Safety and efficacy of sintilimab combined with oxaliplatin/capecitabine as first-line treatment in patients with locally advanced or metastatic gastric/gastroesophageal junction adenocarcinoma in a phase Ib clinical trial

Sintilimab blocks the interaction between programmed death-1 (PD-1) and its ligands. The safety and efficacy of sintilimab combined with oxaliplatin/capecitabine (CapeOx) as first-line treatment were evaluated in patients with gastric (G)/gastroesophageal junction (GEJ) adenocarcinoma in a phase Ib clinical trial. Patients with locally advanced or metastatic G/GEJ adenocarcinoma without previous systemic treatment were enrolled as one cohort of a multi-cohort study. Sintilimab was administered at a dose of 200 mg intravenously (IV) in combination with CapeOx (1000 mg/m2 capecitabine orally, bid, D1–14 and 130 mg/m2 oxaliplatin IV, D1) every 21 days for up to 6 cycles. After combination treatment, patients continued to receive sintilimab (200 mg) at 3 weekly intervals as maintenance therapy until progressive disease (PD), unacceptable toxicity, withdrawal of informed consent, or for up to 24 months. Adverse events (AEs) were monitored to assess safety in terms of their frequency, intensity and causality. The efficacy endpoints included the objective response rate (ORR), disease control rate (DCR), progression-free survival (PFS) and overall survival (OS). Tumor mutation burden (TMB) was evaluated for its association with clinical response. A total of 20 patients were enrolled and received sintilimab plus CapeOx. All patients reported treatment-related AEs (TRAEs). Grade 3–4 TRAEs were found in 11 (55.0%) patients. Seventeen patients obtained partial response and the ORR was 85.0% (95% CI: 62.1–96.8%). Three (15.0%) had stable disease and DCR was 100.0% (95% CI: 83.2–100.0%). As data cutoff of May 1, 2019, the median follow-up was 7.8 months. The median PFS was 7.5 months (95% CI: 6.2–9.4) and median OS had not been reached. The OS rates at 6 months and 12 months were 100.0 and 68.0%. No association was observed between TMB and efficacy. Sintilimab combined with CapeOx as first-line treatment demonstrated acceptable safety and promising efficacy. ClinicalTrials.gov, NCT02937116. Registered 8 October 2016.


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Conclusions: Sintilimab combined with CapeOx as first-line treatment demonstrated acceptable safety and promising efficacy. Trial registration: ClinicalTrials.gov, NCT02937116. Registered 8 October 2016.

Background
The fifth most commonly diagnosed cancer worldwide is gastric cancer (GC), accounting for about 33% of cancer-related deaths globally and the third most common cancer in China with almost half of worldwide new GC cases occurring in China annually [1,2]. The standard treatments exhibit regional differences among western countries, Japan/Korea and China, which are considered to be associated with different screening and early detection methods as well as different biological behaviors, disease characteristics and ethnicity [3][4][5].
Surgical resection is the only radical therapy for gastric/gastroesophageal junction (G/GEJ) cancer. However, systemic chemotherapy is an alternative main therapy for G/GEJ cancer because of the high relapse rate after post-resection surgery and for the many patients diagnosed at an advanced-stage. For advanced G/GEJ cancer, first-line treatment mainly involves platinum-based chemotherapy using a combination of two or three drugs (trastuzumab is given to patients whose tumor is human epidermal growth factor receptor-2 (HER2) positive), but the overall survival (OS) is disappointing, since the maximum OS time has been reported to be 13.8 months [6][7][8][9][10]. Any potential novel drug that will increase patient survival times is urgently needed, in particular for first-line treatment.
Immune checkpoint inhibitor treatment is a new approach for tumor immunotherapy [11,12]. The treatment diminishes the immune system tolerance to tumor cells and improves the effective identification and eradication of tumor cells by blocking T cell inhibition [13]. The programmed death-1 (PD-1) antibody specifically binds to PD-1, thereby inhibiting apoptosis of antigen-specific T cells and thus reducing regulatory T cell (Treg) apoptosis by inhibiting the activation of PD-L1 [14,15].
The efficacy of anti-PD-1 antibodies monotherapy in patients who had prior chemotherapy for advanced GC has been demonstrated and supported by several trials. In the KEYNOTE-012 and KEYNOTE-059 trials, pembrolizumab monotherapy showed objective response rates (ORR) of 22% (n = 36) [16] and 15.5% (n = 148) [17], respectively in PD-L1 positive advanced GC patients after at least two prior systemic therapies. Based on such results, the Food and Drug Administration approved pembrolizumab for third-line treatment of patients with recurrent or advanced GC. In the ATTR ACTION-2 study, nivolumab monotherapy improved OS from 4.1 to 5.3 months (hazard ratio 0.63, 95% CI: 0.51-0.78; P < 0.000), compared with a placebo in advanced GC that was refractory or intolerant to previous treatment regimens [18].
However, between 30 and 60% of patients exhibit no response to PD-1 blockade, which is considered to be associated with T cell exclusion or exhaustion or inadequate T cell trafficking and many immunosuppressive factors accumulate in the tumor microenvironment [19]. New therapy regimens that improve the response and long-term efficacy are desperately needed. The efficacy of anti-PD-1 therapy in combination with chemotherapy has been confirmed in non-small-cell lung cancer [20,21]. In addition to direct tumor killing, conventional cytotoxic chemotherapy has demonstrated immunoregulatory properties by enhancing tumor antigenicity, disturbing immune suppressive pathways, inducing immunogenic cell death, and increasing effector T-cell reactions [22]. It is safe to hypothesize that anti-PD-1 antibodies in combination with chemotherapy may further improve the clinical outcomes of patients with advanced GC. Sintilimab is a highly selective, monoclonal IgG4 antibody that inhibits interactions between PD-1 and its ligands, with strong anti-tumor response [23]. A phase 1a study for dose escalation, has demonstrated the tolerance and pharmacological activity of sintilimab in patients with advanced-stage solid tumors, but there is limited evidence for the efficacy of antibodies against PD-1 plus chemotherapy in Chinese G/GEJ adenocarcinoma patients. Thus, the present trial was conducted to investigate the safety and efficacy of sintilimab combined with CapeOx as first-line therapy for a cohort of patients with G/GEJ adenocarcinoma.

Study design and patients
The present study was an open label, multicenter, phase Ib study to evaluate the safety and efficacy of sintilimab in 6 cohorts of patients with solid tumors. Patients (age range 18-70 years) with cytologically or histologically confirmed unresectable G/GEJ adenocarcinoma were enrolled in the G/GEJ cohort. Tumor, nodes and metastases (TNM) staging has been evaluated according to the Union for International Cancer Control (UICC) TNM classification 8th edition [24]. The patients had received no previous systemic treatment for advanced disease or had disease progression (PD) more than 6 months after systemic adjuvant therapy. Other major inclusion criteria were: at least one measurable lesion as defined by the Response Evaluation Criteria in Solid Tumor (RECIST version 1.1) criteria; score 0 or 1 for Eastern Tumor Collaborative Group Performance Status (ECOG-PS); adequate organ and bone marrow functions and life expectancy ≥12 weeks. Patients with amplification or overexpression of the HER2 gene were excluded from the trial. Appendix 1 contains a complete list of all inclusion and exclusion criteria.
The institutional review boards of all centers approved the protocols and the study was carried out in strict accordance with the declaration of Helsinki principles; all participating patients signed consent forms before taking part.

Procedures
According to NCCN guideline, the preferred first-line chemotherapy regimens for advanced gastric cancer are fluorouracil or capecitabine combined with cisplation or oxaliplatin [25]. However, the results from the REAL-2 study [26] revealed significant clinical benefit of the oxaliplatin/capecitabine (CapeOx) regimen which led to the longest OS time of 11.2 months, compared with other regimens. Oxaliplatin produces less renal toxicity, there is no requirement for hydration and it has a lower emetic potential compared to cisplatin, while capecitabine has no requirement for continuous intravenous (IV) infusion and is administered orally, which should ensure an improved quality of life for patients in their homes. Therefore, a CapeOx regimen has been chosen. During the combination phase, enrolled patients were given sintilimab in combination with CapeOx for up to 6 cycles (every 3 weeks). Each cycle consisted of intravenous sintilimab (200 mg) plus oxaliplatin (130 mg/m 2 ) on day 1 and capecitabine (1000 mg/m 2 twice daily orally) from day 1 to day 14. After combination treatment, patients without PD continued to receive sintilimab (200 mg) at 3 weekly intervals as maintenance therapy until PD, unacceptable toxic effects, withdrawal of informed consent, or for up to 24 months.

Study assessments
Adverse events (AEs) were monitored for 90 days after the last administration of a treatment dose. Responses were assessed by computed tomography (CT) or magnetic resonance imaging (MRI), every 9 weeks until PD, new treatment initiation, withdrawal of informed consent, or death.

Endpoints
Safety was assessed as collected AEs according to their type, frequency, causality and severity grading defined by the National Cancer Institute Common Terminology Criteria (CTCAE) ver. 4.03. The efficacy endpoints were the ORR, disease control rate (DCR), time to response (TTR), duration of response (DOR), progression free survival (PFS) and OS. Efficacy was determined by an investigator according to RECIST v1.1 guidelines.
Exploratory endpoints were to evaluate the correlation of tumor mutation burden (TMB) with clinical efficacy.

Tumor mutation burden analysis
The tumor biopsies and blood samples were collected at baseline. DNA sequences were extracted from biopsies of tumors with matched blood samples and submitted for next generation sequencing using a designed 1622gene panel (Genecast, Beijing, China). TMB was determined by analysis of the quantity of somatic mutations per megabase (Mb). Median TMB was used as a cut-off to define a tumor as high-TMB (H-TMB) and low-TMB (L-TMB).

Statistical analysis
All patients who received at least one study treatment were included in the safety and efficacy analyses. AEs were coded following the Medical Dictionary for Regulatory Activity and tabulated by system organ class and preferred terms. Causality between AEs and the study treatment was assessed by the investigator. ORR was calculated as the proportion of patients who had achieved a complete response (CR) or partial response (PR) and the 95% CIs were evaluated by the binomial distribution. DCR was calculated as the proportion of patients who obtained PR, CR and stable disease (SD) and data are presented with the 95% CIs. Median DOR, TTR, PFS, OS and the PFS and OS rates at 6 and 12 months were determined using the Kaplan-Meier methodology. Fisher's test was used to compare the ORRs between patients with H-TMB and L-TMB.

Results
From 26 Dec, 2017 to 17 Oct 2018, 25 patients were screened and 20 were enrolled in the G/GEJ adenocarcinoma cohort (Fig. 1). The median interval between initial diagnosis and screening was 14 days (range 7-611). Most patients (80.0%) had metastatic disease status and 11 (55.0%) had ECOG scores of 1 ( Table 1). The TNM stage summary is shown in Table 1 and the staging of  each patient in Supplementary Table 1.
One patient achieved a CR after the primary analysis by May 1, 2019. This patient began the study treatment on October 12, 2018 and completed 15 cycles of treatment before CR.

Discussion
In the present study, the results from the G/GEJ adenocarcinoma cohort in a Phase Ib study demonstrated manageable safety and favorable anti-tumor activity of sintilimab combined with a CapeOx regimen as first-line treatment for unresectable advanced metastatic G/GEJ adenocarcinoma. In terms of safety, the incidence and severity of TRAEs with sintilimab and CapeOx were generally consistent with those of known toxic effects of conventional chemotherapy [26][27][28] and previously reported side effects of other anti-PD-1 antibody combined with chemotherapy regimens [29,30]. Platelet count, white blood cell count and neutrophil count decreases were most commonly and mostly grade 1 to 2 reported TRAEs and are expected AEs associated with CapeOx [26][27][28]. Only 1 patient reported discontinuation of investigational drug application due to a TRAE (abnormal hepatic function). No treatmentrelated death occurred in this study and in general, the addition of sintilimab to CapeOx showed a manageable safety profile and did not bear extra safety risks.
Next-generation sequencing (NGS) has researcher enabled to perform target capture sequencing, which has been proposed as a reliable technique to identify mutated driver genes and for the estimation of TMBs. Its use has led to the detection of actionable alterations in various cancer related genes [33]. Regarding high TMB and the efficacy of PD-1 treatments, inconsistent results have been reported in previous studies. Wang et al. (2018) suggested that TMB might be associated with better efficacy for PD-1 monotherapy [32], whereas Mishima et al. [34] did not find a significant relationship between TMB and the response of gastric cancers to PD-1 therapy [34]. The latter data is in accordance with our finding that after treatment with sintilimab in combination with CapeOx, no significant difference in the clinical responses was found between H-TMB and L-TMB patients. However, using the median TMB as a cut-off is difficult to extrapolate to the real world clinic and bias due to the small sample size could not be excluded in the present study. In addition, it has been noted that up to now there is no uniform standard for H-TMB [33] and further investigations are urgently required.

Conclusions
Our results strongly indicate that sintilimab combined with CapeOx is an option for the first-line treatment of patients with advanced or metastatic G/GEJ adenocarcinoma. However, the sample size was small and it was a single-arm study without a comparator. The large scale, doubleblinded and randomized Phase III clinical trial ORIENT-16 for previously untreated advanced G/GEJ adenocarcinoma patients is being conducted to evaluate the efficacy and safety of sintilimab combined with CapeOx vs CapeOx alone (ClinicalTrials.gov Identifier: NCT03745170).

Funding
The study was sponsored by Innovent Biologics, Inc., and co-funded by Eli Lilly and company. The study was also supported by the National Health and LGF20E030004). Innovent Biologics, Inc. involved in the design of the study and collection, analysis, and interpretation of data and in writing the manuscript. All remaining funding bodies had no role in the design of the study and collection, analysis, and interpretation of data and in writing the manuscript.

Availability of data and materials
The datasets generated and/or analyzed during the current study are not publicly available since the new drug is being submitted to the National Medical Products Administration for approval, but are available from the corresponding author on reasonable request.

Ethics approval and consent to participate
The trial protocol was approved by the Institutional Review Boards and Ethical Committee of The First Hospital Affiliated to Zhejiang University School of Medicine and Beijing Cancer Hospital, and the study was carried out strictly following the declaration of Helsinki principles; all participating patients signed consent forms before taking part in the trial. The trial national registration number is NCT02937116.

Consent for publication
Not applicable.

Competing interests
Hui Zhou, Shuyan Wang, Donglei Zhu, Bo Peng are the staff of Innovent Biologics, Inc., Suzhou, China Suzhou, China. Lin Shen is the associate editor of BMC Cancer. All remaining authors declare that they have no competing interests.