Anti-Cancer Agents in Medicinal Chemistry (v.15, #3)

The Cytotoxic and Mechanistic Effects of Aaptamine on Hepatocellular Carcinoma by Qiao-lu Li, Ping-ping Zhang, Pei-qin Wang, Hao-bing Yu, Fan Sun, Wen-zheng Hu, Wen-hui Wu, Xin Zhang, Fei Chen, Zhi-yong Chu, Jun-ping Zhang, Shun-shen Chen, Hou-wen Lin (1-1).
Hepatocellular carcinoma (HCC) is the fifth most common form of cancer and the third most frequent cause of cancer-associated mortality worldwide. We isolated aaptamine from the marine sponge Aaptos, and synthesized derivatives of this compound. Aaptamine and synthetic derivatives displayed various biological activities. This represents the first account of studies on the effects of aaptamine and its derivatives in hepatocarcinogenesis. In this study, Cell Counting Kit (CCK8) was used to evaluate the anti-proliferative effect of aaptamine on HCC in vitro. Additionally, a subcutaneous xenograft model was used to determine if aaptamine could inhibit hepatocellular carcinoma in vivo. We also used RT-PCR and Western blot to analyze the mechanisms behind these effects. Our results showed that aaptamine has anti-proliferation effects on the cell lines LM3 and HepG2. Aaptamine also suppressed the colony-formation ability of HCC cells. We found that aaptamine treatment led to cell cycle arrest in HCC cells, reduced the expression of SOX9 and CDK2. Significant anti-tumor effects were observed in aaptamineadministered tumor-bearing mice as compared to controls. However, structural changes made to aaptamine yielded two derivatives for which all the effects listed above were considerably reduced as compared to the original compound aaptamine. In conclusion, aaptamine is demonstrated for the first time to inhibit liver cancer progression. The aaptamine-induced cell cycle arrest was associated with the increased binding of p21 to Cdk2-cyclin D/E complexes, inhibition of Cdk2 kinase activity in HCC cells. Furthermore, aaptamine appears to be a promising and efficient treatment of liver cancer HCC-LM3 in vivo. We have also uncovered structural changes that might affect the biological activity. The work provides a promising drug candidate for HCC treatment.

In this study, a new dithiolopyrrolone biosynthetic pathway was identified in Saccharothrix algeriensis NRRL B-24137, which was reported to produce a variety of dithiolopyrrolone natural products including thiolutin, a potential drug candidate for tumor angiogenesis inhibition. Bioinformatics analysis of the cluster revealed that it contains all the essential genes for holothin core biosynthesis and several other auxiliary genes. Interestingly, heterologous expression of the gene cluster in Streptomyces albus only induced the production of holomycin, implying that the gene responsible for the N4-methylation and the gene(s) involved in the formation of various acylated chains on N7 position of the holothin may locate outside the gene cluster. Incubation of holomycin with S-adenosyl-L-methionine (SAM) in the cell-free extract of Sa. algeriensis resulted in the production of thiolutin, suggesting that the N4-methyl group of thiolutin is originated from SAM, and the N4-methylation could be in the late stage of biosynthesis of thiolutin type dithiolopyrrolones. An evolution-based model for biosynthesis of thiolutin and its analogs was further proposed based on these results.

PreQ0 Base, an Unusual Metabolite with Anti-cancer Activity from Streptomyces qinglanensis 172205 by Dongbo Xu, Min Ma, Yongfeng Liu, Ting Zhou, Kexin Wang, Zixin Deng, Kui Hong (285-290).
PreQ0 base (7-cyano-7-deazaguanine, compound 1) is the biosynthetic precursor of queuosine-tRNA and important synthetic intermediate for bioactive compounds. It was obtained for the first time as a new natural product from a mangrove actinomycete Streptomyces qinglanensis 172205, during the course of searching for anti-cancer compounds from marine microbes. PreQ0 base showed anti-HeLa (IC50 = 62.0 μg/ml) and anti-HepG2 (IC50 = 80.6 μg/ml) activities, higher cytotoxicity than the positive control, fluorouracil. Furthermore, it exhibited weak α -glucosidase inhibitory activity, but no obvious antimicrobial and Aβ1-42 fibrillation inhibitory activities. In silico analysis of the genome of the strain 172205 revealed a putative biosynthetic gene cluster directing the biosynthesis of PreQ0 base. The gene cluster only contained three Open Reading Frames (ORFs), queC, queD and queE. The absence of the key gene queF encoding 7-cyano-7-deazaguanine reductase catalyzing PreQ0 base to PreQ1 base suggested that the strain only has the capacity of accumulation of PreQ0 base as a metabolite, consistent with our observation in chemical identification.

The malignance of cancers reinforces the need to find potent antineoplastic agents. In the past decades, proteasome has been witnessed as a potential target to fulfil this purpose, as evidenced by the fact that the first-in-class proteasome inhibitor Bortezomib was marketed in 2003. Marizomib (Salinosporamide A, NPI-0052), as a marine natural product, promises to be of high efficacy against multiple myeloma (MM), relapsed/refractory MM and other types of solid tumours. Compared with Bortezomib, it arguably has fewer severe side effects. Marizomib has been termed as orphan drug against multiple myeloma by US Food and Drug Administration (FDA) in 2013 and by European Medicines Agency (EMA) in 2014. As one of the second generation proteasome inhibitors (PIs), Marizomib is expected to bring about a sustained and complete therapeutic to extend cancer patients' life span. In this article, we intended to briefly review the historical developments, mechanisms, pharmacology, biosynthesis and side effects of this agent, aiming to provide concise coverage for a broad readership. In the end, we proposed our perspective for its futuristic applications.

Immune Checkpoint Inhibitors for Non-small-cell Lung Cancer: Does that Represent a ‘New Frontier’? by Sara Pilotto, Stefania Kinspergher, Umberto Peretti, Anna Calio, Luisa Carbognin, Roberto Ferrara, Matteo Brunelli, Marco Chilosi, Giampaolo Tortora, Emilio Bria (307-313).
Advances in the interpretation and understanding of cancer behaviour, particularly of its ability to evade the host immunosurveillance, deregulating the balance between inhibitory and stimulatory factors, led to the development of an innovative category of immunotherapeutic agents, currently under investigation. Although the disappointing data deriving from the employment of vaccines in non-small cell lung cancer (NSCLC), more promising results have been obtained in the early phase trials with immune checkpoint inhibitors, such as cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4), programmed cell death protein-1 (PD-1) and programmed death-ligand 1 (PD-L1) inhibitors. This review delineates the main features of the available immunotherapeutic agents, focusing the discussion on immune checkpoint inhibitors, those that have already demonstrated a relevant clinical activity (such as Ipilimumab and Nivolumab) and those molecules still in early development phase. Moreover, we underline the possible emerging issues deriving from the progressive diffusion of Immuno-Oncology into the standard clinical practice. The careful and accurate identification and management of immune-related toxicities, the validation of more reliable immune response criteria and the increasing research of potential predictive biomarkers are key points of discussion. The perspective is that immunotherapy might represent an effective 'magic bullet', able to change the treatment paradigm of NSCLC, particularly of those subgroups featured by a heavily mutant cancer (squamous histology and smokers), where the immunologic agents contribute in cancer development and progression seems to be strong and, concurrently, the efficacy of standard therapies particularly limited.

Review of Procedures Used for the Extraction of Anti-Cancer Compounds from Tropical Plants by Saurabh Pandey, Paul N. Shaw, Amitha K. Hewavitharana (314-326).
Tropical plants are important sources of anti-cancer lead molecules. According to the US National Cancer Institute, out of the 3000 plants identified as active against cancer using in vitro studies, 70% are of tropical origin. The extraction of bioactive compounds from the plant materials is a fundamental step whose efficiency is critical for the success of drug discovery efforts. There has been no review published of the extraction procedures of anti-cancer compounds from tropical plants and hence the following is a critical evaluation of such procedures undertaken prior to the use of these compounds in cancer cell line studies, during the last five years. It presents a comprehensive analysis of all approaches taken to extract anti-cancer compounds from various tropical plants. (Databases searched were PubMed, SciFinder, Web of Knowledge, Scopus, Embase and Google Scholar).

Although the amount of progress cancer therapy has made in recent years is commendable, considerable limitations still remain. Most agents preferentially target rapidly proliferating cells, thereby destroying tumorigenic growths. Unfortunately, there are many labile cells in the patient that are also rapidly dividing, ultimately perpetuating significant side effects, including immunosuppression. Cytochalasins are microfilament-directed agents most commonly known for their use in basic research to understand cytoskeletal mechanisms. However, such agents also exhibit profound anticancer activity, as indicated by numerous in vitro and in vivo studies. Cytochalasins appear to preferentially damage malignant cells, as shown by their minimal effects on normal epithelial and immune cells. Further, cytochalasins influence the end stages of mitosis, suggesting that such agents could be combined with microtubule-directed agents to elicit a profound synergistic effect on malignant cells. Therefore, it is likely that cytochalasins could be used to supplement current chemotherapeutic measures to improve efficacy rates, as well as decrease the prevalence of drug resistance in the clinical setting.

Gold Nanoparticle-Lignan Complexes Inhibited MCF-7 Cell Proliferation in vitro: A Novel Conjugation for Cancer Therapy by Filiz Bakar, Mehmet G. Caglayan, Feyyaz Onur, Serpil Nebioglu, Ismail M. Palabiyik (336-344).
Nanoparticles, including gold nanoparticles (AuNP), have been used in imaging in cancer treatment and as therapeutic agents and drug delivery vehicles. Particularly lignans, also called phytoestrogens, have strong effects on the treatment of carcinomas due to their antiestrogenic, antiangiogenic and proapoptotic mechanism. The aim of this study is to investigate the antiproliferative effects of three lignans-AuNP conjugates, pinoresinol (PINO), lariciresinol (LARI) and secoisolariciresinol (SECO), on the MCF-7 cell lines. For this purpose, first, thiolated β -cyclodextrin (β-CD) was synthesized to achieve a surface modification of AuNP, and then the β -CD modified AuNP was characterized using the transmission electron microscopy (TEM), UV-Visible and Nuclear Magnetic Resonance (NMR) spectroscopy. Then, the selected lignans were conjugated to the β-CD-modified AuNP, and the antiproliferative effect of these conjugates was monitored. The results suggest that when compared to their non-conjugated forms, the AuNP-bound lignan conjugates prevented the proliferation of the MCF-7 cells significantly. Therefore, these AuNP-conjugated derivatives can be new candidate agents for breast cancer therapy.

NFκB Pathway and microRNA-9 and -21 are Involved in Sensitivity to the Pterocarpanquinone LQB-118 in Different CML Cell Lines by Fernanda Costas C. de Faria, Maria Eduarda Bento Leal, Paula Sabbo Bernardo, Paulo R.R. Costa, Raquel C. Maia (345-352).
Chronic myeloid leukemia (CML), a myeloproliferative disorder characterized by the BCR-ABL oncoprotein, presents its treatment based on tyrosine kinase inhibitors (TKIs), mainly imatinib. However, despite its clinical success, almost 30% of all CML patients demand alternative therapy. In this context, the development of drugs capable of overcoming TKIs resistance is imperative. The pterocarpanquinone-LQB-118 is a novel compound with anti-tumor effect in CML cells whose mechanism of action is being elucidated. Here, we demonstrate that in two CML cell lines exhibiting different biological characteristics, LQB-118 modulates NF?B subcellular localization, apparently independently of the AKT and MAPK pathways, partially inhibits proteasome activity, and alters the expression of microRNAs -9 and -21.

Isothiouronium Salts Reduce NRAS Expression, Induce Apoptosis and Decrease Invasion of Melanoma Cells by Julia Cisilotto, Misael Ferreira, Fabiola Branco Filippin-Monteiro, Adailton Joao Bortoluzzi, Marcus Mandolesi Sa, Tania Beatriz Creczynski-Pasa (353-362).
Melanoma is a very aggressive type of skin cancer. Mutation in BRAF and NRAS are often found in patients with this disease. Therefore, in recent years the search for new molecules that inhibit these proteins has been intensified. After many years with no new treatments for melanoma, the U.S. Food and Drug Administration (FDA) recently approved vemurafenib. However, many patients have already acquired resistance and have experienced severe side effects. Therefore, this work aims to evaluate a new set of compounds including allylic isothiouronium salts (1, 2 and 3), N-phenyl-substituted analog (4) and isothiosemicarbazide salts (5 and 6) for their potential antimelanoma activity. To this end, viability assay, cell cycle analysis, expression of NRAS and BRAF, as well as migration and invasion assay were performed with different melanoma cell lines. Isothiouronium salts 1-3 presented CC50 (concentration required to reduce the cell number by 50%) in a range of 7-28 ?M. Furthermore, salt 1 significantly decreased the expression of NRAS. However, cells incubated with these salts did not disturb the cell cycle phases; instead, an increase in the number of apoptotic cells was observed. Regarding potential antiinvasion effects, both 1 and 2 prevented cell migration as well as cell invasion. Finally, when salts 1 and 2 were associated with vemurafenib, a marked decrease in cell viability was observed when compared to the compounds incubated alone. Briefly, the salts exhibited interesting results, especially 1, which decreased the expression of NRAS, increased apoptotic cells and, when combined with vemurafenib, resulted in a synergistic effect. Therefore, we intend to test compound 1 in pre-clinical studies.

Dual Induction of Mitochondrial Apoptosis and Senescence in Chronic Myelogenous Leukemia by Myrtucommulone A by Cindy Grandjenette, Michael Schnekenburger, Franck Morceau, Fabienne Mack, Katja Wiechmann, Oliver Werz, Mario Dicato, Marc Diederich (363-373).
Despite recent advances in the treatment of chronic myelogenous leukemia (CML), the development of drug resistance and minimal residual disease remain major challenges for the treatment of CML patients, thus highlighting the need to develop innovative new approaches to improve therapeutic outcome. Myrtucommulone A (MCA) is a nonprenylated acylphloroglucinol isolated from the leaves of myrtle, a plant traditionally used in folk medicine. To date, studies addressing bioactivities of myrtle and its specific components are rare. Here, we investigated the biological effects of MCA, focusing on its anti-leukemic activity. As evidenced by fragmented nuclei after Hoechst/propidium iodide staining and poly (ADP-ribose) polymerase cleavage, MCA induces apoptosis in CML cells through down-regulation of anti-apoptotic proteins. Interestingly, we showed that chronic treatment with MCA at low doses induced senescence in CML cells. Taken together, this study highlights the chemotherapeutical potential of this natural product in human leukemia.

Targeting Mitochondrial Citrate Transport in Breast Cancer Cell Lines by Ali Burak Ozkaya, Handan Ak, Sevcan Atay, Hikmet Hakan Aydin (374-381).
Lipogenesis is considered to be a very important aspect of cancer metabolism and targeting de novo lipid synthesis or related pathways are among novel approaches to treat cancer. Many targets of the pathway including ATPcitrate lyase (ACLY), acetyl-CoA carboxylase and fatty acid synthase have been evaluated for their potential in cancer treatment. However the role of citrate transport protein (CTP), another important component of lipogenesis pathway, is not well known for cancer metabolism and cell survival.
Here we report that while chemical inhibition of CTP reduces cytoplasmic citrate levels and limits breast cancer cell viability effectively, siRNA based inhibition had little effect on both. We also compared the effects of CTP inhibition with ACLY and found that the inhibition of ACLY reduced cytoplasmic citrate levels and limited cell viability more effectively than CTP inhibition. Finally we have demonstrated that neither cell cycle arrest nor autophagy was induced in cells treated with CTP or ACLY siRNA. Inhibitions triggered apoptosis but only slightly. Growth inhibitory effects do not occur in normal mammary epithelial MCF-10A cell line.

Synthesis and Anticancer Activity Evaluation of Some Benzothiazole-Piperazine Derivatives by Enise Ece Gurdal, Ebru Buclulgan, Irem Durmaz, Rengul Cetin-Atalay, Mine Yarim (382-389).
Synthesis, characterization and cytotoxic activities of ten benzothiazole-piperazine derivatives were reported. In vitro cytotoxic activities of compounds were screened against hepatocellular (HUH-7), breast (MCF-7) and colorectal (HCT-116) cancer cell lines by sulphorhodamine B assay. Based on the GI50 values of the compounds, most of the benzothiazole-piperazine derivatives are active against HUH-7, MCF-7 and HCT-116 cancer cell lines. Aroyl substituted compounds 1h and 1j were found to be the most active derivatives. In addition, further investigation of compounds 1h and 1j by Hoechst staining and FACS revealed that these compounds cause apoptosis by cell cycle arrest at subG1 phase.

Effectiveness of Two Novel Anionic and Cationic Platinum Complexes in the Treatment of Osteosarcoma by Kentaro Igarashi, Norio Yamamoto, Katsuhiro Hayashi, Akihiko Takeuchi, Shinji Miwa, Akira Odani, Hiroyuki Tsuchiya (390-399).
Aim: This study aimed to characterize the cellular basis of the platinum cytotoxicity of two novel platinum complexes, 3Pt and 1Pt, in comparison with that of cisplatin. 3Pt comprises anionic phosphate moieties, while 1Pt comprises neutral aromatic ligands.
Methods: We compared the cytotoxic potency of 3Pt and 1Pt with that of cisplatin in osteosarcoma cell lines and an orthotopic mouse model.

Results: The cytotoxic potency of 3Pt was markedly higher than that of cisplatin in all cell lines. Both novel platinum complexes showed a complete lack of cross resistance in cisplatin-resistant cells. Caffeine enhanced the cytotoxic potency of these novel platinum complexes, as observed for cisplatin. Apoptosis after drug administration was observed by DNA ladder formation and an annexin V/PI assay. DNA double-strand breaks were confirmed by phosphorylation of histone H2AX. In vivo, the antitumor activity of 3Pt and 1Pt was superior and similar, respectively, to that of cisplatin. Both novel platinum complexes exerted strong antitumor effects on osteosarcoma in vitro and in vivo.

Conclusions: 3Pt may be an effective drug for the treatment of bone cancer because the PO3 moiety has a high affinity to bone, as exhibited by bisphosphonates, and is expected to decrease the incidence of side effects at extraskeletal sites and overcome drug resistance. Cationic 1Pt may also be an effective antitumor drug because of its unique chemical structure and properties. Further investigations to detail the antitumor effects of these ionic Pt complexes on osteosarcoma are warranted.

Mesenchymal Stromal Cells Uptake and Release Paclitaxel without Reducing its Anticancer Activity by Massimo Mariotti, Renato Colognato, Marco Rimoldi, Manuela Rizzetto, Francesca Sisto, Valentina Cocce, Arianna Bonomi, Eugenio Parati, Giulio Alessandri, Renzo Bagnati, Augusto Pessina (400-405).
To improve the drug delivery efficiency on target cells, many strategies have been developed including Mesenchymal Stromal Cells (MSCs) approaches. In a previous study, we found that bone-marrow-derived MSCs (BM-MSCs) were able to incorporate and release the anti-tumor and anti-angiogenic drug, Paclitaxel (PTX). In this study, we evaluated the stability of PTX in standard cell culture conditions by analyzing the metabolites produced by MSCs after their incorporation of the drug. We are able to show that MSCs do not release either 3-OH-PTX or 6-OH-PTX metabolites (having a lower anticancer activity) but release an active PTX molecule together with the isomer 7-Epitaxol, is known to maintain the whole biological activity. This confirms that the simple procedure of MSCs priming with a drug (without any genetic cell manipulation), in our case PTX, does not modify the activity of the molecule and provides a new biological-device to carry and deliver PTX in tumor sites, by contributing to improve drug efficacy and target selectivity in cancer therapy.