Ouabain

Immune cells migrate via actomyosin contractility mediated by myosin IIA activation, wherein the lysosomal Ragulator complex–MPRIP interaction is crucial. However, the precise mechanism underlying lysosome-mediated myosin IIA activation has not been elucidated. Here, we found that calcium efflux from the lysosomal TRPML1 channel promotes leukocyte trafficking by enhancing the interaction between the Ragulator complex and MPRIP. Disrupting the lysosome-anchoring site of Lamtor1 impaired the localization of the Ragulator complex to lysosomes, diminishing the TRPML1-mediated leukocyte migration and interaction between Lamtor1 and MPRIP. Furthermore, ouabain, a cardiac glycoside, dissociated Lamtor1 from lysosomes, inhibiting the interaction between the Ragulator complex and myosin IIA activation, thereby suppressing cell migration. Therapeutically, ouabain ameliorated the severity of MSU-induced gouty arthritis and LPS-induced lung injury in mice by inhibiting leukocyte infiltration. Overall, lysosomes facilitate the interaction between the Ragulator complex and MPRIP by supplying calcium ions through TRPML1 channels, thereby activating myosin IIA and promoting leukocyte migration.

There is an urgent need for new therapeutic strategies against aggressive triple-negative breast cancer (TNBC), and drug repurposing offers a promising, time- and cost-effective solution. We previously reported that TGFβ leads to the tumorigenic role of NDRG1 in TNBC. Here, we aimed to identify drugs that mimic the transcriptomic signature after the inhibition of TGFβ-induced NDRG1 and to determine their antitumor properties. The transcriptomic signature was obtained by RNA sequencing after gene silencing of TGFβ-induced NDRG1 expression in TNBC cells. For the drug repositioning study, the transcriptome was further computationally analyzed by using the Connectivity Map tool. Efavirenz, ouabain, and vinburnine were selected as the repurposed drug candidates to evaluate their therapeutic potential in TNBC models as monotherapies and pairwise combinations. We determined that the candidate drugs significantly reduced tumor cell proliferation, cancer stem cells, self-renewal, clonogenic properties, and migration abilities in TNBC cell lines through the blockade of AKT. Importantly, we validated their translational potential in TNBC patient-derived xenograft organoids in combination with docetaxel. After validating that the drugs decreased p-AKT and Ki67, we demonstrated their antitumor activity in combination with docetaxel in organoids. In addition, drugs also showed efficacy in a docetaxel-resistant TNBC model, supporting their potential to overcome chemoresistance. In conclusion, these findings demonstrate the potential of efavirenz, ouabain, and vinburnine as repurposed agents capable of inhibiting TNBC cell proliferation, stemness, and migration. Their synergistic effects with docetaxel in organoid cultures further underscore their translational relevance and highlight a promising strategy for combination therapies to improve TNBC treatment.