ABSTRACT
BACKGROUND: Conjugation of triterpenoids such as betulinic acid 1 with the Triphenylphosphonium (TPP) group is a powerful approach to generating medicinal compounds. Their development proposes structure optimization in respect of availability and activity towards target cells and organelles. Selection of 1 or its precursor betulonic acid 2 and the optimal linker is of particular importance for drug candidate identification among the TPP-triterpenoid conjugates. OBJECTIVE: In this study, new C-28-TPP conjugated derivatives of 1 and 2 with the alkyl/alkoxyalkyl linkers of variable length were synthesized and compared regarding their anticancer, antibacterial, and mitochondriatargeted effects. METHODS: The TPP conjugates of 1 and 2 [6a-f, 7a-f] were synthesized by the reaction of halogenalkyl esters [3a-f, 4a-f, 5] with triphenylphosphine in acetonitrile upon heating. Cytotoxicity (MTT assay), antibacterial activity (microdilution assay), and mitochondrial effects (flow cytofluorometry) were studied. RESULTS: Conjugation with the TPP group greatly increased the cytotoxicity of the triterpenoids up to 30 times. The conjugates were up to 10-17 times more active against MCF-7 (IC50 = 0.17µM, 72h, 6c) and PC-3 (IC50 = 0.14µM, 72h, 6a) cancer cells than for human skin fibroblasts. The enhanced antibacterial (bactericidal) activity of the TPP-triterpenoid conjugates with MIC for Gram-positive bacteria as low as 2µM (6a, 7a) was for the first time revealed. The conjugates were found to effectively inhibit fluorescence of 2',7'-dichlorofluorescin probe in the cytosol upon oxidation, decrease transmembrane potential, and increase superoxide radical level in mitochondria. CONCLUSION: Relationships between the effects and structure of the TPP-triterpenoid conjugates were evaluated and discussed. Based on the results, 6a can be selected for further preclinical investigation as a potential anticancer compound.
Subject(s)
Anti-Bacterial Agents/chemical synthesis , Antineoplastic Agents/chemical synthesis , Oleanolic Acid/analogs & derivatives , Organophosphorus Compounds/chemical synthesis , Pentacyclic Triterpenes/chemistry , Alkanes/chemistry , Anti-Bacterial Agents/pharmacology , Antineoplastic Agents/pharmacology , Antioxidants/chemical synthesis , Antioxidants/pharmacology , Apoptosis/drug effects , Cytosol/drug effects , Cytosol/ultrastructure , Drug Design , Esters/chemistry , Fluoresceins/chemistry , Fluorescent Dyes/chemistry , Gram-Positive Bacteria/drug effects , Halogens/chemistry , Humans , Mitochondria/drug effects , Mitochondria/ultrastructure , Molecular Structure , Oleanolic Acid/chemistry , Organophosphorus Compounds/pharmacology , PC-3 Cells , Structure-Activity Relationship , Superoxides/chemistry , Superoxides/metabolism , Triterpenes/chemistry , Betulinic AcidABSTRACT
A series of new triphenylphosphonium (TPP) derivatives of the triterpenoid betulin (1, 3-lup-20(29)-ene-3ß,28-diol) have been synthesized and evaluated for cytotoxic effects against human breast cancer (MCF-7), prostate adenocarcinoma (PC-3), vinblastine-resistant human breast cancer (MCF-7/Vinb), and human skin fibroblast (HSF) cells. The TPP moiety was applied as a carrier group through the acyl linker at the 28- or 3- and 28-positions of betulin to promote cellular and mitochondrial accumulation of the resultant compounds. A structure-activity relationship study has revealed the essential role of the TPP group in the biological properties of the betulin derivatives produced. The present results showed that a conjugate of betulin with TPP (3) enhanced antiproliferative activity toward vinblastine-resistant MCF-7 cells, with an IC50 value as low as 0.045 µM.
