Anti-Cancer Agents in Medicinal Chemistry (Formerly Current Medicinal Chemistry - Anti-Cancer Agents) - Volume 17, Issue 2, 2017

Breast cancer is the most common cancer and the most frequent cause of cancer death among women worldwide. Breast cancer is a complex, heterogeneous disease classified into hormone-receptor-positive, human epidermal growth factor receptor-2 overexpressing (HER2+) and triple-negative breast cancer (TNBC) based on histological features. Endocrine therapy, the mainstay of treatment for hormone-responsive breast cancer involves use of selective estrogen receptor modulators (SERMs), selective estrogen receptor downregulators (SERDs) and aromatase inhibitors (AIs). Agents that target estrogen receptor (ER) and HER2 such as tamoxifen and trastuzumab have been the most extensively used therapeutics for breast cancer. Crosstalk between ER and other signalling networks as well as epigenetic mechanisms have been envisaged to contribute to endocrine therapy resistance. TNBC, a complex, heterogeneous, aggressive form of breast cancer in which the cells do not express ER, progesterone receptor or HER2 is refractory to therapy. Several molecular targets are being explored to target TNBC including androgen receptor, epidermal growth factor receptor (EGFR), poly(ADP-ribose) polymerase (PARP), and vascular endothelial growth factor (VEGF). Receptors, protein tyrosine kinases, phosphatases, proteases, PI3K/Akt signalling pathway, microRNAs (miRs) and long noncoding RNAs (lncRNAs) are potential therapeutic targets. miR-based therapeutic approaches include inhibition of oncomiRs by antisense oligonucleotides, restoration of tumour suppressors using miR mimics, and chemical modification of miRs. The lnRNAs HOTAIR, SPRY4-IT1, GAS5, and PANDAR, new players in tumour development and prognosis may have theranostic applications in breast cancer. Several novel classes of mechanism-based drugs have been designed and synthesised for treatment of breast cancer. Integration of nucleic acid sequencing studies with mass spectrometry-based peptide sequencing and posttranslational modifications as well as rational drug design will provide a more comprehensive understanding of the pathophysiology of breast cancer and help in evolving therapeutic strategies.

It is a longstanding debate whether cancer is one disease or a set of very diverse diseases. The goal of this paper is to suggest strongly that most of (if not all) the hallmarks of cancer could be the consequence of the Warburg‘s effect. As a result of the metabolic impairment of the oxidative phosphorylation, there is a decrease in ATP concentration. To compensate the reduced energy yield, there is massive glucose uptake, anaerobic glycolysis, with an up-regulation of the Pentose Phosphate Pathway resulting in increased biosynthesis leading to increased cell division and local pressure. This increased pressure is responsible for the fractal shape of the tumor, the secretion of collagen by the fibroblasts and plays a critical role in metastatic spread. The massive extrusion of lactic acid contributes to the extracellular acidity and the activation of the immune system. The decreased oxidative phosphorylation leads to impairment in CO2 levels inside and outside the cell, with increased intracellular alkalosis and contribution of carbonic acid to extracellular acidosis-mediated by at least two cancer-associated carbonic anhydrase isoforms. The increased intracellular alkalosis is a strong mitogenic signal, which bypasses most inhibitory signals. Mitochondrial disappearance (such as seen in very aggressive tumors) is a consequence of mitochondrial swelling, itself a result of decreased ATP concentration. The transmembrane pumps, which extrude, from the mitochondria, ions, and water, are ATP-dependant. Therapy aiming at increasing both the number and the efficacy of mitochondria could be very useful.

Photodynamic therapy (PDT) is an alternative cancer treatment to conventional surgery, radiotherapy and chemotherapy. It is based on activating a drug with light that triggers the generation of cytotoxic species that promote tumour cell killing. At present, PDT is mainly used in the treatment of wet age-related macular degeneration, for precancerous conditions of the skin (e.g. actinic keratosis) and in the palliative care of advanced cancers, for instance of the bladder or the oesophagus. PDT is still not used as a first line cancer treatment, which is surprising given the first clinical trials by Dougherty’s group dating back to the 1970’s. PDT has significant advantages over surgery or radiation therapy for low lying tumours due to better cosmetic outcome and localised treatment for the patients. However, despite these advantages and significant developments in optical technology that has enabled light penetration to deeper lying tumours, in excess of 5 cm, a lack of phase III clinical trials has slowed down the uptake of PDT by the healthcare sector as a frontline treatment in cancer. However research continues to demonstrate the potential benefits of PDT and the need to stimulate funding and uptake of clinical studies using next generation photosensitizers offering advanced targeted delivery, improved photodynamic dose combined with modern light delivery technologies. This review surveys the available PDT treatments and emerging novel developments in the field with a particular focus on two-photon techniques that are anticipated to improve the effectiveness of PDT in tissues at depth and on next generation drugs that work without the need of the presence of oxygen for photosensitization making them effective where hypoxia has taken hold.

Epigenetic modifications can affect numerous mechanisms used by neoplastic cells to evade immune control. In melanoma epigenetic defects, caused by dysregulations in the expression of genome writers, erasers, or readers, play a significant role in the reduced expression of molecules required for efficient immune recognition as well as antigen presentation and processing. Alterations in gene expression were identified in tumor-associated antigens (TAAs), human leukocyte antigen (HLA) complex, co-stimulatory/accessory molecules, antigen processing machinery (APM), and NKG2D ligands that have shown to be silenced or down-regulated in melanoma. In agreement with the inherent reversibility of epigenetic silencing, epigenetic drugs such as inhibitors of DNA methyltransferases (DNMTs), histone deacetylases (HDACs), histone methyltransferase enhancer of Zeste homolog 2 (EZH2), and modifiers of microRNA (miRNA) dysregulation or antagomirs can restore the expression of these molecules, favouring the recognition of cancer cells by immune responses, reducing the resistance to Natural Killer (NK) and cytotoxic T cells (CTL), and enhancing the functions of antigen presenting cells. Moreover, inhibitors of reader proteins seem to preferentially affect the NF-kB-induced activation of pro-inflammatory cytokine genes. At present an increasing interest is shown toward new combined therapeutic approaches employing epidrugs or new molecular inhibitors and in vivo immunotherapies, such as vaccines and adoptive T-cell transfer (ACT). This review summarizes the current understanding of the role of epidrugs in the modulation of molecules involved in the melanoma immune response and focuses on their future clinical use in new therapeutic combinations for melanoma treatment.

Background: Due to the high level of argininosuccinate synthase (ASS), a key enzyme for the formation of arginine from citrulline, human breast cancers are often resistant to arginine deprivation therapy. An antimetabolite, Lcanavanine (L-CAV), can be incorporated into proteins in the place of arginine, disturbing protein conformation and leading to cellular death. Objectives: This study was designed to investigate the potential of L-CAV to enhance the toxicity of chemotherapeutic drugs in the human breast cancer cell line MCF-7, and determine the most favorable drug combination to exert synergistic interaction in the presence or absence of arginine in the medium. Methods: Combination experiment based on the median-effect principle and mass-action law was conducted using constant ratios of cytotoxic agents as developed by Chou (2006). Results: We observed that L-CAV enhanced the toxicity of cisplatin (CIS) and vinblastine (VIN) in MCF-7, even in the presence of L-ARG. On the other hand, L-CAV potentiated the toxicity of doxorubicin (DOX), paclitaxel (PTX), 5- fluoruracil (5-FU), and amphotericin-B (AMP-B) in cells grown in arginine deprived media. Conclusion: We conclude that the combination of L-CAV with CIS or VIN can potentiate the toxicity for breast cancer cells. Thus this report presents a new possibility for treating human breast cancers known to be resistant to arginine deprivation. This initial study requires further investigation in in vivo experiments and exploration of the molecular mechanism of cellular response in human breast cancer.

Background: The RAPTA-EA1 complex [ruthenium(II)-arene 1,3,5-triaza-7-phosphaadamantane (pta) complex with an arene-tethered ethacrynic acid ligand] has been reported to overcome drug resistance that developed due to the current use of platinum-based treatments. However, the exact mechanism of action of RAPTA-EA1 remains largely unexplored and unknown. Objective: Here we have further studied the effect of RAPTA-EA1 on BRCA1-defective HCC1937 breast cancer cells and compared its effects on BRCA1-competent MCF-7 breast cancer cells. Method: HCC1937 and MCF-7 breast cancer cells were treated with the RAPTA-EA1 complex. The cytotoxicity of ruthenium-induced cells was evaluated by a MTT assay. Cellular uptake of ruthenium was determined by ICP-MS. Cell cycle and apoptosis were assessed using a flow cytometer. Expression of BRCA1 mRNA and its encoded protein was quantitated by a real-time RT-PCR and Western blotting. Results: Differences in cytotoxicity were correlated with the differential accumulations of ruthenium and the induction of apoptosis. The ruthenium complex caused dramatically more damage to the BRCA1 gene in the BRCA1-defective HCC1937 cells than to the BRCA1-competent MCF-7 cells. It decreased the expression of BRCA1 mRNA in the BRCA1-competent cells, while in contrast, its expression increased in the BRCA1-defective cells. However, the expression of the BRCA1 protein was significantly reduced in both types of breast cancer cells. Conclusion: The results presented here have demonstrated a differential cellular response for the BRCA1-defective and BRCA1-competent breast cancer cells to RAPTA-EA1. These findings have provided more insight into the actions and development of the ruthenium-based compounds for use for the treatment of breast cancer.

Background: Lectins are carbohydrate-binding proteins that exhibit remarkable antitumor activities by inducing apoptotic or autophagic cell death. However, the relationship between apoptosis and autophagy induced by lectins has rarely been reported. Agrocybe aegerita lectin (AAL), a lectin isolated from the fungus Agrocybe aegerita, exerts antitumor activity through apoptosis. Objective: To study the relationship between the autophagy and apoptosis induced by AAL in hepatocellular carcinoma (HCC) cells, and then to promote the antitumor effect of AAL. Method: AAL was evaluateted using the CCK-8 kit and the trypan blue assay. Cell autophagy was studied using western blotting, acridine orange straining, transmission electron microscopy, and transient transfection of pEGFPLC3 plasmids. We also evaluated AAL-induced autophagy in Caenorhabditis elegans. Apoptosis was studied using flow cytometry. We also identified the antitumor effects of co-treatment of AAL with chloroquine (CQ) in vitro and in vivo. Results: AAL-treated cell lines showed accumulation of microtubule-associated protein light chain 3 II (LC3-II), formation of EGFP-LC3 puncta and acidic autophagic vacuoles (AVOs), and the induction of autophagosomes. Inhibition of autophagy could enhance apoptosis induced by AAL in HCC cells. Furthermore, co-therapy (AAL and chloroquine) promote antitumor effect of AAL in a murine in situ HCC model. Conclusion: Our findings suggest that inhibition of autophagy exerts a synergistic effect on the antitumor activity of AAL and may be a helpful strategy for reducing the dosage of lectin used in antitumor therapy. The autophagy inhibitor may be a synergist of certain antitumor drugs that can induce both apoptosis and autophagy.

Background: Microtubules act as a useful and strategic molecular target for various anticancer drugs that binds to its distinct sites in tubulin subunits and inhibits its polymerization and ultimately leads to cell death. Moreover, numerous reports highlight the cytotoxic effects of constraint Combretastatin analogs and thiazolidinone derivatives. Objective: Therefore, the present study investigates the potential of thiazolidinone constraint combretastatin analogs as tubulin inhibitors. Method: By incorporating silica supported fluroboric acid, a series of thiazolidinone constraint combretastatin analogs were synthesized in a microwave reactor under solvent free conditions. To optimize the reaction conditions, the detailed investigation was done for the catalytic influence of HBF4-SiO2. All the synthesized analogs were assessed for in-vitro cytotoxicity against THP-1, COLO-205, HCT-116 and A-549 human cancer cell lines. Top hits were further examined for their tubulin polymerization inhibition and their effect on microtubule assembly. The significant cytotoxicity and tubulin polymerization inhibition of the most potent structure was further rationalized by molecular modelling studies. Results: The results stated that CS-2, CS-3 and CS-20 possessed significant cytotoxic potential with the IC50 values ranging from 1.21 to 5.50 μM against THP-1, COLO-205, HCT-116 human cancer cell lines. Established structure activity relationship revealed that the nature of Ring A substantially influences the cytotoxic potential of the compounds. Placement of methoxy substituents on the phenyl ring (Ring A) was found to be the most preferred structural feature. Compound CS-2 was found to considerably inhibit the tubulin polymerization (IC50 value 2.12 μM) and caused disruption of microtubule assembly as demonstrated by immunoflourescence technique. In molecular modelling studies, CS-2 exhibited various hydrophobic as well as hydrogen bonding interactions at colchicine binding site and was found to be stabilized in this cavity. Conclusion: This work provides an efficient methodology for the synthesis of antitubulin thiazolodinonecombretastatin hybrids.

A total of 16 targeted NO-releasing betulinic acid (BA) derivatives were designed and synthesized as potential anticancer agents. Most IC50 values were under 1.0 μM in vitro test against HepG2 and B16. The result suggested that derivatives of BA with α,β-unsaturated ketone skeleton possessed significant cytotoxic activities than the others, among which derivatives with three carbons in diol linker (15b and 15c) exhibited the highest anti-cancer activity. NO-releasing amount detection of partial target compounds suggested that NO-releasing amount of this series of BA derivatives positively correlates with their cytotoxic activities. The anti-angiogenic activity of partial target compounds on zebrafish embryos in our experiment did not show any effects on the SIVs, however, they exhibited different influence on ISVs, with only 15a and 15d better than the negative control.

Enzymatic activity from tumor and adjacent normal tissue of 200 patients involving deoxycytidine kinase (dCK), uridine/cytidine kinase (U/CK), cytidine deaminase (CD) and deoxycytidylate deaminase (dCMPD) was quantified. Patients with brain (17), colon (24), and breast (30) tumors, 53, 67, and 73%, respectively, had an elevated T/N value (Specific Activity of tumor/ Specific Activity of normal tissue) involving dCK and dCMPD suggesting chemotherapy with 5-fluorodeoxycytidine (5-FdC) alone or in combination with thymidine plus deoxytetrahydrouridine, or with the radiosensitizer, 5-chlorodeoxycytidine (5-CldC) plus tetrahydrouridine (H4U). Among patients with colon (19) and pancreatic tumors (40), 53 and 68 %, respectively, displayed T/N values >4 for CD suggesting chemotherapy with 5-FdC, 4-N-methylamino-5-FdC, 5-trifluoromethyldeoxycytidine and radiosensitization with 5- CldC, 4-N-methylamino-5-CldC, 5-iododeoxycytidine and 5-bromodeoxycytidine. The percent of patients with tumors with a T/N value >4 for U/CK in lung (72), colon (23) and breast (28) was 47, 61 and 68, respectively, suggesting zebularine (plus thymidine) treatment for tumors involving gene silencing. Evidence is presented that the 4-N-alkylamino-dC substituted nucleosides and those with large 5-substitutions are activated only via CD to thymidine kinase (TK) using end–points of cytotoxicity and/or radiosensitization: H4U, the inhibitor of CD is an antagonist, cells with low CD or no TK are resistant to the analogs, the end points are indifferent to the dCK status of cells, they are poor substrates for dCK and good substrates for CD, whereas 5-FdC and 5-CldC are good substrates for both enzymes. The analogs present opportunities for Collateral Sensitivity for 5-azacytidine and gemcitabine resistant tumors.

Background: Bruton’s Tyrosine Kinase (BTK) is a one of the Tec tyrosine kinase family. It has an essential role in B-cell development and function. Activation of BTK has been associated with the pathogenesis of many types of lymphomas and leukemia, and involved in non-life threatening autoimmune diseases. Objective: In this study, exhaustive pharmacophore modeling was combined with QSAR analyses to examine the structural requirements for anti-BTK activities. Method: Genetic function algorithm (GFA) was coupled with multiple linear regression (MLR) analysis to select the best combinations of physicochemical descriptors and pharmacophoric hypothesis capable of generating predictive and self-consistent QSAR models. The optimum pharmacophores were decorated with exclusion volumes to improve their receiver operating characteristic (ROC) curve properties. The best predictive QSAR model and its corresponding pharmacophore models were validated by discovering of novel promising BTK inhibitors retrieved from the National Cancer Institute (NCI) database. Results: Several potent hits exhibited anti-proliferative activities on U-937 cell-line in low micromolar IC50, and one active compound showed nontoxic activities on normal fibroblast cell line. Conclusion: Our efforts culminated in the identification of potent BTK ligands having desired inhibitory activities and structurally distinct from known active reference compounds (i.e., training compounds) and represent new chemotypes.

Background: Coumarins are naturally occurring plant metabolites and several synthetic coumarin analogues are known for their various pharmacological properties such as anticoagulant, antimicrobial, anticancer, antioxidant, anti-inflammatory and antiviral properties. Objective; Keeping this promising pharmacological properties in mind, in the present investigation, mono/dihalogenated coumarin analogues CMRN1-CMRN7 have been synthesized and evaluated for their anticancer activity. Method: The cytotoxicity potential of the test compounds was evaluated against UACC-62, MCF-7 and PBM (Peripheral Blood Mononuclear) cell lines using MTT assay. The apoptotic potential of the coumarin compounds was evaluated against UACC-62 cell by assessing membrane change, mitochondria membrane potential, pro-apoptotic changes were investigated using the AnnexinV-PI staining, JC-1, caspase-3 enzyme kits respectively on flow cytometer. Results: The test compounds CMRN1, CMRN2, CMRN4 and CMRN5 have strongly suppressed the cell proliferation of UACC-62 and MCF-7 cancer cell lines. Furthermore the test compounds CMRN1, CMRN2, CMRN4 and CMRN5 exerted antiproliferative effects through apoptosis induction against UACC-62. Conclusion: Compounds CMRN1, CMRN2, CMRN4 and CMRN5 can be considered as lead compounds to arrive at a promising anticancer agents.

Background: Hepatocellular carcinoma (HCC) is related to chronic liver inflammation. M2 polarization of tumor-associated macrophages (TAMs) in the tumor microenvironment promotes liver cancer stem-like cell (LCSLC) self-renewal capability and carcinogenicity. Therefore, reversing M2 polarization of TAMs could be an effective approach to cure HCC. Objective: To evaluate whether 8-bromo-7-methoxychrysin (BrMC) has an effect on M2 polarization of TAMs. Method: LCSLC and conditional medium were obtained by sphere forming assay. Identification of LCSLC were analyzed by sphere forming, wound-healing and invasion assay. TAM and effects of BrMC on it were validated by immunofluorescence staining, ELISA and griess assay. Expressions of cancer stem cell and macrophage marker were analyzed by western blotting. Results: Our results showed that BrMC significantly suppressed the expression of the M2 macrophage marker CD163. Furthermore, BrMC influenced the secretion profile of cytokines of TAMs. Mechanistically, BrMC reversed M2 polarization of TAMs due to inhibition of NF-ΚB activation. Conclusion: BrMC may be a potentially novel flavonoid agent that can be applied for disrupting the interaction of LCSLCs and TAMs.

Background: A novel formulation for cabazitaxel loaded HSA nanoparticle (Cbz-NPs) with non-crosslinking agent participation was reported in this study. Objective: A simple method through unfolding of HSA self-assembling nanoparticle for cabazitaxel (Cbz) overcomes the drawbacks of Cbz with high toxicity, poor solubility and low tissue specificity, and avoids side effects of polysorbate 80 which is commonly used for dissolving Cbz. Method: The optimum condition was obtained by Response surface methodology (RSM). The NPs were analyzed by differential scanning calorimetry (DSC) and drug release in vitro was also determined. Furthermore, cytotoxicity, cellular uptake were assessed. Results: The experimental encapsulation efficacy (EE) is 52.95%, which is close to the predicted value of 62.44%, indicating the correct prediction, and the nanoscale-sized particles enhanced permeability and retention (EPR) effect. Differential scanning calorimetry (DSC) demonstrates an amorphous state of cabazitaxel-NPs, and a sustained release was found in vitro drug release. Human prostate cancer lines PC3 and Human Lung Cancer line A549 were employed for cytotoxicity study by the MTT test. Single solvent with polysorbate 80 showed serious cytotoxicity with the cell viability of only 80% while no toxicity was found in drug-free nanoparticles. Fluorescence intensity of FITC-HSA nanoparticles encapsulating Cbz increased with the incubation time. The cellular localizatiton of cabazitaxel-NPs was observed by confocal microscopy. Conclusion: Cbz-NPs may be considered as a viable opportunity for anticancer drug delivery.

Background: Topical chemotherapy of skin cancers is a promising strategy for reduction of side effects and for improvement of patient compliance. The combination of the chemotherapeutic 5-fluouracil (5-FU) and the anti- EGFR antibody cetuximab is a strategy to inhibit tumor growth. Their skin penetration, however, is hampered by their high hydrophilicity, which could be improved by encapsulation in delivery systems. Furthermore, it is a challenge to encapsulate hydrophilic drugs. The conjugation of an antibody to a liposome, maintaining its activity, is also a difficult task. Objective: Thus, we aimed to develop 5-FU liposomes and cetuximab-conjugated liposomes (immunoliposomes) of 5- FU to improve drug cytotoxicity against skin cancer cells. Method: We characterized them by particle size, zeta potential, loading efficiency and antibody integrity. To optimize the loading efficiency of 5-FU, a series of liposomes were prepared, using different methods and drug-to-lipid ratios. Results: Liposomes containing DSPC and Chol at drug-to-lipid ratio 0.1 prepared by the thin lipid hydration method resulted in the best 5-FU encapsulation and were chosen to conjugate with cetuximab. Cetuximab was directly coupled to preformed liposomes using DSPE-mPEG2000-Mal as an anchor. In A431 skin carcinoma cells, at 72 h, 5-FU liposomes showed a 5-fold lower IC50 than 5-FU solution. Additionally, 5-FU immunoliposomes resulted in a 4-fold lower cetuximab IC50 than cetuximab solution, demonstrating synergism with a combination index lower than 1 and potential to improve 5-FU and cetuximab cytotoxicity. Conclusion: Liposomes and immunoliposomes containing 5-FU were developed and cetuximab remained active as demonstrated in cell culture studies.