Inhibition Of DNA Repair Pathways Research Articles

Novel Therapeutics in Ovarian Cancer: Expanding the Toolbox.

Despite high response rates to initial therapy, most patients with ovarian cancer will ultimately recur and go on to develop resistance to standard treatments. Novel therapies have been developed to overcome drug resistance and alter the tumor immune microenvironment by targeting oncogenic pathways, activating the innate immune response, and enhancing drug delivery. In this review, we discuss the current and future roles of chemotherapy, targeted agents such as poly (ADP-ribose) polymerase (PARP) inhibitors, bevacizumab, and mirvetuximab in the treatment of ovarian cancer. We explore the emerging role of therapeutic targets, including DNA repair pathway inhibitors and novel antibody-drug conjugates. Furthermore, we delve into the role of immunotherapeutic agents such as interleukins as well as immune-promoting agents such as oncolytic viruses and cancer vaccines. Innovative combination therapies using these agents have led to a rapidly evolving treatment landscape and promising results for patients with recurrent ovarian cancer.

Arsenite Impairs BRCA1-Dependent DNA Double-Strand Break Repair, a Mechanism Potentially Contributing to Genomic Instability.

BRCA1 is a key player in maintaining genomic integrity with multiple functions in DNA damage response (DDR) mechanisms. Due to its thiol-rich zinc-complexing domain, the protein may also be a potential target for redox-active and/or thiol-reactive (semi)metal compounds. The latter includes trivalent inorganic arsenic, which is indirectly genotoxic via induction of oxidative stress and inhibition of DNA repair pathways. In the present study, we investigated the effect of NaAsO2 on the transcriptional and functional DDR. Particular attention was paid to the potential impairment of BRCA1-mediated DDR mechanisms by arsenite by comparing BRCA1-deficient and -proficient cells. At the transcriptional level, arsenite itself activated several DDR mechanisms, including a pronounced oxidative stress and DNA damage response, mostly independent of BRCA1 status. However, at the functional level, a clear BRCA1 dependency was observed in both cell cycle regulation and cell death mechanisms after arsenite exposure. Furthermore, in the absence of arsenite, the lack of functional BRCA1 impaired the largely error-free homologous recombination (HR), leading to a shift towards the error-prone non-homologous end-joining (NHEJ). Arsenic treatment also induced this shift in BRCA1-proficient cells, indicating BRCA1 inactivation. Although BRCA1 bound to DNA DSBs induced via ionizing radiation, its dissociation was impaired, similarly to the downstream proteins RAD51 and RAD54. A shift from HR to NHEJ by arsenite was further supported by corresponding reporter gene assays. Taken together, arsenite appears to negatively affect HR via functional inactivation of BRCA1, possibly by interacting with its RING finger structure, which may compromise genomic stability.

Unravelling homologous recombination repair deficiency and therapeutic opportunities in soft tissue and bone sarcoma

Defects in homologous recombination repair (HRR) in tumors correlate with poor prognosis and metastases development. Determining HRR deficiency (HRD) is of major clinical relevance as it is associated with therapeutic vulnerabilities and remains poorly investigated in sarcoma. Here, we show that specific sarcoma entities exhibit high levels of genomic instability signatures and molecular alterations in HRR genes, while harboring a complex pattern of chromosomal instability. Furthermore, sarcomas carrying HRDness traits exhibit a distinct SARC‐HRD transcriptional signature that predicts PARP inhibitor sensitivity in patient‐derived sarcoma cells. Concomitantly, HRDhigh sarcoma cells lack RAD51 nuclear foci formation upon DNA damage, further evidencing defects in HRR. We further identify the WEE1 kinase as a therapeutic vulnerability for sarcomas with HRDness and demonstrate the clinical benefit of combining DNA damaging agents and inhibitors of DNA repair pathways ex vivo and in the clinic. In summary, we provide a personalized oncological approach to treat sarcoma patients successfully.

DDDR-13. MGMT FUNCTION DETERMINES THE DIFFERENTIAL RESPONSE OF ATR AND PARP INHIBITORS WITH DNA DAMAGING AGENTS FOR GBM THERAPY

Abstract The most common cancer therapies including chemo- and radiation therapy are designed to induce cell death by DNA damage. However, DNA damage response (DDR) repair pathways initiated by tumor cells can resist the effect of anticancer drugs thus providing the rationale for combining DNA repair pathway inhibitors with radiation and DNA damaging anticancer drugs. The reliance of different cancer to different DDR mechanism can guide for targeted use of specific DDR inhibitor to maximize tumor cell killing. Here, we show the differential activities of two classes of DDR pathway inhibitors, Ataxia Telangiectasia- and Rad3-related kinase (ATRi) and poly(ADP-ribose) polymerases inhibitors (PARPi) across 20 glioma stem cell (GSC) lines. Using a panel of 3 ATRi, we identified a subgroup of GSCs, showing significant synergism with TMZ combination but resistant to ATRi single agent monotherapy. Interestingly, majority of the synergistic cell lines are associated with MGMT promoter methylation, suggesting that only tumor cells with no MGMT repair will benefit from ATR inhibition. Moreover, we also observe that PARPi + TMZ showed synergism only in MGMT unmethylated GSC cells suggesting that this synergism is a result of the dual function of PARPi in blocking BER repair and blocking MGMT PARylation thus abolishing MGMT mediated repair. Altogether, we believe MGMT methylation status in primary GBM could function as a strong biomarker for patient selection for ATRi or PARPi combination with TMZ in the clinic. We are currently exploring the activity of the triple combination of TMZ + PARPi + ATRi for the small subgroup of GSCs that do not show response to either TMZ + ATRi or PARPi + TMZ combinations.

DNA damage accumulation and repair defects in FLT3-ITD acute myeloid leukemia: Implications for clonal evolution and disease progression.

Acute myeloid leukemia is a group of hematological diseases that have a high mortality rate. During the development of this pathology, hematopoietic cells acquire chromosomal rearrangements and multiple genetic mutations, including FLT3-ITD. FLT3-ITD is a marker associated with a poor clinical prognosis and involves the activation of pathways such as PI3K/AKT, MAPK/ERK, and JAK/STAT that favor the survival and proliferation of leukemic cells. In addition, FLT3-ITD leads to overproduction of reactive oxygen species and defective DNA damage repair, both implicated in the appearance of new mutations and leukemic clones. Thus, the purpose of this review is to illustrate the molecular mechanisms through which FLT3-ITD generates genetic instability and how it facilitates clonal evolution with the generation of more resistant and aggressive cells. Likewise, this article discusses the feasibility of combined therapies with FLT3 inhibitors and inhibitors of DNA repair pathways.

Identification and characterization of mercaptopyrimidine-based small molecules as inhibitors of nonhomologous DNA end joining.

Mercaptopyrimidine derivatives are heterocyclic compounds with potent biological activities including antiproliferative, antibacterial, and anti-inflammatory properties. The present study describes the synthesis and characterization of several mercaptopyrimidine derivatives through condensation of 5,6-diamino-2-mercaptopyrimidin-4-ol with various heterocyclic and aromatic aldehydes. Previous studies have shown that SCR7, synthesized from 5,6-diamino-2-mercaptopyrimidin-4-ol, induced cytotoxicity by targeting cancer cells by primarily inhibiting DNA Ligase IV involved in nonhomologous end joining, one of the major DNA double-strand break repair pathways. Inhibition of DNA repair pathways is considered as an important strategy for cancer therapy. Due to limitations of SCR7 in terms of IC50 in cancer cells, here we have designed, synthesized, and characterized potent derivatives of SCR7 using 5,6-diamino-2-mercaptopyrimidin-4-ol as the starting material. Several synthesized imine compounds exhibited significant improvement in inhibition of end joining and cytotoxicity up to 27-fold lower concentrations than SCR7. Among these, two compounds, SCR116 and SCR132, showed increased cancer cell death in a Ligase IV-dependent manner. Treatment with the compounds also led to reduction in V(D)J recombination efficiency, cell cycle arrest at G2/M phase, accumulation of double-strand breaks inside cells, and improved anti-cancer potential when combined with γ-radiation and radiomimetic drugs. Thus, we describe novel inhibitors of NHEJ with higher efficacy and potential, which can be developed as cancer therapeutics.

Abstract 5428: Evaluating cancer therapies combining radiotherapy with immunotherapy or inhibitors of the DNA damage response

Abstract Ionizing radiation has largely been recognized as a local targeted therapy by a variety of mechanisms, including inducing direct DNA damage of cancerous tissue or contributing to systemic antitumor immunity. The capacity of cancer cells to recognize DNA damages and initiate repair plays a major role in radio-resistance. Furthermore, the irradiated tumor cell death can enhance antitumor immunity by inducing antigen expression on tumor cells and activating lymphocytes. Recent evidence indicates that cancer cells can be made more sensitive to the effects of radiation (radio-sensitization) through inhibition of DNA repair pathways, and a growing body of evidence indicates that cancer immunotherapy may also have radio-sensitizing effects. The combination of radiation therapy and DDR inhibitors/immunotherapy presents a promising strategy for cancer therapy.In order to provide guidance on clinical therapeutic strategy selection, we established a beam-focused radiation platform (RadSource 2000 X-ray irradiator) to evaluate the anti-tumor efficacy of fractionated radiotherapy combination in a panel of cell lines and mouse models. We have tested the combination effect of DDR inhibitor in combination with radiotherapy in vitro and in vivo, both showing radio-sensitization effects and improvement in anti-tumor activity. We have also chosen several syngeneic models to test the combination strategy of radiotherapy and immune checkpoint inhibitors (PD-1 and PD-L1), and performed TIL analysis to explore the possible mechanisms of combination effect. In summary, our beam-focused radiation platform provides insights into the design of new therapeutic strategies and has become an effective tool in pre-clinical research of anti-cancer therapy. Citation Format: Feifei Fan. Evaluating cancer therapies combining radiotherapy with immunotherapy or inhibitors of the DNA damage response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5428.

Cadmium and breast cancer – Current state and research gaps in the underlying mechanisms

Cadmium (Cd), a heavy metal with strong carcinogenic properties has been linked with breast cancer risk. Epidemiological data on the association between Cd exposure and breast cancer are not consistent and suggest that this relationship may be modulated by a number of different factors. The mechanisms of action underlying the molecular effects of Cd, especially in terms of its carcinogenicity, are generally not well understood. Specifically, in the mammary gland, the effects of Cd are considered to be related mainly to its oestrogenic potential, however, several other mechanisms have also been suggested, such as epigenetic alterations, inhibition of DNA repair pathways, induction of oxidative stress, interference with metallothioneins, cadherins and integrins, as well as interactions with xenobiotics. This review summarizes the current state of knowledge in this field, including potential mechanisms of action of Cd in breast cancer initiation and progression, as well as possible ways of protection against its toxicity. Importantly, there are many research gaps in this area since limited evidence is available from experimental studies. Important issues to be further investigated concern exact molecular mechanisms of Cd accumulation in the tissues and Cd-induced activation of eostrogen receptors. Impact on DNA damage and epigenome upon Cd exposure in breast cancer development remains still highly unexplored area and should gain more interest.

DNA Repair Capacity for Personalizing Risk and Treatment Response − Assay Development and Optimization in Human Peripheral Blood Mononuclear Cells (PBMCs)

DNA repair capacity (DRC) is the ability of a cell to repair DNA damage. Differential DRC plays an important role in human disease, including lung and other cancers. Measuring DRC could aid in translational disease research and in personalizing treatment. We developed and optimized a flow cytometry-based assay to measure individual DRC using GFP-expressing plasmids modified by ultraviolet (UV) light for nucleotide excision repair (NER) and restriction enzyme digestion to induce a blunt double-strand cut between promoter and GFP expression regions for nonhomologous end joining (NHEJ). Cryopreserved peripheral blood mononuclear cells (PBMCs) from healthy volunteers were used to measure DRC and optimize the assay. Pathway specificity of the NHEJ DRC assay was confirmed using Ku80-/- MEF cells, which showed a 6-fold reduction in NHEJ compared to Ku80+/+. Using a cell mixing assay, we show a linear correlation between NHEJ DRC and the expected concentration of Ku80. NHEJ DRC measurements in cryopreserved PBMCs are quantifiable with low interindividual and inter-assay variability, and a titratable decrease in NHEJ activity was observed in PBMCs treated with the DNA-PK inhibitor NU7441. Pathway specificity of the NER DRC assay was confirmed by a decrease in measured NER activity in human XPC deficient compared to XPC proficient fibroblasts, with a linear correlation measured between NER DRC and expected XPC concentration by cell mixing assay. NER DRC is quantifiable, reproducible, and titratable in PBMCs from healthy volunteers. We measured both NER and NHEJ DRC in PBMCs obtained from newly diagnosed, untreated lung cancer patients; measured DRC differed in these PBMCs compared to healthy volunteers. With further investigation, measurement of NER and NHEJ DNA repair capacity may be useful in personalizing disease risk and response to DNA damaging therapies and small molecular inhibitors of DNA repair pathways using readily available human PBMCs.

CRISPR screens guide the way for PARP and ATR inhibitor biomarker discovery.

DNA repair pathways are heavily studied for their role in cancer initiation and progression. Due to the large amount of inherent DNA damage in cancer cells, tumor cells profoundly rely on proper DNA repair for efficient cell cycle progression. Several current chemotherapeutics promote excessive DNA damage in cancer cells, thus leading to cell death during cell cycle progression. However, if the tumor has efficient DNA repair mechanisms, DNA-damaging therapeutics may not be as effective. Therefore, directly inhibiting DNA repair pathways alone and in combination with chemotherapeutics that cause DNA damage may result in improved clinical outcomes. Nevertheless, tumors can acquire resistance to DNA repair inhibitors. It is essential to understand the genetic mechanisms underlying this resistance. Genome-wide CRISPR screening has emerged as a powerful tool to identify biomarkers of resistance or sensitivity to DNA repair inhibitors. CRISPR knockout and CRISPR activation screens can be designed to investigate how the loss or overexpression of any human gene impacts resistance or sensitivity to specific inhibitors. This review will address the role of CRISPR screening in identifying biomarkers of resistance and sensitivity to DNA repair pathway inhibitors. We will focus on inhibitors targeting the PARP1 and ATR enzymes, and how the biomarkers identified from CRISPR screens can help inform the treatment plan for cancer patients.

DNA damage response and apoptosis induced by hyperthermia in human umbilical cord blood lymphocytes

While hyperthermia (HT) is a promising modality for cancer treatment, the knowledge on mechanisms of its effect on cells is still limited. We have investigated DNA double-strand break (DSB) and apoptosis induced by HT. Umbilical cord blood lymphocytes (UCBL) were subjected to HT at 43 °C. We have treated cells for 1 h (1 h HT), 2 h (2 h HT) and by combined HT and ice treatment (both lasting 1 h). Enumeration of DSB by 53BP1/γH2AX DNA repair focus formation and early apoptosis by γH2AX pan-staining was conducted by automated fluorescent microscopy. Apoptotic stages and viability were assessed by the annexin/propidium iodide (PI) assay using flow cytometry 0, 18, and 42 h post-treatment. HT induced either immediate (2 h HT) or postponed (1 h HT) DNA damage. The levels of 53BP1 and γH2AX foci differed under the same treatment conditions, suggesting that the ratio of co-localized γH2AX/53BP1 foci to all γH2AX and also to all 53BP1 foci could be a valuable marker. The ratio of co-localized foci increased immediately after 2 h HT regardless the way of assessment. For the first time we show, by both annexin/PI and γH2AX pan-staining assay that apoptosis can be induced during or immediately after the 2 h HT treatment. Our results suggest that HT may induce DSB in dependence on treatment duration and post-treatment time due to inhibition of DNA repair pathways and that HT-induced apoptosis might be dependent or associated with DSB formation in human lymphocytes. Assessment of γH2AX pan-staining in lymphocytes affected by HT may represent a valuable marker of HT treatment side effects.

Immune-Checkpoint Inhibitors Combinations in Metastatic NSCLC: New Options on the Horizon?

The therapeutic targeting of the programmed death-1 (PD-1)/programmed death ligand-1 (PD-L1) axis marked a milestone in the treatment of non-small cell lung cancer (NSCLC), leading to unprecedented response duration and long-term survival for a relevant subgroup of patients affected by non-oncogene-addicted, metastatic disease. However, the biological heterogeneity as well as the occurrence of innate/acquired resistance are well-known phenomena which significantly affect the therapeutic response to immunotherapy. To date, we are moving towards the second phase of the “immune-revolution”, characterized by the advent of new immune-checkpoint inhibitors combinations, aiming to target the main resistance pathways and ultimately increase the number of NSCLC patients who may derive long-term clinical benefit from immunotherapy. In this review, we provide an updated and comprehensive overview of the main PD-1/PD-L1 inhibitors’ combination approaches under clinical investigation in non-oncogene addicted, metastatic NSCLC patients, including checkpoints (other than CTLA-4) as well as “immune-metabolism” modulators, DNA repair pathway inhibitors, antiangiogenic agents, cytokines, and a new generation of vaccines, with the final aim of identifying the most promising options on the horizon.

Inhibition of DNA Repair Pathways and Induction of ROS Are Potential Mechanisms of Action of the Small Molecule Inhibitor BOLD-100 in Breast Cancer.

Simple SummaryBOLD-100 is a novel ruthenium-based drug that has shown anti-tumor effects in several human cancers. In this study, we investigated the biochemical changes associated with BOLD-100 in human breast cancer cell models to better understand how this drug inhibits cancer cell growth. We found that treatment with BOLD-100 induced chemically unstable reactive oxygen species (ROS) and reduced proteins that help repair DNA in breast cancer cells. When combined with other drugs that target the DNA repair pathway, such as olaparib, BOLD-100 promoted more DNA damage and cell death compared with olaparib alone in estrogen receptor negative (ER-) breast cancer cells. ER- breast cancer is an aggressive form of breast cancer without any specific targeted therapy. Thus, our findings provide the rationale for a novel combination therapeutic strategy with BOLD-100 for ER- breast cancer subtype that could be investigated in clinical trials. BOLD-100, a ruthenium-based complex, sodium trans-[tetrachloridobis (1H-indazole) ruthenate (III)] (also known as IT-139, NKP1339 or KP1339), is a novel small molecule drug that demonstrated a manageable safety profile at the maximum tolerated dose and modest antitumor activity in a phase I clinical trial. BOLD-100 has been reported to inhibit the upregulation of the endoplasmic reticulum stress sensing protein GRP78. However, response to BOLD-100 varies in different cancer models and the precise mechanism of action in high-response versus low-response cancer cells remains unclear. In vitro studies have indicated that BOLD-100 induces cytostatic rather than cytotoxic effects as a monotherapy. To understand BOLD-100-mediated signaling mechanism in breast cancer cells, we used estrogen receptor positive (ER+) MCF7 breast cancer cells to obtain gene-metabolite integrated models. At 100 μM, BOLD-100 significantly reduced cell proliferation and expression of genes involved in the DNA repair pathway. BOLD-100 also induced reactive oxygen species (ROS) and phosphorylation of histone H2AX, gamma-H2AX (Ser139), suggesting disruption of proper DNA surveillance. In estrogen receptor negative (ER−) breast cancer cells, combination of BOLD-100 with a PARP inhibitor, olaparib, induced significant inhibition of cell growth and xenografts and increased gamma-H2AX. Thus, BOLD-100 is a novel DNA repair pathway targeting agent and can be used with other chemotherapies in ER− breast cancer.

Altering DNA Repair to Improve Radiation Therapy: Specific and Multiple Pathway Targeting.

Radiation therapy (RT) is widely used in cancer care strategies. Its effectiveness relies mainly on its ability to cause lethal damage to the DNA of cancer cells. However, some cancers have shown to be particularly radioresistant partly because of efficient and redundant DNA repair capacities. Therefore, RT efficacy might be enhanced by using drugs that can disrupt cancer cells' DNA repair machinery. Here we review the recent advances in the development of novel inhibitors of DNA repair pathways in combination with RT. A large number of these compounds are the subject of preclinical/clinical studies and target key enzymes involved in one or more DNA repair pathways. A totally different strategy consists of mimicking DNA double-strand breaks via small interfering DNA (siDNA) to bait the whole DNA repair machinery, leading to its global inhibition.

Discovery of Inhibitors for Proliferating Cell Nuclear Antigen Using a Computational-Based Linked-Multiple-Fragment Screen.

Proliferating cell nuclear antigen (PCNA) is a central factor in DNA replication and repair pathways that plays an essential role in genome stability. The functional roles of PCNA are mediated through an extensive list of protein–protein interactions, each of which transmits specific information in protein assemblies. The flexibility at the PCNA–protein interaction interfaces offers opportunities for the discovery of functionally selective inhibitors of DNA repair pathways. Current fragment-based drug design methodologies can be limited by the flexibility of protein interfaces. These factors motivated an approach to defining compounds that could leverage previously identified subpockets on PCNA that are suitable for fragment-binding sites. Methodologies for screening multiple connected fragment-binding events in distinct subpockets are deployed to improve the selection of fragment combinations. A flexible backbone based on N-alkyl-glycine amides offers a scaffold to combinatorically link multiple fragments for in silico screening libraries that explore the diversity of subpockets at protein interfaces. This approach was applied to discover new potential inhibitors of DNA replication and repair that target PCNA in a multiprotein recognition site. The screens of the libraries were designed to computationally filter ligands based upon the fragments and positions to <1%, which were synthesized and tested for direct binding to PCNA. Molecular dynamics simulations also revealed distinct features of these novel molecules that block key PCNA–protein interactions. Furthermore, a Bayesian classifier predicted 15 of the 16 new inhibitors to be modulators of protein–protein interactions, demonstrating the method’s utility as an effective screening filter. The cellular activities of example ligands with similar affinity for PCNA demonstrate unique properties for novel selective synergy with therapeutic DNA-damaging agents in drug-resistant contexts.

Abstract 3631: Development of targeted nanoformulation of talazoparib for combined chemoradiation therapy in lung cancer

Abstract Poly (ADP-ribose) polymerase (PARP) inhibitor (PARPi) therapy exploits a synthetic lethality strategy in cancers with inherent damage in DNA repair or transcription pathways. Talazoparib is a potent PARPi that is currently indicated for oral inhibitor therapy in several cancer clinical trials. Oral administration of these inhibitors typically results in poor bioavailability and tumor accumulation. In contrast, nanoparticle formulation provides a safe vehicle for parenteral administration of therapeutic drugs with sustainable release reducing systemic toxicity and also protect from surveillance of immune cells, thereby increasing the bioavailability of the drugs in vivo. Moreover, targeting strategy for the nanoparticles will improve the accumulation of drugs in the tumors. Here, we developed a targeted formulation of Talazoparib (NanoTLZ) which was decorated with anti-EGFR antibody as a ligand to ameliorate the cellular uptake of NanoTLZ via EGFR-mediated endocytosis. In vitro tests showed that NanoTLZ is more effective in cell growth inhibition than free Talazoparib. When combined with radiation with different doses from 2-10Gy, NanoTLZ showed a strong radiosensitization effect as evidenced with almost no colonies formation at 6 Gy of radiation dose. The high therapeutic efficacy of combined chemoradiation therapy in Calu 6 cell line can be attributed to the higher accumulation of NanoTLZ in the cancer cells as compared to the free Talazoparib which is also marred with efflux of the drug from the cells. The slow and sustained release of Talazoparib from nanoparticle formulation inside the cells lead enhanced inhibition of DNA repair pathways. These studies provide very encouraging results to evaluate the efficacy of these nanoparticles in lung cancer animal models. Citation Format: Bijay Singh, Mostafa Abdelhalim, Stephanee Warrington, Srinivas Sridhar. Development of targeted nanoformulation of talazoparib for combined chemoradiation therapy in lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3631.

Abstract 3702: Establishment and characterization of a novel MYC/BCL2 double-hit high-grade B-cell lymphoma cell line HLA-3

Abstract The majority of MYC/BCL2 double hit lymphoma (DHL) morphologically resembles diffuse large B-cell lymphoma (DLBCL) or unclassified B-cell lymphoma, with intermediate features of DLBCL and Burkitt’s lymphoma. DHL also typically results in shorter survival time than other lymphomas. To further understand DHL’s biology and identify potential effective agents against DHL, we established a unique MYC/BCL2 high-grade B-cell lymphoma cell line with morphological DLBCL features. The HLA-3 DHL cell line was derived from a MYC/BCL2 high-grade B-cell lymphoma patient-derived xenograft (PDX) model. We performed flow cytometry immunophenotypic analysis and established the HLA-3 cell line after 7 months of continuous culture. We utilized molecular and cellular techniques, including flow cytometry and polymerase chain reaction (PCR) analysis, to characterize the HLA-3 cell line. We performed reverse phase protein array (RPPA) analysis to determine its protein signaling profile. To identify agents with anti-DHL activity, we screened the effects of a panel of agents alone and in combination with ibrutinib on the cell viability of this newly established cell line. The HLA-3 cell line was optimally maintained at a density between 1 and 2 × 106 cells/mL and successfully proliferated in a single-cell suspension without cellular clump formation. The HLA-3 cells were EBV-negative and possessed a germinal center B cell immunophenotype. Moreover, the immunophenotypes of the primary patient tumor cells and HLA-3 cells were virtually identical. The HLA-3 cells were positive for CD19, CD45, CD35, CD10 and HLA-ABC, negative for CD3, CD5, CD40, CD34 and TdT, and were dim for CD22, CD56, CD8, CD4 and CD23. Representative flow cytometry histograms showed 99% of the HLA-3 cells were positive for CD19 and CD45, with no detectable surface kappa and lambda light chains. The HLA-3 cells expressed a high level of CD38, an indicator of MYC rearrangement. Similar to the original lymphoma cells, the HLA-3 cells showed dim/low CD20 expression. Based on RPPA data, we constructed a diagram showing activation of the ATM/Chk2 DNA repair and the IGF1R/PI3K/mTOR signaling pathways in the HLA-3 cells. In support of this upregulated activity, we found that 5/7 tested commercial PI3K/mTOR inhibitors significantly reduced the viability of the HLA-3 cells in a dose-dependent manner, with AZD8055 the most sensitive of the tested inhibitors against the cell line. Further, DNA repair pathway inhibitors BMN673 and RG7112 were effective against the HLA-3 cell line. The newly characterized high-grade B-cell lymphoma cell line will provide useful in vitro and in vivo models for biological studies related to human DHL, which is refractory to current therapies and urgently needs novel therapeutic approaches. This work suggests the PI3K/mTOR and DNA repair pathways may be therapeutic targets for MYC/BCL2 double-hit high-grade B-cell lymphoma. Citation Format: Hui Guo, Hui Zhang, Krystle Nomie, Liang Zhang, Kelley P. Murfin, Michael Wang. Establishment and characterization of a novel MYC/BCL2 double-hit high-grade B-cell lymphoma cell line HLA-3 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3702.

Targeted Therapy and Immune Therapy for Small Cell Lung Cancer

Approximately 15% of the over 220,000 new lung cancers diagnosed each year in the USA are small cell lung cancer (SCLC). The standard of care for SCLC patients has not changed for many years. Therefore, there remains a need to evaluate novel drugs for the management of SCLC patients. In recent years, there is a greater understanding of the molecular alterations that occur in SCLC. There is an expectation that targeting these molecular alterations could provide clinical benefit. Targeting angiogenesis by inhibiting the vascular endothelial growth factor (VEGF) pathway has been evaluated in SCLC patients and has shown only limited clinical benefit. Alterations in DNA repair make these tumors susceptible to DNA repair pathway inhibitors and formed the basis for PARP inhibitor trials. Initial trials with PARP inhibitors have shown promising activity in some SCLC patients. Due to increased expression of anti-apoptotic Bcl-2 proteins, drugs targeting these proteins may also provide clinical benefit. Pre-clinical studies have shown that pathways of self-renewal such as the hedgehog and NOTCH pathways may be altered in SCLCs and could be targeted for therapeutic benefit. Initial trials with drugs targeting these pathways, including drugs-targeting DLL3, a NOTCH ligand, suggest the need for appropriate biomarkers to identify SCLC patients most likely to benefit from these strategies. Trials of immune checkpoint inhibitors have shown that these agents may have therapeutic role in SCLC. As is true in other tumor types, these agents benefit only a proportion of patients but the benefit when observed can be sustained. Tumor mutational burden and PD-L1 expression may predict for clinical benefit with these agents. Ongoing trials will define the role of these agents in management of SCLC patients.

Modeling chemotherapy-drug combinations

Cancer Therapy Pharmacological inhibitors of DNA repair pathways can enhance the efficacy of chemotherapy. Alkan et al. modeled cancer cell responses to various chemotherapies and tested the efficacy of combining chemotherapy with DNA repair inhibition. In addition to the expected synergy between chemotherapy and an inhibitor of ATR (a DNA repair pathway kinase) in cultured cells and in vivo, there were some unexpected differences in outcome when applying low-versus high-dose chemotherapy regimens. Thus, modeling in cells can help inform therapeutic development. Sci. Signal. 11 , eaat0229 (2018).

Abstract 2862: Inhibition of DNA repair pathways in breast cancer is a potential mechanism of action of IT-139

Abstract IT-139 is a novel small-molecule drug that demonstrated a manageable safety profile at the maximum tolerated dose and modest antitumor activity as a monotherapy in a phase I clinical trial. A high affinity for albumin and unique chemistry allow increased uptake and activation of IT-139 within tumor cells, respectively. To date, IT-139 has been reported to inhibit the endoplasmic reticulum stress-sensing protein GRP78. However, different cancer cells show disparate responses to IT-139 and the precise mechanism of action in high-response versus low-response cancer cells remains unclear. In vitro studies have indicated that IT-139 induces cytostatic rather than cytotoxic effects as a monotherapy. In this study, to understand IT-139 mediated signaling mechanism in breast cancer cells, we used estrogen receptor-positive (ER+) MCF7 breast cancer cells to obtain gene-metabolite integrated models following IT-139 treatment (10 or 100 μM for 72 h). Our data showed that IT-139 significantly reduced expression of genes involved in the DNA repair pathway, including BRCA1 and RAD51, following treatment with IT-139 in MCF7 cells. Validation of our findings in other breast cancer cell lines including MDA-MB-175 (ER+), MDA-MB-231 and MDA-MB-468 (both ER-) cells also showed increased phosphorylation of H2AX (Ser139) following IT-139 treatment, suggesting lack of proper DNA surveillance and subsequent accumulation of DNA double-stranded breaks (DSB). Consequently, we investigated the effects of combination treatment approaches with IT-139 and other clinical anticancer therapies that interfere with nucleotide synthesis or DNA damage repair pathways, particularly in ER- breast cancers. Our data showed additive effects of IT-139 in combination with capecitabine (5-FU prodrug) or olaparib (PARP inhibitor) and a synergistic effect with carboplatin in ER- breast cancer cell lines. Further analysis of IT-139 mediated signal transduction in breast cancer cells will reveal whether it can be combined with aforementioned chemotherapies to circumvent resistance. Citation Format: Isabel Conde, Yassi Fallah, Diane Demas, Suzanne Bakewell, Filipa Lynce, Ayesha N. Shajahan-Haq. Inhibition of DNA repair pathways in breast cancer is a potential mechanism of action of IT-139 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2862.