Wu J, et al. - Since cutaneous T-cell lymphoma (CTCL) cells are effectively killed in vitro and ex vivo via triggering the extrinsic apoptotic pathway, researchers found and assessed compounds that trigger high levels of tumor cell death and block tumor cell growth by comparing small molecules that induce extrinsic apoptosis in CTCL. Findings demonstrated that gentian violet (GV, a well-known topical antimicrobial agent) attacked tumor viability and growth in CTCL. GV, although purple at neutral pH, with altered pH can appear colorless. Overall, GV has potential as a novel topical therapy for CTCL that is inexpensive and available worldwide.

Methods

• High-throughput small molecule screening of 1,710 compounds followed by detailed analysis of GV’s ability to promote apoptosis and inhibit proliferation of CTCL cells was carried out from November 5, 2014, to January 30, 2018.
• Using enzyme-linked immunosorbent assays, flow cytometry, and immunoblotting, in vitro and ex vivo analyses were conducted.
• Main outcomes and measures included apoptosis, cleaved caspases, extrinsic apoptotic death receptors and ligands, cell proliferation, nuclear factor–κB expression, and other factors.

Results

• Findings demonstrated cleaved caspase 8 induced in CTCL cells by 1,710 unique compounds.
• Compared with nitrogen mustard (mechlorethamine), more total apoptosis was induced by the nonprescription, topical antimicrobial remedy GV.
• A favorable topical toxicity profile was suggested by the finding that GV induced 4 to 6 times greater apoptosis in CTCL lines than in normal keratinocytes.
• GV increased caspase 8 and upregulated death receptors 4 and 5, tumor necrosis factor (TNF)–related apoptosis-inducing ligand, and Fas ligand, but not the Fas receptor, TNF receptor, or TNF-α ligand.
• As per observations, these results were consistent with induction of extrinsic apoptosis through the Fas and TNF-related apoptosis-inducing ligand pathways.
• Researchers also observed increased phosphorylation of phospholipase C–γ1, Ca2+ influx, and reactive oxygen species, indicating the involvement of key elements of the activation-induced cell death pathway in the mechanism of Fas ligand upregulation.
• In Sézary blood cells, up to 90% CTCL apoptosis was induced by 1-μmol/L GV in ex vivo studies.
• In addition, attenuation in the expression of antiapoptotic myeloid cell leukemia 1 and proproliferative nuclear factor–κB components and increase in inhibitory κB levels were caused by GV; this finding was related to cell cycle arrest and reduced CTCL tumor cell proliferation.
• Furthermore, when used in combination with methotrexate, augmentation in CTCL killing related to GV was evident.