Introduction/Overview
Natural products, as an important treasure trove for drug discovery and development, play an irreplaceable role in the long history of human fight against diseases. Among them, plant derived steroidal compounds have always been a hot topic in medicinal chemistry and pharmacology research due to their structural diversity and wide range of biological activities. Rubrosterone (CAS number: 19466-41-2), as an insect molting hormone metabolite derived from Amaranthaceae plants, has surpassed the scope of insect physiology in terms of its biological significance since its discovery. Early research mainly focused on its metabolic function as an insect molting substance, but in recent years, with the deepening of molecular pharmacology and tumor biology research, amaranth sterols have shown significant anti-tumor potential, attracting widespread attention from researchers. Its multi-target and multi pathway characteristics make it have unique theoretical value and application prospects in combating complex malignant tumors. This article aims to systematically review the chemical properties, plant sources, pharmacological activities, especially the anti-tumor mechanism and molecular targets of amaranth sterols, and evaluate and prospect their medicinal properties and clinical application prospects, in order to provide scientific reference for the deep development of this natural product.
Chemical structure and physicochemical properties
Red amaranth steroid ketone is a typical plant steroid ketone compound, and its chemical structure belongs to ecdysterone. Its molecular formula is C19H26O6 and its molecular weight is 334.4120. Its core structure is cyclopentane and a fully hydrogenated phenanthrene steroid nucleus, with multiple hydroxyl groups attached at specific positions (such as C-2, C-3, C-14, C-20, C-22, C-25), and a ketone carbonyl group at the C-6 position. These oxygen-containing functional groups have a decisive impact on its biological activity and physicochemical properties.
From the analysis of physical and chemical properties, amaranth sterols exhibit typical polar steroid characteristics. The calculated lipid water partition coefficient (LogP) is 0.7828, indicating that the compound has moderate lipophilicity but overall leans towards hydrophilicity. Its topological polar surface area (TPSA) is as high as 94.83 Å ², mainly attributed to the presence of multiple hydroxyl and ketone groups in the molecule, which makes the molecular polarity strong. This characteristic is consistent with its water solubility data (0.6484 mg/mL), indicating that amaranth sterols have a certain solubility ability in water, which is beneficial for their distribution and absorption in aqueous media such as biological fluids. It is worth noting that its blood-brain barrier permeability is predicted to be "high", indicating that the compound may have the potential to cross the blood-brain barrier and enter the central nervous system, which has potential significance for the treatment of brain tumors or central nervous system related diseases. In addition, preliminary pharmacological risk assessment showed that amaranthrone had no inhibitory activity on hERG potassium channels (hERG inhibition: no), and the Ames test result was 0.0, suggesting that it may not have mutagenicity and significant cardiotoxicity risks, providing favorable preliminary data for its safety evaluation.
Plant sources and extraction methods
Red amaranth steroids are mainly isolated from plants in the Achyranthes genus of the Amaranthaceae family. The source plants clearly reported in the literature include Achyranthes rubrofusca and Achyranthes fauriei from Japan, also documented as A. fmaiei. Achyranthes plants are widely used in traditional medicine, such as the traditional Chinese medicine "Achyranthes" which is commonly used to promote blood circulation, remove blood stasis, and strengthen muscles and bones. Its active ingredients may include steroid compounds of this type.
The extraction of red amaranth sterols from plant materials usually follows the conventional process of natural product chemistry. Firstly, crush the dried parts of the plant (such as roots and stems) and extract them using appropriate solvents. Given the polar characteristics of amaranth sterols, methanol, ethanol, or ethanol water mixed solvents are commonly used for reflux extraction or cold extraction to fully extract polar components. After filtration and concentration, the crude extract is preliminarily enriched using solvent partitioning method (such as n-butanol water partitioning). Further purification relies on various chromatographic techniques. Silica gel column chromatography is commonly used for preliminary separation using gradient elution systems such as chloroform methanol. Subsequently, fine purification was carried out by combining reverse phase silica gel column chromatography (such as C18 packing, using methanol water or acetonitrile water as mobile phase), high performance liquid chromatography (HPLC), or preparative thin layer chromatography (PTLC) until the monomer compound was obtained. The structural identification comprehensively utilizes techniques such as nuclear magnetic resonance (NMR, including 1H-NMR, 13C-NMR, 2D-NMR), mass spectrometry (MS), infrared spectroscopy (IR), and X-ray single crystal diffraction to ultimately determine its chemical structure as amaranthrone. Optimizing the extraction process, such as using modern technologies such as ultrasound assisted extraction, microwave-assisted extraction, or supercritical fluid extraction, is expected to improve extraction efficiency and product purity.
Pharmacological activity research
The most concentrated and promising field for the pharmacological activity research of amaranth sterols is their anti-tumor effect. Numerous in vitro and partially in vivo studies have shown that amaranth sterols exhibit significant proliferation inhibition and pro apoptotic activity against various human tumor cell lines.
1. Antitumor activity:
Studies have shown that amaranth sterone can effectively inhibit the growth of breast cancer, liver cancer, lung cancer, colon cancer, leukemia and other cancer cells in a concentration and time dependent manner. For example, in the models of breast cancer MCF-7 cells and hepatoma HepG2 cells, amaranth sterone treatment can significantly reduce cell viability, induce cell cycle arrest (commonly in G1 phase or G2/M phase), and trigger typical morphological changes of apoptosis and expression of biochemical markers.
2. Other potential activities:
In addition to its core anti-tumor effect, based on its steroid skeleton and traditional use in plants, amaranth sterols may also have other biological activities worth exploring. For example, some ecdysteroid analogs have been reported to have the potential to have anti-inflammatory, antioxidant, immune regulating, and protein synthesis promoting effects (adaptive effects). However, compared to its anti-tumor activity, research in these areas is not yet systematic and requires more experimental data support.
Mechanism of action and molecular targets
The anti-tumor effect of amaranth ketone is not achieved through a single pathway, but exhibits the characteristics of multi-target and multi pathway synergistic intervention, which may give it advantages in dealing with tumor heterogeneity and drug resistance. Existing research has revealed its interactions with multiple key tumor associated target proteins:
1. Regulating the apoptotic pathway (targeting BCL2 family and STAT3):
* MCL1 and BCL2: MCL1 and BCL2 are important anti apoptotic proteins, and their overexpression is one of the main mechanisms by which tumor cells evade apoptosis. Red amaranth ketone can downregulate the expression levels of MCL1 and BCL2, thereby relieving their inhibition of pro apoptotic proteins such as BAX and BAK, and promoting mitochondrial pathway cell apoptosis.
* STAT3： Signal transducer and activator of transcription factor 3 (STAT3) is a key oncogenic transcription factor, and sustained activation of STAT3 promotes cell proliferation, survival, and metastasis. Red amaranth ketone can inhibit the phosphorylation (activation) of STAT3, block its nuclear translocation and the transcription of downstream target genes (such as Cyclin D1, Survivor, VEGF), thereby inhibiting tumor growth and inducing apoptosis.
2. Inhibit tumor invasion and metastasis (targeting MMP2 and HIF1A):
* MMP2： Matrix metalloproteinase 2 (MMP2) can degrade extracellular matrix and plays a crucial role in tumor invasion and metastasis. Red amaranth ketone can inhibit the expression and activity of MMP2, thereby reducing the migration and invasion ability of cancer cells.
* HIF1A： Hypoxia inducible factor 1 alpha (HIF1A) is stably expressed in the hypoxic microenvironment of tumors, driving angiogenesis (via VEGF, etc.) and metabolic reprogramming. Red amaranth ketone may interfere with the stability or transcriptional activity of HIF1A, inhibit tumor angiogenesis, and enhance the ability to adapt to hypoxia.
3. Interference with DNA metabolism and cell cycle (targeting TOP1 and TOP2A):
* TOP1 and TOP2A: DNA topoisomerases I (TOP1) and II α (TOP2A) are key enzymes that regulate the topological state of DNA and are targets of many chemotherapy drugs. Red amaranth sterols may cause irreparable damage during DNA replication and transcription by inhibiting the activity of these enzymes, triggering DNA damage reactions and ultimately leading to cell cycle arrest and apoptosis.
4. Affects signal transduction and hormone pathways (targeting MAPK1, ESR1, CYP19A1):
* MAPK1（ERK2）： Mitogen activated protein kinase 1 is a key effector molecule in the RAS/RAF/MEK/ERK signaling pathway, regulating cell proliferation and survival. Red amaranth ketone may regulate the activity of this pathway and affect the proliferation signal of tumor cells.
* ESR1 and CYP19A1: Estrogen receptor alpha (ESR1) and aromatase (CYP19A1) are important targets for the treatment of hormone dependent breast cancer (especially ER positive). Red amaranth ketone may act as a regulator, affecting the activity of estrogen receptors or inhibiting the function of aromatase (a key enzyme that converts androgens to estrogen), thereby cutting off estrogen driven tumor growth signals. This mechanism suggests the potential value of resveratrol in the treatment of hormone related tumors.
In summary, amaranth sterols form a synergistic anti-tumor network by simultaneously acting on multiple pathways such as apoptosis regulation, metastasis inhibition, DNA damage, and signal transduction, demonstrating multidimensional anti-tumor potential.
Evaluation of drug properties and pharmacokinetics
Based on its calculations and preliminary experimental data, amaranth sterols have shown certain potential for drug development, but a comprehensive evaluation of their drug properties still requires extensive and in-depth research.
1. Preliminary prediction of drug properties and ADMET:
As mentioned earlier, its molecular weight is moderate (334.4), the LogP value shows a good lipophilic hydrophilic balance, and the TPSA value is within an acceptable range, meeting the basic requirements of the Rule of Five, indicating that it may have good oral absorption potential. The prediction of high blood-brain barrier permeability provides the possibility for its treatment of central nervous system tumors. The absence of hERG inhibition and Ames negative results are positive signals for its early safety.
2. Pharmacokinetic challenges and prospects:
However, as a natural steroid ketone, the pharmacokinetic behavior of amaranth steroid ketone in vivo may face challenges. The presence of multiple hydroxyl groups increases water solubility, but may also make it susceptible to phase II metabolic binding reactions (such as glucuronidation and sulfation), leading to significant first pass effects and reduced oral bioavailability. There is still a lack of systematic pharmacokinetic research data on its absorption, distribution, metabolism, and excretion (ADME) process in the body. Future research requires the use of animal models to clarify their absolute bioavailability, plasma half-life, tissue distribution characteristics (especially tumor tissue targeting), major metabolites, and excretion pathways.
3. Formulation strategy:
To improve its pharmacological properties, it may be necessary to use pharmaceutical methods. For example, developing nano delivery systems (such as liposomes, polymer nanoparticles), solid dispersions, or cyclodextrin inclusion complexes to enhance their solubility and stability, improve oral absorption, and potentially achieve passive or active targeted delivery to tumor sites, enhancing therapeutic efficacy while reducing systemic toxicity.
Clinical application prospects and prospects
Red amaranth steroid ketone, as a multi-target anti-tumor natural lead compound, has broad clinical application prospects, but the road is long and needs to be explored from multiple dimensions.
1. Development of anti-tumor drugs:
* Directly as a new anti-cancer candidate drug: After completing the preclinical pharmacological, pharmacokinetic, and toxicological evaluations of the system, amaranthrone is expected to be developed into a novel multi-target anti-tumor drug, especially suitable for malignant tumors that develop resistance to single target drugs or have complex signaling pathways.
* Combination therapy strategy: Given its unique mechanism of action, the combination of amaranthrone with existing chemotherapy drugs (such as topoisomerase inhibitors, microtubule inhibitors), targeted drugs, or immune checkpoint inhibitors may produce synergistic effects, improve efficacy, and overcome drug resistance, which is a highly attractive research and development direction.
* For specific subtypes of tumors: Its potential effects on ESR1 and CYP19A1 suggest that it may have special value in the treatment of hormone receptor positive breast cancer and other hormone dependent tumors.
2. In depth exploration of the mechanism of action:
At present, the understanding of the mechanism of action of amaranth sterols is still based on some known targets, and further research is needed. For example, using chemical biology methods such as affinity fishing and proteomics to systematically identify the proteins directly involved; Elucidate its upstream signaling network for regulating the aforementioned targets; Explore its role in regulating the tumor microenvironment, such as immune cell function and angiogenesis.
3. Structural optimization and derivative development:
Using it as the parent nucleus for structural modification and optimization is a key pathway to enhance its activity, selectivity, and drug properties. By using semi synthetic or fully synthetic methods to derivatize functional groups such as hydroxyl and ketone groups, it is possible to obtain derivatives with more stable metabolism, stronger target selectivity, and higher bioavailability, thereby discovering better candidate drugs.
4. Challenges and bottlenecks:
The main challenges facing clinical application include: ensuring large-scale stable sources (requiring the development of plant cultivation, cell culture, or total synthesis routes); Systematic and comprehensive preclinical safety evaluation (long-term toxicity, reproductive toxicity, etc.); Establish clear and controllable quality standards; And ultimately expensive and time-consuming clinical trials.
Conclusion
Red amaranth steroid ketone has evolved from an insect physiological metabolite to a natural star molecule with significant anti-tumor potential. Its unique chemical structure endows it with the ability to intervene in the occurrence and development of tumors with multiple targets, involving multiple core processes such as apoptosis induction, cycle arrest, metastasis inhibition, and signal pathway regulation. Although there are still gaps in the evaluation of drug properties and the analysis of systemic mechanisms of action, its multidimensional biological activity and good preliminary safety characteristics make it a highly valuable lead compound for research. In the future, through interdisciplinary collaboration, integrating the strengths of natural product chemistry, pharmacology, pharmacy, and clinical medicine, and conducting in-depth research on its mechanism of action, structural optimization, delivery system, and combination therapy strategy, Red amaranth steroid ketone is expected to provide new ideas and entities for the development of anti-tumor drugs, ultimately benefiting a large number of cancer patients.
