SOTIO Biotech’s SOT106 has received U.S. FDA Orphan Drug Designation for osteosarcoma — an important milestone both for the ADC field and for sarcoma patients facing high unmet medical need. As SOT106 advances toward first-in-human studies planned for H2 2026, its design offers a clear illustration of where ADC innovation is heading: precise target biology paired with more controlled, site-specific chemistry.

Here’s a closer look at the science behind it.

Target Biology: LRRC15

SOT106 targets LRRC15, a cell-surface protein broadly expressed across sarcoma subtypes and tumor-associated stroma, while showing limited expression in normal tissue. This expression profile makes LRRC15 an attractive “address label” for directing a cytotoxic payload specifically toward the tumor microenvironment, rather than healthy tissue.

Conjugation Chemistry: ConjuAll

SOT106 pairs SOTIO’s proprietary antibody with LigaChem Biosciences’ ConjuAll ADC platform. Unlike conventional conjugation approaches that can generate heterogeneous mixtures of ADC species, site-specific conjugation is designed to produce a more uniform molecule with controlled drug loading and improved reproducibility — both important factors for consistent manufacturing and predictable clinical performance.

From a chemistry standpoint, the platform is particularly notable because it addresses two central challenges in ADC design:

1. How the payload is attached

ConjuAll uses site-specific bioconjugation chemistry to generate highly homogeneous ADCs, allowing tighter control over the relationship between antibody, linker, and payload.

2. How the payload is released

The linker system incorporates beta-glucuronide chemistry, engineered to remain stable in systemic circulation and favor payload release following beta-glucuronidase-mediated cleavage within the tumor environment. In SOT106, the cytotoxic payload is MMAE.

Why SOT106 Is Worth Watching

SOT106 is a carefully engineered delivery system built around four pillars: target selection, linker stability, controlled conjugation, and tumor-selective payload release. The SOTIO–LigaChem collaboration is a strong example of how biology and chemistry increasingly need to work in lockstep in modern ADC development — and SOT106 is a program worth following closely as it advances toward the clinic.

SigutLabs’ Perspective on Linker-Payload Chemistry

Programs like SOT106 highlight exactly the kind of chemistry challenges we work on every day at SigutLabs: designing linkers that balance circulation stability with tumor-selective release, and enabling site-specific, homogeneous conjugation rather than relying on stochastic attachment. Whether it’s cleavable linker chemistry, cysteine-selective or click-based attachment strategies, or custom linker-payload design, our team supports ADC developers from early linker design through gram-scale synthesis and CDMO tech transfer.

If your ADC program needs a chemistry partner, contact us — we’re ready to support your project.