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Lung cancer is a leading cause of cancer-related deaths worldwide. Non-small cell lung cancer (NSCLC) is the most prevalent lung cancer subtype. Ciclopirox olamine (CPX), an off-patent fungicide, has been identified as a new anticancer agent. Prexasertib (PRE), a Chk1 inhibitor, is in phase 1/2 clinical trials in various tumors. The anticancer effect of the combination of CPX with PRE on NSCLC cells is unknown. Here, we show that CPX is synergistic with PRE in inhibiting cell proliferation and inducing apoptosis of NSCLC (A549 and A427) cells. Combined treatment with CPX and PRE significantly increased the cell population in the G1/G0 and sub-G1 phases, compared to the single treatment with CPX or PRE. Concurrently, the combined treatment downregulated the protein levels of cyclins (A, B1), cyclin-dependent kinases 4, 6, 2 (CDK4, CDK6, CDK2), cell division cycle 25 B, C (Cdc25B, Cdc25C), and upregulated the protein levels of the CDK inhibitors p21 and p27, leading to decreased phosphorylation of Rb. In addition, the combined treatment increased DNA damage, evidenced by increased expression of γH2AX. In line with this, the combined treatment induced more apoptosis than either single treatment. This was associated with increased expression of DR4, DR5, Fas, and FADD and decreased expression of survivin, resulting in activation of caspase 8 and caspase 3 as well as cleavage of poly (ADP ribose) polymerase (PARP). Taken together, the results suggest that inhibition of Chk1 with PRE can enhance the anticancer activity of CPX at least partly by decreasing cell proliferation and increasing apoptosis in NSCLC cells. [ABSTRACT FROM AUTHOR]

• Standard of care for pleural mesothelioma has not changed for 20 years. • Repurposing of already approved drugs may result in more effective therapies. • Functional drug sensitivity testing with pleural effusion-derived cells is feasible. • mTOR and Chk1 pathways may be viable targets when treating pleural mesothelioma. Pleural mesothelioma (PM) is an aggressive malignancy with limited treatment options. The first-line therapy has remained unchanged for two decades and consists of pemetrexed in combination with cisplatin. Immune-checkpoint inhibitors (nivolumab plus ipilimumab) have high response rates, resulting in recent updates in treatment recommendations by the U.S. Food and Drug Administration. However, the overall benefits of combination treatment are modest, suggesting that other targeted therapy options should be investigated. We employed high-throughput drug sensitivity and resistance testing on five established PM cell lines using 527 cancer drugs in a 2D setting. Drugs of the greatest potential (n = 19) were selected for further testing in primary cell models derived from pleural effusions of seven PM patients. All established and primary patient-derived PM cell models were sensitive to the mTOR inhibitor AZD8055. Furthermore, another mTOR inhibitor (temsirolimus) showed efficacy in most of the primary patient-derived cells, although a less robust effect was observed when compared with the established cell lines. Most of the established cell lines and all patient-derived primary cells exhibited sensitivity to the PI3K/mTOR/DNA-PK inhibitor LY3023414. The Chk1 inhibitor prexasertib showed activity in 4/5 (80%) of the established cell lines and in 2/7 (29%) of the patient-derived primary cell lines. The BET family inhibitor JQ1 showed activity in four patient-derived cell models and in one established cell line. mTOR and Chk1 pathways had promising results with established mesothelioma cell lines in an ex vivo setting. In patient-derived primary cells, drugs targeting mTOR pathway in particular showed efficacy. These findings may inform novel treatment strategies for PM. [ABSTRACT FROM AUTHOR]

Neuroblastoma is the most common extracranial solid tumor found in children and despite intense multi-modal therapeutic approaches, low overall survival rates of high-risk patients persist. Tumors with heterozygous loss of chromosome 11q and MYCN amplification are two genetically distinct subsets of neuroblastoma that are associated with poor patient outcome. Using an isogenic 11q deleted model system and high-throughput drug screening, we identify checkpoint kinase 1 (CHK1) as a potential therapeutic target for 11q deleted neuroblastoma. Further investigation reveals MYCN amplification as a possible additional biomarker for CHK1 inhibition, independent of 11q loss. Overall, our study highlights the potential power of studying chromosomal aberrations to guide preclinical development of novel drug targets and combinations. Additionally, our study builds on the growing evidence that DNA damage repair and replication stress response pathways offer therapeutic vulnerabilities for the treatment of neuroblastoma. [ABSTRACT FROM AUTHOR]

Neuroblastoma is the most common extracranial solid tumor found in children and despite intense multi-modal therapeutic approaches, low overall survival rates of high-risk patients persist. Tumors with heterozygous loss of chromosome 11q and MYCN amplification are two genetically distinct subsets of neuroblastoma that are associated with poor patient outcome. Using an isogenic 11q deleted model system and high-throughput drug screening, we identify checkpoint kinase 1 (CHK1) as a potential therapeutic target for 11q deleted neuroblastoma. Further investigation reveals MYCN amplification as a possible additional biomarker for CHK1 inhibition, independent of 11q loss. Overall, our study highlights the potential power of studying chromosomal aberrations to guide preclinical development of novel drug targets and combinations. Additionally, our study builds on the growing evidence that DNA damage repair and replication stress response pathways offer therapeutic vulnerabilities for the treatment of neuroblastoma.

CHK1 is a promising molecular target that gained immense attention recently for the development of cancer therapeutics. In this study, a simulation-based investigation was conducted to examine the CHK1 inhibitory activity of cytotoxic xanthone derivatives using a hierarchical workflow for molecular docking, MD simulation, ADME-TOX prediction, and MEP analysis. A molecular docking study was conducted for the forty-three xanthone derivatives along with standard prexasertib into the selected CHK1 protein structures 7AKM and 7AKO. Eight top hits were identified based on their free energy scores, namely L43, L42, L41, L40, L36, L33, L31, and L30, which showed better binding affinity (from − 8.22 to − 8.08 kcal/mol) (from − 8.14 to − 7.9 kcal/mol) toward 7AKM and 7AKO, respectively than the reference prexasertib which emphasizes the validity of our strategy. Furthermore, MD studies support molecular docking results and validate the stability of studied complexes in physiological conditions. These findings confirm that the selected eight xanthones are verifiable CHK1 inhibitors implying a good correlation between in silico and in vitro studies. Moreover, in silico ADME-TOX studies are used to predict the pharmacokinetic, pharmacodynamic, and toxicological properties of the studied eight hits and the standard prexasertib. Indeed, L36 showed the best ADME-TOX profile as it was the only hit without hepatotoxicity among the studied compounds. Besides, it displayed superior binding affinity and satisfied Lipinski, Pfizer, and golden triangle rules indicating a potent drug candidate. The quantitative analysis of electrostatic potential was performed for L36 to identify the reactive sites and possible non-covalent interactions. [ABSTRACT FROM AUTHOR]

Background: Challenges exist in the clinical treatment of luminal estrogen receptor α (ERα)-positive breast cancers (BCs) both to prevent resistance to endocrine therapy (ET) and to treat ET-resistant metastatic BCs (MBC). Therefore, we evaluated if kinases could be new targets for the treatment of luminal primary and MBCs. Methods: ~ 170 kinase inhibitors were applied to MCF-7 cells either with adaptative or genetic resistance to ET drugs and both ERα levels and cell proliferation were measured. Robust-Z-score calculation identified AZD7762 (CHK1/CHK2 inhibitor) as a positive hit. Subsequently, Kaplan–Meier analyses of CHK1 and CHK2 impact on ERα-positive BC patients relapse-free-survival (RFS), bioinformatic evaluations of CHK1 and CHK2 expression and activation status as a function of ERα activation status as well as drug sensitivity studies in ERα-positive BC cell lines, validation of the impact of the ATR:CHK1 and ATM:CHK2 pathways on the control of ERα stability and BC cell proliferation via inhibitor- and siRNA-based approaches, identification of the molecular mechanism required for inhibitor-dependent ERα degradation in BC and the impact of CHK1 and CHK2 inhibition on the 17β-estradiol (E2):ERα signaling, synergy proliferation studies between ET-drugs and clinically relevant CHK1 inhibitors in different luminal BC cell lines, were performed. Results: A reduced CHK1 expression correlates with a longer RFS in women with ERα-positive BCs. Interestingly, women carrying luminal A BC display an extended RFS when expressing low CHK1 levels. Accordingly, CHK1 and ERα activations are correlated in ERα-positive BC cell lines, and the ATR:CHK1 pathway controls ERα stability and cell proliferation in luminal A BC cells. Mechanistically, the generation of DNA replication stress rather than DNA damage induced by ATR:CHK1 pathway inhibition is a prerequisite for ERα degradation. Furthermore, CHK1 inhibition interferes with E2:ERα signaling to cell proliferation, and drugs approved for clinical treatment of primary and MBC (4OH-tamoxifen and the CDK4/CDK6 inhibitors abemaciclib and palbociclib) exert synergic effects with the CHK1 inhibitors in clinical trials for the treatment of solid tumors (AZD7762, MK8776, prexasertib) in preventing the proliferation of cells modeling primary and MBC. Conclusions: CHK1 could be considered as an appealing novel pharmacological target for the treatment of luminal primary and MBCs. [ABSTRACT FROM AUTHOR]

Abstract Background Breast cancer remains as one of the most lethal types of cancer in women. Among various subtypes, triple-negative breast cancer (TNBC) is the most aggressive and hard to treat type of breast cancer. Mechanistically, increased DNA repair and cell cycle checkpoint activation remain as the foremost reasons behind TNBC tumor resistance to chemotherapy and disease recurrence. Methods We evaluated the mechanism of prexasertib-induced regulation of homologous recombination (HR) proteins using 20S proteasome inhibitors and RT-PCR. HR efficiency and DNA damages were evaluated using Dr-GFP and comet assays. DNA morphology and DNA repair focus studies were analyzed using immunofluorescence. UALCAN portal was used to evaluate the expression of RAD51 and survival probability based on tumor stage, subtype, and race in breast cancer patients. Results Our results show that prexasertib treatment promotes both post-translational and transcriptional mediated regulation of BRCA1 and RAD51 proteins. Additionally, prexasertib-treated TNBC cells revealed over 55% reduction in HR efficiency compared to control cells. Based on these results, we hypothesized that prexasertib treatment induced homologous recombination deficiency (HRD) and thus should synergize with PARP inhibitors (PARPi) in TNBC cells. As predicted, combined treatment of prexasertib and PARPi olaparib increased DNA strand breaks, γH2AX foci, and nuclear disintegration relative to single-agent treatment. Further, the prexasertib and olaparib combination was synergistic in multiple TNBC cell lines, as indicated by combination index (CI) values. Analysis of TCGA data revealed elevated RAD51 expression in breast tumors compared to normal breast tissues, especially in TNBC subtype. Interestingly, there was a discrepancy in RAD51 expression in racial groups, with African-American and Asian breast cancer patients showing elevated RAD51 expression compared to Caucasian breast cancer patients. Consistent with these observations, African-American and Asian TNBC patients show decreased survival. Conclusions Based on these data, RAD51 could be a biomarker for aggressive TNBC and for racial disparity in breast cancer. As positive correlation exists between RAD51 and CHEK1 expression in breast cancer, the in vitro preclinical data presented here provides additional mechanistic insights for further evaluation of the rational combination of prexasertib and olaparib for improved outcomes and reduced racial disparity in TNBC.

• Results show potential sensitization of CHK1 inhibitor with RT or targeted agents. • The safety profile observed is consistent with prior prexasertib studies. • The PK of prexasertib is not affected by concomitant cisplatin or cetuximab. This study explored the feasibility of safely combining prexasertib, with cisplatin-radiotherapy (Part A) or cetuximab-radiotherapy (Part B) in patients with previously untreated, locoregionally advanced head and neck squamous cell carcinoma (HNSCC). Escalating doses of prexasertib were administered in each combination using a modified Time-to-Event Continual Reassessment Method. Pharmacokinetic (PK) analysis was performed using standard non-compartmental methods of analysis. Antitumor activity was evaluated using RECIST version 1.1. In Part A, 7 patients received 20 mg/m2 prexasertib and cisplatin-radiotherapy. This dose exceeded the maximum tolerated dose (MTD); no other prexasertib dose was assessed. In Part B, 18 patients received prexasertib (20–40 mg/m2) and cetuximab-radiotherapy. The 30 mg/m2 dose of prexasertib was determined as the MTD. Febrile neutropenia was the dose-limiting toxicity in each arm. Most common treatment-emergent adverse events with both combinations were neutropenia, thrombocytopenia, dysphagia, stomatitis, dry mouth, anemia, radiation skin injury [reported term radiation dermatitis], and nausea. PK of prexasertib was consistent with previously published data following prexasertib monotherapy. Overall response rate in Parts A and B was 71.4% and 83.3%, respectively. The small number of patients and follow-up limits the interpretation of efficacy data. This study did not establish a safe dose of cisplatin-radiotherapy. However, it demonstrates the proof-of-principle that prexasertib could be safely combined with cetuximab-radiotherapy. These data will provide the basis to leverage the potential radio-sensitization properties of a CHK1 inhibitor in combination with radiation or other targeted agents in a variety of therapeutic settings. [ABSTRACT FROM AUTHOR]

In our previous study, we showed that prexasertib, a checkpoint kinase 1 (Chk1) inhibitor, enhances the effects of standard drugs for pancreatic cancer, including gemcitabine (GEM), S-1, and the combination of GEM and S-1 (GS). The combination of prexasertib and GS has a strong antitumor effect and induces apoptosis in pancreatic cancer cells by downregulating anti-apoptotic protein Bcl-2. In the present study, we investigated the combined effect of GEM, S-1, and prexasertib with a selective Bcl-2 inhibitor (venetoclax) and a non-selective Bcl-2 inhibitor (navitoclax) in SUIT-2 pancreatic cancer cells. An MTT assay revealed that the combination of prexasertib with navitoclax showed a synergistic effect but the combination with venetoclax did not. Investigation of the pancreatic cancer cell lines SUIT-2, MIA PaCa-2, and BxPC-3 revealed that BxPC-3 also showed a high synergistic effect when combined with prexasertib and navitoclax but not venetoclax. Mechanistic analysis of the combined effect showed that apoptosis was induced. Bcl-2 knockdown with siRNA and prexasertib treatment did not induce apoptosis, whereas Bcl-xL knockdown with siRNA and prexasertib treatment resulted in strong induction of apoptosis. In addition, among the three cell lines, the combined effect of prexasertib and navitoclax resulted in increased apoptotic cell death because the protein expression levels of Bcl-xL and Chk1 were higher. Our results demonstrate that the combination of prexasertib and navitoclax has a strong antitumor effect and induces apoptosis in pancreatic cancer cells by downregulating Bcl-xL. Simultaneous inhibition of Chk1 and Bcl-xL could be a new strategy for treating pancreatic cancer. [ABSTRACT FROM AUTHOR]

Progress in the systemic control of osteosarcoma has been limited over the past decades thus indicating the urgent clinical need for the development of novel treatment strategies. Therefore, we have recently developed new preclinical models to study promising novel agents for the treatment of pediatric osteosarcoma. The checkpoint kinase (chk) inhibitor prexasertib (LY2606368) and its salt form (LSN2940930) have recently been shown to be active in adult and pediatric malignancies, including sarcoma. We have now tested the potency of prexasertib in clonogenic survival assays in two new lines of primary patient‐derived osteosarcoma cells and in two established osteosarcoma cell lines as a single agent and in combination with cisplatin and the poly ADP‐ribose polymerase (PARP) inhibitor talazoparib. Prexasertib alone results in strongly reduced clonogenic survival at low nanomolar concentrations and acts by affecting cell cycle progression, induction of apoptosis and induction of double‐stranded DNA breakage at concentrations that are well below clinically tolerable and safe plasma concentrations. In combination with cisplatin and talazoparib, prexasertib acts in a synergistic fashion. Chk1 inhibition by prexasertib and its combination with the DNA damaging agent cisplatin and the PARP‐inhibitor talazoparib thus emerges as a potential new treatment option for pediatric osteosarcoma which will now have to be tested in preclinical primary patient derived in vivo models and clinical studies. What's new? Treatment options and outcomes for osteosarcoma have changed very little in decades. New treatment strategies are thus urgently needed. In this study, the authors found that the checkpoint inhibitor 'prexasertib' increased apoptosis and DNA damage in patient‐derived osteosarcoma cells, at very low concentrations. In addition, when combined with cisplatin and talazoparib, prexasertib acted in a synergistic fashion. This drug thus represents a promising therapeutic candidate for further preclinical and clinical development in osteosarcoma. [ABSTRACT FROM AUTHOR]

Summary: Purpose The primary objective was to determine the recommended Phase 2 dose (RP2D) of checkpoint kinase 1 inhibitor, prexasertib, in combination with the p38 mitogen-activated protein kinase inhibitor, ralimetinib, which may be safely administered to patients with advanced cancer. Methods This Phase 1, nonrandomized, open-label, dose-escalation study of prexasertib+ralimetinib included patients with advanced and/or metastatic cancer, followed by a planned cohort expansion in patients with colorectal or non-small-cell lung cancer with KRAS and/or BRAF mutations. Intravenous prexasertib was administered at 60 mg/m2 (days 1 and 15 of a 28-day cycle), together with oral ralimetinib every 12 h (days 1 to 14 at 100 mg [Cohort 1, n = 3] or 200 mg [Cohort 2, n = 6]). Dose escalations for each agent were planned using a model-based 3 + 3 escalation paradigm. Safety was assessed using Common Terminology Criteria for Adverse Events (CTCAE) v4.0X. Tumor response was determined by Response Evaluation Criteria in Solid Tumors (RECIST) v1.1. Results Nine patients were treated; 3 experienced dose-limiting toxicities, all in Cohort 2, prohibiting further dose escalation. The most common ≥Grade 3 adverse event was neutrophil count decreased; other reported ≥Grade 3 hematological toxicities included febrile neutropenia and anemia. The pharmacokinetics of prexasertib+ralimetinib was comparable to the monotherapy population profile for each agent. One patient achieved a best overall response of stable disease (for 2 cycles); there were no complete/partial responses. Conclusions This study did not achieve its primary objective of establishing an RP2D of combination prexasertib + ralimetinib that could be safely administered to patients with advanced cancer. [ABSTRACT FROM AUTHOR]

Checkpoint kinases 1 and 2 (CHK1 and CHK2) are important multifunctional proteins of the kinase family. Their main function is to regulate DNA replication and DNA damage response. If a cell is exposed to exogenous damage to its DNA, CHK1/CHK2 stops the cell cycle to give time to the cellular mechanisms to repair DNA breakage and apoptosis too, if the damage is not repairable to activate programmed cell death. CHK1/CHK2 plays a crucial role in the repair of recombination-mediated double-stranded DNA breaks. The other important functions performed by these proteins are the beginning of DNA replication, the stabilization of replication forks, the resolution of replication stress and the coordination of mitosis, even in the absence of exogenous DNA damage. Prexasertib (LY2606368) is a small ATP-competitive selective inhibitor of CHK1 and CHK2. In preclinical studies, prexasertib in monotherapy has shown to induce DNA damage and tumor cells apoptosis. The preclinical data and early clinical studies advocate the use of prexasertib in solid tumors both in monotherapy and in combination with other drugs (antimetabolites, PARP inhibitors and platinum-based chemotherapy). The safety and the efficacy of combination therapies with prexasertib need to be better evaluated in ongoing clinical trials. [ABSTRACT FROM AUTHOR]

Prexasertib is a novel inhibitor of checkpoint kinase 1. The primary objective of this study was to evaluate prexasertib tolerability in Japanese patients with advanced solid tumors. This nonrandomized single‐arm open‐label phase 1 study of prexasertib consisted of 2 dose levels, 80 mg/m2 and the global‐recommended dose based on a US study of 105 mg/m2, administered intravenously once every 14 days (n = 6 for each dose). Transition to the higher dose proceeded if the frequency of dose‐limiting toxicity observed in cycle 1 was <33% at the lower dose. Safety measures, pharmacokinetics and antitumor activity were assessed. A total of 12 patients were treated. Two patients, one in each dose group, experienced dose‐limiting toxicities of febrile neutropenia, one grade 4 and the other grade 3; both patients recovered and continued the study treatment. The grade 4 treatment‐emergent adverse events related to study treatment were neutropenia (6 patients [50.0%]), leukopenia (4 patients [33.3%]), and 1 instance each (8.3%) of anemia, febrile neutropenia and thrombocytopenia. Neutropenia was generally transient and reversible; 11 patients (91.7%) required granulocyte colony‐stimulating factor treatment during the study. There were no discontinuations due to adverse events or deaths. The prexasertib pharmacokinetics displayed dose‐independent and time‐independent behavior across both dose levels, similar to the profile observed in the US‐based phase 1 study. Eight patients had a best overall response of stable disease. These data are consistent with the known safety profile for prexasertib and confirm its tolerability in Japanese patients with advanced solid tumors. [ABSTRACT FROM AUTHOR]

LC MS/MS methods to measure prexasertib in mouse plasma and Ringer’s solution containing 0.5% BSA (Ringer’s/BSA) were developed and validated. Liquid-liquid extraction with tert -butyl methyl ether was used to extract prexasertib from mouse plasma and Ringer’s/BSA. Reverse phase chromatography with gradient elution was performed to separate prexasertib from the endogenous interference in the matrix, followed by MS detection using positive ion MRM mode. The initial calibration curve for mouse plasma samples ranged from 1 to 500 ng/ml, and after validation of that curve and use in a preliminary study another calibration curve (0.2–200 ng/ml) was created to enable the quantitation of prexasertib at lower concentrations. The method described was precise and accurate with %CV in precision studies of ≤ 6.7% and accuracies within 95.0–110% of nominal target concentration across all concentrations tested for both matrices. This validated method was successfully applied in the analysis of prexasertib in mouse plasma and dialysate samples collected during a cerebral microdialysis study. [ABSTRACT FROM AUTHOR]

We previously showed that prexasertib, a checkpoint kinase 1 (Chk1) inhibitor, and navitoclax, a Bcl-2 and Bcl-xL inhibitor, induced a synergistic inhibitory effect on cell proliferation in vitro . Here, we investigated the effect of the simultaneous knockdown of Chk1 and each antiapoptotic protein of the Bcl-2 family (Bcl-2, Bcl-xL, or Mcl-1) with small interfering RNAs on apoptosis in three pancreatic cancer cell lines. Only simultaneous knockdown of Chk1 and Bcl-xL induced significant apoptosis compared with single knockdown in all three cell lines. We evaluated the anti-tumour effects of combined prexasertib and navitoclax treatment in a mouse xenograft model. Treatment to control volume ratios were calculated as 63.2% for prexasertib, 79.4% for navitoclax, and 36.8% for prexasertib and navitoclax. These findings suggest that the simultaneous inhibition of Chk1 and Bcl-xL may be an effective treatment for pancreatic cancer.