Selective obstruction of the mTORC2 complex by a naturally occurring cholestane saponin (OSW-1) for inhibiting prostate cancer cell growth

Advances in antitumor activity and mechanism of natural steroidal saponins: A review of advances, challenges, and future prospects

BACKGROUND

Cancer, the second leading cause of death worldwide following cardiovascular diseases, presents a formidable challenge in clinical settings due to the extensive toxic side effects associated with primary chemotherapy drugs employed for cancer treatment. Furthermore, the emergence of drug resistance against specific chemotherapeutic agents has further complicated the situation. Consequently, there exists an urgent imperative to investigate novel anticancer drugs. Steroidal saponins, a class of natural compounds, have demonstrated notable antitumor efficacy. Nonetheless, their translation into clinical applications has remained unrealized thus far. In light of this, we conducted a comprehensive systematic review elucidating the antitumor activity, underlying mechanisms, and inherent limitations of steroidal saponins. Additionally, we propose a series of strategic approaches and recommendations to augment the antitumor potential of steroidal saponin compounds, thereby offering prospective insights for their eventual clinical implementation.

PURPOSE

This review summarizes steroidal saponins' antitumor activity, mechanisms, and limitations.

METHODS

The data included in this review are sourced from authoritative databases such as PubMed, Web of Science, ScienceDirect, and others.

RESULTS

A comprehensive summary of over 40 steroidal saponin compounds with proven antitumor activity, including their applicable tumor types and structural characteristics, has been compiled. These steroidal saponins can be primarily classified into five categories: spirostanol, isospirostanol, furostanol, steroidal alkaloids, and cholestanol. The isospirostanol and cholestanol saponins are found to have more potent antitumor activity. The primary antitumor mechanisms of these saponins include tumor cell apoptosis, autophagy induction, inhibition of tumor migration, overcoming drug resistance, and cell cycle arrest. However, steroidal saponins have limitations, such as higher cytotoxicity and lower bioavailability. Furthermore, strategies to address these drawbacks have been proposed.

CONCLUSION

In summary, isospirostanol and cholestanol steroidal saponins demonstrate notable antitumor activity and different structural categories of steroidal saponins exhibit variations in their antitumor signaling pathways. However, the clinical application of steroidal saponins in cancer treatment still faces limitations, and further research and development are necessary to advance their potential in tumor therapy.

Steroidal glycosides from Ornithogalum thyrsoides bulbs and their cytotoxicity toward HL-60 human promyelocytic leukemia cells and SBC-3 human small-cell lung cancer cells

Ornithogalum thyrsoides Jacq belongs to the Asparagaceae family and is cultivated for ornamental purposes. The authors have previously reported several cholestane- and spirostan-type steroidal glycosides from O. thyrsoides. Conventional TLC analysis of the methanolic bulb extract of O. thyrsoides suggested the presence of unprecedented compounds; therefore, a detailed phytochemical investigation of the extract was performed and 35 steroidal glycosides (1-35), including 21 previously undescribed ones (1-21) were collected. The structures of 1-21 were determined mainly by analyses of their 1H and 13C NMR spectra with the aid of two-dimensional NMR spectroscopy. The isolated compounds were classified into three distinct groups: furostan-type (1, 2, 8-12, and 22), spirostan-type (3-7 and 23-26), and cholestane-type (13-21 and 27-35). Although the C/D-ring junction of the steroidal skeleton is typically trans-oriented, except for some cardiotonic and pregnane-type steroidal derivatives, 7 possess a cis C/D-ring junction. This is the first reported instance of such a configuration in spirostan-type steroidal derivatives, marking it as a finding of significant interest. Compounds 1-35 were evaluated for cytotoxicity against HL-60 human promyelocytic leukemia cells and SBC-3 human small-cell lung cancer cells. Compounds 3-6, 9, 17-21, 23-25, and 30-35 demonstrated cytotoxicity in a dose-dependent manner with IC50 values ranging from 0.000086 to 18 μM and from 0.00014 to 37 μM toward HL-60 and SBC-3 cells, respectively. Compound 19, which is obtained in a good yield and shows relatively potent cytotoxicity among the undescribed compounds, induces apoptosis in HL-60 cells, accompanied by arresting the cell cycle of HL-60 cells at the G2/M phase. In contrast, 19 causes oxidative stress-associated necrosis in SBC-3 cells. The cytotoxic mechanism of 19 is different between HL-60 and SBC-3 cells.

Comparative Analysis of Metabolic Compositions and Trace Elements of Ornithogalum caudatum with Different Growth Years

As a traditional medicine with extensive history, Ornithogalum caudatum has high nutritional and medicinal value. However, its quality evaluation criteria are insufficient because it is not included in the pharmacopeia. Simultaneously, it is a perennial plant, and the medicinal ingredients change with the growth years. Currently, studies on the synthesis and accumulation of metabolites and elements in O. caudatum during different growth years are unavailable. To address this issue, in this study, the 8 main active substances, metabolism profiles, and 12 trace elements of O. caudatum from different growth years (1, 3, and 5 years old) were analyzed. The main substances of O. caudatum changed significantly in different years of growth. Saponin and sterol contents increased with age; however, the polysaccharide content decreased. For metabolism profiling, ultrahigh-performance liquid chromatography tandem mass spectrometry was performed. Among the three groups, 156 differential metabolites with variable importance in projection values >1.0 and p < 0.05 were identified. Among the differential metabolites, 16 increased with increasing years of growth and have the potential to become age-identified markers. A trace element study showed that the contents of K, Ca, and Mg were higher, and the ratio of Zn/Cu was less than 0.1%. Heavy metal ions in O. caudatum did not increase with age. The results of this study provide a basis to evaluate the edible values of O. caudatum and facilitate further exploitation.

Anticancer effects of OSW-1 on glioma cells via regulation of the PI3K/AKT signal pathway: A network pharmacology approach and experimental validation in vitro and in vivo

Background: Gliomas are the most common primary intracranial malignant tumors with poor prognosis, despite the remarkable advances in medical technology that have been made. OSW-1, isolated from Ornithogalum saundersiae, possesses anticancer activity against various malignant cancer cells. However, the effects of OSW-1 on gliomas and its potential mechanisms remain unclear.

Methods: Network pharmacology was employed for predicting potential key targets and mechanisms of the anticancer effects of OSW-1 on glioma. Experiments, including the Cell Counting Kit-8, colony formation, and flow cytometry, were performed to investigate how OSW-1 affects the biological behavior of glioma cells in vitro. Western blotting was used to detect changes in related proteins, such as those involved in the cell cycle, apoptosis, and signaling pathways. The nude mouse xenograft model was used to detect the effect of OSW-1 on inhibiting the proliferation of glioma cells in vivo.

Results: An “OSW-1-Targets-Glioma” intersection network consisting of 151 intersecting genes was acquired to construct a “Protein–Protein Interaction network” and predict the top 10 core targets. According to the Kyoto Encyclopedia of Genes and Genomes pathway analysis, the PI3K/AKT signaling pathway was the top 3-ranked pathway, with 38 enriched intersecting genes. The glioma T98G and LN18 cell lines were used to verify the predictions. OSW-1 significantly inhibited the viability and proliferation of glioma cells in a dose- and time-dependent manner. Flow cytometry showed that OSW-1 arrested the cell cycle at the G2/M phase, and the apoptotic ratio of glioma cells increased significantly with increasing concentrations. Western blotting revealed that the expression levels of p-PI3K and p-AKT1 in glioma cells treated with OSW-1 were significantly lower than those in the controls; however, 740Y-P, a PI3K activator, significantly reversed the inactivation of the PI3K/AKT signaling pathway caused by OSW-1. Furthermore, the mouse xenograft model confirmed the suppressive effect of OSW-1 on tumor growth in vivo.

Conclusion: OSW-1 is a promising anti-glioma chemotherapeutic drug owing to its anticancer effects via downregulation of the PI3K/AKT signaling pathway. However, OSW-1 still has a long way to go to become a real anti-glioma drug.