Dual Targeting of WEE1 and PLK1 by AZD1775 Elicits Single Agent Cellular Anticancer Activity

New Horizons of Synthetic Lethality in Cancer: Current Development and Future Perspectives

In recent years, synthetic lethality has been recognized as a solid paradigm for anticancer therapies. The discovery of a growing number of synthetic lethal targets has led to a significant expansion in the use of synthetic lethality, far beyond poly(ADP-ribose) polymerase inhibitors used to treat BRCA1/2-defective tumors. In particular, molecular targets within DNA damage response have provided a source of inhibitors that have rapidly reached clinical trials. This Perspective focuses on the most recent progress in synthetic lethal targets and their inhibitors, within and beyond the DNA damage response, describing their design and associated therapeutic strategies. We will conclude by discussing the current challenges and new opportunities for this promising field of research, to stimulate discussion in the medicinal chemistry community, allowing the investigation of synthetic lethality to reach its full potential.

Small molecule agents for triple negative breast cancer: Current status and future prospects

Triple-negative breast cancer (TNBC) is a subtype of breast cancer with poor prognosis. The number of cases increased by 2.26 million in 2020, making it the most commonly diagnosed cancer type in the world. TNBCs lack hormone receptor (HR) and human epidermal growth factor 2 (HER2), which limits treatment options. Currently, paclitaxel-based drugs combined with other chemotherapeutics remain the main treatment for TNBC. There is currently no consensus on the best therapeutic regimen for TNBC. However, there have been successful clinical trials exploring large-molecule monoclonal antibodies, small-molecule targeted drugs, and novel antibody-drug conjugate (ADC). Although monoclonal antibodies have produced clinical success, their large molecular weight can limit therapeutic benefits. It is worth noting that in the past 30 years, the FDA has approved small molecule drugs for HER2-positive breast cancers. The lack of effective targets and the occurrence of drug resistance pose significant challenges in the treatment of TNBC. To improve the prognosis of TNBC, it is crucial to search for effective targets and to overcome drug resistance. This review examines the clinical efficacy, adverse effects, resistance mechanisms, and potential solutions of targeted small molecule drugs in both monotherapies and combination therapies. New therapeutic targets, including nuclear export protein 1 (XPO1) and hedgehog (Hh), are emerging as potential options for researchers and become integrated into clinical trials for TNBC. Additionally, there is growing interest in the potential of targeted protein degradation chimeras (PROTACs), degraders of rogue proteins, as a future therapy direction. This review provides potentially valuable insights with clinical implications.

Adavosertib and beyond: Biomarkers, drug combination and toxicity of WEE1 inhibitors

WEE1 kinase is renowned as an S-G2 checkpoint inhibitor activated by ATR-CHK1 in response to replication stress. WEE1 inhibition enhances replication stress and effectively circumvents checkpoints into mitosis, which triggers significant genetic impairs and culminates in cell death. This approach has been validated clinically for its promising anti-tumor efficacy across various cancer types, notably in cases of ovarian cancers. Nonetheless, the initial stage of clinical trials has shown that the first-in-human WEE1 inhibitor adavosertib is limited by dose-limiting adverse events. As a result, recent efforts have been made to explore predictive biomarkers and smart combination schedules to alleviate adverse effects. In this review, we focused on the exploration of therapeutic biomarkers, as well as schedules of combination utilizing WEE1 inhibitors and canonical anticancer drugs, according to the latest preclinical and clinical studies, indicating that the optimal application of WEE1 inhibitors will likely be as part of dose-reducing combination and be tailored to specific patient populations.

Combination of QSAR Modeling and Hybrid-Based Consensus Scoring to Identify Dual-Targeting Inhibitors of PLK1 and p38γ

Polo-like kinase 1 (PLK1) and p38γ mitogen-activated protein kinase (p38γ) play important roles in cancer pathogenesis by controlling cell cycle progression and are therefore attractive cancer targets. The design of multitarget inhibitors may offer synergistic inhibition of distinct targets and reduce the risk of drug-drug interactions to improve the balance between therapeutic efficacy and safety. We combined deep-learning-based quantitative structure-activity relationship (QSAR) modeling and hybrid-based consensus scoring to screen for inhibitors with potential activity against the targeted proteins. Using this combination strategy, we identified a potent PLK1 inhibitor (compound 4) that inhibited PLK1 activity and liver cancer cell growth in the nanomolar range. Next, we deployed both our QSAR models for PLK1 and p38γ on the Enamine compound library to identify dual-targeting inhibitors against PLK1 and p38γ. Likewise, the identified hits were subsequently subjected to hybrid-based consensus scoring. Using this method, we identified a promising compound (compound 14) that could inhibit both PLK1 and p38γ activities. At nanomolar concentrations, compound 14 inhibited the growth of human hepatocellular carcinoma and hepatoblastoma cells in vitro. This study demonstrates the combined screening strategy to identify novel potential inhibitors for existing targets.

Myt1 overexpression mediates resistance to cell cycle and DNA damage checkpoint kinase inhibitors

Cell cycle checkpoint kinases serve as important therapeutic targets for various cancers. When they are inhibited by small molecules, checkpoint abrogation can induce cell death or further sensitize cancer cells to other genotoxic therapies. Particularly aberrant Cdk1 activation at the G2/M checkpoint by kinase inhibitors causing unscheduled mitotic entry and mitotic arrest was found to lead to DNA damage and cell death selectively in cancer cells. Promising drugs inhibiting kinases like Wee1 (Adavosertib), Wee1+Myt1 (PD166285), ATR (AZD6738) and Chk1 (UCN-01) have been developed, but clinical data has shown variable efficacy for them with poorly understood mechanisms of resistance. Our lab recently identified Myt1 as a predictive biomarker of acquired resistance to the Wee1 kinase inhibitor, Adavosertib. Here, we investigate the role of Myt1 overexpression in promoting resistance to inhibitors (PD166285, UCN-01 and AZD6738) of other kinases regulating cell cycle progression. We demonstrate that Myt1 confers resistance by compensating Cdk1 inhibition in the presence of these different kinase inhibitors. Myt1 overexpression leads to reduced premature mitotic entry and decreased length of mitosis eventually leading to increased survival rates in Adavosertib treated cells. Elevated Myt1 levels also conferred resistance to inhibitors of ATR or Chk1 inhibitor. Our data supports that Myt1 overexpression is a common mechanism by which cancer cells can acquire resistance to a variety of drugs entering the clinic that aim to induce mitotic catastrophe by abrogating the G2/M checkpoint.

Double-strand DNA break repair: molecular mechanisms and therapeutic targets

Double-strand break (DSB), a significant DNA damage brought on by ionizing radiation, acts as an initiating signal in tumor radiotherapy, causing cancer cells death. The two primary pathways for DNA DSB repair in mammalian cells are nonhomologous end joining (NHEJ) and homologous recombination (HR), which cooperate and compete with one another to achieve effective repair. The DSB repair mechanism depends on numerous regulatory variables. DSB recognition and the recruitment of DNA repair components, for instance, depend on the MRE11-RAD50-NBS1 (MRN) complex and the Ku70/80 heterodimer/DNA-PKcs (DNA-PK) complex, whose control is crucial in determining the DSB repair pathway choice and efficiency of HR and NHEJ. In-depth elucidation on the DSB repair pathway's molecular mechanisms has greatly facilitated for creation of repair proteins or pathways-specific inhibitors to advance precise cancer therapy and boost the effectiveness of cancer radiotherapy. The architectures, roles, molecular processes, and inhibitors of significant target proteins in the DSB repair pathways are reviewed in this article. The strategy and application in cancer therapy are also discussed based on the advancement of inhibitors targeted DSB damage response and repair proteins.

Potential agnostic role of BRCA alterations in patients with several solid tumors: One for all, all for one?

Germline BRCA1/2 alterations in the Homologous Recombination (HR) pathway are considered as main susceptibility biomarkers to Hereditary Breast and Ovarian Cancers (HBOC). The modern molecular biology technologies allowed to characterize germline and somatic BRCA1/2 alterations in several malignancies, broadening the landscape of BRCA1/2-alterated tumors. In the last years, BRCA genetic testing, beyond the preventive value, also assumed a predictive and prognostic significance for patient management. The approval of molecules with agnostic indication is leading to a new clinical model, defined "mutational". Among these drugs, the Poly (ADP)-Ribose Polymerase inhibitors (PARPi) for BRCA1/2-deficient tumors were widely studied leading to increasing therapeutic implications. In this Review we provided an overview of the main clinical studies describing the association between BRCA-mutated tumors and PARPi response, focusing on the controversial evidence about the potential agnostic indication based on BRCA1/2 alterations in several solid tumors.

A new wave of innovations within the DNA damage response

Genome instability has been identified as one of the enabling hallmarks in cancer. DNA damage response (DDR) network is responsible for maintenance of genome integrity in cells. As cancer cells frequently carry DDR gene deficiencies or suffer from replicative stress, targeting DDR processes could induce excessive DNA damages (or unrepaired DNA) that eventually lead to cell death. Poly (ADP-ribose) polymerase (PARP) inhibitors have brought impressive benefit to patients with breast cancer gene (BRCA) mutation or homologous recombination deficiency (HRD), which proves the concept of synthetic lethality in cancer treatment. Moreover, the other two scenarios of DDR inhibitor application, replication stress and combination with chemo- or radio- therapy, are under active clinical exploration. In this review, we revisited the progress of DDR targeting therapy beyond the launched first-generation PARP inhibitors. Next generation PARP1 selective inhibitors, which could maintain the efficacy while mitigating side effects, may diversify the application scenarios of PARP inhibitor in clinic. Albeit with unavoidable on-mechanism toxicities, several small molecules targeting DNA damage checkpoints (gatekeepers) have shown great promise in preliminary clinical results, which may warrant further evaluations. In addition, inhibitors for other DNA repair pathways (caretakers) are also under active preclinical or clinical development. With these progresses and efforts, we envision that a new wave of innovations within DDR has come of age.

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.

Selective Wee1 Inhibitors Led to Antitumor Activity In Vitro and Correlated with Myelosuppression

Wee1 is a tyrosine kinase that is highly expressed in several cancer types. Wee1 inhibition can lead to suppression of tumor cell proliferation and sensitization of cells to the effects of DNA-damaging agents. AZD1775 is a nonselective Wee1 inhibitor for which myelosuppression has been observed as a dose-limiting toxicity. We have applied structure-based drug design (SBDD) to rapidly generate highly selective Wee1 inhibitors that demonstrate better selectivity than AZD1775 against PLK1, which is known to cause myelosuppression (including thrombocytopenia) when inhibited. While selective Wee1 inhibitors described herein still achieved in vitro antitumor efficacy, thrombocytopenia was still observed in vitro.

Development of Cell Permeable NanoBRET Probes for the Measurement of PLK1 Target Engagement in Live Cells

PLK1 is a protein kinase that regulates mitosis and is both an important oncology drug target and a potential antitarget of drugs for the DNA damage response pathway or anti-infective host kinases. To expand the range of live cell NanoBRET target engagement assays to include PLK1, we developed an energy transfer probe based on the anilino-tetrahydropteridine chemotype found in several selective PLK inhibitors. Probe 11 was used to configure NanoBRET target engagement assays for PLK1, PLK2, and PLK3 and measure the potency of several known PLK inhibitors. In-cell target engagement for PLK1 was in good agreement with the reported cellular potency for the inhibition of cell proliferation. Probe 11 enabled the investigation of the promiscuity of adavosertib, which had been described as a dual PLK1/WEE1 inhibitor in biochemical assays. Live cell target engagement analysis of adavosertib via NanoBRET demonstrated PLK activity at micromolar concentrations but only selective engagement of WEE1 at clinically relevant doses.

Development of Cell Permeable NanoBRET Probes for the Measurement of PLK1 Target Engagement in Live Cells

PLK1 is a protein kinase that regulates mitosis and is both an important oncology drug target and a potential anti target of drugs for the DNA damage response pathway or anti-infective host kinases. To expand the range of live cell NanoBRET target engagement assays to include PLK1 we developed an energy transfer probe based on the anilino-tetrahydropteridine chemotype found in several selective PLK inhibitors. Probe 11 was used to configure NanoBRET target engagement assays for PLK1, PLK2, and PLK3 and measure the potency of several known PLK inhibitors. In cell target engagement for PLK1 was in good agreement with the reported cellular potency for inhibition of cell proliferation. Probe 11 enabled investigation of the promiscuity of adavosertib, which had been described as a dual PLK1/WEE1 inhibitor in biochemical assays. Live cell target engagement analysis of adavosertib by NanoBRET demonstrated PLK activity at micromolar concentrations but only selective engagement of WEE1 at clinically relevant doses.

Combined Inhibition of IAPs and WEE1 Enhances TNFα- and Radiation-Induced Cell Death in Head and Neck Squamous Carcinoma

Head and neck squamous cell carcinoma (HNSCC) remains a prevalent diagnosis with current treatment options that include radiotherapy and immune-mediated therapies, in which tumor necrosis factor-α (TNFα) is a key mediator of cytotoxicity. However, HNSCC and other cancers often display TNFα resistance due to activation of the canonical IKK-NFκB/RELA pathway, which is activated by, and induces expression of, cellular inhibitors of apoptosis proteins (cIAPs). Our previous studies have demonstrated that the IAP inhibitor birinapant sensitized HNSCC to TNFα-dependent cell death in vitro and radiotherapy in vivo. Furthermore, we recently demonstrated that the inhibition of the G2/M checkpoint kinase WEE1 also sensitized HNSCC cells to TNFα-dependent cell death, due to the inhibition of the pro-survival IKK-NFκB/RELA complex. Given these observations, we hypothesized that dual-antagonist therapy targeting both IAP and WEE1 proteins may have the potential to synergistically sensitize HNSCC to TNFα-dependent cell death. Using the IAP inhibitor birinapant and the WEE1 inhibitor AZD1775, we show that combination treatment reduced cell viability, proliferation and survival when compared with individual treatment. Furthermore, combination treatment enhanced the sensitivity of HNSCC cells to TNFα-induced cytotoxicity via the induction of apoptosis and DNA damage. Additionally, birinapant and AZD1775 combination treatment decreased cell proliferation and survival in combination with radiotherapy, a critical source of TNFα. These results support further investigation of IAP and WEE1 inhibitor combinations in preclinical and clinical studies in HNSCC.

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.

Advances in the application of proteomics in lung cancer

Although the incidence and mortality of lung cancer have decreased significantly in the past decade, it is still one of the leading causes of death, which greatly impairs people’s life and health. Proteomics is an emerging technology that involves the application of techniques for identifying and quantifying the overall proteins in cells, tissues and organisms, and can be combined with genomics, transcriptomics to form a multi-omics research model. By comparing the content of proteins between normal and tumor tissues, proteomics can be applied to different clinical aspects like diagnosis, treatment, and prognosis, especially the exploration of disease biomarkers and therapeutic targets. The applications of proteomics have promoted the research on lung cancer. To figure out potential applications of proteomics associated with lung cancer, we summarized the role of proteomics in studies about tumorigenesis, diagnosis, prognosis, treatment and resistance of lung cancer in this review, which will provide guidance for more rational application of proteomics and potential therapeutic strategies of lung cancer.

Design, synthesis, and biological evaluation of Wee1 kinase degraders

Proteolysis targeting chimera (PROTAC) technology has received widespread attention in recent years as a promising strategy for drug development. Herein, we report a series of novel Wee1 degraders, which were designed and synthesized based on PROTAC technology by linking AZD1775 with CRBN ligands through linkers of different lengths and types. All degraders could effectively and completely degrade cellular Wee1 protein in MV-4-11 cell line at IC₅₀ concentrations. Preliminary assessments identified 42a as the most active degrader, which possessed potent antiproliferative activity and induced CRBN- and proteasome-dependent degradation of Wee1. Moreover, 42a also exhibited a time- and concentration-dependent depletion manner and inducing cell cycle arrest in G0/G1 phase and cancer cell apoptosis. More importantly, 42a showed acceptable in vitro and in vivo pharmacokinetic properties and displayed rapid and sustained Wee1 degradation ability in vivo. Taken together, these findings contribute to understanding the development of PROTACs and demonstrate that our Wee1-targeting PROTAC strategy has potential novel applications in cancer therapy.

Applications of CRISPR/Cas technology against drug-resistant lung cancers: an update

Out of all the cancer types, the most prevalent one is lung cancer. Multiple genes and signaling pathways play role in the progression of lung cancer. Considering the wider prevalence and fatality of lung cancer it has become the focus of current cancer research. Though currently used approaches have shown positive results against lung cancer but success against non-small cell lung cancer (NSCLC) still looms as an enigma for the entire research fraternity. The development of resistance against inhibitors within a short span is one of the reasons responsible for the failure and relapse of lung cancer. Under these prevailing conditions genome/gene-editing technology using clustered regularly interspaced short palindromic repeat (CRISPR) and CRISPR associated proteins (Cas), popularly known as CRISPR/Cas technology offers a convenient and flexible method for inducing precise changes within the lung cancer cell. Additionally, CRISPR-barcoding and CRISPR knockout screens at the genome-wide level can help in the functional investigation of specific mutations and identification of novel cancer drivers respectively. Several variants of the CRISPR/Cas system are being developed to limit off-targeting with enhanced precision. The present review article updates the usefulness of CRISPR/Cas technology against various types of lung cancers.

Characterizing genes associated with cancer using the CRISPR/Cas9 system: A systematic review of genes and methodological approaches

The CRISPR/Cas9 system enables a versatile set of genomes editing and genetic-based disease modeling tools due to its high specificity, efficiency, and accessible design and implementation. In cancer, the CRISPR/Cas9 system has been used to characterize genes and explore different mechanisms implicated in tumorigenesis. Different experimental strategies have been proposed in recent years, showing dependency on various intrinsic factors such as cancer type, gene function, mutation type, and technical approaches such as cell line, Cas9 expression, and transfection options. However, the successful methodological approaches, genes, and other experimental factors have not been analyzed. We, therefore, initially considered more than 1,300 research articles related to CRISPR/Cas9 in cancer to finally examine more than 400 full-text research publications. We summarize findings regarding target genes, RNA guide designs, cloning, Cas9 delivery systems, cell enrichment, and experimental validations. This analysis provides valuable information and guidance for future cancer gene validation experiments.

Polo-like Kinase 1 Inhibitors in Human Cancer Therapy: Development and Therapeutic Potential

Polo-like kinase 1 (PLK1) plays an important role in a variety of cellular functions, including the regulation of mitosis, DNA replication, autophagy, and the epithelial-mesenchymal transition (EMT). PLK1 overexpression is often associated with cell proliferation and poor prognosis in cancer patients, making it a promising antitumor target. To date, at least 10 PLK1 inhibitors (PLK1i) have been entered into clinical trials, among which the typical kinase domain (KD) inhibitor BI 6727 (volasertib) was granted "breakthrough therapy designation" by the FDA in 2013. Unfortunately, many other KD inhibitors showed poor specificity, resulting in dose-limiting toxicity, which has greatly impeded their development. Researchers recently discovered many PLK1i with higher selectivity, stronger potency, and better absorption, distribution, metabolism, and elimination (ADME) characteristics. In this review, we emphasize the structure-activity relationships (SARs) of PLK1i, providing insights into new drugs targeting PLK1 for antitumor clinical practice.

Multidrug Resistance in Cancer: Understanding Molecular Mechanisms, Immunoprevention and Therapeutic Approaches

Cancer is one of the leading causes of death worldwide. Several treatments are available for cancer treatment, but many treatment methods are ineffective against multidrug-resistant cancer. Multidrug resistance (MDR) represents a major obstacle to effective therapeutic interventions against cancer. This review describes the known MDR mechanisms in cancer cells and discusses ongoing laboratory approaches and novel therapeutic strategies that aim to inhibit, circumvent, or reverse MDR development in various cancer types. In this review, we discuss both intrinsic and acquired drug resistance, in addition to highlighting hypoxia- and autophagy-mediated drug resistance mechanisms. Several factors, including individual genetic differences, such as mutations, altered epigenetics, enhanced drug efflux, cell death inhibition, and various other molecular and cellular mechanisms, are responsible for the development of resistance against anticancer agents. Drug resistance can also depend on cellular autophagic and hypoxic status. The expression of drug-resistant genes and the regulatory mechanisms that determine drug resistance are also discussed. Methods to circumvent MDR, including immunoprevention, the use of microparticles and nanomedicine might result in better strategies for fighting cancer.

Selective Wee1 degradation by PROTAC degraders recruiting VHL and CRBN E3 ubiquitin ligases

The Ser/Thr protein kinase Wee1 plays a regulatory role at the G₂/M checkpoint by phosphorylating CDK1 when DNA is damaged to allow time for DNA to repair, disruption of which is a key approach to sensitise cancer cells to DNA-damaging therapies. The main selective inhibitor for Wee1 undergoing development in clinical trials, AZD1775, however, has been shown to have off target effects towards other protein kinases with similar potency. Here we describe the synthesis and assessment of a series of Wee1-degrading PROTACs using AZD1775 linked to either the VHL ligand VH032 or to the CRBN ligand pomalidomide using different types and lengths of linkers. The conversion of AZD1775 into a PROTAC induces selective Wee1 degradation for compounds of both series depending on the nature of the linker.

Inhibition of Polo-like Kinase 1 by HMN-214 Blocks Cell Cycle Progression and Inhibits Neuroblastoma Growth

Polo-like kinase 1 (PLK1) is an essential cell cycle mitotic kinase component that plays an important role in cell cycle progression and has been reported to be involved in various cancers, including neuroblastoma (NB). PLK1 also regulates G2/M transition, chromosomal segregation, spindle assembly maturation, and mitotic exit. NB is an early embryonic-stage heterogeneous solid tumor and accounts for 15% of all pediatric cancer-related deaths. Therefore, we aimed to develop a targeting strategy for PLK1 by repurposing HMN-214 in NB. HMN-214 is a prodrug of HMN-176 and is known to selectively interfere with PLK1 function. In the present study, we performed the transcriptomic analysis of a large cohort of primary NB patient samples and revealed that PLK1 expression is inversely correlated with the overall survival of NB patients. Additionally, we found that PLK1 strongly correlates with NB disease and stage progression. HMN-214 significantly inhibited NB proliferation and colony formation in both MYCN-amplified and -nonamplified cell lines in a dose-dependent manner. Furthermore, HMN-214 induces apoptosis and significantly obstructs the cell cycle at the G2/M phase in NB cells by inhibiting multiple cell-cycle-related genes, such as PLK1, WEE1, CDK1, CDK2, Cyclin B1, CHK1, and CHK2. HMN-214 significantly inhibits cell cycle regulator CDK1 and the phosphorylation and activation of PLK1 in NB. In the NB 3D spheroid tumor model, HMN-214 significantly and in a dose-dependent manner inhibits spheroid tumor mass and growth. Overall, our study highlights that targeting PLK1 using HMN-214 is a novel therapeutic approach for NB.

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.

The non-canonical target PARP16 contributes to polypharmacology of the PARP inhibitor talazoparib and its synergy with WEE1 inhibitors

PARP inhibitors (PARPis) display single-agent anticancer activity in small cell lung cancer (SCLC) and other neuroendocrine tumors independent of BRCA1/2 mutations. Here, we determine the differential efficacy of multiple clinical PARPis in SCLC cells. Compared with the other PARPis rucaparib, olaparib, and niraparib, talazoparib displays the highest potency across SCLC, including SLFN11-negative cells. Chemical proteomics identifies PARP16 as a unique talazoparib target in addition to PARP1. Silencing PARP16 significantly reduces cell survival, particularly in combination with PARP1 inhibition. Drug combination screening reveals talazoparib synergy with the WEE1/PLK1 inhibitor adavosertib. Global phosphoproteomics identifies disparate effects on cell-cycle and DNA damage signaling thereby illustrating underlying mechanisms of synergy, which is more pronounced for talazoparib than olaparib. Notably, silencing PARP16 further reduces cell survival in combination with olaparib and adavosertib. Together, these data suggest that PARP16 contributes to talazoparib's overall mechanism of action and constitutes an actionable target in SCLC.

Targeting DNA repair pathway in cancer: Mechanisms and clinical application

Over the last decades, the growing understanding on DNA damage response (DDR) pathways has broadened the therapeutic landscape in oncology. It is becoming increasingly clear that the genomic instability of cells resulted from deficient DNA damage response contributes to the occurrence of cancer. One the other hand, these defects could also be exploited as a therapeutic opportunity, which is preferentially more deleterious in tumor cells than in normal cells. An expanding repertoire of DDR-targeting agents has rapidly expanded to inhibitors of multiple members involved in DDR pathways, including PARP, ATM, ATR, CHK1, WEE1, and DNA-PK. In this review, we sought to summarize the complex network of DNA repair machinery in cancer cells and discuss the underlying mechanism for the application of DDR inhibitors in cancer. With the past preclinical evidence and ongoing clinical trials, we also provide an overview of the history and current landscape of DDR inhibitors in cancer treatment, with special focus on the combination of DDR-targeted therapies with other cancer treatment strategies.

Targeting Wee1 kinase as a therapeutic approach in Hematological Malignancies

Hematologic malignancies include various diseases that develop from hematopoietic stem cells of bone marrow or lymphatic organs. Currently, conventional DNA-damage-based chemotherapy drugs are approved as standard therapeutic regimens for these malignancies. Although many improvements have been made, patients with relapsed or refractory hematological malignancies have a poor prognosis. Therefore, novel and practical therapeutic approaches are required for the treatment of these diseases. Interestingly several studies have shown that targeting Wee1 kinase in the Hematological malignancies, including AML, ALL, CML, CLL, DLBCL, BL, MCL, etc., can be an effective therapeutic strategy. It plays an essential role in regulating the cell cycle process by abrogating the G2-M cell-cycle checkpoint, which provides time for DNA damage repair before mitotic entry. Consistently, Wee1 overexpression is observed in various Hematological malignancies. Also, in healthy normal cells, repairing DNA damages occurs due to G1-S checkpoint function; however, in the cancer cells, which have an impaired G1-S checkpoint, the damaged DNA repair process depends on the G2-M checkpoint function. Thus, Wee1 inhibition could be a promising target in the presence of DNA damage in order to potentiate multiple therapeutic drugs. This review summarized the potentials and challenges of Wee1 inhibition combined with other therapies as a novel effective therapeutic strategy in Hematological malignancies.

CCNE1 copy number is a biomarker for response to combination WEE1-ATR inhibition in ovarian and endometrial cancer models

CCNE1-amplified ovarian cancers (OVCAs) and endometrial cancers (EMCAs) are associated with platinum resistance and poor survival, representing a clinically unmet need. We hypothesized that dysregulated cell-cycle progression promoted by CCNE1 overexpression would lead to increased sensitivity to low-dose WEE1 inhibition and ataxia telangiectasia and Rad3-related (ATR) inhibition (WEE1i-ATRi), thereby optimizing efficacy and tolerability. The addition of ATRi to WEE1i is required to block feedback activation of ATR signaling mediated by WEE1i. Low-dose WEE1i-ATRi synergistically decreases viability and colony formation and increases replication fork collapse and double-strand breaks (DSBs) in a CCNE1 copy number (CN)-dependent manner. Only upon CCNE1 induction does WEE1i perturb DNA synthesis at S-phase entry, and addition of ATRi increases DSBs during DNA synthesis. Inherent resistance to WEE1i is overcome with WEE1i-ATRi, with notable durable tumor regressions and improved survival in patient-derived xenograft (PDX) models in a CCNE1-level-dependent manner. These studies demonstrate that CCNE1 CN is a clinically tractable biomarker predicting responsiveness to low-dose WEE1i-ATRi for aggressive subsets of OVCAs/EMCAs.

Targeted protein degradation: A promise for undruggable proteins

Protein homeostasis, or "proteostasis," is indispensable for a balanced, healthy environment within the cell. However, when natural proteostasis mechanisms are overwhelmed from excessive loads of dysregulated proteins, their accumulation can lead to disease initiation and progression. Recently, the induced degradation of such disease-causing proteins by heterobifunctional molecules, i.e., PROteolysis TArgeting Chimeras (PROTACs), is emerging as a potential therapeutic modality. In the 2 decades since the PROTAC concept was proposed, several additional Targeted Protein Degradation (TPD) strategies have also been explored to target previously undruggable proteins, such as transcription factors. In this review, we discuss the progress and evolution of the TPD field, the breadth of the proteins targeted by PROTACs and the biological effects of their degradation.

Efficacy and Biomarker Analysis of Adavosertib in Differentiated Thyroid Cancer

Differentiated thyroid cancer (DTC) patients are usually known for their excellent prognoses. However, some patients with DTC develop refractory disease and require novel therapies with different therapeutic mechanisms. Targeting Wee1 with adavosertib has emerged as a novel strategy for cancer therapy. We determined the effects of adavosertib in four DTC cell lines. Adavosertib induces cell growth inhibition in a dose-dependent fashion. Cell cycle analyses revealed that cells were accumulated in the G2/M phase and apoptosis was induced by adavosertib in the four DTC tumor cell lines. The sensitivity of adavosertib correlated with baseline Wee1 expression. In vivo studies showed that adavosertib significantly inhibited the xenograft growth of papillary and follicular thyroid cancer tumor models. Adavosertib therapy, combined with dabrafenib and trametinib, had strong synergism in vitro, and revealed robust tumor growth suppression in vivo in a xenograft model of papillary thyroid cancer harboring mutant BRAF^V600E, without appreciable toxicity. Furthermore, combination of adavosertib with lenvatinib was more effective than either agent alone in a xenograft model of follicular thyroid cancer. These results show that adavosertib has the potential in treating DTC.

Efficacy of adavosertib therapy against anaplastic thyroid cancer

Wee1 is a kinase that regulates the G2/M progression by the inhibition of CDK1, which is critical for ensuring DNA damage repair before initiation of mitotic entry. Targeting Wee1 may be a potential strategy in the treatment of anaplastic thyroid cancer, a rare but lethal disease. The therapeutic effects of adavosertib, a Wee1 inhibitor for anaplastic thyroid cancer was evaluated in this study. Adavosertib inhibited cell growth in three anaplastic thyroid cancer cell lines in a dose-dependent manner. Cell cycle analysis revealed cells were accumulated in the G2/M phase. Adavosertib induced caspase-3 activity and led to apoptosis. Adavosertib monotherapy showed significant retardation of the growth of two anaplastic thyroid cancer tumor models. The combination of adavosertib with dabrafenib and trametinib revealed strong synergism in vitro and demonstrated robust suppression of tumor growth in vivo in anaplastic thyroid cancer xenograft models with BRAFV600E mutation. The combination of adavosertib with either sorafenib or lenvatinib also demonstrated synergism in vitro and had strong inhibition of tumor growth in vivo in an anaplastic thyroid cancer xenograft model. No appreciable toxicity appeared in mice treated with either a single agent or combination treatment. Our findings suggest adavosertib holds the promise for the treatment of patients with anaplastic thyroid cancer.

CDK2-Mediated Upregulation of TNFα as a Mechanism of Selective Cytotoxicity in Acute Leukemia

Although inhibitors of the kinases CHK1, ATR, and WEE1 are undergoing clinical testing, it remains unclear how these three classes of agents kill susceptible cells and whether they utilize the same cytotoxic mechanism. Here we observed that CHK1 inhibition induces apoptosis in a subset of acute leukemia cell lines in vitro, including TP53-null acute myeloid leukemia (AML) and BCR/ABL-positive acute lymphoid leukemia (ALL), and inhibits leukemic colony formation in clinical AML samples ex vivo. In further studies, downregulation or inhibition of CHK1 triggered signaling in sensitive human acute leukemia cell lines that involved CDK2 activation followed by AP1-dependent TNF transactivation, TNFα production, and engagement of a TNFR1- and BID-dependent apoptotic pathway. AML lines that were intrinsically resistant to CHK1 inhibition exhibited high CHK1 expression and were sensitized by CHK1 downregulation. Signaling through this same CDK2-AP1-TNF cytotoxic pathway was also initiated by ATR or WEE1 inhibitors in vitro and during CHK1 inhibitor treatment of AML xenografts in vivo. Collectively, these observations not only identify new contributors to the antileukemic cell action of CHK1, ATR, and WEE1 inhibitors, but also delineate a previously undescribed pathway leading from aberrant CDK2 activation to death ligand-induced killing that can potentially be exploited for acute leukemia treatment. SIGNIFICANCE: This study demonstrates that replication checkpoint inhibitors can kill AML cells through a pathway involving AP1-mediated TNF gene activation and subsequent TP53-independent, TNFα-induced apoptosis, which can potentially be exploited clinically.

Structure-activity relationships of Wee1 inhibitors: A review

Wee1 kinase plays an important role in regulating G2/M checkpoint and S phase, and the inhibition of it will lead to mitotic catastrophe in cancer cells with p53 mutation or deletion. Therefore, the mechanism of Wee1 kinase in cancer treatment and the development of its inhibitors have become a research hotspot. However, although a variety of Wee1 inhibitors with different scaffolds and considerable activity have been successfully identified, so far no one has systematically summarized the structure-activity relationships (SARs) of Wee1 inhibitors. Previous reviews mainly focused on its mechanism and clinical application. To facilitate the rational design and development of Wee1 inhibitors in the future, this paper systematically summarizes its structural types, SARs and binding modes according to the Wee1 inhibitors reported in scientific journals, and also summarizes the regulatory effect of Wee1 kinase on cell cycle and the progress of its inhibitors in clinical application.

A scalable CRISPR/Cas9-based fluorescent reporter assay to study DNA double-strand break repair choice

Double-strand breaks (DSBs) are the most toxic type of DNA lesions. Cells repair these lesions using either end protection- or end resection-coupled mechanisms. To study DSB repair choice, we present the Color Assay Tracing-Repair (CAT-R) to simultaneously quantify DSB repair via end protection and end resection pathways. CAT-R introduces DSBs using CRISPR/Cas9 in a tandem fluorescent reporter, whose repair distinguishes small insertions/deletions from large deletions. We demonstrate CAT-R applications in chemical and genetic screens. First, we evaluate 21 compounds currently in clinical trials which target the DNA damage response. Second, we examine how 417 factors involved in DNA damage response influence the choice between end protection and end resection. Finally, we show that impairing nucleotide excision repair favors error-free repair, providing an alternative way for improving CRISPR/Cas9-based knock-ins. CAT-R is a high-throughput, versatile assay to assess DSB repair choice, which facilitates comprehensive studies of DNA repair and drug efficiency testing.

CRISPR/Cas9 for overcoming drug resistance in solid tumors

OBJECTIVES

In this review, we focus on the application of clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR associated nuclease 9 (Cas9), as a powerful genome editing system, in the identification of resistance mechanisms and in overcoming drug resistance in the most frequent solid tumors.

DATA ACQUISITION

Data were collected by conducting systematic searching of scientific English literature using specific keywords such as "cancer", "CRISPR" and related combinations.

RESULTS

The review findings revealed the importance of CRISPR/Cas9 system in understanding drug resistance mechanisms and identification of resistance-related genes such as PBRM1, SLFN11 and ATPE1 in different cancers. We also provided an overview of genes, including RSF1, CDK5, and SGOL1, whose disruption can synergize with the currently available drugs such as paclitaxel and sorafenib.

CONCLUSION

The data suggest CRISPR/Cas9 system as a useful tool in elucidating the molecular basis of drug resistance and improving clinical outcomes. Graphical abstract The mechanisms of CRISPR/Cas9-mediated genome editing and double-strand breaks (DSBs) repair.

Inhibition of ATR Increases the Sensitivity to WEE1 Inhibitor in Biliary Tract Cancer

Purpose

Currently, the DNA damage response (DDR) pathway represents a key target for new cancer drug development. Advanced biliary tract cancer (BTC) has a poor prognosis because of the lack of efficacious treatment options. Although DNA repair pathway alterations have been reported in many patients with BTC, little is known regarding the effects of DDR-targeted agents against BTC.

Materials and Methods

In this study, nine BTC cell lines were exposed to the WEE1 inhibitor (AZD1775). In vitro, MTT assay, colony-forming assay, cell cycle analysis, phospho-histone H3 staining assay, Transwell migration assay, and western blot were performed. Then, to enhance the antitumor effect of AZD1775, the combination treatment of WEE1 inhibitor and ataxia telangiectasia mutated and Rad3 related (ATR) inhibitor (AZD6738) was conducted using MTT assay and comet assay. Finally, HuCCT-1 and SNU2670 xenograft models were established to confirm the anti-tumor effect of AZD1775 alone. Furthermore, the combination treatment was also evaluated in SNU2670 xenograft models.

Results

AZD1775 blocked the phosphorylation of CDC2 and CDC25C in all cell lines, but significantly increased apoptosis and S phase arrest in sensitive cells. However, increased p-ATR and phosphorylated ataxia telangiectasia mutated levels were observed in less sensitive cells. In addition, in vitro and in vivo data illustrated that AZD1775 combined with AZD6738 exerted more potent anti-tumor effects than either drug alone. Although WEE1 inhibition has promising anti-tumor effects in some BTC cells, the addition of ATR inhibitors could enhance its efficacy.

Conclusion

Taken together, this study supports further clinical development of DDR-targeted strategies as monotherapy or combination regimens for BTC.

PLK1/NF-κB feedforward circuit antagonizes the mono-ADP-ribosyltransferase activity of PARP10 and facilitates HCC progression

Dysregulation of PARP10 has been implicated in various tumor types and plays a vital role in delaying hepatocellular carcinoma (HCC) progression. However, the mechanisms controlling the expression and activity of PARP10 in HCC remain mostly unknown. The crosstalk between PLK1, PARP10, and NF-κB pathway in HCC was determined by performing different in vitro and in vivo assays, including mass spectrometry, kinase, MARylation, chromatin immunoprecipitation, and luciferase reporter measurements. Functional examination was performed by using small chemical drug, cell culture, and mice HCC models. Correlation between PLK1, NF-κB, and PARP10 expression was determined by analyzing clinical samples of HCC patients with using immunohistochemistry. PLK1, an important regulator for cell mitosis, directly interacts with and phosphorylates PARP10 at T601. PARP10 phosphorylation at T601 significantly decreases its binding to NEMO and disrupts its inhibition to NEMO ubiquitination, thereby enhancing the transcription activity of NF-κB toward multiple target genes and promoting HCC development. In turn, NF-κB transcriptionally inhibits the PARP10 promoter activity and leads to its downregulation in HCC. Interestingly, PLK1 is mono-ADP-ribosylated by PARP10 and the MARylation of PLK1 significantly inhibits its kinase activity and oncogenic function in HCC. Clinically, the expression levels of PLK1 and phosphor-p65 show an inverse correlation with PARP10 expression in human HCC tissues. These findings are the first to uncover a PLK1/PARP10/NF-κB signaling circuit that underlies tumorigenesis and validate PLK1 inhibitors, alone or with NF-κB antagonists, as potential effective therapeutics for PARP10-expressing HCC.

Wee1 Inhibition Enhances the Anti-Tumor Effects of Capecitabine in Preclinical Models of Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is an aggressive subtype defined by lack of hormone receptor expression and non-amplified HER2. Adavosertib (AZD1775) is a potent, small-molecule, ATP-competitive inhibitor of the Wee1 kinase that potentiates the activity of many DNA-damaging chemotherapeutics and is currently in clinical development for multiple indications. The purpose of this study was to investigate the combination of AZD1775 and capecitabine/5FU in preclinical TNBC models. TNBC cell lines were treated with AZD1775 and 5FU and cellular proliferation was assessed in real-time using IncuCyte^® Live Cell Analysis. Apoptosis was assessed via the Caspase-Glo 3/7 assay system. Western blotting was used to assess changes in expression of downstream effectors. TNBC patient-derived xenograft (PDX) models were treated with AZD1775, capecitabine, or the combination and assessed for tumor growth inhibition. From the initial PDX screen, two of the four TNBC PDX models demonstrated a better response in the combination treatment than either of the single agents. As confirmation, two PDX models were expanded for statistical comparison. Both PDX models demonstrated a significant growth inhibition in the combination versus either of the single agents. (TNBC012, p < 0.05 combo vs. adavosertib or capecitabine, TNBC013, p < 0.01 combo vs. adavosertib or capecitabine.) An enhanced anti-proliferative effect was observed in the adavosertib/5FU combination treatment as measured by live cell analysis. An increase in apoptosis was observed in two of the four cell lines in the combination when compared to single-agent treatment. Treatment with adavosertib as a single agent resulted in a decrease in p-CDC2 in a dose-dependent manner that was also observed in the combination treatment. An increase in γH2AX in two of the four cell lines tested was also observed. No significant changes were observed in Bcl-xL following treatment in any of the cell lines. The combination of adavosertib and capecitabine/5FU demonstrated enhanced combination effects both in vitro and in vivo in preclinical models of TNBC. These results support the clinical investigation of this combination in patients with TNBC, including those with brain metastasis given the CNS penetration of both agents.

WEE1 kinase limits CDK activities to safeguard DNA replication and mitotic entry

Precise execution of the cell division cycle is vital for all organisms. The Cyclin dependent kinases (CDKs) are the main cell cycle drivers, however, their activities must be precisely fine-tuned to ensure orderly cell cycle progression. A major regulatory axis is guarded by WEE1 kinase, which directly phosphorylates and inhibits CDK1 and CDK2. The role of WEE1 in the G2/M cell-cycle phase has been thoroughly investigated, and it is a focal point of multiple clinical trials targeting a variety of cancers in combination with DNA-damaging chemotherapeutic agents. However, the emerging role of WEE1 in S phase has so far largely been neglected. Here, we review how WEE1 regulates cell-cycle progression highlighting the importance of this kinase for proper S phase. We discuss how its function is modulated throughout different cell-cycle stages and provide an overview of how WEE1 levels are regulated. Furthermore, we outline recent clinical trials targeting WEE1 and elaborate on the mechanisms behind the anticancer efficacy of WEE1 inhibition. Finally, we consider novel biomarkers that may benefit WEE1-inhibition approaches in the clinic.

Design, synthesis and biological evaluation of 3-nitro-1,8-naphthalimides as potential antitumor agents

A series of 3-nitro-naphthalimides 1(1a-1h) were designed and synthesized as antitumor agents. MTT assay results showed that all these compounds exhibited obvious antiproliferative activity against SKOV3, HepG2, A549, T-24 and SMMC-7721 cancer cell lines, while compound 1a displayed the best antiproliferative activity against HepG2 and T-24 cell lines in comparison with mitonafide, with IC₅₀ of 9.2 ± 1.8 and 4.133 ± 0.9 μM, respectively. In vivo antiproliferative activity assay results showed that compound 1a exhibited good antiproliferative activity in the HepG2 and T-24 models, compared with mitonafide. Action mechanism results showed that compound 1a could induced the damage of DNA and the inhibition topo I, accompanying by inducing the G2-stage arresting and the apoptosis of T-24 cancer cells through up-regulating expression levels of cyclin B1, cdc 2-pTy, Wee1, γH2AX, p21, Bax and cytochrome c and down-regulating expression of Bcl-2.

Development and Characterization of a Wee1 Kinase Degrader

The G1/S cell cycle checkpoint is frequently dysregulated in cancer, leaving cancer cells reliant on a functional G2/M checkpoint to prevent excessive DNA damage. Wee1 regulates the G2/M checkpoint by phosphorylating CDK1 at Tyr15 to prevent mitotic entry. Previous drug development efforts targeting Wee1 resulted in the clinical-grade inhibitor, AZD1775. However, AZD1775 is burdened by dose-limiting adverse events, and has off-target PLK1 activity. In an attempt to overcome these limitations, we developed Wee1 degraders by conjugating AZD1775 to the cereblon (CRBN)-binding ligand, pomalidomide. The resulting lead compound, ZNL-02-096, degrades Wee1 while sparing PLK1, induces G2/M accumulation at 10-fold lower doses than AZD1775, and synergizes with Olaparib in ovarian cancer cells. We demonstrate that ZNL-02-096 has CRBN-dependent pharmacology that is distinct from AZD1775, which justifies further evaluation of selective Wee1 degraders.

Upregulation of Myt1 Promotes Acquired Resistance of Cancer Cells to Wee1 Inhibition

Adavosertib (also known as AZD1775 or MK1775) is a small-molecule inhibitor of the protein kinase Wee1, with single-agent activity in multiple solid tumors, including sarcoma, glioblastoma, and head and neck cancer. Adavosertib also shows promising results in combination with genotoxic agents such as ionizing radiation or chemotherapy. Previous studies have investigated molecular mechanisms of primary resistance to Wee1 inhibition. Here, we investigated mechanisms of acquired resistance to Wee1 inhibition, focusing on the role of the Wee1-related kinase Myt1. Myt1 and Wee1 kinases were both capable of phosphorylating and inhibiting Cdk1/cyclin B, the key enzymatic complex required for mitosis, demonstrating their functional redundancy. Ectopic activation of Cdk1 induced aberrant mitosis and cell death by mitotic catastrophe. Cancer cells with intrinsic adavosertib resistance had higher levels of Myt1 compared with sensitive cells. Furthermore, cancer cells that acquired resistance following short-term adavosertib treatment had higher levels of Myt1 compared with mock-treated cells. Downregulating Myt1 enhanced ectopic Cdk1 activity and restored sensitivity to adavosertib. These data demonstrate that upregulating Myt1 is a mechanism by which cancer cells acquire resistance to adavosertib. SIGNIFICANCE: Myt1 is a candidate predictive biomarker of acquired resistance to the Wee1 kinase inhibitor adavosertib.

Enhancing direct cytotoxicity and response to immune checkpoint blockade following ionizing radiation with Wee1 kinase inhibition

Tumor cells activate the G2/M cell cycle checkpoint in response to ionizing radiation (IR) and effector immune cell-derived granzyme B to facilitate repair and survival. Wee1 kinase inhibition reverses the ability of tumor cells to pause at G2/M. Here, we hypothesized that AZD1775, a small molecule inhibitor of Wee1 kinase, could sensitize tumor cells to IR and T-lymphocyte killing and improve responses to combination IR and programmed death (PD)-axis immune checkpoint blockade (ICB). Multiple models of head and neck carcinoma, lung carcinoma and melanoma were used in vitro and in vivo to explore this hypothesis. AZD1775 reversed G2/M cell cycle checkpoint activation following IR, inducing cell death. Combination IR and AZD1775 induced accumulation of DNA damage in M-phase cells and was rescued with nucleoside supplementation, indicating mitotic catastrophe. Combination treatment enhanced control of syngeneic MOC1 tumors in vivo, and on-target effects of systemic AZD1775 could be localized with targeted IR. Combination treatment enhanced granzyme B-dependent T-lymphocyte killing through reversal of additive G2/M cell cycle block induced by IR and granzyme B. Combination IR and AZ1775-enhanced CD8⁺ cell-dependent MOC1 tumor growth control and rate of complete rejection of established tumors in the setting of PD-axis ICB. Functional assays demonstrated increased tumor antigen-specific immune responses in sorted T-lymphocytes. The combination of IR and AZD1775 not only lead to enhanced tumor-specific cytotoxicity, it also enhanced susceptibility to T-lymphocyte killing and responses to PD-axis ICB. These data provide the pre-clinical rationale for the combination of these therapies in the clinical trial setting.

Wee1 Rather Than Plk1 Is Inhibited by AZD1775 at Therapeutically Relevant Concentrations

Wee1 kinase is an inhibitor of cyclin-dependent kinase (cdk)s, crucial cell cycle progression drivers. By phosphorylating cdk1 at tyrosine 15, Wee1 inhibits activation of cyclin B-cdk1 (Cdk1), preventing cells from entering mitosis with incompletely replicated or damaged DNA. Thus, inhibiting Wee1, alone or in combination with DNA damaging agents, can kill cancer cells by mitotic catastrophe, a tumor suppressive response that follows mitosis onset in the presence of under-replicated or damaged DNA. AZD1775, an orally available Wee1 inhibitor, has entered clinical trials for cancer treatment following this strategy, with promising results. Recently, however, AZD1775 has been shown to inhibit also the polo-like kinase homolog Plk1 in vitro, casting doubts on its mechanism of action. Here we asked whether, in the clinically relevant concentration range, AZD1775 inhibited Wee1 or Plk1 in transformed and non-transformed human cells. We found that in the clinically relevant, nanomolar, concentration range AZD1775 inhibited Wee1 rather than Plk1. In addition, AZD1775 treatment accelerated mitosis onset overriding the DNA replication checkpoint and hastened Plk1-dependent phosphorylation. On the contrary selective Plk1 inhibition exerted opposite effects. Thus, at therapeutic concentrations, AZD1775 inhibited Wee1 rather than Plk1. This information will help to better interpret results obtained by using AZD1775 both in the clinical and experimental settings and provide a stronger rationale for combination therapies.

Molecular and enzoinformatics perspectives of targeting Polo-like kinase 1 in cancer therapy

Cancer is a disease that has been the focus of scientific research and discovery and continues to remain so. Polo-like kinases (PLKs) are basically serine/threonine kinase enzymes that control cell cycle from yeast to humans. PLK-1 stands for 'Polo-like kinase-1'. It is the most investigated protein among PLKs. It is crucial for intracellular processes, hence a 'hot' anticancer drug-target. Accelerating innovations in Enzoinformatics and associated molecular visualization tools have made it possible to literally perform a 'molecular level walk' traversing through and observing the minutest contours of the active site of relevant enzymes. PLK-1 as a protein consists of a kinase domain at the protein N-terminal and a Polo Box Domain (PBD) at the C-terminal connected by a short inter-domain linking region. PBD has two Polo-Boxes. PBD of PLK-1 gives the impression of "a small clamp sandwiched between two clips", where the two Polo Boxes are the 'clips' and the 'phosphopeptide' is the small 'clamp'. Broadly, two major sites of PLK-1 can be potential targets: one is the adenosine-5'-triphosphate (ATP)-binding site in the kinase domain and the other is PBD (more preferred due to specificity). Targeting PLK-1 RNA and the interaction of PLK-1 with a key binding partner can also be approached. However, the list of potent small molecule inhibitors targeting the PBD site of PLK-1 is still not long enough and needs due input from the scientific community. Recently, eminent scientists have proposed targeting the 'Y'-shaped pocket of PLK-1-PBD and encouraged design of ligands that should be able to concurrently bind to two or more modules of the 'Y' pocket. Hence, it is suggested that during molecular interaction analyses, particular focus should be kept on the moiety in each ligand/drug candidate which directly interacts with the amino acid residue(s) that belong(s) to one of the three binding modules which together create this Y-shaped cavity. This obviously includes (but it is not limited to) the 'shallow cleft'-forming residues i.e. Trp414, H538 and K540, as significance of these binding residues has been consistently highlighted by many studies. The present article attempts to give a concise yet critically updated overview of targeting PLK-1 for cancer therapy.

Differential Sensitivity to CDK2 Inhibition Discriminates the Molecular Mechanisms of CHK1 Inhibitors as Monotherapy or in Combination with the Topoisomerase I Inhibitor SN38

DNA damage activates checkpoints to arrest cell cycle progression in S and G2 phases, thereby providing time for repair and recovery. The combination of DNA-damaging agents and inhibitors of CHK1 (CHK1i) is an emerging strategy for sensitizing cancer cells. CHK1i induce replication on damaged DNA and mitosis before repair is complete, and this occurs in a majority of cell lines. However, ∼15% of cancer cell lines are hypersensitive to single-agent CHK1i. As both abrogation of S phase arrest and single-agent activity depend on CDK2, this study resolved how activation of CDK2 can be essential for both replication and cytotoxicity. S phase arrest was induced with the topoisomerase I inhibitor SN38; the addition of CHK1i rapidly activated CDK2, inducing S phase progression that was inhibited by the CDK2 inhibitor CVT-313. In contrast, DNA damage and cytotoxicity induced by single-agent CHK1i in hypersensitive cell lines were also inhibited by CVT-313 but at 20-fold lower concentrations. The differential sensitivity to CVT-313 is explained by different activity thresholds required for phosphorylation of CDK2 substrates. While the critical CDK2 substrates are not yet defined, we conclude that hypersensitivity to single-agent CHK1i depends on phosphorylation of substrates that require high CDK2 activity levels. Surprisingly, CHK1i did not increase SN38-mediated cytotoxicity. In contrast, while inhibition of WEE1 also abrogated S phase arrest, it more directly activated CDK1, induced premature mitosis, and enhanced cytotoxicity. Hence, while high activity of CDK2 is critical for cytotoxicity of single-agent CHK1i, CDK1 is additionally required for sensitivity to the drug combination.

Combined Aurora Kinase A (AURKA) and WEE1 Inhibition Demonstrates Synergistic Antitumor Effect in Squamous Cell Carcinoma of the Head and Neck

PURPOSE

Human papillomavirus (HPV)-negative head and neck squamous cell carcinomas (HNSCC) commonly bear disruptive mutations in TP53, resulting in treatment resistance. In these patients, direct targeting of p53 has not been successful, but synthetic lethal approaches have promise. Although Aurora A kinase (AURKA) is overexpressed and an oncogenic driver, its inhibition has only modest clinical effects in HPV-negative HNSCC. We explored a novel combination of AURKA and WEE1 inhibition to overcome intrinsic resistance to AURKA inhibition.Experimental Design: AURKA protein expression was determined by fluorescence-based automated quantitative analysis of patient specimens and correlated with survival. We evaluated treatment with the AURKA inhibitor alisertib (MLN8237) and the WEE1 inhibitor adavosertib (AZD1775), alone or in combination, using in vitro and in vivo HNSCC models.

RESULTS

Elevated nuclear AURKA correlated with worse survival among patients with p16(-) HNSCC. Alisertib caused spindle defects, G₂-M arrest and inhibitory CDK1 phosphorylation, and cytostasis in TP53 mutant HNSCC FaDu and UNC7 cells. Addition of adavosertib to alisertib instead triggered mitotic entry and mitotic catastrophe. Moreover, in FaDu and Detroit 562 xenografts, this combination demonstrated synergistic effects on tumor growth and extended overall survival compared with either vehicle or single-agent treatment.

CONCLUSIONS

Combinatorial treatment with adavosertib and alisertib leads to synergistic antitumor effects in in vitro and in vivo HNSCC models. These findings suggest a novel rational combination, providing a promising therapeutic avenue for TP53-mutated cancers.

Development of Potent Pyrazolopyrimidinone-Based WEE1 Inhibitors with Limited Single-Agent Cytotoxicity for Cancer Therapy

WEE1 kinase regulates the G₂ /M cell-cycle checkpoint, a critical mechanism for DNA repair in cancer cells that can confer resistance to DNA-damaging agents. We previously reported a series of pyrazolopyrimidinones based on AZD1775, a known WEE1 inhibitor, as an initial investigation into the structural requirements for WEE1 inhibition. Our lead inhibitor demonstrated WEE1 inhibition in the same nanomolar range as AZD1775, and potentiated the effects of cisplatin in medulloblastoma cells, but had reduced single-agent cytotoxicity. These results prompted the development of a more comprehensive series of WEE1 inhibitors. Herein we report a series of pyrazolopyrimidinones and identify a more potent WEE1 inhibitor than AZD1775 and additional compounds that demonstrate that WEE1 inhibition can be achieved with reduced single-agent cytotoxicity. These studies support that WEE1 inhibition can be uncoupled from the potent cytotoxic effects observed with AZD1775, and this may have important ramifications in the clinical setting where WEE1 inhibitors are used as chemosensitizers for DNA-targeted chemotherapy.

Augmented antitumor activity by olaparib plus AZD1775 in gastric cancer through disrupting DNA damage repair pathways and DNA damage checkpoint

BACKGROUND

Targeting poly ADP-ribose polymerase (PARP) has been recently identified as a promising option against gastric cancer (GC). However, PARP inhibitors alone achieve limited efficacy. Combination strategies, especially with homologous recombination (HR) impairment, are of great hope to optimize PARP inhibitor's efficacy and expand target populations but remains largely unknown. Herein, we investigated whether a WEE1/ Polo-like kinase 1 (PLK1) dual inhibitor AZD1775 reported to impair HR augmented anticancer activity of a PARP inhibitor olaparib and its underlying mechanisms.

METHODS

GC cell lines and in vivo xenografts were employed to determine antitumor activity of PARP inhibitor combined with WEE1/PLK1 dual inhibitor AZD1775. Western blot, genetic knockdown by siRNA, flow cytometry, Immunohistochemistry were performed to explore the underlying mechanisms.

RESULTS

AZD1775 dually targeting WEE1/PLK1 enhanced effects of olaparib on growth inhibition and apoptotic induction in GC cells. Mechanistic investigations elucidate that WEE1/PLK1 blockade downregulated several HR-related proteins and caused an accumulation in γH2AX. As confirmed in both GC cell lines and mice bearing GC xenografts, these effects were enhanced by AZD1775-olaparib combination compared to olaparib alone, suggesting that disrupting HR-mediated DNA damage repairs (DDR) by WEE1/PLK1 blockade might be responsible for improved GC cells' response to PARP inhibitors. Given the DNA damage checkpoint as a primary target of WEE1 inhibition, our data also demonstrate that AZD1775 abrogated olaparib-activated DNA damage checkpoint through CDC2 de-phosphorylation, followed by mitotic progression with unrepaired DNA damage (marked by increased pHH3-stained and γH2AX-stained cells, respectively).

CONCLUSIONS

PARP inhibitor olaparib combined with WEE1/PLK1 dual inhibitor AZD1775 elicited potentiated anticancer activity through disrupting DDR signaling and the DNA damage checkpoint. It sheds light on the combination strategy of WEE1/PLK1 dual inhibitors with PARP inhibitors in the treatment of GC, even in HR-proficient patients.