Anti-angiogenesis effects of meisoindigo on chronic myelogenous leukemia in vitro

Discovery of meisoindigo derivatives as noncovalent and orally available Mpro inhibitors: their therapeutic implications in the treatment of COVID-19

The progressive emergence of SARS-CoV-2 variants has necessitated the urgent exploration of novel therapeutic strategies to combat the COVID-19 pandemic. The SARS-CoV-2 main protease (Mpro) represents an evolutionarily conserved therapeutic target for drug discovery. This study highlights the discovery of meisoindigo (Mei), derived from the traditional Chinese medicine (TCM) Indigo naturalis, as a novel non-covalent and nonpeptidic Mpro inhibitor. Substantial optimizations and structure-activity relationship (SAR) studies, guided by a structure-based drug design approach, led to the identification of several Mei derivatives, including S5-27 and S5-28, exhibiting low micromolar inhibition against SARS-CoV-2 Mpro with high binding affinity. Notably, S5-28 provided significant protection against wild-type SARS-CoV-2 in HeLa-hACE2 cells, with EC50 up to 2.66 μM. Furthermore, it displayed favorable physiochemical properties and remarkable gastrointestinal and metabolic stability, demonstrating its potential as an orally bioavailable drug for anti-COVID-19 therapy. This research presents a promising avenue for the development of new antiviral agents, offering hope in the ongoing battle against COVID-19.

Discovery of a Meisoindigo-Derived PROTAC as the ATM Degrader: Revolutionizing Colorectal Cancer Therapy via Synthetic Lethality with ATR Inhibitors

Meisoindigo (Mei) has long been recognized in chronic myeloid leukemia (CML) treatment. To elucidate its molecular target and mechanisms, we embarked on designing and synthesizing a series of Mei-derived PROTACs. Through this endeavor, VHL-type PROTAC 9b was identified to be highly cytotoxic against SW620, SW480, and K562 cells. Employing DiaPASEF-based quantitative proteomic analysis, in combination with extensive validation assays, we unveiled that 9b potently and selectively degraded ATM across SW620 and SW480 cells in a ubiquitin-proteasome-dependent manner. 9b-induced selective ATM degradation prompted DNA damage response cascades, thereby leading to the cell cycle arrest and cell apoptosis. This pioneering discovery renders the advent of ATM degradation for anti-cancer therapy. Notably, 9b-induced ATM degradation synergistically enhanced the efficacy of ATR inhibitor AZD6738 both in vitro and in vivo. This work establishes the synthetic lethality-inducing properties of ATR inhibitors in the ATM-deficient context, thereby providing new avenues to innovative therapies for colorectal cancer.

Indirubin-3'-monoxime acts as proteasome inhibitor: Therapeutic application in multiple myeloma

BACKGROUND

Multiple myeloma (MM) is still an incurable malignancy of plasma cells. Proteasome inhibitors (PIs) work as the backbone agent and have greatly improved the outcome in majority of newly diagnosed patients with myeloma. However, drug resistance remains the major obstacle causing treatment failure in clinical practice. Here, we investigated the effects of Indirubin-3'-monoxime (I3MO), one of the derivatives of Indirubin, in the treatment of MM.

METHODS

MM patient primary samples and human cell lines were examined. I3MO effects on myeloma treatment and the underling molecular mechanisms were investigated via in vivo and in vitro study.

FINDINGS

Our results demonstrated the anti-MM activity of I3MO in both drug- sensitive and -resistance MM cells. I3MO sensitizes MM cells to bortezomib-induced apoptosis. Mechanistically, I3MO acts as a multifaceted regulator of cell death, which induced DNA damage, cell cycle arrest, and abrogates NF-κB activation. I3MO efficiently down-regulated USP7 expression, promoted NEK2 degradation, and suppressed NF-κB signaling in MM. Our study reported that I3MO directly bound with and caused the down-regulation of PA28γ (PSME3), and PA200 (PSME4), the proteasome activators. Knockdown of PSME3 or PSME4 caused the inhibition of proteasome capacity and the overload of paraprotein, which sensitizes MM cells to bortezomib-mediated growth arrest. Clinical data demonstrated that PSME3 and PSME4 are over-expressed in relapsed/refractory MM (RRMM) and associated with inferior outcome.

INTERPRETATION

Altogether, our study indicates that I3MO is agent triggering proteasome inhibition and represents a promising therapeutic strategy to improve patient outcome in MM.

FUNDINGS

A full list of funding can be found in the acknowledgements.

Dimerization of 3-Chlorooxindoles Mediated by Potassium Ethylxanthate: Synthesis of Isoindigos

A novel dimerization of 3-chlorooxindoles promoted by potassium ethylxanthate to access isoindigo derivatives is described. The reactions readily proceeded at room temperature in a short reaction time. The mechanistic study revealed that 3-chlorooxindole is initially converted to O-ethyl S-(2-oxoindolin-3-yl) carbonodithioate which subsequently undergoes dimerization upon elimination of carbon disulfide. In almost all cases, analytically pure isoindigos were isolated in moderate to good yields without the requirement of chromatographic purification.

Methylisoindigo preferentially kills cancer stem cells by interfering cell metabolism via inhibition of LKB1 and activation of AMPK in PDACs

Pancreatic ductal adenocarcinoma (PDAC) clinically has a very poor prognosis. No small molecule is available to reliably achieve cures. Meisoindigo is chemically related to the natural product indirubin and showed substantial efficiency in clinical chemotherapy for CML in China. However, its effect on PDAC is still unknown. Our results showed strong anti-proliferation effect of meisoindigo on gemcitabine-resistant PDACs. Using a recently established primary PDAC cell line, called Jopaca-1 with a larger CSCs population as model, we observed a reduction of CD133+ and ESA+/CD44+/CD24+ populations upon treatment and concomitantly a decreased expression of CSC-associated genes, and reduced cellular mobility and sphere formation. Investigating basic cellular metabolic responses, we detected lower oxygen consumption and glucose uptake, while intracellular ROS levels increased. This was effectively neutralized by the addition of antioxidants, indicating an essential role of the cellular redox balance. Further analysis on energy metabolism related signaling revealed that meisoindigo inhibited LKB1, but activated AMPK. Both of them were involved in cellular apoptosis. Additional in situ hybridization in tissue sections of PDAC patients reproducibly demonstrated co-expression and -localization of LKB1 and CD133 in malignant areas. Finally, we detected that CD133+/CD44+ were more vulnerable to meisoindigo, which could be mimicked by LKB1 siRNAs. Our results provide the first evidence, to our knowledge, that LKB1 sustains the CSC population in PDACs and demonstrate a clear benefit of meisoindigo in treatment of gemcitabine-resistant cells. This novel mechanism may provide a promising new treatment option for PDAC.

Antiproliferative activity of the isoindigo 5'-Br in HL-60 cells is mediated by apoptosis, dysregulation of mitochondrial functions and arresting cell cycle at G0/G1 phase

Our new compound, 5'-Br [(E)-1-(5'-bromo-2'-oxoindolin-3'-ylidene)-6-ethyl-2,3,6,9-tetrahydro-2,9-dioxo-1H-pyrrolo[3,2-f]quinoline-8-carboxylic acid], had shown strong, selective antiproliferative activity against different cancer cell lines. Here, we aim to comprehensively characterize the mechanisms associated with its cytotoxicity in the human promyelocytic leukemia HL-60 cells. We focused at studying the involvement of apoptotic pathway and cell cycle effects. 5'-Br significantly inhibited proliferation by inducing caspase-dependent apoptosis. Involvement of caspase independent mechanism is also possible due to observed inability of z-VAD-FMK to rescue apoptotic cells. 5'-Br was found to trigger intrinsic apoptotic pathway as indicated by depolarization of the mitochondrial inner membrane, decreased level of cellular ATP, modulated expression and phosphorylation of Bcl-2 leading to loss of its association with Bax, and increased release of cytochrome c. 5'-Br treated cells were found arrested at G0/G1 phase with modulation in protein levels of cyclins, dependent kinases and their inhibitors. Expression and enzymatic activity of CDK2 and CDK4 was found inhibited. Retinoblastoma protein (Rb) phosphorylation was also inhibited whereas p21 protein levels were increased. These results suggest that the antiproliferative mechanisms of action of 5'-Br could involve apoptotic pathways, dysregulation of mitochondrial functions and disruption of cell cycle checkpoint.

Synthesis and biological evaluation of new pyridone-annelated isoindigos as anti-proliferative agents

A selected set of substituted pyridone-annelated isoindigos 3a-f has been synthesized via interaction of 5- and 6-substituted oxindoles 2a-f with 6-ethyl-1,2,9-trioxopyrrolo[3,2-f]quinoline-8-carboxylic acid (1) in acetic acid at reflux. Among these isoindigos, the 5'-chloro and 5'-bromo derivatives 3b and 3d show strong and selective antiproliferative activities against a panel of human hematological and solid tumor cell-lines, but not against noncancerous cells, suggesting their potential use as anticancer agents. In all the tested cell lines, compound 3b was a 25%-50% more potent inhibitor of cell growth than 3d, suggesting the critical role of the substitution at 5'-position of the benzo-ring E. The IC50 values after 48 hours incubation with the 5'-chloro compound 3b were 6.60 µM in K562, 8.21 µM in THP-1, 8.97 µM in HepG2, 11.94 µM in MCF-7 and 14.59 µM in Caco-2 cancer cells, while the IC50 values in noncancerous HEK-293 and L-929 were 30.65 µM and 40.40 µM, respectively. In addition, compound 3b induced higher levels apoptosis in K562 cells than 3d, as determined by annexin V/7-AAD flowcytometry analysis. Therefore, further characterization of the antitproliferative mechanisms of compounds 3b and 3d may provide a novel chemotherapeutic agents.

Design, synthesis and biological evaluation of N-alkyl or aryl substituted isoindigo derivatives as potential dual cyclin-dependent kinase 2 (CDK2)/glycogen synthase kinase 3β (GSK-3β) phosphorylation inhibitors

A series of N-alkyl or aryl substituted isoindigo derivatives have been synthesized and their anti-proliferative activity was evaluated by Sulforhodamine B (SRB) assay. Some of the target compounds exhibited significant antitumor activity, including compounds 6h and 6k (against K562 cells), 6i (against HeLa cells) and 6j (against A549 cells). N-(p-methoxy-phenyl)-isoindigo (6k) exhibited a high and selective anti-proliferative activity against K562 cells (IC50 7.8 μM) and induced the apoptosis of K562 cells in a dose-dependent manner. Compound 6k arrested the cell cycle at S phase in K562 cells by decreasing the expression of cyclin A and CDK2, which played critical roles in DNA replication and passage through G2 phase. Moreover, compound 6k down-regulated the expression of p-GSK-3β (Ser9), β-catenin and c-myc proteins, up-regulated the expression of GSK-3β, consequently, suppressed Wnt/β-catenin signaling pathway and induced the apoptosis of K562 cells. The binding mode of compound 6k with GSK-3β was simulated using molecular docking tools. All of these studies gave a better understanding to the molecular mechanisms of this class of agents and clues to develop dual CDK2/GSK-3β (Ser9) phosphorylation inhibitors applied in cancer chemotherapy.

Evaluation of meisoindigo, an indirubin derivative: in vitro antileukemic activity and in vivo pharmacokinetics

Meisoindigo has been a routine therapeutic agent in the clinical treatment of chronic myelogenous leukemia (CML) in China since the 1980s. In the present study, the in vitro antileukemic activity of meisoindigo was investigated in acute promyelocytic leukemia (APL) cells, acute myeloid leukemia (AML) cells, and myelomonocytic leukemia cells (NB4, NB4.007/6, HL-60 and U937) comprising both retinoic acid-sensitive and retinoic acid-resistant cells. We found that meisoindigo effectively inhibited the growth and/or proliferation of these four cell types at µM levels. The effects of meisoindigo in these cells are related to its proliferation inhibition and apoptosis induction, and are independent of cell cycle arrest, indicating that meisoindigo could be possible in the treatment of APL, AML and retinoic acid resistant APL. The in vivo pharmacokinetics of meisoindigo and its major circulatory metabolites in rat plasma were then investigated by a newly developed and validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. The profiles of plasma concentration versus time were plotted and the relevant pharmacokinetic parameters were calculated for meisoindigo and its reductive metabolites. The plasma concentrations of meisoindigo after oral administration were much lower than the in vitro IC50s determined in the leukemic cells. The contradicting poor pharmacokinetic characteristics and the established clinical efficacy of meisoindigo could indicate the presence of active metabolites in vivo.

12-Deoxyphorbol 13-palmitate inhibit VEGF-induced angiogenesis via suppression of VEGFR-2-signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

12-Deoxyphorbol 13-palmitate (G) is one toxic compound isolated from Euphorbia fischeriana, an Asian spice used for cancer treatment as a folk remedy. However, whether 12-deoxyphorbol 13-palmitate affects angiogenesis remains unclear.

AIM OF THE STUDY

To explore the in vitro and in vivo antiangiogenic effects of 12-deoxyphorbol 13-palmitate and its underlying mechanisms.

MATERIALS AND METHODS

We explored antigenic functions in human umbilical vein endothelial cells (HUVEC) by 12-deoxyphorbol 13-palmitate, including proliferation, migration and metastasis through matrigel plug assay, chorioallantoic membrane assay, in vitro migration assay, tube formation assay, motility assay. Antibody chip was applied to screen differentially expressed proteins modulated by 12-deoxyphorbol 13-palmitate, and was further confirmed by RT-PCR and western blot analysis. Tumor xenograft mice were applied to investigate whether 12-deoxyphorbol 13-palmitate could inhibit microvessel density in vivo.

RESULTS

12-Deoxyphorbol 13-palmitate inhibited vascular endothelial growth factor (VEGF)-induced angiogenic processes in vitro, such as proliferation, in vitro migration, and tube formation of HUVEC. In chorioallantoic membrane assay, 12-deoxyphorbol 13-palmitate significantly inhibited neovessel formation. Antibody chip technology demonstrated decreased expression of TIMP-1, TIMP-2, VEGF, basic fibroblast growth factor (bFGF), matrix metalloproteinases (MMP)-2, VEGFR-2 and VEGFR-3 proteins in HUVEC after 24h. In addition, 12-deoyphorbol 13-palmitate inhibited the in vivo growth of MCF-7 cells in grafted mouse model. Immunohistochemistry staining showed decreased microvessel density (CD31) and attenuated VEGFR-2 signaling pathways by 12-deoxyphorbol 13-palmitate.

CONCLUSION

12-Deoxyphorbol 13-palmitate may be utilized to target active angiogenesis through VEGF/VEGFR2 signal pathway for cancer.

Exploring the anticancer activity of functionalized isoindigos: synthesis, drug-like potential, mode of action and effect on tumor-induced xenografts

Meisoindigo has been used as an indirubin substitute for the treatment of chronic myeloid leukemia (CML) for several years. In view of its poor solubility and erratic absorption, several investigations have focused on developing analogues with more desirable physicochemical profiles. Here, we investigated the structure-activity relationship (SAR) of meisoindigo with respect to its antiproliferative activity on leukemic K562 cells and found that appending a phenalkyl side chain onto the lactam NH resulted in analogues that retained good activity. Furthermore, analogues in which the phenyl ring was substituted with a basic heterocycle were significantly more soluble than meisoindigo while retaining acceptable antiproliferative profiles. The most promising analogue (E)-1-(2-(4-methylpiperazin-1-yl)ethyl)-[3,3'-biindolinylidene]-2,2'-dione (5-4) is more potent than meisoindigo across a panel of malignant cells, with at least 40 times greater solubility than meisoindigo, little or no tendency to aggregate in solution and capable of significantly extending the lifespans of animals with K562 induced xenografts. Mechanistically, it induced apoptotic cell death and disrupted the progression of K562 cells from the G(1) to G(2) phase. Taken together, our findings highlighted the feasibility of addressing the physicochemical deficits of the isoindigo scaffold by systematic modifications which was achieved without overt loss of growth inhibitory activity.

Herbs in hemato-oncological care: an evidence-based review of data on efficacy, safety, and drug interactions

Herbal remedies are clearly a complementary and alternative modality used frequently by patients with hemato-oncological neoplasias during the course of their specific treatment. This review focuses on the potential safety and efficacy of herbs which are either used often or even on a daily basis by patients with hematological malignancies or indicated in the herbal pharmacopeias utilized by various traditional systems of medicine, in order to improve the well-being of patients with these cancers. Traditional medicine worldwide is a source for ongoing laboratory research related to the activity of herbs on cultured cell lines derived from patients with leukemia, lymphoma, and myeloma. Although the number of clinical studies in the field of hemato-oncology is limited, there appears to be potential efficacy in studies of mistletoe (Viscum album), green tea, Indian and Middle-Eastern spices, and some traditional Chinese, American, and European herbs. In addition to the potential efficacy of herbs, safety issues are also reviewed here, particularly, the documented and potential side effects, herb-drug interactions, and matters of quality control. Based on the above issues, the authors suggest enhancing doctor-patient communication regarding herbal use by adopting a patient-centered attitude based on scientific perspective.

A novel 7-azaisoindigo derivative-induced cancer cell apoptosis and mitochondrial dysfunction mediated by oxidative stress

This research focused on a novel 7-azaisoindigo derivative [namely N(1)-(n-butyl)-7-azaisoindigo, 7-AI-b], and investigated its molecular antitumor mechanism by exploring the means of cell death and the effects on mitochondrial function. 7-AI-b inhibited cancer cell proliferation in a dose- and time-dependent way. The morphological and nuclei changes in H(2) B-GFP-labeled HeLa cells were observed using a live cell system. The results suggested that cell death induced by 7-AI-b is closely related to apoptosis. 7-AI-b induced release of cytochrome C from mitochondria to cytosol and activation of caspase-3, showing that the apoptosis is mediated by the mitochondrial pathway. Furthermore, our data indicated that 7-AI-b triggers apoptosis through reactive oxygen species (ROS): cellular ROS levels were increased after 3 h exposure of 7-AI-b, which was reversed by the ROS scavenger N-acetyl-L-cysteine. As a consequence, 7-AI-b-mediated cell death, mitochondrial transmembrane potential collapse and ATP level were partly blocked by N-acetyl-L-cysteine. Further study showed that 7-AI-b could induce mitochondrial dysfunction: collapse of the mitochondrial transmembrane potential and reduction of intracellular ATP level. In summary, the novel synthesized 7-AI-b was demonstrated to be effective in killing cancer cells via an ROS-promoted and mitochondria- and caspase-dependent apoptotic pathway.

Indirubin shows anti-angiogenic activity in an in vivo zebrafish model and an in vitro HUVEC model

AIM OF THE STUDY

Indirubin is an active ingredient of the traditional Chinese medicine, Dang Gui Long Hui Wan, commonly used for the treatment of chronic myelocytic leukemia (CML) and other inflammatory conditions. These anti-leukemic and anti-inflammatory activities may be mediated by anti-angiogenic action. To investigate the anti-angiogenic activity of indirubin, we tested its inhibitory effect on blood vessel formation in zebrafish embryos and on endothelial cell proliferation in culture.

MATERIALS AND METHODS

The anti-angiogenic activity of indirubin was tested using transgenic zebrafish embryos with fluorescent vasculature and human umbilical vein endothelial cells (HUVECs). Apoptosis was analyzed with a terminal deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL) assay.

RESULTS

Indirubin dose-dependently inhibited intersegmental vessel formation in zebrafish embryos. It also inhibited HUVEC proliferation by the induction of cellular apoptosis and cell-cycle arrest at the G0/G1 phase.

CONCLUSIONS

The anti-angiogenic activity of indirubin may partly contribute to its anti-leukemic and anti-psoriatic properties and may be valuable for the treatment of diseases with excessive angiogenesis. The zebrafish model of angiogenesis was further validated in this study.

Meisoindigo is a promising agent with in vitro and in vivo activity against human acute myeloid leukemia

Meisoindigo, a derivative of Indigo naturalis, has been used in China for chronic myeloid leukemia. In vitro cell line studies have shown that this agent might induce apoptosis and myeloid differentiation of acute myeloid leukemia (AML). In this study, we explored its mechanisms and potential in AML. NB4, HL-60, and U937 cells and primary AML cells were used to examine its effects and the NOD/SCID animal model was used to evaluate its in vivo activity. Meisoindigo inhibited the growth of leukemic cells by inducing marked apoptosis and moderate cell-cycle arrest at the G(0)/G(1) phase. It down-regulated anti-apoptotic Bcl-2, and up-regulated pro-apoptotic Bak and Bax and cell-cycle related proteins, p21and p27. Furthermore, it induced myeloid differentiation, as demonstrated by morphologic changes, up-regulation of CD11b, and increased nitroblue tetrazolium reduction activity in all cell lines tested. In addition, meisoindigo down-regulated the expression of human telomerase reverse transcriptase and enhanced the cytotoxicity of conventional chemotherapeutic agents, cytarabine and idarubicin. As with the results from cell lines, meisoindigo also induced apoptosis, up-regulated p21 and p27, and down-regulated Bcl-2 in primary AML cells. The in vivo anti-leukemic activity of meisoindigo was also demonstrated by decreased spleen size in a dose-dependent manner. Taking these results together, meisoindigo is a potential agent for AML.

Synthesis and evaluation of functionalized isoindigos as antiproliferative agents

A series of functionalized isoindigos structurally related to meisoindigo (1-methylisoindigo), a therapeutic agent used for the treatment of a form of leukemia, were synthesized and evaluated for antiproliferative activities on a panel of human cancer cells. Two promising compounds (1-phenpropylisoindigo and 1-(p-methoxy-phenethyl)-isoindigo) that were more potent than meisoindigo and comparable to 6-bromoindirubin-3'-oxime on leukemic K562 and liver HuH7 cells were identified. Structure-activity relationships showed the importance of keeping one of the lactam NH in an unsubstituted state. Substitution of the other lactam NH with aryl or arylalkyl side chains retained or improved activity in most instances. An intact exocyclic double bond was also essential, possibly to maintain planarity and rigidity of the isoindigo scaffold. None of the compounds were found to inhibit CDK2 in an in vitro assay, in spite of reports linking the antiproliferative activities of meisoindigo and other isoindigos to CDK2 inhibition. Hence, these functionalized isoindigos disrupted cell growth and proliferation by other mechanistic pathways that did not involve CDK2 inhibition.

Transforming growth factor-beta1 enhanced vascular endothelial growth factor synthesis in mesenchymal stem cells

Angiogenesis is essential for transplantation of mesenchymal stem cells (MSCs). Vascular endothelial growth factor (VEGF) is one of the most potent angiogenic factors identified to date. Elevated VEGF levels in MSCs correlate with the potential of MSCs transplantation. As an indirect angiogenic agent, transforming growth factor-beta1 (TGF-beta1) plays a pivotal role in the regulation of vasculogenesis and angiogenesis. However, the effect of TGF-beta1 on VEGF synthesis in MSCs is still unknown. Besides, the intracellular signaling mechanism by which TGF-beta1 stimulates this process remains poorly understood. In this article, we demonstrated that exposure of MSCs to TGF-beta1 stimulated the synthesis of VEGF. Meanwhile, TGF-beta1 stimulated the phosphorylation of Akt and extracellular signal-regulated kinase 1/2 (ERK1/2). Moreover, Ly 294002, a specific inhibitor of phosphatidylinositol-3-kinase (PI3K)/Akt significantly attenuated the VEGF synthesis stimulated by TGF-beta1. Additionally, U0126, a specific inhibitor of ERK1/2, also significantly attenuated the TGF-beta1-stimulated VEGF synthesis. These results indicated that TGF-beta1 enhanced VEGF synthesis in MSCs, and the Akt and ERK1/2 activation were involved in this process.