S-phase targeted treatment triggers caspase-dependent lytic immunogenic cell death with pyroptotic features in cancers.

Immunogenic cell death (ICD) is a type of cell death that can enhance anti-tumour immune responses of chemotherapies and targeted therapies by releasing DAMPs and cytokines that activate dendritic cells and T cells, thereby engaging the patient's immune system to combat the cancer. Pyroptosis and necroptosis are strongly immunogenic because they release DAMPs and inflammatory signals through pore-forming proteins, whereas apoptosis can be tolerogenic. This immunogenic response is contingent on a functional immune system. Unfortunately, most conventional chemotherapies and many targeted therapies also impair the immune system. Here, we investigated the mechanism by which the tumour-selective treatment of Checkpoint kinase 1 inhibitor (CHK1i) combined with low-dose hydroxyurea (LDHU) promotes ICD and anti-tumour immunity. We show that CHK1i+LDHU induces S-phase arrest and caspase-dependent lytic cell death with features of pyroptosis, including gasdermin E cleavage, but cell death was not dependent solely on gasdermin cleavage. Inhibiting caspases was sufficient to block both tumour cell killing and treatment immunogenicity. The mechanism does not rely on any single caspase or gasdermin, consistent with the contributions from multiple caspase-dependent processes. By contrast, doxorubicin that predominantly triggers apoptosis was less effective at stimulating anti-tumour immune responses despite triggering similar levels of cell death. These findings demonstrate that caspase-dependent lytic cell death with pyroptotic features promotes a more effective stimulus for anti-tumour immunity.