Methods of Analysis and Identification of Betulin and Its Derivatives

This scientific work presents practical and theoretical material on the methods of analysis and identification of betulin and its key derivatives. The properties of betulin and its derivatives, which are determined by the structural features of this class of compounds and their tendency to form dimers, polymorphism and isomerization, are considered. This article outlines ways to improve not only the bioavailability but also the solubility of triterpenoids, as well as any hydrophobic drug substances, through chemical transformations by introducing various functional groups, such as carboxyl, hydroxyl, amino, phosphate/phosphonate and carbonyl. The authors of this article summarized the physicochemical characteristics of betulin and its compounds, systematized the literature data on IR and NMR spectroscopy and gave the melting temperatures of key acids and aldehydes based on betulin.

Redox-Responsive Hyaluronic Acid-Tacrolimus Conjugate: Synthesis, Characterization, and In Vitro Immunosuppressive Activity

A redox-responsive macromolecular prodrug of tacrolimus, HA-ss-Tac, was constructed by conjugation of tacrolimus (TAC, FK506) through its succinate ester to cystamine-modified hyaluronic acid (HA-Cys), and its physicochemical properties and immunosuppressive activity were studied. The synthesized HA-ss-TAC was determined to contain 8% of chemically loaded TAC with significantly enhanced water solubility. The release study showed a sustained release of drug through slow degradation of linker-drug bonds. In vitro inhibition of proliferation of T- and B-lymphocytes was almost comparable to that of TAC, implying that the biologically active compound could be released from the conjugate. The polymeric prodrug lacks obvious cytotoxicity on Raw 264.7 macrophages and significantly suppressed the production of inflammatory cytokines IL-2 and IL-1β by LPS-activated cells. Additionally, the cellular uptake study of the FITC-labeled conjugate confirmed the HA receptor-mediated internalization of the conjugate into targeted cells, thus avoiding systemic side effects. Taken together, the HA-ss-TAC prodrug could be an optimal prodrug for intravenous administration based on this preliminary data and can be expected to have improved therapeutic efficacy.

Antioxidant Activity of New Copolymer Conjugates of Methoxyoligo(Ethylene Glycol)Methacrylate and Betulin Methacrylate with Cerium Oxide Nanoparticles In Vitro

The synthesis of two new copolymer conjugates of methoxyoligo(ethylene glycol)methacrylate MPEGMA and betulin methacrylate BM was developed via RAFT polymerization. The molar content of BM units was equal to 9–10 and 13–16 mol%, respectively (HPLC, ¹H and ¹³C NMR); molar weights were equal to 75000–115000. CeO₂ NPs as a component of the hybrid material were synthesized for the preparation of the composition with copolymer conjugates of MPEGMA and BM. We showed a significant increase in G6PDH and GR activities by 21–51% and 9–132%, respectively, which was due to the increase in NADPH concentration under the action of copolymers in vitro. The actions of copolymers and CeO₂ NPs combination were stronger than those of the individual components: the SOD activity increased by more than 30%, the catalase activity increased dose-dependently from 13 to 45%, and the GR activity increased to 49%. The maximum increase in enzyme activity was observed for the G6PDH from 54% to 151%. The MDA level dose-dependently increased by 3–15% under the action of copolymers compared with the control, and dose-dependently decreased by 3–12% in samples containing CeO₂ NPs only. CeO₂ NP–copolymer compositions can be used for the design of new biomimetic medical products with controlled antioxidant properties.

Orthogonal Design of Supramolecular Prodrug Vesicles via Water-Soluble Pillar[5]arene and Betulinic Acid Derivative for Dual Chemotherapy

Supramolecular prodrug vesicles with efficient property for dual chemotherapy have been successfully constructed based on the orthogonal self-assembly between a water-soluble pillar[5]arene host (WP5) and a betulinic acid guest (BA-D) as well as doxorubicin (DOX). Under the acidic microenvironment of cancer cells, both the encapsulated anticancer drug DOX and prodrug BA-D can be effectively released from DOX-loaded WP5⊃BA-D prodrug vesicles for combinational chemotherapy. Furthermore, bioexperiments indicate that DOX-loaded prodrug vesicles can obviously enhance the anticancer efficiency based on the cooperative effect of DOX and BA-D, while remarkably reducing the systematic toxicity in tumor-mice, displaying great potential applications in combinational chemotherapy for cancer treatments.

Substituted dienes prepared from betulinic acid - Synthesis, cytotoxicity, mechanism of action, and pharmacological parameters

A set of new substituted dienes were synthesized from betulinic acid by its oxidation to 30-oxobetulinic acid followed by the Wittig reaction. Cytotoxicity of all compounds was tested in vitro in eight cancer cell lines and two noncancer fibroblasts. Almost all dienes were more cytotoxic than betulinic acid. Compounds 4.22, 4.30, 4.33, 4.39 had IC₅₀ below 5 μmol/L; 4.22 and 4.39 were selected for studies of the mechanism of action. Cell cycle analysis revealed an increase in the number of apoptotic cells at 5 × IC₅₀ concentration, where activation of irreversible changes leading to cell death can be expected. Both 4.22 and 4.39 led to the accumulation of cells in the G0/G1 phase with partial inhibition of DNA/RNA synthesis at 1 × IC₅₀ and almost complete inhibition at 5 × IC₅₀. Interestingly, compound 4.39 at 5 × IC₅₀ caused the accumulation of cells in the S phase. Higher concentrations of tested drugs probably inhibit more off-targets than lower concentrations. Mechanisms disrupting cellular metabolism can induce the accumulation of cells in the S phase. Both compounds 4.22 and 4.39 trigger selective apoptosis in cancer cells via intrinsic pathway, which we have demonstrated by changes in the expression of the crucial apoptosis-related protein. Pharmacological parameters of derivative 4.22 were superior to 4.39, therefore 4.22 was the finally selected candidate for the development of anticancer drug.

Synthesis of Gelatin-Based Dual-Targeted Nanoparticles of Betulinic Acid for Antitumor Therapy

Betulinic acid (BA) is a natural antitumor agent and has biological activity against multiple human tumor cell lines with low cytotoxicity to normal cells, while the high hydrophobicity and the short half-life of this compound limit its clinical application. Here, gelatin-based dual-targeted nanoparticles of BA are promising to solve this problem. Hydrophobic BA is loaded in cyclodextrin to increase its solubility and prolong the circulation time in vivo. The nanoscale drug delivery systems can further enhance the bioavailability and the antitumor effect of BA and are passively targeted to the tumor tissue sites by enhanced permeability and retention effect. The RGD sequence of gelatin specifically recognizes tumor cells and brings agents into tumor cells. The nanoparticles were characterized by transmission electron microscopy, Fourier transform infrared, nuclear magnetic resonance, etc. In addition, we observed antitumor activity of the nanoparticles using both cell-based assays and mouse xenograft tumors, which proved that betulinic acid/gelatin-γ-cyclodextrin nanoparticles had a better tumor inhibition effect than betulinic acid/γ-cyclodextrin inclusion compound.

Delivery Systems for Birch-bark Triterpenoids and their Derivatives in Anticancer Research

Birch-bark triterpenoids and their semi-synthetic derivatives possess a wide range of biological activities including cytotoxic effects on various tumor cell lines. However, due to the low solubility and bioavailability, their medicinal applications are rather limited. The use of various nanotechnology-based drug delivery systems is a rapidly developing approach to the solubilization of insufficiently bioavailable pharmaceuticals. Herein, the drug delivery systems deemed to be applicable for birch-bark triterpenoid structures are reviewed. The aforementioned disadvantages of birch-bark triterpenoids and their semi-synthetic derivatives can be overcome through their incorporation into organic nanoparticles, which include various dendrimeric systems, as well as embedding the active compounds into polymer matrices or complexation with carbohydrate nanoparticles without covalent bonding. Some of the known triterpenoid delivery systems consist of nanoparticles featuring inorganic cores covered with carbohydrates or other polymers. Methods for delivering the title compounds through encapsulation and emulsification into lipophilic media are also suitable. Besides, the birch-bark triterpenoids can form self-assembling systems with increased bio-availability. Even more, the self-assembling systems are used as carriers for delivering other chemotherapeutic agents. Another advantage besides increased bioavailability and anticancer activity is the reduced overall systemic toxicity in most of the cases, when triterpenoids are delivered with any of the carriers.

Design and synthesis of pentacyclic triterpene conjugates and their use in medicinal research

Triterpenoids are natural products from plants and many other organisms that have various biological activities, such as antitumor, antiviral, antimicrobial, and protective activities. This review covers the synthesis and biological evaluation of pentacyclic triterpene (PT) conjugates with other molecules that have been found to increase the IC₅₀ or improve the pharmacological profile of the parent PT. Some of these molecules are designed to target specific proteins or cellular organelles, which has resulted in highly selective lead structures for drug development. Other PT conjugates are useful for investigating their mechanism of action. This concept has been very successful: 1) Many compounds, especially mitochondria-targeting PT conjugates, have reached a selective cytotoxicity at low nanomolar concentrations in cancer cells. 2) A number of PT conjugates have had high activity against HIV or the influenza virus. 3) Fluorescent PT conjugates have been able to visualize the PT in living cells, which has allowed quantification of the uptake and distribution of the PT within the cell. 4) Biotinylated PT conjugates have been used to identify target proteins, which may help to show their mechanism of action. 5) A large number of PT conjugates with polyethylene glycol (PEG), polyamines, etc. form nanometer-sized micelles that have a much better pharmacological profile than the PT alone. In summary, the connection of a PT to an appropriate modifying molecule has resulted in extremely useful semisynthetic compounds with a high potential to treat cancer or viral infections or compounds that are useful for the study of the mechanism of action of PTs at the molecular level.

Betulinic Acid Suppresses Breast Cancer Metastasis by Targeting GRP78-Mediated Glycolysis and ER Stress Apoptotic Pathway

Targeting aberrant metabolism is a promising strategy for inhibiting cancer growth and metastasis. Research is now geared towards investigating the inhibition of glycolysis for anticancer drug development. Betulinic acid (BA) has demonstrated potent anticancer activities in multiple malignancies. However, its regulatory effects on glycolysis and the underlying molecular mechanisms are still unclear. BA inhibited invasion and migration of highly aggressive breast cancer cells. Moreover, BA could suppress aerobic glycolysis of breast cancer cells presenting as a reduction of lactate production, quiescent energy phenotype transition, and downregulation of aerobic glycolysis-related proteins. In this study, glucose-regulated protein 78 (GRP78) was also identified as the molecular target of BA in inhibiting aerobic glycolysis. BA treatment led to GRP78 overexpression, and GRP78 knockdown abrogated the inhibitory effect of BA on glycolysis. Further studies demonstrated that overexpressed GRP78 activated the endoplasmic reticulum (ER) stress sensor PERK. Subsequent phosphorylation of eIF2α led to the inhibition of β-catenin expression, which resulted in the inhibition of c-Myc-mediated glycolysis. Coimmunoprecipitation assay revealed that BA interrupted the binding between GRP78 and PERK, thereby initiating the glycolysis inhibition cascade. Finally, the lung colonization model validated that BA inhibited breast cancer metastasis in vivo, as well as suppressed the expression of aerobic glycolysis-related proteins. In conclusion, our study not only provided a promising drug for aerobic glycolysis inhibition but also revealed that GRP78 is a novel molecular link between glycolytic metabolism and ER stress during tumor metastasis.

Betulin and its derivatives as novel compounds with different pharmacological effects

Betulin (B) and Betulinic acid (BA) are natural pentacyclic lupane-structure triterpenoids which possess a wide range of pharmacological activities. Recent evidence indicates that B and BA have several properties useful for the treatment of metabolic disorders, infectious diseases, cardiovascular disorders, and neurological disorders. In the current review, we discuss B and BA structures and derivatives and then comprehensively explain their pharmacological effects in relation to various diseases. We also explain antiviral, antibacterial and anti-cancer effects of B and BA. Finally, we discuss the delivery methods, in which these compounds most effectively target different systems.

Recent Developments in the Functionalization of Betulinic Acid and Its Natural Analogues: A Route to New Bioactive Compounds

Betulinic acid (BA) and its natural analogues betulin (BN), betulonic (BoA), and 23-hydroxybetulinic (HBA) acids are lupane-type pentacyclic triterpenoids. They are present in many plants and display important biological activities. This review focuses on the chemical transformations used to functionalize BA/BN/BoA/HBA in order to obtain new derivatives with improved biological activity, covering the period since 2013 to 2018. It is divided by the main chemical transformations reported in the literature, including amination, esterification, alkylation, sulfonation, copper(I)-catalyzed alkyne-azide cycloaddition, palladium-catalyzed cross-coupling, hydroxylation, and aldol condensation reactions. In addition, the synthesis of heterocycle-fused BA/HBA derivatives and polymer‒BA conjugates are also addressed. The new derivatives are mainly used as antitumor agents, but there are other biological applications such as antimalarial activity, drug delivery, bioimaging, among others.

Therapeutic applications of betulinic acid nanoformulations

Betulinic acid (BA), a naturally occurring plant-derived pentacyclic triterpenoid, has gained attention in recent years owing to its broad-spectrum biological and medicinal properties. Despite the pharmacological activity of BA, it has been associated with some drawbacks, such as poor aqueous solubility and short half-life in vivo, which limit therapeutic application. To solve these problems, much work in recent years has focused on enhancing BA's aqueous solubility, half-life, and efficacy by using nanoscale drug delivery systems. Several different kinds of nanoscale delivery systems-including polymeric nanoparticles, magnetic nanoparticles, liposomes, polymeric conjugates, nanoemulsions, cyclodextrin complexes, and carbon nanotubes-have been developed for the delivery of BA. Here, we focus on the recent developments of novel nanoformulations used to deliver BA in order to improve its efficacy.

Design, Synthesis, and Cancer Cell Growth Inhibitory Activity of Triphenylphosphonium Derivatives of the Triterpenoid Betulin

A series of new triphenylphosphonium (TPP) derivatives of the triterpenoid betulin (1, 3-lup-20(29)-ene-3β,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.

Development and evaluation of long-circulating nanoparticles loaded with betulinic acid for improved anti-tumor efficacy

The clinical application of betulinic acid (BA), a natural pentacyclic triterpenoid with promising antitumor activity, is hampered due to its extremely poor water solubility and relatively short half-life in the systemic circulation. In order to address these issues, herein, we developed betulinic acid loaded polylactide-co-glycolide- monomethoxy polyethylene glycol nanoparticles (PLGA-mPEG NPs). The PLGA-mPEG co-polymer was synthesized and characterized using NMR and FT-IR. BA loaded PLGA-mPEG NPs were prepared by an emulsion solvent evaporation method. The developed nanoparticles had a desirable particle size (∼147nm) and exhibited uniform spherical shape under transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The PLGA-mPEG NPs were able to decrease the uptake by macrophages (i.e. J774A.1 and Raw 264.7 cells) as compared to PLGA nanoparticles. In vitro cytotoxicity in MCF7 and PANC-1 cells demonstrated enhanced cytotoxicity of BA loaded PLGA-mPEG NPs as compared to free BA. The cellular uptake study in both the cell lines demonstrated time dependent uptake behavior. The enhanced cytotoxicity of BA NPs was also supported by increased cellular apoptosis, mitochondrial membrane potential loss, generation of high reactive oxygen species (ROS) and cell cycle arrest. Further, intravenous pharmacokinetics study revealed that BA loaded PLGA-mPEG NPs could prolong the circulation of BA and remarkably enhance half-life by ∼7.21 folds. Consequently, in vivo studies in Ehrlich tumor (solid) model following intravenous administration demonstrated superior antitumor efficacy of BA NPs as compared to native BA. Moreover, BA NPs treated Ehrlich tumor mice demonstrated no biochemical, hematological and histological toxicities. These findings collectively indicated that the BA loaded PLGA-mPEG NPs might serve as a promising nanocarrier for improved therapeutic efficacy of betulinic acid.

Injectable doxorubicin-loaded hydrogels based on dendron-like β-cyclodextrin–poly(ethylene glycol) conjugates

Dendron-like CD–PEG conjugates with multiple acrylates were synthesized facilely, which can incorporate adamantane-modified doxorubicin and further be crosslinked by POEGMS, to give injectable doxorubicin-loaded hydrogels.

Synthesis, characterization and augmented anticancer potential of PEG-betulinic acid conjugate

Betulinic acid (BA), a pentacyclic lupine-type triterpene, is reported to inhibit cell growth in a variety of cancers. However, its efficacy is limited by its poor aqueous solubility and relatively short half-life. In this study, BA-monomethoxy polyethylene glycol (mPEG) conjugate was synthesized by covalent coupling the C-28 carboxylic acid position of BA with amine groups of mPEG, in order to improve its solubility and anticancer efficacy. mPEG-BA conjugate was characterized using various analytical techniques including NMR, FT-IR and MALDI-MS. The mPEG-BA conjugate was cytotoxic, demonstrated internalization and induced cell apoptosis in Hep3B and Huh7 hepatic cancer cells. The western-blot analysis revealed, marked decrease in Bcl-2/Bax ratio, and increase in cleaved-PARP and cleaved-caspase-3 expressions. In vivo studies in Ehrlich ascites tumor (EAT) model following intravenous administration demonstrated significant reduction in tumor volume in case of PEGylated BA as compare to native BA. Furthermore, PEGylated BA treated EAT mice showed no biochemical and histological toxicities. These findings demonstrate the potential of PEGylated BA in cancer therapy, with improved water solubility and efficacy.

Betulinic Acid and its Derivatives as Potential Antitumor Agents

Betulinic acid (BA) is a lupane-type pentacyclic triterpene, distributed ubiquitously throughout the plant kingdom. BA and its derivatives demonstrate multiple bioactivities, particularly an antitumor effect. This review critically describes the recent research on isolation, synthesis, and derivatization of BA and its natural analogs betulin and 23-hydroxybetulinic acid. The subsequent part of the review focuses on the current knowledge of antitumor properties, combination treatments, and pharmacological mechanisms of these compounds. A 3D-QSAR analysis of 62 BA derivatives against human ovarian cancer A2780 is also included to provide information concerning the structure-cytotoxicity relationships of these compounds.

Design, synthesis and in vivo antitumor efficacy of novel eight-arm-polyethylene glycol–pterostilbene prodrugs

Illustration of 8arm-PEG–pterostilbene. In contrast to linear PEG, the 8arm-PEG significantly increased drug-binding capacity.

A self-assembled nanoparticle platform based on poly(ethylene glycol)–diosgenin conjugates for co-delivery of anticancer drugs

We developed a nanoparticle platform based on poly(ethylene glycol)–diosgenin (mPEG–DGN) conjugates for co-delivery of anticancer drug HCPT.

Self-assembled targeted folate-conjugated eight-arm-polyethylene glycol–betulinic acid nanoparticles for co-delivery of anticancer drugs

Folate-8arm-PEG–betulinic acid nanoparticles prepared via a self-assembly process are stable in circulation, resulting in the EPR effect of solid tumors, and are efficiently internalized by cancer cells.