Induction of Methuosis in Breast Cancer Stem Cells by a Cobalt(III) Complex Evokes Immunotherapeutic Response.

Cancer stem cells (CSCs) drive metastasis and relapse and are resistant to conventional apoptosis-inducing chemotherapies. Methuosis, a non-apoptotic form of cell death, is largely unexplored for anti-CSC therapy. Here we report a cobalt(III)-cyclam complex (1) incorporating pyrene and diflunisal moieties that induces features consistent with methuosis in a CSC model. Mechanistic investigations revealed that 1 induces phenotypes consistent with methuosis in breast CSCs, including extensive cytoplasmic vacuolation, elevated Rab7 and LAMP1 expression, activation of JNK and p38 MAPK pathways, G2/M cell-cycle arrest, augmented intracellular reactive oxygen species levels, and disruption of the mitochondrial membrane potential. Beyond direct cytotoxicity, 1 induces an anti-breast CSC immunogenic response by perturbing the inhibitory damage-associated molecular patterns axis through cyclooxygenase-2 downregulation. When formulated as polymeric nanoparticles and evaluated in a murine metastatic triple-negative breast cancer model, 1 penetrates tumour tissue and suppresses tumour growth more than cisplatin. The nanoparticle formulation activates anti-tumour immunity, characterised by enhanced infiltration of T cells and mature dendritic cells in tumours and tumour-draining lymph nodes. Intratumoral T-cell recruitment is associated with M2-to-M1 macrophage polarisation and depletion of myeloid-derived suppressor cells. This work identifies 1 as the first metal complex shown to induce features consistent with methuosis in a CSC model.