Structure-based design, synthesis and biological testing of etoposide analog epipodophyllotoxin-N-mustard hybrid compounds designed to covalently bind to topoisomerase II and DNA

Synthesis and antiproliferative activities of steroidal lactam conjugates bearing a new nitrogen mustard

Alkylating agents are potent anticancer compounds that exert their anticancer properties through the inhibition of cell replication and transcription leading to cell death. Despite the numerous benefits, these agents also have serious drawbacks such as their high toxicity and low specificity towards cancer cells. As previously reported by our group, conjugation of alkylating agents with azasteroids can reduce their systemic toxicity and enhance their anticancer activity. In this work, novel steroidal alkylating agents bearing POPAM-OH were synthesized and their anticancer efficacy was evaluated in vitro and in vivo. All the novel hybrids demonstrated high antiproliferative effects against 5 different cancer cell lines in the low micromolar range. Treatment of SCID mice bearing SKOV-3 or PC-3 tumor xenografts with the most potent hybrid 19 led to significant reduction of tumor size (tumor inhibition TI = 95% in SKOV3 models and TI = 85.2% in PC3 models). Importantly, the acute toxicity of hybrid 19 (LD₁₀ = 36 μΜ, LD₅₀ = 62 μΜ) in CB17 SCID mice exhibited three-fold decrease compared to the acute toxicity of previously reported hybrids of POPAM-NH₂. This is an important finding since systemic cytotoxicity is a critical limitation of alkylating agents. Collectively, the steroidal conjugates of POPAM-OH displayed significant anticancer efficacy and reduced toxicity in vitro and in vivo rendering them as good candidates for cancer therapy.

In silico study of natural antioxidants

Antioxidants are the body's defense system against the damage of reactive oxygen species, which are usually produced in the body through various physiological processes. There are various sources of these antioxidants such as endogenous antioxidants in the body and exogenous food sources. This chapter provides important information on methods used to investigate antioxidant activity and sources of plant antioxidants. Over the past two decades, numerous studies have demonstrated the importance of in silico research in the development of novel natural and synthesized antioxidants. In silico methods such as quantitative structure-activity relationships (QSAR), pharmacophore, docking, and virtual screenings are play critical roles in designing effective antioxidants that may be synthesized and tested later. This chapter introduces the available in silico approaches for different classes of antioxidants. Many successful applications of in silico methods in the development and design of novel antioxidants are thoroughly discussed. The QSAR, pharmacophore, molecular docking techniques, and virtual screenings process summarized here would help readers to find out the proper mechanism for the interaction between the free radicals and antioxidant compounds. Furthermore, this chapter focuses on introducing new QSAR models in combination with other in silico methods to predict antioxidants activity and design more active antioxidants. In silico studies are essential to explore largely unknown plant tissue, food sources for antioxidant synthesis, as well as saving time and money in such studies.

Have molecular hybrids delivered effective anti-cancer treatments and what should future drug discovery focus on?

INTRODUCTION

Cancer continues to be a big threat and its treatment is a huge challenge among the medical fraternity. Conventional anti-cancer agents are losing their efficiency which highlights the need to introduce new anti-cancer entities for treating this complex disease. A hybrid molecule has a tendency to act through varied modes of action on multiple targets at a given time. Thus, there is the significant scope with hybrid compounds to tackle the existing limitations of cancer chemotherapy.

AREA COVERED

This perspective describes the most significant hybrids that spring hope in the field of cancer chemotherapy. Several hybrids with anti-proliferative/anti-tumor properties currently approved or in clinical development are outlined, along with a description of their mechanism of action and identified drug targets.

EXPERT OPINION

The success of molecular hybridization in cancer chemotherapy is quite evident by the number of molecules entering into clinical trials and/or have entered the drug market over the past decade. Indeed, the recent advancements and co-ordinations in the interface between chemistry, biology, and pharmacology will help further the advancement of hybrid chemotherapeutics in the future.List of abbreviations: Deoxyribonucleic acid, DNA; national cancer institute, NCI; peripheral blood mononuclear cells, PBMC; food and drug administration, FDA; histone deacetylase, HDAC; epidermal growth factor receptor, EGFR; vascular endothelial growth factor receptor, VEGFR; suberoylanilide hydroxamic acid, SAHA; farnesyltransferase inhibitor, FTI; adenosine triphosphate, ATP; Tamoxifen, TAM; selective estrogen receptor modulator, SERM; structure activity relationship, SAR; estrogen receptor, ER; lethal dose, LD; half maximal growth inhibitory concentration, GI₅₀; half maximal inhibitory concentration, IC₅₀.

Design, synthesis and biological evaluation of 1,4-dihydroxyanthraquinone derivatives as anticancer agents

The novel hydroxyanthraquinone derivatives containing nitrogen-mustard and thiophene group were designed to covalently bind to topoisomerase II, and their structures were confirmed by nuclear magnetic resonance and high resolution mass spectrometer technologies in this article. The in vitro cytotoxicity against different cancer cell lines and one normal liver cell line (L02) was evaluated by MTT assay. Compound A1 was the most potent anti-proliferative agent against the human liver cancer HepG-2 cells (IC₅₀ = 12.5 μM), and there is no obvious growth inhibitory effect on normal liver tissue L02 cells. The good cytotoxicity and selectivity of compound A1 suggest that it could be a promising lead for further optimization. The mechanisms of action about compound A1 and A4 were further investigated through analysis of cell apoptosis. Confocal microscopy tracks the location of compound A1 in the cell, which could enter the cytoplasm and nucleus, and induce severe deformation of the nucleus. The docking study demonstrated that A1 could interact with the catalytic active site in topoisomerase II.

Therapeutic Potential of Nitrogen Mustard Based Hybrid Molecules

As medicine advances, cancer is still among one of the major health problems, posing significant threats to human health. New anticancer agents features with novel scaffolds and/or unique mechanisms of action are highly desirable for the treatment of cancers, especially those highly aggressive and drug-resistant ones. Nitrogen mustard has been widely used as an anticancer drug since the discovery of its antitumor effect in the 1942. However, the lack of selectivity to cancer cells restricts the wide usage of a mass of nitrogen mustard agents to achieve further clinical significance. Discovery of antitumor hybrids using nitrogen mustards as key functional groups has exhibited enormous potential in the drug development. Introduction of nitrogen mustards resulted in improvement in the activity, selectivity, targetability, safety, pharmacokinetics and pharmacodynamics properties of corresponding lead compounds or agents. Herein, the recently developed nitrogen mustard based hybrids have been introduced in the cancer therapy.

Paclitaxel and etoposide-loaded Poly (lactic-co-glycolic acid) microspheres fabricated by coaxial electrospraying for dual drug delivery

In this study, we fabricated paclitaxel (PTX) and etoposide (ETP) loaded Poly (lactic-co-glycolic acid) (PLGA) microspheres with core-shell structures and particle sizes ranging from 1 to 4 µm by coaxial electrospraying. The microspheres were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM). The drug loading rate and entrapment efficiency of the microspheres were detected by high performance liquid chromatograph (HPLC). Moreover, the drug release profiles and degradation of drug-loaded PLGA microspheres in vitro were investigated, respectively. The distinct layered structure that existed in the manufactured core-shell microspheres can be observed by TEM. The in vitro release profiles indicated that the PLGA/PTX + ETP (PLGA/PE) microspheres exhibited the controlled release of two drugs in a sequential manner. Cell Counting Kit-8 was used to detect the toxic and side effects of the microspheres on bone tumor cells. PTX and ETP for combination drug therapy loaded microspheres had more cytotoxic effect on saos-2 osteosarcoma cells than the individual drugs. In conclusion, core-shell PLGA microspheres by electrospraying for combination drug therapy is promising for medicine applications, the PLGA/PE microspheres have some potential for osteosarcoma treatment.

The potential of combi-molecules with DNA-damaging function as anticancer agents

DNA-damaging agents, such as methylating agents, chloroethylating agents and platinum-based agents, have been extensively used as anticancer drugs. However, the side effects, high toxicity, lack of selectivity and resistance severely limit their clinical applications. In recent years, a strategy combining a DNA-damaging agent with a bioactive molecule (e.g., enzyme inhibitors) or carrier (e.g., steroid hormone and DNA intercalators) to produce a new 'combi-molecule' with improved efficacy or selectivity has been attempted to overcome these drawbacks. The combi-molecule simultaneously acts on two targets and is expected to possess better potency than the parent compounds. Many studies have shown DNA-damaging combi-molecules exhibiting excellent anticancer activity in vitro and in vivo. This review focuses on the development of combi-molecules, which possess increased DNA-damaging potency, anticancer efficacy and tumor selectivity and reduced side reactions than the parent compounds. The future opportunities and challenges in the discovery of combi-molecules were also discussed.

An overview of molecular hybrids in drug discovery

INTRODUCTION

The hybridization of biologically active molecules is a powerful tool for drug discovery used to target a variety of diseases. It offers the prospect of better drugs for the treatment of a number of illnesses including cancer, malaria, tuberculosis and AIDS. Hybrid drugs can provide combination therapies in a single multi-functional agent and, by doing so, be more specific and powerful than conventional classic treatments. This research field is in great expansion and attracts many researchers worldwide.

AREA COVERED

This review covers the main research published between early 2013 to mid-2015 and takes into account several previous reviews on the subject. Its intention is to showcase the most recent advances reported towards the development of molecular hybrids in drug discovery. Particular attention is given to anticancer hybrids throughout the review.

EXPERT OPINION

Current advances show that molecular hybrids of biologically active molecules can lead to powerful therapeutics. Natural products play a key role in this field. It is also believed that toxin hybrids present a great opportunity for future progress and should be further explored. Furthermore, the synthesis of hybrid organometallics should be systematically studied as it can lead to potent drugs. The crucial requirement for growth still remains the efficacy of synthesis. Hence, the development of efficient synthetic methods allowing rapid access to diverse series of hybrids must be further investigated by researchers.

Mechanisms of Action and Reduced Cardiotoxicity of Pixantrone; a Topoisomerase II Targeting Agent with Cellular Selectivity for the Topoisomerase IIα Isoform

Pixantrone is a new noncardiotoxic aza-anthracenedione anticancer drug structurally related to anthracyclines and anthracenediones, such as doxorubicin and mitoxantrone. Pixantrone is approved in the European Union for the treatment of relapsed or refractory aggressive B cell non-Hodgkin lymphoma. This study was undertaken to investigate both the mechanism(s) of its anticancer activity and its relative lack of cardiotoxicity. Pixantrone targeted DNA topoisomerase IIα as evidenced by its ability to inhibit kinetoplast DNA decatenation; to produce linear double-strand DNA in a pBR322 DNA cleavage assay; to produce DNA double-strand breaks in a cellular phospho-histone γH2AX assay; to form covalent topoisomerase II-DNA complexes in a cellular immunodetection of complex of enzyme-to-DNA assay; and to display cross-resistance in etoposide-resistant K562 cells. Pixantrone produced semiquinone free radicals in an enzymatic reducing system, although not in a cellular system, most likely due to low cellular uptake. Pixantrone was 10- to 12-fold less damaging to neonatal rat myocytes than doxorubicin or mitoxantrone, as measured by lactate dehydrogenase release. Three factors potentially contribute to the reduced cardiotoxicity of pixantrone. First, its lack of binding to iron(III) makes it unable to induce iron-based oxidative stress. Second, its low cellular uptake may limit its ability to produce semiquinone free radicals and redox cycle. Finally, because the β isoform of topoisomerase II predominates in postmitotic cardiomyocytes, and pixantrone is demonstrated in this study to be selective for topoisomerase IIα in stabilizing enzyme-DNA covalent complexes, the attenuated cardiotoxicity of this agent may also be due to its selectivity for targeting topoisomerase IIα over topoisomerase IIβ.

Structure-based design, synthesis and biological testing of piperazine-linked bis-epipodophyllotoxin etoposide analogs

Drugs that target DNA topoisomerase II, such as the epipodophyllotoxin etoposide, are a clinically important class of anticancer agents. A recently published X-ray structure of a ternary complex of etoposide, cleaved DNA and topoisomerase IIβ showed that the two intercalated etoposide molecules in the complex were separated by four DNA base pairs. Thus, using a structure-based design approach, a series of bis-epipodophyllotoxin etoposide analogs with piperazine-containing linkers was designed to simultaneously bind to these two sites. It was hypothesized that two-site binding would produce a more stable cleavage complex, and a more potent anticancer drug. The most potent bis-epipodophyllotoxin, which was 10-fold more growth inhibitory toward human erythroleukemic K562 cells than etoposide, contained a linker with eight methylene groups. All of the mono- and bis-epipodophyllotoxins, in a variety of assays, showed strong evidence that they targeted topoisomerase II. COMPARE analysis of NCI 60-cell GI50 endpoint data was also consistent with these compounds targeting topoisomerase II.

Synthesis of novel aryl dithian valeryl podophyllotoxin ester derivatives as potential antitubulin agents

L4 can cause A549 cell cycle arrest in the G2/M phase potently by disrupting tubulin polymerization.

Cellular mechanisms of the cytotoxicity of the anticancer drug elesclomol and its complex with Cu(II)

The potent anticancer drug elesclomol, which forms an extremely strong complex with copper, is currently undergoing clinical trials. However, its mechanism of action is not well understood. Treatment of human erythroleukemic K562 cells with either elesclomol or Cu(II)-elesclomol caused an immediate halt in cell growth which was followed by a loss of cell viability after several hours. Treatment of K562 cells also resulted in induction of apoptosis as measured by annexin V binding. Elesclomol or Cu(II)-elesclomol treatment caused a G1 cell cycle block in synchronized Chinese hamster ovary cells. Elesclomol and Cu(II)-elesclomol induced DNA double strand breaks in K562 cells, suggesting that they may also have exerted their cytotoxicity by damaging DNA. Cu(II)-elesclomol also weakly inhibited DNA topoisomerase I (5.99.1.2) but was not active against DNA topoisomerase IIα (5.99.1.3). Elesclomol or Cu(II)-elesclomol treatment had little effect on the mitochondrial membrane potential of viable K562 cells. NCI COMPARE analysis showed that Cu(II)-elesclomol exerted its cytotoxicity by mechanisms similar to other cytotoxic copper chelating compounds. Experiments with cross-resistant cell lines overexpressing several ATP-binding cassette (ABC) type efflux transporters showed that neither elesclomol nor Cu(II)-elesclomol were cross-resistant to cells overexpressing either ABCB1 (Pgp) or ABCG2 (BCRP), but that cells overexpressing ABCC1 (MRP1) were slightly cross-resistant. In conclusion, these results showed that elesclomol caused a rapid halt in cell growth, induced apoptosis, and may also have inhibited cell growth, in part, through its ability to damage DNA.