Biology subjects

Pawelczak, K. S.

Publications and source records attributed to Pawelczak, K. S..

4 recordsLinked to original sources

bioRxiv2025

Chemical inhibition of RPA gap protection sensitizes BRCA1-deficient cancers to PARP inhibition

Poly (ADP-ribose) polymerase inhibitors (PARPi) are standard of care for many BRCA1 deficient cancers, though few cures are achieved. We sought to determine if targeting the protection of the single-strand DNA gaps induced by PARPi in BRCA-deficient cancers could increase efficacy. Replication protein A (RPA) participates in critical protein-protein and protein-DNA interactions to protect single-stranded DNA (ssDNA) and support DNA metabolism. We have reported the optimization of small molecule RPA inhibitors (RPAi) that target protein-ssDNA interactions to chemically exhaust RPA and elicit single-agent anticancer activity. RPAi sensitizes cells to PARPi in BRCA1-deficient non-cancerous cells, where ssDNA gap formation drives therapeutic efficacy. We show that RPAi treatment abolishes PARPi-induced replication gap protection, resulting in genomic instability via replication fork degradation and chromosomal integrity, and that, in vivo, the RPA and PARP targeted combination abrogates cancer growth in a BRCA1-mutant breast cancer model. We find that genetic predispositions to ssDNA gap accumulation correlate with RPAi sensitivity, and BRCA1-proficient cells remain sensitive to combination treatment but require more PARP inhibition to increase ssDNA gaps. RPAi-PARPi combination activity in patient-derived ovarian cancer models demonstrates the utility of targeting gap protection to increase PARPi sensitivity and circumvent resistance. Collectively, this work provides a unifying mechanism of chemical RPA exhaustion as a cancer therapeutic strategy. One Sentence SummaryInhibition of single-strand DNA gap protection potentiates PARP targeted treatment of BRCA1 deficient cancers.

cancer biology↗

bioRxiv2020

Chemical exhaustion of RPA in cancer treatment

Replication protein A (RPA) plays essential roles in DNA replication, repair, recombination and the DNA-damage response (DDR). We have developed second generation RPA inhibitors (RPAis) that block the RPA-DNA interaction. These DNA-binding inhibitors (DBis) can elicit a state of cellular RPA exhaustion resulting in single agent in vitro anticancer activity across a broad spectrum of cancers and in vivo activity in two non-small cell lung cancer models. The cellular response to RPAi treatment suggests a threshold exists before RPA inhibition induces cell death. Chemical RPA exhaustion potentiates the anticancer activity of other DDR inhibitors as well as traditional DNA damaging cancer therapeutics. Consistent with the chemical RPA exhaustion model, we demonstrate that the effects of RPAi on replication fork dynamics and DNA damage signaling are similar to other known DDR inhibitors. In accordance with the RPA threshold model, retrospective analysis of lung cancer patient data demonstrates high RPA expression as a negative prognostic biomarker for overall survival in smoking-related lung cancers. Similarly, relative expression of RPA is a predictive marker for response to chemotherapy. These observations are consistent with the increase in RPA expression serving as an adaptive mechanism that allows tolerance of the genotoxic stress resulting from carcinogen exposure. These data demonstrate a unique mechanism of action of RPAis eliciting a state of RPA exhaustion that impacts the DDR and may provide an effective therapeutic option for difficult to treat lung cancers. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=130 SRC="FIGDIR/small/404640v1_ufig1.gif" ALT="Figure 1"> View larger version (18K): org.highwire.dtl.DTLVardef@d662e4org.highwire.dtl.DTLVardef@f68b11org.highwire.dtl.DTLVardef@241c0corg.highwire.dtl.DTLVardef@ad7398_HPS_FORMAT_FIGEXP M_FIG C_FIG

cancer biology↗

bioRxiv2020

Discovery and Development of Novel DNA-PK Inhibitors by Targeting the unique Ku-DNA Interaction

DNA-dependent protein kinase (DNA-PK) plays a critical role in the non-homologous end joining (NHEJ) repair pathway and the DNA damage response (DDR). DNA-PK has therefore been pursued for the development of anti-cancer therapeutics in combination with ionizing radiation (IR). We report the discovery of a new class of DNA-PK inhibitors that act via a novel mechanism of action, inhibition of the Ku-DNA interaction. We have developed a series of highly potent and specific Ku-DNA binding inhibitors (Ku-DBis) that block the Ku-DNA interaction and inhibit DNA-PK kinase activity. Ku-DBis directly interact with the Ku and inhibit in vitro NHEJ, cellular NHEJ, and potentiate the activity of IR and radiomimetics. Analysis of Ku-null cells demonstrates that Ku-DBis cellular activity is a direct result of Ku inhibition, as Ku-null cells are insensitive to Ku-DBis. The utility of Ku-DBis was also demonstrated in a CRISPR gene-editing model where we demonstrate that the efficiency of gene insertion events was increased in cells pre-treated with Ku-DBis, consistent with inhibition of NHEJ and activation of homologous recombination to facilitate gene insertion. These data demonstrate the discovery and application of new series of compounds that modulate DNA repair pathways via a unique mechanism of action.

biochemistry↗

bioRxiv2020

Platinum-Induced Ubiquitination of Phosphorylated H2AX by RING1A is Mediated by Replication Protein A in Ovarian Cancer

Platinum resistance is a common occurrence in high grade serous ovarian cancer (HGSOC) and a major cause of OC deaths. Platinum agents form DNA crosslinks, which activate nucleotide excision repair (NER), fanconi anemia (FA) and homologous recombination repair (HRR) pathways. Chromatin modifications occur in the vicinity of DNA damage and play an integral role in the DNA damage response (DDR). Chromatin modifiers, including polycomb repressive complex 1 (PRC1) members, and chromatin structure are frequently dysregulated in OC and can potentially contribute to platinum resistance. However, the role of chromatin modifiers in the repair of platinum DNA damage in OC is not well understood. We demonstrate that the PRC1 complex member RING1A mediates monoubiquitination of lysine 119 of phosphorylated H2AX ({gamma}H2AXub1) at sites of platinum DNA damage in OC cells. After platinum treatment, our results reveal that NER and HRR both contribute to RING1A localization and {gamma}H2AX monoubiquitination. Importantly, replication protein A (RPA), involved in both NER and HRR, mediates RING1A localization to sites of damage. Furthermore, RING1A deficiency impaired the activation of the G2/M DNA damage checkpoint and reduced the ability of OC cells to repair platinum DNA damage. Elucidating the role of RING1A in the DDR to platinum agents will allow for the identification of therapeutic targets to improve the response of OC to standard chemotherapy regimens.

cancer biology↗