Retinoblastoma is the most common intraocular
cancer in childhood. Loss of function in both copies of the RB1 gene is the causal mutation of
retinoblastoma. Current treatment for
retinoblastoma includes the use of chemotherapeutic agents, such as the
DNA damaging agent
etoposide, which is a
topoisomerase II poison that mainly generates
DNA double-strand breaks (DSBs) and
genome instability. Unfaithful repairing of DSBs could lead to secondary
cancers and serious side effects. Previously, we found that RB knocked-down mammalian cells depend on a highly mutagenic pathway, the micro-homology mediated end joining (MMEJ) pathway, to repair DSBs.
Poly ADP ribose polymerase 1 (PARP1) is a major
protein in promoting the MMEJ pathway. In this study, we explored the effects of
olaparib, a
PARP inhibitor, in killing
retinoblastoma cells.
Retinoblastoma cell line Y79 and primary
retinoblastoma cells expressed the
cone-rod homeobox protein (CRX), a photoreceptor-specific marker. No detectable RB expression was found in these cells. The co-treatment of
olaparib and
etoposide led to enhanced cell death in both the Y79 cells and the primary
retinoblastoma cells. Our results demonstrated the killing effects in
retinoblastoma cells by
PARP inhibitor olaparib after inducing
DNA double-strand breaks. The use of
olaparib in combination with
etoposide could improve the cell-killing effects. Thus, lower dosages of
etoposide can be used to treat
retinoblastoma, which would potentially lead to a lower level of DSBs and a relatively more stable genome.