Elucidating Mechanisms of Replication-associated Synthetic lethality with RB loss and PARP inhibition

Gutierrez Zamalloa, Luis

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Elucidating Mechanisms of Replication-associated Synthetic lethality with RB loss and PARP inhibition

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The retinoblastoma tumor suppressor protein (RB) interacts physically and functionally with a number of epigenetic modifying enzymes to control transcriptional regulation, respond to replication stress, promote DNA damage repair pathways, and regulate genome stability. To better understand how disruption of RB function impacts epigenetic regulation of genome stability and determine whether such changes may represent exploitable weaknesses of RB-deficient cancer cells, an imaging-based screen was performed to identify epigenetic inhibitors that promote DNA damage and compromise viability of RB-deficient cells. From the 96 drugs tested, I found that inhibitors of poly(ADP-ribose) polymerase (PARP) are the most efficient and specific to RB-deficient cells compared to isogeneic control cells. Mechanistically, I report that loss of RB alone leads to high levels of replication-dependent poly-ADP ribosylation (PARylation) and that preventing PARylation through inhibition of PARP enzymes enables RB-deficient cells to progress to mitosis with unresolved replication stress and under-replicated DNA. These defects contribute to high levels of DNA damage, decreased proliferation, and compromised cell viability. I demonstrate this sensitivity is conserved across a panel of inhibitors that target both PARP1 and PARP2 and can be suppressed by re-expression of the RB protein. Together, these data indicate that inhibitors of PARP1 and PARP2 may be clinically relevant for RB-deficient cancers.

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