SOT106 now holds both orphan drug and fast track designations across soft tissue sarcoma and osteosarcoma ahead of a first-in-human trial.
The FDA has granted orphan drug designation to SOT106, an investigational antibody-drug conjugate (ADC), for the treatment of patients with soft tissue sarcoma (STS), and fast track designation to the agent for the treatment of patients with osteosarcoma.1
Notably, with these additions, SOT106 now holds both designations in both indications. The agent previously
SOT106 has not yet entered clinical testing; the designations were supported by target biology and preclinical findings. SOT106 targets leucine-rich repeat-containing 15 (LRRC15), which is expressed across multiple prevalent sarcoma subtypes. Preclinical studies, including patient-derived xenograft (PDX) models of both osteosarcoma and STS, showed that SOT106 had antitumor activity and was well tolerated.1
In early preclinical studies, the ADC demonstrated tumor regression in an LRRC15 low-expressing PDX model of pediatric osteosarcoma in which a first-generation LRRC15-targeting ADC was ineffective, in addition to producing complete responses across STS subtypes, non–small cell lung cancer, and head and neck squamous cell carcinoma models.4
“These additional designations mark another important milestone for SOT106 and reflect the growing momentum behind our ADC portfolio,” said Radek Spisek, MD, PhD, chief executive officer of SOTIO in a news release.1 “Patients with sarcoma continue to face limited treatment options, underscoring the need for innovative targeted therapies. As we advance SOT106 toward the clinic, we believe it has the potential to become an important treatment option for patients in need.”
Sotio expects to initiate a first-in-human trial of SOT106 later in 2026, and no clinical efficacy or safety data for the agent have been reported to date.3
SOT106 pairs a LRRC15-directed antibody conjugated to the microtubule-disrupting agent monomethyl auristatin E (MMAE), linked via LigaChem Biosciences' ConjuAll site-specific conjugation technology and releases the payload selectively within the tumor.1,4,5 Once the ADC binds LRRC15 at the cell surface, it is then internalized and trafficked to the lysosome, where the payload is released to block microtubule polymerization and induce cell death. Since MMAE is membrane permeable, the free payload can also enter neighboring cells, producing a bystander effect.
LRRC15 is expressed both on malignant cells and in the tumor stroma of mesenchymal cancers, including a broad subset of sarcomas, whereas its expression in normal adult tissue is limited, supporting its selection as an ADC target. Preclinical models showed a favorable pharmacokinetic and safety profile, in vivo stability, and a high therapeutic index, with Sotio describing SOT106 as a potentially best-in-class LRRC15-directed ADC.
Targeted strategies have helped to improve outcomes in select sarcoma subtypes. In the
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"Our preparations for expected bezuclastinib launches in both GIST and systemic mastocytosis later [in 2026] are well underway,” said Andrew Robbins, president and chief executive officer of Cogent Biosciences, stated in a news release about the regulatory decision.
