Semisynthesis of 5-O-ester derivatives of renieramycin T and their cytotoxicity against non-small-cell lung cancer cell lines.

The semisynthesis of 5-O-ester derivatives of renieramycin T was accomplished through the photoredox reaction of renieramycin M (1), a bistetrahydroisoquinolinequinone alkaloid isolated from the Thai blue sponge Xestospongia sp. This process led to the conversion of compound 1 to renieramycin T (2), which was subsequently subjected to Steglich esterification with appropriate acylating agents containing linear alkyl, N-tert-butoxycarbonyl-L-amino, and heterocyclic aromatic substituent. Notably, the one-pot transformation, combining the photoredox reaction and esterification led to the formation of 7-O-ester derivatives of renieramycin S due to hydrolysis. Subsequently, the in vitro cytotoxicity of the 17 semisynthesized derivatives against human non-small-cell lung cancer (NSCLC) cells in parallel with normal cell lines was evaluated. Among the tested compounds, 5-O-(3-propanoyl) ester of renieramycin T (3b) exhibited potent cytotoxic activity with half-maximal inhibitory concentration (IC50) values at 33.44 and 33.88 nM against H292 and H460 cell lines, respectively. These values were within the same range as compound 1 (IC50 = 34.43 and 35.63 nM) and displayed twofold higher cytotoxicity compared to compound 2 (IC50 = 72.85 and 83.95 nM). The steric characteristics and aromatic orientation of the 5-O-ester substituents played significant roles in their cytotoxicity. Notably, derivative 3b induced apoptosis with minimal necrosis, in contrast to the parental compound 1. Hence, the relationship between the structure and cytotoxicity of renieramycin-ecteinascidin hybrid alkaloids was investigated. This study emphasizes the potential of the series of 5-O-ester derivatives of renieramycin T as promising leads for the further development of potential anti-NSCLC agents.

Light-Mediated Transformation of Renieramycins and Semisynthesis of 4'-Pyridinecarbonyl-Substituted Renieramycin-Type Derivatives as Potential Cytotoxic Agents against Non-Small-Cell Lung Cancer Cells.

The semisynthesis of renieramycin-type derivatives was achieved under mild and facile conditions by attaching a 1,3-dioxole-bridged phenolic moiety onto ring A of the renieramycin structure and adding a 4'-pyridinecarbonyl ester substituent at its C-5 or C-22 position. These were accomplished through a light-induced intramolecular photoredox reaction using blue light (4 W) and Steglich esterification, respectively. Renieramycin M (4), a bis-tetrahydroisoquinolinequinone compound isolated from the Thai blue sponge (Xestospongia sp.), served as the starting material. The cytotoxicity of the 10 natural and semisynthesized renieramycins against non-small-cell lung cancer (NSCLC) cell lines was evaluated. The 5-O-(4'-pyridinecarbonyl) renieramycin T (11) compound exhibited high cytotoxicity with half-maximal inhibitory concentration (IC50) values of 35.27 ± 1.09 and 34.77 ± 2.19 nM against H290 and H460 cells, respectively. Notably, the potency of compound 11 was 2-fold more than that of renieramycin T (7) and equal to those of 4 and doxorubicin. Interestingly, the renieramycin-type derivatives with a hydroxyl group at C-5 and C-22 exhibited weak cytotoxicity. In silico molecular docking and dynamics studies confirmed that the mitogen-activated proteins, kinase 1 and 3 (MAPK1 and MAPK3), are suitable targets for 11. Thus, the structure-cytotoxicity study of renieramycins was extended to facilitate the development of potential anticancer agents for NSCLC cells.

Transformation of Renieramycin M into Renieramycins T and S by Intramolecular Photoredox Reaction of 7-Methoxy-6-methyl-1,2,3,4-tetrahydroisoquinoline-5,8-dione Derivatives.

In connection with our studies of biologically active 1,2,3,4-tetrahydroisoquinoline marine natural products, we describe herein a useful intramolecular photoredox transformation of 7-methoxy-6-methyl-1,2,3,4-tetrahydroisoquinoline-5,8-dione tricyclic models into 5-hydroxy-tetrahydroisoquinol[1,3]dioxoles in excellent yields. We applied this methodology to the transformation of renieramycin M into renieramycins T and S and the transformation of saframycin A. The results of cytotoxicity studies are also presented.

5-O-(N-Boc-l-Alanine)-Renieramycin T Induces Cancer Stem Cell Apoptosis via Targeting Akt Signaling.

Cancer stem cells (CSCs) drive aggressiveness and metastasis by utilizing stem cell-related signals. In this study, 5-O-(N-Boc-l-alanine)-renieramycin T (OBA-RT) was demonstrated to suppress CSC signals and induce apoptosis. OBA-RT exerted cytotoxic effects with a half-maximal inhibitory concentration of approximately 7 µM and mediated apoptosis as detected by annexin V/propidium iodide using flow cytometry and nuclear staining assays. Mechanistically, OBA-RT exerted dual roles, activating p53-dependent apoptosis and concomitantly suppressing CSC signals. A p53-dependent pathway was indicated by the induction of p53 and the depletion of anti-apoptotic Myeloid leukemia 1 (Mcl-1) and B-cell lymphoma 2 (Bcl-2) proteins. Cleaved poly (ADP-ribose) polymerase (Cleaved-PARP) was detected in OBA-RT-treated cells. Interestingly, OBA-RT exerted strong CSC-suppressing activity, reducing the ability to form tumor spheroids. In addition, OBA-RT could induce apoptosis in CSC-rich populations and tumor spheroid collapse. CSC markers, including prominin-1 (CD133), Octamer-binding transcription factor 4 (Oct4), and Nanog Homeobox (Nanog), were notably decreased after OBA-RT treatment. Upstream CSCs regulating active Akt and c-Myc were significantly decreased; indicating that Akt may be a potential target of action. Computational molecular modeling revealed a high-affinity interaction between OBA-RT and an Akt molecule. This study has revealed a novel CSC inhibitory effect of OBA-RT via Akt inhibition, which may improve cancer therapy.

22-O-(N-Boc-L-glycine) ester of renieramycin M inhibits migratory activity and suppresses epithelial-mesenchymal transition in human lung cancer cells.

The incidence of metastasis stage crucially contributes to high recurrence and mortality rate in lung cancer patients. Unfortunately, no available treatment inhibits migration, a key metastasis process in lung cancer. In this study, the effect of 22-O-(N-Boc-L-glycine) ester of renieramycin M (22-Boc-Gly-RM), a semi-synthetic amino ester derivative of bistetrahydroisoquinolinequinone alkaloid isolated from Xestospongia sp., on migratory behavior of human lung cancer cells was investigated. Following 24 h of treatment, 22-Boc-Gly-RM at non-toxic concentrations (0.5-1 µM) effectively restrained motility of human lung cancer H460 cells assessed through wound healing, transwell migration, and multicellular spheroid models. The capability to invade through matrix component was also repressed in H460 cells cultured with 0.1-1 µM 22-Boc-Gly-RM. The dose-dependent reduction of phalloidin-stained actin stress fibers corresponded with the downregulated Rac1-GTP level presented via western blot analysis in 22-Boc-Gly-RM-treated cells. Treatment with 0.1-1 µM of 22-Boc-Gly-RM obviously caused suppression of p-FAK/p-Akt signal and consequent inhibition of epithelial-to-mesenchymal transition (EMT), which was evidenced with augmented level of E-cadherin and reduction of N-cadherin expression. The alteration of invasion-related proteins in 22-Boc-Gly-RM-treated H460 cells was indicated by the diminution of matrix metalloproteinases (MT1-MMP, MMP-2, MMP-7, and MMP-9), as well as the upregulation of tissue inhibitors of metalloproteinases (TIMP), TIMP2, and TIMP3. Thus, 22-Boc-Gly-RM is a promising candidate for anti-metastasis treatment in lung cancer through inhibition of migratory features associated with suppression on EMT.

Jorunnamycin A Suppresses Stem-Like Phenotypes and Sensitizes Cisplatin-Induced Apoptosis in Cancer Stem-Like Cell-Enriched Spheroids of Human Lung Cancer Cells.

It has been recognized that cancer stem-like cells (CSCs) in tumor tissue crucially contribute to therapeutic failure, resulting in a high mortality rate in lung cancer patients. Due to their stem-like features of self-renewal and tumor formation, CSCs can lead to drug resistance and tumor recurrence. Herein, the suppressive effect of jorunnamycin A, a bistetrahydroisoquinolinequinone isolated from Thai blue sponge Xestospongia sp., on cancer spheroid initiation and self-renewal in the CSCs of human lung cancer cells is revealed. The depletion of stemness transcription factors, including Nanog, Oct-4, and Sox2 in the lung CSC-enriched population treated with jorunnamycin A (0.5 µM), resulted from the activation of GSK-3ß and the consequent downregulation of ß-catenin. Interestingly, pretreatment with jorunnamycin A at 0.5 µM for 24 h considerably sensitized lung CSCs to cisplatin-induced apoptosis, as evidenced by upregulated p53 and decreased Bcl-2 in jorunnamycin A-pretreated CSC-enriched spheroids. Moreover, the combination treatment of jorunnamycin A (0.5 µM) and cisplatin (25 µM) also diminished CD133-overexpresssing cells presented in CSC-enriched spheroids. Thus, evidence on the regulatory functions of jorunnamycin A may facilitate the development of this marine-derived compound as a novel chemotherapy agent that targets CSCs in lung cancer treatment.

Chemistry of Renieramycins. Part 19: Semi-Syntheses of 22-O-Amino Ester and Hydroquinone 5-O-Amino Ester Derivatives of Renieramycin M and Their Cytotoxicity against Non-Small-Cell Lung Cancer Cell Lines.

Two new series of synthetic renieramycins including 22-O-amino ester and hydroquinone 5-O-amino ester derivatives of renieramycin M were semi-synthesized and evaluated for their cytotoxicity against the metastatic non-small-cell lung cancer H292 and H460 cell lines. Interestingly, the series of 22-O-amino ester derivatives displayed a potent cytotoxic activity greater than the hydroquinone derivatives. The most cytotoxic derivative of the series was the 22-O-(N-Boc-l-glycine) ester of renieramycin M (5a: IC50 3.56 nM), which showed 7-fold higher potency than renieramycin M (IC50 24.56 nM) and 61-fold more than jorunnamycin A (IC50 217.43 nM) against H292 cells. In addition, 5a exhibited a significantly higher cytotoxic activity than doxorubicin (ca. 100 times). The new semi-synthetic renieramycin derivatives will be further studied and developed as potential cytotoxic agents for non-small-cell lung cancer treatment.

Synergistic Cytotoxicity of Renieramycin M and Doxorubicin in MCF-7 Breast Cancer Cells.

Renieramycin M (RM) is a KCN-stabilized tetrahydroisoquinoline purified from the blue sponge Xestospongia sp., with nanomolar IC50s against several cancer cell lines. Our goal is to evaluate its combination effects with doxorubicin (DOX) in estrogen receptor positive MCF-7 breast cancer cells. MCF-7 cells were treated simultaneously or sequentially with various combination ratios of RM and DOX for 72 h. Cell viability was determined using the MTT assay. Synergism or antagonism was determined using curve-shift analysis, combination index method and isobologram analysis. Synergism was observed with pharmacologically achievable concentrations of DOX when administered simultaneously, but not sequentially. The IC95 values of RM and DOX after combination were reduced by up to four-fold and eight-fold, respectively. To gain insights on the mechanism of synergy, real-time profiling, cell cycle analysis, apoptosis assays, and transcriptome analysis were conducted. The combination treatment displayed a similar profile with DNA-damaging agents and induced a greater and faster cell killing. The combination treatment also showed an increase in apoptosis. DOX induced S and G2/M arrest while RM did not induce significant changes in the cell cycle. DNA replication and repair genes were downregulated commonly by RM and DOX. p53 signaling and cell cycle checkpoints were regulated by DOX while ErbB/PI3K-Akt, integrin and focal adhesion signaling were regulated by RM upon combination. Genes involved in cytochrome C release and interferon gamma signaling were regulated specifically in the combination treatment. This study serves as a basis for in vivo studies and provides a rationale for using RM in combination with other anticancer drugs.

Jorunnamycin A from Xestospongia sp. Suppresses Epithelial to Mesenchymal Transition and Sensitizes Anoikis in Human Lung Cancer Cells.

Metastasis is a key driving force behind the high mortality rate associated with lung cancer. Herein, we report the first study revealing the antimetastasis activity of jorunnamycin A, a bistetrahydroisoquinolinequinone isolated from a Thai blue sponge Xestospongia sp. evidenced by its inhibition of epithelial to mesenchymal transition (EMT), sensitization of anoikis, and suppression of anchorage-independent survival in human lung cancer cells. Treatment with jorunnamycin A (0.05-0.5 µM) altered the expression of p53 and Bcl-2 family proteins, particularly causing the down-regulation of antiapoptosis Bcl-2 and Mcl-1 proteins. Under detachment conditions for 12 h, jorunnamycin A-treated cells exhibited diminution of pro-survival proteins p-Akt and p-Erk as well as the survival-promoting factor caveolin-1. Corresponding with the inhibition on the Akt and Erk pathway as well as activation of p53, there was an increase in the epithelial marker E-cadherin and a remarkable decrease of EMT markers and associated proteins including vimentin, snail, and claudin-1. As the loss of anchorage dependence is an important barrier to metastasis, the observed inhibitory effects of jorunnamycin A on the coordinating networks of EMT and anchorage-independent growth emphasize the potential development of jorunnamycin A as an effective agent against lung cancer metastasis.

Renieramycin T Induces Lung Cancer Cell Apoptosis by Targeting Mcl-1 Degradation: A New Insight in the Mechanism of Action.

Among malignancies, lung cancer is the major cause of cancer death. Despite the advance in lung cancer therapy, the five-year survival rate is extremely restricted due to therapeutic failure and disease relapse. Targeted therapies selectively inhibiting certain molecules in cancer cells have been accepted as promising ways to control cancer. In lung cancer, evidence has suggested that the myeloid cell leukemia 1 (Mcl-1) protein, an anti-apoptotic member of the Bcl-2 family, is a target for drug action. Herein, we report the Mcl-1 targeting activity of renieramycin T (RT), a marine-derived tetrahydroisoquinoline alkaloid that was isolated from the Thai blue sponge Xestospongia sp. RT was shown to be dominantly toxic to lung cancer cells compared to the normal cells in the lung. The cytotoxicity of this compound toward lung cancer cells was mainly exerted through apoptosis induction. For the mechanism of action, we found that RT mediated activation of p53 protein and caspase-9 and -3 activations. While others Bcl-2 family proteins (Bcl-2, Bak, and Bax) were minimally changed in response to RT, Mcl-1 protein was dramatically diminished. We further performed the cycloheximide experiment and found that the half-life of Mcl-1 was significantly shortened by RT treatment. When MG132, a potent selective proteasome inhibitor, was utilized, it could restore the Mcl-1 level. Furthermore, immunoprecipitation analysis revealed that RT significantly increased the formation of Mcl-1-ubiquitin complex compared to the non-treated control. In conclusion, we report the potential apoptosis induction of RT with a mechanism of action involving the targeting of Mcl-1 for ubiquitin-proteasomal degradation. As Mcl-1 is critical for cancer cell survival and chemotherapeutic failure, this novel information regarding the Mcl-1-targeted compound would be beneficial for the development of efficient anti-cancer strategies or targeted therapies.

5-O-Acetyl-Renieramycin T from Blue Sponge Xestospongia sp. Induces Lung Cancer Stem Cell Apoptosis.

Lung cancer is one of the most significant cancers as it accounts for almost 1 in 5 cancer deaths worldwide, with an increasing incident rate. Management of the cancer has been shown to frequently fail due to the ability of the cancer cells to resist therapy as well as metastasis. Recent evidence has suggested that the poor response to the current treatment drugs and the ability to undergo metastasis are driven by cancer stem cells (CSCs) within the tumor. The discovery of novel compounds able to suppress CSCs and sensitize the chemotherapeutic response could be beneficial to the improvement of clinical outcomes. Herein, we report for the first time that 5-O-acetyl-renieramycin T isolated from the blue sponge Xestospongia sp. mediated lung cancer cell death via the induction of p53-dependent apoptosis. Importantly, 5-O-acetyl-renieramycin T induced the death of CSCs as represented by the CSC markers CD44 and CD133, while the stem cell transcription factor Nanog was also found to be dramatically decreased in 5-O-acetyl-renieramycin T-treated cells. We also found that such a CSC suppression was due to the ability of the compound to deplete the protein kinase B (AKT) signal. Furthermore, 5-O-acetyl-renieramycin T was able to significantly sensitize cisplatin-mediated apoptosis in the lung cancer cells. Together, the present research findings indicate that this promising compound from the marine sponge is a potential candidate for anti-cancer approaches.

Apoptosis-inducing Effect of Hydroquinone 5-O-Cinnamoyl Ester Analog of Renieramycin M on Non-small Cell Lung Cancer Cells.

BACKGROUND: A newly-synthesized derivative of renieramycin M (RM), an anticancer lead compound isolated from the blue sponge Xestospongia sp., hydroquinone 5-O-cinnamoyl ester (CIN-RM), was investigated here for its activity against non-small cell lung cancer cells. MATERIALS AND METHODS: Cytotoxicity effects of CIN-RM and RM on H292 lung cancer cells were determined by the MTT assay. We also investigated the mechanism of CIN-RM-mediated apoptosis and mechanism of action of this compound by western blotting. RESULTS: CIN-RM showed more potent cytotoxicity than its parental compound (RM) against H292 lung cancer cells. At concentrations of 15-60 µM, CIN-RM significantly induced apoptosis by increasing expression of apoptosis-inducing factor (AIF) and activation of caspase-3 and -9. For up-stream mechanism, CIN-RM mediated apoptosis through a p53-dependent mechanism, that consequently down-regulated anti-apoptotic B-cell lymphoma 2 (BCL2), while increasing the level of pro-apoptotic BCL2-associated X (BAX). In addition, phosphorylation of pro-survival protein AKT was found to be dramatically reduced. CONCLUSION: This study revealed the potential of CIN-RM for apoptosis induction and in the development of a novel anticancer agent.

Semisynthesis and biological evaluation of prenylated resveratrol derivatives as multi-targeted agents for Alzheimer's disease.

A series of prenylated resveratrol derivatives were designed, semisynthesized and biologically evaluated for inhibition of ß-secretase (BACE1) and amyloid-ß (Aß) aggregation as well as free radical scavenging and neuroprotective and neuritogenic activities, as potential novel multifunctional agents against Alzheimer's disease (AD). The results showed that compound 4b exhibited good anti-Aß aggregation (IC50 = 4.78 µM) and antioxidant activity (IC50 = 41.22 µM) and moderate anti-BACE1 inhibitory activity (23.70% at 50 µM), and could be a lead compound. Moreover, this compound showed no neurotoxicity along with a greater ability to inhibit oxidative stress on P19-derived neuronal cells (50.59% cell viability at 1 nM). The neuritogenic activity presented more branching numbers (9.33) and longer neurites (109.74 µm) than the control, and was comparable to the quercetin positive control. Taken together, these results suggest compound 4b had the greatest multifunctional activities and might be a very promising lead compound for the further development of drugs for AD.

Chemistry of Renieramycins. 17. A New Generation of Renieramycins: Hydroquinone 5-O-Monoester Analogues of Renieramycin M as Potential Cytotoxic Agents against Non-Small-Cell Lung Cancer Cells.

A series of hydroquinone 5-O-monoester analogues of renieramycin M were semisynthesized via bishydroquinonerenieramycin M (5) prepared from renieramycin M (1), a major cytotoxic bistetrahydroisoquinolinequinone alkaloid isolated from the Thai blue sponge Xestospongia sp. All 20 hydroquinone 5-O-monoester analogues possessed cytotoxicity with IC50 values in nanomolar concentrations against the H292 and H460 human non-small-cell lung cancer (NSCLC) cell lines. The improved cytotoxicity toward the NSCLC cell lines was observed from the 5-O-monoester analogues such as 5-O-acetyl ester 6a and 5-O-propanoyl ester 7e, which exhibited 8- and 10-fold increased cytotoxicity toward the H292 NSCLC cell line (IC50 3.0 and 2.3 nM, respectively), relative to 1 (IC50 24 nM). Thus, the hydroquinone 5-O-monoester analogues are a new generation of the renieramycins to be further developed as potential marine-derived drug candidates for lung cancer treatment.

Renieramycin M Attenuates Cancer Stem Cell-like Phenotypes in H460 Lung Cancer Cells.

BACKGROUND/AIM: Cancer stem cells (CSCs) are a subpopulation of cancer cells that possess self-renewal and differentiation capacities. CSCs contribute to drug-resistance, cancer recurrence and metastasis, thus development of CSC-targeted therapeutic strategies has recently received significant attention in cancer research. In this study, the potential efficacy of renieramycin M (RM) isolated from the sponge Xestospongia species, was examined against lung CSCs. MATERIALS AND METHODS: Colony and spheroid formation assays, as well as western blotting analysis of lung CSC protein markers were employed to determine the CSC-like phenotypes of H460 lung cancer cells after treatment with RM at non-toxic concentrations. RESULTS: RM treatment reduced significantly colony and spheroid formation of H460 cells. Moreover, the CSC markers CD133, CD44 and ALDH1A1 of CSC-enriched H460 cells were reduced significantly following RM treatment. CONCLUSION: RM could be a potent anti-metastatic agent by suppressing lung CSC-like phenotypes in H460 cells.

Phenanthrenes from Eulophia macrobulbon as Novel Phosphodiesterase-5 Inhibitors.

Phosphodiesterase 5 (PDE5) inhibitors can be used for the treatment of erectile dysfunction and pulmonary hypertension. In order to search for new leads of PDE5 inhibitors, we investigated the chemical constituents of the tubers of Eulophia macrobulbon (E.C. Parish & Rchb. f.) Hook. f. A new phenanthrene, 9,10-dihydro-4-(4'-hydroxybenzyl)-2,5-dimethoxyphenanthrene-1,7-dio (1) and three known phenanthrenes i.e., 1-(4'-hydroxybenzyl)-4,8- dimethoxyphenanthrene-2,7-diol (2), (9,10-dihydro-2,5-dimethoxyphenanthrene-1,7-diol (3) and 1,5,7-trimethoxyphenanthrene-2,6-diol). (4) were isolated Among these, 2 was the most potent PDE5 inhibitor (IC50 =1.67±0.54 µM) evaluated by the [3H]cGMP radioassay method, whereas 1 showed mild activity (IC50 = 62.3±3.3 µM). Their inhibitory selectivities against PDE5 over PDE6 were also studied. This study suggests phenanthrenes as a new class of PDE5 inhibitors.

Bishydroquinone Renieramycin M Induces Apoptosis of Human Lung Cancer Cells Through a Mitochondria-dependent Pathway.

BACKGROUND: Renieranycin M (RM), a bistetrahydro-isoquinolinequinone isolated from the Thai blue sponge, Xestospongia sp. was reported to be a potent anti-lung cancer agent. Modification at quinone ring enhanced apoptosis over necrosis. Thus, bishydroquinone renieramycin M (HQ-RM) was prepared and evaluated for apoptosis induction in lung cancer cells. METHODS: HQ-RM was examined for cytotoxicity and apoptosis induction in human lung cancer H292 cells by 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyltetrazoliumbromide and Hoechst/propidium iodide staining, respectively. The key molecular markers of mitochondrial apoptosis pathway were determined by western blot analysis. RESULTS: HQ-RM exhibited stronger cytotoxicity than RM. HQ-RM reduced vitality of lung cancer cells in a dose-dependent manner. Nuclear staining assay indicated that apoptotic cell death was the main mechanism of toxicity caused by HQ-RM. Protein analysis revealed that HQ-RM-mediated apoptosis involved the increase of pro-apoptotic B-cell lymphoma 2 associated X (BAX) protein, and the decrease of anti-apoptosis myeloid cell leukemia 1 (MCL1) and B-cell lymphoma 2 (BCL2) proteins. Moreover, caspase-9 and -3 and Poly (ADP-ribose) polymerase (PARP) were dramatically cleaved in response to HQ-RM treatment. CONCLUSION: HQ-RM has highly potent anticancer activity, greater than its parental RM, and induces lung cancer cell apoptosis through a mitochondrial apoptosis caspase-dependent mechanism. This information benefits the development of this compound for cancer therapy.

Chemistry of Renieramycins. 15. Synthesis of 22-O-Ester Derivatives of Jorunnamycin A and Their Cytotoxicity against Non-Small-Cell Lung Cancer Cells.

Eighteen 22-O-ester derivatives of jorunnamycin A (2) were prepared via 2, and their cytotoxicity against human non-small-cell lung cancer (NSCLC) cells was evaluated. Preliminary study of the structure-cytotoxicity relationship revealed that the ester part containing a nitrogen-heterocyclic ring elevated the cytotoxicity of the 22-O-ester derivatives. Among them, 22-O-(4-pyridinecarbonyl) ester 6a is the most potent compound (IC50 1.1 and 1.6 nM), exhibiting 21-fold and 5-fold increases in cytotoxicity against the H292 and H460 NSCLC cell lines, respectively, relative to renieramycin M (1), the major cytotoxic bistetrahydroisoquinolinequinone alkaloid of the Thai blue sponge Xestospongia sp.

Chemistry of Ecteinascidins. Part 5: An Additional Proof of Cytotoxicity Evaluation of Ecteinascidin 770 Derivatives.

Eleven 2'-N-acyl derivatives (5a-k) were prepared from ecteinascidin 770 (Et 770: 1b) via known 18,6'-O-bisallyl-protected compound (3) in three steps. Their in vitro cytotoxicities were determined by measuring IC50 values against human cell lines HCT116 and DU145. 5-Isoxazolecarboylamide derivative (5i) and 4-methoxybenzoylamide derivative (5k) were found to be promising leads for further optimization.