Discovery and Optimization of Betulinic Acid Derivatives as Novel Potent CD73 Inhibitors

Betulonic acid: A review on its sources, biological activities, and molecular mechanisms

Pentacyclic triterpenoids represent a significant class of phytochemicals, categorized into oleanane, ursane, friedelane, and lupane. Among these, betulonic acid stands out as a lupane-type pentacyclic triterpenoid found in numerous plants. Its diverse biological properties, including anti-tumor, anti-viral, anti-inflammatory, anti-bacterial, and hepato-protective effects, have been extensively documented. To further explore the therapeutic potential of betulonic acid and its derivatives, we provide a comprehensive review of their sources, biological activities, and molecular mechanisms. We aim for this synthesis of data to stimulate fresh perspectives on betulonic acid and its potential in drug discovery.

Enhanced ZBTB10 expression induced by betulinic acid inhibits gastric cancer progression by inactivating the ARRDC3/ITGB4/PI3K/AKT pathway

BACKGROUND

Gastric cancer (GC) ranks as the fourth leading cause of cancer-related deaths worldwide, with most patients diagnosed at advanced stages due to the absence of reliable early detection biomarkers.

METHODS

RNA-sequencing was conducted to identify the differentially expressed genes between GC tissues and adjacent normal tissues. CCK8, EdU, colony formation, transwell, flow cytometry and xenograft assays were adopted to explore the biological function of ZBTB10 and betulinic acid (BA) in GC progression. RNA-sequencing and phospho-proteomic profiling were performed to analyze the signaling pathways associated with ZBTB10-inhibiting GC progression. Chromatin immunoprecipitation, Co-immunoprecipitation and luciferase reporter assay were employed to elucidate the potential molecular regulatory mechanisms of ZBTB10 in GC.

RESULTS

ZBTB10 was one of the most significantly downregulated genes in GC tissues, and higher expression levels of ZBTB10 was correlated with better prognosis in patients with GC. Functional studies revealed that ZBTB10 overexpression and BA inhibited GC progression both in vitro and in vivo. Mechanistically, ZBTB10 enhanced ARRDC3 expression by binding to a specific response element in the ARRDC3 promoter region. Elevated ARRDC3 then directly interacted with β-4 integrin (ITGB4), leading to its ubiquitination and degradation. This cascade ultimately resulted in the downregulation of PI3K and AKT phosphorylation level. Moreover, ZBTB10 was a key target for BA in GC and BA inhibited GC progression through regulating the ZBTB10/ARRDC3/ITGB4/PI3K/AKT axis.

CONCLUSIONS

Our findings reveal that BA holds promise as an effective therapeutic strategy for GC, and the ZBTB10/ARRDC3/ITGB4/PI3K/AKT axis may serve as a novel diagnostic and therapeutic target.

Novel C-3 and C-20 derived analogs of betulinic acid as potent cytotoxic agents: design, synthesis, in vitro and in silico studies

In this report, novel derivatives of betulinic acid were designed and synthesized by targeting the C-3-OH group and C-20 olefinic bond in an endeavour to develop potent antitumor agents. These analogs were screened for their anticancer activity against six different human cancer cell lines including breast cancer MCF-7, lung cancer A549, colon cancer HCT-116, leukemia MOLT-4, prostate carcinoma cell PC-3 and pancreatic cancer cell Miapaca-2 by MTT assay. Many derivatives displayed better cytotoxicity than the parent compound BA. More significantly compounds 9b, 9e, 10 and 11a were found to have more promising activity than BA. Compound 11a was the most potent analog with IC50 values of 7.15 (MCF-7), 8.0 (A549), 3.13 (HCT-116), 13.88 (MOLT-4), 8.0 (PC-3) and 6.96 (MiaPaCa-2) μM. In addition to experimental investigations, in silico aspects were evaluated for the parent compound, BA and 11a derivative based on its potential bioactive behaviour. The representative compounds were optimized structurally using density functional theory (DFT). GaussView 6.1 graphical interface associated GAUSSIAN 09 (Revision C.01) software package was used for the calculations under 6-311g(d,p)/B3LYP formalism using under a SMD model (water as solvent) for the parent compound BA and 11a to explain the respective bioactive behaviour. This was followed by molecular docking studies suggesting that compound 11a binds efficiently with all the three proteins with the docking score of -7.2 kcal mol-1 in the case of matrix metalloproteinase-2 (PDB ID: 1HOV) and poly[ADP-ribose] polymerase-1 (PDB ID: 1UK0) and -6.7 kcal mol-1 in the case of TRAF2 (PDB ID: 2X7F). Further, molecular dynamics studies between 11a and the three proteins were carried out using Desmond Maestro v11.3 to study protein-ligand interactions and protein stability.

Development of CD73 Inhibitors in Tumor Immunotherapy and Opportunities in Imaging and Combination Therapy

CD73 is a member of the membrane-bound enucleotidase family, which catalyzes the extracellular hydrolysis of adenosine monophosphate (AMP) to produce anti-inflammatory and immunosuppressive adenosine. As a novel checkpoint protein, CD73 is overexpressed in the immune system of various tumors, where adenosine is abundantly enriched. A large number of monoclonal antibodies (mAbs), nucleotides, and non-nucleotides as potent CD73 inhibitors are being discovered, providing opportunities for novel tumor immunotherapy. Currently, 18 CD73 inhibitors are in clinical trials, showing promising results in combination therapy for various solid tumors. The development of CD73-specific companion positron emission tomography imaging ligands holds potential for facilitating diagnosis, patient selection, and treatment efficacy evaluation throughout the entire process of CD73-targeted therapeutic development.

CD73: agent development potential and its application in diabetes and atherosclerosis

CD73, an important metabolic and immune escape-promoting gene, catalyzes the hydrolysis of adenosine monophosphate (AMP) to adenosine (ADO). AMP has anti-inflammatory and vascular relaxant properties, while ADO has a strong immunosuppressive effect, suggesting that CD73 has pro-inflammatory and immune escape effects. However, CD73 also decreased proinflammatory reaction, suggesting that CD73 has a positive side to the body. Indeed, CD73 plays a protective role in diabetes, while with age, CD73 changes from anti-atherosclerosis to pro-atherosclerosis. The upregulation of CD73 with agents, including AGT-5, Aire-overexpressing DCs, Aspirin, BAFFR-Fc, CD4+ peptide, ICAs, IL-2 therapies, SAgAs, sCD73, stem cells, RAD51 inhibitor, TLR9 inhibitor, and VD, decreased diabetes and atherosclerosis development. However, the downregulation of CD73 with agents, including benzothiadiazine derivatives and CD73 siRNA, reduced atherosclerosis. Notably, many CD73 agents were investigated in clinical trials. However, no agents were used to treat diabetes and atherosclerosis. Most agents were CD73 inhibitors. Only FP-1201, a CD73 agonist, was investigated in clinical trials but its further development was discontinued. In addition, many lncRNAs, circRNAs, and genes are located at the same chromosomal location as CD73. In particular, circNT5E promoted CD73 expression. circNT5E may be a promising target for agent development. This mini-review focuses on the current state of knowledge of CD73 in diabetes, atherosclerosis, and its potential role in agent development.

Small molecular CD73 inhibitors: Recent progress and future perspectives

The occurrence and development of the tumor are very complex biological processes. In recent years, a large number of research data shows that CD73 is closely related to tumor growth and metastasis. It has been confirmed that the cascade hydrolysis of extracellular ATP to adenosine is one of the most important immunosuppressive regulatory pathways in the tumor microenvironment. The metabolite adenosine can mediate immunosuppression by activating adenosine receptor (such as A2A) on effector Immune cells and enable tumor cells to achieve immune escape. Therefore, attenuating or completely removing adenosine-mediated immunosuppression in the tumor microenvironment by inhibiting CD73 is a promising approach in the treatment of solid tumors. This paper focuses on the research progress of CD73 enzyme and CD73 small molecule inhibitors, and is expected to provide some insights into the development of small-molecule antitumor drugs targeting CD73.

Bifunctionalized Betulinic Acid Conjugates with C-3-Monodesmoside and C-28-Triphenylphosphonium Moieties with Increased Cancer Cell Targetability

A convenient synthesis is presented for a new class of bioactive bifunctionalized conjugates of lupane-type triterpenoids with triphenylphosphonium (TPP) and glycopyranosyl targeting moieties. The main synthesis steps include glycosylation of haloalkyl esters of the triterpene acid at the C-3 position by the imidate derivatives of glycopyranose followed by the product modification at the C-28 position with triphenylphosphine. The conjugates of betulinic acid (BetA) with TPP and d-glucose, l-rhamnose, or d-mannose moieties were thus synthesized as potential next-generation BetA-derived anticancer compounds. LC-MS/MS analysis in glucose-free physiological solution indicated that the glycosides showed better accumulation in PC-3 prostate cancer cells than both BetA and TPP-BetA conjugate, while the transporting effect of monosaccharide residues increased as follows: d-mannose < l-rhamnose ≈ d-glucose. At saturated concentrations, the glycosides caused a disturbing effect on mitochondria with a more drastic drop in transmembrane potential but weaker overproduction of mitochondrial reactive oxygen species (ROS) compared to TPP-BetA conjugate. Cytotoxicity of the glycosides in culture medium was comparable with or higher than that of the nonglycosylated conjugate, depending on the cancer cell line, whereas the compounds were less active toward primary fibroblasts. Glycosylation tended to increase pro-apoptotic and decrease pro-autophagic activities of the BetA derivatives. Cytotoxicity of the synthesized glycosides was considered in comparison with the summarized data on the natural and modified BetA glycosides. The results obtained are important for the development of bifunctionalized conjugates of triterpenoids with an increased cancer cell targetability.

Molecular Dynamics Simulations of the Human Ecto-5'-Nucleotidase (h-ecto-5'-NT, CD73): Insights into Protein Flexibility and Binding Site Dynamics

Human ecto-5'-nucleotidase (h-ecto-5'-NT, CD73) is a homodimeric Zn2+-binding metallophosphoesterase that hydrolyzes adenosine 5'-monophosphate (5'-AMP) to adenosine and phosphate. h-Ecto-5'-NT is a key enzyme in purinergic signaling pathways and has been recognized as a promising biological target for several diseases, including cancer and inflammatory, infectious, and autoimmune diseases. Despite its importance as a biological target, little is known about h-ecto-5'-NT dynamics, which poses a considerable challenge to the design of inhibitors of this target enzyme. Here, to explore h-ecto-5'-NT flexibility, all-atom unbiased molecular dynamics (MD) simulations were performed. Remarkable differences in the dynamics of the open (catalytically inactive) and closed (catalytically active) conformations of the apo-h-ecto-5'-NT were observed during the simulations, and the nucleotide analogue inhibitor AMPCP was shown to stabilize the protein structure in the closed conformation. Our results suggest that the large and complex domain motion that enables the h-ecto-5'-NT open/closed conformational switch is slow, and therefore, it could not be completely captured within the time scale of our simulations. Nonetheless, we were able to explore the faster dynamics of the h-ecto-5'-NT substrate binding site, which is mainly located at the C-terminal domain and well conserved among the protein's open and closed conformations. Using the TRAPP ("Transient Pockets in Proteins") approach, we identified transient subpockets close to the substrate binding site. Finally, conformational states of the substrate binding site with higher druggability scores than the crystal structure were identified. In summary, our study provides valuable insights into h-ecto-5'-NT structural flexibility, which can guide the structure-based design of novel h-ecto-5'-NT inhibitors.

Advances in CD73 inhibitors for immunotherapy: Antibodies, synthetic small molecule compounds, and natural compounds

Tumors, a disease with a high mortality rate worldwide, have become a serious threat to human health. Exonucleotide-5'-nucleotidase (CD73) is an emerging target for tumor therapy. Its inhibition can significantly reduce adenosine levels in the tumor microenvironment. It has a better therapeutic effect on adenosine-induced immunosuppression. In the immune response, extracellular ATP exerts immune efficacy by activating T cells. However, dead tumor cells release excess ATP, overexpress CD39 and CD73 on the cell membrane and catabolize this ATP to adenosine. This leads to further immunosuppression. There are a number of inhibitors of CD73 currently under investigation. These include antibodies, synthetic small molecule inhibitors and a number of natural compounds with prominent roles in the anti-tumor field. However, only a small proportion of the CD73 inhibitors studied to date have successfully reached the clinical stage. Therefore, effective and safe inhibition of CD73 in oncology therapy still holds great therapeutic potential. This review summarizes the currently reported CD73 inhibitors, describes their inhibitory effects and pharmacological mechanisms, and provides a brief review of them. It aims to provide more information for further research and development of CD73 inhibitors.

Targeting ecto-5'-nucleotidase: A comprehensive review into small molecule inhibitors and expression modulators

The purinergic signaling has drawn attention from academia and more recently from pharmaceutical industries as a potential therapeutic route for cancer treatment, since ATP may act as chemotactic agent and possess in vitro antineoplastic activity. On the other way, adenosine, produced in extracellular medium by ecto-5'-NT, acts as immunosuppressor and is related to neoangiogenesis, vasculogenesis and evasion to the immune system. Consequently, inhibitors of ecto-5'-NT may prevent tumor progression, reducing adenosine concentrations, preventing escape from the host's immune system and slowing cancer's growth. This review aims to highlight important biochemical and structural features of ecto-5'NT, highlight its expression profile in normal and cancer cell lines detailing compounds which may act as expression regulators and to review the several classes of ecto-5'NT inhibitors developed in the past 12 years, in order to build a general structure-activity relationship model to guide further compound design.

Application of a fluorine strategy in the lead optimization of betulinic acid to the discovery of potent CD73 inhibitors

The ecto-5'-nucleotidase (CD73) is an important enzyme in the adenosine pathway and catalyzes the extracellular hydrolysis of adenosine monophosphate (AMP) yielding adenosine which is involved in the inflammation and immunosuppression. Inhibitors of CD73 have potential as novel immunotherapy agents for the treatment of cancer and infection. In this study, we discovered a series of fluorinated betulinic acid derivatives as potent CD73 inhibitors by a fluorine scanning strategy. Among these, three compounds ZM522, ZM553 and ZM557 exhibited inhibitory activity with IC₅₀ values of 0.56 uM, 0.74 uM and 0.47 uM, respectively. In addition, these compounds showed a 7-fold, 5-fold and 8-fold increase in activity compared to the positive control drug α, β-methylene adenosine diphosphate (APCP) against the human CD73 enzyme. Two of these (ZM522 and ZM553) also exhibited effective interferon gamma (INF-γ) elevation and indicated the regulation of rescued T cell activation. Therefore, our study provides both a lead optimization strategy and potential compounds for further development of small molecule CD73 inhibitors.

3-[(1H-Benzo[d][1,2,3]triazol-1-yl)oxy]propyl 9-hydroxy-5a,5b,8,8,11a-pentamethyl-1-(prop-1-en-2-yl)icosahydro-3aH-cyclopenta[a]chrysene-3a-carboxylate

We herein report on the synthesis of a pentacyclic triterpene functionalized through derivation of betulinic acid with hydroxybenzotriazole. The compound was fully characterized by proton (1H-NMR), carbon-13 (13C-NMR), heteronuclear single quantum coherence (HSQC) and distortionless enhancement by polarization transfer (DEPT-135 and DEPT-90) nuclear magnetic resonance. Ultraviolet (UV), and Fourier-transform infrared (FTIR) spectroscopies as well as and high-resolution mass spectrometry (HRMS) were also adopted. Computational studies were conducted to foresee the interactions between compound 3 and phosphodiesterase 9, a relevant target in the field of neurodegenerative diseases. Additionally, preliminary calculation of physico-chemical descriptors was performed to evaluate the drug-likeness of compound 3.