Targeting DNA repair in chronic lymphocytic leukemia cells with a novel acyclic nucleotide analogue, GS-9219.
OBJECTIVE
GS-9219 is a cell-permeable prodrug of the acyclic nucleotide analogue 9-(2-phosphonylmethoxyethyl)guanine (PMEG); the incorporation of the active metabolite PMEG diphosphate (PMEGpp) into DNA results in DNA chain termination due to the lack of a 3'-hydroxyl moiety. We hypothesized that the incorporation of PMEGpp into DNA during repair resynthesis would result in the inhibition of DNA repair and the accumulation of DNA breaks in chronic lymphocytic leukemia (CLL) cells that would activate signaling pathways to cell death.


METHODS
To test this hypothesis, CLL cells were irradiated with UV light to stimulate nucleotide excision repair pathways, enabling the incorporation of PMEGpp into DNA. The combination effects of GS-9219 and DNA-damaging agents and the signaling mechanisms activated in response to DNA repair inhibition by GS-9219, as well as changes in CLL cell viability, were investigated.


RESULTS
PMEGpp was incorporated into DNA in CLL cells when nucleotide excision repair was activated by UV. Following PMEGpp incorporation, DNA repair was inhibited, which led to the accumulation of DNA strand breaks. The presence of DNA strand breaks activated the phosphatidylinositol 3-kinase-like protein kinase family members ataxia-telangiectasia mutated and DNA-dependent protein kinase. P53 was phosphorylated and stabilized in response to the inhibition of DNA repair. P53 targeted proteins, Puma and Bax, were up-regulated and activated. The combination of GS-9219 and DNA-damaging agents resulted in more cell death than the sum of the single agents alone.


CONCLUSIONS
GS-9219 inhibits DNA repair in CLL cells, an action that stimulates signaling pathways for apoptosis induction.
Departments of Experimental Therapeutics and Leukemia, The University of Texas M.D. Anderson Cancer Center, USA.
Cheng-Yu
CY
Tsai
Adrian S
AS
Ray
Daniel B
DB
Tumas
Michael J
MJ
Keating
Hans
H
Reiser
William
W
Plunkett
D000409:Alanine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D002851:Chromatography, High Pressure Liquid; D004249:DNA Damage; D004260:DNA Repair / Q000187:drug effects* / Q000528:radiation effects; D004273:DNA, Neoplasm / Q000737:chemistry / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006147:Guanine / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D008954:Models, Biological; D015394:Molecular Structure; D009943:Organophosphorus Compounds / Q000737:chemistry / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D011687:Purines / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects / Q000528:radiation effects; D014407:Tumor Cells, Cultured; D014466:Ultraviolet Rays; D051028:bcl-2-Associated X Protein / Q000235:genetics / Q000378:metabolism
D051017:Apoptosis Regulatory Proteins; C438378:BBC3 protein, human; D004273:DNA, Neoplasm; D009943:Organophosphorus Compounds; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011687:Purines; D051028:bcl-2-Associated X Protein; C531423:rabacfosadine; C063380:9-((2-phosphonylmethoxy)ethyl)guanine; D006147:Guanine; D000409:Alanine