STCube New Drug Demonstrates Improved Survival Rates in Colorectal Cancer

STCube announced on the 22nd that its immune-oncology drug under development, 'Nelmastobat,' increased the median progression-free survival (mPFS) without disease progression to 4.4 months in patients with advanced metastatic colorectal cancer who have undergone third-line or later treatments, enhancing the likelihood of success in developing a first-in-class innovative drug.

This is more than twice the efficacy compared to the average mPFS of 2 months with existing standard treatments such as Stivarga or Lonsurf. The research team led by Professor Suhyun Lee from the Department of Oncology at Korea University Anam Hospital will present on the "Excellent safety and promising anticancer activity of Nelmastobat combined with capecitabine in metastatic colorectal cancer" at the American Society of Clinical Oncology Gastrointestinal Cancers Symposium (ASCO GI 2025) held in the United States from the 23rd to the 25th.

Professor Lee’s team is conducting a researcher-initiated clinical trial (IIT) phase 1b/2 to evaluate the safety and efficacy of Nelmastobat combined with capecitabine in metastatic colorectal cancer patients who have undergone third-line or later treatments. Currently in phase 2, the interim analysis results of 12 MSS (microsatellite stable) colorectal cancer patients enrolled in phase 1b were disclosed for the first time at this ASCO GI.

The goal of phase 1b is to determine the maximum tolerated dose (MTD) and recommended phase 2 dose (RP2D) of Nelmastobat combination therapy. The research team confirmed the safety and potential anticancer activity of Nelmastobat combination therapy and investigated the correlation between BTN1A1 expression rate as a biomarker and treatment efficacy through immunohistochemistry (IHC) analysis.

Safety evaluation results from phase 1b showed no unexpected adverse reactions in patients with advanced metastatic colorectal cancer treated with Nelmastobat combination therapy. Side effects related to Nelmastobat were mild grade 1 fatigue, while hand-foot syndrome (HFS), nausea, and other symptoms were confirmed as chemotherapy-related side effects from capecitabine.

In efficacy evaluation, the objective response rate (ORR) was 17%, with 2 partial responses (PR) reported among 12 patients. The clinical benefit rate (CBR) at 16 weeks (4 months) was 66.7% (8 out of 12 patients), and an mPFS of 4.4 months was achieved at the data cutoff for the abstract. Phase 2 is currently ongoing with capecitabine at 1000 mg/m2 and Nelmastobat at 800 mg doses.

Professor Suhyun Lee stated, "Despite enrolling patients who have effectively undergone fourth-line or later treatments with no therapeutic alternatives, PFS of over 4 months has been reported," adding, "This shows superior results compared to existing treatments."

Nelmastobat targets the newly discovered immune checkpoint protein BTN1A1. STCube is conducting clinical trials of Nelmastobat as a new immune-oncology therapy targeting resistant cancer cells, based on the unique characteristics of BTN1A1 expressed in dormant cancer cells and chemo-resistant cancer cells.

Seunghan Yoo, Chief Scientific Officer (CSO) of STCube, explained, "In the ongoing clinical trials, we confirmed that a high expression rate of BTN1A1 is highly correlated with improved patient survival," adding, "BTN1A1 will become a new diagnostic marker for patients who do not respond to PD-1 or PD-L1 targeted therapies."