Phase II study of ceralasertib (AZD6738) in combination with durvalumab in patients with advanced gastric cancer

Abstract

Background: Targeting the DNA damage repair (DDR) pathways is an attractive strategy for boosting cancer immunotherapy. Ceralasertib (AZD6738) is an oral kinase inhibitor of ataxia telangiectasia and Rad3 related protein, which is a master regulator of DDR. We conducted a phase II trial of ceralasertib plus durvalumab in patients with previously treated advanced gastric cancer (AGC) to demonstrate the safety, tolerability, and clinical activity of the combination.

Methods: This phase II, open-label, single-center, non-randomized study was designed to evaluate the efficacy and safety of ceralasertib in combination with durvalumab in patients with AGC. The study drug regimen was ceralasertib (240 mg two times a day) days 15-28 in a 28-day cycle in combination with durvalumab (1500 mg) at day 1 every 4 weeks. The primary end point was overall response rate (ORR) by Response Evaluation Criteria in Solid Tumors (V.1.1). Exploratory biomarker analysis was performed using fresh tumor biopsies in all enrolled patients.

Results: Among 31 patients, the ORR, disease control rate, median progression-free survival (PFS), and overall survival were 22.6% (95% CI 9.6% to 41.1%), 58.1% (95% CI 39.1% to 75.5%), 3.0 (95% CI 2.1 to 3.9) months, and 6.7 (95% CI 3.8 to 9.6) months, respectively. Common adverse events were manageable with dose modification. A subgroup of patients with a loss of ataxia telangiectasia mutated (ATM) expression and/or high proportion of mutational signature attributable to homologous repair deficiency (sig. HRD) demonstrated a significantly longer PFS than those with intact ATM and low sig. HRD (5.60 vs 1.65 months; HR 0.13, 95% CI 0.045 to 0.39; long-rank p<0.001). During the study treatment, upregulation of the innate immune response by cytosolic DNA, activation of intratumoral lymphocytes, and expansion of circulating tumor-reactive CD8 +T cell clones were identified in responders. Enrichment of the tumor vasculature signature was associated with treatment resistance.

Conclusions: Ceralasertib plus durvalumab has promising antitumor activity, with durable responses in patients with refractory AGC. Thus, a biomarker-driven trial is required.

Trial registration: NCT03780608.

Keywords: clinical trials, phase II as topic; gastrointestinal neoplasms; genome instability; programmed cell death 1 receptor.

Conflict of interest statement

Competing interests: ED, SS, PGSM, A-BL, II-A, and LK are employees and stockholders of AstraZeneca. JL has served a consultant/advisory role in Mirati, Seattle Genetics, and Oncologie. W-YP has equity for Geninus. The other authors declare that they have no conflicts of interest.

© Author(s) (or their employer(s)) 2022. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.

Figures

Figure 1

Response to ceralasertib in combination with durvalumab (A) A waterfall plot of best response to ceralasertib in combination with durvalumab in patients with advanced gastric cancer. The y-axis represents the percentage of maximum tumor reduction assessed according to RECIST V.1.1. Among 31 participants, overall, 30 were eligible for this analysis, because one patient (ID16) died from ischemic stroke before response evaluation. The upper and lower dotted lines represent 20% tumor growth and 30% tumor reduction, respectively, which define progressive disease and partial response. (B) A swimmer plot demonstrating the clinical courses of study participants. The left panel shows the expression of PD-L1 and ATM, and responses to prior immunotherapy. White blocks with a cross indicate unavailable data; white blocks in the prior ICI column indicate no prior ICI treatment. The diamond-shaped points indicate the time from study enrollment to the detection of the first response. Patients who were on study treatment at the cut-off date are marked by arrows heading to the right. (C, D) Kaplan-Meier curves of PFS and OS among the enrolled patients. N/A, not available; PFS, progression-free survival; RECIST, Response Evaluation Criteria in Solid Tumors; OS, overall survival.

Figure 2

Exploratory biomarker analysis. (A) Landscape of genetic alterations in study samples obtained from 24 patients with advanced gastric cancer (AGC). Top to bottom: non-synonymous tumor mutational burden (TMB) in the exome, response to the study treatment, durability of clinical response, subtype of gastric cancer defined by The Cancer Genome Atlas (TCGA), microsatellite stability, HER2 expression, PD-L1 positivity, ATM expression, homologous recombination repair status, somatic singe nucleotide variations in selected canonical oncogenes and tumor suppressor genes, mutational signatures of somatic mutations, and the proportion of single base substitution subtypes in each sample. Response was defined to be durable if treatment duration was more than 6 months. Samples with ATM loss and/or high HRD signature were considered to have deficient homologous recombination repair. We assessed the enrichment of mutation groups in responders or non-responders using two-tailed Student’s t-test. Genes are grouped by pathway or function. The corresponding log-transformed p values are illustrated on the right with bar plots: Black bars represent comparison of responders (PR) and progressors (SD, PD) and gray bars represent comparison of PR and PD. Significantly enriched mutation groups in responders are marked by asterisks (*). (B) The exonic tumor mutational burden in patients with PR, SD, and PD to the study treatment. The statistical significance of the differences was estimated by the Wilcoxon signed-rank test. (C) A scatter plot simultaneously demonstrating the PFS, x-axis, best response from baseline in tumor size (y-axis), ATM expression (color), and proportion of mutational signature attributable to deficient HRD signature, size). (D) Kaplan-Meier plots of PFS among study patients according to ATM expression and proportion of HRD signature. Samples with HRD signature proportion higher than the average were defined as those with high proportion of HRD signature (sig. HRDHi). (E) A forest plot demonstrating multivariate analysis of factors associated with PFS. HRs and corresponding p values were estimated using multivariate cox regression hazard model. CIN, chromosomal instability; CPS, combined positive score; GS, genomically stable; HR, homologous recombination; HRD, homologous recombination deficiency; mPFS, median progression-free survival; MSI, microsatellite instability; PD, progressive disease; PFS, progression-free survival; PR, partial response; SBS, single-base substitution; SD, stable disease; TMB, tumor mutational burden.

Figure 3

Evolving tumor microenvironment during treatment with ceralasertib plus durvalumab. (A) Changes in TMB and neoantigen ratio (the number of neoantigen divided by the total sum of mutation count) during the study treatment. Changes during treatment were calculated by subtracting TMB or neoantigen ratio of pre-treatment from that of on-treatment. The statistical significance of the differences was estimated by the Wilcoxon signed-rank test. (B) A heatmap illustrating changes in single-sample gene set enrichment analysis (ssGSEA) scores of significant pathways during the study treatment. The ssGSEA scores were obtained from whole transcriptome sequencing (WTS) data from pretreatment and on-treatment samples of eight study participants, and we calculated the changes by subtracting the ssGSEA score of pretreatment from that of on-treatment. The statistical significance was estimated via Wilcoxon rank-sum test. PD, progressive disease; PR, partial response; SD, stable disease; TMB, tumor mutational burden.

Figure 4

Association of cellular composition of peripheral blood mononuclear cells with ceralasertib plus durvalumab response. We performed single-cell RNA sequencing and T cell receptor (TCR) sequencing on peripheral blood samples from eight patients. (A) Uniform manifold approximation and projection (UMAP) visualization of 19,621 cells in the T cell and NK cell lineage from pretreatment (n=8) and on-treatment (n=7) peripheral blood samples. (B) Proportion of T/NK cells in pretreatment peripheral blood samples. Box plots show the difference in proportion of T/NK cell subtypes, which are categorized into CD4+ T cells, CD8+ T cells, NK cells, and γδ T cells, between responders (partial response, n=4) and progressors (progressive disease, n=4). The p values were estimated by Wilcoxon rank sum test. The stacked bar plots to the right of each box plot show the relative proportions of more subdivided cell types. (C) Change in the proportion of T/NK sub-cell types in peripheral blood during treatment. The p values from paired Wilcoxon signed-rank test are shown. (D) Change in the clonality of TCR repertoire during treatment. The change is calculated by subtracting TCR clonality of pretreatment from that of on-treatment. (E) Scatterplot of CD8+ T cell clone (n=1380 clones) frequencies of pretreatment and on-treatment. CD8+ T cell clones were categorized into four groups based on the Fisher’s exact test. CD8+ T cell clones, which were newly detected on-treatment, were defined as novel clones (red). CD8+ T cell clones that significantly expanded after treatment were defined as expanded clones (yellow). CD8+ T cell clones that significantly contracted after treatment were defined as contracted clones (blue). The rest of the clones were defined as persistent clones (gray). (F) Box plot comparing frequencies of novel and expanded CD8+ T cell clones at on-treatment timepoint. The p values were estimated by Wilcoxon rank sum test. (G) Heatmap showing expression levels of genes known to be highly expressed in tumor-specific T cells at on-treatment timepoint in PR patients (n=4) and PD patients (n=3). (H) Box plot for comparing binding affinity score of PR (n=2) and PD (n=1) suitable for this analysis. The affinity score was estimated between newly emerged neo-peptides presented by MHC (pMHC) and novel or expanded CD8+ TCRs by ergo II. The p values of Wilcoxon rank sum test are shown. All box plots describe the median and IQR. MHC, major histocompatibility complex; TCR, T cell receptor.

Figure 5

Tumor microenvironment associated with response to ceralasertib in combination with durvalumab (A) Dot plot showing enriched pathways in pre-treatment samples of non-responders compared with those of progressors. Threshold for selection was FDR |0.5|; p value from Wilcoxon rank sum test