Advances and challenges in betulinic acid therapeutics and delivery systems for breast cancer prevention and treatment

Abstract

Breast cancer (BC) is the leading cause of cancer-related death among women worldwide. Due to limited treatment options for patients with advanced BC, preventive and innovative therapeutic strategies are essential to combat this disease. Therefore, finding safe and effective anticancer treatments remains a significant challenge in the 21st century. Plant-derived triterpenoids, widely used for medicinal purposes, exhibit various biological activities. Most triterpenoids are cytotoxic to multiple tumor cells and demonstrate anticancer effects in preclinical animal models. One example is betulinic acid (BA), a natural product mainly extracted from the bark of birch trees. BA is a promising anti-tumor compound with numerous pharmacological properties. However, its poor water solubility limits its optimal therapeutic potential. Additionally, the low BA content in plants hampers large-scale production from these sources. To address these issues, extensive research has focused on producing BA through chemical synthesis and biotransformation. Furthermore, several BA derivatives have been developed through structural modifications, and various delivery systems have been created to improve solubility and enhance therapeutic efficacy. This review discusses recent advances and challenges related to BA and its derivatives in preventing and treating breast tumors, as well as the potential obstacles and future directions for improving delivery systems in BC therapy.

Fig. 1. (a) Chemical classifications and detailed structures of each group. The chemical structures of (b) Betulin (BE) and (c) Betulinic acid (BA). This figure has been reproduced from ref. . Copyright: 2024 by the authors. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Fig. 2. The number of articles published (book chapters, reviews, and research articles) on BA in the last nine years (search conducted using keywords “betulinic acid” and “breast cancer” according to the Science Direct database on 07 January 2025, from 2016 to 2024).

Fig. 3. Highlights the various health benefits of BA along with their associated mechanisms. This is an original drawing, and the diagram was created using Biorender.

Fig. 4. BA is a plant-derived pentacyclic lupane-type triterpenoid obtained through plant extraction, chemical synthesis, or microbial biotransformation. This is an original drawing, and the diagram was created using Biorender.

Fig. 5. Preparation of aptamer-bound BA analogue (Apt-2cNP). This figure has been reproduced from ref. . Copyright: 2024 by the authors. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Fig. 6. SCRaMbLE of a BA-producing strain, followed by quick screening, creates a diverse library. BA synthesis involves rerouting flux from the natural mevalonate pathway (top left) through three foreign enzymes: AtLUS1, BPLO, and AtATR1. Four genes—AtLUS1, BPLO, tHMG1, and ERG9—are expressed from a URA+ CEN/ARS plasmid, while AtATR1 is inserted into the genome at the HO locus on chromosome IV (right). This figure has been reproduced from ref. . Copyright: 2020 by the authors. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Fig. 7. (a). Reaction scheme showing the biosynthetic pathway of BA using engineered yeast S. cerevisiae. (b). Overview of the multimodular strategy for producing BA-related triterpenoids in Y. lipolytica. The BA biosynthesis pathway is divided into four modules: the red arrow indicates the heterologous CYP/CPR module (CYP-lupeol C-28 oxidase, CPR-CPR-NADPH-cytochrome P450 reductase). The yellow arrow shows the MVA module, which includes three genes (ERG1, ERG9, and HMG1). The green arrow depicts the redox cofactor supply module, featuring four introduced genes (EMC, EMT, and Rtme – encoding malic enzyme, responsible for NADPH generation, and Gapc – encoding glyceraldehyde-3-phosphate dehydrogenase, responsible for NADH production). The blue arrow represents the acetyl-CoA generation module, with seven endogenous genes overexpressed (ACL1 and ACL2, encoding ATP citrate lyase, to increase acetyl-CoA levels directly; PXA1, MFE1, PEX10, POT1, and TGL3, which participate in the β-oxidation pathway and are responsible for fatty acid catabolism to produce acetyl-CoA). This figure has been reproduced from ref. . Copyright: 2019 by the authors. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Fig. 8. Apoptosis induction through the mitochondrial pathway in activated cancer cells by BA, involving (a) p53 gene and (b) Smac and AIF proteins. This figure (a) has been reproduced from ref. with permission from Elsevier Science Ltd, Copyright 2016. This figure (b) has been reproduced from ref. . Copyright: 2021 by the authors. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Fig. 9. NF-kB Inhibition by BA in cancer treatment. This figure has been reproduced from ref. with permission from Elsevier Science Ltd, Copyright 2016.

Fig. 10. Regulation of the growth of the cancer cell via Sp transcription factors. This figure has been reproduced from ref. . Copyright: 2021 by the authors. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Fig. 11. Some common nanomaterials and carrier types used as controlled release systems for therapeutic applications, including 0D, 1D, and 2D materials. This figure has been reproduced from ref. . Copyright: 2024 by the authors. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Fig. 12. Several FDA-approved drugs are currently available to treat BC. This figure has been reproduced from ref. . Copyright: 2024 by the authors. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Fig. 13. Soluplus-BA micelles inhibit the proliferation of MDA-MB-231 cells. (a) MDA-MB-231 cells were treated with Soluplus, BA, and Soluplus-BA micelles for 48 hours; cell viability was assessed using the MTT assay. (b) MDA-MB-231 cells were seeded in 6-well plates and treated with BA and Soluplus-BA for 48 hours. After replacing the media with fresh culture medium, the cells were cultured for an additional 10 days and stained with crystal violet. (c) Cell uptake assay. MDA-MB-231 cells were treated with free cou6 and Soluplus-cou6 micelles for 3, 5, and 15 minutes. (d) Soluplus-BA micelles trigger a ROS-mediated mitochondrial apoptosis pathway. MDA-MB-231 cells were treated with Soluplus-BA and BA for 48 hours. After treatment, cells were stained with DCFH-DA for 20 minutes or JC-1 for 30 minutes and photographed under a fluorescence microscope. This figure has been reproduced from ref. . Copyright: 2021 by the authors. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Fig. 14. Compound 6 inhibited BC cell viability and colony formation. (a) MCF-10A cells were less sensitive to 6 treatments. MCF-7 and MCF-10A cell lines were incubated with specified concentrations of compound 6 for 72 hours. An MTT assay was conducted to assess cell viability. (b) Compound 6 suppressed the colony formation of MCF-7 cells. (c) The data are presented as mean ± SEM from three independent experiments compared to the control. This figure has been reproduced from ref. with permission from Elsevier Science Ltd, Copyright 2019.

Fig. 15. Demonstrates the morphology of the harvested tumors after administration of Taxol^®, PTX-NP, BA-NP, PTX-BA-NP, or control (saline) (means ± SDs, n = 3). *p < 0.05, **p < 0.01. This figure has been reproduced from ref. with permission from Elsevier Science Ltd, Copyright 2019.

Fig. 16. Cytotoxicity of 4T1 cells treated with various formulations (a) and the percentage of induced apoptosis (b). This figure has been reproduced from ref. with permission from Elsevier Science Ltd, Copyright 2020.