Anti-cancer activity of carbamate derivatives of melampomagnolide B

Cytotoxicity Activity of Some meso-Dihydroguaiaretic Acid Derivatives and Mode of Action of the Most Active Compound

The aim of this study was to screen sixteen meso-1 semi-synthetic derivatives bearing ether, esther, carbamate, phosphate or aminoether functional groups against five cancer cell lines: MCF-7 (breast), A549 (lung), HepG2 (liver), HeLa (cervix), and DU145 (prostate) at 25 μM using the MTT assay. Results from the screening showed that two derivatives had the lowest percentage of cell viability at 25 μM, the aminoether derivative meso-11 and the esther derivative meso-20 against A549 (44.15±0.78 %) and MCF-7 (41.60±0.92 %), respectively. Then, it was determined the IC50 value of each compound against their most sensitive cancer cell line. Results showed that aminoether derivative meso-11 showed potent cytotoxicity against A549 (IC50 =17.11±2.11 μM), whereas it resulted more cytotoxic against the LL-47 lung normal cell line (IC50 =9.49±1.19 μM) having a Selective Index (SI) of 0.55. On the other hand, the esther derivative meso-20 exhibited potent activity against MCF-7 (IC50 =18.20±1.98 μM), whereas it displayed moderate cytotoxicity against the MCF-10 breast normal cell line (IC50 =41.22±2.17 μM) with a SI of 2.2. Finally, studies on the mechanism of action of meso-20 indicated disruption of MCF-7 plasma membrane in vitro and the AMPK activation in silico.

Antitumor properties of novel sesquiterpene lactone analogs as NFκB inhibitors that bind to the IKKβ ubiquitin-like domain (ULD)

Melampomagnolide B (MMB, 3) is a parthenolide (PTL, 1) based sesquiterpene lactone that has been used as a template for the synthesis of a plethora of lead anticancer agents owing to its reactive C-10 primary hydroxyl group. Such compounds have been shown to inhibit the IKKβ subunit, preventing phosphorylation of the cytoplasmic IκB inhibitory complex. The present study focuses on the synthesis and in vitro antitumor properties of novel benzyl and phenethyl carbamates of MMB (7a-7k). Screening of these MMB carbamates identified analogs with potent growth inhibition properties against a panel of 60 human cancer cell lines (71% of the molecules screened had GI₅₀ values < 2 μM). Two analogs, the benzyl carbamate 7b and the phenethyl carbamate7k, were the most active compounds. Lead compound 7b inhibited cell proliferation in M9 ENL AML cells, and in TMD-231, OV-MD-231 and SUM149 breast cancer cell lines. Interestingly, mechanistic studies showed that 7b did not inhibit p65 phosphorylation in M9 ENL AML and OV-MD-231 cells, but did inhibit phophorylation of both p65 and IκBα in SUM149 cells. 7b also reduced NFκB binding to DNA in both OV-MD-231 and SUM149 cells. Molecular docking studies indicated that 7b and 7k are both predicted to interact with the ubiquitin-like domain (ULD) of the IKKβ subunit. These data suggest that in SUM149 cells, 7b is likely acting as an allosteric inhibitor of IKKβ, whereas in M9 ENL AML and OV-MD-231 cells 7b is able to inhibit an event after IκB/p65/p50 phosphorylation by IKKβ that leads to inhibition of NFκB activation and reduction in NFκB-DNA binding. Analog 7b was by far the most potent compound in either carbamate series, and was considered an important lead compound for further optimization and development as an anticancer agent.

Design, synthesis, and cytotoxic activities of novel hybrids of parthenolide and thiazolidinedione via click chemistry

A series of novel parthenolide-thiazolidinedione hybrids have been synthesized via a click chemistry-mediated coupling between parthenolide and thiazolidinedione, and evaluated for their cytotoxic activities. The results indicated that all the hybrids showed moderate cytotoxic effects on human cancer cell lines, including human erythroleukemia cell line (HEL), prostate (PC3), and breast (MDA-MB-231) by MTT assay. In particular, compound VI-6 exhibited the best cytotoxic activities against the MDA-MB-231 cells with IC₅₀ value of 2.07 µM, which was about eight times more active than that of the original compound (PTL). These interesting results might be used to develop novel lead scaffolds for potential anticancer agents.

Advances in chemistry and bioactivity of parthenolide

(−)-Parthenolide is a germacrane sesquiterpene lactone, available in ample amounts from the traditional medical plant feverfew (Tanacetum parthenium).

Amphiphilic irinotecan–melampomagnolide B conjugate nanoparticles for cancer chemotherapy

Melampomagnolide B (MMB) is a natural sesquiterpene lactone product structurally related to parthenolide (PTL). Although MMB has been widely used to treat various types of cancers, such as glioma, leukemia and colon cancer, the effective delivery of MMB to cancer cells remains a challenge. An amphiphilic drug–drug conjugate (ADDC) strategy has been proposed and developed as a promising drug self-delivery system for cancer therapy because of its simple preparation, carrier-free nature, and high therapeutic activity. Herein, we present a new ADDC, which is synthesized by linking the hydrophilic anticancer drug irinotecan (Ir) and the hydrophobic anticancer drug MMB through a carbonate bond. The obtained amphiphilic irinotecan–melampomagnolide B conjugate (Ir–C–MMB) can self-assemble in water into stable nanoparticles with an average diameter of around 122.1 nm. After cellular uptake, the carbonate bond between the hydrophilic drug and hydrophobic drug can be cleaved to release free Ir and MMB under acidic conditions, which exhibit a synergistic effect in tumor cells. MTT results reveal that the Ir–C–MMB nanoparticles can effectively inhibit proliferation of cancer cells. The apoptosis data indicate that the apoptosis rate of cells treated with Ir–C–MMB nanoparticles is about 50% within 24 h, which is much higher than that of free Ir or MMB. Our results suggest that this ADDC strategy could be used as a drug delivery platform for MMB and its derivatives, and that it offers effective synergistic therapeutic efficacy.

Ir–C–MMB nanoparticles can be easily fabricated using an ADDC strategy, and used as a MMB drug self-delivery platform for synergistic cancer therapy.

Derivatisation of parthenolide to address chemoresistant chronic lymphocytic leukaemia

Parthenolide is a natural product that exhibits anti-leukaemic activity, however, its clinical use is limited by its poor bioavailability. It may be extracted from feverfew and protocols for growing, extracting and derivatising it are reported. A novel parthenolide derivative with good bioavailability and pharmacological properties was identified through a screening cascade based on in vitro anti-leukaemic activity and calculated "drug-likeness" properties, in vitro and in vivo pharmacokinetics studies and hERG liability testing. In vitro studies showed the most promising derivative to have comparable anti-leukaemic activity to DMAPT, a previously described parthenolide derivative. The newly identified compound was shown to have pro-oxidant activity and in silico molecular docking studies indicate a prodrug mode of action. A synthesis scheme is presented for the production of amine 7 used in the generation of 5f.

MMB triazole analogs are potent NF-κB inhibitors and anti-cancer agents against both hematological and solid tumor cells

Triazole derivatives of melampomagnolide B (MMB) have been synthesized via click chemistry methodologies and screened against a panel of 60 human cancer cell lines. Several derivatives showed promising anti-cancer activity, affording growth inhibition (GI₅₀) values in the nanomolar range (GI₅₀ = 0.02-0.99 μM). Lead compound 7h exhibited EC₅₀ values of 400 nM and 700 nM, respectively, against two AML clinical specimens. Compound 7h was significantly more potent than parthenolide as an inhibitor of p65 phosphorylation in both hematological and solid tumor cell lines, indicating its ability to inhibit the NF-κB pathway. In TMD-231 breast cancer cells, treatment with 7h reduced DNA binding activity of NF-κB through inhibition of IKK-β mediated p65 phosphorylation and caused elevation of basal IκBα levels through inhibition of constitutive IκBα turnover and NF-κB activation. Molecular docking and dynamic modeling studies indicated that 7h interacts with the kinase domain of the monomeric IKKβ subunit, leading to inhibition of IKKβ activation, and compromising phosphorylation of downstream targets of the NF-κB pathway; dynamic modeling studies show that this interaction also causes unwinding of the α-helix of the NEMO binding site on IKKβ. Molecular docking studies with 10, a water-soluble analog of 7h, demonstrate that this analog interacts with the dimerization/oligomerization domain of monomeric IKKβ and may inhibit oligomer formation and subsequent autophosphorylation. Sesquiterpene lactones 7h and 10 are considered ideal candidates for potential clinical development.

Succinamide derivatives of melampomagnolide B and their anti-cancer activities

A series of succinamide derivatives of melampomagnolide B have been synthesized by coupling MMB monosuccinate (2) with various heterocyclic amines to afford compounds 3a-3l. MMB monosuccinate was also reacted with terminal diaminoalkanes to afford dimeric succinamido analogs of MMB (4a-4h). These succinamide analogs of MMB were evaluated for their anti-cancer activity against a panel of sixty human cancer cell lines. Analogs 3d-3i and dimers 4f-4g exhibited promising anti-cancer activity with GI50 values ranging from 0.28 to 33.5µM against most of the cell lines in the panel. The dimeric analogs 4f and 4g were identified as lead compounds with GI50 values in the nanomolar range (GI50=280-980nM) against several cell lines in the panel; i.e. leukemia cell lines CCRF-CEM, HL-60(TB), K-562, MOLT-4, RPMI-8226 and SR; and solid tumor cell lines NCI-H522 (non-small cell lung cancer), SW-620 and HCT-116 (colon cancer), LOX IMVI (melanoma), RXF 393 (renal cancer), and MCF7, BT-549 and MDA-MB-468 (breast cancer). Succinamide analogs 3a, 3c-3l and 4b-4h were also evaluated for their apoptotic activity against M9-ENL1 acute myelogenous leukemia cells; compounds 3h-3j and 4g were equipotent with parthenolide, exhibiting LC50 values in the range 4.1-8.1μM. Molecular docking studies indicate that these molecules interact covalently with the highly conserved Cys-46 residue of the N-terminal lobe (1-109) of human IKKβ to inhibit the NFκB transcription factor complex, resulting in down-regulation of anti-apoptotic genes under NFκB control.

Indole carboxylic acid esters of melampomagnolide B are potent anticancer agents against both hematological and solid tumor cells

A series of novel, heteroaryl carboxylic acid conjugates of the sesquiterpene melampomagnolide-B (MMB, 3) has been evaluated as antitumor agents against an NCI panel of 64 human hematopoetic and solid tumor cell lines. The indole-3-acrylic acid conjugate 7j and the indole-3-carboxylic acid conjugate 7k were found to be the most potent analogs in the series. Compounds 7j and 7k exhibited remarkable growth inhibition, with GI₅₀ values in the range 0.03-0.30 μM and 0.04-0.28 μM, respectively, against the cell lines in the leukemia sub-panel, and GI₅₀ values of 0.05-0.40 μM and 0.04-0.61 μM, respectively, against 90% of the solid tumor cell lines in the NCI panel. Compound 7a was particularly effective against the sub-panel of breast cancer cell lines with GI₅₀ values in the range <0.01-0.30 μM. Compounds 7j, 7a and its water soluble analog 7p also exhibited potent anticancer activity against rat 9L-SF gliosarcoma cells in culture. Compound 7j was the most potent compound in the series in the M9-ENL1 AML cell assay with a lethal dose concentration EC₅₀ value of 720 nM, and exhibited the greatest cytotoxicity against a collection of primary AML stem cell specimens, which included a specimen that was unresponsive to PTL, affording EC₅₀ values in the range 0.33-1.0 μM in three out of four specimens. The results from this study provide further evidence that analogs of the sesquiterpene MMB can be designed to afford molecules with significantly improved anticancer activity. Thus, both 7j and 7k are considered potential lead molecules in the search for new anticancer agents that can be used as treatments for both hematopoetic and solid tumors.

Identification of a melampomagnolide B analog as a potential lead molecule for treatment of acute myelogenous leukemia

A series of carbamate derivatives of the antileukemic sesquiterpene melampomagnolide B (MMB) has been synthesized utilizing a 1,2,4-triazole carbamate conjugate of MMB as an intermediate synthon. Five imidazole- and benzimidazole-carbamate analogs of MMB (8a-8e) were prepared and evaluated for anti-leukemic activity against cultured M9 ENL1 AML cells. All the analogs exhibited improved anti-leukemic activity (EC₅₀=0.90-3.93μM) when compared to parthenolide and the parent sesquiterpene, MMB (EC₅₀=7.0μM and 15.5μM, respectively). The imidazole carbamate analog, 8a (EC₅₀=0.9μM), was 16 times more potent than MMB. The comparative bioavailabilities of 8a and MMB were determined in BALB/c mice following oral dosing of these compounds. It has been demonstrated that the absolute plasma bioavailabilities of MMB and 8a were 6.7±0.8%, and 45.5±2%, respectively. These results indicate that, compared to MMB, the PK parameters for 8a display significantly improved bioavailability and exposure after oral administration. Analog 8a is considered to be a potential clinical candidate for treatment of acute myelogenous leukemia.

Alkyne Ligation Handles: Propargylation of Hydroxyl, Sulfhydryl, Amino, and Carboxyl Groups via the Nicholas Reaction

The Nicholas reaction has been applied to the installation of alkyne ligation handles. Acid-promoted propargylation of hydroxyl, sulfhydryl, amino, and carboxyl groups using dicobalt hexacarbonyl-stabilized propargylium ions is reported. This method is useful for introduction of propargyl groups into base-sensitive molecules, thereby expanding the toolbox of methods for the incorporation of alkynes for bio-orthogonal reactions. High-value molecules are used as the limiting reagent, and various propargylium ion precursors are compared.

Dioxol and dihydrodioxin analogs of 2- and 3-phenylacetonitriles as potent anti-cancer agents with nanomolar activity against a variety of human cancer cells

A small library of (Z)-2-(benzo[d][1,3]dioxol-5-yl) and (Z)-2,3-dihydrobenzo[b][1,4]dioxin-6-yl analogs of 2- and 3-phenylacetonitriles has been synthesized and evaluated for their anti-cancer activities against a panel of 60 human cancer cell lines. The dihydrodioxin analog 3j and dioxol analogs 5e and 7e exhibited the most potent anti-cancer activity of all the analogs synthesized in this study, with GI50 values of <100 nM against almost all of the cell lines in the human cancer cell panel. Of these three, only compound 3j inhibited tubulin polymerization to any degree in vitro. The binding modes of 3j and the structurally related tubulin-inhibitor DMU-212 were determined by virtual docking studies with tubulin dimer. Compound 3j docked at the colchicine-binding site at the dimer interface of tubulin. The Full-Fitness (FF) score of 3j was observed to be substantially higher than DMU-212, which agrees well with the observed anti-cancer potency (GI50 values). The mechanism by which dioxol analogs 5e and 7e exert their cytotoxic effects remains unknown at this stage, but it is unlikely that they affect tubulin dynamics. Nevertheless, these findings suggest that both dioxol and dihydrodioxin analogs of phenylacrylonitrile may have potential for development as clinical candidates to treat a variety of human cancers.

Isatin Derived Spirocyclic Analogues with α-Methylene-γ-butyrolactone as Anticancer Agents: A Structure-Activity Relationship Study

Design, synthesis, and evaluation of α-methylene-γ-butyrolactone analogues and their evaluation as anticancer agents is described. SAR identified a spirocyclic analogue 19 that inhibited TNFα-induced NF-κB activity, cancer cell growth and tumor growth in an ovarian cancer model. A second iteration of synthesis and screening identified 29 which inhibited cancer cell growth with low-μM potency. Our data suggest that an isatin-derived spirocyclic α-methylene-γ-butyrolactone is a suitable core for optimization to identify novel anticancer agents.

Heterobimetallic dinuclear lanthanide alkoxide complexes as acid–base bifunctional catalysts for synthesis of carbamates under solvent-free conditions

Heterobimetallic dinuclear lanthanide alkoxide complexes Ln₂Na₈(OCH₂CH₂NMe₂)₁₂(OH)₂ [Ln: I (Nd), II (Sm), III (Yb) and IV (Y)] were used as efficient acid–base bifunctional catalysts for the synthesis of carbamates and the N-Boc protection of amines.

Dimers of Melampomagnolide B Exhibit Potent Anticancer Activity against Hematological and Solid Tumor Cells

Novel carbamate (7a-7h) and carbonate (7i, 7j, and 8) dimers of melampomagnolide B have been synthesized by reaction of the melampomagnolide-B-triazole carbamate synthon 6 with various terminal diamino- and dihydroxyalkanes. Dimeric carbamate products 7b, 7c, and 7f exhibited potent growth inhibition (GI50 = 0.16-0.99 μM) against the majority of cell lines in the NCI panel of 60 human hematological and solid tumor cell lines. Compound 7f and 8 exhibited anticancer activity that was 300-fold and 1 × 10(6)-fold more cytotoxic than DMAPT, respectively, at a concentration of 10 μM against rat 9L-SF gliosarcoma cells. Compounds 7a-7j and 8 were also screened against M9-ENL1 and acute myelogenous leukemia (AML) primary cell lines and exhibited 2- to 10-fold more potent antileukemic activity against M9-ENL1 cells (EC50 = 0.57-2.90 μM) when compared to parthenolide (EC50 = 6.0) and showed potent antileukemic activity against five primary AML cell lines (EC50 = 0.76-7.3 μM).

Chemical Library Screening and Structure-Function Relationship Studies Identify Bisacodyl as a Potent and Selective Cytotoxic Agent Towards Quiescent Human Glioblastoma Tumor Stem-Like Cells

Cancer stem-like cells reside in hypoxic and slightly acidic tumor niches. Such microenvironments favor more aggressive undifferentiated phenotypes and a slow growing "quiescent state" which preserves them from chemotherapeutic agents that essentially target proliferating cells. Our objective was to identify compounds active on glioblastoma stem-like cells, including under conditions that mimick those found in vivo within this most severe and incurable form of brain malignancy. We screened the Prestwick Library to identify cytotoxic compounds towards glioblastoma stem-like cells, either in a proliferating state or in more slow-growing "quiescent" phenotype resulting from non-renewal of the culture medium in vitro. Compound effects were assessed by ATP-level determination using a cell-based assay. Twenty active molecules belonging to different pharmacological classes have thus been identified. Among those, the stimulant laxative drug bisacodyl was the sole to inhibit in a potent and specific manner the survival of quiescent glioblastoma stem-like cells. Subsequent structure-function relationship studies led to identification of 4,4'-dihydroxydiphenyl-2-pyridyl-methane (DDPM), the deacetylated form of bisacodyl, as the pharmacophore. To our knowledge, bisacodyl is currently the only known compound targeting glioblastoma cancer stem-like cells in their quiescent, more resistant state. Due to its known non-toxicity in humans, bisacodyl appears as a new potential anti-tumor agent that may, in association with classical chemotherapeutic compounds, participate in tumor eradication.

Synthesis and antileukemic activities of C1-C10-modified parthenolide analogues

Parthenolide (PTL) is a sesquiterpene lactone natural product with anti-proliferative activity to cancer cells. Selective eradication of leukemic stem cells (LSCs) over healthy hematopoietic stem cells (HSCs) by PTL has been demonstrated in previous studies, which suggests PTL and related molecules may be useful for targeting LSCs. Eradication of LSCs is required for curative therapy. Chemical optimizations of PTL to improve potency and pharmacokinetic parameters have focused largely on the α-methylene-γ-butyrolactone, which is essential for activity. Conversely, we evaluated modifications to the C1-C10 olefin and benchmarked new inhibitors to PTL with respect to inhibitory potency across a panel of cancer cell lines, ability to target drug-resistant acute myeloid leukemia (AML) cells, efficacy for inhibiting clonal growth of AML cells, toxicity to healthy bone marrow cells, and efficiency for promoting intracellular reactive oxygen species (ROS) levels. Cyclopropane 4 was found to possess less toxicity to healthy bone marrow cells, enhanced potency for the induction of cellular ROS, and similar broad-spectrum anti-proliferative activity to cancer cells in comparison to PTL.