On May 25, 2020 CStone Pharmaceuticals ("CStone" or the "Company", HKEX: 2616) reported that in an abstract at the 2020 American Society of Clinical Oncology (ASCO) (Free ASCO Whitepaper) Annual Meeting, it will release updated results from the CS1001-101 study of the Company’s anti-PD-L1 monoclonal antibody CS1001 (Press release, CStone Pharmaceauticals, MAY 25, 2020, View Source [SID1234558551]).

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"We are pleased that CS1001 in combination with platinum-based chemotherapy has demonstrated promising anti-tumor activity and good safety, and that the PoC data supports its development," said Dr. Jason Yang, Chief Medical Officer of CStone. "CStone has already completed subject enrollment for the Phase III study of CS1001, in which CS1001 will be used in combination with platinum-based chemotherapy for first-line treatment of advanced NSCLC. The top-line data from the Phase III trial are expected to be published in the coming months. It is worth mentioning that this trial is the first Phase III study in China targeting first-line NSCLC treatment with both squamous and non-squamous sub-populations involved; hence, its results are highly anticipated."

About the CS1001-101 study

The CS1001-101 study is a Phase I study designed to evaluate the safety, tolerability, pharmacokinetics, and anti-tumor activity of CS1001 in patients with advanced solid tumors or lymphomas. The results of CS1001-101 study to be released at this year’s ASCO (Free ASCO Whitepaper) Annual Meeting are efficacy data from the Phase Ib cohort study, which is a proof of concept (POC) study aiming to assess the efficacy and safety of CS1001 in combination with platinum-based chemotherapy for first-line treatment of NSCLC.

Phase Ⅰb Study Results

21 and 20 patients were respectively enrolled in the non-squamous and squamous NSCLC cohorts.

Efficacy data

• As of July 1, 2019, 10 patients from each of the two cohorts had reached partial response (PR), resulting in an ORR of 47.6% for the non-squamous NSCLC cohort, and 58.8% for the squamous NSCLC cohort. The median duration of response (mDoR) and median progression-free survival (mPFS) endpoints were not reached due to the short median follow-up duration prior to the data cutoff (non-squamous NSCLC: 5.4 months; squamous NSCLC: 3.9 months).

• Updated efficacy data collected during the most recent follow-up period (the median follow-up duration as of February 19, 2020: non-squamous NSCLC: 13.4 months; squamous NSCLC: 11.3 months) are shown in the table below.

ORR (%)

mPFS (months), 95% CI

mDoR (months), 95% CI

Non-squamous NSCLC cohort of the CS1001 Phase Ib study (N=21)

47.6 6.5 (4.40, 11.7)
8.7 (1.77, -)
Squamous NSCLC cohort of the CS1001 Phase Ib study (N=20)

75.0 8.4 (8.18, -)
6.4 (6.24, -)
Safety data

• As of the data cutoff on July 1, 2019, 18 patients (85.7%) in the non-squamous NSCLC cohort reported CS1001-related AEs, and 6 patients (28.6%) reported TRAEs of Grade 3 or higher. 5 patients reported immune-related AEs (irAEs), with the most common irAEs being elevated alanine aminotransferase (ALT) levels (N=4, Grade ≤2) and elevated aspartate aminotransferase (AST) levels (N=3, Grade ≤2).

• In the squamous NSCLC cohort, 18 patients (90.0%) reported TRAEs, of which 5 patients (25%) had TRAEs of Grade 3 or higher. IrAEs occurred in 3 patients with rash (N=2, Grade ≤2) being the most common irAE.

• There were no TRAEs leading to study withdrawal.

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About CS1001

CS1001 is an investigational monoclonal antibody directed against PD-L1, currently being developed by CStone. Authorized by the U.S. based Ligand Corporation, CS1001 is developed by the OMT transgenic animal platform, which can generate fully human antibodies in one step. As a fully human, full-length anti-PD-L1 monoclonal antibody, CS1001 mirrors natural G-type immunoglobulin 4 (IgG4) human antibody, which can reduce the risk of immunogenicity and potential toxicities in patients, potentially representing a unique advantage over similar drugs.

CS1001 has completed a Phase I dose-escalation study in China, in which it demonstrated good tolerability and produced sustained clinical benefits during the Phase Ia stage of the study.

CS1001 is being investigated in a number of ongoing clinical trials, including one Phase I bridging study in the U.S., one multi-arm Phase Ib study, two Phase II registrational studies, and four Phase III studies in China, for several tumor types.