Sacituzumab Tirumotecan vs MMAE-ADCs in Advanced Urothelial Carcinoma (FUSCC-SPARE-UC-01)

Metastatic urothelial carcinoma (mUC) is associated with a poor prognosis, and traditional platinum-based chemotherapy offers limited clinical benefit with significant toxicity. In recent years, the emergence of antibody-drug conjugates (ADCs) has transformed the treatment landscape of mUC. Nectin-4-directed enfortumab vedotin (EV) and HER2-directed disitamab vedotin (DV) have demonstrated breakthrough survival benefits in multiple pivotal clinical studies. EV plus pembrolizumab (EVP) and DV plus toripalimab (DVT) have been approved and are increasingly adopted as first-line treatments for mUC, with growing utilization in Chinese clinical practice.

However, as patient survival extends, the long-term safety profile of ADCs has become a major clinical challenge. Both EV and DV utilize MMAE as their cytotoxic payload, a potent microtubule- targeting agent. Non-specific uptake of these ADCs may lead to the release of MMAE within peripheral nerves, potentially causing microtubule dysregulation. By interfering with microtubule dynamics and inhibiting microtubule-dependent axonal transport, MMAE is thought to contribute to the development of peripheral neuropathy. Clinical data indicate that EV and DV cause a high incidence of peripheral neuropathy. Numbness, pain, and motor dysfunction significantly impair patients' activities of daily living (ADLs). Given the absence of effective prophylactic or therapeutic agents for peripheral neuropathy, clinical management is currently limited to dose reductions or complete treatment discontinuation, which will inevitably diminish anti-tumor efficacy.

Sacituzumab tirumotecan (sac-TMT) is a novel TROP2-directed ADC delivering a topoisomerase I (Topo-I) inhibitor payload. This payload induces DNA double-strand breaks within the cell nucleus, completely avoiding interference with the cytoskeletal microtubule system. This mechanistic difference fundamentally eliminates the biological basis for axonal transport blockade. Preliminary data from the Phase 1/2 MK-2870-001/KL264-01 study showed that sac-TMT achieved an overall objective response rate (ORR) of 31% and a median overall survival (OS) of 12.1 months in previously treated mUC patients, demonstrating a favorable efficacy profile. Notably, no typical drug-related peripheral neurotoxicity events were observed, highlighting a neuroprotective advantage.

The SPARE-UC-01 study is a head-to-head, Phase II clinical trial to compare the neurotoxicity and anti-tumor efficacy of sac-TMT versus sequential MMAE-based ADC therapy. The study targets a population that has progressed on or is intolerant to prior EVP or DVT. By comparing sac-TMT to the sequential use of alternative MMAE-based ADCs, the research aims to provide an evidence-based sequential treatment strategy. The study utilizes an integrated evaluation system designed to quantitatively capture the spectrum of neurotoxicity. This includes investigator-assessed NCI-CTCAE v5.0 scoring of Peripheral Neuropathy Progression Rate (PNPR), instrument-based nerve conduction studies (NCS), and patient- reported quality-of-life outcomes (PROs). Such a three-dimensional paradigm ensures that both structural nerve damage and functional disability are accurately documented. In view of the substantial population of patients who undergo discontinuation of MMAE-ADCs due to cumulative neurotoxicity, an observational cohort has been established within this study. This cohort aims to characterize the clinical utility of sac-TMT in these patients. Given that its payload does not target the microtubule system, sac-TMT is expected to provide effective treatment without introducing additional neurotoxicity.