The Marine Natural Compound Aplysinamisine I Selectively Induces Apoptosis and Exhibits Synergy with Taxol™ in Triple-Negative Breast Cancer Spheroids

Triple-negative breast cancers (TNBC) lack estrogen, progesterone, and express little, if any, HER2 receptors on their surface. No targeted therapies exist for this aggressive form of breast cancer. A library of enriched fractions from marine organisms was screened in a multi-parametric cytotoxicity assay using MDA-MB-231 and MDA-MB-468 TNBC cells, grown as spheroids (3D cultures). Spheroids better resemble tumors and are considered more clinically predictive. The assay measures apoptosis via the cleavage of caspase 3/7, viability via DNA content, and loss of membrane integrity via 7AAD staining at 24 h of treatment. Fractions were also tested in a traditional 2D MTT assay at 72 h. A fraction from the sponge <i>Aplysina</i> was active in the 3D assay. Aplysinamisine I was identified as the compound responsible for the activity. Aplysinamisine I induces apoptosis in MDA-MB-268 spheroids with an IC₅₀ of 2.9 ± 0.28 µM at 24 h. This novel activity is the most potent for the compound to date. Its IC₅₀ in the MTT assay at 72 h is >80 µM. Striking synergy with Taxol™ is shown in both cell lines. Proteomic analysis led to a differential protein expression profile. Through bioinformatics, this profile led to the hypothesis that the inhibition of nucleophosmin is the potential mode of action of the compound. However, initial studies show only a modest decrease in nucleophosmin expression in spheroids treated with aplysinamisine I.