On August 30, 2020 CStone Pharmaceuticals (SUZHOU) Co., Ltd. ("CStone", HKEX: 2616) reported that the US Food and Drug Administration (FDA) has completed their review of the Investigational New Drug (IND) application for anti-PD-L1 monoclonal antibody sugemalimab (CS1001) monotherapy in the relapsed or refractory extranodal natural killer (NK)/T-cell lymphoma (R/R ENKTL) with study may proceed (SMP) letter received (Press release, CStone Pharmaceauticals, AUG 30, 2020, View Source [SID1234564157]).

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Sugemalimab is an investigational fully human, full-length anti-PD-L1 monoclonal antibody developed by CStone. Compared with other drugs of the same class, sugemalimab has a lower risk of immunogenicity and potential toxicities in patients. CS1001-201 is a single-arm, multicenter pivotal Phase II clinical study designed to evaluate sugemalimab monotherapy in R/R ENKTL. The IND clearance indicates that the ongoing CS1001-201 study in China will be extended to the US.

ENKTL is a subtype of mature T cell and NK cell lymphoma. Epidemiology of the disease is characterized by higher incidence rates in Asia than in Europe or North America. In China, ENKTL accounts for approximately 6% of all lymphoma cases[1]. R/R ENKTL is highly malignant and aggressive, and has a poor prognosis. Patients with R/R ENKTL lack effective salvage treatments if standard L-asparaginase-based regimens fail, and do not respond well to traditional treatments. For these patients, clinicians almost run out of treatment choices because the disease progresses rapidly with an extremely short overall survival (OS) as indicated by historically reported 1-year OS rate <20%[2]. The currently approved targeted monotherapy in China has a complete response (CR) rate of approximately 6%[3],[4]. There are vast unmet medical needs in this patient population of which the first-line treatment has failed. Sugemalimab is expected to provide new treatment options for these patients.

Dr. Jason Yang, Chief Medical Officer of CStone, commented: "For the treatment of ENKTL, CR rate is a critical outcome measure. Data reported for CS1001-201 study on 2019 ASH (Free ASH Whitepaper) meeting shows that sugemalimab demonstrated a CR rate of 33.3% with a durable response, an objective response rate (ORR) of 43.3%, and 1-year OS rate of 72.4%. These results represent a major breakthrough compared to current treatment options and support sugemalimab as a potential conditioning regimen for hematopoietic stem cell transplantation. We will work closely with the US FDA and the National Medical Products Administration (NMPA), to bring sugemalimab to R/R ENKTL patients worldwide soon."

Overview of the CS1001-201 trial

CS1001-201 is a single-arm, multicenter Phase II clinical study designed to evaluate sugemalimab monotherapy in R/R ENKTL. The primary endpoint of the trial is ORR assessed by an independent radiological review committee.

According to updated results reported at the 2019 American Society of Hematology (ASH) (Free ASH Whitepaper) Annual Meeting, as of October 8, 2019, a total of 32 patients with R/R ENKTL were enrolled in the study. All patients received sugemalimab 1200 mg intravenously every 3 weeks until disease progression or intolerable toxicity. The median duration of follow-up was 6.54 months (range, 0.72–15.64).

Preliminary efficacy data

Sugemalimab demonstrated robust efficacy with a high CR rate and durable response in R/R ENKTL patients:

Among the 30 efficacy-evaluable patients, the investigator-assessed ORR was 43.3%
10 patients (33.3%) achieved CR and were still in remission
3 patients (10.0%) achieved partial response (PR), and 1 additional patient achieved PR after pseudo-progression
The median duration of response (DoR) was not reached, and the maximum DoR was 10.9+ months
The 1-year OS was 72.4% (95% CI: 52.0%–85.2%)
Safety data

Sugemalimab was well tolerated in patients with R/R ENKTL:

30 patients (93.8%) reported treatment-emergent adverse events (TEAEs), 24 patients (75.0%) reported treatment-related adverse event (TRAEs), of which 3 (9.4%) had Grade >3 TRAEs
Grade 5 AEs were reported in 3 patients (9.4%), and none were assessed as related to sugemalimab
Immune-related AEs (irAEs) were reported in 5 patients (15.6%); except for one case of Grade 3 rash, all irAEs were Grade 1 in severity
TEAEs that led to permanent treatment discontinuation occurred in 4 patients (12.5%)
No deaths due to AEs were assessed as related to sugemalimab
About Sugemalimab

Sugemalimab is an investigational anti-PD-L1 monoclonal antibody discovered by CStone. Authorized by the U.S.-based Ligand Corporation, sugemalimab is developed by the OmniRat transgenic animal platform, which can generate fully human antibodies in one stop. As a fully human, full-length anti-PD-L1 monoclonal antibody, sugemalimab mirrors the natural G-type immunoglobulin 4 (IgG4) human antibody, which can reduce the risk of immunogenicity and potential toxicities in patients, a unique advantage over similar drugs.

Sugemalimab has completed a Phase I dose-escalation study in China. During Phase 1a and 1b stages of the study, sugemalimab showed good antitumor activity and good tolerability in multiple tumor types.

Currently, sugemalimab is being investigated in a number of ongoing clinical trials. In addition to a Phase I bridging study in the U.S., the clinical program in China includes one multi-arm Phase Ib study for several tumor types, one Phase II registrational study for lymphoma, and four Phase III registrational studies, respectively, for stage III/IV NSCLC, gastric cancer, and esophageal cancer.