ABSTRACT
PARP inhibitors (PARPis) have been used to induce synthetic lethality in BRCA-deficient tumors in clinical trials with limited success. We hypothesized that RAD52-mediated DNA repair remains active in PARPi-treated BRCA-deficient tumor cells and that targeting RAD52 should enhance the synthetic lethal effect of PARPi. We show that RAD52 inhibitors (RAD52is) attenuated single-strand annealing (SSA) and residual homologous recombination (HR) in BRCA-deficient cells. Simultaneous targeting of PARP1 and RAD52 with inhibitors or dominant-negative mutants caused synergistic accumulation of DSBs and eradication of BRCA-deficient but not BRCA-proficient tumor cells. Remarkably, Parp1-/-;Rad52-/- mice are normal and display prolonged latency of BRCA1-deficient leukemia compared with Parp1-/- and Rad52-/- counterparts. Finally, PARPi+RAD52i exerted synergistic activity against BRCA1-deficient tumors in immunodeficient mice with minimal toxicity to normal cells and tissues. In conclusion, our data indicate that addition of RAD52i will improve therapeutic outcome of BRCA-deficient malignancies treated with PARPi.
Subject(s)
BRCA1 Protein/genetics , BRCA2 Protein/genetics , Poly (ADP-Ribose) Polymerase-1/genetics , Rad52 DNA Repair and Recombination Protein/genetics , Animals , BRCA1 Protein/deficiency , BRCA2 Protein/deficiency , DNA Repair/drug effects , Female , Fusion Proteins, bcr-abl/genetics , Fusion Proteins, bcr-abl/metabolism , Homologous Recombination/drug effects , Humans , Imatinib Mesylate/pharmacology , Kaplan-Meier Estimate , Leukemia, Myeloid, Acute/metabolism , Leukemia, Myeloid, Acute/mortality , Leukemia, Myeloid, Acute/pathology , Male , Mice , Mice, Inbred NOD , Mice, Knockout , Phthalazines/pharmacology , Piperazines/pharmacology , Poly (ADP-Ribose) Polymerase-1/antagonists & inhibitors , Poly (ADP-Ribose) Polymerase-1/deficiency , Rad52 DNA Repair and Recombination Protein/antagonists & inhibitors , Rad52 DNA Repair and Recombination Protein/deficiency , Synthetic Lethal Mutations , Tumor Suppressor p53-Binding Protein 1/deficiency , Tumor Suppressor p53-Binding Protein 1/geneticsABSTRACT
RAD52 is involved in homologous recombination and DNA repair. This study focuses on lung cancer progression and how the DNA repair gene, Rad52, enables tumor cells to have sufficient genome integrity, i.e., the ability to repair lethal DNA damage, to avoid cell death. In this report, we analyze the phenotypic differences between wild type and Rad52-/- in inhibition of tumor phenotypes including cell growth, viability, cytolysis, and immune profiling. We demonstrated that loss of Rad52 not only increases the death of cells undergoing carcinogen-induced transformation in vivo, but that Rad52 loss also augments in vivo antitumor activity through an enhanced capacity for direct killing of LLC tumor cells by stimulated Rad52-/- NK and CD8+ T cells. We hypothesize that upon DNA damage, wild type cells attempt to repair DNA lesions, but those cells that survive will continue to divide with damage and a high likelihood of progressing to malignancy. Loss of Rad52, however, appears to increase genomic instability beyond a manageable threshold, acceding the damaged cells to death before they are able to become tumor cells. Our results suggest a key role for the complex interplay between the DNA damage response and host immunity in determining risk for Squamous Cell Lung Carcinoma.
Subject(s)
CD8-Positive T-Lymphocytes/metabolism , Carcinoma, Lewis Lung/immunology , Carcinoma, Squamous Cell/immunology , Immunologic Surveillance , Killer Cells, Natural/metabolism , Rad52 DNA Repair and Recombination Protein/genetics , Animals , Carcinoma, Lewis Lung/genetics , Carcinoma, Squamous Cell/genetics , Cell Proliferation , Cell Survival , DNA Damage , Disease Progression , Gene Knockout Techniques , Humans , Mice , Rad52 DNA Repair and Recombination Protein/deficiencyABSTRACT
Diploid Saccharomyes cerevisae strains lacking the RAD52 gene required for homologous recombination have a very high rate of chromosome loss. Two of four isolates subcultured â¼20 times (â¼500 cell divisions) became haploid. These strains were capable of mating with wild-type haploids to produce diploid progeny capable of undergoing meiosis to produce four viable spores.
