB/R and increased melphalan sensitivity of the cells. Moreover, in untreated PBMCs from MM patients, we found an inverse correlation between the local chromatin condensation and the repair capacity of the cells. Particularly, we observed a progressive, significant increase in the looseness of the local chromatin structure, from HC to MM patients, with responders showing more condensed chromatin structure compared to non-responders (all P<0.05). Finally, microarray analyses of untreated PBMCs from MM patients consistently point to an altered expression of several DNA damage response-related genes in MM patients compared to HC. Particularly, responders’ PBMCs showed upregulation of ATR, CHEK2, XPA, XRCC1 and CHEK2 genes and downregulation of ATM, MPG, UNG, CDKN1A and CDC25C compared to non-responders (in all cases, fold changes between groups were >2, P<0.001), suggesting that perturbation in the molecular components of DDR/R pathways also plays an important role in the therapeutic action of genotoxic drugs.
Conclusion
Responders to melphalan therapy are characterized by lower efficiencies of NER and DSB/R mechanisms resulting in higher accumulation of the extremely cytotoxic ICLs and DSBs lesions which in turn, triggers the induction of the apoptotic pathway. Moreover, the potentiation of melphalan cytotoxicity by DSB/R inhibition offers a promising strategy toward improvement of existing regimens.
Session topic: E-poster
Keyword(s): DNA repair, Melphalan, Myeloma
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