The IPR inhibitor desmethylxestospongin B reduces tumor cell migration, invasion and metastasis by impairing lysosome acidification and β1-integrin recycling.

Cancer is the second leading cause of death worldwide. >90 % of cancer-related deaths are due to metastasis, a process that depends on the ability of cancer cells to leave the primary tumor, migrate, and colonize different tissues. Inositol 1,4,5-trisphosphate receptor (IPR)-mediated Ca signaling plays an essential role in maintaining the homeostasis of cancer cells and the sustained proliferation. Desmethylxestospongin B (dmXeB) is a specific inhibitor of the IPR that selectively arrests cell proliferation and promotes cancer cell death at high concentrations. However, whether migration, invasion and metastasis can be affected by this drug is unknown. Here, by using the highly metastatic triple negative breast cancer (TNBC) cell line MDA-MB-231, we demonstrate that a prolonged inhibition of IPR-mediated Ca signals with dmXeB significantly reduces cell migration and invasion in vitro and metastasis in vivo. We found that this phenomenon was independent of the bioenergetic control of IPR over the mitochondria and AMPK activation. Furthermore, employing a tandem LC3-GFP-mcherry assay, we found that prolonged inhibition of IPR with dmXeB leads to diminished autophagic flux. This reduction can be attributed to impaired lysosomal acidification, as evidenced by assessments using DQ-BSA and pHrodo. Since cell migration requires appropriate assembly and disassembly of focal adhesions, along with the internalization and recycling of integrins via autophagy, we explored the dependency of integrin recycling from autophagosomes, finding that IPR inhibition with dmXeB impaired the recycling of β1-integrins, which accumulated within autophagosomes. Our findings reveal an unexpected effect of IPR inhibition with dmXeB in cancer cells that could represent a novel therapeutic strategy for the treatment of cancer metastasis.