Synthesis, Anticancer, and Antibacterial Activity of Betulinic and Betulonic Acid C-28-Triphenylphosphonium Conjugates with Variable Alkyl Linker Length

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 are discussed. Based on the results, 6a can be selected for further preclinical investigation as a potential anticancer compound.

Triphenilphosphonium Analogs of Chloramphenicol as Dual-Acting Antimicrobial and Antiproliferating Agents

“…It should be noted that antiproliferative activity was also detected in TPP and Cn-TPP itself, which seems to be related to the depolarization of the mitochondrial membrane potential [ 27 , 28 , 29 , 30 ]. In this regard, we consider these data on the use of CAM-Cn-TPP derivatives as one of the possible approaches to anti-cancer therapy, requiring more careful study and titration of concentrations and doses.…”

“…It has been reported that along with their antibacterial properties, TPP derivatives of various structures exhibit antiproliferative effects [27][28][29][30]. Most cancer cells possess functional mitochondria, but the oncogenic transformation itself often increases mitochondrial metabolism [31].…”

“…Ultimately, this may allow cancer cells to be discriminated according to their degree of aggressiveness. The conjugation of TPP with various bioactive compounds [19,29,30] or nanocrystals [36] gives chimeric molecules an increased cellular accessibility and enhances their cytotoxicity against tumor cells. For this reason, TPP conjugates with paclitaxel [37] and doxorubicin [38] have recently been suggested to treat drug-resistant cancers.…”

Triterpenoids as Reactive Oxygen Species Modulators of Cell Fate

“…The development of a derivative of compound 17 with a mitochondrial targeting tag at C-28 would promote the opening of the mitochondrial permeability transition pore, increasing apoptosis. 55 The general triphenylphosphonium cation moiety was strategically synthesized in two steps from compound 17 . Briefly, compound 17 was treated with base, and the α,ω-dibromo alkane in DMF, the resultant product, was purified and treated with excess triphenylphosphine to yield the triphenylphosphonium (TPP) conjugate, compound 17a ( Figure 7 ).…”

Synthesis of 3-O-Acetyl-11-keto-β-boswellic Acid (AKBA)-Derived Amides and Their Mitochondria-Targeted Antitumor Activities

“… 11 Coincidentally, C-28-TPP conjugated derivatives of betulinic acid with the alkyl/alkoxyalkyl linkers of variable length were up to 10–17 times more active against MCF-7 than for human skin fibroblasts. 12 …”