DNA-damaging Anticancer Agents Research Articles

The prognostic impact of SLFN11 gene expression in metastatic colorectal cancer (mCRC).

254 Background: SLFN11 was recently identified as a dominant determinant of response to DNA-damaging anticancer agents. Several studies showed SLFN11 expression led to better sensitivity to topoisomerase inhibitors and PARP inhibitors. However, clinical evidence in mCRC has been lacking. Methods: Two independent cohorts (CALGB/SWOG 80405 trial and a real-world patient [Caris CODEai] cohort) were included in this study. Patients were stratified into SLFN11 -high and -low groups based on the median SLFN11 gene expression levels. Survival outcomes were compared between SLFN11 -high and SLFN11 -low in irinotecan-treated and oxaliplatin-treated patients. Median time was estimated using Kaplan-Meier method and Cox models were used for covariate adjustment. Endpoints of interest were progression-free survival (PFS) and overall survival (OS). Results: In the CALGB/SWOG 80405 trial cohort, 433 patients were included (110 treated with FOLFIRI-based chemotherapy and 323 treated with FOLFOX-based chemotherapy). In patients treated with FOLFIRI-based chemotherapy, SLFN11 -low patients exhibited numerically better PFS (median PFS, 13.4 vs 11.2 months, log-rank p = 0.03, adjusted hazard ratio [HR] = 0.86, 95% confidence interval [CI] 0.55-1.39, p = 0.50) and OS (median OS, 39.6 vs 30.3 months, log-rank p = 0.02, adjusted HR = 0.73, 95% CI 0.46-1.16, p = 0.19) compared to SLFN11 -high patients. In patients treated with FOLFOX-based chemotherapy, SLFN11 -low patients exhibited numerically better PFS (median PFS 11.2 vs 9.8 months, log-rank p = 0.03, adjusted HR = 0.83, 95% CI 0.65-1.05, p = 0.12) and OS (31.1 vs 26.1 months, log-rank p = 0.07, adjusted HR = 0.84, 95% CI 0.65-1.08, p = 0.16) compared to SLFN11 -high patients. No significant interaction was observed between treatment and SLFN11 expression in terms of PFS ( p = 0.69) and OS ( p = 0.44). In the Caris CODEai cohort, a better OS in SLFN11 -low patients than in SLFN11 -high patients was observed in irinotecan-treated patients ( N = 2906) (median OS, 25.5 vs 21.7 months, HR = 0.90, 95% CI 0.82-1.00, p = 0.048). However, no significant difference in OS between SLFN11 -low and SLFN11-high was observed in oxaliplatin-treated patients ( N = 4428) (median OS, 39.5 vs 35.8 months, HR = 0.98, 95% CI 0.90-1.06, p = 0.56). Conclusions: Low SLFN11 expression showed a potential for better prognosis in mCRC patients receiving irinotecan- and oxaliplatin-containing chemotherapies. These findings are not consistently aligned with preclinical data and clinical evidence in other cancer types previously reported. Further investigation is warranted to better understand the biological role and clinical implication of SLFN11 in mCRC.

Abstract 5943: Development of a SMART theranostic agent for precision pancreatic cancer therapeutics

Abstract Pancreatic cancer is predicted to emerge as the second leading cause of cancer-related deaths in the United States by 2030. Pancreatic ductal adenocarcinoma (PDAC) - the most common form of pancreatic cancer - is often diagnosed as metastatic disease and has demonstrated the least improvement in overall survival over the last three decades with incidence rising by 0.5% to 1.0% per year due in part to lack of effective and tumor-selective treatment strategies. One approach to reduce host toxicity is the development of novel molecules and innovative therapeutic approaches that are nontoxic to normal cells but can be activated only under tumor-specific conditions for lethality, which we coined as SMART (Selective Method of Activation for Response in Tumors) therapeutic agents. We utilized explicit properties and biomarkers present in PDAC tumors but not in normal tissues to develop a SMART DNA-damaging anti-cancer agent with both therapeutic and diagnostic (theranostic) activities. We evaluated the tumoricidal effect of our SMART agent using long-term survival assays in PDAC cell lines and 3D co-culture spheroids, as well as in tumor xenograft model studies in mice. We also tested the ability of our SMART agent to treat, detect/diagnose (via click chemistry), and identify critical resistance mechanisms (via proteomics) as a single agent or as a chemosensitizer with predictive tumor biomarkers for tumor-selective therapeutic response. We found that our SMART small molecule induces tumor-selective lethal effects as a monotherapy or in combination with DNA repair inhibitors or small molecules known to generate hydrogen peroxide (H2O2) in a tumor-selective manner for activation. Using “click” chemistry, we detected and quantified the incorporation of our SMART small molecule as a DNA-damaging agent via flow cytometry that correlated with therapeutic response, which is a feature that could facilitate the stratification, treatment monitoring, and management of patients with pancreatic cancers. We also found that our SMART agent is less toxic and more effective as a monotherapy than cisplatin in PDAC cell line-derived xenograft studies in mice. Overall, our novel SMART theranostic agent could provide a significant advancement as they are preferentially activated under tumor-specific conditions to induce tumor-selective therapeutic response. Furthermore, the diagnostic component our SMART agent could provide oncologists with essential information to make rapid clinical decisions on treatment strategies. Our SMART agent is also remarkably versatile as it can be utilized as a chemosensitizer or as a chemical probe to identify targetable vulnerabilities to potentiate its therapeutic effects at lower doses. Citation Format: Edward A. Motea, Jarrett J. Smith, Oluwasijibomi Ketiku. Development of a SMART theranostic agent for precision pancreatic cancer therapeutics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5943.

The crucial role of single-stranded DNA binding in enhancing sensitivity to DNA-damaging agents for Schlafen 11 and Schlafen 13

Schlafen (SLFN) 11 enhances cellular sensitivity to various DNA-damaging anticancer agents. Among the human SLFNs (SLFN5/11/12/13/14), SLFN11 is unique in its drug sensitivity and ability to block replication under DNA damage. In biochemical analysis, SLFN11 binds single-stranded DNA (ssDNA), and this binding is enhanced by the dephosphorylation of SLFN11. In this study, human cell-based assays demonstrated that a point mutation at the ssDNA-binding site of SLFN11 or a constitutive phosphorylation mutant abolished SLFN11-dependent drug sensitivity. Additionally, we discovered that nuclear SLFN13 with a point mutation mimicking the DNA-binding site of SLFN11 was recruited to chromatin, blocked replication, and enhanced drug sensitivity. Through generating multiple mutants and structure analyses of SLFN11 and SLFN13, we identified protein phosphatase 2A as a binding partner of SLFN11 and the putative binding motif in SLFN11. These findings provide crucial insights into the unique characteristics of SLFN11, contributing to a better understanding of its mechanisms.

Abstract LB301: Molecular pharmacology and broad synergy of the novel ATR inhibitor M1774 with DNA damaging anticancer agents

Abstract Ataxia telangiectasia and Rad3-related (ATR) checkpoint kinase orchestrates DNA damage response and repair pathways stimulated by replicative stresses. Recent studies have established that pharmacological inhibition of ATR is clinically promising. As M1774 is an oral ATR inhibitor in clinical development, we explored the molecular basis by which M1774 induces cancer cell death. As a single agent, we found that M1774 suppresses cancer cell viability at nanomolar concentrations with a potency higher than ceralasertib and berzosertib, but lower than gartisertib (M4344) and elimusertib in the small cell lung cancer (SCLC) cell lines H146, H82, and DMS114. We found that M1774 efficiently suppresses the ATR/CHK1 checkpoints. While M1774 alone induced apoptosis and G2/M cell cycle arrest at micromolar concentrations, at a non-toxic low dose, M1774 enhanced TOP1 inhibitor-mediated cancer cell death by preventing replication arrest and inducing DNA damage detected by EdU and γH2AX staining. Tandem mass tagging (TMT) coupled with mass spectrometry revealed that M1774 combined with SN-38 increases the expression of replication-related proteins (TIPIN, CDC45, TIMELESS, and RPA1) and G2/M-related proteins (PLK1 and CCNB1). To establish the synergistic combinations of M1774 with clinical anticancer DNA damaging agents in preclinical models, we performed experiments in cancer cell lines, patient-derived organoids, and xenograft models. Low doses of M1774 significantly synergized with the clinical TOP1 inhibitor SN-38, the TOP2 inhibitor etoposide, cisplatin, and the PARP inhibitor talazoparib in SCLC cell lines. We also found that M1774 significantly reversed chemoresistance to DNA-damaging agents in cancer cells lacking SLFN11 expression, suggesting that SLFN11 expression can be utilized for combination therapy with M1774 as a biomarker. The synergistic efficacy between M1774 and DNA-damaging agents was confirmed in SCLC patient-derived organoids, colon cancer patient-derived organoids, and H82 SCLC xenografts. Together, these results provide insights into the molecular mechanism and potential combination strategies for M1774 in cancer therapy. Citation Format: Ukhyun Jo, Yasuhiro Arakawa, Astrid Zimmermann, Daiki Taniyama, Makito Mizunuma, Lisa M Jenkins, Suresh Kumar, Frank T Zenke, Yves Pommier. Molecular pharmacology and broad synergy of the novel ATR inhibitor M1774 with DNA damaging anticancer agents [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB301.

Abstract 5731: Apoptosis Inducing Agent 1 enhances cancer therapy-induced apoptosis by direct interaction with BAX and BAK

Abstract Many of the most effective anti-cancer therapies induce apoptosis in cancer cells by damaging DNA. Even when effective at eradicating primary cancers, DNA-damaging anti-cancer agents cause mutations that can lead to the development of secondary cancers. Furthermore, DNA damage responses are dependent on wild-type p53, which is mutated in over 50% of cancers and causes resistance to therapies. Fortunately, many p53 mutant cancers continue to express high levels of the pro-apoptotic, pore-forming proteins BAX and BAK and are consequently “primed for apoptosis.” Primed cells are highly sensitive to pro-apoptotic signals and this vulnerability can be exploited using inhibitors of pro-survival BCL-2 family proteins such as the BCL-2 inhibitor ABT-199, which has been successful as therapy for chronic lymphocytic and acute myeloid leukemias (AML). Furthermore, most irreplaceable cells within healthy tissues are apoptosis resistant and express low levels of BAX and BAK. We therefore hypothesized that direct activators of BAX or BAK could be effective single-agent therapies for primed cancers and chemo-/radio-sensitizers for unprimed cancers. Using WT versus BAX -/- BAK -/- HeLa cells, we performed a high-throughput screen of nearly 100,000 compounds to identify small molecules that could directly activate BAX or BAK. 196 compounds were identified as hits and multiple orthogonal validation studies identified Apoptosis Inducing Agent 1 (AIA1) as the most specific and potent putative activator of BAX and BAK. Further validation studies demonstrated that AIA1 directly induces cytochrome c release from mitochondria in a BAX/BAK dependent manner and strongly enhances BIM-mediated activation of BAX and BAK and permeabilization of liposomes. Single-agent AIA treatment triggers apoptotic cell death in a broad panel of cancer cell lines and also sensitizes cancer cells to chemotherapeutic agents and especially BH3 mimetics targeting pro-survival BCL-2 family proteins. Importantly, AIA1 sensitizes ovarian cancer cells to BCL-XL inhibitors and AML cells to BCL-2 inhibitors regardless of p53 status. In vivo, AIA1 suppresses tumor growth and prolongs overall survival in both ovarian cancer and AML xenograft models without causing weight loss, thrombocytopenia or leukopenia. Notably, unprimed cancer cells that don’t immediately undergo apoptosis in response to single-agent AIA1 treatment upregulate expression of BAX and BAK, pro-survival proteins (BCL-XL, BCL-2, MCL-1) and pro-apoptotic proteins (BIM, BID, PUMA, Noxa) to produce a more highly primed apoptosis pathway and setting the stage for increased sensitivity to BH3 mimetics. Based on these findings, AIA1 may exploit and induce apoptotic vulnerabilities in cancers in a p53-independent manner and represent a safer strategy to target primed cancer cells while eliminating the potential for secondary malignancies and p53-mediated resistance. Citation Format: Xingping Qin, Cameron Fraser, Adam Presser, Johan KE Spetz, Stacey J. Yu, Gary A. Bradshaw, Marian Kalocsay, Bo R. Rueda, Tudor Moldoveanu, Kristopher A. Sarosiek. Apoptosis Inducing Agent 1 enhances cancer therapy-induced apoptosis by direct interaction with BAX and BAK. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5731.

Cancer Cells Upregulate Tau to Gain Resistance to DNA Damaging Agents

Recent reports suggested a role for microtubules in double-strand-DNA break repair. We herein investigated the role of the microtubule-associated protein Tau in radio- and chemotherapy. Noticeably, a lowered expression of Tau in breast cancer cell lines resulted in a significant decrease in mouse-xenograft breast tumor volume after doxorubicin or X-ray treatments. Furthermore, the knockdown of Tau impaired the classical nonhomologous end-joining pathway and led to an improved cellular response to both bleomycin and X-rays. Investigating the mechanism of Tau's protective effect, we found that one of the main mediators of response to double-stranded breaks in DNA, the tumor suppressor p53-binding protein 1 (53BP1), is sequestered in the cytoplasm as a consequence of Tau downregulation. We demonstrated that Tau allows 53BP1 to translocate to the nucleus in response to DNA damage by chaperoning microtubule protein trafficking. Moreover, Tau knockdown chemo-sensitized cancer cells to drugs forming DNA adducts, such as cisplatin and oxaliplatin, and further suggested a general role of Tau in regulating the nuclear trafficking of DNA repair proteins. Altogether, these results suggest that Tau expression in cancer cells may be of interest as a molecular marker for response to DNA-damaging anti-cancer agents. Clinically targeting Tau could sensitize tumors to DNA-damaging treatments.

A Multimodal Genotoxic Anticancer Drug Characterized by Pharmacogenetic Analysis in Caenorhabditis elegans.

New anticancer therapeutics require extensive in vivo characterization to identify endogenous and exogenous factors affecting efficacy, to measure toxicity and mutagenicity, and to determine genotypes that result in therapeutic sensitivity or resistance. We used Caenorhabditis elegans as a platform with which to characterize properties of the anticancer therapeutic CX-5461. To understand the processes that respond to CX-5461-induced damage, we generated pharmacogenetic profiles for a panel of C. elegans DNA replication and repair mutants with common DNA-damaging agents for comparison with the profile of CX-5461. We found that multiple repair pathways, including homology-directed repair, microhomology-mediated end joining, nucleotide excision repair, and translesion synthesis, were needed for CX-5461 tolerance. To determine the frequency and spectrum of CX-5461-induced mutations, we used a genetic balancer to capture CX-5461-induced mutations. We found that CX-5461 is mutagenic, resulting in both large copy number variations and a high frequency of single-nucleotide variations (SNVs), which are consistent with the pharmacogenetic profile for CX-5461. Whole-genome sequencing of CX-5461-exposed animals found that CX-5461-induced SNVs exhibited a distinct mutational signature. We also phenocopied the CX-5461 photoreactivity observed in clinical trials and demonstrated that CX-5461 generates reactive oxygen species when exposed to UVA radiation. Together, the data from C. elegans demonstrate that CX-5461 is a multimodal DNA-damaging anticancer agent.

Nuclear protein phosphatase Wip1 regulate sensitivity of human colorectal cancer cells to DNA damaging anti-cancer agents

Nuclear protein phosphatase Wip1 regulate sensitivity of human colorectal cancer cells to DNA damaging anti-cancer agents

Direct Analysis of Incorporation of an Anticancer Drug into DNA at Single-Molecule Resolution

Identifying positions at which anticancer drug molecules incorporate into DNA is essential to define mechanisms underlying their activity, but current methodologies cannot yet achieve this. The thymidine fluorine substitution product trifluridine (FTD) is a DNA-damaging anticancer agent thought to incorporate into thymine positions in DNA. This mechanism, however, has not been directly confirmed. Here, we report a means to detect FTD in a single-stranded oligonucleotide using a method to distinguish single molecules by differences in electrical conductance. Entire sequences of 21-base single-stranded DNAs with and without incorporated drug were determined based on single-molecule conductances of the drug and four deoxynucleosides, the first direct observation of its kind. This methodology may foster rapid development of more effective anticancer drugs.

Cell-based chemical fingerprinting identifies telomeres and lamin A as modifiers of DNA damage response in cancer cells

Telomere maintenance by telomerase activity supports the infinite growth of cancer cells. MST-312, a synthetic telomerase inhibitor, gradually shortens telomeres at non-acute lethal doses and eventually induces senescence and apoptosis of telomerase-positive cancer cells. Here we report that MST-312 at higher doses works as a dual inhibitor of telomerase and DNA topoisomerase II and exhibits acute anti-proliferative effects on cancer cells and xenografted tumours in vivo. Our cell-based chemical fingerprinting approach revealed that cancer cells with shorter telomeres and lower expression of lamin A, a nuclear architectural protein, exhibited higher sensitivity to the acute deleterious effects of MST-312, accompanied by formation of telomere dysfunction-induced foci and DNA double-strand breaks. Telomere elongation and lamin A overexpression attenuated telomeric and non-telomeric DNA damage, respectively, and both conferred resistance to apoptosis induced by MST-312 and other DNA damaging anticancer agents. These observations suggest that sufficient pools of telomeres and a nuclear lamina component contribute to the cellular robustness against DNA damage induced by therapeutic treatment in human cancer cells.

Identification of New Potential APE1 Inhibitors by Pharmacophore Modeling and Molecular Docking

Apurinic/apyrimidinic endonuclease 1 (APE1) is an enzyme responsible for the initial step in the base excision repair pathway and is known to be a potential drug target for treating cancers, because its expression is associated with resistance to DNA-damaging anticancer agents. Although several inhibitors already have been identified, the identification of novel kinds of potential inhibitors of APE1 could provide a seed for the development of improved anticancer drugs. For this purpose, we first classified known inhibitors of APE1. According to the classification, we constructed two distinct pharmacophore models. We screened more than 3 million lead-like compounds using the pharmacophores. Hits that fulfilled the features of the pharmacophore models were identified. In addition to the pharmacophore screen, we carried out molecular docking to prioritize hits. Based on these processes, we ultimately identified 1,338 potential inhibitors of APE1 with predicted binding affinities to the enzyme.

Abstract LB-319: Development and characterization of ADC999: A novel, potent orally available Wee1 inhibitor with robust antitumor efficacy in vivo

Abstract Wee1 is a tyrosine kinase that phosphorylates cyclin-dependent kinase 1 (CDC2) to inactivate the CDC2/cyclinB complex. Wee1 is therefore a key regulator of the cell cycle, maintaining the G2 checkpoint arrest to allow for pre-mitotic repair upon genomic stress. Unlike normal cells, most p53-deficient tumors lack a functional G1 checkpoint and instead rely on the G2 checkpoint for DNA repair. Abrogation of the G2 checkpoint by a Wee1 inhibitor has been shown to sensitize p53-deficient tumors to a variety of DNA-damaging anticancer agents. Strong chemosensitization has also been demonstrated in multiple pre-clinical models using targeted agents including CHK1 or PARP inhibitors. These studies combined with recent clinical data demonstrating robust anti-tumor activity in combination with carboplatin or as a single agent in tumors under high replicative stress make Wee1 a promising target for anticancer therapy. With only one inhibitor (AZD1775) in clinical development and very few reports of compounds at the preclinical stage, the development of alternative Wee1 inhibitors is of significant medical relevance. In this study, we describe the development of a novel and highly potent small molecule inhibitor of Wee1 (ADC999) and subsequent analogs. These inhibitors exhibit single digit nM IC50 values against Wee1 and good overall selectivity profiles against the kinome. In cells, target engagement was demonstrated through the inhibition of both CDC2- and CDK2-dependent Wee1 phosphorylation. In line with the mechanism of action, γH2AX and apoptosis induction was also observed in a dose-dependent manner. Further profiling in a panel of cell lines indicated strong anti-proliferative activity both in combination with cytotoxics and in monotherapy. Single agent activity was observed in multiple cancer types, including gynecological, lung and breast. In vivo, oral administration of ADC999 as a single agent led to excellent antitumor activity in a KRAS-mutant non-small cell lung carcinoma xenograft model. Responses ranged from dose-dependent tumor growth inhibition to complete and sustained regressions. ADC999 was well tolerated following a daily dosing regimen and over a prolonged period with no adverse effects observed. Evaluation of ADC999 anti-tumor activity will also be discussed in a panel of genetically-characterized patient-derived xenografts (PDXs) both as monotherapy (mini-trial design) and in combination with PARP inhibitors. In summary, we describe the development and profiling of a novel, highly potent orally available Wee1 inhibitor with robust antitumor efficacy in vivo. This inhibitor and potential back-up compounds will provide new opportunities to fully exploit the therapeutic potential of Wee1 inhibition both as standalone intervention and in combination modalities. Citation Format: Gerald Gavory, Colin O'Dowd, Ewelina Rozycka, Caroline Boyd, Beronia Gorges, Estelle McLean, Julien Daubriac, Shane Rountree, Steven Shepherd, Stephanie Burton, Mary McFarland, Adam Treder, Andy Wilkinson, Frank Burkamp, Tim Harrison. Development and characterization of ADC999: A novel, potent orally available Wee1 inhibitor with robust antitumor efficacy in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-319. doi:10.1158/1538-7445.AM2017-LB-319

Abstract B17: Development of novel, potent orally available Wee1 inhibitors with robust antitumor efficacy in vivo

Abstract Wee1 is a tyrosine kinase that phosphorylates cyclin-dependent kinase 1 (CDC2) to inactive the CDC2/cyclinB complex. Wee1 is therefore a key regulator of the cell cycle, maintaining the G2 checkpoint arrest to allow for pre-mitotic repair upon genomic stress. Unlike normal cells, most p53-deficient tumors lack a functional G1 checkpoint and instead rely on the G2 checkpoint for DNA repair. Abrogation of the G2 checkpoint by a Wee1 inhibitor therefore sensitizes p53-deficient tumors to DNA-damaging anticancer agents and enhances their cytotoxic effect. Strong evidence for chemo-sensitization has been demonstrated in multiple pre-clinical models and also in clinical trials. These clinical observations combined with recent reports demonstrating single agent efficacy make Wee1 a promising target for anticancer therapy. With only one inhibitor (AZD1775) in clinical development and very few reports of compounds at the preclinical stage, the development of alternative Wee1 inhibitors is of significant medical relevance. In this study, we describe the development of novel and highly potent small molecule inhibitors of Wee1 emanating from 2 distinct chemical series (ADC730, ADC999). These inhibitors exhibit single digit nM IC50 values versus the enzyme and good selectivity profiles against the kinome. In cells, target engagement was demonstrated through the inhibition of both CDC2- and CDK2-dependent Wee1 phosphorylation. In line with the mechanism of action, gH2AX and apoptosis induction was also observed in a dose-dependent manner. Further profiling in panels of cell lines indicated strong anti-proliferative activity both in combination with cytotoxics (i.e. gemcitabine) and in monotherapy. Single agent activity was observed in multiple cancer types, including gynecological, lung, colorectal and breast. In vivo, oral administration of ADC730 in combination with gemcitabine resulted in significant dose-dependent growth reduction in a HT29 tumor xenograft model and the combination was synergistic. Dosed orally and as single agents, both ADC730 and ADC999 also demonstrated excellent antitumor activity in the A427 KRAS-mutant lung carcinoma xenograft model. Responses ranged from dose-dependent tumor growth inhibition to complete regressions. ADC730 and ADC999 were well tolerated in these studies with no signs of adverse effects observed. In summary, we describe the development and profiling of novel, highly potent orally available Wee1 inhibitors with robust antitumor efficacy in vivo. These inhibitors will provide new opportunities to fully exploit the therapeutic potential of Wee1 inhibition, either as standalone intervention or in combination modalities. Citation Format: Gerald Gavory, Colin O'Dowd, Ewelina Rozycka, Caroline Boyd, Beronia Gorges, Estelle McLean, Shane Rountree, Steven Sheperd, Stephanie Burton, Mary McFarland, Dominic Janssen, Adam Treder, Andy Wilkinson, Frank Burkamp, Tim Harrison. Development of novel, potent orally available Wee1 inhibitors with robust antitumor efficacy in vivo [abstract]. In: Proceedings of the AACR Special Conference on DNA Repair: Tumor Development and Therapeutic Response; 2016 Nov 2-5; Montreal, QC, Canada. Philadelphia (PA): AACR; Mol Cancer Res 2017;15(4_Suppl):Abstract nr B17.

Phosphorylated fraction of H2AX as a measurement for DNA damage in cancer cells and potential applications of a novel assay.

Phosphorylated H2AX (γ-H2AX) is a sensitive marker for DNA double-strand breaks (DSBs), but the variability of H2AX expression in different cell and tissue types makes it difficult to interpret the meaning of the γ-H2AX level. Furthermore, the assays commonly used for γ-H2AX detection utilize laborious and low-throughput microscopy-based methods. We describe here an ELISA assay that measures both phosphorylated H2AX and total H2AX absolute amounts to determine the percentage of γ-H2AX, providing a normalized value representative of the amount of DNA damage. We demonstrate the utility of the assay to measure DSBs introduced by either ionizing radiation or DNA-damaging agents in cultured cells and in xenograft models. Furthermore, utilizing the NCI-60 cancer cell line panel, we show a correlation between the basal fraction of γ-H2AX and cellular mutation levels. This additional application highlights the ability of the assay to measure γ-H2AX levels in many extracts at once, making it possible to correlate findings with other cellular characteristics. Overall, the γ-H2AX ELISA represents a novel approach to quantifying DNA damage, which may lead to a better understanding of mutagenic pathways in cancer and provide a useful biomarker for monitoring the effectiveness of DNA-damaging anticancer agents.

Abstract LB-159: A novel, potent and selective inhibitor of Wee1 with robust antitumor activity in various cancer xenograph models

Abstract Wee1 is a tyrosine kinase that phosphorylates cyclin-dependent kinase 1 (CDK1/CDC2) to inactive the CDC2/cyclinB complex. Wee1 is therefore a key regulator of the cell cycle, maintaining the G2 checkpoint arrest to allow for premitotic repair in case of DNA damage. Unlike normal cells, most p53-deficient tumors lack a functional G1 checkpoint and instead rely on the G2 checkpoint for DNA repair. Abrogation of the G2 checkpoint by a Wee1 inhibitor may therefore sensitize p53-deficient tumors to DNA-damaging anticancer agents and enhance their cytotoxic effect. Strong evidence for chemo-sensitization has been demonstrated from multiple pre-clinical models and also from clinical trials. In particular, treatment in combination with carboplatin recently showed encouraging antitumor activity in patients with p53-mutated ovarian cancer refractory or resistant to standard first-line therapy. These clinical observations combined with recent reports demonstrating single agent efficacy in specific contexts make Wee1 a promising target for anticancer therapy. With only one inhibitor in clinical development (AZD1775) and very limited reports at the preclinical stage, the development of alternative, novel Wee1 inhibitors may have significant therapeutic value. In this study, we describe the development and characterization of ADC730, a potent and highly selective small molecule Wee1 inhibitor. ADC730 inhibits Wee1 kinase activity with an IC50 of <5 nM and demonstrates excellent selectivity when profiled against a diverse panel of kinases. In cellular assays, ADC730 potently inhibited CDC2-dependent Wee1 phosphorylation. Further studies in a panel of cancer cell lines demonstrated strong anti-proliferative activity of ADC730 both in combination with gemcitabine or in monotherapy modalities. Single agent activity was observed in multiple cancer types including lung and kidney. gH2AX foci formation followed by apoptosis induction were typically observed in a dose-dependent manner for the most sensitive cell lines. In vivo, oral administration of ADC730 (10, 30 mg/kg/day) in combination with gemcitabine caused a significant dose-dependent growth reduction of HT29 tumors and the combination was synergistic. ADC730 was well tolerated in all cases with no signs of adverse effects. Dosed orally as a single agent (10, 30 mg/kg/day), ADC730 also demonstrated robust dose-dependent anti-tumor efficacy in the A427 lung carcinoma model with inhibition of tumor growth consistent with the pharmacodynamic modulation of Wee1 signaling. In comparison and under similar experimental conditions, AZD1775 demonstrated similar efficacy profiles at significantly higher doses. To conclude, we describe the development and profiling towards candidate nomination of ADC730, a novel potent highly selective Wee1 inhibitor with robust efficacy in cancer xenograft models both in combination and single agent modalities. Subsequent analogs and examples with potentially enhanced profiles will also be described. Citation Format: Gerald Gavory, Colin O’Dowd, Frank Burkamp, Shane Rountree, Ewelina Rozycka, Caroline Boyd, Beronia Gorges, Stephanie Burton, Andy Wilkinson, Steven Shepherd, Dominic Janssen, Mary McFarland, Shane Rountree, Tim Harrison. A novel, potent and selective inhibitor of Wee1 with robust antitumor activity in various cancer xenograph models. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-159.

A novelly synthesized phenanthroline derivative is a promising DNA-damaging anticancer agent inhibiting G1/S checkpoint transition and inducing cell apoptosis in cancer cells.

The study mainly aimed to determine the biological function of a novelly synthesized phenanthroimidazole derivative, named L233, and to explore its potential mechanisms. Cell survival was examined using the MTT assays, and the DNA-damaging role of L233 was explored using the comet assay. Moreover, the western blotting assays and immunofluorescence assays were used to detect DNA damage biomarkers. Afterward, the flow cytometry was used to assess the effects of L233 on cell cycle distribution. As for the detection of cell apoptosis upon L233 treatment, the Hoechst 33342 staining, flow cytometry, and western blotting assays were all put into practice. We find that L233 inhibits tumor cell growth more efficiently and safely than cisplatin. Moreover, it is a DNA-damaging agent, interrupting the cell cycle G1/S checkpoint transition and inducing cell apoptosis by not only activating ATM/CHK1 signaling pathway, but also targeting CHK1 to reduce the expression of RAP80 and PARP-1 to compromise the DNA damage repair in tumor cells. In summary, L233 is a promising anticancer drug for the development of novel chemotherapies in the future.

Lactate and choline metabolites detected in vitro by nuclear magnetic resonance spectroscopy are potential metabolic biomarkers for PI3K inhibition in pediatric glioblastoma.

The phosphoinositide 3-kinase (PI3K) pathway is believed to be of key importance in pediatric glioblastoma. Novel inhibitors of the PI3K pathway are being developed and are entering clinical trials. Our aim is to identify potential non-invasive biomarkers of PI3K signaling pathway inhibition in pediatric glioblastoma using in vitro nuclear magnetic resonance (NMR) spectroscopy, to aid identification of target inhibition and therapeutic response in early phase clinical trials of PI3K inhibitors in childhood cancer. Treatment of SF188 and KNS42 human pediatric glioblastoma cell lines with the dual pan-Class I PI3K/mTOR inhibitor PI-103, inhibited the PI3K signaling pathway and resulted in a decrease in phosphocholine (PC), total choline (tCho) and lactate levels (p<0.02) as detected by phosphorus (31P)- and proton (1H)-NMR. Similar changes were also detected using the pan–Class I PI3K inhibitor GDC-0941 which lacks significant mTOR activity and is entering Phase II clinical trials. In contrast, the DNA damaging agent temozolomide (TMZ), which is used as current frontline therapy in the treatment of glioblastoma postoperatively (in combination with radiotherapy), increased PC, glycerophosphocholine (GPC) and tCho levels (p<0.04). PI-103-induced NMR changes were associated with alterations in protein expression levels of regulatory enzymes involved in glucose and choline metabolism including GLUT1, HK2, LDHA and CHKA. Our results show that by using NMR we can detect distinct biomarkers following PI3K pathway inhibition compared to treatment with the DNA-damaging anti-cancer agent TMZ. This is the first study reporting that lactate and choline metabolites are potential non-invasive biomarkers for monitoring response to PI3K pathway inhibitors in pediatric glioblastoma.

Effect of DNA repair deficiencies on the cytotoxicity of drugs used in cancer therapy - a review.

Tumor cells often have defects in DNA repair pathways that make them vulnerable to specific DNA-damaging anticancer agents. The identification of DNA repair defects in tumor cells and the evaluation of their influence on the cytotoxicity of anticancer drugs are active areas of scientific investigation that may help rationalize and improve cancer chemotherapy. This article reviews the available data on the influence of defects in proteins involved in the major DNA repair pathways (i.e., homologous recombination, non-homologous end joining, base excision repair, nucleotide excision repair, mismatch repair, Fanconi anemia repair, translesion synthesis and direct reversal repair) on the cytotoxicity of the FDA-approved anticancer drugs. It is shown that specific deficiencies in these DNA repair pathways alter the cytotoxicity of 60 anticancer drugs, including classical DNA-targeting drugs (e.g., alkylating agents, cytotoxic antibiotics, DNA topoisomerase inhibitors and antimetabolites) and other drugs whose primary pharmacological target is not the DNA (e.g., antimitotic agents, hormonal and targeted therapies). This information may help predict response to anticancer drugs in patients with tumors having specific DNA repair defects.

HuR Posttranscriptionally Regulates WEE1: Implications for the DNA Damage Response in Pancreatic Cancer Cells

HuR (ELAV1), an RNA-binding protein abundant in cancer cells, primarily resides in the nucleus, but under specific stress (e.g., gemcitabine), HuR translocates to the cytoplasm in which it tightly modulates the expression of mRNA survival cargo. Here, we demonstrate for the first time that stressing pancreatic ductal adenocarcinoma (PDA) cells by treatment with DNA-damaging anticancer agents (mitomycin C, oxaliplatin, cisplatin, carboplatin, and a PARP inhibitor) results in HuR's translocation from the nucleus to the cytoplasm. Importantly, silencing HuR in PDA cells sensitized the cells to these agents, whereas overexpressing HuR caused resistance. HuR's role in the efficacy of DNA-damaging agents in PDA cells was, in part, attributed to the acute upregulation of WEE1 by HuR. WEE1, a mitotic inhibitor kinase, regulates the DNA damage repair pathway, and therapeutic inhibition of WEE1 in combination with chemotherapy is currently in early phase trials for the treatment of cancer. We validate WEE1 as a HuR target in vitro and in vivo by demonstrating (i) direct binding of HuR to WEE1's mRNA (a discrete 56-bp region residing in the 3' untranslated region) and (ii) HuR siRNA silencing and overexpression directly affects the protein levels of WEE1, especially after DNA damage. HuR's positive regulation of WEE1 increases γ-H2AX levels, induces Cdk1 phosphorylation, and promotes cell-cycle arrest at the G2-M transition. We describe a novel mechanism that PDA cells use to protect against DNA damage in which HuR posttranscriptionally regulates the expression and downstream function of WEE1 upon exposure to DNA-damaging agents.

Identification of dual DNA-PK MDR1 inhibitors for the potentiation of cytotoxic drug activity

Inhibition of DNA repair is an attractive therapeutic approach to enhance the activity of DNA-damaging anticancer chemotherapeutic agents. Similarly, blockade of the multidrug-resistance protein 1 (MDR1) can overcome efflux-mediated resistance. DNA-dependent protein kinase (DNA-PK) is essential for the non-homologous end-joining DNA repair pathway. NU7441 is a potent DNA-PK inhibitor (IC50=14nM) that is used widely to study the effects of DNA-PK inhibition in vitro. In growth inhibition studies, 1μM NU7441 sensitised vincristine-resistant CCRF-CEM VCR/R leukaemia cells (1200-fold resistant) to a range of MDR1 substrates, including doxorubicin (8-fold, p=0.03), vincristine (14-fold, p=0.01) and etoposide (63-fold, p=0.02), compared with 1.4-fold (p=0.02), 2.2-fold (p=0.04) and 3.6-fold (p=0.01) sensitisation, respectively, in parental CCRF-CEM cells. This difference in NU7441 sensitivity was confirmed in another two parental and MDR1-overexpressing cell line pairs. A doxorubicin fluorescence assay showed that in MDR1-overexpressing canine kidney MDCKII-MDR1 cells, 1μM NU7441 increased doxorubicin nuclear fluorescence 16-fold. NU7441 and 3 structurally related compounds (NU7742 (an NU7441 analogue that does not inhibit DNA-PK – IC50>10μM), DRN1 (DNA-PK-inhibitory atropisomeric NU7441 derivative – IC50=2nM) and DRN2 (DNA-PK non-inhibitory atropisomeric NU7441 derivative - IC50=7μM)) all increased intracellular vincristine accumulation in the CCRF-CEM VCR/R cells to a level similar to verapamil, as measured by LC–MS. This paper demonstrates that NU7441 is a dual DNA-PK and MDR1 inhibitor, and this extends the therapeutic potential of the compound when used in combination with MDR substrates.