On December 11, the world's first CDK2/4/6 inhibitor, Culmerciclib Capsules (Saitanxin^®), received a drug registration approval letter from the National Medical Products Administration (NMPA). It is approved for use in combination with fulvestrant for patients with hormone receptor-positive, human epidermal growth factor receptor 2-negative (HR+/HER2-) locally advanced or metastatic breast cancer who have previously received endocrine therapy. 

Culmerciclib is a new-generation triple CDK inhibitor independently developed by Chia Tai Tianqing, a core enterprise of Sino Biopharm (1177.HK). It provides a brand-new treatment solution for clinical issues such as drug resistance to CDK4/6 inhibitors and reducing myelosuppression. 

Overcoming CDK4/6 Drug Resistance! A New Option for Breast Cancer Treatment

Breast cancer is the "number one cancer" among women globally and in China. HR+/HER2- breast cancer is the most common subtype, accounting for about 65%-70% of all breast cancer cases^[1]. Guidelines such as the Chinese Society of Clinical Oncology (CSCO) Breast Cancer Guidelines (2025) recommend CDK4/6 inhibitors in combination with endocrine therapy as the first-line treatment for advanced HR+/HER2- breast cancer^[2,3]. However, the subsequent issue of drug resistance has become a pressing clinical problem to be solved. 

Culmerciclib is a First-in-Class (FIC) CDK2/4/6 inhibitor globally. It has varying inhibitory effects on CDK2, CDK4, and CDK6 kinases, with a strong selective inhibitory capacity for CDK4 kinase. This helps delay the drug resistance issue of CDK4/6 inhibitors in clinical practice and reduce myelosuppression^[4]. 

At the Innovation Session of the 2024 Annual Meeting of Chinese Society of Clinical Oncology (CSCO), the first publicly disclosed results of the CULMINATE-1 study^[5] showed that the median progression-free survival (mPFS), the primary endpoint, in the Culmerciclib plus fulvestrant group reached 16.62 months. This was a significant extension of 9.16 months compared to the fulvestrant group, bringing a 64% reduction in the risk of disease progression or death (HR=0.36, p<0.0001). In terms of depth of response, the confirmed objective response rate (ORR) in the ITT population was significantly improved (40.21% vs 12.12%, p<0.0001). Compared with historical data, it is the only drug in similar studies with this value exceeding 40%, allowing more patients to achieve response. In terms of safety, the most common treatment-related adverse events (TRAEs) in the Culmerciclib plus fulvestrant group were mostly Grade 1-2 and were manageable. Hematological toxicities such as ≥Grade 3 myelosuppression were minimal, ensuring adherence for long-term treatment. 

Comprehensive Layout Across All Subtypes and Treatment Cycles, Multiple Breakthroughs in the Breast Cancer Pipeline

Culmerciclib has great clinical potential, and indications covering the entire treatment cycle of breast cancer are being developed simultaneously. Among them, significant clinical breakthroughs have been achieved in its use in combination with fulvestrant for the first-line treatment of advanced HR+/HER2- breast cancer and as adjuvant therapy for early HR+ breast cancer. In July 2025, a marketing application was successfully submitted for Culmerciclib plus fulvestrant injection for the initial endocrine treatment of patients with locally advanced or metastatic HR+/HER2- breast cancer. At the European Society for Medical Oncology (ESMO) Congress 2025, the clinical study results of CULMINATE-2 for this indication were publicly disclosed for the first time^[6]: the mPFS for Culmerciclib plus fulvestrant versus placebo plus fulvestrant was NR (not reached) vs. 20.2 months, with a 44% reduction in the risk of disease progression/death (HR=0.56, p=0.0004). The ORR was significantly higher than the control group (59.3% vs. 42.3%, p=0.0009). In subgroups with poor prognosis, such as those with visceral metastasis and metastases to liver, it demonstrated a more significant PFS advantage. 

Focusing on the field of breast cancer treatment, Sino Biopharm has established a layout covering all molecular subtypes, including HER2+, HER2-low, HR+/HER2-, and triple-negative breast cancer (TNBC). In terms of the treatment cycle, it systematically covers the entire spectrum of treatment scenarios from neoadjuvant, first-line, second-line and above, to adjuvant therapy, striving to provide new treatment options for more patients. Since July, TQB2102 (an HER2 bispecific ADC) intended for the treatment of HER2+ breast cancer has been granted Breakthrough Therapy Designation twice. The indication under development for HER2-low expression has entered Phase III clinical trials. Similarly, TQB2930 (an HER2 bispecific antibody), also for the treatment of HER2+ breast cancer, is currently in Phase III clinical trials. 

References:
[1] Wu Hao, Lyu Qing. Epidemiological trends of breast cancer globally and in China and implications for prevention and control: An interpretation of the "Global Cancer Statistics Report" 2018-2022 [J]. Chinese Journal of Bases and Clinics in General Surgery, 2024, 31(07):796-802. 
[2] National Comprehensive Cancer Network.NCCN Clinical Practice Guidelines in Oncology (NCCN Guideline).Breast Cancer, version 5.2023[EB/OL].[2024-01-12]. 
[3] Chinese Society of Clinical Oncology Guidelines Working Committee. Chinese Society of Clinical Oncology Guidelines for the Diagnosis and Treatment of Breast Cancer 2024 [M]. Beijing: People's Medical Publishing House. 
[4] Xu Z, Liu Y, Song B, et al.Discovery and preclinical evaluations of TQB3616, a novel CDK4-biased inhibitor.Bioorganic & Medicinal Chemistry Letters 2024; 107.
[5] TQB3616 in combination with fulvestrant for hormone receptor-positive, HER2-negative advanced breast cancer: A Phase 3, randomized, double-blind, parallel-controlled clinical trial, 2024 CSCO, Innovation Session on September 27. 
[6] Erwei song, et al.Culmerciclib plus fulvestrant as first-line treatment for HR+/HER2- advanced breast cancer cancer:A phase 3 trial(CULMINATE-2),ESMO 2025 LBA25.

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