Ethyl 2-amino-6-(3,5-dimethoxyphenyl)-4-(2-ethoxy-2-oxoethyl)-4H-chromene-3-carboxylate (CXL017): a novel scaffold that resensitizes multidrug resistant leukemia cells to chemotherapy

Acid-Promoted Multicomponent Reaction To Synthesize 4-Phosphorylated 4H-Chromenes

An effective multicomponent reaction for the synthesis of 4-phosphorylated 4H-chromenes via a tandem phosphorylation/alkylation/cyclization/dehydration sequence with water as the only byproduct was developed. Extensive mechanistic investigations involving in situ NMR experiments, time control experiments, and in situ HRMS experiment allowed us to elucidate the order of each subreaction to arrive at a complete understanding of the underlying mechanism of this multicomponent reaction. Mechanistic data confirm that the reaction begins with a phospha-aldol-elimination, followed by addition of a ketone enolate, intermolecular alkylation, intramolecular cyclization, and dehydration under acidic conditions.

Recent advances in small molecule and peptide inhibitors of glucose-regulated protein 78 for cancer therapy

Glucose-regulated protein 78 (GRP78) is one of key endoplasmic reticulum (ER) chaperone proteins that regulates the unfolded protein response (UPR) to maintain ER homeostasis. As a core factor in the regulation of the UPR, GRP78 takes a critical part in the cellular processes required for tumorigenesis, such as proliferation, metastasis, anti-apoptosis, immune escape and chemoresistance. Overexpression of GRP78 is closely correlated with tumorigenesis and poor prognosis in various malignant tumors. Targeting GRP78 is regarded as a potentially promising therapeutic strategy for cancer therapy. Although none of the GRP78 inhibitors have been approved to date, there have been several studies of GRP78 inhibitors. Herein, we comprehensively review the structure, physiological functions of GRP78 and the recent progress of GRP78 inhibitors, and discuss the structures, in vitro and in vivo efficacies, and merits and demerits of these inhibitors to inspire further research. Additionally, the feasibility of GRP78-targeting proteolysis-targeting chimeras (PROTACs), disrupting GRP78 cochaperone interactions, or covalent inhibition are also discussed as novel strategies for drugs discovery targeting GRP78, with the hope that these strategies can provide new opportunities for targeted GRP78 antitumor therapy.

Tandem phospha-Michael addition/cyclization/dehydration of 2-hydroxychalcones with H-phosphine oxides for the synthesis of 4-phosphorylated 4H-chromenes

A Hg(OTf)2-catalyzed tandem phospha-Michael addition/cyclization/dehydration of 2-hydroxychalcones with H-phosphine oxides is presented. This protocol provides a new and supplementary approach for the preparation of 4-phosphorylated 4H-chromenes in good yields (up to 99%). In addition, this domino reaction allows the successful construction of two new C-P and C-O bonds in a one-pot operation.

Chronic exposure to the gibberellin derivative GA-13315 sensitizes breast cancer MCF-7 cells but not colon cancer HCT116 cells to irinotecan

13-Chlorine-3,15-dioxy-gibberellic acid methyl ester (GA-13315) is a gibberellin derivative that exhibits selective cytotoxicity to multidrug resistant MCF-7/ADR cells and reverses drug resistance when administered at subtoxic doses in combination with chemotherapy drugs. The present study aimed to investigate the impact of chronic GA-13315 exposure on the chemosensitivity of MCF-7 and HCT116 cell lines. Cells were administered a subtoxic dose of 1 µM GA-13315 for 12 weeks and the sensitivity of the cells to GA-13315, irinotecan and cisplatin, was assessed. The Cell Counting Kit-8 assay results demonstrated that the chronic exposure did not induce resistance to GA-13315, in either MCF-7 or HCT116 cells. Notably, MCF-7 cells were sensitized to irinotecan following exposure to GA-13315; however, HCT116 cells were not. The sensitizing effect of GA-13315 was associated with the alterations of topoisomerase 1 (Top1) protein expression, tyrosyl DNA phosphodiesterase 1 and checkpoint kinase 1. Further analysis indicated that GA-13315 caused DNA fragmentation; however, DNA damage was not mediated by a Top1-dependent molecular mechanism, as GA-13315 was revealed not to be a Top1 poison, despite inhibiting the catalytic activity of Top1. Taken together, the results of the present study indicated that GA-13315 may be used for sensitizing MCF-7 cells to irinotecan, as the chronic exposure of GA-13315 to MCF-7 cells still showed sensitizing effects to irinotecan.

Exploring the Therapeutic Potential of Membrane Transport Proteins: Focus on Cancer and Chemoresistance

Improving the therapeutic efficacy of conventional anticancer drugs represents the best hope for cancer treatment. However, the shortage of druggable targets and the increasing development of anticancer drug resistance remain significant problems. Recently, membrane transport proteins have emerged as novel therapeutic targets for cancer treatment. These proteins are essential for a plethora of cell functions ranging from cell homeostasis to clinical drug toxicity. Furthermore, their association with carcinogenesis and chemoresistance has opened new vistas for pharmacology-based cancer research. This review provides a comprehensive update of our current knowledge on the functional expression profile of membrane transport proteins in cancer and chemoresistant tumours that may form the basis for new cancer treatment strategies.

CXL146, a Novel 4H-Chromene Derivative, Targets GRP78 to Selectively Eliminate Multidrug-Resistant Cancer Cells

The 78-kDa glucose-regulated protein (GRP78), an endoplasmic reticulum (ER) chaperone, is a master regulator of the ER stress. A number of studies revealed that high levels of GRP78 protein in cancer cells confer multidrug resistance (MDR) to therapeutic treatment. Therefore, drug candidate that reduces GRP78 may represent a novel approach to eliminate MDR cancer cells. Our earlier studies showed that a set of 4H-chromene derivatives induced selective cytotoxicity in MDR cancer cells. In the present study, we elucidated its selective mechanism in four MDR cancer cell lines with one lead candidate (CXL146). Cytotoxicity results confirmed the selective cytotoxicity of CXL146 toward the MDR cancer cell lines. We noted significant overexpression of GRP78 in all four MDR cell lines compared with the parental cell lines. Unexpectedly, CXL146 treatment rapidly and dose-dependently reduced GRP78 protein in MDR cancer cell lines. Using human leukemia (HL) 60/mitoxantrone (MX) 2 cell line as the model, we demonstrated that CXL146 treatment activated the unfolded protein response (UPR); as evidenced by the activation of inositol-requiring enzyme 1α, protein kinase R-like ER kinase, and activating transcription factor 6. CXL146-induced UPR activation led to a series of downstream events, including extracellular signal-regulated kinase 1/2 and c-Jun N-terminal kinase activation, which contributed to CXL146-induced apoptosis. Targeted reduction in GRP78 resulted in reduced sensitivity of HL60/MX2 toward CXL146. Long-term sublethal CXL146 exposure also led to reduction in GRP78 in HL60/MX2. These data collectively support GRP78 as the target of CXL146 in MDR treatment. Interestingly, HL60/MX2 upon long-term sublethal CXL146 exposure regained sensitivity to mitoxantrone treatment. Therefore, further exploration of CXL146 as a novel therapy in treating MDR cancer cells is warranted. SIGNIFICANCE STATEMENT: Multidrug resistance is one major challenge to cancer treatment. This study provides evidence that cancer cells overexpress 78-kDa glucose-regulated protein (GRP78) as a mechanism to acquire resistance to standard cancer therapies. A chromene-based small molecule, CXL146, selectively eliminates cancer cells with GRP78 overexpression via activating unfolded protein response-mediated apoptosis. Further characterization indicates that CXL146 and standard therapies complementarily target different populations of cancer cells, supporting the potential of CXL146 to overcome multidrug resistance in cancer treatment.

An Indole-Chalcone Inhibits Multidrug-Resistant Cancer Cell Growth by Targeting Microtubules

Multidrug resistance and toxic side effects are the major challenges in cancer treatment with microtubule-targeting agents (MTAs), and thus, there is an urgent clinical need for new therapies. Chalcone, a common simple scaffold found in many natural products, is widely used as a privileged structure in medicinal chemistry. We have previously validated tubulin as the anticancer target for chalcone derivatives. In this study, an α-methyl-substituted indole-chalcone (FC77) was synthesized and found to exhibit an excellent cytotoxicity against the NCI-60 cell lines (average concentration causing 50% growth inhibition = 6 nM). More importantly, several multidrug-resistant cancer cell lines showed no resistance to FC77, and the compound demonstrated good selective toxicity against cancer cells versus normal CD34⁺ blood progenitor cells. A further mechanistic study demonstrated that FC77 could arrest cells that relate to the binding to tubulin and inhibit the microtubule dynamics. The National Cancer Institute COMPARE analysis and molecular modeling indicated that FC77 had a mechanism of action similar to that of colchicine. Overall, our data demonstrate that this indole-chalcone represents a novel MTA template for further development of potential drug candidates for the treatment of multidrug-resistant cancers.

Exploring the Structure-Activity Relationship and Mechanism of a Chromene Scaffold (CXL Series) for Its Selective Antiproliferative Activity toward Multidrug-Resistant Cancer Cells

Multidrug resistance (MDR) is one major barrier in cancer management, which urges for new drugs to help treat MDR malignancies and elucidate MDR mechanisms. A series of chromene compounds (the CXL series) demonstrate increased antiproliferative activity toward MDR acute-myeloid-leukemia (AML) cells. The structure-activity relationship (SAR) of the antiproliferative potency has been partly characterized, whereas the structural determinants contributing to selectivity have not been investigated. In this study, three series of CXL compounds were synthesized and evaluated in HL60 and HL60/MX2 leukemia cells. The results not only confirmed previous SAR studies but also, for the first time, provided structural insights into the selectivity for MDR HL60/MX2 cells. Using the lead compounds as probes, we demonstrated that their modulation of intracellular-calcium homeostasis results in their antiproliferative potency and selectivity. Three candidates also demonstrate excellent in vitro safety profiles between cancer cells and normal cells, which will be evaluated in vivo in future studies.

4H-Chromene-based anticancer agents towards multi-drug resistant HL60/MX2 human leukemia: SAR at the 4th and 6th positions

4H-Chromene-based compounds, for example, CXL017, CXL035, and CXL055, have a unique anticancer potential that they selectively kill multi-drug resistant cancer cells. Reported herein is the extended structure-activity relationship (SAR) study, focusing on the ester functional group at the 4th position and the conformation at the 6th position. Sharp SARs were observed at both positions with respect to cellular cytotoxic potency and selectivity between the parental HL60 and the multi-drug resistant HL60/MX2 cells. These results provide critical guidance for future medicinal optimization.

Indium triflate catalyzed microwave-assisted alkenylation of methoxyphenols: synthesis of indenes and chromenes

In(OTf)3 catalyzed microwave-assisted alkenylation of methoxyphenols was investigated. Exclusive formation of either indenes or chromenes was observed depending on the position of the methoxy group on phenol. The structures of 1H-inden-4-ol derivatives (4a-e) and 4H-chromene derivatives (5a-j) were established by NMR ((1)H & (13)C) and high-resolution mass spectra, which were further supported by single crystal X-ray analysis of 4c and 5a.

The calcium-signaling toolkit: Updates needed

Here, we review the role of Ca(2+) in apoptosis, namely that ER Ca(2+) depletion or a sustained elevation of cytosolic or mitochondrial Ca(2+) concentration are sufficient to trigger apoptosis. These concepts have emerged by the use of ER stressor agents that decrease the ER Ca(2+) pool by inhibiting SERCA pumps. However, aside from their well-known actions on Ca(2+) homeostasis disruption leading to apoptosis, new evidence show that some ER Ca(2+) modulators have significant implications in other Ca(2+)-mediated or Ca(2+)-independent pathways determining cell fate suggesting a more complex regulation of apoptosis by intracellular Ca(2+). Here, we discuss the crucial interplay between Ca(2+) mediated apoptosis, the Unfold Protein Response and autophagy determining cell fate, and the molecular compounds that have been used to depict these pathways. This review of the literature clearly shows the need for new inhibitors that do not interfere concomitantly with autophagy and Ca(2+) signaling. This article is part of a Special Issue entitled: Calcium and Cell Fate. Guest Editors: Jacques Haiech, Claus Heizmann, Joachim Krebs, Thierry Capiod and Olivier Mignen.

Synthesis of functional 4H-chromenes from phenols and acetophenones under solvent- and metal-free conditions

Sulfuric-acid-promoted tandem reaction of phenols with acetophenones under solvent- and metal-free conditions has been developed, which afforded functional 4H-chromenes in good yields with water as the side product.

A novel SERCA inhibitor demonstrates synergy with classic SERCA inhibitors and targets multidrug-resistant AML

Drug resistance exists as a major obstacle in the treatment of cancer, and drug molecules that retain effectiveness against resistant cancers are a high clinical priority. Ethyl 2-amino-6-(3,5-dimethoxyphenyl)-4-(2-ethoxy-2-oxoethyl)-4H-chromene-3-carboxylate (CXL017) was recently identified as a promising lead for the treatment of multidrug-resistant leukemia, which elicits its cytotoxic effect, in part, through inhibition of the sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA). Herein initial experiments with SERCA1a and CXL017 demonstrated no significant effect on calcium affinity, competed with ATP, and induced a dose-dependent decrease in ATPase activity. Among all CXLs tested, (-)-CXL017 exhibited the greatest SERCA inhibition with an IC50 = 13.5 ± 0.5 μM. Inhibitor combination studies were used to assess potential interactions between (-)-CXL017 and well-known SERCA inhibitors: thapsigargin, cyclopiazonic acid, and 2,5-di-tert-butylhydroquinone. Surprisingly, (-)-CXL017 exhibited marked synergy with each of the known SERCA inhibitors, whereas all combinations of the known inhibitors yielded additive effects, indicating that (-)-CXL017 may bind at a unique allosteric site. Treatment of parental (HL60) and multidrug-resistant (HL60/MX2) acute myeloid leukemia cells with the known SERCA inhibitors revealed that all of these inhibitors demonstrate selective cytotoxicity (7.7-400-fold) for the resistant cell line. Within the CXL series, a positive correlation exists between SERCA inhibition and cytotoxicity in HL60/MX2 but not HL60. (-)-CXL017 was also shown to enhance the cytotoxicity of thapsigargin in HL60/MX2 cells. Given the elevated SERCA levels and ER calcium content in HL60/MX2, SERCA likely plays a significant role in the collateral sensitivity of this multidrug-resistance cell line to CXL molecules as well as known SERCA inhibitors.

Overexpression of Mcl-1 confers multidrug resistance, whereas topoisomerase IIβ downregulation introduces mitoxantrone-specific drug resistance in acute myeloid leukemia

Drug resistance is a serious challenge in cancer treatment and can be acquired through multiple mechanisms. These molecular changes may introduce varied extents of resistance to different therapies and need to be characterized for optimal therapy choice. A recently discovered small molecule, ethyl-2-amino-6-(3,5-dimethoxyphenyl)-4-(2-ethoxy-2-oxoethyl)-4H-chromene-3-carboxylate) (CXL017), reveals selective cytotoxicity toward drug-resistant leukemia. A drug-resistant acute myeloid leukemia cell line, HL60/MX2, also failed to acquire resistance to CXL017 upon chronic exposure and regained sensitivity toward standard therapies. In this study, we investigated the mechanisms responsible for HL60/MX2 cells' drug resistance and the molecular basis for its resensitization. Results show that the HL60/MX2 cell line has an elevated level of Mcl-1 protein relative to the parental cell line, HL60, and its resensitized cell line, HL60/MX2/CXL017, whereas it has a reduced level of topoisomerase IIβ. Mcl-1 overexpression in HL60/MX2 cells is mainly regulated through phospho-extracellular signal-regulated protein kinases 1 and 2-mediated Mcl-1 stabilization, whereas the reduction of topoisomerase IIβ in HL60/MX2 cells is controlled through genetic downregulation. Upregulating Mcl-1 introduces multidrug resistance to standard therapies, whereas its downregulation results in significant cell death. Downregulating topoisomerase IIβ confers resistance specifically to mitoxantrone, not to other topoisomerase II inhibitors. Overall, these data suggest that Mcl-1 overexpression is a critical determinant for cross-resistance to standard therapies, whereas topoisomerase IIβ downregulation is specific to mitoxantrone resistance.