The first ADC bearing the ferroptosis inducer RSL3 as a payload with conservation of the fragile electrophilic warhead

The iron-dependent, non-apoptotic cell death, known as ferroptosis is an emerging strategy for the development of anticancer drugs. RSL3 was identified as an activator of ferroptosis through the inhibition of the glutathione peroxidase 4 (GPX4) which plays a crucial role in the cellular lipid oxidative stress. RSL3 is characterized by the presence of an electrophilic chloroacetyl moiety, namely warhead which covalently bonds to the catalytic and nucleophilic selenocysteine residue (Sec46) of GPX4. Like the major ferroptosis inducers, RSL3 suffers from lack of selectivity toward tumor cells. In this study, we report the first synthesis of an antibody-drug conjugate (ADC) containing RSL3 fragment and trastuzumab with the aim to deliver the agent selectively to tumors. The synthesis uses a judiciously chosen strategy to preserve the vital but fragile warhead. Full characterization of the ADC was accomplished, demonstrating the generation of a homogeneous DAR 8 conjugate. The robustness of the synthesis was successfully applied to another ADC associating the anti-CD74 mAb milatuzumab. The ADC induces ferroptotic cell death through reactive oxygen species accumulation and increases the activity of doxorubicin. The ADC associating trastuzumab and RSL3 may therefore offer potential applications in vectorized therapy alone or in combination with conventional chemotherapies.