The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
Identity is verified. The requested target is human CHEK1 (synonym CHK1), encoding checkpoint kinase 1, UniProt O14757. The literature describes the same 476-amino-acid serine/threonine kinase, with an N-terminal catalytic domain and C-terminal regulatory region. This agrees with the supplied protein description and protein-kinase/CAMK-family domain annotations. It is not CHEK2/CHK2 and not the unrelated CHK tyrosine kinase. Human structural work describes CHK1 as a 476-residue nuclear protein whose kinase domain occupies approximately residues 1–265 (tapiaalveal2009regulationofchk1 pages 1-2, chen2000implicationsforchk1 pages 1-2).
CHK1 is the principal effector kinase of the ATR replication-stress checkpoint. Its primary function is to phosphorylate proteins that restrain cyclin-dependent kinase activity, suppress inappropriate replication-origin firing, stabilize or protect stressed replication forks, coordinate homologous recombination, and delay cell-cycle progression through intra-S and G2/M checkpoints. It is therefore better understood as an active regulator of normal DNA replication than merely as an emergency “damage checkpoint” (melia2024thepotentialfor pages 4-6, sorensen2012safeguardinggenomeintegrity pages 6-6, blasius2011aphosphoproteomicscreen pages 1-2).
Recent translational evidence remains mixed. Biomarker-selected preclinical models—particularly CCNE1-amplified, PARP-inhibitor-resistant, or extrachromosomal-DNA-positive cancers—show strong CHK1 dependence. Clinical studies demonstrate activity in selected ovarian cancers and with low-dose gemcitabine, but unselected SRA737 monotherapy produced no objective responses. Myelosuppression, normal-cell essentiality, and the absence of validated predictive biomarkers remain major limitations (kristeleit2023aphase12 pages 6-7, jones2023aphaseiii pages 1-2, giudice2024thechk1inhibitor pages 1-2, xu2024chk1inhibitorsra737 pages 1-2, tang2024enhancingtranscription–replicationconflict pages 1-2).
The following table summarizes the functional annotation and distinguishes clinical from preclinical evidence.
| Aspect | Current annotation | Key evidence | Translational relevance |
|---|---|---|---|
| Verified identity | Human CHEK1 (synonym CHK1), UniProt O14757; serine/threonine-protein kinase Chk1. This matches the supplied UniProt identity and is distinct from CHEK2/CHK2 and the unrelated CHK tyrosine kinase. | Human CHK1 is experimentally described as a 476-aa checkpoint kinase and nuclear protein (chen2000implicationsforchk1 pages 1-2). | Confirms that the functional and inhibitor evidence pertains to the requested human target. |
| Architecture and family | 476 aa; conserved N-terminal catalytic domain at approximately residues 1–265, followed by a flexible linker and less-conserved C-terminal regulatory region. Its canonical bilobal kinase fold agrees with the supplied CAMK-family and protein-kinase-domain annotations (tapiaalveal2009regulationofchk1 pages 1-2, chen2000implicationsforchk1 pages 1-2). | A 1.7-Å human CHK1 structure revealed an ATP-binding cleft between the kinase lobes. The isolated kinase domain was approximately 20-fold more active than full-length CHK1, supporting C-terminal autoinhibition (chen2000implicationsforchk1 pages 1-2, chen2000implicationsforchk1 pages 8-9). | Explains ATP-competitive inhibitor binding to the N-terminal domain and how C-terminal phosphorylation can regulate activity. |
| Catalytic function | ATP-dependent protein-serine/threonine phosphorylation: ATP + protein Ser/Thr → ADP + phosphoprotein. | Human CHK1 bound AMP-PNP in its catalytic cleft; the L84G gatekeeper mutant retained kinase activity and transferred phosphate from a bulky ATP analogue to substrates (blasius2011aphosphoproteomicscreen pages 2-4, chen2000implicationsforchk1 pages 1-2). | Establishes CHK1 as an enzymatically druggable kinase and enables direct substrate mapping. |
| Substrate specificity | Refined preference: R/K-R/K-d/e-t-S*/T*-X-r/k-r. Uppercase residues indicate strong preferences, lowercase positions indicate weaker preferences, and the asterisk marks the phosphoacceptor (blasius2011aphosphoproteomicscreen pages 9-11). | An analogue-sensitive CHK1 phosphoproteomic screen identified 268 sites in 171 proteins and experimentally refined the motif (blasius2011aphosphoproteomicscreen pages 9-11, blasius2011aphosphoproteomicscreen pages 2-4). | Useful for predicting substrates and designing pharmacodynamic assays, although motif matching alone does not prove physiological phosphorylation. |
| Upstream activation | Replication stress activates ATR, which phosphorylates CHK1 at Ser317 and Ser345 through a Claspin-dependent process; CHK1 subsequently autophosphorylates at Ser296 (melia2024thepotentialfor pages 4-6, blasius2011aphosphoproteomicscreen pages 1-2). | Mammalian experiments demonstrate strong ATR dependence of S317 and S345 phosphorylation following DNA damage or replication blockage (niida2007specificroleof pages 1-2). | Phospho-CHK1 is a pathway-engagement marker, although its sensitivity as a quantitative ATR biomarker can be limited. |
| Localization | CHK1 is predominantly nuclear but dynamically distributed between the nucleus and cytoplasm; DNA damage increases centrosomal association. S317 contributes to chromatin release, whereas S345 affects cytoplasmic localization (niida2007specificroleof pages 1-2, chen2000implicationsforchk1 pages 1-2). | Mammalian localization and phosphosite-mutant experiments linked compartmentalization to checkpoint integrity, centrosomal protection, and avoidance of mitotic catastrophe (niida2007specificroleof pages 1-2). | Localization governs access to nuclear, chromatin-associated, cytoplasmic, and centrosomal substrates; total abundance may not reflect functional activity. |
| CDC25 substrates | Direct phosphorylation inhibits CDC25-mediated CDK activation. Human examples include CDC25A Ser123 and CDC25C Ser216; the latter promotes 14-3-3 binding and reduces nuclear accumulation (blasius2011aphosphoproteomicscreen pages 2-4, chen2000implicationsforchk1 pages 1-2). | Human CHK1 phosphorylates all CDC25 isoforms. CDC25A inhibition restrains S-phase CDKs, whereas CDC25C inhibition maintains inhibitory CDK1 phosphorylation and G2 arrest (melia2024thepotentialfor pages 4-6, chen2000implicationsforchk1 pages 8-9). | CHK1 inhibition stabilizes CDC25A, elevates CDK activity and origin firing, and can drive replication or mitotic catastrophe. |
| Other substrates | CHK1 phosphorylates RAD51 Thr309, supporting homologous recombination, and KAP1 Ser473 after genotoxic or replication stress. Candidate substrates include FEN1, RIF1, TICRR/Treslin, and Ku70 (melia2024thepotentialfor pages 4-6, blasius2011aphosphoproteomicscreen pages 9-11). | KAP1 Ser473 was validated using chemical genetics and kinase-depletion or inhibition experiments, although its downstream consequence remained unresolved (blasius2011aphosphoproteomicscreen pages 9-11). | Demonstrates coordination of repair and replication beyond CDC25 control; KAP1 Ser473 may serve as a pharmacodynamic readout. |
| Primary biological role | Central effector of the ATR–CHK1 replication-stress checkpoint: suppresses excessive origin firing, stabilizes stalled forks, restrains CDK activity, supports replication restart and repair, and enforces intra-S and G2/M delays (melia2024thepotentialfor pages 4-6, sorensen2012safeguardinggenomeintegrity pages 6-6, blasius2011aphosphoproteomicscreen pages 1-2). | CHK1 loss or inhibition causes excess CDK activity, late-origin firing, fork abandonment or breakage, γH2AX accumulation, and cell death; mammalian viability depends on CHK1 (sorensen2012safeguardinggenomeintegrity pages 6-6, blasius2011aphosphoproteomicscreen pages 1-2). | Tumors with oncogene-driven replication stress or defective G1 control can become CHK1-dependent, but normal-cell essentiality narrows the therapeutic window. |
| SRA737 monotherapy — clinical, 2023 | Phase I/II NCT02797964 treated 107 patients; the recommended phase II dose was 800 mg once daily. No complete or partial responses occurred, although stable-disease rates varied by cohort (kristeleit2023aphase12 pages 6-7). | Any-grade diarrhea, nausea, and vomiting occurred in 63%, 60%, and 46%; grade 3 or higher neutropenia occurred in 8% at the recommended dose or above. Investigators did not support further monotherapy development (kristeleit2023aphase12 pages 6-7). | Supports combination rather than unselected single-agent development; limited activity and possible cardiac risk remain concerns. |
| SRA737 plus gemcitabine — clinical, 2023 | A phase I/II study enrolled 143 patients. The recommended regimen was SRA737 500 mg plus gemcitabine 250 mg/m². Overall response rate was 10.8%, including 25% in anogenital cancer (jones2023aphaseiii pages 1-2). | At the recommended dose, grade 3 or higher anemia, neutropenia, and thrombocytopenia occurred in 11.7%, 16.7%, and 10%, respectively (jones2023aphaseiii pages 1-2). | Demonstrates feasible pharmacological induction of replication stress with low-dose chemotherapy, but efficacy requires confirmation in biomarker-selected cohorts. |
| Prexasertib — clinical, 2024 | Phase II NCT02203513 enrolled 49 heavily pretreated, BRCA-wild-type, platinum-resistant HGSOC patients; 39 were RECIST-evaluable. Overall response rate was 30.8%, and median PFS was 4 and 6 months in the two cohorts (giudice2024thechk1inhibitor pages 1-2). | The trial stopped early because of COVID-19 and termination of the drug supply. High POLA1, POLE, and GINS3 expression was associated post hoc with lack of benefit (giudice2024thechk1inhibitor pages 1-2). | Provides an activity signal but not definitive efficacy; hematologic toxicity and the need for validated predictive biomarkers remain important limitations. |
| SRA737 in ovarian cancer — preclinical, 2024 | In CCNE1-amplified and PARP-inhibitor-resistant HGSOC models, SRA737 increased replication stress, destabilized forks, impaired homologous recombination, and prolonged survival; combination with PARP inhibition increased regression in patient-derived xenografts (xu2024chk1inhibitorsra737 pages 1-2). | Approximately 20% of HGSOCs are CCNE1-amplified and about 50% have defective homologous-recombination repair, defining candidate populations (xu2024chk1inhibitorsra737 pages 1-2). | Supports biomarker-directed trials in CCNE1-amplified or PARP-inhibitor-resistant ovarian cancer; evidence remains preclinical. |
| BBI-2779 and ecDNA — preclinical, 2024 | ecDNA-positive cancers exhibited slower DNA synthesis, elevated transcription–replication conflict, DNA breaks, and CHK1 activation. Oral CHK1 inhibitor BBI-2779 preferentially killed ecDNA-positive cells (tang2024enhancingtranscription–replicationconflict pages 1-2). | In an FGFR2-ecDNA gastric-cancer mouse model, BBI-2779 suppressed growth, prevented ecDNA-mediated resistance to infigratinib, and produced sustained regression (tang2024enhancingtranscription–replicationconflict pages 1-2). | Introduces ecDNA as a potential CHK1-dependency biomarker and combination strategy, but clinical efficacy and safety remain unestablished. |
| Overall assessment | CHK1 is a mechanistically validated, druggable guardian of replication-fork integrity, but translation is constrained by normal-tissue essentiality, myelosuppression, weak unselected monotherapy activity, and uncertain biomarkers (khamidullina2024keyproteinsof pages 12-13, kristeleit2023aphase12 pages 6-7). | Recent evidence favors rational combinations and selection by replication-stress states such as CCNE1 amplification, PARP-inhibitor resistance, or ecDNA rather than CHEK1 expression alone (giudice2024thechk1inhibitor pages 1-2, xu2024chk1inhibitorsra737 pages 1-2, tang2024enhancingtranscription–replicationconflict pages 1-2). | In the cited 2023–2024 literature, CHK1 inhibition remained investigational rather than an established standard-of-care therapy. |
Table: Compact evidence map linking verified CHEK1 molecular function and localization to replication-checkpoint biology and recent translational studies. Clinical and preclinical findings are explicitly distinguished, with quantitative outcomes and major limitations.
The gene symbol CHEK1 matches “checkpoint kinase 1” or “serine/threonine-protein kinase Chk1.” The organism is Homo sapiens, and the matching protein is UniProt O14757. Structural literature reports a 476-amino-acid human CHK1 protein, directly consistent with the requested entry. No evidence reviewed required reassignment to a similarly named gene (chen2000implicationsforchk1 pages 1-2).
The protein has two broad functional regions:
These observations align with the supplied InterPro annotations for a protein-kinase domain, ATP-binding site, serine/threonine active site, kinase-like fold, and CHK1 catalytic domain. The structural evidence supports placement in the protein-kinase superfamily and is compatible with the supplied CAMK-group classification (chen2000implicationsforchk1 pages 1-2).
CHK1 is an ATP-dependent protein serine/threonine kinase. Its net reaction is:
ATP + protein-L-serine/protein-L-threonine → ADP + phosphoprotein.
The human structure contains an ATP-binding catalytic cleft and binds the non-hydrolysable ATP analogue AMP-PNP. Chemical-genetic substitution of ATP-pocket gatekeeper Leu84 with glycine produced an analogue-sensitive CHK1 that remained active and transferred thiophosphate from a bulky ATP analogue to direct substrates, experimentally confirming ATP-dependent phosphotransfer (blasius2011aphosphoproteomicscreen pages 2-4, chen2000implicationsforchk1 pages 1-2).
CHK1 does not phosphorylate every exposed serine or threonine. An analogue-sensitive human-cell phosphoproteomic screen refined its preferred local sequence to approximately R/K-R/K-d/e-t-S/T-X-r/k-r, where the asterisk marks the phosphoacceptor, uppercase positions are strongly preferred, and lowercase positions represent weaker preferences or counter-selection relationships. The screen identified 268 sites in 171 proteins, although candidate status from a screen is not equivalent to physiological validation (blasius2011aphosphoproteomicscreen pages 9-11, blasius2011aphosphoproteomicscreen pages 2-4).
Substrate selection in cells also depends on compartment, scaffolds, cell-cycle state, and damage-dependent release of CHK1 from chromatin. Accordingly, sequence matching alone should not be treated as proof that a protein is a CHK1 substrate.
Replication stress generates RPA-coated single-stranded DNA at stalled forks. This recruits ATR–ATRIP and accessory factors including TOPBP1, the RAD9–RAD1–HUS1 complex and ETAA1. ATR then phosphorylates CHK1, with Claspin acting as an important mediator (melia2024thepotentialfor pages 4-6, kciuk2026targetingatrchk1and pages 2-5).
The best-established human regulatory sites are:
The simple model is that C-terminal phosphorylation relieves autoinhibition and changes interactions or localization, rather than activating an otherwise completely inactive catalytic domain. Human crystallography found an active-like kinase fold without activation-loop phosphorylation, while localization studies showed non-equivalent roles for Ser317 and Ser345 (niida2007specificroleof pages 1-2, chen2000implicationsforchk1 pages 1-2, chen2000implicationsforchk1 pages 8-9).
CHK1 phosphorylates all three human CDC25 isoforms, but CDC25A and CDC25C are the most clearly connected to replication and G2 checkpoints (chen2000implicationsforchk1 pages 8-9).
Thus, CHK1 does not itself phosphorylate DNA or repair lesions. Its core signaling action is to phosphorylate regulatory proteins—especially CDC25 phosphatases—thereby keeping CDK activity below the threshold that would trigger additional origin firing or premature mitosis.
CHK1 phosphorylates RAD51 Thr309, supporting homologous-recombination functions after replication stress. It also influences Cdc7/Cdc45 loading, TLK1 and PCNA ubiquitination, integrating origin control, fork management, and repair (melia2024thepotentialfor pages 4-6).
Chemical genetics validated KAP1/TRIM28 Ser473 as a DNA-damage-responsive CHK1/CHK2 site. Its phosphorylation was reduced by kinase inhibition or depletion, but it did not concentrate at laser-induced damage tracks, suggesting phosphorylation occurs away from the primary damage focus. Its precise physiological consequence remains unresolved, making it more secure as a pathway readout than as a fully understood functional output (blasius2011aphosphoproteomicscreen pages 9-11).
Other phosphoproteomic candidates include FEN1, RIF1, TICRR/Treslin and Ku70. These findings broaden the likely CHK1 network but require substrate-by-substrate validation (blasius2011aphosphoproteomicscreen pages 9-11).
Evidence qualification: Some literature assigns WEE1 phosphorylation directly to CHK1, but especially clear mechanistic evidence in the retrieved sources derives from Schizosaccharomyces pombe. It should not be presented uncritically as proof of an equivalent direct human reaction. In human cells, ATR–CHK1 and WEE1 clearly cooperate to maintain inhibitory CDK phosphorylation, regardless of whether every proposed edge is direct (tapiaalveal2009regulationofchk1 pages 1-2, tapiaalveal2009regulationofchk1 pages 2-4).
CHK1 executes its principal functions intracellularly; it is neither secreted nor a membrane transporter. It is predominantly associated with the nucleus, consistent with roles in DNA replication, chromatin signaling and cell-cycle control. Human structural literature called it a nuclear protein, while mammalian phosphosite-mutant studies showed dynamic distribution between nucleus and cytoplasm (niida2007specificroleof pages 1-2, chen2000implicationsforchk1 pages 1-2).
Localization is regulated rather than static:
Functionally, CHK1 therefore acts at replication-associated nuclear/chromatin compartments and, after activation or redistribution, on nucleoplasmic, cytoplasmic and centrosomal targets.
CHK1’s most precise pathway assignment is the ATR–CHK1 arm of the DNA-damage response. Stalled forks or processed lesions expose single-stranded DNA, ATR activates CHK1, and CHK1 reduces CDK activity through CDC25 inhibition. This suppresses late or dormant origin firing, stabilizes replication intermediates, permits repair or restart, and prevents entry into mitosis with incompletely replicated DNA (melia2024thepotentialfor pages 4-6, sorensen2012safeguardinggenomeintegrity pages 6-6, kciuk2026targetingatrchk1and pages 2-5).
CHK1 is active during unperturbed S phase as well as after exogenous damage. Its loss causes excessive origin firing, replication-fork abandonment or cleavage, γH2AX accumulation and cell death. This explains why mammalian CHK1 is essential and why complete inhibition has a narrow therapeutic window (sorensen2012safeguardinggenomeintegrity pages 6-6, blasius2011aphosphoproteomicscreen pages 1-2).
By inhibiting CDC25C and sustaining inhibitory CDK1 phosphorylation, CHK1 prevents premature mitosis. This gives cells time to finish replication and repair damage. CHK1 inhibition can consequently produce mitotic catastrophe when damaged cells are forced through G2/M (melia2024thepotentialfor pages 4-6, chen2000implicationsforchk1 pages 1-2).
RAD51 regulation and fork stabilization connect CHK1 to homologous recombination. Inhibiting CHK1 can impair HR, destabilize forks, and sensitize tumors to PARP inhibitors or replication-stressing chemotherapy (melia2024thepotentialfor pages 4-6, xu2024chk1inhibitorsra737 pages 1-2).
CHK1 is required for mammalian cellular viability and early development. This is biologically consistent with a kinase that protects every S phase, but it also predicts on-target toxicity in rapidly dividing normal tissues (blasius2011aphosphoproteomicscreen pages 1-2). Human genetic evidence further links CHEK1 dysfunction to early embryonic/zygotic arrest, although database association scores should be interpreted as aggregated evidence rather than proof of a broad clinical syndrome (OpenTargets Search: -CHEK1).
Cancer cells frequently carry TP53, RB1, ATM or other defects that weaken the G1 checkpoint. Oncogene activation—including MYC, RAS/KRAS or CCNE1 amplification—also creates high replication stress. Such cells can become unusually dependent on the remaining ATR–CHK1–WEE1 pathway to survive S phase and avoid catastrophic DNA breakage (hannaway2022theinvestigationof pages 74-81, khamidullina2024keyproteinsof pages 12-13, sorensen2012safeguardinggenomeintegrity pages 6-6).
CHK1 inhibitors can kill cells by at least three related mechanisms:
Experts increasingly regard “high replication stress” as mechanistically important but insufficiently precise as a clinical biomarker. TP53 status alone is inconsistent, and recent studies favor composite or context-specific markers such as CCNE1 amplification, PARP-inhibitor resistance, replication-gene expression, or ecDNA (sorensen2012safeguardinggenomeintegrity pages 6-6, giudice2024thechk1inhibitor pages 1-2, xu2024chk1inhibitorsra737 pages 1-2, tang2024enhancingtranscription–replicationconflict pages 1-2).
The 2023 phase I/II study of oral SRA737, NCT02797964, treated 107 patients with advanced cancers. The maximum tolerated dose was 1,000 mg daily and the recommended phase II dose was 800 mg daily. No complete or partial responses occurred. Stable-disease control lasting at least four cycles ranged from 33.3% in colorectal cancer to 75% in a very small head-and-neck cohort. Any-grade diarrhea, nausea and vomiting occurred in 63%, 60% and 46%; grade ≥3 neutropenia occurred in 8% at the recommended dose or higher. The investigators concluded that single-agent activity did not justify continued monotherapy development and favored combinations. Two ischemic cardiac events and one marked ejection-fraction decrease meant that cardiac risk could not be excluded (published April 2023; DOI: https://doi.org/10.1038/s41416-023-02279-x) (kristeleit2023aphase12 pages 6-7).
A 2023 phase I/II study enrolled 143 patients; 77 received at least 500 mg SRA737 with 250 mg/m² gemcitabine. The recommended regimen was SRA737 500 mg plus low-dose gemcitabine 250 mg/m². Overall response rate was 10.8%, rising to 25% in anogenital cancer. At the recommended dose, grade ≥3 anemia, neutropenia and thrombocytopenia occurred in 11.7%, 16.7% and 10%, respectively. The combination exploits gemcitabine-mediated dNTP depletion and fork stalling while removing CHK1-mediated protection (published November 2023; DOI: https://doi.org/10.1158/1078-0432.CCR-22-2074) (jones2023aphaseiii pages 1-2).
A 2024 phase II analysis of NCT02203513 enrolled 49 heavily pretreated, BRCA-wild-type, platinum-resistant recurrent high-grade serous ovarian carcinoma patients; 39 were RECIST-evaluable. Overall response rate was 30.8%, with cohort-specific rates of 33.3% and 28.6%. Median progression-free survival was 4 and 6 months, respectively. The study stopped early because of COVID-19 and loss of investigational-drug supply, so the planned primary analysis was incomplete. High pretreatment expression of POLA1, POLE and GINS3 was associated post hoc with PFS below six months, and POLA1 silencing sensitized cell models to CHK1 inhibition. These are hypothesis-generating—not validated—resistance biomarkers (published March 2024; DOI: https://doi.org/10.1038/s41467-024-47215-6) (giudice2024thechk1inhibitor pages 1-2).
Prexasertib is a dual CHK1/CHK2 inhibitor rather than a perfectly CHK1-selective probe. Reviews describe stabilization of CDC25A, increased replication stress and replication catastrophe as principal effects; hematologic toxicity, especially neutropenia, has repeatedly limited dosing (khamidullina2024keyproteinsof pages 12-13, bouberhan2023theevolvingrole pages 5-7).
A July 2024 iScience study found that SRA737 monotherapy prolonged survival in CCNE1-amplified ovarian-cancer models, while SRA737 plus PARP inhibition increased regression in PARP-inhibitor-resistant and CCNE1-amplified patient-derived xenografts. Mechanistically, CHK1 inhibition increased replication stress, destabilized forks and impaired HR. Approximately 20% of HGSOCs are CCNE1-amplified, while roughly 50% have defective HR repair, defining clinically meaningful candidate populations. These results remain preclinical (DOI: https://doi.org/10.1016/j.isci.2024.109978) (xu2024chk1inhibitorsra737 pages 1-2).
A November 2024 Nature study showed that oncogene-bearing extrachromosomal DNA undergoes pervasive transcription, slower replication and elevated transcription–replication conflicts. ecDNA-positive tumors displayed increased ssDNA-associated signaling, double-strand breaks and CHK1 activation. Genetic CHK1 loss or pharmacological inhibition preferentially killed ecDNA-positive cells. The oral inhibitor BBI-2779 suppressed growth and prevented ecDNA-mediated resistance to the FGFR inhibitor infigratinib in an FGFR2-ecDNA gastric-cancer mouse model, producing sustained regression. This is a compelling mechanism-based biomarker concept, but no clinical efficacy or human safety has yet been established in the cited study (DOI: https://doi.org/10.1038/s41586-024-07802-5) (tang2024enhancingtranscription–replicationconflict pages 1-2).
The established application of CHEK1 today is primarily as:
The reviewed 2023–2024 evidence does not establish CHK1 inhibition as routine standard-of-care therapy. Trials of prexasertib and SRA737 have generally remained phase I/II, and several completed or terminated without regulatory adoption. Thus, “real-world implementation” is presently clinical-trial participation, translational biomarker testing and preclinical combination development—not routine prescribing.
The most defensible current view is that CHK1 is a high-confidence mechanistic target but an incompletely translated therapeutic target. Unselected monotherapy has generally been weak, whereas rational combinations and tumors with demonstrable replication-stress dependencies show greater promise. Future trials should prospectively define the dependency state, confirm pharmacodynamic target engagement, and separate CHK1-specific effects from CHK2 or other kinase inhibition.
References
(tapiaalveal2009regulationofchk1 pages 1-2): Claudia Tapia-Alveal, Teresa M Calonge, and Matthew J O'Connell. Regulation of chk1. Cell Division, 4:8-8, Apr 2009. URL: https://doi.org/10.1186/1747-1028-4-8, doi:10.1186/1747-1028-4-8. This article has 125 citations and is from a peer-reviewed journal.
(chen2000implicationsforchk1 pages 1-2): Ping Chen, Chun Luo, Yali Deng, Kevin Ryan, James Register, Stephen Margosiak, Anna Tempczyk-Russell, Binh Nguyen, Pamela Myers, Karen Lundgren, Chen-Chen Kan, and Patrick M O'Connor. Implications for chk1 regulation: the 1.7 å crystal structure of human cell cycle checkpoint kinase chk1. Cell, 100:681-692, Mar 2000. URL: https://doi.org/10.1016/s0092-8674(00)80704-7, doi:10.1016/s0092-8674(00)80704-7. This article has 159 citations and is from a highest quality peer-reviewed journal.
(melia2024thepotentialfor pages 4-6): Emma Melia and Jason L. Parsons. The potential for targeting g2/m cell cycle checkpoint kinases in enhancing the efficacy of radiotherapy. Cancers, 16:3016, Aug 2024. URL: https://doi.org/10.3390/cancers16173016, doi:10.3390/cancers16173016. This article has 18 citations.
(sorensen2012safeguardinggenomeintegrity pages 6-6): C. S. Sorensen and R. G. Syljuasen. Safeguarding genome integrity: the checkpoint kinases atr, chk1 and wee1 restrain cdk activity during normal dna replication. Nucleic Acids Research, 40:477-486, Sep 2012. URL: https://doi.org/10.1093/nar/gkr697, doi:10.1093/nar/gkr697. This article has 401 citations and is from a highest quality peer-reviewed journal.
(blasius2011aphosphoproteomicscreen pages 1-2): Melanie Blasius, Josep V Forment, Neha Thakkar, Sebastian A Wagner, Chunaram Choudhary, and Stephen P Jackson. A phospho-proteomic screen identifies substrates of the checkpoint kinase chk1. Genome Biology, 12:R78-R78, Aug 2011. URL: https://doi.org/10.1186/gb-2011-12-8-r78, doi:10.1186/gb-2011-12-8-r78. This article has 182 citations and is from a highest quality peer-reviewed journal.
(kristeleit2023aphase12 pages 6-7): Rebecca Kristeleit, Ruth Plummer, Robert Jones, Louise Carter, Sarah Blagden, Debashis Sarker, Tobias Arkenau, Thomas R. Jeffry Evans, Sarah Danson, Stefan N. Symeonides, Gareth J. Veal, Barbara J. Klencke, Mark M. Kowalski, and Udai Banerji. A phase 1/2 trial of sra737 (a chk1 inhibitor) administered orally in patients with advanced cancer. British Journal of Cancer, 129:38-45, Apr 2023. URL: https://doi.org/10.1038/s41416-023-02279-x, doi:10.1038/s41416-023-02279-x. This article has 49 citations and is from a domain leading peer-reviewed journal.
(jones2023aphaseiii pages 1-2): Robert Jones, Ruth Plummer, Victor Moreno, Louise Carter, Desamparados Roda, Elena Garralda, Rebecca Kristeleit, Debashis Sarker, Tobias Arkenau, Patricia Roxburgh, Harriet S. Walter, Sarah Blagden, Alan Anthoney, Barbara J. Klencke, Mark M. Kowalski, and Udai Banerji. A phase i/ii trial of oral sra737 (a chk1 inhibitor) given in combination with low-dose gemcitabine in patients with advanced cancer. Clinical Cancer Research, 29:331-340, Nov 2023. URL: https://doi.org/10.1158/1078-0432.ccr-22-2074, doi:10.1158/1078-0432.ccr-22-2074. This article has 53 citations and is from a highest quality peer-reviewed journal.
(giudice2024thechk1inhibitor pages 1-2): Elena Giudice, Tzu-Ting Huang, Jayakumar R. Nair, Grant Zurcher, Ann McCoy, Darryl Nousome, Marc R. Radke, Elizabeth M. Swisher, Stanley Lipkowitz, Kristen Ibanez, Duncan Donohue, Tyler Malys, Min-Jung Lee, Bernadette Redd, Elliot Levy, Shraddha Rastogi, Nahoko Sato, Jane B. Trepel, and Jung-Min Lee. The chk1 inhibitor prexasertib in brca wild-type platinum-resistant recurrent high-grade serous ovarian carcinoma: a phase 2 trial. Nature Communications, Mar 2024. URL: https://doi.org/10.1038/s41467-024-47215-6, doi:10.1038/s41467-024-47215-6. This article has 55 citations and is from a highest quality peer-reviewed journal.
(xu2024chk1inhibitorsra737 pages 1-2): Haineng Xu, Sarah B. Gitto, Gwo-Yaw Ho, Sergey Medvedev, Kristy Shield-Artin, Hyoung Kim, Sally Beard, Yasuto Kinose, Xiaolei Wang, Holly E. Barker, Gayanie Ratnayake, Wei-Ting Hwang, Ryan J. Hansen, Bryan Strouse, Snezana Milutinovic, Christian Hassig, Matthew J. Wakefield, Cassandra J. Vandenberg, Clare L. Scott, and Fiona Simpkins. Chk1 inhibitor sra737 is active in parp inhibitor resistant and ccne1 amplified ovarian cancer. Jul 2024. URL: https://doi.org/10.1016/j.isci.2024.109978, doi:10.1016/j.isci.2024.109978. This article has 11 citations and is from a peer-reviewed journal.
(tang2024enhancingtranscription–replicationconflict pages 1-2): Jun Tang, Natasha E. Weiser, Guiping Wang, Sudhir Chowdhry, Ellis J. Curtis, Yanding Zhao, Ivy Tsz-Lo Wong, Georgi K. Marinov, Rui Li, Philip Hanoian, Edison Tse, Salvador Garcia Mojica, Ryan Hansen, Joshua Plum, Auzon Steffy, Snezana Milutinovic, S. Todd Meyer, Jens Luebeck, Yanbo Wang, Shu Zhang, Nicolas Altemose, Christina Curtis, William J. Greenleaf, Vineet Bafna, Stephen J. Benkovic, Anthony B. Pinkerton, Shailaja Kasibhatla, Christian A. Hassig, Paul S. Mischel, and Howard Y. Chang. Enhancing transcription–replication conflict targets ecdna-positive cancers. Nov 2024. URL: https://doi.org/10.1038/s41586-024-07802-5, doi:10.1038/s41586-024-07802-5. This article has 136 citations and is from a highest quality peer-reviewed journal.
(chen2000implicationsforchk1 pages 8-9): Ping Chen, Chun Luo, Yali Deng, Kevin Ryan, James Register, Stephen Margosiak, Anna Tempczyk-Russell, Binh Nguyen, Pamela Myers, Karen Lundgren, Chen-Chen Kan, and Patrick M O'Connor. Implications for chk1 regulation: the 1.7 å crystal structure of human cell cycle checkpoint kinase chk1. Cell, 100:681-692, Mar 2000. URL: https://doi.org/10.1016/s0092-8674(00)80704-7, doi:10.1016/s0092-8674(00)80704-7. This article has 159 citations and is from a highest quality peer-reviewed journal.
(blasius2011aphosphoproteomicscreen pages 2-4): Melanie Blasius, Josep V Forment, Neha Thakkar, Sebastian A Wagner, Chunaram Choudhary, and Stephen P Jackson. A phospho-proteomic screen identifies substrates of the checkpoint kinase chk1. Genome Biology, 12:R78-R78, Aug 2011. URL: https://doi.org/10.1186/gb-2011-12-8-r78, doi:10.1186/gb-2011-12-8-r78. This article has 182 citations and is from a highest quality peer-reviewed journal.
(blasius2011aphosphoproteomicscreen pages 9-11): Melanie Blasius, Josep V Forment, Neha Thakkar, Sebastian A Wagner, Chunaram Choudhary, and Stephen P Jackson. A phospho-proteomic screen identifies substrates of the checkpoint kinase chk1. Genome Biology, 12:R78-R78, Aug 2011. URL: https://doi.org/10.1186/gb-2011-12-8-r78, doi:10.1186/gb-2011-12-8-r78. This article has 182 citations and is from a highest quality peer-reviewed journal.
(niida2007specificroleof pages 1-2): Hiroyuki Niida, Yuko Katsuno, Birendranath Banerjee, M. Prakash Hande, and Makoto Nakanishi. Specific role of chk1 phosphorylations in cell survival and checkpoint activation. Apr 2007. URL: https://doi.org/10.1128/mcb.01611-06, doi:10.1128/mcb.01611-06. This article has 225 citations and is from a domain leading peer-reviewed journal.
(khamidullina2024keyproteinsof pages 12-13): Alvina I. Khamidullina, Yaroslav E. Abramenko, Alexandra V. Bruter, and Victor V. Tatarskiy. Key proteins of replication stress response and cell cycle control as cancer therapy targets. International Journal of Molecular Sciences, 25:1263, Jan 2024. URL: https://doi.org/10.3390/ijms25021263, doi:10.3390/ijms25021263. This article has 78 citations.
(kciuk2026targetingatrchk1and pages 2-5): Mateusz Kciuk, Katarzyna Wanke, Beata Marciniak, Damian Kołat, Marta Aleksandrowicz, Somdutt Mujwar, Tarik Ainane, and Renata Kontek. Targeting atr-chk1 and atm-chk2 axes in pancreatic cancer—a comprehensive review of literature. International Journal of Molecular Sciences, 27:1152, Jan 2026. URL: https://doi.org/10.3390/ijms27031152, doi:10.3390/ijms27031152. This article has 7 citations.
(tapiaalveal2009regulationofchk1 pages 2-4): Claudia Tapia-Alveal, Teresa M Calonge, and Matthew J O'Connell. Regulation of chk1. Cell Division, 4:8-8, Apr 2009. URL: https://doi.org/10.1186/1747-1028-4-8, doi:10.1186/1747-1028-4-8. This article has 125 citations and is from a peer-reviewed journal.
(OpenTargets Search: -CHEK1): Open Targets Query (-CHEK1, 5 results). Buniello, A. et al. (2025). Open Targets Platform: facilitating therapeutic hypotheses building in drug discovery. Nucleic Acids Research.
(hannaway2022theinvestigationof pages 74-81): NL Hannaway. The investigation of circulating biomarkers and potential mechanisms of resistance in the atr/chk1 signalling pathway in response to chk1 inhibitor therapy. Unknown journal, 2022.
(bouberhan2023theevolvingrole pages 5-7): Sara Bouberhan, Liron Bar-Peled, Yusuke Matoba, Varvara Mazina, Lauren Philp, and Bo R. Rueda. The evolving role of dna damage response in overcoming therapeutic resistance in ovarian cancer. Cancer Drug Resistance, 6:345-357, Jun 2023. URL: https://doi.org/10.20517/cdr.2022.146, doi:10.20517/cdr.2022.146. This article has 12 citations.