PARP1 Inhibition Radiosensitizes Models of Inflammatory Breast Cancer to Ionizing Radiation.

Sustained locoregional control of disease is a significant issue in patients with inflammatory breast cancer (IBC), with local control rates of 80% or less at 5 years. Given the unsatisfactory outcomes for these patients, there is a clear need for intensification of local therapy, including radiation. Inhibition of the DNA repair protein PARP1 has had little efficacy as a single agent in breast cancer outside of studies restricted to patients with BRCA mutations; however, PARP1 inhibition (PARPi) may lead to the radiosensitization of aggressive tumor types. Thus, this study investigates inhibition of PARP1 as a novel and promising radiosensitization strategy in IBC. In multiple existing IBC models (SUM-149, SUM-190, MDA-IBC-3), PARPi (AZD2281-olaparib and ABT-888-veliparib) had limited single-agent efficacy (IC50 > 10 μmol/L) in proliferation assays. Despite limited single-agent efficacy, submicromolar concentrations of AZD2281 in combination with RT led to significant radiosensitization (rER 1.12-1.76). This effect was partially dependent on BRCA1 mutational status. Radiosensitization was due, at least in part, to delayed resolution of double strand DNA breaks as measured by multiple assays. Using a SUM-190 xenograft model in vivo, the combination of PARPi and RT significantly delays tumor doubling and tripling times compared with PARPi or RT alone with limited toxicity. This study demonstrates that PARPi improves the effectiveness of radiotherapy in IBC models and provides the preclinical rationale for the opening phase II randomized trial of RT ± PARPi in women with IBC (SWOG 1706, NCT03598257).

Michmerhuizen AR ，Pesch AM ，Moubadder L ，Chandler BC ，Wilder-Romans K ，Cameron M ，Olsen E ，Thomas DG ，Zhang A ，Hirsh N ，Ritter CL ，Liu M ，Nyati S ，Pierce LJ ，Jagsi R ，Speers C ... -  《-》

Combined EGFR1 and PARP1 Inhibition Enhances the Effect of Radiation in Head and Neck Squamous Cell Carcinoma Models.

Head and neck squamous cell carcinoma (HNSCC) is a challenging cancer with little change in five-year overall survival rate of 50-60% over the last two decades. Radiation with or without platinum-based drugs remains the standard of care despite limited benefit and high toxicity. HNSCCs often overexpress epidermal growth factor receptor (EGFR) and inhibition of EGFR signaling enhances radiation sensitivity by interfering with repair of radiation-induced DNA breaks. Poly (adenosine diphosphate-ribose) polymerase-1 (PARP1) also participates in DNA damage repair, but its inhibition provides benefit in cancers that lack DNA repair by homologous recombination (HR) such as BRCA-mutant breast cancer. HNSCCs in contrast are typically BRCA wild-type and proficient in HR repair, making it challenging to apply anti-PARP1 therapy in this model. A recently published study showed that a combination of EGFR and PARP1 inhibition induced more DNA damage and greater growth control than each single agent in HNSCC cells. This led us to hypothesize that a combination of EGFR and PARP1 inhibition would enhance the efficacy of radiation to a greater extent than each single agent, providing a rationale for paradigm-shifting combinatorial approaches to improve the standard of care in HNSCC. Here, we report a proof-of-concept study using Detroit562 HNSCC cells, which are proficient for DNA repair by both HR and non-homologous end joining (NHEJ) mechanisms. We tested the effect of adding cetuximab and/or olaparib (inhibitors of EGFR and PARP1, respectively) to radiation and compared it to that of cisplatin and radiation combination, which is the standard of care. Our results demonstrate that the combination of cetuximab and olaparib with radiation was superior to the combination of any single drug with radiation in terms of induction of unrepaired DNA damage, induction of senescence, apoptosis and clonogenic death, and tumor growth control in mouse xenografts. Combined with our recently published phase I safety data on cetuximab/olaparib/radiation triple combination, the data reported here demonstrate a potential for combining biologically-based therapies that might optimize radiosensitization in HNSCC.

Frederick BA ，Gupta R ，Atilano-Roque A ，Su TT ，Raben D ... -  《-》

PARP1 Trapping and DNA Replication Stress Enhance Radiosensitization with Combined WEE1 and PARP Inhibitors.

KRAS mutations in non-small cell lung cancer (NSCLC) cause increased levels of DNA damage and replication stress, suggesting that inhibition of the DNA damage response (DDR) is a promising strategy for radiosensitization of NSCLC. This study investigates the ability of a WEE1 inhibitor (AZD1775) and a PARP inhibitor (olaparib) to radiosensitize KRAS-mutant NSCLC cells and tumors. In addition to inhibiting the DDR, these small-molecule inhibitors of WEE1 and PARP induce DNA replication stress via nucleotide exhaustion and PARP trapping, respectively. As monotherapy, AZD1775 or olaparib alone modestly radiosensitized a panel of KRAS-mutant NSCLC lines. The combination of agents, however, significantly increased radiosensitization. Furthermore, AZD1775-mediated radiosensitization was rescued by nucleotide repletion, suggesting a mechanism involving AZD1775-mediated replication stress. In contrast, radiosensitization by the combination of AZD1775 and olaparib was not rescued by nucleosides. Whereas both veliparib, a PARP inhibitor that does not efficiently trap PARP1 to chromatin, and PARP1 depletion radiosensitized NSCLC cells as effectively as olaparib, which does efficiently trap PARP, only olaparib potentiated AZD1775-mediated radiosensitization. Taken together, these mechanistic data demonstrate that although nucleotide depletion is sufficient for radiosensitization by WEE1 inhibition alone, and inhibition of PARP catalytic activity is sufficient for radiosensitization by olaparib alone, PARP1 trapping is required for enhanced radiosensitization by the combination of WEE1 and PARP inhibitors.Implications: This study highlights DNA replication stress caused by nucleotide depletion and PARP1 trapping as an important mechanism of radiosensitization in KRAS-mutant tumors and supports further development of DNA replication as a therapeutic target. Mol Cancer Res; 16(2); 222-32. ©2017 AACR.

Parsels LA ，Karnak D ，Parsels JD ，Zhang Q ，Vélez-Padilla J ，Reichert ZR ，Wahl DR ，Maybaum J ，O'Connor MJ ，Lawrence TS ，Morgan MA ... -  《-》

The PARP1 selective inhibitor saruparib (AZD5305) elicits potent and durable antitumor activity in patient-derived BRCA1/2-associated cancer models.

Poly (ADP-ribose) polymerase 1 and 2 (PARP1/2) inhibitors (PARPi) are targeted therapies approved for homologous recombination repair (HRR)-deficient breast, ovarian, pancreatic, and prostate cancers. Since inhibition of PARP1 is sufficient to cause synthetic lethality in tumors with homologous recombination deficiency (HRD), PARP1 selective inhibitors such as saruparib (AZD5305) are being developed. It is expected that selective PARP1 inhibition leads to a safer profile that facilitates its combination with other DNA damage repair inhibitors. Here, we aimed to characterize the antitumor activity of AZD5305 in patient-derived preclinical models compared to the first-generation PARP1/2 inhibitor olaparib and to identify mechanisms of resistance. Thirteen previously characterized patient-derived tumor xenograft (PDX) models from breast, ovarian, and pancreatic cancer patients harboring germline pathogenic alterations in BRCA1, BRCA2, or PALB2 were used to evaluate the efficacy of AZD5305 alone or in combination with carboplatin or an ataxia telangiectasia and Rad3 related (ATR) inhibitor (ceralasertib) and compared it to the first-generation PARPi olaparib. We performed DNA and RNA sequencing as well as protein-based assays to identify mechanisms of acquired resistance to either PARPi. AZD5305 showed superior antitumor activity than the first-generation PARPi in terms of preclinical complete response rate (75% vs. 37%). The median preclinical progression-free survival was significantly longer in the AZD5305-treated group compared to the olaparib-treated group (> 386 days vs. 90 days). Mechanistically, AZD5305 induced more replication stress and genomic instability than the PARP1/2 inhibitor olaparib in PARPi-sensitive tumors. All tumors at progression with either PARPi (39/39) showed increase of HRR functionality by RAD51 foci formation. The most prevalent resistance mechanisms identified were the acquisition of reversion mutations in BRCA1/BRCA2 and the accumulation of hypomorphic BRCA1. AZD5305 did not sensitize PDXs with acquired resistance to olaparib but elicited profound and durable responses when combined with carboplatin or ceralasertib in 3/6 and 5/5 models, respectively. Collectively, these results show that the novel PARP1 selective inhibitor AZD5305 yields a potent antitumor response in PDX models with HRD and delays PARPi resistance alone or in combination with carboplatin or ceralasertib, which supports its use in the clinic as a new therapeutic option.

Herencia-Ropero A ，Llop-Guevara A ，Staniszewska AD ，Domènech-Vivó J ，García-Galea E ，Moles-Fernández A ，Pedretti F ，Domènech H ，Rodríguez O ，Guzmán M ，Arenas EJ ，Verdaguer H ，Calero-Nieto FJ ，Talbot S ，Tobalina L ，Leo E ，Lau A ，Nuciforo P ，Dienstmann R ，Macarulla T ，Arribas J ，Díez O ，Gutiérrez-Enríquez S ，Forment JV ，O'Connor MJ ，Albertella M ，Balmaña J ，Serra V ... -  《Genome Medicine》

Radiosensitization with combined use of olaparib and PI-103 in triple-negative breast cancer.

Jang NY ，Kim DH ，Cho BJ ，Choi EJ ，Lee JS ，Wu HG ，Chie EK ，Kim IA ... -  《BMC CANCER》