Simultaneous Targeting of DNA Polymerase Theta and PARP1 or RAD52 Triggers Dual Synthetic Lethality in Homologous Recombination–Deficient Leukemia Cells

DNA polymerase theta (Polq, encoded by POLQ gene) plays an essential role in Polq-mediated end-joining (TMEJ) of DNA double-strand breaks (DSB). Inhibition of Polq is synthetic lethal in homologous recombination (HR)-deficient tumor cells. However, DSBs can be also repaired by PARP1 and RAD52-mediated mechanisms. Because leukemia cells accumulate spontaneous DSBs, we tested if simultaneous targeting of Polq and PARP1 or RAD52 enhance the synthetic lethal effect in HR-deficient leukemia cells. Transformation potential of the oncogenes inducing BRCA1/2-deficiency (BCR-ABL1 and AML1-ETO) was severely limited in Polq^-/-;Parp1^-/- and Polq^-/-;Rad52^-/- cells when compared with single knockouts, which was associated with accumulation of DSBs. Small-molecule inhibitor of Polq (Polqi) when combined with PARP or RAD52 inhibitors (PARPi, RAD52i) caused accumulation of DSBs and exerted increased effect against HR-deficient leukemia and myeloproliferative neoplasm cells. Implications: In conclusion, we show that PARPi or RAD52i might improve therapeutic effect of Polqi against HR-deficient leukemias.