Evaluation of the Lysyl Oxidase-Like 2 (LOXL2) inhibitory activity of pimaranes and their glycosyl derivatives

Lysyl oxidase (LOX) and LOX-like 1-4 (LOXL 1-4) enzymes catalyze the cross-linking of elastin and collagen in the extracellular matrix, facilitating cell migration and invasion. The inhibition of these enzymes, particularly LOXL2, has been suggested as a therapeutic strategy to prevent breast cancer metastasis. In this work, new natural LOXL2 inhibitors were searched from Aeollanthus rydingianus, a medicinal plant rich in bioactive products. Five pimarane diterpenoids, two isolated from the plant and three derivatives, were tested. These compounds have been described for their bioactive properties such as anti-tumor, anti-inflammatory, analgesic, and antibacterial activities. In this regard, we intended to explore the mechanisms of these compounds by studying their effects on LOXL2 activity. Two pimarane diterpenoids showed a mild LOXL2 inhibitory activity as evaluated by an Amplex Ultra Red-based technique. The cytotoxicity of the most active compound was analyzed by the MTT assay in the MDA-MB-231 cell line, representative of triple-negative breast cancer. This compound decreased cell viability as single agent and increased the cytotoxic effect of doxorubicin. Its glycoconjugate was considerably more toxic, likely due to a higher uptake by cancer cells.