Regulation of the human WEE1Hu CDK tyrosine 15-kinase during the cell cycle

The Role of Radiosensitizing Drugs in Osteosarcoma Treatment: Mechanisms and Clinical Perspectives

Osteosarcoma is a highly malignant bone tumor that is resistant to radiotherapy and is associated with poor treatment outcomes and prognoses. Understanding the mechanisms of radioresistance and finding strategies to enhance the radiosensitivity is crucial for improving clinical efficacy. The aim of this review was to address the approaches for enhancing the efficacy of radiotherapy in osteosarcoma, thereby improving patient outcomes. Specifically, we have focused on the mechanisms of radiosensitization and the relationship between drugs that enhance radiosensitivity and cancer. These mechanisms involve a delay in DNA damage repair, promotion of apoptosis, inhibition of angiogenesis, and regulation of the tumor microenvironment. In addition, we have summarized the effects of these drugs on the proliferation, migration, invasion and apoptosis of osteosarcoma cell lines. Finally, we have discussed the therapeutic effects and adverse reactions of these drugs in other cancers, providing valuable guidance for clinical treatment strategies tailored to patients with osteosarcoma.

Mechanism of RPA phosphocode priming and tuning by Cdk1/Wee1 signaling circuit

Replication protein A (RPA) is a heterotrimeric single-strand DNA binding protein that is integral to DNA metabolism. Segregation of RPA functions in response to DNA damage is fine-tuned by hyperphosphorylation of the RPA32 subunit that is dependent on Cyclin-dependent kinase (Cdk)-mediated priming phosphorylation at the Ser-23 and Ser-29 sites. However, the mechanism of priming-driven hyperphosphorylation of RPA remains unresolved. Furthermore, the modulation of cell cycle progression by the RPA-Cdk axis is not clearly understood. Here, we uncover that the RPA70 subunit is also phosphorylated by Cdk1 at Thr-191. This modification is crucial for the G2 to M phase transition. This function is enacted through reciprocal regulation of Cdk1 activity through a feedback circuit espoused by stabilization of Wee1 kinase. The Thr-191 phosphosite on RPA70 is also crucial for priming hyperphosphorylation of RPA32 in response to DNA damage. Structurally, phosphorylation by Cdk1 primes RPA by reconfiguring the domains to release the N-terminus of RPA32 and the two protein-interaction domains that markedly enhances the efficiency of multisite phosphorylation by other kinases. Our findings establish a unique phosphocode-dependent feedback mechanism between RPA and RPA-regulating kinases that is fine-tuned to enact bipartite functions in cell cycle progression and DNA damage response.

Effect of Sortilin1 on promoting angiogenesis and systemic metastasis in hepatocellular carcinoma via the Notch signaling pathway and CD133

Hepatocellular carcinoma (HCC) is known to be lethal disease. However, its prognosis remains poor, primarily because the precise oncogenic mechanisms underlying HCC progression remain elusive, thus hampering effective treatment. Here, we aimed to identify the potential oncogenes in HCC and elucidate the underlying mechanisms of their action. To identify potential candidate genes, an integrative analysis of eight publicly available genomic datasets was performed, and the functional implications of the identified genes were assessed in vitro and in vivo. Sortilin 1 (SORT1) was identified as a potential candidate oncogene in HCC, and its overexpression in HCC cells was confirmed by analyzing spatial transcriptomic and single-cell data. Silencing SORT1 in Huh-7 and Hep3B cells significantly reduced HCC progression in vitro and in vivo. Functional analyses of oncogenic pathways revealed that SORT1 expression regulated the Notch signaling pathway activation and CD133 expression. Furthermore, analysis of epigenetic regulation of the candidate gene and its clinical implications using The Cancer Genome Atlas Liver Hepatocellular Carcinoma (TCGA LIHC) and our HCC cohort (AJOU_HCC cohort) data demonstrated an inverse correlation between the methylation status of the SORT1 promoter region, specifically at the cg16988986 site, and SORT1 mRNA expression, indicating the epigenetic regulation of SORT1 in HCC. In addition, the distinct methylation status of cg16988986 was significantly associated with patient survival. In conclusion, SORT1 plays a pivotal role in HCC by activating the Notch signaling pathway and increasing CD133 expression. These findings suggest SORT1 as a promising therapeutic target for HCC.

Oxidative stress mediates nucleocytoplasmic shuttling of KPNA2 via AKT1-CDK1 axis-regulated S62 phosphorylation

Karyopherin α 2 (KPNA2, importin α1), a transport factor shuttling between the nuclear and cytoplasmic compartments, is involved in the nuclear import of proteins and participates in cellular processes such as cell cycle regulation, apoptosis, and transcriptional regulation. However, it is still unclear which signaling regulates the nucleocytoplasmic distribution of KPNA2 in response to cellular stress. In this study, we report that oxidative stress increases nuclear retention of KPNA2 through alpha serine/threonine-protein kinase (AKT1)-mediated reduction of serine 62 (S62) phosphorylation. We first found that AKT1 activation was required for H2O2-induced nuclear accumulation of KPNA2. Immunoprecipitation and quantitative proteomic analysis revealed that the phosphorylation of KPNA2 at S62 was decreased under H2O2-induced oxidative stress. We showed that cyclin-dependent kinase 1 (CDK1), a kinase responsible for KPNA2 S62 phosphorylation, contributes to the localization of KPNA2 in the cytoplasm. AKT1 knockdown increased KPNA2 S62 phosphorylation and inhibited CDK1 activation. Furthermore, H2O2-induced AKT1 activation promoted nuclear KPNA2 interaction with nucleophosmin 1 (NPM1), resulting in attenuation of NPM1-mediated cyclin D1 gene transcription. Thus, we infer that the AKT1-CDK1 axis regulates the nucleocytoplasmic shuttling and function of KPNA2 through spatiotemporal regulation of KPNA2 S62 phosphorylation under oxidative stress conditions.

Crosstalk among WEE1 Kinase, AKT, and GSK3 in Nav1.2 Channelosome Regulation

The signaling complex around voltage-gated sodium (Nav) channels includes accessory proteins and kinases crucial for regulating neuronal firing. Previous studies showed that one such kinase, WEE1-critical to the cell cycle-selectively modulates Nav1.2 channel activity through the accessory protein fibroblast growth factor 14 (FGF14). Here, we tested whether WEE1 exhibits crosstalk with the AKT/GSK3 kinase pathway for coordinated regulation of FGF14/Nav1.2 channel complex assembly and function. Using the in-cell split luciferase complementation assay (LCA), we found that the WEE1 inhibitor II and GSK3 inhibitor XIII reduce the FGF14/Nav1.2 complex formation, while the AKT inhibitor triciribine increases it. However, combining WEE1 inhibitor II with either one of the other two inhibitors abolished its effect on the FGF14/Nav1.2 complex formation. Whole-cell voltage-clamp recordings of sodium currents (INa) in HEK293 cells co-expressing Nav1.2 channels and FGF14-GFP showed that WEE1 inhibitor II significantly suppresses peak INa density, both alone and in the presence of triciribine or GSK3 inhibitor XIII, despite the latter inhibitor's opposite effects on INa. Additionally, WEE1 inhibitor II slowed the tau of fast inactivation and caused depolarizing shifts in the voltage dependence of activation and inactivation. These phenotypes either prevailed or were additive when combined with triciribine but were outcompeted when both WEE1 inhibitor II and GSK3 inhibitor XIII were present. Concerted regulation by WEE1 inhibitor II, triciribine, and GSK3 inhibitor XIII was also observed in long-term inactivation and use dependency of Nav1.2 currents. Overall, these findings suggest a complex role for WEE1 kinase-in concert with the AKT/GSK3 pathway-in regulating the Nav1.2 channelosome.

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.

Homologous recombination proficient subtypes of high-grade serous ovarian cancer: treatment options for a poor prognosis group

Approximately 50% of tubo-ovarian high-grade serous carcinomas (HGSCs) have functional homologous recombination-mediated (HR) DNA repair, so-called HR-proficient tumors, which are often associated with primary platinum resistance (relapse within six months after completion of first-line therapy), minimal benefit from poly(ADP-ribose) polymerase (PARP) inhibitors, and shorter survival. HR-proficient tumors comprise multiple molecular subtypes including cases with CCNE1 amplification, AKT2 amplification or CDK12 alteration, and are often characterized as "cold" tumors with fewer infiltrating lymphocytes and decreased expression of PD-1/PD-L1. Several new treatment approaches aim to manipulate these negative prognostic features and render HR-proficient tumors more susceptible to treatment. Alterations in multiple different molecules and pathways in the DNA damage response are driving new drug development to target HR-proficient cancer cells, such as inhibitors of the CDK or P13K/AKT pathways, as well as ATR inhibitors. Treatment combinations with chemotherapy or PARP inhibitors and agents targeting DNA replication stress have shown promising preclinical and clinical results. New approaches in immunotherapy are also being explored, including vaccines or antibody drug conjugates. Many approaches are still in the early stages of development and further clinical trials will determine their clinical relevance. There is a need to include HR-proficient tumors in ovarian cancer trials and to analyze them in a more targeted manner to provide further evidence for their specific therapy, as this will be crucial in improving the overall prognosis of HGSC and ovarian cancer in general.

Mechanistic insights into DNA damage recognition and checkpoint control in plants

The plant DNA damage response (DDR) pathway safeguards genomic integrity by rapid recognition and repair of DNA lesions that, if unrepaired, may cause genome instability. Most frequently, DNA repair goes hand in hand with a transient cell cycle arrest, which allows cells to repair the DNA lesions before engaging in a mitotic event, but consequently also affects plant growth and yield. Through the identification of DDR proteins and cell cycle regulators that react to DNA double-strand breaks or replication defects, it has become clear that these proteins and regulators form highly interconnected networks. These networks operate at both the transcriptional and post-transcriptional levels and include liquid-liquid phase separation and epigenetic mechanisms. Strikingly, whereas the upstream DDR sensors and signalling components are well conserved across eukaryotes, some of the more downstream effectors are diverged in plants, probably to suit unique lifestyle features. Additionally, DDR components display functional diversity across ancient plant species, dicots and monocots. The observed resistance of DDR mutants towards aluminium toxicity, phosphate limitation and seed ageing indicates that gaining knowledge about the plant DDR may offer solutions to combat the effects of climate change and the associated risk for food security.

Comprehensive multi-omics analysis reveals WEE1 as a synergistic lethal target with hyperthermia through CDK1 super-activation

Hyperthermic intraperitoneal chemotherapy's role in ovarian cancer remains controversial, hindered by limited understanding of hyperthermia-induced tumor cellular changes. This limits developing potent combinatory strategies anchored in hyperthermic intraperitoneal therapy (HIPET). Here, we perform a comprehensive multi-omics study on ovarian cancer cells under hyperthermia, unveiling a distinct molecular panorama, primarily characterized by rapid protein phosphorylation changes. Based on the phospho-signature, we pinpoint CDK1 kinase is hyperactivated during hyperthermia, influencing the global signaling landscape. We observe dynamic, reversible CDK1 activity, causing replication arrest and early mitotic entry post-hyperthermia. Subsequent drug screening shows WEE1 inhibition synergistically destroys cancer cells with hyperthermia. An in-house developed miniaturized device confirms hyperthermia and WEE1 inhibitor combination significantly reduces tumors in vivo. These findings offer additional insights into HIPET, detailing molecular mechanisms of hyperthermia and identifying precise drug combinations for targeted treatment. This research propels the concept of precise hyperthermic intraperitoneal therapy, highlighting its potential against ovarian cancer.

Phase I/II Study of the WEE1 Inhibitor Adavosertib (AZD1775) in Combination with Carboplatin in Children with Advanced Malignancies: Arm C of the AcSé-ESMART Trial

PURPOSE

AcSé-ESMART Arm C aimed to define the recommended dose and activity of the WEE1 inhibitor adavosertib in combination with carboplatin in children and young adults with molecularly enriched recurrent/refractory malignancies.

PATIENTS AND METHODS

Adavosertib was administered orally, twice every day on Days 1 to 3 and carboplatin intravenously on Day 1 of a 21-day cycle, starting at 100 mg/m2/dose and AUC 5, respectively. Patients were enriched for molecular alterations in cell cycle and/or homologous recombination (HR).

RESULTS

Twenty patients (median age: 14.0 years; range: 3.4-23.5) were included; 18 received 69 treatment cycles. Dose-limiting toxicities were prolonged grade 4 neutropenia and grade 3/4 thrombocytopenia requiring transfusions, leading to two de-escalations to adavosertib 75 mg/m2/dose and carboplatin AUC 4; no recommended phase II dose was defined. Main treatment-related toxicities were hematologic and gastrointestinal. Adavosertib exposure in children was equivalent to that in adults; both doses achieved the cell kill target. Overall response rate was 11% (95% confidence interval, 0.0-25.6) with partial responses in 2 patients with neuroblastoma. One patient with medulloblastoma experienced unconfirmed partial response and 5 patients had stable disease beyond four cycles. Seven of these eight patients with clinical benefit had alterations in HR, replication stress, and/or RAS pathway genes with or without TP53 alterations, whereas TP53 pathway alterations alone (8/10) or no relevant alterations (2/10) were present in the 10 patients without benefit.

CONCLUSIONS

Adavosertib-carboplatin combination exhibited significant hematologic toxicity. Activity signals and identified potential biomarkers suggest further studies with less hematotoxic DNA-damaging therapy in molecularly enriched pediatric cancers.

Drug-Resistant Epithelial Ovarian Cancer: Current and Future Perspectives

Epithelial ovarian cancer (EOC) is a complex disease with diverse histological subtypes, which, based on the aggressiveness and course of disease progression, have recently been broadly grouped into type I (low-grade serous, endometrioid, clear cell, and mucinous) and type II (high-grade serous, high-grade endometrioid, and undifferentiated carcinomas) categories. Despite substantial differences in pathogenesis, genetics, prognosis, and treatment response, clinical diagnosis and management of EOC remain similar across the subtypes. Debulking surgery combined with platinum-taxol-based chemotherapy serves as the initial treatment for High Grade Serous Ovarian Carcinoma (HGSOC), the most prevalent one, and for other subtypes, but most patients exhibit intrinsic or acquired resistance and recur in short duration. Targeted therapies, such as anti-angiogenics (e.g., bevacizumab) and PARP inhibitors (for BRCA-mutated cancers), offer some success, but therapy resistance, through various mechanisms, poses a significant challenge. This comprehensive chapter delves into emerging strategies to address these challenges, highlighting factors like aberrant miRNAs, metabolism, apoptosis evasion, cancer stem cells, and autophagy, which play pivotal roles in mediating resistance and disease relapse in EOC. Beyond standard treatments, the focus of this study extends to alternate targeted agents, including immunotherapies like checkpoint inhibitors, CAR T cells, and vaccines, as well as inhibitors targeting key oncogenic pathways in EOC. Additionally, this chapter covers disease classification, diagnosis, resistance pathways, standard treatments, and clinical data on various emerging approaches, and advocates for a nuanced and personalized approach tailored to individual subtypes and resistance mechanisms, aiming to enhance therapeutic outcomes across the spectrum of EOC subtypes.

Combined inhibition of Wee1 and Chk1 as a therapeutic strategy in multiple myeloma

Multiple myeloma (MM) is a hematological malignancy characterized by an abnormal clonal proliferation of malignant plasma cells. Despite the introduction of novel agents that have significantly improved clinical outcome, most patients relapse and develop drug resistance. MM is characterized by genomic instability and a high level of replicative stress. In response to replicative and DNA damage stress, MM cells activate various DNA damage signaling pathways. In this study, we reported that high CHK1 and WEE1 expression is associated with poor outcome in independent cohorts of MM patients treated with high dose melphalan chemotherapy or anti-CD38 immunotherapy. Combined targeting of Chk1 and Wee1 demonstrates synergistic toxicities on MM cells and was associated with higher DNA double-strand break induction, as evidenced by an increased percentage of γH2AX positive cells subsequently leading to apoptosis. The therapeutic interest of Chk1/Wee1 inhibitors' combination was validated on primary MM cells of patients. The toxicity was specific of MM cells since normal bone marrow cells were not significantly affected. Using deconvolution approach, MM patients with high CHK1 expression exhibited a significant lower percentage of NK cells whereas patients with high WEE1 expression displayed a significant higher percentage of regulatory T cells in the bone marrow. These data emphasize that MM cell adaptation to replicative stress through Wee1 and Chk1 upregulation may decrease the activation of the cell-intrinsic innate immune response. Our study suggests that association of Chk1 and Wee1 inhibitors may represent a promising therapeutic approach in high-risk MM patients characterized by high CHK1 and WEE1 expression.

Synthetic lethal interaction between WEE1 and PKMYT1 is a target for multiple low-dose treatment of high-grade serous ovarian carcinoma

Ovarian cancer is driven by genetic alterations that necessitate protective DNA damage and replication stress responses through cell cycle control and genome maintenance. This creates specific vulnerabilities that may be exploited therapeutically. WEE1 kinase is a key cell cycle control kinase, and it has emerged as a promising cancer therapy target. However, adverse effects have limited its clinical progress, especially when tested in combination with chemotherapies. A strong genetic interaction between WEE1 and PKMYT1 led us to hypothesize that a multiple low-dose approach utilizing joint WEE1 and PKMYT1 inhibition would allow exploitation of the synthetic lethality. We found that the combination of WEE1 and PKMYT1 inhibition exhibited synergistic effects in eradicating ovarian cancer cells and organoid models at a low dose. The WEE1 and PKMYT1 inhibition synergistically promoted CDK activation. Furthermore, the combined treatment exacerbated DNA replication stress and replication catastrophe, leading to increase of the genomic instability and inflammatory STAT1 signalling activation. These findings suggest a new multiple low-dose approach to harness the potency of WEE1 inhibition through the synthetic lethal interaction with PKMYT1 that may contribute to the development of new treatments for ovarian cancer.

Understanding DNA Damage Response and DNA Repair in Multiple Myeloma

Multiple myeloma (MM) is a plasma cell malignancy characterized by several genetic abnormalities, including chromosomal translocations, genomic deletions and gains, and point mutations. DNA damage response (DDR) and DNA repair mechanisms are altered in MM to allow for tumor development, progression, and resistance to therapies. Damaged DNA rarely induces an apoptotic response, given the presence of ataxia-telangiectasia mutated (ATM) loss-of-function or mutations, as well as deletions, mutations, or downregulation of tumor protein p53 (TP53) and tumor protein p73 (TP73). Moreover, DNA repair mechanisms are either hyperactive or defective to allow for rapid correction of the damage or permissive survival. Medications used to treat patients with MM can induce DNA damage, by either direct effects (mono-adducts induced by melphalan), or as a result of reactive oxygen species (ROS) production by proteasome inhibitors such as bortezomib. In this review, we will describe the mechanisms of DDR and DNA repair in normal tissues, the contribution of these pathways to MM disease progression and other phenotypes, and the potential therapeutic opportunities for patients with MM.

Dynamic regulatory phosphorylation of mouse CDK2 occurs during meiotic prophase I

During prophase I of meiosis, DNA double-strand breaks form throughout the genome, with a subset repairing as crossover events, enabling the accurate segregation of homologous chromosomes during the first meiotic division. The mechanism by which DSBs become selected to repair as crossovers is unknown, although the crossover positioning and levels in each cell indicate it is a highly regulated process. One of the proteins that localises to crossover sites is the serine/threonine cyclin-dependent kinase CDK2. Regulation of CDK2 occurs via phosphorylation at tyrosine 15 (Y15) and threonine 160 (T160) inhibiting and activating the kinase, respectively. In this study we use a combination of immunofluorescence staining on spread spermatocytes and fixed testis sections, and STA-PUT gravitational sedimentation to isolate cells at different developmental stages to further investigate the temporal phospho regulation of CDK2 during prophase I. Western blotting reveals differential levels of the two CDK2 isoforms (CDK233kDa and CDK239kDa) throughout prophase I, with inhibitory phosphorylation of CDK2 at Y15 occurring early in prophase I, localising to telomeres and diminishing as cells enter pachynema. Conversely, the activatory phosphorylation on T160 occurs later, specifically the CDK233kDa isoform, and T160 signal is detected in spermatogonia and pachytene spermatocytes, where it co-localises with the Class I crossover protein MLH3. Taken together, our data reveals intricate control of CDK2 both with regards to levels of the two CDK2 isoforms, and differential regulation via inhibitory and activatory phosphorylation.

Synthetic and Medicinal Chemistry Approaches Toward WEE1 Kinase Inhibitors and Its Degraders

WEE1 is a checkpoint kinase critical for mitotic events, especially in cell maturation and DNA repair. Most cancer cells' progression and survival are linked with elevated levels of WEE1 kinase. Thus, WEE1 kinase has become a new promising druggable target. A few classes of WEE1 inhibitors are designed by rationale or structure-based techniques and optimization approaches to identify selective acting anticancer agents. The discovery of the WEE1 inhibitor AZD1775 further emphasized WEE1 as a promising anticancer target. Therefore, the current review provides a comprehensive data on medicinal chemistry, synthetic approaches, optimization methods, and the interaction profile of WEE1 kinase inhibitors. In addition, WEE1 PROTAC degraders and their synthetic procedures, including a list of noncoding RNAs necessary for regulation of WEE1, are also highlighted. From the standpoint of medicinal chemistry, the contents of this compilation serve as an exemplar for the further design, synthesis, and optimization of promising WEE1-targeted anticancer agents.

A phase Ib study of adavosertib, a selective Wee1 inhibitor, in patients with locally advanced or metastatic solid tumors

Adavosertib selectively inhibits Wee1, which regulates intra-S and G2/M cell-cycle checkpoints. This study investigated dosing schedules for adavosertib monotherapy, determining the maximum tolerated dose (MTD) and recommended Phase II dose (RP2D) in patients with advanced solid tumors.Patients received oral adavosertib qd or bid on a 5/9 schedule (5 days on treatment, 9 days off) in 14-day cycles, or qd on one of two 5/2 schedules (weekly, or for 2 of 3 weeks) in 21-day cycles. Safety, efficacy, and pharmacokinetic analyses were performed.Sixty-two patients (female, 64.5%; median age, 61.5 years; most common primary tumors: lung [24.2%], ovary [21.0%]) received treatment (qd schedules, n = 50; bid schedules, n = 12) for 1.8 months (median). Median time to maximum adavosertib concentration was 2.2-4.1 h; mean half-life was 5-12 h. Adverse events (AEs) caused dose reductions, interruptions and discontinuations in 17 (27.4%), 25 (40.3%) and 4 (6.5%) patients, respectively. Most common grade ≥ 3 AEs were anemia, neutropenia (each n = 9, 14.5%) and diarrhea (n = 8, 12.9%). Seven (11.3%) patients experienced 10 treatment-related serious AEs (pneumonia n = 2 [3.2%], dehydration n = 2 [3.2%], anemia n = 1 [1.6%], febrile neutropenia n = 1 [1.6%], and thrombocytopenia n = 1 [1.6%]). Overall objective response rate was 3.4% (2/58); disease control rate was 48.4% (30/62); median progression-free survival was 2.7 months.MTDs were 125 mg (bid 5/9) and 300 mg (qd 5/9 and 5/2 for 2 of 3 weeks); RP2D was 300 mg (qd 5/2 for 2 of 3 weeks). The safety profile was manageable, acceptable, and generally concordant with the known safety profile.

Genetic Regulation of Mitosis-Meiosis Fate Decision in Plants: Is Callose an Oversighted Polysaccharide in These Processes?

Timely progression of the meiotic cell cycle and synchronized establishment of male meiosis in anthers are key to ascertaining plant fertility. With the discovery of novel regulators of the plant cell cycle, the mechanisms underlying meiosis initiation and progression appear to be more complex than previously thought, requiring the conjunctive action of cyclins, cyclin-dependent kinases, transcription factors, protein-protein interactions, and several signaling components. Broadly, cell cycle regulators can be classified into two categories in plants based on the nature of their mutational effects: (1) those that completely arrest cell cycle progression; and (2) those that affect the timing (delay or accelerate) or synchrony of cell cycle progression but somehow complete the division process. Especially the latter effects reflect evasion or obstruction of major steps in the meiosis but have sometimes been overlooked due to their subtle phenotypes. In addition to meiotic regulators, very few signaling compounds have been discovered in plants to date. In this review, we discuss the current state of knowledge about genetic mechanisms to enter the meiotic processes, referred to as the mitosis-meiosis fate decision, as well as the importance of callose (β-1,3 glucan), which has been unsung for a long time in male meiosis in plants.

Maize CDKA2;1a and CDKB1;1 kinases have different requirements for their activation and participate in substrate recognition

Cyclin-dependent kinases (CDKs), in association with cyclins, control cell cycle progression by phosphorylating a large number of substrates. In animals, activation of CDKs regularly requires both the association with a cyclin and then phosphorylation of a highly conserved threonine residue in the CDK activation loop (the classical mechanism), mediated by a CDK-activating kinase (CAK). In addition to this typical mechanism of activation, some CDKs can also be activated by the association of a cyclin to a monomeric CDK previously phosphorylated by CAK although not all CDKs can be activated by this mechanism. In animals and yeast, cyclin, in addition to being required for CDK activation, provides substrate specificity to the cyclin/CDK complex; however, in plants both the mechanisms of CDKs activation and the relevance of the CDK-associated cyclin for substrate targeting have been poorly studied. In this work, by co-expressing proteins in E. coli, we studied maize CDKA2;1a and CDKB1;1, two of the main types of CDKs that control the cell cycle in plants. These kinases could be activated by the classical mechanism and by the association of CycD2;2a to a phosphorylated intermediate in its activation loop, a previously unproven mechanism for the activation of plant CDKs. Unlike CDKA2;1a, CDKB1;1 did not require CAK for its activation, since it autophosphorylated in its activation loop. Phosphorylation of CDKB1;1 and association of CycD2;2 was not enough for its full activation as association of maize CKS, a scaffolding protein, differentially stimulated substrate phosphorylation. Our results suggest that both CDKs participate in substrate recognition.

SIRT1 deacetylates WEE1 and sensitizes cancer cells to WEE1 inhibition

The cell-cycle checkpoint kinase WEE1 is emerging as a therapeutic target for cancer treatment. However, how its catalytic activity is regulated remains poorly understood, and reliable biomarkers for predicting response to WEE1 inhibitor remain to be identified. Here we identify an evolutionarily conserved segment surrounding its Lys177 residue that inhibits WEE1 activity through an intermolecular interaction with the catalytic kinase domain. Upon DNA damage, CHK1-dependent phosphorylation of WEE1 at Ser642 primes GCN5-mediated acetylation at Lys177, resulting in dissociation of the inhibitory segment from the kinase domain and subsequent activation of WEE1 and cell-cycle checkpoints. Conversely, SIRT1 associates with and deacetylates WEE1, which maintains it in an inactive state. Consequently, SIRT1 deficiency induces WEE1 hyperacetylation and activation, rendering cancer cells resistant to WEE1 inhibition. These results suggest that SIRT1 expression level and abundance of WEE1 Lys177 acetylation in tumor cells can serve as useful biomarkers for predicting WEE1 inhibitor sensitivity or resistance.

Modeling the Circadian Control of the Cell Cycle and Its Consequences for Cancer Chronotherapy

The mammalian cell cycle is governed by a network of cyclin/Cdk complexes which signal the progression into the successive phases of the cell division cycle. Once coupled to the circadian clock, this network produces oscillations with a 24 h period such that the progression into each phase of the cell cycle is synchronized to the day-night cycle. Here, we use a computational model for the circadian clock control of the cell cycle to investigate the entrainment in a population of cells characterized by some variability in the kinetic parameters. Our numerical simulations showed that successful entrainment and synchronization are only possible with a sufficient circadian amplitude and an autonomous period close to 24 h. Cellular heterogeneity, however, introduces some variability in the entrainment phase of the cells. Many cancer cells have a disrupted clock or compromised clock control. In these conditions, the cell cycle runs independently of the circadian clock, leading to a lack of synchronization of cancer cells. When the coupling is weak, entrainment is largely impacted, but cells maintain a tendency to divide at specific times of day. These differential entrainment features between healthy and cancer cells can be exploited to optimize the timing of anti-cancer drug administration in order to minimize their toxicity and to maximize their efficacy. We then used our model to simulate such chronotherapeutic treatments and to predict the optimal timing for anti-cancer drugs targeting specific phases of the cell cycle. Although qualitative, the model highlights the need to better characterize cellular heterogeneity and synchronization in cell populations as well as their consequences for circadian entrainment in order to design successful chronopharmacological protocols.

A hybrid deep forest-based method for predicting synergistic drug combinations

Combination therapy is a promising approach in treating multiple complex diseases. However, the large search space of available drug combinations exacerbates challenge for experimental screening. To predict synergistic drug combinations in different cancer cell lines, we propose an improved deep forest-based method, ForSyn, and design two forest types embedded in ForSyn. ForSyn handles imbalanced and high-dimensional data in medium-/small-scale datasets, which are inherent characteristics of drug combination datasets. Compared with 12 state-of-the-art methods, ForSyn ranks first on four metrics for eight datasets with different feature combinations. We conduct a systematic analysis to identify the most appropriate configuration parameters. We validate the predictive value of ForSyn with cell-based experiments on several previously unexplored drug combinations. Finally, a systematic analysis of feature importance is performed on the top contributing features extracted by ForSyn. The resulting key genes may play key roles on corresponding cancers.

PBRM1, SETD2 and BAP1 - the trinity of 3p in clear cell renal cell carcinoma

Biallelic inactivation of the tumour suppressor gene Von Hippel-Lindau (VHL) occurs in the vast majority of clear cell renal cell carcinoma (ccRCC) instances, disrupting cellular oxygen-sensing mechanisms to yield a state of persistent pseudo-hypoxia, defined as a continued hypoxic response despite the presence of adequate oxygen levels. However, loss of VHL alone is often insufficient to drive oncogenesis. Results from genomic studies have shown that co-deletions of VHL with one (or more) of three genes encoding proteins involved in chromatin modification and remodelling, polybromo-1 gene (PBRM1), BRCA1-associated protein 1 (BAP1) and SET domain-containing 2 (SETD2), are common and important co-drivers of tumorigenesis. These genes are all located near VHL on chromosome 3p and are often altered following cytogenetic rearrangements that lead to 3p loss and precede the establishment of ccRCC. These three proteins have multiple roles in the regulation of crucial cancer-related pathways, including protection of genomic stability, antagonism of polycomb group (PcG) complexes to maintain a permissive transcriptional landscape in physiological conditions, and regulation of genes that mediate responses to immune checkpoint inhibitor therapy. An improved understanding of these mechanisms will bring new insights regarding cellular drivers of ccRCC growth and therapy response and, ultimately, will support the development of novel translational therapeutics.

Temporal phosphoproteomics reveals WEE1-dependent control of 53BP1 pathway

Wee1-like protein kinase (WEE1) restrains activities of cyclin-dependent kinases (CDKs) in S and G2 phase. Inhibition of WEE1 evokes drastic increase in CDK activity, which perturbs replication dynamics and compromises cell cycle checkpoints. Notably, WEE1 inhibitors such as adavosertib are tested in cancer treatment trials; however, WEE1-regulated phosphoproteomes and their dynamics have not been systematically investigated. In this study, we identified acute time-resolved alterations in the cellular phosphoproteome following WEE1 inhibition with adavosertib. These treatments acutely elevated CDK activities with distinct phosphorylation dynamics revealing more than 600 potential uncharacterized CDK sites. Moreover, we identified a major role for WEE1 in controlling CDK-dependent phosphorylation of multiple clustered sites in the key DNA repair factors MDC1, 53BP1, and RIF1. Functional analysis revealed that WEE1 fine-tunes CDK activities to permit recruitment of 53BP1 to chromatin. Thus, our findings uncover WEE1-controlled targets and pathways with translational potential for the clinical application of WEE1 inhibitors.

DNA Damage Response in Cancer Therapy and Resistance: Challenges and Opportunities

Resistance to chemo- and radiotherapy is a common event among cancer patients and a reason why new cancer therapies and therapeutic strategies need to be in continuous investigation and development. DNA damage response (DDR) comprises several pathways that eliminate DNA damage to maintain genomic stability and integrity, but different types of cancers are associated with DDR machinery defects. Many improvements have been made in recent years, providing several drugs and therapeutic strategies for cancer patients, including those targeting the DDR pathways. Currently, poly (ADP-ribose) polymerase inhibitors (PARP inhibitors) are the DDR inhibitors (DDRi) approved for several cancers, including breast, ovarian, pancreatic, and prostate cancer. However, PARPi resistance is a growing issue in clinical settings that increases disease relapse and aggravate patients' prognosis. Additionally, resistance to other DDRi is also being found and investigated. The resistance mechanisms to DDRi include reversion mutations, epigenetic modification, stabilization of the replication fork, and increased drug efflux. This review highlights the DDR pathways in cancer therapy, its role in the resistance to conventional treatments, and its exploitation for anticancer treatment. Biomarkers of treatment response, combination strategies with other anticancer agents, resistance mechanisms, and liabilities of treatment with DDR inhibitors are also discussed.

Exploring the genetic space of the DNA damage response for cancer therapy through CRISPR-based screens

The concepts of synthetic lethality and viability have emerged as powerful approaches to identify vulnerabilities and resistances within the DNA damage response for the treatment of cancer. Historically, interactions between two genes have had a longstanding presence in genetics and have been identified through forward genetic screens that rely on the molecular basis of the characterized phenotypes, typically caused by mutations in single genes. While such complex genetic interactions between genes have been studied extensively in model organisms, they have only recently been prioritized as therapeutic strategies due to technological advancements in genetic screens. Here, we discuss synthetic lethal and viable interactions within the DNA damage response and present how CRISPR-based genetic screens and chemical compounds have allowed for the systematic identification and targeting of such interactions for the treatment of cancer.

Revisiting the multisite phosphorylation that produces the M-phase supershift of key mitotic regulators

The term M-phase supershift denotes the phosphorylation-dependent substantial increase in the apparent molecular weight of numerous proteins of varied biological functions during M-phase induction. Although the M-phase supershift of multiple key mitotic regulators has been attributed to the multisite phosphorylation catalyzed by the Cdk1/cyclin B/Cks complex, this view is challenged by multiple lines of paradoxical observations. To solve this problem, we reconstituted the M-phase supershift of Xenopus Cdc25C, Myt1, Wee1A, APC3, and Greatwall in Xenopus egg extracts and characterized the supershift-producing phosphorylations. Our results demonstrate that their M-phase supershifts are each due to simultaneous phosphorylation of a considerable portion of S/T/Y residues in a long intrinsically disordered region that is enriched in both S/T residues and S/TP motifs. Although the major mitotic kinases in Xenopus egg extracts, Cdk1, MAPK, Plx1, and RSK2, are able to phosphorylate the five mitotic regulators, they are neither sufficient nor required to produce the M-phase supershift. Accordingly, inhibition of the four major mitotic kinase activities in Xenopus oocytes did not inhibit the M-phase supershift in okadaic acid-induced oocyte maturation. These findings indicate that the M-phase supershift is produced by a previously unrecognized category of mitotic phosphorylation that likely plays important roles in M-phase induction.

Hypoxia-induced GLT8D1 promotes glioma stem cell maintenance by inhibiting CD133 degradation through N-linked glycosylation

Gliomas are the most aggressive primary brain tumors. However, no significant improvement in survival has been achieved with the addition of temozolomide (TMZ) or radiation as initial therapy, although many clinical efforts have been carried out to target various signaling pathways or putative driver mutations. Here, we report that glycosyltransferase 8 domain containing 1 (GLT8D1), induced by HIF-1α under a hypoxic niche, significantly correlates with a higher grade of glioma, and a worse clinical outcome. Depletion of GLT8D1 inhibits self-renewal of glioma stem cell (GSC) in vitro and represses tumor growth in glioma mouse models. GLT8D1 knockdown promotes cell cycle arrest at G2/M phase and cellular apoptosis with or without TMZ treatment. We reveal that GLT8D1 impedes CD133 degradation through the endosomal-lysosomal pathway by N-linked glycosylation and protein-protein interaction. Directly blocking the GLT8D1/CD133 complex formation by CD133N1~108 (referred to as FECD133), or inhibiting GLT8D1 expression by lercanidipine, suppresses Wnt/β-catenin signaling dependent tumorigenesis both in vitro and in patient-derived xenografts mouse model. Collectively, these findings offer mechanistic insights into how hypoxia promotes GLT8D1/CD133/Wnt/β-catenin signaling during glioma progression, and identify GLT8D1 as a potential therapeutic target in the future.

Combined evaluation of both WEE1 and phosphorylated cyclin dependent kinase 1 expressions in oral squamous cell carcinomas predicts cancer recurrence and progression

Background/purpose

Materials and methods

Results

Conclusion

Targeting WEE1/AKT restores p53-dependent NK cell activation to induce immune checkpoint blockade responses in 'cold' melanoma

Immunotherapy has revolutionized cancer treatment. Unfortunately, most tumor types do not respond to immunotherapy due to a lack of immune infiltration or 'cold' tumor microenvironment (TME), a contributing factor in treatment failure. Activation of the p53 pathway can increase apoptosis of cancer cells, leading to enhanced antigen presentation, and can stimulate natural killer (NK) cells through expression of stress ligands. Therefore, modulation of the p53 pathway in cancer cells with wildtype TP53 has the potential to enhance tumor immunogenicity to NK cells, produce an inflammatory TME, and ultimately lead to tumor regression. In this study, we report simultaneous targeting of the AKT/WEE1 pathways is a novel and tolerable approach to synergistically induce p53 activation to inhibit tumor development. This approach reduced the growth of melanoma cells and induced plasma membrane surface localization of the ER-resident protein calreticulin, an indicator of immunogenic cell death (ICD). Increase in ICD led to enhanced expression of stress ligands recognized by the activating NK cell receptor NKG2D, promoting tumor lysis. WEE1/AKT inhibition resulted in recruitment and activation of immune cells, including NK cells, in the TME, triggering an inflammatory cascade that transformed the 'cold' TME of B16F10 melanoma into a 'hot' TME that responded to anti-PD-1, resulting in complete regression of established tumors. These results suggest that AKT/WEE1 pathway inhibition is a potential approach to broaden the utility of class-leading anti-PD-1 therapies by enhancing p53-mediated, NK cell-dependent tumor inflammation and supports the translation of this novel approach to further improve response rates for metastatic melanoma.

The expanding role of WEE1

Upon DNA damage, complex transduction cascades are unleashed to locate, recognise and repair affected lesions. The process triggers a pause in the cell cycle until the damage is resolved. Even under physiologic conditions, this deliberate interruption of cell division is essential to ensure orderly DNA replication and chromosomal segregation. WEE1 is an established regulatory protein in this vast fidelity-monitoring machinery. Its involvement in the DNA damage response and cell cycle has been a subject of study for decades. Emerging studies have also implicated WEE1 directly and indirectly in other cellular functions, including chromatin remodelling and immune response. The expanding role of WEE1 in pathophysiology is matched by the keen surge of interest in developing WEE1-targeted therapeutic agents. This review summarises WEE1 involvement in the cell cycle checkpoints, epigenetic modification and immune signalling, as well as the current state of WEE1 inhibitors in cancer therapeutics.

An enhanced cascade-based deep forest model for drug combination prediction

Combination therapy has shown an obvious curative effect on complex diseases, whereas the search space of drug combinations is too large to be validated experimentally even with high-throughput screens. With the increase of the number of drugs, artificial intelligence techniques, especially machine learning methods, have become applicable for the discovery of synergistic drug combinations to significantly reduce the experimental workload. In this study, in order to predict novel synergistic drug combinations in various cancer cell lines, the cell line-specific drug-induced gene expression profile (GP) is added as a new feature type to capture the cellular response of drugs and reveal the biological mechanism of synergistic effect. Then, an enhanced cascade-based deep forest regressor (EC-DFR) is innovatively presented to apply the new small-scale drug combination dataset involving chemical, physical and biological (GP) properties of drugs and cells. Verified by the dataset, EC-DFR outperforms two state-of-the-art deep neural network-based methods and several advanced classical machine learning algorithms. Biological experimental validation performed subsequently on a set of previously untested drug combinations further confirms the performance of EC-DFR. What is more prominent is that EC-DFR can distinguish the most important features, making it more interpretable. By evaluating the contribution of each feature type, GP feature contributes 82.40%, showing the cellular responses of drugs may play crucial roles in synergism prediction. The analysis based on the top contributing genes in GP further demonstrates some potential relationships between the transcriptomic levels of key genes under drug regulation and the synergism of drug combinations.

Cancer-Related Intracellular Signalling Pathways Activated by DOXorubicin/Cyclodextrin-Graphene-Based Nanomaterials

In the last decade, nanotechnological progress has generated new opportunities to improve the safety and efficacy of conventional anticancer therapies. Compared with other carriers, graphene nanoplatforms possess numerous tunable functionalities for the loading of multiple bioactive compounds, although their biocompatibility is still a debated concern. Recently, we have investigated the modulation of genes involved in cancer-associated canonical pathways induced by graphene engineered with cyclodextrins (GCD). Here, we investigated the GCD impact on cells safety, the HEp-2 responsiveness to Doxorubicin (DOX) and the cancer-related intracellular signalling pathways modulated by over time exposure to DOX loaded on GCD (GCD@DOX). Our studies evidenced that both DOX and GCD@DOX induced p53 and p21 signalling resulting in G0/G1 cell cycle arrest. A genotoxic behaviour of DOX was reported via detection of CDK (T14/Y15) activation and reduction of Wee-1 expression. Similarly, we found a cleavage of PARP by DOX within 72 h of exposure. Conversely, GCD@DOX induced a late cleavage of PARP, which could be indicative of less toxic effect due to controlled release of the drug from the GCD nanocarrier. Finally, the induction of the autophagy process supports the potential recycling of DOX with the consequent limitation of its toxic effects. Together, these findings demonstrate that GCD@DOX is a biocompatible drug delivery system able to evade chemoresistance and doxorubicin toxicity.

KIAA1429 is a potential prognostic marker in colorectal cancer by promoting the proliferation via downregulating WEE1 expression in an m6A-independent manner

N6-methyladenosine (m6A), the most abundant mRNA modification in mammals, is involved in the metabolism of mRNA. KIAA1429 is regarded as the largest m6A methyltransferase and plays an important role in m6A modification. However, the prognostic value and function of KIAA1429 in colorectal cancer (CRC) are unclear. Quantitative real-time PCR and immunohistochemical assays were performed to evaluate the expression of KIAA1429 in CRC tissues. Kaplan-Meier survival curves and log-rank tests were used to assess the association between KIAA1429 expression and the prognosis of patients with CRC. CCK-8 assays, colony formation assays, cell cycle assays, and xenograft experiments were performed to investigate the effect of KIAA1429 on cell proliferation. RNA immunoprecipitation, methylated RNA immunoprecipitation assays, and RNA stability assays were conducted to explore the underlying mechanism. KIAA1429 was significantly upregulated in CRC tissues compared with adjacent normal tissues. Patients with higher expression of KIAA1429 had shorter overall survival than those with lower expression. Functionally, KIAA1429 promoted CRC cell proliferation in vitro and in vivo. Mechanistically, KIAA1429 negatively regulated the expression of WEE1 by decreasing its stability in an m6A-independent manner by binding to the third segment in the 3'-UTR of WEE1 mRNA. Moreover, butyrate decreased the expression of KIAA1429 by downregulating the level of the transcription factor NFκB1. Our findings indicated that KIAA1429 plays an oncogenic role in CRC cells by inhibiting the expression of WEE1 in an m6A-independent manner and is associated with poor survival in CRC patients. These results suggested that KIAA1429 might be a potential prognostic marker for CRC.

Two genes related to reproductive development in the juvenile prawn, Macrobrachium nipponense: Molecular characterization and transcriptional response to nanoplastic exposure

Plastic pollution in the form of nanoplastics poses a global threat to aquatic ecosystems and the organisms inhabiting them. However, few studies have been conducted on the effects of nanoplastic exposure on reproductive development in crustaceans. In order to address this issue, juvenile oriental river prawns (Macrobrachium nipponense) were exposed to different concentrations of 75-nm polystyrene nanoplastics (0, 5, 10, 20, 40 mg/L) for 28 days. In order to study the regulation of reproduction-related genes in the presence of nanoplastics, the Wee1 protein kinase gene (Wee1) and OTU domain ubiquitin aldehyde binding protein gene (OTUB) were selected. In this study, for the first time, the full-length cDNA of Mn-Wee1 and Mn-OTUB were cloned from M. nipponense. Homologous alignments revealed that Mn-Wee1 had a highly conserved function-critical sequence, and that Mn-OTUB was more closely related to OTUB1 than OTUB2. With increasing concentration of nanoplastics, the expression of both genes increased initially, then decreased. The inhibition of expression of Wee1 and OTUB occurred in 40 mg/L group, respectively. Analysis of the data also indicated that nanoplastic exposure might have differing effects on gene expression in M. nipponense male and female reproductive organs.

Wee1 Kinase: A Potential Target to Overcome Tumor Resistance to Therapy

During the cell cycle, DNA suffers several lesions that need to be repaired prior to entry into mitosis to preserve genome integrity in daughter cells. Toward this aim, cells have developed complex enzymatic machinery, the so-called DNA damage response (DDR), which is able to repair DNA, temporarily stopping the cell cycle to provide more time to repair, or if the damage is too severe, inducing apoptosis. This DDR mechanism is considered the main source of resistance to DNA-damaging therapeutic treatments in oncology. Recently, cancer stem cells (CSCs), which are a small subset of tumor cells, were identified as tumor-initiating cells. CSCs possess self-renewal potential and persistent tumorigenic capacity, allowing for tumor re-growth and relapse. Compared with cancer cells, CSCs are more resistant to therapeutic treatments. Wee1 is the principal gatekeeper for both G2/M and S-phase checkpoints, where it plays a key role in cell cycle regulation and DNA damage repair. From this perspective, Wee1 inhibition might increase the effectiveness of DNA-damaging treatments, such as radiotherapy, forcing tumor cells and CSCs to enter into mitosis, even with damaged DNA, leading to mitotic catastrophe and subsequent cell death.

Differential Effects of Combined ATR/WEE1 Inhibition in Cancer Cells

Simple Summary

Cancer cells often show elevated replication stress and loss of cell cycle checkpoints. The ataxia telangiectasia and Rad3-related (ATR) and WEE1 kinases play roles in protecting cancer cells from high replication stress and in regulating the remaining cell cycle checkpoints. Inhibitors of ATR or WEE1 therefore have the potential to selectively kill cancer cells and are currently being tested in clinical trials. However, more studies are needed to understand how these inhibitors work in various types of cancer and to find the most effective ways of using them. Here, we have explored whether simultaneous treatment with ATR and WEE1 inhibitors is a promising approach. Effects were investigated in cell lines from osteosarcoma and lung cancer. We expect our results to be of importance for future treatment strategies with these inhibitors.

Abstract

Inhibitors of WEE1 and ATR kinases are considered promising for cancer treatment, either as monotherapy or in combination with chemo- or radiotherapy. Here, we addressed whether simultaneous inhibition of WEE1 and ATR might be advantageous. Effects of the WEE1 inhibitor MK1775 and ATR inhibitor VE822 were investigated in U2OS osteosarcoma cells and in four lung cancer cell lines, H460, A549, H1975, and SW900, with different sensitivities to the WEE1 inhibitor. Despite the differences in cytotoxic effects, the WEE1 inhibitor reduced the inhibitory phosphorylation of CDK, leading to increased CDK activity accompanied by ATR activation in all cell lines. However, combining ATR inhibition with WEE1 inhibition could not fully compensate for cell resistance to the WEE1 inhibitor and reduced cell viability to a variable extent. The decreased cell viability upon the combined treatment correlated with a synergistic induction of DNA damage in S-phase in U2OS cells but not in the lung cancer cells. Moreover, less synergy was found between ATR and WEE1 inhibitors upon co-treatment with radiation, suggesting that single inhibitors may be preferable together with radiotherapy. Altogether, our results support that combining WEE1 and ATR inhibitors may be beneficial for cancer treatment in some cases, but also highlight that the effects vary between cancer cell lines.

A MYBL2 complex for RRM2 transactivation and the synthetic effect of MYBL2 knockdown with WEE1 inhibition against colorectal cancer

Ribonucleotide reductase (RR) is a unique enzyme for the reduction of NDPs to dNDPs, the building blocks for DNA synthesis and thus essential for cell proliferation. Pan-cancer profiling studies showed that RRM2, the small subunit M2 of RR, is abnormally overexpressed in multiple types of cancers; however, the underlying regulatory mechanisms in cancers are still unclear. In this study, through searching in cancer-omics databases and immunohistochemistry validation with clinical samples, we showed that the expression of MYBL2, a key oncogenic transcriptional factor, was significantly upregulated correlatively with RRM2 in colorectal cancer (CRC). Ectopic expression and knockdown experiments indicated that MYBL2 was essential for CRC cell proliferation, DNA synthesis, and cell cycle progression in an RRM2-dependent manner. Mechanistically, MYBL2 directly bound to the promoter of RRM2 gene and promoted its transcription during S-phase together with TAF15 and MuvB components. Notably, knockdown of MYBL2 sensitized CRC cells to treatment with MK-1775, a clinical trial drug for inhibition of WEE1, which is involved in a degradation pathway of RRM2. Finally, mouse xenograft experiments showed that the combined suppression of MYBL2 and WEE1 synergistically inhibited CRC growth with a low systemic toxicity in vivo. Therefore, we propose a new regulatory mechanism for RRM2 transcription for CRC proliferation, in which MYBL2 functions by constituting a dynamic S-phase transcription complex following the G1/early S-phase E2Fs complex. Doubly targeting the transcription and degradation machines of RRM2 could produce a synthetic inhibitory effect on RRM2 level with a novel potential for CRC treatment.

MYBL2 and ATM suppress replication stress in pluripotent stem cells

Replication stress, a major cause of genome instability in cycling cells, is mainly prevented by the ATR-dependent replication stress response pathway in somatic cells. However, the replication stress response pathway in embryonic stem cells (ESCs) may be different due to alterations in cell cycle phase length. The transcription factor MYBL2, which is implicated in cell cycle regulation, is expressed a hundred to a thousand-fold more in ESCs compared with somatic cells. Here we show that MYBL2 activates ATM and suppresses replication stress in ESCs. Consequently, loss of MYBL2 or inhibition of ATM or Mre11 in ESCs results in replication fork slowing, increased fork stalling and elevated origin firing. Additionally, we demonstrate that inhibition of CDC7 activity rescues replication stress induced by MYBL2 loss and ATM inhibition, suggesting that uncontrolled new origin firing may underlie the replication stress phenotype resulting from loss/inhibition of MYBL2 and ATM. Overall, our study proposes that in addition to ATR, a MYBL2-MRN-ATM replication stress response pathway functions in ESCs to control DNA replication initiation and prevent genome instability.

Expanding roles of cell cycle checkpoint inhibitors in radiation oncology

PURPOSE

Radiation-induced activation of cell cycle checkpoints have been of long-standing interest. The WEE1, CHK1 and ATR kinases are key factors in cell cycle checkpoint regulation and are essential for the S and G2 checkpoints. Here, we review the rationale for why inhibitors of WEE1, CHK1 and ATR could be beneficial in combination with radiation.

CONCLUSIONS

Combined treatment with radiation and inhibitors of these kinases results in checkpoint abrogation and subsequent mitotic catastrophe. This might selectively radiosensitize tumor cells, as they often lack the p53-dependent G1 checkpoint and therefore rely more on the G2 checkpoint to repair DNA damage. Further affecting the repair of radiation damage, inhibition of WEE1, CHK1 or ATR also specifically suppresses the homologous recombination repair pathway. Moreover, inhibition of these kinases can induce massive replication stress during S phase of the cell cycle, likely contributing to eliminate radioresistant S phase cells. Intriguingly, recent findings suggest that cell cycle checkpoint inhibitors in combination with radiation can also enhance anti-tumor immune effects. Altogether, the expanding knowledge about the functional roles of WEE1, CHK1 and ATR inhibitors support that they are promising candidates for use in combination with radiation treatment.

The ATR-WEE1 kinase module inhibits the MAC complex to regulate replication stress response

DNA damage response is a fundamental mechanism to maintain genome stability. The ATR-WEE1 kinase module plays a central role in response to replication stress. Although the ATR-WEE1 pathway has been well studied in yeasts and animals, how ATR-WEE1 functions in plants remains unclear. Through a genetic screen for suppressors of the Arabidopsis atr mutant, we found that loss of function of PRL1, a core subunit of the evolutionarily conserved MAC complex involved in alternative splicing, suppresses the hypersensitivity of atr and wee1 to replication stress. Biochemical studies revealed that WEE1 directly interacts with and phosphorylates PRL1 at Serine 145, which promotes PRL1 ubiquitination and subsequent degradation. In line with the genetic and biochemical data, replication stress induces intron retention of cell cycle genes including CYCD1;1 and CYCD3;1, which is abolished in wee1 but restored in wee1 prl1. Remarkably, co-expressing the coding sequences of CYCD1;1 and CYCD3;1 partially restores the root length and HU response in wee1 prl1. These data suggested that the ATR-WEE1 module inhibits the MAC complex to regulate replication stress responses. Our study discovered PRL1 or the MAC complex as a key downstream regulator of the ATR-WEE1 module and revealed a novel cell cycle control mechanism.

Clinical Candidates Targeting the ATR-CHK1-WEE1 Axis in Cancer

Selective killing of cancer cells while sparing healthy ones is the principle of the perfect cancer treatment and the primary aim of many oncologists, molecular biologists, and medicinal chemists. To achieve this goal, it is crucial to understand the molecular mechanisms that distinguish cancer cells from healthy ones. Accordingly, several clinical candidates that use particular mutations in cell-cycle progressions have been developed to kill cancer cells. As the majority of cancer cells have defects in G1 control, targeting the subsequent intra‑S or G2/M checkpoints has also been extensively pursued. This review focuses on clinical candidates that target the kinases involved in intra‑S and G2/M checkpoints, namely, ATR, CHK1, and WEE1 inhibitors. It provides insight into their current status and future perspectives for anticancer treatment. Overall, even though CHK1 inhibitors are still far from clinical establishment, promising accomplishments with ATR and WEE1 inhibitors in phase II trials present a positive outlook for patient survival.

Targeting multiple signaling pathways: the new approach to acute myeloid leukemia therapy

Acute myeloid leukemia (AML) is the most common form of acute leukemia in adults and the second most common form of acute leukemia in children. Despite this, very little improvement in survival rates has been achieved over the past few decades. This is partially due to the heterogeneity of AML and the need for more targeted therapeutics than the traditional cytotoxic chemotherapies that have been a mainstay in therapy for the past 50 years. In the past 20 years, research has been diversifying the approach to treating AML by investigating molecular pathways uniquely relevant to AML cell proliferation and survival. Here we review the development of novel therapeutics in targeting apoptosis, receptor tyrosine kinase (RTK) signaling, hedgehog (HH) pathway, mitochondrial function, DNA repair, and c-Myc signaling. There has been an impressive effort into better understanding the diversity of AML cell characteristics and here we highlight important preclinical studies that have supported therapeutic development and continue to promote new ways to target AML cells. In addition, we describe clinical investigations that have led to FDA approval of new targeted AML therapies and ongoing clinical trials of novel therapies targeting AML survival pathways. We also describe the complexity of targeting leukemia stem cells (LSCs) as an approach to addressing relapse and remission in AML and targetable pathways that are unique to LSC survival. This comprehensive review details what we currently understand about the signaling pathways that support AML cell survival and the exceptional ways in which we disrupt them.

Overexpression of Cyclin E1 or Cdc25A leads to replication stress, mitotic aberrancies, and increased sensitivity to replication checkpoint inhibitors

Oncogene-induced replication stress, for instance as a result of Cyclin E1 overexpression, causes genomic instability and has been linked to tumorigenesis. To survive high levels of replication stress, tumors depend on pathways to deal with these DNA lesions, which represent a therapeutically actionable vulnerability. We aimed to uncover the consequences of Cyclin E1 or Cdc25A overexpression on replication kinetics, mitotic progression, and the sensitivity to inhibitors of the WEE1 and ATR replication checkpoint kinases. We modeled oncogene-induced replication stress using inducible expression of Cyclin E1 or Cdc25A in non-transformed RPE-1 cells, either in a TP53 wild-type or TP53-mutant background. DNA fiber analysis showed Cyclin E1 or Cdc25A overexpression to slow replication speed. The resulting replication-derived DNA lesions were transmitted into mitosis causing chromosome segregation defects. Single cell sequencing revealed that replication stress and mitotic defects upon Cyclin E1 or Cdc25A overexpression resulted in genomic instability. ATR or WEE1 inhibition exacerbated the mitotic aberrancies induced by Cyclin E1 or Cdc25A overexpression, and caused cytotoxicity. Both these phenotypes were exacerbated upon p53 inactivation. Conversely, downregulation of Cyclin E1 rescued both replication kinetics, as well as sensitivity to ATR and WEE1 inhibitors. Taken together, Cyclin E1 or Cdc25A-induced replication stress leads to mitotic segregation defects and genomic instability. These mitotic defects are exacerbated by inhibition of ATR or WEE1 and therefore point to mitotic catastrophe as an underlying mechanism. Importantly, our data suggest that Cyclin E1 overexpression can be used to select patients for treatment with replication checkpoint inhibitors.

FUCCI Real-Time Cell-Cycle Imaging as a Guide for Designing Improved Cancer Therapy: A Review of Innovative Strategies to Target Quiescent Chemo-Resistant Cancer Cells

Simple Summary

Chemotherapy of solid tumors has made very slow progress over many decades. A major problem has been that solid tumors very often contain non-dividing cells due to lack of oxygen deep in the tumor and these non-dividing cells resist most currently-used chemotherapy which usually only targets dividing cells. The present review demonstrates how a unique imaging system, FUCCI, which color codes cells depending on whether they are in a dividing or non-dividing phase, is being used to design very novel therapy that targets non-dividing cancer cells which can greatly improve the efficacy of cancer chemotherapy.

Abstract

Progress in chemotherapy of solid cancer has been tragically slow due, in large part, to the chemoresistance of quiescent cancer cells in tumors. The fluorescence ubiquitination cell-cycle indicator (FUCCI) was developed in 2008 by Miyawaki et al., which color-codes the phases of the cell cycle in real-time. FUCCI utilizes genes linked to different color fluorescent reporters that are only expressed in specific phases of the cell cycle and can, thereby, image the phases of the cell cycle in real-time. Intravital real-time FUCCI imaging within tumors has demonstrated that an established tumor comprises a majority of quiescent cancer cells and a minor population of cycling cancer cells located at the tumor surface or in proximity to tumor blood vessels. In contrast to most cycling cancer cells, quiescent cancer cells are resistant to cytotoxic chemotherapy, most of which target cells in S/G₂/M phases. The quiescent cancer cells can re-enter the cell cycle after surviving treatment, which suggests the reason why most cytotoxic chemotherapy is often ineffective for solid cancers. Thus, quiescent cancer cells are a major impediment to effective cancer therapy. FUCCI imaging can be used to effectively target quiescent cancer cells within tumors. For example, we review how FUCCI imaging can help to identify cell-cycle-specific therapeutics that comprise decoy of quiescent cancer cells from G₁ phase to cycling phases, trapping the cancer cells in S/G₂ phase where cancer cells are mostly sensitive to cytotoxic chemotherapy and eradicating the cancer cells with cytotoxic chemotherapy most active against S/G₂ phase cells. FUCCI can readily image cell-cycle dynamics at the single cell level in real-time in vitro and in vivo. Therefore, visualizing cell cycle dynamics within tumors with FUCCI can provide a guide for many strategies to improve cell-cycle targeting therapy for solid cancers.

Improving the Efficacy of Tumor Radiosensitization Through Combined Molecular Targeting

Chemoradiation, either alone or in combination with surgery or induction chemotherapy, is the current standard of care for most locally advanced solid tumors. Though chemoradiation is usually performed at the maximum tolerated doses of both chemotherapy and radiation, current cure rates are not satisfactory for many tumor entities, since tumor heterogeneity and plasticity result in chemo- and radioresistance. Advances in the understanding of tumor biology, a rapidly growing number of molecular targeting agents and novel technologies enabling the in-depth characterization of individual tumors, have fuelled the hope of entering an era of precision oncology, where each tumor will be treated according to its individual characteristics and weaknesses. At present though, molecular targeting approaches in combination with radiotherapy or chemoradiation have not yet proven to be beneficial over standard chemoradiation treatment in the clinical setting. A promising approach to improve efficacy is the combined usage of two targeting agents in order to inhibit backup pathways or achieve a more complete pathway inhibition. Here we review preclinical attempts to utilize such dual targeting strategies for future tumor radiosensitization.

Wee1 Kinase Inhibitor AZD1775 Effectively Sensitizes Esophageal Cancer to Radiotherapy

PURPOSE

Esophageal cancer is a deadly malignancy with a 5-year survival rate of only 5% to 20%, which has remained unchanged for decades. Esophageal cancer possesses a high frequency of TP53 mutations leading to dysfunctional G1 cell-cycle checkpoint, which likely makes esophageal cancer cells highly reliant upon G2-M checkpoint for adaptation to DNA replication stress and DNA damage after radiation. We aim to explore whether targeting Wee1 kinase to abolish G2-M checkpoint sensitizes esophageal cancer cells to radiotherapy.

EXPERIMENTAL DESIGN

Cell viability was assessed by cytotoxicity and colony-forming assays, cell-cycle distribution was analyzed by flow cytometry, and mitotic catastrophe was assessed by immunofluorescence staining. Human esophageal cancer xenografts were generated to explore the radiosensitizing effect of AZD1775 in vivo.

RESULTS

The IC50 concentrations of AZD1775 on esophageal cancer cell lines were between 300 and 600 nmol/L. AZD1775 (100 nmol/L) as monotherapy did not alter the viability of esophageal cancer cells, but significantly radiosensitized esophageal cancer cells. AZD1775 significantly abrogated radiation-induced G2-M phase arrest and attenuation of p-CDK1-Y15. Moreover, AZD1775 increased radiation-induced mitotic catastrophe, which was accompanied by increased γH2AX levels, and subsequently reduced survival after radiation. Importantly, AZD1775 in combination with radiotherapy resulted in marked tumor regression of esophageal cancer tumor xenografts.

CONCLUSIONS

Abrogation of G2-M checkpoint by targeting Wee1 kinase with AZD1775 sensitizes esophageal cancer cells to radiotherapy in vitro and in mouse xenografts. Our findings suggest that inhibition of Wee1 by AZD1775 is an effective strategy for radiosensitization in esophageal cancer and warrants clinical testing.

PTEN and DNA-PK determine sensitivity and recovery in response to WEE1 inhibition in human breast cancer

Inhibition of WEE1 kinase by AZD1775 has shown promising results in clinical cancer trials, but markers predicting AZD1775 response are lacking. Here we analysed AZD1775 response in a panel of human breast cancer (BC) cell lines by global proteome/transcriptome profiling and identified two groups of basal-like BC (BLBCs): ‘PTEN low’ BLBCs were highly sensitive to AZD1775 and failed to recover following removal of AZD1775, while ‘PTEN high’ BLBCs recovered. AZD1775 induced phosphorylation of DNA-PK, protecting cells from replication-associated DNA damage and promoting cellular recovery. Deletion of DNA-PK or PTEN, or inhibition of DNA-PK sensitized recovering BLBCs to AZD1775 by abrogating replication arrest, allowing replication despite DNA damage. This was linked to reduced CHK1 activation, increased cyclin E levels and apoptosis. In conclusion, we identified PTEN and DNA-PK as essential regulators of replication checkpoint arrest in response to AZD1775 and defined PTEN as a promising biomarker for efficient WEE1 cancer therapy.

The impact of MCM6 on hepatocellular carcinoma in a Southern Chinese Zhuang population

Minichromosome maintenance complex component 6 (MCM6) is involved in tumorigenesis of hepatocellular carcinoma (HCC). Because its effect on different populations remains unclear, this study investigated the impact of MCM6 on HCC in Southern Chinese Zhuang population. In addition to assessing the global mRNA levels of MCM6 based on The Cancer Genome Atlas database (TCGA) and The Gene Expression Omnibus database (GEO), associations between MCM6 mRNA levels and clinicopathological features were analyzed. High MCM6 levels were associated with high alpha-fetoprotein (AFP) (>20 ng/mL in serum) (P < 0.0001) and advanced clinical stage (III + IV) (P < 0.001). Higher MCM6 was associated with poorer outcomes (P < 0.01) in these databases. Furthermore, the mRNA and protein expression of MCM6 in the Guangxi Zhuang population was detected by quantitative polymerase chain reaction (qPCR), western blot, and immunohistochemistry (IHC). The results showed that MCM6 levels were up-regulated in the Zhuang population with HCC. Higher MCM6 protein levels were correlated with larger tumor size (>5 cm) (P = 0.038) and advanced clinical stage (III + IV) (p = 0.023). Bioinformatic enrichment analysis of MCM6 and its interacting proteins (CDT1,WEE1,TRIM28 and MKI67) suggested that in addition to being involved in the cell cycle process, these complexes could also be involved in protein binding, pre-replication complex assemble, and nucleus metabolism. Based on the protein-protein interaction (PPI) network with module screen, the interactions between MCM6 and its potential interacting proteins were further studied through protein docking with hot spot analysis. Additionally, the results of the algorithms combining the ROC of MCM6 and its interacting proteins showed that combination biomarker analysis has better HCC diagnosis ability than the single MCM6 test. The combination of MCM6 and TRIM28 was more suitable for the Guangxi Zhuang population. Overall, our study suggests that MCM6 plays an important role in the growth of HCC. MCM6 could be an optimal biomarker for diagnosing HCC and a potential molecular target for HCC therapy in the Zhuang population.

The Roles of Cyclin-Dependent Kinases in Cell-Cycle Progression and Therapeutic Strategies in Human Breast Cancer

Cyclin-dependent kinases (CDKs) are serine/threonine kinases whose catalytic activities are regulated by interactions with cyclins and CDK inhibitors (CKIs). CDKs are key regulatory enzymes involved in cell proliferation through regulating cell-cycle checkpoints and transcriptional events in response to extracellular and intracellular signals. Not surprisingly, the dysregulation of CDKs is a hallmark of cancers, and inhibition of specific members is considered an attractive target in cancer therapy. In breast cancer (BC), dual CDK4/6 inhibitors, palbociclib, ribociclib, and abemaciclib, combined with other agents, were approved by the Food and Drug Administration (FDA) recently for the treatment of hormone receptor positive (HR+) advanced or metastatic breast cancer (A/MBC), as well as other sub-types of breast cancer. Furthermore, ongoing studies identified more selective CDK inhibitors as promising clinical targets. In this review, we focus on the roles of CDKs in driving cell-cycle progression, cell-cycle checkpoints, and transcriptional regulation, a highlight of dysregulated CDK activation in BC. We also discuss the most relevant CDK inhibitors currently in clinical BC trials, with special emphasis on CDK4/6 inhibitors used for the treatment of estrogen receptor-positive (ER+)/human epidermal growth factor 2-negative (HER2−) M/ABC patients, as well as more emerging precise therapeutic strategies, such as combination therapies and microRNA (miRNA) therapy.