Checkpoint Kinase Research Articles

MDB-65. RESULTS FROM THE SJ-ELIOT PHASE 1 CLINICAL TRIAL EVALUATING PREXASERTIB (LY2606368) IN COMBINATION WITH CYCLOPHOSPHAMIDE OR GEMCITABINE FOR CHILDREN AND ADOLESCENTS WITH REFRACTORY OR RECURRENT MEDULLOBLASTOMA

Abstract BACKGROUND SJ-ELIOT (NCT04023669) was a phase 1 trial that explored the combination of the checkpoint kinase inhibitor, prexasertib with the DNA-damaging agents, cyclophosphamide and gemcitabine, in recurrent or refractory medulloblastoma. METHODS Participants ≥ 1 year and < 25 years were stratified to one of two treatment strata: stratum A prexasertib and cyclophosphamide and stratum B prexasertib and gemcitabine. Patients with Group 3/4 medulloblastoma were assigned to either stratum A or B, whereas patients with SHH medulloblastoma were assigned to stratum A. A Rolling-6 design was used. RESULTS Fifteen patients were enrolled on stratum A and six patients on stratum B. The study was closed early due to drug supply issues. In stratum A, three patients were escalated to dose level (DL) 3 and none had dose limiting toxicity (DLT). For stratum B, of the first three patients enrolled on DL1, two had DLTs (grade 3 hypotension) related to drug reactions. Consequently, stratum B was amended to add hydrocortisone prophylaxis. A further three patients were enrolled. One patient had a grade 3 DLT (ALT increase). The remaining two patients electively stopped therapy within the first two courses. One patient on stratum A, with SHH TP53 mutant, MYCN amplified medulloblastoma, achieved a complete sustained response, received 12 cycles, and electively stopped treatment after 408 days. They progressed nine months later. The remaining 14 patients on stratum A progressed. There were no objective responses on stratum B. Median PFS were 1.9 and 2.1 months for stratum A and B respectively. CONCLUSIONS The MTD/RP2D was not established for either arm. In stratum A, DL3 was tolerated, whereas DL1 for Stratum B was not tolerated. Despite robust preclinical data, no efficacy signal was observed. Intriguingly, one patient with a highly aggressive tumor (SHH TP53 mutant, MYCN amplified) appeared to derive a sustained benefit from the combination of prexasertib and cyclophosphamide.

Inhibition of Melanoma Cell Growth by Salvianolic Acid A through CHK2-CDC25A Pathway Modulation.

This study investigated the impact of salvianolic acids, derived from Danshen, on melanoma cell growth. Specifically, we assessed the ability of salvianolic acid A (Sal A) to modulate melanoma cell proliferation. We used human melanoma A2058 and A375 cell lines to investigate the effects of Sal A on cell proliferation and death by measuring bromodeoxyuridine incorporation and lactate dehydrogenase release. We assessed cell viability and cycle progression using water soluble tetrazolium salt-1 (WST-1) mitochondrial staining and propidium iodide. Additionally, we used a phospho-kinase array to investigate intracellular kinase phosphorylation, specifically measuring the influence of Sal A on checkpoint kinase-2 (Chk-2) via western blot analysis. Sal A inhibited the growth of A2058 and A375 cells dose-responsively and induced cell cycle arrest at the G2/M phase. Notably, Sal A selectively induces Chk-2 phosphorylation without affecting Chk-1, thereby degrading Chk-2-regulated genes Cdc25A and Cdc2. However, Sal A does not affect the Chk1-Cdc25C pathway. Salvianolic acids, especially Sal A, effectively hinder melanoma cell growth by inducing Chk-2 phosphorylation and disrupting G2/M checkpoint regulation.

CHK1 inhibitor induced PARylation by targeting PARG causes excessive replication and metabolic stress and overcomes chemoresistance in ovarian cancer

Chemoresistance contributes to the majority of deaths in women with ovarian cancer (OC). Altered DNA repair and metabolic signaling is implicated in mediating therapeutic resistance. DNA damage checkpoint kinase 1 (CHK1) integrates cell cycle and DNA repair in replicating cells, and its inhibition causes replication stress, repair deficiency and cell cycle dysregulation. We observed elevated Poly-ADP-ribosylation (PAR) of proteins (PARylation) and subsequent decrease in cellular NAD+ levels in OC cells treated with the CHK1 inhibitor prexasertib, indicating activation of NAD+ dependent DNA repair enzymes poly-ADP-ribose polymerases (PARP1/2). While multiple PARP inhibitors are in clinical use in treating OC, tumor resistance to these drugs is highly imminent. We reasoned that inhibition of dePARylation by targeting Poly (ADP-ribose) glycohydrolase (PARG) would disrupt metabolic and DNA repair crosstalk to overcome chemoresistance. Although PARG inhibition (PARGi) trapped PARylation of the proteins and activated CHK1, it did not cause any significant OC cell death. However, OC cells deficient in CHK1 were hypersensitive to PARGi, suggesting a role for metabolic and DNA repair crosstalk in protection of OC cells. Correspondingly, OC cells treated with a combination of CHK1 and PARG inhibitors exhibited excessive replication stress-mediated DNA lesions, cell cycle dysregulation, and mitotic catastrophe compared to individual drugs. Interestingly, increased PARylation observed in combination treatment resulted in depletion of NAD+ levels. These decreased NAD+ levels were also paralleled with reduced aldehyde dehydrogenase (ALDH) activity, which requires NAD+ to maintain cancer stem cells. Furthermore, prexasertib and PARGi combinations exhibited synergistic cell death in OC cells, including an isogenic chemoresistant cell line and 3D organoid models of primary patient-derived OC cell lines. Collectively, our data highlight a novel crosstalk between metabolism and DNA repair involving replication stress and NAD+-dependent PARylation, and suggest a novel combination therapy of CHK1 and PARG inhibitors to overcome chemoresistance in OC.

Abstract B005: Regulation of replication-induced PARP1/PARP2 activation by base excision repair: Implications for PARP and PARG inhibitor resistance

Abstract Acquired poly (ADP-ribose) polymerases (PARP)-inhibitor (PARPi) and/or poly (ADP-ribose) glycohydrolase (PARG)-inhibitor (PARGi) resistance in BRCA1/2-defective tumors is common, emphasizing the need for identifying new targets. Protein poly ADP-ribosylation (PARylation) is a posttranslational modification of proteins catalyzed by PARP to form poly-(APD-ribose) (PAR) chains on itself and chromatin-associated proteins in response to DNA damage. Our study reveals that PARylation occurs in a replication-, PARP1-, and PARP2-dependent manner even in undamaged cells. Using proximity labeling, specifically Split-TurboID, we found that replication-dependent PARylation recruits the base excision repair (BER) factors XRCC1, POLB, APTX, and LIG3. These factors, in turn, suppress further PARylation. The BER factors XRCC1, POLB, APTX, or LIG3 promote PARPi and PARGi resistance as loss of these replication-associated BER (R-BER) factors re-sensitizes cancer cells to these inhibitors. Of interest, BRCA1 and BRCA2 localize with R-BER factors in undamaged cells. Lastly, XRCC1, POLB, APTX, and LIG3 depletion activate the S-phase checkpoint kinase CHK1, and targeting either this kinase or ATR under these conditions overcomes PARGi resistance in glioblastoma and ovarian cancer cells. In conclusion, our data highlight the crucial role of R-BER in protecting the cell during S-phase and propose a potential intervention strategy for resistant tumors. Citation Format: Md Ibrahim, Md Maruf Khan, Wynand P. Roos, Rasha Q. Al-Rahaleh, Faisal Hayat, Marie E. Migaud, Robert W. Sobol. Regulation of replication-induced PARP1/PARP2 activation by base excision repair: Implications for PARP and PARG inhibitor resistance [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Expanding and Translating Cancer Synthetic Vulnerabilities; 2024 Jun 10-13; Montreal, Quebec, Canada. Philadelphia (PA): AACR; Mol Cancer Ther 2024;23(6 Suppl):Abstract nr B005.

Cell cycle machinery in oncology: A comprehensive review of therapeutic targets.

The cell cycle is tightly regulated to ensure controlled cell proliferation. Dysregulation of the cell cycle machinery is a hallmark of cancer that leads to unchecked growth. This review comprehensively analyzes key molecular regulators of the cell cycle and how they contribute to carcinogenesis when mutated or overexpressed. It focuses on cyclins, cyclin-dependent kinases (CDKs), CDK inhibitors, checkpoint kinases, and mitotic regulators as therapeutic targets. Promising strategies include CDK4/6 inhibitors like palbociclib, ribociclib, and abemaciclib for breast cancer treatment. Other possible targets include the anaphase-promoting complex/cyclosome (APC/C), Skp2, p21, and aurora kinase inhibitors. However, challenges with resistance have limited clinical successes so far. Future efforts should focus on combinatorial therapies, next-generation inhibitors, and biomarkers for patient selection. Targeting the cell cycle holds promise but further optimization is necessary to fully exploit it as an anti-cancer strategy across diverse malignancies.

Multi-step control of homologous recombination via Mec1/ATR suppresses chromosomal rearrangements

The Mec1/ATR kinase is crucial for genome stability, yet the mechanism by which it prevents gross chromosomal rearrangements (GCRs) remains unknown. Here we find that in cells with deficient Mec1 signaling, GCRs accumulate due to the deregulation of multiple steps in homologous recombination (HR). Mec1 primarily suppresses GCRs through its role in activating the canonical checkpoint kinase Rad53, which ensures the proper control of DNA end resection. Upon loss of Rad53 signaling and resection control, Mec1 becomes hyperactivated and triggers a salvage pathway in which the Sgs1 helicase is recruited to sites of DNA lesions via the 911-Dpb11 scaffolds and phosphorylated by Mec1 to favor heteroduplex rejection and limit HR-driven GCR accumulation. Fusing an ssDNA recognition domain to Sgs1 bypasses the requirement of Mec1 signaling for GCR suppression and nearly eliminates D-loop formation, thus preventing non-allelic recombination events. We propose that Mec1 regulates multiple steps of HR to prevent GCRs while ensuring balanced HR usage when needed for promoting tolerance to replication stress.

ImmunoSarc II master trial (phase II of sunitinib and nivolumab): Results from the dedifferentiated chondrosarcoma (DDCS) cohort—A GEIS, ISG and UCL study.

11506 Background: Dedifferentiated chondrosarcoma (DDCS) is a rare aggressive CS subtype with a dismal prognosis and no standard of care systemic therapy. For those with advanced, metastatic disease, retrospective chemotherapy studies demonstrate short-term median progression-free survival (PFS) of around 3 to 5.5 months. Benefit from checkpoint and tyrosine kinase inhibitors has been reported, however clinical trial data is scarce, and endpoints are not well defined, thus benchmarking outcomes is challenging. The IMMUNOSARC I master-trial exploring sunitinib plus nivolumab in multiple sarcoma subtypes, detected potential activity in DDCS leading to a specific cohort within the phase II trial IMMUNOSARC II (NCT03277924). Methods: Patients (pts) with ECOG 0-1, centrally confirmed and progressive, measurable DDCS were eligible and treated with sunitinib 37.5 mg/d for 14 days (induction phase), followed by 25 mg/d, in combination with nivolumab 240 mg every 2 weeks until progressive disease (PD) or intolerance. Imaging assessments were performed every 8 weeks. Main endpoint was 6-m PFSR with one-arm survival design (type I error α 0.05, power 0.90, H0 40%, H1 70%) and a Brookmeyer-Crowley like test was assumed with at least 14 of 23 pts required without progression at 6 months. Results: Between December 2019 and October 2023, 24 pts with a median age of 60 years (38-76) were enrolled in 7 centres. Sixteen pts (66%), were male. Pts had received a median of 1 (0-2) prior lines of therapy. In total, 23 pts were evaluable with a median follow-up of 20.1 months (95%CI: 11.6-28.6). Median PFS, according to local site assessment, was 5.6 months (95%CI: 4.5-6.7); the 6m-PFSR was 10 of 23 pts (46%); (95%CI: 23-66) and median overall survival 10.3 months (95%CI: 6.7-13.9). In 19 pts with RECIST measurable response, 5 pts (26.3%) achieved a partial response; 10 (52.6%) stable disease and 4 (21.1%) PD. End-of-treatment reasons were PD in 21 pts (87%), toxicity 1 pt (4.2%) with two pts (8.4%) ongoing. For safety population, the most relevant study drug-related G3-4 toxicities were neutropenia (20.9%), anemia (16.7%), and increased ALT (12.5%). Conclusions: Sunitinib and nivolumab demonstrated encouraging activity in advanced DDCS that did not meet the primary endpoint, but compares favourably with previous analyses of cytotoxic and targeted therapy. The combination is worthy of further exploration in conjunction with reaching a consensus on clinically meaningful endpoints in this challenging population. Translational studies to identify potential predictive biomarkers are ongoing. Clinical trial information: NCT03277924 .

Use of Gynecologic Cancer Intergroup (GCIG) CA125 criteria to evaluate cell cycle checkpoint kinase 1 inhibitor (CHK1i) prexasertib response and disease progression (PD) in recurrent high-grade serous ovarian cancer (HGSOC).

e17536 Background: Data suggest discordance between serum biomarker CA125 and Response Evaluation Criteria in Solid Tumors (RECIST) response and/or PD in chemotherapies and PARP inhibitors. Here, we investigated the impact of CA125 on prognosis and its relationship with RECIST response/PD in HGSOC patients treated with a CHK1i, prexasertib. Methods: All relapsed HGSOC patients in this post-hoc analysis were treated with prexasertib at 105 mg/m2 IV every 14 days in a 28-day cycle until RECIST v1.1 PD, unacceptable toxicity, or consent withdrawal (NCT02203513). CA125 was assessed every cycle and CT scans obtained every two cycles. GCIG CA125 response was defined as >50% reduction confirmed after 28 days and PD as > 2X upper limit of normal (ULN) if baseline was normal or doubling of nadir if baseline was elevated. Patients with baseline CA125 < 2X ULN or nadir > 750 units/mL were not eligible for analysis. Clinical benefit rate (CBR; CR + PR + SD ≥ 6 months) was analyzed by Fisher’s exact test. Progression-free survival (PFS) and overall survival (OS) were estimated by Kaplan-Meier curves and univariate (UV) and multivariate (MV) hazard ratios by Cox regression models. Positive predictive value (PPV) and negative predictive value (NPV) confidence intervals (CI) were estimated by the Wilson-Brown method. Results: Eighty-one patients received at least two cycles of prexasertib between January 2015 and November 2020, out of which 72 were evaluable by both RECIST and GCIG CA125 response criteria. CBR in the CA125 response (CA125-R) group (24/32; 75%) was significantly higher than the CA125 non-responder (CA125-N) group (12/40; 30%; p<0.001). CA125 response tended to occur prior to RECIST response (median: 28 days; IQR: 28, 30). PFS was improved in CA125-R at 8.0 months vs. CA125-N at 3.5 months (UV HR: 0.34, 95% CI: 0.21-0.56; MV HR: 0.35, 95% CI: 0.20-0.59). OS was improved in CA125-R at 19.8 months vs. CA125-N at 10.3 months (HR: 0.43, 95% CI: 0.26-0.71; MV HR: 0.45, 95% CI: 0.27-0.75). No significant differences in PFS or OS were observed between subgroups by BRCA mutation status, platinum-sensitivity, FIGO stage, baseline CA125 value, or previous PARP inhibitor therapy in MV analysis. Out of 70 patients evaluable by RECIST and CA125 PD criteria, 43 patients had CA125 PD and 24 of those had RECIST PD occur within one cycle of CA125 PD (PPV: 59%; 95% CI: 43-72). Of the 27 patients without a CA125 PD, 9 patients also did not have a RECIST PD (NPV: 33%; 95% CI: 19-52). Conclusions: GCIG CA125 response is an independent predictor of response to CHK1i in HGSOC prior to the first restaging scans and is associated with a higher CBR and improved PFS and OS. However, GCIG CA125 PD has poor PPV and NPV within a one cycle window, indicating that CA125 alone is not sufficient in monitoring for PD in HGSOC treated with CHK1i.

The thioredoxin system determines CHK1 inhibitor sensitivity via redox-mediated regulation of ribonucleotide reductase activity

Checkpoint kinase 1 (CHK1) is critical for cell survival under replication stress (RS). CHK1 inhibitors (CHK1i’s) in combination with chemotherapy have shown promising results in preclinical studies but have displayed minimal efficacy with substantial toxicity in clinical trials. To explore combinatorial strategies that can overcome these limitations, we perform an unbiased high-throughput screen in a non-small cell lung cancer (NSCLC) cell line and identify thioredoxin1 (Trx1), a major component of the mammalian antioxidant-system, as a determinant of CHK1i sensitivity. We establish a role for redox recycling of RRM1, the larger subunit of ribonucleotide reductase (RNR), and a depletion of the deoxynucleotide pool in this Trx1-mediated CHK1i sensitivity. Further, the TrxR inhibitor auranofin, an approved anti-rheumatoid arthritis drug, shows a synergistic interaction with CHK1i via interruption of the deoxynucleotide pool. Together, we show a pharmacological combination to treat NSCLC that relies on a redox regulatory link between the Trx system and mammalian RNR activity.

DNA Damage Checkpoints Govern Global Gene Transcription and Exhibit Species-Specific Regulation on HOF1 in Candida albicans.

DNA damage checkpoints are essential for coordinating cell cycle arrest and gene transcription during DNA damage response. Exploring the targets of checkpoint kinases in Saccharomyces cerevisiae and other fungi has expanded our comprehension of the downstream pathways involved in DNA damage response. While the function of checkpoint kinases, specifically Rad53, is well documented in the fungal pathogen Candida albicans, their targets remain poorly understood. In this study, we explored the impact of deleting RAD53 on the global transcription profiles and observed alterations in genes associated with ribosome biogenesis, DNA replication, and cell cycle. However, the deletion of RAD53 only affected a limited number of known DNA damage-responsive genes, including MRV6 and HMX1. Unlike S. cerevisiae, the downregulation of HOF1 transcription in C. albicans under the influence of Methyl Methanesulfonate (MMS) did not depend on Dun1 but still relied on Rad53 and Rad9. In addition, the transcription factor Mcm1 was identified as a regulator of HOF1 transcription, with evidence of dynamic binding to its promoter region; however, this dynamic binding was interrupted following the deletion of RAD53. Furthermore, Rad53 was observed to directly interact with the promoter region of HOF1, thus suggesting a potential role in governing its transcription. Overall, checkpoints regulate global gene transcription in C. albicans and show species-specific regulation on HOF1; these discoveries improve our understanding of the signaling pathway related to checkpoints in this pathogen.

Apelin-13 improves pulmonary epithelial barrier function in a mouse model of LPS-induced acute lung injury by inhibiting Chk1-mediated DNA damage

Apelin-13, a type of active peptide, can alleviate lipopolysaccharide (LPS)-induced acute lung injury (ALI). However, the specific mechanism is unclear. Cell cycle checkpoint kinase 1 (Chk1) plays an important role in DNA damage. Here, we investigated the regulatory effect of Apelin on Chk1 in ALI. Chk1-knockout and −overexpression mice were used to explore the role of Chk1 in LPS-induced ALI mice treated with or without Apelin-13. In addition, A549 cells were also treated with LPS to establish a cell model. Chk1 knockdown inhibited the destruction of alveolar structure, the damage of lung epithelial barrier function, and DNA damage in the ALI mouse model. Conversely, Chk1 overexpression had the opposite effect. Furthermore, Apelin-13 reduced Chk1 expression and DNA damage to improve the impaired lung epithelial barrier function in the ALI model. However, the high expression of Chk1 attenuated the protective effect of Apelin-13 on ALI. Notably, Apelin-13 promoted Chk1 degradation through autophagy to regulate DNA damage in LPS-treated A549 cells. In summary, Apelin-13 regulates the expression of Chk1 by promoting autophagy, thereby inhibiting epithelial DNA damage and repairing epithelial barrier function.

Targeting WEE1 enhances the antitumor effect of KRAS-mutated non-small cell lung cancer harboring TP53 mutations

The clinical development of Kirsten rat sarcoma virus (KRAS)-G12C inhibitors for the treatment of KRAS-mutant lung cancer is limited by the presence of co-mutations, intrinsic resistance, and the emergence of acquired resistance. Therefore, innovative strategies for enhancing apoptosis in KRAS-mutated non-small cell lung cancer (NSCLC) are urgently needed. Through CRISPR-Cas9 knockout screening using a library of 746 crRNAs and drug screening with a custom library of 432 compounds, we discover that WEE1 kinase inhibitors are potent enhancers of apoptosis, particularly in KRAS-mutant NSCLC cells harboring TP53 mutations. Mechanistically, WEE1 inhibition promotes G2/M transition and reduces checkpoint kinase 2 (CHK2) and Rad51 expression in the DNA damage response (DDR) pathway, which is associated with apoptosis and the repair of DNA double-strand breaks, leading to mitotic catastrophe. Notably, the combined inhibition of KRAS-G12C and WEE1 consistently suppresses tumor growth. Our results suggest targeting WEE1 as a promising therapeutic strategy for KRAS-mutated NSCLC with TP53 mutations.

Novel imidazolone derivatives as potential dual inhibitors of checkpoint kinases 1 and 2: Design, synthesis, cytotoxicity evaluation, and mechanistic insights

Applying various drug design strategies including ring variation, substituents variation, and ring fusion, two series of 2-(alkylthio)-5-(arylidene/heteroarylidene)imidazolones and imidazo[1,2-a]thieno[2,3-d]pyrimidines were designed and prepared as dual potential Chk1 and Chk2 inhibitors. The newly synthesized hybrids were screened in NCI 60 cell line panel where the most active derivatives 4b, d-f, and 6a were further estimated for their five dose antiproliferative activity against the most sensitive tumor cells including breast MCF-7 and MDA-MB-468 and non-small cell lung cancer EKVX as well as normal WI-38 cell. Noticeably, increasing the carbon chain attached to thiol moiety at C-2 of imidazolone scaffold elevated the cytotoxic activity. Hence, compounds 4e and 4f, containing S-butyl fragment, exhibited the most antiproliferative activity against the tested cells where 4f showed extremely potent selectivity toward them. As well, compound 6a, containing imidazothienopyrimidine core, exerted significant cytotoxic activity and selectivity toward the examined cells. The mechanistic investigation of the most active cytotoxic analogs was achieved through the evaluation of their inhibitory activity against Chk1 and Chk2. Results revealed that 4f displayed potent dual inhibition of both Chk1 and Chk2 with IC50 equal 0.137 and 0.25 μM, respectively. It also promoted its antiproliferative and Chk suppression activity via EKVX cell cycle arrest at S phase through stimulating the apoptotic approach. The apoptosis induction was also emphasized by elevating the expression of Caspase-3 and Bax, that are accompanied by Bcl-2 diminution. The in silico molecular docking and ADMET profiles of the most active analogs have been carried out to evaluate their potential as significant anticancer drug candidates.

Abstract PO5-23-08: Adenylosuccinate lyase is essential for proliferation and mitochondrial function of endocrine therapy resistant breast cancer cells

Abstract Eighty percent of breast cancers express estrogen receptor alpha (ERα, ESR1) at the time of diagnosis. Endocrine therapy (ET) is the standard treatment that either block estrogen mediated ER activation (such as tamoxifen, fulvestrant) or suppress estrogen synthesis (such as exemestane, letrozole, or anastrozole). While ET is initially effective, emergence of ET-resistance is common and possess a major clinical challenge. Hence, there is an ongoing need to develop new treatments for ET-resistant-ERα positive breast cancer. In this study we investigated the role of adenylosuccinate lyase (ADSL), an enzyme of the de-novo purine biosynthesis pathway as a potential target of ET-resistant breast cancer. The protein level of ADSL in two independent ET-resistant cell line model LCC9 and T47D-4HT cells were significantly higher in comparison to its parental ET-sensitive cell lines, MCF7 and T47D cells, respectively. Transient knockdown of ADSL using two independent siRNA in both LCC9 and T47D-4HT cells results in a significant decrease of cell growth, colony, and spheroid formation. Notably, reduced ADSL levels in LCC9 cells prevented the cells from progressing from G1 to S phase of cell cycle with concurrent elevation of cyclin D1/D3, CDK2/4, and cyclin E. On the other hand, in T47D-4HT cells, ADSL reduction caused cells to accumulate in S-phase of cell cycle and showed lower levels of total cyclin D1 protein. Mechanistically, in LCC9 cells (but not in T47D-4HT cells), ADSL depletion induced DNA replication stress which activates (phosphorylate) ataxia-telangiectasia-mutated-and-Rad3-related kinase (ATR) and its major downstream effector checkpoint kinase 1 (Chk1) that in turn failed to de-phosphorylate the inhibitory-phospho-groups of cyclin-dependent kinase 2 (CDK2). In addition, ADSL depletion perturbed the mitochondrial function in both LCC9 and T47D-4HT cells. Oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) was lower in both the cells along with the mitochondrial membrane potential. Pertinently, lower concentration of AICAR (5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside), a product of ADSL enzyme function, partially rescued the cell growth and restored mitochondrial membrane potential in ADSL-depleted LCC9 cells. To further understand the global effects of ADSL depletion we performed RNA-sequencing of LCC9 and T47D-4HT cells after ADSL depletion and compared with respective control siRNA transfected cells followed by gene set enrichment analysis. Intriguingly, diverse effect was observed in LCC9 and T47D-4HT cells as very few genes were found to be commonly regulated between these two cell lines. Analysis of clinical data sets revealed high level of ADSL transcript was associated with adverse progression free survival and overall survival in breast cancer patients treated with endocrine therapies. Overall, our findings demonstrate that ADSL-mediated de novo purine synthesis is critical for cellular growth, proliferation, and mitochondrial function of endocrine therapy-resistant breast cancer cells. Therefore, targeting ADSL is a novel potential therapeutic approach for ERα positive ET- resistant breast cancer. Citation Format: Anil Yadav, Lu Jin, Robert Clarke, Surojeet Sengupta. Adenylosuccinate lyase is essential for proliferation and mitochondrial function of endocrine therapy resistant breast cancer cells [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-23-08.

Predictive DNA damage signaling for low‑dose ionizing radiation.

Numerous studies have attempted to develop biological markers for the response to radiation for broad and straightforward application in the field of radiation. Based on a public database, the present study selected several molecules involved in the DNA damage repair response, cell cycle regulation and cytokine signaling as promising candidates for low‑dose radiation‑sensitive markers. The HuT 78 and IM‑9 cell lines were irradiated in a concentration‑dependent manner, and the expression of these molecules was analyzed using western blot analysis. Notably, the activation of ataxia telangiectasia mutated (ATM), checkpoint kinase 2 (CHK2), p53 and H2A histone family member X (H2AX) significantly increased in a concentration‑dependent manner, which was also observed in human peripheral blood mononuclear cells. To determine the radioprotective effects of cinobufagin, as an ATM and CHK2 activator, an in vivo model was employed using sub‑lethal and lethal doses in irradiated mice. Treatment with cinobufagin increased the number of bone marrow cells in sub‑lethal irradiated mice, and slightly elongated the survival of lethally irradiated mice, although the difference was not statistically significant. Therefore, KU60019, BML‑277, pifithrin‑α, and nutlin‑3a were evaluated for their ability to modulate radiation‑induced cell death. The use of BML‑277 led to a decrease in radiation‑induced p‑CHK2 and γH2AX levels and mitigated radiation‑induced apoptosis. On the whole, the present study provides a novel approach for developing drug candidates based on the profiling of biological radiation‑sensitive markers. These markers hold promise for predicting radiation exposure and assessing the associated human risk.

DNA Checkpoint Gene Mutation as a Biomarker for Immune Checkpoint Inhibitor Therapy in Advanced Biliary Tract Cancer.

The DNA checkpoint (DNACHK) pathway is engaged in signaling the need for cell cycle arrest. This pathway is being actively researched to assess its role in cancer immunotherapy. A total of 62 patients participated in this study. These patients were treated with immune checkpoint inhibitors (ICIs) for advanced biliary tract cancers (BTCs) from March 2020 to August 2022 at Samsung Medical Center. DNACHK mutated were defined as genomic alterations, such as single nucleotide variants, multi-nucleotide variants, and short insertion and deletions in seven genes; checkpoint kinase 1 (CHEK1), checkpoint kinase 2 (CHEK2), BRCA1, DNA repair-associated (BRCA1), the serine/threonine kinase ATM, the serine/threonine kinase ATR, mediator of DNA damage checkpoint 1 (MDC1) and tumor protein p53 binding protein 1 (TP53BP1). We analyzed the effect of DNACHK mutations on the efficacy of ICIs in advanced BTCs. Patient median age at diagnosis was 68.0 years. 10 patients (16.1%) had GB cancer; the remaining patients (n=52, 83.9%) were diagnosed with cholangiocarcinoma. Thirty-seven (59.7%) patients were categorized into the DNACHK wild-type (WT) group and 25 (40.3%) into the DNACHK mutated (MT) group. The most observed DNA checkpoint mutations were ATM mutations (n=14). Patients in the DNACHK MT group had better disease control rate (DCR) than patients in the DNACHK WT (60.0% vs. 48.6%, p=0.53). Median overall survival (OS) was 8.1 months (95% CI 5.1-22.8) in the MT group and 5.6 months (95%CI 3.1-11.0) in the WT group (p=0.33). The DNACHK pathway is expected to serve as a potential biomarker for ICI treatment.

Degradation-Based Protein Profiling: A Case Study of Celastrol.

Natural products, while valuable for drug discovery, encounter limitations like uncertainty in targets and toxicity. As an important active ingredient in traditional Chinese medicine, celastrol exhibits a wide range of biological activities, yet its mechanism remains unclear. In this study, they introduced an innovative "Degradation-based protein profiling (DBPP)" strategy, which combined PROteolysis TArgeting Chimeras (PROTAC) technology with quantitative proteomics and Immunoprecipitation-Mass Spectrometry (IP-MS) techniques, to identify multiple targets of natural products using a toolbox of degraders. Taking celastrol as an example, they successfully identified its known targets, including inhibitor of nuclear factor kappa B kinase subunit beta (IKKβ), phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PI3Kα), and cellular inhibitor of PP2A (CIP2A), as well as potential new targets such as checkpoint kinase 1 (CHK1), O-GlcNAcase (OGA), and DNA excision repair protein ERCC-6-like (ERCC6L). Furthermore, the first glycosidase degrader is developed in this work. Finally, by employing a mixed PROTAC toolbox in quantitative proteomics, they also achieved multi-target identification of celastrol, significantly reducing costs while improving efficiency. Taken together, they believe that the DBPP strategy can complement existing target identification strategies, thereby facilitating the rapid advancement of the pharmaceutical field.

Mechanism of Musashi2 affecting radiosensitivity of lung cancer by modulating DNA damage repair.

Identifying new targets for overcoming radioresistance is crucial for improving the efficacy of lung cancer radiotherapy, given that tumor cell resistance is a leading cause of treatment failure. Recent research has spotlighted the significance of Musashi2 (MSI2) in cancer biology. In this study, we first demonstrated that MSI2 plays a key function in regulating the radiosensitivity of lung cancer. The expression of MSI2 is negatively correlated with overall survival in cancer patients, and the knockdown of MSI2 inhibits tumorigenesis and increases radiosensitivity of lung cancer cells. Cellular radiosensitivity, which is closely linked to DNA damage, is influenced by MSI2 interaction with ataxia telangiectasia mutated and Rad3-related kinase (ATR) and checkpoint kinase 1 (CHK1) post-irradiation; moreover, knockdown of MSI2 inhibits the ATR-mediated DNA damage response pathway. RNA-binding motif protein 17 (RBM17), which is implicated in DNA damage repair, exhibits increased interaction with MSI2 post-irradiation. We found that knockdown of RBM17 disrupted the interaction between MSI2 and ATR post-irradiation and increased the radiosensitivity of lung cancer cells. Furthermore, we revealed the potential mechanism of MSI2 recruitment into the nucleus with the assistance of RBM17 to activate ATR to promote radioresistance. This study provides novel insights into the potential application of MSI2 as a new target in lung cancer radiotherapy.

ELK3 destabilization by speckle-type POZ protein suppresses prostate cancer progression and docetaxel resistance.

Accumulating evidence demonstrates that the activity regulation of ELK3, a member of the E26 transformation-specific oncogene family, is critical to regulating cell proliferation, migration, and survival in human cancers. However, the molecular mechanisms of how ELK3 induces chemoresistance in prostate cancer (PCa) have not been elucidated. In this study, we found that SPOP and ELK3 are an interacting partner. The interaction between SPOP and ELK3 resulted in increased ELK3 ubiquitination and destruction, assisted by checkpoint kinase-mediated ELK3 phosphorylation. Notably, the modulation of SPOP-mediated ELK3 protein stability affected the c-Fos-induced cell proliferation and invasion of PCa cells. The clinical involvement of the SPOP-ELK3 axis in PCa development was confirmed by an immunohistochemical assay on 123 PCa tissues, with an inverse correlation between increased ELK3 and decreased SPOP being present in ~80% of the specimens. This observation was supported by immunohistochemistry analysis using a SPOP-mutant PCa specimen. Finally, docetaxel treatment induced cell death by activating checkpoint kinase- and SPOP-mediated ELK3 degradation, while SPOP-depleted or SPOP-mutated PCa cells showed cell death resistance. Notably, this observation was correlated with the protein levels of ELK3. Taken together, our study reveals the precise mechanism of SPOP-mediated degradation of ELK3 and provides evidence that SPOP mutations contribute to docetaxel resistance in PCa.

Novel Amidine Derivative K1586 Sensitizes Colorectal Cancer Cells to Ionizing Radiation by Inducing Chk1 Instability.

Checkpoint kinase 1 (Chk1) is a key mediator of the DNA damage response that regulates cell cycle progression, DNA damage repair, and DNA replication. Small-molecule Chk1 inhibitors sensitize cancer cells to genotoxic agents and have shown preclinical activity as single agents in cancers characterized by high levels of replication stress. However, the underlying genetic determinants of Chk1-inhibitor sensitivity remain unclear. Although treatment options for advanced colorectal cancer are limited, radiotherapy is effective. Here, we report that exposure to a novel amidine derivative, K1586, leads to an initial reduction in the proliferative potential of colorectal cancer cells. Cell cycle analysis revealed that the length of the G2/M phase increased with K1586 exposure as a result of Chk1 instability. Exposure to K1586 enhanced the degradation of Chk1 in a time- and dose-dependent manner, increasing replication stress and sensitizing colorectal cancer cells to radiation. Taken together, the results suggest that a novel amidine derivative may have potential as a radiotherapy-sensitization agent that targets Chk1.