Ferroptosis is caused by the iron-mediated accumulation of lipid peroxidation, which is distinct from apoptosis and necroptosis. Necrostatin-1 inhibits receptor-interacting serine/threonine-protein kinase 1 (RIPK1) to initiate necroptosis; it also inhibits indoleamine 2,3-dioxygenase (IDO) to regulate tumor immunity. However, few studies have examined the off-target effect of necrostatin-1 on the ferroptosis pathway. The present study examined whether necrostatin-1 could interrupt ferroptosis induced by system xc- inhibitors (sulfasalazine and erastin) and a glutathione peroxidase 4 inhibitor (RSL3) in Huh7 and SK-HEP-1 cells. Necrostatin-1 completely prevented decreases in cell viability induced by sulfasalazine and erastin; it partially blunted decreases in cell viability induced by RSL3. Necrostatin-1, ferrostatin-1, and deferoxamine repressed sulfasalazine-provoked membrane permeabilization, as detected by 7-aminoactinomycin D staining and lipid peroxidation measured using a C11-BODIPY probe. However, other RIPK1 inhibitors (necrostatin-1s and GSK2982772) and an IDO inhibitor (1-methyl-D-tryptophan) did not recover the decrease in cell viability induced by sulfasalazine. Necrostatin-1 potentiated sulfasalazine-induced expression of xCT, a catalytic subunit of system xc- in these cells. These results demonstrated that necrostatin-1 blocked ferroptosis through a mechanism independent from RIPK1 and IDO inhibition in Huh7 and SK-HEP-1 cells, indicating that its antioxidant activity should be considered when using necrostatin-1 as a RIPK1 inhibitor.

Angiosarcomas are a group of vascular cancers that form malignant blood vessels. These malignancies are seemingly inflamed primarily due to their pathognomonic nature, which consists of irregular endothelium and tortuous blood channels. PIK3CA mutations are oncogenic and disrupt the PI3K pathway. In this study, we aimed to define the molecular and functional consequences of oncogenic PIK3CA mutations in angiosarcoma. We first generated two isogenic hemangiosarcoma cell lines harboring the H1047R hotspot mutations in PIK3CA gene using CRISPR/Cas9. We found PIK3CA-mutant cells established distinct molecular signatures in global gene expression and chromatin accessibility, which were associated with enrichment of immune cytokine signaling, including IL-6, IL-8, and MCP-1. These molecular processes were disrupted by the PI3K-α specific inhibitor, alpelisib. We also observed that the molecular distinctions in PIK3CA-mutant cells were linked to metabolic reprogramming in glycolytic activity and mitochondrial respiration. Our multi-omics analysis revealed that activating PIK3CA mutations regulate molecular machinery that contributes to phenotypic alterations and resistance to alpelisib. Furthermore, we identified potential therapeutic vulnerabilities of PIK3CA mutations in response to PI3K-α inhibition mediated by MAPK signaling. In summary, we demonstrate that PIK3CA mutations perpetuate PI3K activation and reinforce immune enrichment to promote drug resistance in vascular cancers.

Ferroptosis has emerged as a promising therapeutic vulnerability of diverse malignancies, yet the regulatory circuits adopted by each in cholangiocarcinoma (CCA) subtypes remain incompletely understood. We integrated the genome-wide CRISPR–Cas9 loss-of-function screens and transcriptomic profiles of the Cancer Dependency Map and then systematically assessed the essentiality of ferroptosis suppressor genes (FSGs) in the intrahepatic (iCCA) and extrahepatic (eCCA) subtypes. Nineteen and 16 essential FSGs were identified in iCCA and eCCA, respectively, among which GPX4 exhibited a significantly higher dependency in iCCA. Pharmacological inhibition of GPX4 with RSL3 markedly reduced cell viability and induced lipid peroxidation in iCCA cell lines, whereas eCCA cell lines displayed pronounced resistance associated with elevated GPX4 expression. A transcriptomic comparison revealed enrichment of WNT signaling in eCCA. Co-treatment with the tankyrase inhibitor XAV-939 and RSL3 enhanced growth inhibition of eCCA cells, indicating that WNT signaling contributed to ferroptosis resistance. These findings indicate that iCCA exhibits a preferential dependency on GPX4, whereas WNT–β-catenin signaling mediates resistance in eCCA. Collectively, the results clarify the molecular basis of subtype-specific ferroptosis vulnerability and offer a rationale for combinatorial therapeutic strategies that integrate GPX4 and WNT pathway inhibition when treating refractory eCCA.