A Phase I/II Trial of Oral SRA737 (a Chk1 Inhibitor) Given in Combination with Low-Dose Gemcitabine in Patients with Advanced Cancer

Advancements in the Understanding of Small-Cell Neuroendocrine Cervical Cancer: Where We Stand and What Lies Ahead

Small-cell neuroendocrine cervical carcinoma (SCNCC) is a rare yet aggressive gynecological malignancy associated with dismal clinical outcomes. Its rarity has led to a limited number of retrospective studies and an absence of prospective research, posing significant challenges for evidence-based treatment approaches. As a result, most gynecologic oncology centers have limited experience with this tumor, emphasizing the urgent need for a comprehensive review and summary. This article systematically reviews the pathogenesis, immunohistochemical and molecular characteristics, prognostic factors, and clinical management of gynecologic SCNCC. We specifically focused on reviewing the distinct genomic characteristics of SCNCC identified via next-generation sequencing technologies, including loss of heterozygosity (LOH), somatic mutations, structural variations (SVs), and microRNA alterations. The identification of these actionable genomic events offers promise for discovering new molecular targets for drug development and enhancing therapeutic outcomes. Additionally, we delve deeper into key clinical challenges, such as determining the optimal treatment modality between chemoradiation and surgery for International Federation of Gynecology and Obstetrics (FIGO) stage I phase patients within a precision stratification framework, as well as the role of targeted therapy within the homologous recombination (HR) pathway, immune checkpoint inhibitors (ICIs), and prophylactic cranial irradiation (PCI) in the management of SCNCC. Finally, we anticipate the utilization of multiple SCNCC models, including cancer tissue-originated spheroid (CTOS) lines and patient-derived xenografts (PDXs), to decipher driver events and develop individualized therapeutic strategies for clinical application.

Therapeutic Targeting of DNA Repair Pathways in Pediatric Extracranial Solid Tumors: Current State and Implications for Immunotherapy

DNA damage is fundamental to tumorigenesis, and the inability to repair DNA damage is a hallmark of many human cancers. DNA is repaired via the DNA damage repair (DDR) apparatus, which includes five major pathways. DDR deficiencies in cancers give rise to potential therapeutic targets, as cancers harboring DDR deficiencies become increasingly dependent on alternative DDR pathways for survival. In this review, we summarize the DDR apparatus, and examine the current state of research efforts focused on identifying vulnerabilities in DDR pathways that can be therapeutically exploited in pediatric extracranial solid tumors. We assess the potential for synergistic combinations of different DDR inhibitors as well as combinations of DDR inhibitors with chemotherapy. Lastly, we discuss the immunomodulatory implications of targeting DDR pathways and the potential for using DDR inhibitors to enhance tumor immunogenicity, with the goal of improving the response to immune checkpoint blockade in pediatric solid tumors. We review the ongoing and future research into DDR in pediatric tumors and the subsequent pediatric clinical trials that will be critical to further elucidate the efficacy of the approaches targeting DDR.

Synthetic lethal combination of CHK1 and WEE1 inhibition for treatment of castration-resistant prostate cancer

WEE1 and CHEK1 (CHK1) kinases are critical regulators of the G2/M cell cycle checkpoint and DNA damage response pathways. The WEE1 inhibitor AZD1775 and the CHK1 inhibitor SRA737 are in clinical trials for various cancers, but have not been thoroughly examined in prostate cancer, particularly castration-resistant (CRPC) and neuroendocrine prostate cancers (NEPC). Our data demonstrated elevated WEE1 and CHK1 expressions in CRPC and NEPC cell lines and patient samples. AZD1775 resulted in rapid and potent cell killing with comparable IC50s across different prostate cancer cell lines, while SRA737 displayed time-dependent progressive cell killing with 10- to 20-fold differences in IC50s. Notably, their combination synergistically reduced the viability of all CRPC cell lines and tumor spheroids in a concentration- and time-dependent manner. Importantly, in a transgenic mouse model of NEPC, both agents alone or in combination suppressed tumor growth, improved overall survival, and reduced the incidence of distant metastases, with SRA737 exhibiting remarkable single agent anticancer activity. Mechanistically, SRA737 synergized with AZD1775 by blocking AZD1775-induced feedback activation of CHK1 in prostate cancer cells, resulting in increased mitotic entry and accumulation of DNA damage. In summary, this preclinical study shows that CHK1 inhibitor SRA737 alone and its combination with AZD1775 offer potential effective treatments for CRPC and NEPC.

Investigations of the novel checkpoint kinase 1 inhibitor SRA737 in non-small cell lung cancer and colorectal cancer cells of differing tumour protein 53 gene status

Aim

In response to DNA damage the serine/threonine-specific protein kinase checkpoint kinase 1 (CHK1) is activated allowing cells to enter S phase (S) and G2 phase (G2) cell-cycle arrest. CHK1 inhibitors are expected to prevent cells from entering such arrest, thereby enhancing DNA damage-induced cytotoxicity. In contrast, normal cells with intact ataxia-telangiectasia mutated (ATM), CHK2 and tumour suppressor protein 53 (P53) signalling are still able to enter cell-cycle arrest using the functioning G1/S checkpoint, thereby being rescued from enhanced cytotoxicity. The main objective of this work is to investigate the in vitro effects of the novel CHK1 inhibitor SRA737 on pairs of non-small cell lung cancer (NSCLC) and colorectal cancer (CRC) cell lines, all with genetic aberrations rendering them susceptible to replication stress but of differing tumour protein 53 (TP53) gene status, focusing on DNA damage induction and the subsequent effects on cell proliferation and viability.

Methods

NSCLC cell lines H23 [TP53 mutant (MUT)] and A549 [TP53 wild-type (WT)] and CRC cell lines HT29 (TP53 MUT) and HCT116 (TP53 WT) were incubated with differing micromolar concentrations of SRA737 for 24 h and then analysed using alkaline comet and phosphorylated H2A.X variant histone (γH2AX)-foci assays to assess mostly DNA single strand break and double strand break damage, respectively. Cell-counting/trypan blue staining was also performed to assess cell proliferation/viability.

Results

Clear concentration-dependent increases in comet formation and γH2AX-foci/cell were noted for the TP53 MUT cells with no or lower increases being noted in the corresponding TP53 WT cells. Also, greater anti-proliferative and cell killing effects were noted in the TP53 MUT cells than in the TP53 WT cells.

Conclusions

This study's data suggests that P53 status/functioning is a key factor in determining the sensitivity of NSCLC and CRC cancer cells towards CHK1 inhibition, even in circumstances conducive to high replicative stress.

Actionable Driver Events in Small Cell Lung Cancer

Small cell lung cancer (SCLC) stands out as the most aggressive form of lung cancer, characterized by an extremely high proliferation rate and a very poor prognosis, with a 5-year survival rate that falls below 7%. Approximately two-thirds of patients receive their diagnosis when the disease has already reached a metastatic or extensive stage, leaving chemotherapy as the remaining first-line treatment option. Other than the recent advances in immunotherapy, which have shown moderate results, SCLC patients cannot yet benefit from any approved targeted therapy, meaning that this cancer remains treated as a uniform entity, disregarding intra- or inter-tumoral heterogeneity. Continuous efforts and technological improvements have enabled the identification of new potential targets that could be used to implement novel therapeutic strategies. In this review, we provide an overview of the most recent approaches for SCLC treatment, providing an extensive compilation of the targeted therapies that are currently under clinical evaluation and inhibitor molecules with promising results in vitro and in vivo.

A Phase I Expansion Cohort Study Evaluating the Safety and Efficacy of the CHK1 Inhibitor LY2880070 with Low-dose Gemcitabine in Patients with Metastatic Pancreatic Adenocarcinoma

PURPOSE

Combining gemcitabine with CHK1 inhibition has shown promise in preclinical models of pancreatic ductal adenocarcinoma (PDAC). Here, we report the findings from a phase I expansion cohort study (NCT02632448) investigating low-dose gemcitabine combined with the CHK1 inhibitor LY2880070 in patients with previously treated advanced PDAC.

PATIENTS AND METHODS

Patients with metastatic PDAC were treated with gemcitabine intravenously at 100 mg/m2 on days 1, 8, and 15, and LY2880070 50 mg orally twice daily on days 2-6, 9-13, and 16-20 of each 21-day cycle. Pretreatment tumor biopsies were obtained from each patient for correlative studies and generation of organoid cultures for drug sensitivity testing and biomarker analyses.

RESULTS

Eleven patients with PDAC were enrolled in the expansion cohort between August 27, 2020 and July 30, 2021. Four patients (36%) experienced drug-related grade 3 adverse events. No objective radiologic responses were observed, and all patients discontinued the trial by 3.2 months. In contrast to the lack of efficacy observed in patients, organoid cultures derived from biopsies procured from two patients demonstrated strong sensitivity to the gemcitabine/LY2880070 combination and showed treatment-induced upregulation of replication stress and DNA damage biomarkers, including pKAP1, pRPA32, and γH2AX, as well as induction of replication fork instability.

CONCLUSIONS

No evidence of clinical activity was observed for combined low-dose gemcitabine and LY2880070 in this treatment-refractory PDAC cohort. However, the gemcitabine/LY2880070 combination showed in vitro efficacy, suggesting that drug sensitivity for this combination in organoid cultures may not predict clinical benefit in patients.

Replicative stress in gastroesophageal cancer is associated with chromosomal instability and sensitivity to DNA damage response inhibitors

Gastroesophageal adenocarcinoma (GEA) is an aggressive malignancy with chromosomal instability (CIN). To understand adaptive responses enabling DNA damage response (DDR) and CIN, we analyzed matched normal, premalignant, and malignant gastric lesions from human specimens and a carcinogen-induced mouse model, observing activation of replication stress, DDR, and p21 in neoplastic progression. In GEA cell lines, expression of DDR markers correlated with ploidy abnormalities, such as number of high-level focal amplifications and whole-genome duplication (WGD). Integrating TP53 status, ploidy abnormalities, and DDR markers into a compositive score helped predict GEA cell lines with enhanced sensitivity to Chk1/2 and Wee1 inhibition, either alone or combined with irinotecan (SN38). We demonstrate that Chk1/2 or Wee1 inhibition combined with SN38/irinotecan shows greater anti-tumor activity in human gastric cancer organoids and an in vivo xenograft mouse model. These findings indicate that specific DDR biomarkers and ploidy abnormalities may predict premalignant progression and response to DDR pathway inhibitors.

Synthetic lethal combination of CHK1 and WEE1 inhibition for treatment of castration-resistant prostate cancer

WEE1 and CHEK1 (CHK1) kinases are critical regulators of the G2/M cell cycle checkpoint and DNA damage response pathways. The WEE1 inhibitor AZD1775 and the CHK1 inhibitor SRA737 are in clinical trials for various cancers, but have not been examined in prostate cancer, particularly castration-resistant (CRPC) and neuroendocrine prostate cancers (NEPC). Our data demonstrated elevated WEE1 and CHK1 expressions in CRPC/NEPC cell lines and patient samples. AZD1775 resulted in rapid and potent cell killing with comparable IC50s across different prostate cancer cell lines, while SRA737 displayed time-dependent progressive cell killing with 10- to 20-fold differences in IC50s. Notably, their combination synergistically reduced the viability of all CRPC cell lines and tumor spheroids in a concentration- and time-dependent manner. Importantly, in a transgenic mouse model of NEPC, both agents alone or in combination suppressed tumor growth, improved overall survival, and reduced the incidence of distant metastases, with SRA737 exhibiting remarkable single agent anticancer activity. Mechanistically, SRA737 synergized with AZD1775 by blocking AZD1775-induced feedback activation of CHK1 in prostate cancer cells, resulting in increased mitotic entry and accumulation of DNA damage. In summary, this preclinical study shows that CHK1 inhibitor SRA737 alone and its combination with AZD1775 offer potential effective treatments for CRPC and NEPC.

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.

A Phase 1/2 trial of SRA737 (a Chk1 inhibitor) administered orally in patients with advanced cancer

BACKGROUND

This was a first-in-human Phase 1/2 open-label dose-escalation study of the novel checkpoint kinase 1 (Chk1) inhibitor SRA737.

METHODS

Patients with advanced solid tumours enrolled in dose-escalation cohorts and received SRA737 monotherapy orally on a continuous daily (QD) dosing schedule in 28-day cycles. Expansion cohorts included up to 20 patients with prospectively selected, pre-specified response predictive biomarkers.

RESULTS

In total, 107 patients were treated at dose levels from 20-1300 mg. The maximum tolerated dose (MTD) of SRA737 was 1000 mg QD, the recommended Phase 2 dose (RP2D) was 800 mg QD. Common toxicities of diarrhoea, nausea and vomiting were generally mild to moderate. Dose-limiting toxicity at daily doses of 1000 and 1300 mg QD SRA737 included gastrointestinal events, neutropenia and thrombocytopenia. Pharmacokinetic analysis at the 800 mg QD dose showed a mean Cmin of 312 ng/mL (546 nM), exceeding levels required to cause growth delay in xenograft models. No partial or complete responses were seen.

CONCLUSIONS

SRA737 was well tolerated at doses that achieved preclinically relevant drug concentrations but single agent activity did not warrant further development as monotherapy. Given its mechanism of action resulting in abrogating DNA damage repair, further clinical development of SRA737 should be as combination therapy.

CLINICAL TRIAL REGISTRATION

Clinicaltrials.gov NCT02797964.

The Adaptive Mechanisms and Checkpoint Responses to a Stressed DNA Replication Fork

DNA replication is a tightly controlled process that ensures the faithful duplication of the genome. However, DNA damage arising from both endogenous and exogenous assaults gives rise to DNA replication stress associated with replication fork slowing or stalling. Therefore, protecting the stressed fork while prompting its recovery to complete DNA replication is critical for safeguarding genomic integrity and cell survival. Specifically, the plasticity of the replication fork in engaging distinct DNA damage tolerance mechanisms, including fork reversal, repriming, and translesion DNA synthesis, enables cells to overcome a variety of replication obstacles. Furthermore, stretches of single-stranded DNA generated upon fork stalling trigger the activation of the ATR kinase, which coordinates the cellular responses to replication stress by stabilizing the replication fork, promoting DNA repair, and controlling cell cycle and replication origin firing. Deregulation of the ATR checkpoint and aberrant levels of chronic replication stress is a common characteristic of cancer and a point of vulnerability being exploited in cancer therapy. Here, we discuss the various adaptive responses of a replication fork to replication stress and the roles of ATR signaling that bring fork stabilization mechanisms together. We also review how this knowledge is being harnessed for the development of checkpoint inhibitors to trigger the replication catastrophe of cancer cells.