A Homodimer of Withaferin A Formed by Base-Promoted Elimination of Acetic Acid from 27-O-Acetylwithaferin A Followed by a Diels-Alder Reaction.

Treatment of 27-O-acetylwithaferin A (2) with the non-nucleophilic base, 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU), afforded 5ß,6ß-epoxy-4ß-hydroxy-1-oxo-witha-2(3),23(24),25(27)-trienolide (3) and 4, a homodimer of withaferin A resulting from a Diels-Alder [4 + 2] type cycloaddition of the intermediate α,ß-dimethylene-δ-lactone (9). Structures of 3 and 4 were elucidated using HRMS and 1D and 2D NMR spectroscopic data. The structure of 4 was also confirmed by single crystal X-ray crystallographic analysis of its bis-4-O-p-nitrobenzoate (8). Formation of withaferin A homodimer (4) as the major product suggests regio- and stereoselectivity of the Diels-Alder [4 + 2] cycloaddition reaction of 9. Acetylation of 2-4 afforded their acetyl derivatives 5-7, respectively. Compounds 2-4 and 6-8 were evaluated for their cytotoxic activities against four prostate cancer (PC) cell lines (LNCaP, 22Rv1, DU-145, and PC-3) and normal human foreskin fibroblast (HFF) cells. Significantly, 4 exhibited improved activity compared to the other compounds for most of the tested cell lines.

Biosynthesis of Cytosporones in Leotiomycetous Filamentous Fungi.

Polyketides with the isochroman-3-one pharmacophore are rare among fungal natural products as their biosynthesis requires an unorthodox S-type aromatic ring cyclization. Genome mining uncovered a conserved gene cluster in select leotiomycetous fungi that encodes the biosynthesis of cytosporones, including isochroman-3-one congeners. Combinatorial biosynthesis in total biosynthetic and biocatalytic formats in Saccharomyces cerevisiae and in vitro reconstitution of key reactions with purified enzymes revealed how cytosporone structural and bioactivity diversity is generated. The S-type acyl dihydroxyphenylacetic acid (ADA) core of cytosporones is assembled by a collaborating polyketide synthase pair. Thioesterase domain-catalyzed transesterification releases ADA esters, some of which are known Nur77 modulators. Alternatively, hydrolytic release allows C6 hydroxylation by a flavin-dependent monooxygenase, yielding a trihydroxybenzene moiety. Reduction of the C9 carbonyl by a short chain dehydrogenase/reductase initiates isochroman-3-one formation, affording cytosporones with cytotoxic and antimicrobial activity. Enoyl di- or trihydroxyphenylacetic acids are generated as shunt products, while isocroman-3,4-diones are formed by autoxidation. The cytosporone pathway offers novel polyketide biosynthetic enzymes for combinatorial synthetic biology to advance the production of "unnatural" natural products for drug discovery.

Argentatin C Analogues with Potential Antinociceptive Activity and Other Triterpenoid Constituents from the Aerial Parts of Parthenium incanum.

Four new triterpenes, 25-dehydroxy-25-methoxyargentatin C (1), 20S-hydroxyargentatin C (2), 20S-hydroxyisoargentatin C (3), and 24-epi-argentatin C (4), together with 10 known triterpenes (5-14) were isolated from the aerial parts of Parthenium incanum. The structures of 1-4 were elucidated by detailed analysis of their spectroscopic data, and the known compounds 5-14 were identified by comparison of their spectroscopic data with those reported. Since argentatin C (11) was found to exhibit antinociceptive activity by decreasing the excitability of rat and macaque dorsal root ganglia (DRG) neurons, 11 and its new analogues 1-4 were evaluated for their ability to decrease the excitability of rat DRG neurons. Of the argentatin C analogues tested, 25-dehydroxy-25-methoxyargentatin C (1) and 24-epi-argentatin C (4) decreased neuronal excitability in a manner comparable to 11. Preliminary structure-activity relationships for the action potential-reducing effects of argentatin C (11) and its analogues 1-4, and their predicted binding sites in pain-relevant voltage-gated sodium and calcium channels (VGSCs and VGCCs) in DRG neurons are presented.

The natural product argentatin C attenuates postoperative pain via inhibition of voltage-gated sodium and T-type voltage-gated calcium channels.

BACKGROUND AND PURPOSE: Postoperative pain occurs in as many as 70% of surgeries performed worldwide. Postoperative pain management still relies on opioids despite their negative consequences, resulting in a public health crisis. Therefore, it is important to develop alternative therapies to treat chronic pain. Natural products derived from medicinal plants are potential sources of novel biologically active compounds for development of safe analgesics. In this study, we screened a library of natural products to identify small molecules that target the activity of voltage-gated sodium and calcium channels that have important roles in nociceptive sensory processing. EXPERIMENTAL APPROACH: Fractions derived from the Native American medicinal plant, Parthenium incanum, were assessed using depolarization-evoked calcium influx in rat dorsal root ganglion (DRG) neurons. Further separation of these fractions yielded a cycloartane-type triterpene identified as argentatin C, which was additionally evaluated using whole-cell voltage and current-clamp electrophysiology, and behavioural analysis in a mouse model of postsurgical pain. KEY RESULTS: Argentatin C blocked the activity of both voltage-gated sodium and low-voltage-activated (LVA) calcium channels in calcium imaging assays. Docking analysis predicted that argentatin C may bind to NaV 1.7-1.9 and CaV 3.1-3.3 channels. Furthermore, argentatin C decreased Na+ and T-type Ca2+ currents as well as excitability in rat and macaque DRG neurons, and reversed mechanical allodynia in a mouse model of postsurgical pain. CONCLUSION AND IMPLICATIONS: These results suggest that the dual effect of argentatin C on voltage-gated sodium and calcium channels supports its potential as a novel treatment for painful conditions.

Physachenolide C is a Potent, Selective BET Inhibitor.

A pulldown using a biotinylated natural product of interest in the 17ß-hydroxywithanolide (17-BHW) class, physachenolide C (PCC), identified the bromodomain and extra-terminal domain (BET) family of proteins (BRD2, BRD3, and BRD4), readers of acetyl-lysine modifications and regulators of gene transcription, as potential cellular targets. BROMOscan bromodomain profiling and biochemical assays support PCC as a BET inhibitor with increased selectivity for bromodomain (BD)-1 of BRD3 and BRD4, and X-ray crystallography and NMR studies uncovered specific contacts that underlie the potency and selectivity of PCC toward BRD3-BD1 over BRD3-BD2. PCC also displays characteristics of a molecular glue, facilitating proteasome-mediated degradation of BRD3 and BRD4. Finally, PCC is more potent than other withanolide analogues and gold-standard pan-BET inhibitor (+)-JQ1 in cytotoxicity assays across five prostate cancer (PC) cell lines regardless of androgen receptor (AR)-signaling status.

Discovery of diminazene as a dual inhibitor of SARS-CoV-2 human host proteases TMPRSS2 and furin using cell-based assays.

The proteases TMPRSS2 (transmembrane protease serine 2) and furin are known to play important roles in viral infectivity including systematic COVID-19 infection through priming of the spike protein of SARS-CoV-2 and related viruses. To discover small-molecules capable of inhibiting these host proteases, we established convenient and cost-effective cell-based assays employing Vero cells overexpressing TMPRSS2 and furin. A cell-based proteolytic assay for broad-spectrum protease inhibitors was also established using human prostate cancer cell line LNCaP. Evaluation of camostat, nafamostat, and gabexate in these cell-based assays confirmed their known TMPRSS2 inhibitory activities. Diminazene, a veterinary medicinal agent and a known furin inhibitor was found to inhibit both TMPRSS2 and furin with IC50s of 1.35 and 13.2 µM, respectively. Establishment and the use of cell-based assays for evaluation TMPRSS2 and furin inhibitory activity and implications of dual activity of diminazene vs TMPRSS2 and furin are presented.

Selective Toxicity of Secondary Metabolites from the Entomopathogenic Bacterium Photorhabdus luminescens sonorensis against Selected Plant Parasitic Nematodes of the Tylenchina Suborder.

Entomopathogenic Photorhabdus bacteria (Enterobacteriaceae: Gamma-proteobacteria), the natural symbionts of Heterorhabditis nematodes, are a rich source for the discovery of biologically active secondary metabolites (SMs). This study describes the isolation of three nematicidal SMs from in vitro culture supernatants of the Arizona-native Photorhabdus luminescens sonorensis strain Caborca by bioactivity-guided fractionation. Nuclear magnetic resonance spectroscopy and comparison to authentic synthetic standards identified these bioactive metabolites as trans-cinnamic acid (t-CA), (4E)-5-phenylpent-4-enoic acid (PPA), and indole. PPA and t-CA displayed potent, concentration-dependent nematicidal activities against the root-knot nematode (Meloidogyne incognita) and the citrus nematode (Tylenchulus semipenetrans), two economically and globally important plant parasitic nematodes (PPNs) that are ubiquitous in the United States. Southwest. Indole showed potent, concentration-dependent nematistatic activity by inducing the temporary rigid paralysis of the same targeted nematodes. While paralysis was persistent in the presence of indole, the nematodes recovered upon removal of the compound. All three SMs were found to be selective against the tested PPNs, exerting little effects on non-target species such as the bacteria-feeding nematode Caenorhabditis elegans or the entomopathogenic nematodes Steinernema carpocapsae, Heterorhabditis bacteriophora, and Hymenocallis sonorensis. Moreover, none of these SMs showed cytotoxicity against normal or neoplastic human cells. The combination of t-CA + PPA + indole had a synergistic nematicidal effect on both targeted PPNs. Two-component mixtures prepared from these SMs revealed complex, compound-, and nematode species-dependent interactions. These results justify further investigations into the chemical ecology of Photorhabdus SMs, and recommend t-CA, PPA and indole, alone or in combinations, as lead compounds for the development of selective and environmentally benign nematicides against the tested PPNs. IMPORTANCE Two phenylpropanoid and one alkaloid secondary metabolites were isolated and identified from culture filtrates of Photorhabdus l. sonorensis strain Caborca. The three identified metabolites showed selective nematicidal and/or nematistatic activities against two important plant parasitic nematodes, the root-knot nematode (Meloidogyne incognita) and the citrus nematode (Tylenchulus semipenetrans). The mixture of all three metabolites had a synergistic nematicidal effect on both targeted nematodes, while other combinations showed compound- and nematode-dependent interactions.

Production and Structural Diversification of Withanolides by Aeroponic Cultivation of Plants of Solanaceae: Cytotoxic and Other Withanolides from Aeroponically Grown Physalis coztomatl.

Withanolides constitute one of the most interesting classes of natural products due to their diversity of structures and biological activities. Our recent studies on withanolides obtained from plants of Solanaceae including Withania somnifera and a number of Physalis species grown under environmentally controlled aeroponic conditions suggested that this technique is a convenient, reproducible, and superior method for their production and structural diversification. Investigation of aeroponically grown Physalis coztomatl afforded 29 withanolides compared to a total of 13 obtained previously from the wild-crafted plant and included 12 new withanolides, physacoztolides I-M (9-13), 15α-acetoxy-28-hydroxyphysachenolide C (14), 28-oxophysachenolide C (15), and 28-hydroxyphysachenolide C (16), 5α-chloro-6ß-hydroxy-5,6-dihydrophysachenolide D (17), 15α-acetoxy-5α-chloro-6ß-hydroxy-5,6-dihydrophysachenolide D (18), 28-hydroxy-5α-chloro-6ß-hydroxy-5,6-dihydrophysachenolide D (19), physachenolide A-5-methyl ether (20), and 17 known withanolides 3-5, 8, and 21-33. The structures of 9-20 were elucidated by the analysis of their spectroscopic data and the known withanolides 3-5, 8, and 21-33 were identified by comparison of their spectroscopic data with those reported. Evaluation against a panel of prostate cancer (LNCaP, VCaP, DU-145, and PC-3) and renal carcinoma (ACHN) cell lines, and normal human foreskin fibroblast (WI-38) cells revealed that 8, 13, 15, and 17-19 had potent and selective activity for prostate cancer cell lines. Facile conversion of the 5,6-chlorohydrin 17 to its 5,6-epoxide 8 in cell culture medium used for the bioassay suggested that the cytotoxic activities observed for 17-19 may be due to in situ formation of their corresponding 5ß,6ß-epoxides, 8, 27, and 28.

Physachenolide C induces complete regression of established murine melanoma tumors via apoptosis and cell cycle arrest.

Melanoma is an aggressive skin cancer that metastasizes to other organs. While immune checkpoint blockade with anti-PD-1 has transformed the treatment of advanced melanoma, many melanoma patients fail to respond to anti-PD-1 therapy or develop acquired resistance. Thus, effective treatment of melanoma still represents an unmet clinical need. Our prior studies support the anti-cancer activity of the 17ß-hydroxywithanolide class of natural products, including physachenolide C (PCC). As single agents, PCC and its semi-synthetic analog demonstrated direct cytotoxicity in a panel of murine melanoma cell lines, which share common driver mutations with human melanoma; the IC50 values ranged from 0.19-1.8 µM. PCC treatment induced apoptosis of tumor cells both in vitro and in vivo. In vivo treatment with PCC alone caused the complete regression of established melanoma tumors in all mice, with a durable response in 33% of mice after discontinuation of treatment. T cell-mediated immunity did not contribute to the therapeutic efficacy of PCC or prevent tumor recurrence in YUMM2.1 melanoma model. In addition to apoptosis, PCC treatment induced G0-G1 cell cycle arrest of melanoma cells, which upon removal of PCC, re-entered the cell cycle. PCC-induced cycle cell arrest likely contributed to the in vivo tumor recurrence in a portion of mice after discontinuation of treatment. Thus, 17ß-hydroxywithanolides have the potential to improve the therapeutic outcome for patients with advanced melanoma.

Ring A/B-Modified 17ß-Hydroxywithanolide Analogues as Antiproliferative Agents for Prostate Cancer and Potentiators of Immunotherapy for Renal Carcinoma and Melanoma.

Physachenolide C (1) is a 17ß-hydroxywithanolide natural product with a unique anticancer potential, as it exhibits potent and selective in vitro antiproliferative activity against prostate cancer (PC) cells and promotes TRAIL-induced apoptosis of renal carcinoma (RC) and poly I:C-induced apoptosis of melanoma cells. To explore the effect of ring A/B modifications of physachenolide C (1) on these biological activities, 23 of its natural and semisynthetic analogues were evaluated. Analogues 4-23 were prepared by chemical transformations of a readily accessible compound, physachenolide D (2). Compound 1 and its analogues 2-23 were evaluated for their antiproliferative activity against PC (LNCaP and 22Rv1), RC (ACHN), and melanoma (M14 and SK-MEL-28) cell lines and normal human foreskin fibroblast (HFF) cells. Most of the active analogues had selective and potent activity in reducing cell number for PC cell lines, some showing selectivity for androgen-independent and enzalutamide-resistant 22Rv1 cells compared to androgen-dependent LNCaP cells. Analogues with IC50s below 5.0 µM against ACHN cells, when tested in the presence of TRAIL, showed a significantly increased ability to reduce cell number, and those analogues active against the M14 and SK-MEL-28 cell lines exhibited enhanced activity when combined with poly I:C. These data provide additional structure-activity relationship information for 17ß-hydroxywithanolides and suggest that selective activities of some analogues may be exploited to develop natural products-based tumor-specific agents for cancer chemotherapy.

Strobiloscyphones A-F, 6-Isopentylsphaeropsidones and Other Metabolites from Strobiloscypha sp. AZ0266, a Leaf-Associated Fungus of Douglas Fir.

Six new 6-isopentylsphaeropsidones, strobiloscyphones A-F (1-6), and a new hexadecanoic acid, (2Z,4E,6E)-8,9-dihydroxy-10-oxohexadeca-2,4,6-trienoic acid (7), together with sphaeropsidone (8) and its known synthetic analogue 5-dehydrosphaeropsidone (9) were isolated from Strobiloscypha sp. AZ0266, a fungus inhabiting the leaf litter of Douglas fir (Pseudotsuga menziesii). The structures of 1-7 were established on the basis of their high-resolution mass and 1D and 2D NMR spectroscopic data, and their relative and/or absolute configurations were determined by NOE, comparison of experimental and calculated ECD spectra, and application of the modified Mosher's ester method. Of these, strobiloscyphone F (6) contains a novel highly oxygenated tetracyclic oxireno-octahydrodibenzofuran ring system. Natural products 1, 6, and 9 and the semisynthetic analogue 12 derived from 8 exhibited cytotoxic activity, whereas 9 and 12 showed antimicrobial activity. Possible biosynthetic pathways to 1-6, 8, and 9 are proposed.

Structure-Activity Relationships of Withanolides as Antiproliferative Agents for Multiple Myeloma: Comparison of Activity in 2D Models and a 3D Coculture Model.

Multiple myeloma (MM) is a hematological cancer in which relapse and resistance are highly frequent. Therefore, alternatives to conventional treatments are necessary. Withaferin A, a withanolide isolated from Withania somnifera, has previously shown promising activity against various MM models. In the present study, structure-activity relationships (SARs) were evaluated using 56 withanolides. The antiproliferative activity was assessed in three MM cell lines and in a 3D MM coculture model to understand the in vitro activity of compounds in models of various complexity. While the results obtained in 2D allowed a quick and simple evaluation of cytotoxicity used for a first selection, the use of the 3D MM coculture model allowed filtering compounds that perform better in a more complex setup. This study shows the importance of the last model as a bridge between 2D and in vivo studies to select the most active compounds and ultimately lead to a reduction of animal use for more sustained in vivo studies. NF-κB inhibition was determined to evaluate if this could be one of the targeted pathways. The most active compounds, withanolide D (2) and 38, should be further evaluated in vivo.

Cycloartane- and Lanostane-Type Triterpenoids from the Resin of Parthenium argentatum AZ-2, a Byproduct of Guayule Rubber Production.

A total of 12 new cycloartane- and lanostane-type triterpenoids including 16-deoxyargentatin A (1), 16-deoxyisoargentatin A (2), 7-oxoisoargentatin A (3), 24-epi-argentatin H (4), 24-O-p-anisoylargentatin C (5), 24-O-trans-cinnamoylargentatin C (6), 16-dehydroargentatin C (7), 16,17(20)-didehydroargentatin C (8), isoargentatin C (9), isoargentatin H (10), 3-epi-quisquagenin (11), and isoquisquagenin (12) together with 10 known triterpenoids (13-22) were isolated from the resin of Parthenium argentatum AZ-2 obtained as a byproduct of Bridgestone guayule rubber production. The structures of new triterpenoids 1-12 and argentatin H (13), which has previously been characterized as its diacetate (23), were elucidated by extensive analysis of their spectroscopic data and chemical conversions, and the known compounds 14-22 were identified by comparison of their spectroscopic data with those reported. Of these, 13, 14, and 18 exhibited weak cytotoxic activity for several cancer cell lines.

Small-Molecule Natural Product Physachenolide C Potentiates Immunotherapy Efficacy by Targeting BET Proteins.

Screening for sensitizers of cancer cells to TRAIL-mediated apoptosis identified a natural product of the 17ß-hydroxywithanolide (17-BHW) class, physachenolide C (PCC), as a promising hit. In this study, we show that PCC was also able to sensitize melanoma and renal carcinoma cells to apoptosis in response not only to TRAIL, but also to the synthetic polynucleotide poly I:C, a viral mimetic and immune activator, by reducing levels of antiapoptotic proteins cFLIP and Livin. Both death receptor and TLR3 signaling elicited subsequent increased assembly of a proapoptotic ripoptosome signaling complex. Administration of a combination of PCC and poly I:C in human M14 melanoma xenograft and a syngeneic B16 melanoma model provided significant therapeutic benefit as compared with individual agents. In addition, PCC enhanced melanoma cell death in response to activated human T cells in vitro and in vivo in a death ligand-dependent manner. Biochemical mechanism-of-action studies established bromo and extraterminal domain (BET) proteins as major cellular targets of PCC. Thus, by targeting of BET proteins to reduce antiapoptotic proteins and enhance caspase-8-dependent apoptosis of cancer cells, PCC represents a unique agent that can potentially be used in combination with various immunotherapeutic approaches to promote tumor regression and improve outcome. SIGNIFICANCE: These findings demonstrate that PCC selectively sensitizes cancer cells to immune-mediated cell death, potentially improving the efficacy of cancer immunotherapies. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/81/12/3374/F1.large.jpg.

Cytotoxic Physalins from Aeroponically Grown Physalis acutifolia.

Aeroponically grown Physalis acutifolia afforded five new and six known withanolides including 10 physalins. The structures of the new withanolides, acutifolactone (1), 5ß,6ß-epoxyphysalin C (2), 5α-chloro-6ß-hydroxyphysalin C (3), and an inseparable mixture of 5ß,6ß-epoxy-2,3-dihydrophysalin F-3ß-O-sulfate (4) and 5ß,6ß-epoxy-2,3-dihydrophysalin C-3ß-O-sulfate (5), were elucidated by analysis of their spectroscopic data and chemical interconversions. The known withanolides were identified as physalins B (6), D (7), F (8), H (9), I (10), and U (11) by comparison of their spectroscopic data with those reported. Evaluation of 1-11 and the derivatives, 13 and 13a, obtained from 4 and 5 against a panel of four human cancer cell lines [NCI-H460 (non-small-cell lung), SF-268 (CNS glioma), PC-3 (prostate adenocarcinoma), and MCF-7 (breast adenocarcinoma)] and normal human lung fibroblast (WI-38) cells revealed that physalins 2, 3, 8, and 9 exhibited selective cytotoxic activity to at least one of the cancer cell lines tested compared to the normal cells and that 7, 10, and 11 were inactive up to a concentration of 10.0 µM. These data provided some preliminary structure-activity relationships and suggested that the mechanism of cytotoxic activity of physalins may differ from other classes of withanolides.

Teratopyrones A-C, Dimeric Naphtho-γ-Pyrones and Other Metabolites from Teratosphaeria sp. AK1128, a Fungal Endophyte of Equisetum arvense.

Bioassay-guided fractionation of a cytotoxic extract derived from a solid potato dextrose agar (PDA) culture of Teratosphaeria sp. AK1128, a fungal endophyte of Equisetum arvense, afforded three new naphtho-γ-pyrone dimers, teratopyrones A-C (1-3), together with five known naphtho-γ-pyrones, aurasperone B (4), aurasperone C (5), aurasperone F (6), nigerasperone A (7), and fonsecin B (8), and two known diketopiperazines, asperazine (9) and isorugulosuvine (10). The structures of 1-3 were determined on the basis of their spectroscopic data. Cytotoxicity assay revealed that nigerasperone A (7) was moderately active against the cancer cell lines PC-3M (human metastatic prostate cancer), NCI-H460 (human non-small cell lung cancer), SF-268 (human CNS glioma), and MCF-7 (human breast cancer), with IC50s ranging from 2.37 to 4.12 µM while other metabolites exhibited no cytotoxic activity up to a concentration of 5.0 µM.

Intrinsic and Extrinsic Programming of Product Chain Length and Release Mode in Fungal Collaborating Iterative Polyketide Synthases.

Combinatorial biosynthesis with fungal polyketide synthases (PKSs) promises to produce unprecedented bioactive "unnatural" natural products (uNPs) for drug discovery. Genome mining of the dothideomycete Rhytidhysteron rufulum uncovered a collaborating highly reducing PKS (hrPKS)-nonreducing PKS (nrPKS) pair. These enzymes produce trace amounts of rare S-type benzenediol macrolactone congeners with a phenylacetate core in a heterologous host. However, subunit shuffling and domain swaps with voucher enzymes demonstrated that all PKS domains are highly productive. This contradiction led us to reveal novel programming layers exerted by the starter unit acyltransferase (SAT) and the thioesterase (TE) domains on the PKS system. First, macrocyclic vs linear product formation is dictated by the intrinsic biosynthetic program of the TE domain. Next, the chain length of the hrPKS product is strongly influenced in trans by the off-loading preferences of the nrPKS SAT domain. Last, TE domains are size-selective filters that facilitate or obstruct product formation from certain priming units. Thus, the intrinsic programs of the SAT and TE domains are both part of the extrinsic program of the hrPKS subunit and modulate the observable metaprogram of the whole PKS system. Reconstruction of SAT and TE phylogenies suggests that these domains travel different evolutionary trajectories, with the resulting divergence creating potential conflicts in the PKS metaprogram. Such conflicts often emerge in chimeric PKSs created by combinatorial biosynthesis, reducing biosynthetic efficiency or even incapacitating the system. Understanding the points of failure for such engineered biocatalysts is pivotal to advance the biosynthetic production of uNPs.

Reversal of Peripheral Neuropathic Pain by the Small-Molecule Natural Product Physalin F via Block of CaV2.3 (R-Type) and CaV2.2 (N-Type) Voltage-Gated Calcium Channels.

No universally efficacious therapy exists for chronic pain, a disease affecting one-fifth of the global population. An overreliance on the prescription of opioids for chronic pain despite their poor ability to improve function has led to a national opioid crisis. In 2018, the NIH launched a Helping to End Addiction Long-term plan to spur discovery and validation of novel targets and mechanisms to develop alternative nonaddictive treatment options. Phytochemicals with medicinal properties have long been used for various treatments worldwide. The natural product physalin F, isolated from the Physalis acutifolia (family: Solanaceae) herb, demonstrated antinociceptive effects in models of inflammatory pain, consistent with earlier reports of its anti-inflammatory and immunomodulatory activities. However, the target of action of physalin F remained unknown. Here, using whole-cell and slice electrophysiology, competition binding assays, and experimental models of neuropathic pain, we uncovered a molecular target for physalin F's antinociceptive actions. We found that physalin F (i) blocks CaV2.3 (R-type) and CaV2.2 (N-type) voltage-gated calcium channels in dorsal root ganglion (DRG) neurons, (ii) does not affect CaV3 (T-type) voltage-gated calcium channels or voltage-gated sodium or potassium channels, (iii) does not bind G-protein coupled opioid receptors, (iv) inhibits the frequency of spontaneous excitatory postsynaptic currents (EPSCs) in spinal cord slices, and (v) reverses tactile hypersensitivity in models of paclitaxel-induced peripheral neuropathy and spinal nerve ligation. Identifying CaV2.2 as a molecular target of physalin F may spur its use as a tool for mechanistic studies and position it as a structural template for future synthetic compounds.

Rational Reprogramming of O-Methylation Regioselectivity for Combinatorial Biosynthetic Tailoring of Benzenediol Lactone Scaffolds.

O-Methylation modulates the pharmacokinetic and pharmacodynamic (PK/PD) properties of small-molecule natural products, affecting their bioavailability, stability, and binding to targets. Diversity-oriented combinatorial biosynthesis of new chemical entities for drug discovery and optimization of known bioactive scaffolds during drug development both demand efficient O-methyltransferase (OMT) biocatalysts with considerable substrate promiscuity and tunable regioselectivity that can be deployed in a scalable and sustainable manner. Here we demonstrate efficient total biosynthetic and biocatalytic platforms that use a pair of fungal OMTs with orthogonal regiospecificity to produce unnatural O-methylated benzenediol lactone polyketides. We show that rational, structure-guided active-site cavity engineering can reprogram the regioselectivity of these enzymes. We also characterize the interplay of engineered regioselectivity with substrate plasticity. These findings will guide combinatorial biosynthetic tailoring of unnatural products toward the generation of diverse chemical matter for drug discovery and the PK/PD optimization of bioactive scaffolds for drug development.