Anticancer effect and neurotoxicity of S-(+)-deoxytylophorinidine, a new phenanthroindolizidine alkaloid that interacts with nucleic acids

Muyocoxanthones O-S: Undescribed xanthones with antioxidative damage bioactivity to cardiomyocytes from the endophytic fungus Muyocopron laterale

The metabolites from the endophytic fungus Muyocopron laterale hosted in the medicinal plant Tylophora ovata were investigated, and five undescribed xanthones, muyocoxanthones O-S, along with seven known compounds were isolated. Their structures were elucidated by HR-ESI-MS, NMR, and ECD calculations. Compounds were evaluated for their anti-cardiomyocyte oxidative damage activity using a model of oxidative damage induced by cell hypoxia incubation. Muyocoxanthones O-Q and blennolide L exhibited moderate activity against oxidative damage to cardiomyocytes with relative viabilities of 62.4, 54.8, 60.3 and 54.9%, respectively.

Phenanthroindolizidine Alkaloids Isolated from Tylophora ovata as Potent Inhibitors of Inflammation, Spheroid Growth, and Invasion of Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC), representing the most aggressive form of breast cancer with currently no targeted therapy available, is characterized by an inflammatory and hypoxic tumor microenvironment. To date, a broad spectrum of anti-tumor activities has been reported for phenanthroindolizidine alkaloids (PAs), however, their mode of action in TNBC remains elusive. Thus, we investigated six naturally occurring PAs extracted from the plant Tylophora ovata: O-methyltylophorinidine (1) and its five derivatives tylophorinidine (2), tylophoridicine E (3), 2-demethoxytylophorine (4), tylophoridicine D (5), and anhydrodehydrotylophorinidine (6). In comparison to natural (1) and for more-in depth studies, we also utilized a sample of synthetic O-methyltylophorinidine (1s). Our results indicate a remarkably effective blockade of nuclear factor kappa B (NFκB) within 2 h for compounds (1) and (1s) (IC50 = 17.1 ± 2.0 nM and 3.3 ± 0.2 nM) that is different from its effect on cell viability within 24 h (IC50 = 13.6 ± 0.4 nM and 4.2 ± 1 nM). Furthermore, NFκB inhibition data for the additional five analogues indicate a structure–activity relationship (SAR). Mechanistically, NFκB is significantly blocked through the stabilization of its inhibitor protein kappa B alpha (IκBα) under normoxic as well as hypoxic conditions. To better mimic the TNBC microenvironment in vitro, we established a 3D co-culture by combining the human TNBC cell line MDA-MB-231 with primary murine cancer-associated fibroblasts (CAF) and type I collagen. Compound (1) demonstrates superiority against the therapeutic gold standard paclitaxel by diminishing spheroid growth by 40% at 100 nM. The anti-proliferative effect of (1s) is distinct from paclitaxel in that it arrests the cell cycle at the G0/G1 state, thereby mediating a time-dependent delay in cell cycle progression. Furthermore, (1s) inhibited invasion of TNBC monoculture spheroids into a matrigel®-based environment at 10 nM. In conclusion, PAs serve as promising agents with presumably multiple target sites to combat inflammatory and hypoxia-driven cancer, such as TNBC, with a different mode of action than the currently applied chemotherapeutic drugs.

Oxazaborolidine-catalyzed reductive parallel kinetic resolution of ketones from β-nitro-azabicycles for the synthesis of chiral hypoestestatins 1, 2

A novel approach for the synthesis of 13a-methyl tylophora alkaloids has been reported. The key features included two different synthetic pathways targeted at transforming the β-nitro-azabicycle to the phenanthrene core. The successful steps involved the oxidation of the nitro-piperidine moiety to the corresponding α,β-unsaturated ketone, and an oxidative biaryl coupling reaction for phenanthrene ring formation. Finally, the desired product was obtained via a formal reductive removal of the hydroxyl group. This methodology has been applied for the synthesis of 13a-methyl tylophora alkaloids in up to 65% yield over six steps from β-nitro-azabicycles. Both natural and unnatural enantioenriched hypoestestatins 1 and 2, and related compounds were synthesized using parallel kinetic resolution of the CBS-oxazaborolidine-catalyzed reduction of racemic ketones to provide two separable diastereomeric alcohols in combined yields up to 91% and with high enantioselectvity (up to 89% ee). In addition, the catalytic asymmetric reduction to seco-hypoestestatins 1 and 2 has been reported for the first time. Thus, the ability to develop the racemic mixtures to both enatioenriched forms offers benefit for various biological assays in the future.

Biologically active indolizidine alkaloids

Indolizidine alkaloids are chemical constituents isolated from various marine and terrestrial plants and animals, including but not limited to trees, fungi, ants, and frogs, with a myriad of important biological activities. In this review, we discuss the biological activity and pharmacological effects of indolizidine alkaloids and offer new avenues toward the discovery of new and better drugs based on these naturally occurring compounds.

Design, Synthesis, and Antitobacco Mosaic Virus Activity of Water-Soluble Chiral Quaternary Ammonium Salts of Phenanthroindolizidines Alkaloids

To study the influence of the substituent at the N-10 position on antiviral activity, the chiral quaternary ammonium salt derivatives of R- and S-tylophorine were designed, synthesized, and evaluated for antiviral activity against tobacco mosaic virus (TMV). The bioassay results indicated that most of the designed structural analogues showed good in vivo anti-TMV activity, among which propargyl quaternary ammonium salt compound S-7b showed the best anti-TMV activities (80.5%, 77.6%, 76.6%, 82.1%) at 500 μg/mL both in vitro and in vivo in the laboratory. In the field trials of antiviral efficacy against TMV, S-7b as well exhibited better activities than control plant virus inhibitors. The stability of compound S-7b was obviously increased, and its solubility was more than 500-times higher than that of S-tylophorine. Therefore, chiral quaternary ammonium salt S-7b was expected to be developed as a promising candidate as an inhibitor of plant virus.

6-OH-Phenanthroquinolizidine Alkaloid and Its Derivatives Exert Potent Anticancer Activity by Delaying S Phase Progression

To discover new phenanthroindolizidine and phenanthroquinolizidine alkaloids as potential anticancer drug candidates, non-natural 6-O-desmethylcryptopleurine (2) and its derivatives were prepared. Most of the new compounds exhibited potent antiproliferative activity against A549 and BEL-7402 cells, with the lowest IC₅₀ being 3 nM. Optically pure 2-R was further evaluated against a panel of 30 cancer cell lines and found to inhibit the proliferation of all tested cell lines, including three multidrug-resistant cell lines, with an average IC₅₀ value of 2.1 nM, which is much lower than that of previously reported phenanthroindolizidine DCB-3503 (1, IC₅₀: 166.7 nM). A mechanistic evaluation showed that 2-R potently inhibited cell growth and colony formation, which are associated with a delay in S phase progression through the inhibition of DNA synthesis. These results along with further study on the safety profile of these compounds will facilitate the discovery of new phenanthroindolizidine and phenanthroquinolizidine alkaloids for use as anticancer drug candidates.

Phenanthroindolizidine alkaloids from Tylophora atrofolliculata with hypoxia-inducible factor-1 (HIF-1) inhibitory activity

Phenanthroindolizidine alkaloids from T. atrofolliculata with potent HIF-1 inhibitory effects.

The novel anti-neuroblastoma agent PF403, inhibits proliferation and invasion in vitro and in brain xenografts

Neuroblastoma is the most common cancer in infants and the fourth most common cancer in children. Our previous study showed that PF403 had a potent antitumor ability. In the present study, we evaluated the anti-neuroblastoma property of PF403 and investigated the underlying mechanisms. MTT assay, colony formation assay and flow cytometry assay were used to assess cytotoxicity of PF403 on SH-SY5Y cells. Transwell assay was chosen to estimate the anti-invasion ability of PF403 on neuroblastoma cells. The protein expression was detected by western blot analysis. The SH-SY5Y brain xenograft model was used to assess in vivo antitumor activity of PF403. PF403-mediated SH-SY5Y cell death was found to be dose- and time-dependent, and PF403 was able to limit invasion and metastasis of neuroblastoma cells. MRI and pathology analysis proved that the pro-drug of PF403, CAT3, inhibited SH-SY5Y cells in vivo. PF403 decreased expression of phosphorylated FAK, MMP-2 and MMP-9 proteins, and downregulated the activity of PI3K/AKT and Raf/ERK pathways, followed by regulation of the proteins expression of Bcl-2 family, activated caspase-3, -9 and PARP and initiation of apoptosis of neuroblastoma cells. PF403 exerted cytotoxicity against SH-SY5Y neuroblastoma cell both in vitro and in vivo, and inhibited its invasion ability, suggesting PF403 has potential as a new anticancer drug for the treatment of neuroblastoma.

Development and validation of a liquid chromatography-tandem mass spectroscopy method for simultaneous determination of (+)-(13aS)-deoxytylophorinine and its pharmacologically active 3-O-desmethyl metabolite in rat plasma

CAT ((+)-(13aS)-deoxytylophorinine) is a novel anticancer drug belonging to phenanthroindolizidine alkaloids. A sensitive and reliable liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for simultaneous quantification of CAT and its pharmacologically active 3-O-desmethyl metabolite (S-4) was developed and validated in rat plasma using rotundine as the internal standard (IS). CAT, S-4 and IS were extracted by acetonitrile protein precipitation and separated on an Eclipse XDB-C18 column (1.8 μm, 4.6 mm × 50 mm) with acetonitrile-water (27:73, v/v) mobile phase containing 0.1% formic acid at a 0.4 mL/min flow rate. Positive ion electrospray ionization in multiple reaction monitoring mode was employed to measure CAT, S-4 and IS by monitoring the transitions m/z 364.2→70.1 for CAT, 350.1→70.1 for S-4 and 356.2→192.2 for IS. Good linear correlation (r(2)>0.991) was achieved for CAT and S-4 over the range of 0.214-128.16 and 0.044-11.00 ng/mL, respectively. The lower limit of quantification was 0.214 ng/mL for CAT and 0.044 ng/mL for S-4, using 50 μL rat plasma samples. The intra- and inter-day precisions were not exceed 15% and the accuracy ranged between 94.80% and 108.22%. The average extraction recoveries of both analytes were greater than 94.62%. The method was successfully applied to the pharmacokinetic study of CAT and S-4 in rats after oral administration.

Integrated rapid resolution liquid chromatography-tandem mass spectrometric approach for screening and identification of metabolites of the potential anticancer agent 3,6,7-trimethoxyphenanthroindolizidine in rat urine

An integrated approach combining data acquisition using MS(E) and multi-period product ion scan (mpMS/MS), with high-resolution characteristic extracted ion chromatograms (hcXIC) as a data mining method, was developed for in vivo drug metabolites screening and identification. This approach is illustrated by analyzing metabolites of a potential anticancer agent, 3,6,7-trimethoxyphenanthroindolizidine (CAT) in rat urine based on rapid resolution liquid chromatography combined with tandem mass spectrometry (RRLC-MS/MS). Untargeted full-scan MS(E) enabled the high-throughput acquisition of potential metabolites, and targeted mpMS/MS contributed to the sensitivity and specificity of the acquisition of molecules of interest. The data processing method hcXIC, based on the structure of CAT, was shown to be highly effective for the metabolite discovery. Through the double-filtering effect of the characteristic ion and accurate mass, conventional extracted ion chromatograms that contained a substantial number of false-positive peaks were simplified into chromatograms essentially free of endogenous interferences. As a result, 21 metabolites were detected in rat urine after oral administration of CAT. Based on the characteristic fragmentation patterns of the phenanthroindolizidine alkaloid, the structures of 9 metabolites were identified. Furthermore, the interpretation of the MS/MS spectra of these metabolites enabled the determination of demethylation position as well as the differentiation between N-oxidized and hydroxylated metabolites.

Synthesis, biological evaluation and mechanism studies of deoxytylophorinine and its derivatives as potential anticancer agents

Previous studies indicated that (+)-13a-(S)-deoxytylophorinine (1) showed profound anti-cancer activities both in vitro and in vivo and could penetrate the blood brain barrier to distribute well in brain tissues. CNS toxicity, one of the main factors to hinder the development of phenanthroindolizidines, was not obviously found in 1. Based on its fascinating activities, thirty-four derivatives were designed, synthesized; their cytotoxic activities in vitro were tested to discover more excellent anticancer agents. Considering the distinctive mechanism of 1 and interesting SAR of deoxytylophorinine and its derivatives, the specific impacts of these compounds on cellular progress as cell signaling transduction pathways and cell cycle were proceeded with seven representative compounds. 1 as well as three most potent compounds, 9, 32, 33, and three less active compounds, 12, 16, 35, were selected to proform this study to have a relatively deep view of cancer cell growth-inhibitory characteristics. It was found that the expressions of phospho-Akt, Akt, phospho-ERK, and ERK in A549 cells were greater down-regulated by the potent compounds than by the less active compounds in the Western blot analysis. To the best of our knowledge, this is the first report describing phenanthroindolizidines alkaloids display influence on the crucial cell signaling proteins, ERK. Moreover, the expressions of cyclin A, cyclin D1 and CDK2 proteins depressed more dramatically when the cells were treated with 1, 9, 32, and 33. Then, these four excellent compounds were subjected to flow cytometric analysis, and an increase in S-phase was observed in A549 cells. Since the molecular level assay results of Western blot for phospho-Akt, Akt, phospho-ERK, ERK, and cyclins were relevant to the potency of compounds in cellular level, we speculated that this series of compounds exhibit anticancer activities through blocking PI3K and MAPK signaling transduction pathways and interfering with the cell cycle progression.