TPP-alantolactone conjugates and their nanotherapeutic forms for antitumor application

Delocalized positive charge and high hydrophobicity of triarylphosphonium (TPP) groups facilitate a penetration of the TPP-conjugated molecules through the cell and mitochondrial membranes, which result in their accumulating in tumor cells. Combining mitochondrial strategies with nanotechnology-based delivery systems is a challenge to the new cancer therapy approaches. Using synthetic approach for targeted delivery of small molecules with antitumor activity into mitochondria, the quaternary γ-oxoalkylphosphonium salts (TPP–alantolactone, TPP–AL) were synthesized under mild conditions with high yields. First time mitochondria-targeted lipid nanosystems, namely, liposomes and solid lipid nanoparticles (SLN) modified with TPP–AL were prepared and characterized. TPP–alantolactones showed a high in vitro cytotoxicity. The highest cytotoxicity against human duodenal adenocarcinoma cell lines (HuTu 80) occurred at IC₅₀ = 0.4 µM with a high selectivity of 17.5. Cytotoxicity is increased up to 520-fold when tested TPP–alantolactone-SLN (TPP–AL–SLN) against M-HeLa cancer cell lines. The enhanced cellular uptake and accumulation of curcumin-labeled-TPP–AL–SLN were shown by confocal microscopy. TPP–AL caused a significant depolarization of mitochondrial membrane in the HuTu 80 cancer cells, increased ROS production and over expression of caspase-9, suggesting an intrinsic mitochondrial mechanism for triggering apoptosis. A significant delay of cells in the G0/G1 phase compared to the control was revealed. In addition to the anti-tumor effect TPP–AL exhibit a bactericidal activity, i.e. they are dual-action drugs. TPP–AL are noticeably active against gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), with a minimum bactericidal concentration (MBC) of 7.8 µM, which is close to the antibiotic norfloxacin. TPP-derived sesquiterpene lactones-decorated nanosystems showed a high potential as antitumor agents for the targeted delivery to the mitochondria of tumor cells.