Synthesis and Biological Evaluation of Manassantin Analogues for Hypoxia-Inducible Factor 1α Inhibition

Manassantin A inhibits tumour growth under hypoxia through the activation of chaperone-mediated autophagy by modulating Hsp90 activity

BACKGROUND

Chaperon-mediated autophagy (CMA) has taken on a new emphasis in cancer biology. However, the roles of CMA in hypoxic tumours are poorly understood. We investigated the anti-tumour effects of the natural product ManA through the activation of CMA in tumour progression under hypoxia.

METHODS

The effect of ManA on CMA activation was assessed in mouse xenograft models and cells. The gene expressions of HIF-1α, HSP90AA1, and transcription factor EB (TFEB) were analysed using The Cancer Genome Atlas (TCGA) datasets to assess the clinical relevance of CMA.

RESULTS

ManA activates photoswitchable CMA reporter activity and inhibits Hsp90 chaperone function by disrupting the Hsp90/F1F0-ATP synthase complex. Hsp90 inhibition enhances the interaction between CMA substrates and LAMP-2A and TFEB nuclear localisation, suggesting CMA activation by ManA. ManA-activated CMA retards tumour growth and displays cooperative anti-tumour activity with anti-PD-1 antibody. TCGA datasets show that a combined expression of HSP90AA1High/HIF1AHigh or TFEBLow/HIF1AHigh is strongly correlated with poor prognosis in patients with lung cancer.

CONCLUSIONS

ManA-induced CMA activation by modulating Hsp90 under hypoxia induces HIF-1α degradation and reduces tumour growth. Thus, inducing CMA activity by targeting Hsp90 may be a promising therapeutic strategy against hypoxic tumours.

Steppogenin suppresses tumor growth and sprouting angiogenesis through inhibition of HIF-1α in tumors and DLL4 activity in the endothelium

BACKGROUND

Hypoxia is a characteristic feature of many solid tumors. As an adaptive response to hypoxia, tumor cells activate hypoxia-inducible factor-1α (HIF-1α). Under hypoxic conditions, angiogenesis mediated by HIF-1α is involved in the growth and metastasis of tumor cells. During the angiogenic process, differentiated tip endothelial cells (ECs) characterized by high expression of DLL4 promote angiogenic germination through filopodia. Inhibitors of HIF-1α or DLL4 have been widely studied PURPOSE: We tried to find inhibitors targeting both HIF-1α and DLL4 in tumor which have not yet been developed.

STUDY DESIGN

In this study, we examined a natural compound that inhibits sprouting angiogenesis and tumor growth by targeting both HIF-1α and DLL4 under hypoxic conditions.

METHODS

After examining cell viability of 70 selected natural compounds, we assessed the effects of compounds on HIF-1α and DLL4 transcriptional activity using a dual-luciferase reporter assay. Western blot analysis, immunofluoresecnt assay and real-time qPCR were performed to identify expression of proteins, such as HIF-1α and DLL4, as well as HIF-1α target genes under hypoxic conditions. In vitro angiogenesis assay and in vivo allograft tumor experiment were performed to investigate inhibition of tumor growth through anti-angiogenic activity.

RESULTS

Among these compounds, steppogenin, which is extracted from the root bark of Morus alba l, respectively inhibited the transcriptional activity of HIF-1α under hypoxic conditions in HEK293T cells and vascular endothelial growth factor (VEGF)-induced DLL4 expression in vascular ECs in a dose-dependent manner. In tumor cells and retinal pigment epithelial cells, steppogenin significantly suppressed HIF-1α protein levels under hypoxic conditions as well as VEGF-induced DLL4 expression in ECs. Furthermore, steppogenin suppressed hypoxia-induced vascular EC proliferation and migration as well as VEGF-induced sprouting of EC spheroids.

CONCLUSION

These results suggest that the natural compound steppogenin could potentially be used to treat angiogenic diseases, such as those involving solid tumors, because of its dual inhibition of HIF-1α and DLL4.

Manassantin B attenuates obesity by inhibiting adipogenesis and lipogenesis in an AMPK dependent manner

Saururus chinensis (S chinensis) has been used as an herb to treat edema, jaundice, and gonorrhea. Manassantin B (MNSB), a dineolignan isolated from S chinensis, was identified as a potent adipogenesis/lipogenesis inhibitor (IC₅₀  = 9.3 nM). To explore the underlying mechanism, both adipogenesis and lipogenesis were measured in differentiated 3T3-L1 preadipocytes, murine primary preadipocytes and adipose tissue explants upon MNSB treatment. Key regulators of adipogenesis/lipogenesis were downregulated by MNSB treatment, mainly resulting from increased phosphorylation of AMPK which was identified as a vital regulator of adipogenesis and lipogenesis. Moreover, MNSB did not increase AMPK phosphorylation in 3T3-L1 cells transfected with Prkaa1 (encoding protein kinase AMP-activated catalytic subunit alpha 1) siRNA or adipose tissue explants isolated from adipose-specific Prkaa1-disrupted mice (Prkaa1^Δad ). In diet-induced obese C57BL/6N mice, MNSB displayed preventive and therapeutic effects on obesity accompanied by decreased adipocyte size. MNSB was also found to increase AMPK phosphorylation both in subcutaneous white adipose tissue and brown adipose tissue in vivo. These findings suggest that MNSB can be a new therapeutic agent for the prevention and treatment of obesity and other related metabolic disorders.

Smart Fluorescent Probe Strategy for Precision Targeting Hypoxic Tumor

Both nitroreductase and the folate receptor are highly expressed in hypoxic tumors. The folate receptor is a potential target for tumors, and nitroreductase can selectively turn on the fluorescence of probes by reducing the nitro group to an amino group. Karan et al. (Karana, S., Cho, M., Lee, H., Lee, H., Park, H., Sundararajan, M., Sessler, J., and Hong, K. Near-infrared fluorescent probe activated by nitroreductase for in vitro and in vivo hypoxic tumor detection. J. Med. Chem. 2021) developed a near-infrared fluorescent probe for hypoxia tumor imaging analysis in vitro and in vivo using folate as the targeting site. This promising strategy may promote advances in precision diagnosis and treatment models of malignant tumors. This Viewpoint looks ahead to new possibilities rendered by their studies.

Oroxylin A reverses hypoxia-induced cisplatin resistance through inhibiting HIF-1α mediated XPC transcription

Hypoxia is a key concern during the treatment of non-small cell lung cancer (NSCLC), and hypoxia-inducible factor 1 alpha (HIF-1α) has been associated with increased tumor resistance to therapeutic modalities such as cisplatin. Compensatory activation of nucleotide excision repair (NER) pathway is the major mechanism that accounts for cisplatin resistance. In the present study, we suggest a novel strategy to improve the treatment of NSCLC and overcome the hypoxia-induced cisplatin resistance by cotreatment with Oroxylin A, one of the main bioactive flavonoids of Scutellariae radix. Based on the preliminary screening, we found that xeroderma pigmentosum group C (XPC), an important DNA damage recognition protein involved in NER, dramatically increased in hypoxic condition and contributed to hypoxia-induced cisplatin resistance. Further data suggested that Oroxylin A significantly reversed the hypoxia-induced cisplatin resistance through directly binding to HIF-1α bHLH-PAS domain and blocking its binding to HRE3 transcription factor binding sites on XPC promoter which is important to hypoxia-induced XPC transcription. Taken together, our findings not only demonstrate a crucial role of XPC dependent NER in hypoxia-induced cisplatin resistance, but also suggest a previously unrecognized tumor suppressive mechanism of Oroxylin A in NSCLC which through sensitization of cisplatin-mediated growth inhibition and apoptosis under hypoxia.

Structural basis of the UDP-diacylglucosamine pyrophosphohydrolase LpxH inhibition by sulfonyl piperazine antibiotics

The UDP-2,3-diacylglucosamine pyrophosphate hydrolase LpxH is an essential lipid A biosynthetic enzyme that is conserved in the majority of gram-negative bacteria. It has emerged as an attractive novel antibiotic target due to the recent discovery of an LpxH-targeting sulfonyl piperazine compound (referred to as AZ1) by AstraZeneca. However, the molecular details of AZ1 inhibition have remained unresolved, stymieing further development of this class of antibiotics. Here we report the crystal structure of Klebsiella pneumoniae LpxH in complex with AZ1. We show that AZ1 fits snugly into the L-shaped acyl chain-binding chamber of LpxH with its indoline ring situating adjacent to the active site, its sulfonyl group adopting a sharp kink, and its N-CF₃-phenyl substituted piperazine group reaching out to the far side of the LpxH acyl chain-binding chamber. Intriguingly, despite the observation of a single AZ1 conformation in the crystal structure, our solution NMR investigation has revealed the presence of a second ligand conformation invisible in the crystalline state. Together, these distinct ligand conformations delineate a cryptic inhibitor envelope that expands the observed footprint of AZ1 in the LpxH-bound crystal structure and enables the design of AZ1 analogs with enhanced potency in enzymatic assays. These designed compounds display striking improvement in antibiotic activity over AZ1 against wild-type K. pneumoniae, and coadministration with outer membrane permeability enhancers profoundly sensitizes Escherichia coli to designed LpxH inhibitors. Remarkably, none of the sulfonyl piperazine compounds occupies the active site of LpxH, foretelling a straightforward path for rapid optimization of this class of antibiotics.

A Review of Traditional Uses, Phytochemistry, and Pharmacological Properties of the Genus Saururus

The genus Saururus, belonging to Saururaceae, contains two species, S. cernuus L. and S. chinensis (Lour) Baill. with common utilization in traditional medicine from Asia to North America for the treatment of edema, beriberi, jaundice, leucorrhea, urinary tract infections, hypertension, hepatitis diseases, and tumors. An extensive review of literature was made on traditional uses, phytochemistry, and ethnopharmacology of Saururus using ethno-botanical books, published articles, and electronic databases. The 147 of chemical constituents have been isolated and identified from S. cernuus and S. chinensis, and lignans, flavonoids, alkaloids, anthraquinones, saponins, and phenols are the major constituents. Various pharmacological investigations in many in vitro and in vivo models have revealed the potential of the genus Saururus with anti-inflammatory, antitumor, anti-oxidant, hepatoprotective, antimelanogenic, lipid-lowering, and bone protective activities, supporting the rationale behind numerous of its traditional uses. Due to the noteworthy pharmacological properties, Saururus can be a better option for new drug discovery. Data regarding many aspects of this plant such as toxicology, pharmacokinetics, quality-control measures, and the clinical value of the active compounds is still limited which call for additional studies.

Structure-activity relationships study of neolamellarin A and its analogues as hypoxia inducible factor-1 (HIF-1) inhibitors

The novel marine pyrrole alkaloid neolamellarin A derived from sponge has been shown to inhibit hypoxia-induced HIF-1 activity. In this work, we designed and synthesized neolamellarin A and its series of derivatives by a convergent synthetic strategy. The HIF-1 inhibitory activity and cytotoxicity of these compounds were evaluated in Hela cells by dual-luciferase reporter gene assay and MTT assay, respectively. The results showed that neolamellarin A 1 (IC₅₀ = 10.8 ± 1.0 μM) and derivative 2b (IC₅₀ = 11.9 ± 3.6 μM) had the best HIF-1 inhibitory activity and low cytotoxicity. Our SAR research focused on the effects of key regions aliphatic carbon chain length, aromatic ring substituents and C-7 substituent on biological activity, providing a basis for the subsequent research on the development of novel pyrrole alkaloids as HIF-1 inhibitors and design of small molecule probes for target protein identification.

Hypoxia-inducible factor-1 (HIF-1) inhibitors from the last decade (2007 to 2016): A "structure-activity relationship" perspective

Tumor hypoxia is a common feature in most solid tumors and is associated with overexpression of the hypoxia response pathway. Overexpression of the hypoxia-inducible factor (HIF-1) protein leads to angiogenesis, metastasis, apoptosis resistance, and many other pro-tumorigenic responses in cancer development. HIF-1 is a promising target in cancer drug development to increase the patient's response to chemotherapy and radiotherapy as well as the survival rate of cancer patients. Since up to 1% of genes are hypoxia-sensitive, a target-specific HIF-1 inhibitor may be a better clinical candidate in cancer drug discovery. Though no HIF-1 inhibitor is clinically available to date, a lot of effort has been applied during the last decade in search of potent HIF-1 inhibitors. In this review, we will summarize the structure-activity relationship of ten different chemotypes reported to be HIF-1 inhibitors in the last decade (2007-2016), their mechanisms of action for HIF-1 inhibition, progress in the way of target-specific inhibitors, and problems associated with current inhibitors. It is anticipated that the results of these research on the medicinal chemistry of HIF-1 inhibitors will provide decent information in the design and development of future inhibitors.

The lignan manassantin is a potent and specific inhibitor of mitochondrial complex I and bioenergetic activity in mammals

Dineolignans manassantin A and B from the plant Saururus cernuus are used in traditional medicine to manage a wide range of ailments such as edema, jaundice, and gonorrhea. Cell-based studies have identified several molecular target candidates of manassantin including NF-κB, MAPK, STAT3, and hypoxia-inducible factor 1α (HIF-1α). It is unclear whether or how these structurally diverse proteins or pathways mediate any of the medical benefits of manassantin in vivo Moreover, it has recently been reported that manassantin causes developmental arrest in zebrafish by inhibiting the mitochondrial complex I, but it is unknown whether manassantin inhibits mitochondrial respiration in intact mammalian cells and live animals. Here, we present direct evidence that manassantin potently and specifically inhibits the mitochondrial complex I and bioenergetic activity in mammalian systems. Manassantin had no effect on complex II- or complex IV-mediated respiration. Of note, it decreased NADH-ubiquinone reductase activity but not the activity of NADH-ferricyanide reductase. Treatment with manassantin reduced cellular ATP levels and concomitantly stimulated AMP-activated protein kinase in vitro and in vivo As an adaptive response to manassantin-induced bioenergetic deficiency, mammalian cells up-regulated aerobic glycolysis, a process mediated by AMP-activated protein kinase (AMPK) independently of HIF-1α. Together these results demonstrate a biologically important activity of manassantin in the control of complex I-mediated respiration and its profound effects on oxygen utilization, energy homeostasis, and glucose metabolism in mammalian cells.

Discovery of Manassantin A Protein Targets Using Large-Scale Protein Folding and Stability Measurements

Manassantin A is a natural product that has been shown to have anticancer activity in cell-based assays, but has a largely unknown mode-of-action. Described here is the use of two different energetics-based approaches to identify protein targets of manassantin A. Using the stability of proteins from rates of oxidation technique with an isobaric mass tagging strategy (iTRAQ-SPROX) and the pulse proteolysis technique with a stable isotope labeling with amino acids in cell culture strategy (SILAC-PP), over 1000 proteins in a MDA-MB-231 cell lysate grown under hypoxic conditions were assayed for manassantin A interactions (both direct and indirect). A total of 28 protein hits were identified with manassantin A-induced thermodynamic stability changes. Two of the protein hits (filamin A and elongation factor 1α) were identified using both experimental approaches. The remaining 26 hit proteins were only assayed in either the iTRAQ-SPROX or the SILAC-PP experiment. The 28 potential protein targets of manassantin A identified here provide new experimental avenues along which to explore the molecular basis of manassantin A's mode of action. The current work also represents the first application iTRAQ-SPROX and SILAC-PP to the large-scale analysis of protein-ligand binding interactions involving a potential anticancer drug with an unknown mode-of-action.

LXY6090 - a novel manassantin A derivative - limits breast cancer growth through hypoxia-inducible factor-1 inhibition

Hypoxia-inducible factor-1 (HIF-1) represents a novel antitumor target owing to its involvement in vital processes considered hallmarks of cancer phenotypes. Manassantin A (MA) derived from Saururus cernuus has been reported as a selective HIF-1 inhibitor. Herein, the structure of MA was optimized to achieve new derivatives with simple chemical properties while retaining its activity. LXY6090 was designed to replace the central tetrahydrofuran moiety of MA with a cyclopentane ring and was identified as a potent HIF-1 inhibitor with an IC50 value of 4.11 nM. It not only inhibited the activity of HIF-1 in breast cancer cells but also downregulated the protein level of HIF-1α, which depended on von Hippel-Lindau for proteasome degradation. The related biological evaluation showed that the activity of HIF-1 target genes, VEGF and IGF-2, was decreased by LXY6090 in breast cancer cell lines. LXY6090 presented potent antitumor activity in vitro. Furthermore, LXY6090 showed in vivo anticancer efficacy by decreasing the HIF-1α expression in nude mice bearing MX-1 tumor xenografts. In conclusion, our data provide a basis for the future development of the novel compound LXY6090 as a potential therapeutic agent for breast cancer.