Summit Bets Bispecific Against Best-in-Class: No Proof-of-Concept, Exceptional Efficacy Bar

Summit Therapeutics Initiates HARMONi-GU1 Study for Urothelial Carcinoma

Summit Therapeutics has initiated the multi-regional, randomized Phase II/III HARMONi-GU1 study to evaluate ivonescimab in combination with enfortumab vedotin (EV) for previously untreated locally advanced or metastatic urothelial carcinoma. The trial, expected to enroll around 800 participants, will compare this regimen against the current standard of care, pembrolizumab and EV. The initial Phase II stage will determine the recommended Phase III dose, while the Phase III portion will assess progression-free survival and overall survival. This expansion marks a significant step in Summit's global development program for ivonescimab into additional tumor types.

• The HARMONi-GU1 trial is a multi-regional, global, randomized Phase II/III study enrolling approximately 800 participants. It aims to compare ivonescimab plus enfortumab vedotin against pembrolizumab plus enfortumab vedotin in patients with previously untreated locally advanced or metastatic urothelial carcinoma. The Phase II stage will establish the optimal dose, while the Phase III stage will primarily evaluate progression-free survival and overall survival.
• Ivonescimab is an investigational tetravalent, intentionally-engineered bispecific antibody targeting both programmed cell death protein 1 (PD-1) and vascular endothelial growth factor (VEGF). Its dual mechanism is considered scientifically compelling for bladder cancer, as both angiogenesis and immune evasion are critical features of urothelial carcinoma biology, suggesting a potential therapeutic advantage.
• The initiation of HARMONi-GU1 further expands Summit Therapeutics' global ivonescimab development program, which already includes 16 ongoing Phase III studies across various cancer types. Originally engineered by Akeso, ivonescimab has been administered to over 4,000 patients in clinical research worldwide and used in over 70,000 individuals in commercial settings in China, demonstrating its broad clinical experience.

Targeting Key Drivers of Urothelial Carcinoma with Ivonescimab

The development and progression of urothelial carcinoma are driven by distinct and often mutually exclusive genetic alterations that define its molecular subtypes. A primary pathway, characteristic of low-grade, non-muscle-invasive bladder cancer (NMIBC), involves frequent mutations in Fibroblast Growth Factor Receptor 3 (FGFR3), which are often found alongside mutations in PIK3CA. In contrast, high-grade and muscle-invasive tumors are predominantly characterized by mutations in TP53 and RB1. These high-grade cancers typically exhibit greater genomic instability, a higher tumor mutational burden (TMB), and an APOBEC mutational signature. The alterations in FGFR3 and TP53 are largely mutually exclusive, highlighting two divergent carcinogenic routes in urothelial carcinoma. Other key genetic events include inactivating mutations in Notch pathway components and activating mutations in RAS genes, which are themselves mutually exclusive with FGFR3 mutations.

These genetic drivers converge on critical signaling pathways and cellular processes that promote tumorigenesis and metastasis. Dysregulation of receptor tyrosine kinase (RTK) signaling is a central theme, with the loss of Notch signaling function emerging as a key event that enhances proliferation by increasing ERK1/2 phosphorylation. Concurrently, activation of the Sonic Hedgehog (Shh) signaling pathway promotes epithelial-mesenchymal transition (EMT), a process integral to invasion, drug resistance, and metastatic progression. The biology of cancer stem cells (CSCs) is also pivotal, as these cells are implicated in tumor initiation, recurrence, and therapeutic resistance. CSCs can arise from differentiated tumor cells and can be induced into a dormant, chemoresistant state by factors in the tumor microenvironment, such as IFN-γ.

Addressing Unmet Needs in Advanced Urothelial Carcinoma

Despite significant advances in treating locally advanced or metastatic urothelial carcinoma (la/mUC), including the success of antibody-drug conjugates and immune checkpoint inhibitors, major unmet needs persist. A large proportion of patients are ineligible for standard cisplatin-based chemotherapy or experience limited long-term benefit from available therapies due to resistance. This has driven research to focus on specific patient populations and biomarker-driven strategies to improve outcomes.

• Cisplatin-Ineligible Patients: A primary focus is the substantial population of patients who are ineligible for cisplatin due to comorbidities. These patients often experience rapid disease progression, representing a critical therapeutic gap and a key population for novel treatment strategies.

• Biomarker-Driven Patient Selection: A pressing need exists for validated, predictive biomarkers to guide treatment and improve patient selection. Current markers like PD-L1 expression have limited utility, creating a need to define and validate the role of target expression levels for ADCs (e.g., NECTIN-4, TROP2, HER2) to enable more precise therapeutic application.

• Populations with Specific Molecular Alterations: Research is increasingly targeting patient subgroups defined by specific molecular profiles. This includes patients with FGFR2 and FGFR3 alterations, for whom the targeted inhibitor erdafitinib is approved, and those with HER2-expressing tumors, particularly the micropapillary subtype, which show the highest HER2 expression rates.

• Overcoming Therapeutic Resistance: A significant challenge is overcoming primary and acquired resistance to chemotherapy, immunotherapy, and targeted agents, which frequently limits durable disease control. Consequently, a major area of investigation involves developing rational combination therapies—such as combining erdafitinib with immunotherapy—to enhance efficacy and prolong patient survival.

Ivonescimab's Expanding Pipeline Beyond Urothelial Carcinoma

Beyond urothelial carcinoma, ivonescimab's clinical development program is rapidly expanding, with a significant focus on non-small cell lung cancer (NSCLC), where it recently gained its first approval. The pipeline also includes investigations into a variety of other solid tumors, such as breast, ovarian, and pancreatic cancers. These trials are evaluating ivonescimab both as a monotherapy and in combination with chemotherapy, radiotherapy, and other immunotherapies across different treatment settings.