DNA Damage Response Inhibitors Research Articles

APE1 promotes non-homologous end joining by initiating DNA double-strand break formation and decreasing ubiquitination of artemis following oxidative genotoxic stress

BackgroundApurinic/apyrimidinic endonuclease 1 (APE1) imparts radio-resistance by repairing isolated lesions via the base excision repair (BER) pathway, but whether and how it is involved in the formation and/or repair of DSBs remains mostly unknown.MethodsImmunoblotting, fluorescent immunostaining, and the Comet assay were used to investigate the effect of APE1 on temporal DSB formation. Chromatin extraction, 53BP1 foci and co-immunoprecipitation, and rescue assays were used to evaluate non-homologous end joining (NHEJ) repair and APE1 effects. Colony formation, micronuclei measurements, flow cytometry, and xenograft models were used to examine the effect of APE1 expression on survival and synergistic lethality. Immunohistochemistry was used to detect APE1 and Artemis expression in cervical tumor tissues.ResultsAPE1 is upregulated in cervical tumor tissue compared to paired peri-tumor, and elevated APE1 expression is associated with radio-resistance. APE1 mediates resistance to oxidative genotoxic stress by activating NHEJ repair. APE1, via its endonuclease activity, initiates clustered lesion conversion to DSBs (within 1 h), promoting the activation of the DNA-dependent protein kinase catalytic subunit (DNA-PKcs), a key kinase in the DNA damage response (DDR) and NHEJ pathway. APE1 then participates in NHEJ repair directly by interacting with DNA- PKcs. Additionally, APE1 promotes NHEJ activity by decreasing the ubiquitination and degradation of Artemis, a nuclease with a critical role in the NHEJ pathway. Overall, APE1 deficiency leads to DSB accumulation at a late phase following oxidative stress (after 24 h), which also triggers activation of Ataxia-telangiectasia mutated (ATM), another key kinase of the DDR. Inhibition of ATM activity significantly promotes synergistic lethality with oxidative stress in APE1-deficient cells and tumors.ConclusionAPE1 promotes NHEJ repair by temporally regulating DBS formation and repair following oxidative stress. This knowledge provides new insights into the design of combinatorial therapies and indicates the timing of administration and maintenance of DDR inhibitors for overcoming radio-resistance.

Let's not take DNA breaks for granted. The importance of direct detection of DNA breaks for the successful development of DDR inhibitors.

Successful development of a drug candidate requires availability of robust methods that enable precise and quantitative assessment of the biological effects exerted by the molecule of interest. In case of DNA Damage Response inhibitors, the most proximal readout of their efficiency is the level of induced DNA damage, usually - DNA breaks. Here we review the methods that are currently used for the assessment of the level of DNA damage, with special attention to their specificity and sensitivity. We also discuss the most common problems and challenges related to the classic IF or IHC methods that indirectly report on the activation of DNA repair mechanisms as the downstream effects of occurrence of the DNA lesions. Finally, we highlight the advent of new tools, such as STRIDE, which have the potential to transform the landscape of DDR functional biomarkers.

DNA Repair Deficiency Regulates Immunity Response in Cancers: Molecular Mechanism and Approaches for Combining Immunotherapy

Defects in DNA repair pathways can lead to genomic instability in multiple tumor types, which contributes to tumor immunogenicity. Inhibition of DNA damage response (DDR) has been reported to increase tumor susceptibility to anticancer immunotherapy. However, the interplay between DDR and the immune signaling pathways remains unclear. In this review, we will discuss how a deficiency in DDR affects anti-tumor immunity, highlighting the cGAS-STING axis as an important link. We will also review the clinical trials that combine DDR inhibition and immune-oncology treatments. A better understanding of these pathways will help exploit cancer immunotherapy and DDR pathways to improve treatment outcomes for various cancers.

Abstract P2-17-03: Preclinical study of trastuzumab deruxtecan (T-Dxd; DS-8201a) in combination with DNA damage response pathway inhibitors in HER2-low/Hormone receptor negative breast cancer patient-derived xenograft models

Abstract Background: Triple negative breast cancer (TNBC), defined by negative hormone receptor (HR) status and the lack of HER2 gene amplification, is a significant clinical challenge because of its aggressive clinical course and association with a poor prognosis. Recent studies demonstrated that approximately a third of TNBC has low expression of HER2, so called HER2-low TNBC, which could be targeted by the new generation HER2-directed antibody-drug conjugate (ADC). Trastuzumab deruxtecan (also known as T-Dxd, DS-8201a) is a novel HER2-directed ADC with a topoisomerase 1 inhibitor payload and a tetrapeptide-based cleavable linker, which has been FDA approved for patients with metastatic HER2-positive, or amplified breast cancer. T-Dxd has also shown to improve survival outcomes when compared to physicians’ choice chemotherapy in patients with metastatic HR-negative/HER2-low breast cancer in the Phase 3 DESTINY-Breast04 trial. However, resistance is invariable. We hypothesize that small molecule inhibitors against DNA damage response (DDR) pathways could potentiate the DNA damaging effect of T-Dxd and improve its anti-tumor activity in HER2-low TNBC. Method: We conducted preclinical experiments to assess the anti-tumor activity of T-Dxd and each of the DDR pathway inhibitors, including the ATR inhibitor AZD6738, the ATM inhibitor AZD1390, and the PARP inhibitor olaparib, as well as the Wee 1 inhibitor AZD1775, either alone or in combination, compared to the vehicle treatment, in a panel of HER2-low TNBC PDX models in vivo, as well as mechanistic studies using HER2-low TNBC cell lines in vitro. HER2-low was defined as 1+ or 2+ on HER2 immunohistochemistry. Results: Four HER2-low TNBC PDX models, including WHIM2 (TP53 mutated, basal-like), WHIM6 (TP53 WT, basal-like), WHIM12 (TP53, PIK3CA, and PTEN mutated, claudin-low), and WHIM30 (BRCA1 and TP53 mutated, basal-like), as well as a panel of 4 TNBC cell lines with variable HER2 expression were included in the study. We demonstrated that the addition of DDR pathway inhibitors to T-Dxd led to further tumor shrinkage and delayed tumor progression in HER2-low TNBC PDX models in vivo and induced synergistic anti-tumor effects in vitro. Enhanced DNA damaging effect and apoptosis induction were observed with combination therapies in vitro. Biomarker analysis on xenograft tumors harvested 3 days following treatment with either Vehicle, T-Dxd, olaparib, or T-Dxd plus olaparib in WHIM6, was also performed, which demonstrated that the addition of olaparib enhanced DNA damage (increased pH2AX), and promoted apoptosis (increased cleaved PARP). Further mechanistic studies in HER2-low TNBC cell lines demonstrated the formation of DNA topoisomerase 1 covalent complexes (TopoIcc) following treatment with T-Dxd. Interestingly, while the formation of Topolcc was reduced with the addition of either ATR or ATM inhibitor, no reduction was observed with the addition of olaparib. Additionally, we observed that combination therapies reduced cell migration in vitro. The combination of olaparib with T-Dxd, in particular, reduced mammosphere formation and Epithelial Mesenchymal Transition (EMT) modulation markers, including SNAIL, SLUG and/or TWIST. Conclusion: Our study demonstrated that the combination of T-Dxd and DDR pathway inhibitors induced additive or synergistic anti-tumor effect in HER2-low TNBC. Our data from the studies of cell lines and PDX models provided preclinical rationale for the combination of T-Dxd and DDR pathway inhibitors in patients with HER2-low TNBC. The olaparib combination showed unique mechanistic characteristics compared with other DDR inhibitors, which are being further examined in additional HER2-low TNBC models. Citation Format: Adrian Gonzalez-Gonzalez, Zhanfang Guo, Alice Meroni, Emily Cybulla, Jeremy Hoog, Alessandro Vindigni, Cynthia Ma. Preclinical study of trastuzumab deruxtecan (T-Dxd; DS-8201a) in combination with DNA damage response pathway inhibitors in HER2-low/Hormone receptor negative breast cancer patient-derived xenograft models [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-17-03.

Abstract P2-26-09: Synergistic activity of PI3K inhibitor in combination with AZD6738, ATR inhibitor in breast cancer preclinical model via DNA damage response pathway

Abstract Background: The PI3K inhibition has been an appealing approach for anticancer therapy due to its crucial role in cell growth, proliferation, and survival in various cancers. Emerging data suggest the PI3K pathway is also involved in DNA replication and genome stability, making DNA damage response (DDR) inhibitors as an attractive combination treatment for PI3K pathway blockades. Here, to enhance the efficacy of PI3K inhibitors, we investigated the novel approach combining PI3K inhibitors (alpelisib, AZD8835, AZD8186, NVP-BKM120) with DDR blockade using ATR inhibitor (AZD6738) in breast cancer preclinical models. Methods: Hormone receptor-positive breast cancer cells, MCF7 (PIK3CA E545K mutation) and T47D (PIK3CA H1047R mutation) were used. First, cell viability and the synergistic effect of combination drug was carried out by MTT assy. Next, western blot, cell cycle analysis, apoptosis assay, and immunocytochemistry were conducted to validate the hypothesis. Finally, tumor xenograft experiments were conducted using BALB/c nude mice to validate the in vitro data. Results: A synergistic antiproliferative effect was observed over a wide range of combination (PI3K inhibitor + ATR inhibitor) concentrations (even in a lower concentration as 1/10 x IC50) in vitro, suggesting that when alpelisib is combined with an ATR inhibitor, there may be possibility of lowering the effective dosage of alpelisib. After confirmation of the strong synergistic effect in sub-G1/G0-G1 arrest-mediated apoptosis by the combination treatment, we demonstrated that expressions of phospho ATR, ATM, and CHK1 were suppressed but -H2AX markedly increased by combination treatment as compared to PI3K inhibitors and ATR inhibitor alone. This suggests that combination treatment activates apoptotic pathway through enhanced DNA double strand breaks. Finally, the in vivo study showed that the combination treatment group tended to show a greater tumor growth inhibition compared with PI3K inhibitor or ATR inhibitor alone. Conclusion: The combined inhibition of PI3K and ATR showed a synergistic anticancer effect in vitro and in vivo. ATR inhibitor in combination with PI3K inhibitor merits further clinical investigation to enhance the activity of PI3K inhibitor for the treatment of PIK3CA mutated breast cancer patients. Citation Format: Yong Wha Moon, Mithun Gosh, Nahee Park, Kamal Pandey, Nar Bahadur Katwal, Sa Deok Hong. Synergistic activity of PI3K inhibitor in combination with AZD6738, ATR inhibitor in breast cancer preclinical model via DNA damage response pathway [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-26-09.

Chlorin e6-induced photodynamic effect facilitates immunogenic cell death of lung cancer as a result of oxidative endoplasmic reticulum stress and DNA damage

Suppression of the immune microenvironment is an important endogenous contributor to treatment failure in lung cancer. Photodynamic therapy (PDT) is widely used in the treatment of malignant tumors owing to its photo-selectivity and minimal side effects. Some studies have shown the ability of photodynamic action not only to cause photo-cytotoxicity to tumor cells but also to induce immunogenic cell death (ICD). However, the mechanism by which PDT enhances tumor immunogenicity is poorly understood. The present study aimed to explore the immunogenicity effect of PDT on lung cancer and to reveal the underlying mechanism. First, we searched for effective conditions for PDT-induced apoptosis in lung cancer cells. Just as expected, chlorin e6 (Ce6) PDT could enhance the immunogenicity of lung cancer cells alongside the induction of apoptosis, characterized by up-regulation of CRT, HSP90, HMGB1 and MHC-I. Further results showed the generation of ROS by Ce6 PDT under the above conditions, which is an oxidative damaging agent. Simultaneously, PDT induced endoplasmic reticulum (ER) stress in cells, as evidenced by enhanced Tht staining and up-regulated CHOP and GRP78 expression. Moreover, PDT led to DNA damage response (DDR) as well. However, the redox inhibitor NAC abolished the ER stress and DDR caused by PDT. More importantly, NAC also attenuated PDT-induced improvement of immunogenicity in lung cancer. On this basis, the PDT-induced CRT up-regulation was found to be attenuated in response to inhibition of ER stress. In addition, PDT-induced increase in HMGB1 and HSP90 release was blocked by inhibition of DDR. In summary, Ce6 PDT could produce ROS under certain conditions, which leads to ER stress that promotes CRT translocation to the cell membrane, and the resulting DNA damage causes the expression and release of nuclear HMGB1 and HSP90, thereby enhancing the immunogenicity of lung cancer. This current study elucidates the mechanism of PDT in ameliorating the immunogenicity of lung cancer, providing a rationale for PDT in regulating the immune microenvironment for the treatment of malignant tumors.

2-Hydroxy-3-methylanthraquinone inhibits homologous recombination repair in osteosarcoma through the MYC-CHK1-RAD51 axis

BackgroundOsteosarcoma is a malignant bone tumor that usually affects adolescents aged 15–19 y. The DNA damage response (DDR) is significantly enhanced in osteosarcoma, impairing the effect of systemic chemotherapy. Targeting the DDR process was considered a feasible strategy benefitting osteosarcoma patients. However, the clinical application of DDR inhibitors is not impressive because of their side effects. Chinese herbal medicines with high anti-tumor effects and low toxicity in the human body have gradually gained attention. 2-Hydroxy-3-methylanthraquinone (HMA), a Chinese medicine monomer found in the extract of Oldenlandia diffusa, exerts significant inhibitory effects on various tumors. However, its anti-osteosarcoma effects and defined molecular mechanisms have not been reported.MethodsAfter HMA treatment, the proliferation and metastasis capacity of osteosarcoma cells was detected by CCK-8, colony formation, transwell assays and Annexin V-fluorescein isothiocyanate/propidium iodide staining. RNA-sequence, plasmid infection, RNA interference, Western blotting and immunofluorescence assay were used to investigate the molecular mechanism and effects of HMA inhibiting osteosarcoma. Rescue assay and CHIP assay was used to further verified the relationship between MYC, CHK1 and RAD51.ResultsHMA regulate MYC to inhibit osteosarcoma proliferation and DNA damage repair through PI3K/AKT signaling pathway. The results of RNA-seq, IHC, Western boltting etc. showed relationship between MYC, CHK1 and RAD51. Rescue assay and CHIP assay further verified HMA can impair homologous recombination repair through the MYC-CHK1-RAD51 pathway.ConclusionHMA significantly inhibits osteosarcoma proliferation and homologous recombination repair through the MYC-CHK1-RAD51 pathway, which is mediated by the PI3K-AKT signaling pathway. This study investigated the exact mechanism of the anti-osteosarcoma effect of HMA and provided a potential feasible strategy for the clinical treatment of human osteosarcoma.Graphical

The endocytosis inhibitor dynasore induces a DNA damage response pathway that can be manipulated for enhanced apoptosis

Endocytosis has been shown to play an important role in cancer proliferation and metastasis. Recent studies have accumulated evidence that endocytosis inhibitors suppress in vitro and in vivo proliferation and migration. In addition, endocytosis inhibition has been shown to induce apoptosis, but its mechanism remains largely unclear. In this study, we found that the endocytosis inhibitor dynasore causes a cell viability reduction in multiple cancer cell lines, especially in hematopoietic cancers. Dynasore induced massive apoptosis and an S-phase progression delay. In addition, dynasore activated the ATR-Chk1 DNA damage response, which suggests a single-stranded DNA exposure induced by DNA replication stress. Furthermore, an ATR inhibitor sensitized the dynasore-induced apoptosis. These findings suggest that endocytosis inhibitors may have an ability to suppress DNA replication, a common mechanism of genotoxic chemotherapies targeting cancer, and that the anti-cancer effects of endocytosis inhibitors may be sensitized by DNA damage response inhibitors.

Targeted thorium-227 conjugates as treatment options in oncology.

Targeted alpha therapy (TAT) is a promising approach for addressing unmet needs in oncology. Inherent properties make α-emitting radionuclides well suited to cancer therapy, including high linear energy transfer (LET), penetration range of 2-10 cell layers, induction of complex double-stranded DNA breaks, and immune-stimulatory effects. Several alpha radionuclides, including radium-223 (223Ra), actinium-225 (225Ac), and thorium-227 (227Th), have been investigated. Conjugation of tumor targeting modalities, such as antibodies and small molecules, with a chelator moiety and subsequent radiolabeling with α-emitters enables specific delivery of cytotoxic payloads to different tumor types. 223Ra dichloride, approved for the treatment of patients with metastatic castration-resistant prostate cancer (mCRPC) with bone-metastatic disease and no visceral metastasis, is the only approved and commercialized alpha therapy. However, 223Ra dichloride cannot currently be complexed to targeting moieties. In contrast to 223Ra, 227Th may be readily chelated, which allows radiolabeling of tumor targeting moieties to produce targeted thorium conjugates (TTCs), facilitating delivery to a broad range of tumors. TTCs have shown promise in pre-clinical studies across a range of tumor-cell expressing antigens. A clinical study in hematological malignancy targeting CD22 has demonstrated early signs of activity. Furthermore, pre-clinical studies show additive or synergistic effects when TTCs are combined with established anti-cancer therapies, for example androgen receptor inhibitors (ARI), DNA damage response inhibitors such as poly (ADP)-ribose polymerase inhibitors or ataxia telangiectasia and Rad3-related kinase inhibitors, as well as immune checkpoint inhibitors.

Combination DNA Damage Response (DDR) Inhibitors to Overcome Drug Resistance in Ovarian Cancer.

The DNA damage response (DDR) results in activation of a series of key target kinases that respond to different DNA damage insults. DDR inhibitors such as PARP inhibitors lead to the accumulation of DNA damage in tumor cells and ultimately apoptosis. However, responses to DDRi monotherapy in the clinic are not durable and resistance ultimately develops. DDRi-DDRi combinations such as PARPi-ATRi, PAPRi-WEE1i and PARPi-AsiDNA can overcome multiple resistance mechanisms to PARP inhibition. In addition, DDRi-DDRi combinations can provide viable treatment options for patients with platinum-resistant disease. In the present chapter we discuss rationale of DDRi-DDRi strategies that capitalize on genomic alterations found in ovarian cancer and other solid tumors and may provide in the near future new treatment options for these patients.

Chinese medicine formula ‘Baipuhuang Keli’ inhibits triple-negative breast cancer by hindering DNA damage repair via MAPK/ERK pathway

Ethnopharmacological relevanceBaipuhuang Keli (BPH, constituted by Bai Tou Weng (Pulsatilla chinensis (Bunge) Regel), Pu Gong Ying (Taraxacum mongolicum Hand.-Mazz.), Huang Qin (Scutellaria baicalensis Georgi), Huang Bo (Phellodendron amurense Rupr.)) is a Chinese herbal formula with clearing heat and cooling blood, and removing toxin effects, which is suit for the case of breast cancer. Aim of the studyHere, we aim to explore the effects of BPH on triple-negative breast cancer (TNBC) and its potential mechanisms. Materials and methodsIn this study, cell viability assay, colony formation assay, soft agar assay, cell proliferation curve assay, and EdU assay were employed to determine the anti-proliferation effect induced by BPH. Cell cycle distribution was detected by flow cytometry. DNA damage in cells treated with BPH was indicated by comet assay, immunofluorescence, and Western Blot. Both the 4T1 orthotopic tumor model and the MDA-MB-231 subcutaneous tumor model were used to assess in vivo effect of BPH (312.5, and 625 mg/kg). The protein expression levels of the DNA damage response (DDR) pathway and the MAPK/ERK pathway were detected by Western Blot. ResultsOur results indicated that TNBC cells were more sensitive to BPH than mammary epithelial cells. Cell proliferation of TNBC cells was significantly inhibited by BPH in a dose-dependent manner. Moreover, BPH induced DNA damage in TNBC cells in a concentration and time-dependent manner. DDR of TNBC cells was inhibited by BPH. MAPK/ERK pathway was inhibited in cells treated with BPH, and DNA damage can be reversed while EGF was added to activate MAPK/ERK pathway. The 4T1 orthotopic tumor model and the MDA-MB-231 subcutaneous tumor model further confirmed that BPH inhibited TNBC proliferation via inhibition of DDR and MAPK/ERK pathway in vivo. ConclusionsCollectively, we proved that BPH is a potential anticancer Chinese herbal formula for TNBC in the manner of in vitro and in vivo experiments.

Interference with pathways activated by topoisomerase inhibition alters the surface expression of PD-L1 and MHC I in colon cancer cells.

Topoisomerase inhibitors are clinically used to treat various cancer types, including colorectal cancer. These drugs also activate signaling pathways that modulate cell survival and immune cell functions. Immunotherapy is promising for certain tumors, including microsatellite instable colorectal cancer, but not for microsatellite stable colorectal cancer. The reasons for this lack of responsiveness are largely unknown. Understanding how colorectal cancer cell-surface proteins interact with tumor-resident immune cells may offer an opportunity to identify molecules that, if targeted, may render tumor cells visible to immune cells. The present study used flow cytometry, fluorescent staining and immunoblotting to examine if inhibition of pathways activated by topoisomerase-targeting drugs may modulate the outcomes of treatment through effects on cell cycle arrest and apoptosis, and by altering surface expression levels of programmed death-ligand 1 (PD-L1) or major histocompatibility complex protein I (MHC I). Inhibition of either NF-κB or DNA-damage response (DDR) potently enhanced cell death in combination with topoisomerase inhibition, while only NF-κB inhibition increased MHC I. PD-L1 upregulation was moderately affected by NF-κB or DDR inhibitors, while both topoisomerase inhibitors and DNA damaging agents may enhance the surface expression of MHC I molecules on colon cancer cells. Such enhanced expression of MHC I may be suppressed by inhibitors of ataxia-telangiectasia mutated or checkpoint kinase kinases. Additionally, adaptive tolerance to topoisomerase inhibition caused altered cell cycle response, and reduced the expression levels of both PD-L1 and MHC I on both microsatellite instable and stable colon cancer cell lines. Therefore, targeted modulation of DDR pathways, PD-L1, MHC I or other immune regulators in colon cancer cells may make them more visible to immune cells and enable rational combination of conventional therapy with immunotherapy.

Targeting the DNA Damage Response Machinery for Lung Cancer Treatment.

Lung cancer is considered the most commonly diagnosed cancer and one of the leading causes of death globally. Despite the responses from small-cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC) patients to conventional chemo- and radiotherapies, the current outcomes are not satisfactory. Recently, novel advances in DNA sequencing technologies have started to take off which have provided promising tools for studying different tumors for systematic mutation discovery. To date, a limited number of DDR inhibition trials have been conducted for the treatment of SCLC and NSCLC patients. However, strategies to test different DDR inhibitor combinations or to target multiple pathways are yet to be explored. With the various biomarkers that have either been recently discovered or are the subject of ongoing investigations, it is hoped that future trials would be designed to allow for studying targeted treatments in a biomarker-enriched population, which is defensible for the improvement of prognosis for SCLC and NSCLC patients. This review article sheds light on the different DNA repair pathways and some of the inhibitors targeting the proteins involved in the DNA damage response (DDR) machinery, such as ataxia telangiectasia and Rad3-related protein (ATR), DNA-dependent protein kinase (DNA-PK), and poly-ADP-ribose polymerase (PARP). In addition, the current status of DDR inhibitors in clinical settings and future perspectives are discussed.

DNA Damage Response in Cancer Therapy and Resistance: Challenges and Opportunities

Resistance to chemo- and radiotherapy is a common event among cancer patients and a reason why new cancer therapies and therapeutic strategies need to be in continuous investigation and development. DNA damage response (DDR) comprises several pathways that eliminate DNA damage to maintain genomic stability and integrity, but different types of cancers are associated with DDR machinery defects. Many improvements have been made in recent years, providing several drugs and therapeutic strategies for cancer patients, including those targeting the DDR pathways. Currently, poly (ADP-ribose) polymerase inhibitors (PARP inhibitors) are the DDR inhibitors (DDRi) approved for several cancers, including breast, ovarian, pancreatic, and prostate cancer. However, PARPi resistance is a growing issue in clinical settings that increases disease relapse and aggravate patients' prognosis. Additionally, resistance to other DDRi is also being found and investigated. The resistance mechanisms to DDRi include reversion mutations, epigenetic modification, stabilization of the replication fork, and increased drug efflux. This review highlights the DDR pathways in cancer therapy, its role in the resistance to conventional treatments, and its exploitation for anticancer treatment. Biomarkers of treatment response, combination strategies with other anticancer agents, resistance mechanisms, and liabilities of treatment with DDR inhibitors are also discussed.

Glutathione-sensitive nanoparticles enhance the combined therapeutic effect of checkpoint kinase 1 inhibitor and cisplatin in prostate cancer.

Prostate cancer (PCa) is the second most common malignant tumor among males. Traditional treatments for PCa, which include surgery and endocrine therapy, have shown limited success, and more effective therapies are needed. Cisplatin (DDP) is an approved chemotherapeutic drug that causes DNA damage in cancer, whereas AZD7762, an inhibitor of CHK1, can significantly inhibit DNA repair. The effective therapeutic combination of cisplatin and the DNA damage response inhibitor AZD7762 has been considered to be a potential solution to the resistance to cisplatin and the adverse reactions that occur in many cancers. However, the co-transmission of cisplatin and AZD7762 and the unsatisfactory tumor-targeting efficacy of this therapy remain problems to be solved. Here, we confirmed the combined therapeutic efficacy of cisplatin and AZD7762 in PCa. Furthermore, we show that the glutathione-targeted Cys8E nanoparticles we synthesized, which have high drug-loading capacity, remarkable stability, and satisfactory release efficiency, enhanced the therapeutic efficacy of this treatment and reduced the required dosages of these drugs both in vitro and in vivo. Overall, we propose combination therapy of cisplatin and AZD7762 for PCa and facilitate it using Cys8E nanoparticles, which allow for better drug loading release, higher release efficiency, and more accurate tumor-targeting efficacy.

BMN673 Is a PARP Inhibitor with Unique Radiosensitizing Properties: Mechanisms and Potential in Radiation Therapy.

BMN673 is a relatively new PARP inhibitor (PARPi) that exhibits superior efficacy in vitro compared to olaparib and other clinically relevant PARPi. BMN673, similar to most clinical PARPi, inhibits the catalytic activities of PARP-1 and PARP-2 and shows impressive anticancer potential as monotherapy in several pre-clinical and clinical studies. Tumor resistance to PARPi poses a significant challenge in the clinic. Thus, combining PARPi with other treatment modalities, such as radiotherapy (RT), is being actively pursued to overcome such resistance. However, the modest to intermediate radiosensitization exerted by olaparib, rucaparib, and veliparib, limits the rationale and the scope of such combinations. The recently reported strong radiosensitizing potential of BMN673 forecasts a paradigm shift on this front. Evidence accumulates that BMN673 may radiosensitize via unique mechanisms causing profound shifts in the balance among DNA double-strand break (DSB) repair pathways. According to one of the emerging models, BMN673 strongly inhibits classical non-homologous end-joining (c-NHEJ) and increases reciprocally and profoundly DSB end-resection, enhancing error-prone DSB processing that robustly potentiates cell killing. In this review, we outline and summarize the work that helped to formulate this model of BMN673 action on DSB repair, analyze the causes of radiosensitization and discuss its potential as a radiosensitizer in the clinic. Finally, we highlight strategies for combining BMN673 with other inhibitors of DNA damage response for further improvements.

Highlights from Recent Cancer Literature

Highlights from Recent Cancer Literature

H3.3-G34 mutations impair DNA repair and promote cGAS/STING-mediated immune responses in pediatric high-grade glioma models.

Pediatric high-grade gliomas (pHGGs) are the leading cause of cancer-related deaths in children in the USA. Sixteen percent of hemispheric pediatric and young adult HGGs encode Gly34Arg/Val substitutions in the histone H3.3 (H3.3-G34R/V). The mechanisms by which H3.3-G34R/V drive malignancy and therapeutic resistance in pHGGs remain unknown. Using a syngeneic, genetically engineered mouse model (GEMM) and human pHGG cells encoding H3.3-G34R, we demonstrate that this mutation led to the downregulation of DNA repair pathways. This resulted in enhanced susceptibility to DNA damage and inhibition of the DNA damage response (DDR). We demonstrate that genetic instability resulting from improper DNA repair in G34R-mutant pHGG led to the accumulation of extrachromosomal DNA, which activated the cyclic GMP-AMP synthase/stimulator of IFN genes (cGAS/STING) pathway, inducing the release of immune-stimulatory cytokines. We treated H3.3-G34R pHGG-bearing mice with a combination of radiotherapy (RT) and DNA damage response inhibitors (DDRi) (i.e., the blood-brain barrier-permeable PARP inhibitor pamiparib and the cell-cycle checkpoint CHK1/2 inhibitor AZD7762), and these combinations resulted in long-term survival for approximately 50% of the mice. Moreover, the addition of a STING agonist (diABZl) enhanced the therapeutic efficacy of these treatments. Long-term survivors developed immunological memory, preventing pHGG growth upon rechallenge. These results demonstrate that DDRi and STING agonists in combination with RT induced immune-mediated therapeutic efficacy in G34-mutant pHGG.

STINGing the immune system: lessons learned through a model of G34-mutant pediatric high-grade glioma.

Pediatric high-grade gliomas (pHGGs) are aggressive diseases with poor outcomes. The diverse molecular heterogeneity in these rare tumors and inadequate tumor models have limited the development of effective therapies. In this issue of the JCI, Haase et al. produced a genetically engineered mouse model of H3.3-G34R-mutant pHGG to help identify vulnerabilities in DNA repair pathways. The authors designed a therapy that combined radiation with DNA damage response inhibitors to induce an adaptive immune response and extend survival. These findings suggest that combinations of small-molecule therapies with immunotherapies could drive a more durable response and improve mortality for patients with pHGG.

CTIM-02. TIP: PHASE I/II STUDY OF STEREOTACTIC RADIOSURGERY WITH CONCURRENT OLAPARIB FOLLOWED BY ADJUVANT DURVALUMAB AND PHYSICIAN’S CHOICE SYSTEMIC THERAPY IN SUBJECTS WITH BREAST CANCER BRAIN METASTASES

Abstract BACKGROUND Despite progress in the treatment of brain metastasis (BrM) for HER2+ breast cancer (BC), outcomes for patients with HER2-negative BC BrM remain poor. Current standard of care consists of local therapies, including surgery and radiotherapy, followed by systemic therapy. Preclinical studies show inhibitors of poly(ADP-ribose) polymerase (PARP) are effective with radiation therapy as a DNA damage response inhibitor. Triple negative BC (TNBC) has higher rates of homologous recombination deficiency compared to other BC subtypes, and together with HER2-negative, BRCA-mutated BC would be particularly sensitive to PARP inhibition. PARP inhibition also shows promising efficacy combined with immunotherapy in patients with germline BRCA-mutant and metastatic TNBC in clinical trials (MEDIOLA, TOPACIO). In addition, immunotherapy with stereotactic radiosurgery (SRS) is associated with favorable intracranial control and survival in patients with BrM. We hypothesize that this biologically-rational combination will enhance local control of SRS-treated BrM through synergy with PARP inhibition, while controlling micrometastatic disease in the brain and extracranial sites via potentiation of the immune response. METHOD We are conducting a multi-institution, Phase I/II trial of SRS plus olaparib, followed by durvalumab (with physician’s choice systemic therapy), for patients with TNBC (any BRCA status) or HER2-negative with BRCA-mutated (germline or somatic) BC BrM [NCT04711824]. The primary objectives are to evaluate safety and tolerability (Phase I) and determine intracranial disease control at 6 months (Phase II) of this treatment combination. Secondary objectives include determining clinical activity via intracranial and global progression-free survival, overall survival, and intracranial and extracranial response rate. Exploratory objectives will assess potential biomarkers of treatment response, including changes in circulating tumor cells and DNA in blood and cerebrospinal fluid, germline and tumor mutations in DNA repair pathway genes, and PD-L1 expression, as well as quality of life and patient-reported outcomes. A surgical sub-study will evaluate olaparib concentration/distribution in resected BrM.