Cationic amphiphilic drugs induce accumulation of cytolytic lysoglycerophospholipids in the lysosomes of cancer cells and block their recycling into common membrane glycerophospholipids.

Lysosomes are acidic organelles responsible for lipid catabolism, and their functions can be disrupted by cationic amphiphilic drugs that neutralize lumenal pH and thereby inhibit most lysosomal hydrolases. These drugs can also induce lysosomal membrane permeabilization and cancer cell death, but the underlying mechanism remains elusive. Here, we uncover that the cationic amphiphilic drugs induce a substantial accumulation of cytolytic lysoglycerophospholipids within the lysosomes of cancer cells, and thereby prevent the recycling of lysoglycerophospholipids to produce common membrane glycerophospholipids. Using quantitative mass spectrometry-based shotgun lipidomics, we demonstrate that structurally diverse cationic amphiphilic drugs, along with other types of lysosomal pH-neutralizing reagents, elevate the amounts of lysoglycerophospholipids in MCF7 breast carcinoma cells. Lysoglycerophospholipids constitute ∼11 mol% of total glycerophospholipids in lysosomes purified from MCF7 cells, compared with ∼1 mol% in the cell lysates. Treatment with cationic amphiphilic drug siramesine further elevates the lysosomal lysoglycerophospholipid content to ∼24 mol% of total glycerophospholipids. Exogenously added traceable lysophosphatidylcholine is rapidly acylated to form diacylphosphatidylcholine, but siramesine treatment sequesters the lysophosphatidylcholine in the lysosomes and prevents it from undergoing acylation. These findings shed light on the unexplored role of lysosomes in the recycling of lysoglycerophospholipids and uncover the mechanism of action of promising anticancer agents.

Annexin A7 mediates lysosome repair independently of ESCRT-III.

Lysosomes are crucial organelles essential for various cellular processes, and any damage to them can severely compromise cell viability. This study uncovers a previously unrecognized function of the calcium- and phospholipid-binding protein Annexin A7 in lysosome repair, which operates independently of the Endosomal Sorting Complex Required for Transport (ESCRT) machinery. Our research reveals that Annexin A7 plays a role in repairing damaged lysosomes, different from its role in repairing the plasma membrane, where it facilitates repair through the recruitment of ESCRT-III components. Notably, our findings strongly suggest that Annexin A7, like the ESCRT machinery, is dispensable for membrane contact site formation within the newly discovered phosphoinositide-initiated membrane tethering and lipid transport (PITT) pathway. Instead, we speculate that Annexin A7 is recruited to damaged lysosomes and promotes repair through its membrane curvature and cross-linking capabilities. Our findings provide new insights into the diverse mechanisms underlying lysosomal membrane repair and highlight the multifunctional role of Annexin A7 in membrane repair.

Identification of lysosome-targeting drugs with anti-inflammatory activity as potential invasion inhibitors of treatment resistant HER2 positive cancers.

PURPOSE: Most HER2 positive invasive cancers are either intrinsic non-responsive or develop resistance when treated with 1st line HER2 targeting drugs. Both 1st and 2nd line treatments of HER2 positive cancers are aimed at targeting the HER2 receptor directly, thereby strongly limiting the treatment options of HER2/ErbB2 inhibition resistant invasive cancers. METHODS: We used phenotypic high throughput microscopy screening to identify efficient inhibitors of ErbB2-induced invasion using 1st line HER2 inhibitor trastuzumab- and pertuzumab-resistant, p95-ErbB2 expressing breast cancer cells in conjunction with the Prestwick Chemical Library®. The screening entailed a drug's ability to inhibit ErbB2-induced, invasion-promoting positioning of lysosomes at the cellular periphery, a phenotype that defines their invasiveness. In addition, we used high throughput microscopy and biochemical assays to assess the effects of the drugs on lysosomal membrane permeabilization (LMP) and autophagy, two features connected to cancer treatment. Using 2nd line HER2 inhibitor lapatinib resistant 3-dimensional model systems, we assessed the effects of the drugs on ErbB2 positive breast cancer spheroids and developed a high-throughput invasion assay for HER2 positive ovarian cancer organoids for further evaluation. RESULTS: We identified Auranofin, Colchicine, Monensin, Niclosamide, Podophyllotoxin, Quinacrine and Thiostrepton as efficient inhibitors of invasive growth of 2nd line HER2 inhibitor lapatinib resistant breast cancer spheroids and ovarian cancer organoids. We classified these drugs into four groups based on their ability to target lysosomes by inducing autophagy and/or LMP, i.e., drugs inducing early LMP, early autophagy with late LMP, late LMP, or neither. CONCLUSIONS: Our results indicate that targetable lysosome-engaging cellular pathways downstream of ErbB2 contribute to invasion. They support lysosomal trafficking as an attractive target for therapy aiming at preventing the spreading of cancer cells. Since these drugs additionally possess anti-inflammatory activities, they could serve as multipurpose drugs simultaneously targeting infection/inflammation and cancer spreading.