Novel cis-restricted β-lactam combretastatin A-4 analogues display anti-vascular and anti-metastatic properties in vitro

Antiangiogenic activity of the penicillin derivative TAP7f in melanoma

Previously , we demonstrated that the non-antibiotic penicillin derivative TAP7f inhibited melanoma metastasis in vitro and in vivo through the downregulation of β-catenin and integrin αVβ3. As angiogenesis is required for tumor growth and metastasis, we decided to explore the possible antiangiogenic effect of TAP7f. We found that TAP7f inhibited proliferation, migration, tube formation, and actin cytoskeleton organization of human endothelial cells. In a gel plug assay, an in vivo model for angiogenesis, TAP7f also blocked vascular formation induced by fibroblast growth factor 2. Furthermore, when murine B16-F10 melanoma cells pre-treated with TAP7f were injected intradermally in mice, we observed a decrease in the number and thickness of the capillaries surrounding the tumor. Additionally, TAP7f downregulated vascular endothelial growth factor (VEGF) and platelet-derived growth factor-B (PDGF-B) expression in B16-F10 cells and VEGF receptor expression in HMEC-1 endothelial cells. When the antitumor effect of TAP7f was studied in C57BL/6 J mice challenged with B16-F10 melanoma cells, a significant reduction of tumor growth was observed. Furthermore, a decreased expression of VEGF, PDGF-B, and the endothelial cell marker CD34 was observed in tumors from TAP7f-treated mice. Together, our results suggest that the antiangiogenic activity of TAP7f contributes to its antitumor and antimetastatic action and positions this penicillin derivative as an alternative or complementary agent for the treatment of melanoma. KEY MESSAGES: • TAP7f inhibits proliferation, migration, tube formation, and actin cytoskeleton organization of endothelial cells. • TAP7f downregulates VEGF receptor expression in endothelial cells. • TAP7f downregulates VEGF and PDGF expression in melanoma cells. • TAP7f inhibits angiogenesis in vivo.

Synthesis and Antiproliferative Evaluation of 3-Chloroazetidin-2-ones with Antimitotic Activity: Heterocyclic Bridged Analogues of Combretastatin A-4

Antimitotic drugs that target tubulin are among the most widely used chemotherapeutic agents; however, the development of multidrug resistance has limited their clinical activity. We report the synthesis and biological properties of a series of novel 3-chloro-β-lactams and 3,3-dichloro-β-lactams (2-azetidinones) that are structurally related to the tubulin polymerisation inhibitor and vascular targeting agent, Combretastatin A-4. These compounds were evaluated as potential tubulin polymerisation inhibitors and for their antiproliferative effects in breast cancer cells. A number of the compounds showed potent activity in MCF-7 breast cancer cells, e.g., compound 10n (3-chloro-4-(3-hydroxy-4-methoxy-phenyl)-1-(3,4,5-trimethoxyphenyl)azetidin-2-one) and compound 11n (3,3-dichloro-4-(3-hydroxy-4-methoxyphenyl)-1-(3,4,5-trimethoxyphenyl)-azetidin-2-one), with IC₅₀ values of 17 and 31 nM, respectively, and displayed comparable cellular effects to those of Combretastatin A-4. Compound 10n demonstrated minimal cytotoxicity against non-tumorigenic HEK-293T cells and inhibited the in vitro polymerisation of tubulin with significant G₂/M phase cell cycle arrest. Immunofluorescence staining of MCF-7 cells confirmed that β-lactam 10n caused a mitotic catastrophe by targeting tubulin. In addition, compound 10n promoted apoptosis by regulating the expression of pro-apoptotic protein BAX and anti-apoptotic proteins Bcl-2 and Mcl-1. Molecular docking was used to explore the potential molecular interactions between novel 3-chloro-β-lactams and the amino acid residues of the colchicine binding active site cavity of β-tubulin. Collectively, these results suggest that 3-chloro-2-azetidinones, such as compound 10n, could be promising lead compounds for further clinical anti-cancer drug development.

Combretastatins: An Overview of Structure, Probable Mechanisms of Action and Potential Applications

Combretastatins are a class of closely related stilbenes (combretastatins A), dihydrostilbenes (combretastatins B), phenanthrenes (combretastatins C) and macrocyclic lactones (combretastatins D) found in the bark of Combretum caffrum (Eckl. & Zeyh.) Kuntze, commonly known as the South African bush willow. Some of the compounds in this series have been shown to be among the most potent antitubulin agents known. Due to their structural simplicity many analogs have also been synthesized. Combretastatin A4 phosphate is the most frequently tested compounds in preclinical and clinical trials. It is a water-soluble prodrug that the body can rapidly metabolize to combretastatin A4, which exhibits anti-tumor properties. In addition, in vitro and in vivo studies on combretastatins have determined that these compounds also have antioxidant, anti-inflammatory and antimicrobial effects. Nano-based formulations of natural or synthetic active agents such as combretastatin A4 phosphate exhibit several clear advantages, including improved low water solubility, prolonged circulation, drug targeting properties, enhanced efficiency, as well as fewer side effects. In this review, a synopsis of the recent literature exploring the combretastatins, their potential effects and nanoformulations as lead compounds in clinical applications is provided.

Recent Advances in β-lactam Derivatives as Potential Anticancer Agents

Cancer, accounts for around 10 million deaths annually, is the second leading cause of death globally. The continuous emergency of drug-resistant cancers and the low specificity of anticancer agents are the main challenges in the control and eradication of cancers, so it is imperative to develop novel anticancer agents. Immense efforts have been made in developing new lead compounds and novel chemotherapeutic strategies for the treatment of various forms of cancers in recent years. β-Lactam derivatives constitute versatile and attractive scaffolds for the drug discovery since these kinds of compounds possess a variety of pharmacological properties, and some of them exhibited promising potency against both drug-sensitive and drug-resistant cancer cell lines. Thus, β-lactam moiety is a useful template for the development of novel anticancer agents. This review will provide an overview of β-lactam derivatives with the potential therapeutic application for the treatment of cancers covering articles published between 2000 and 2020. The mechanisms of action, the critical aspects of design and structureactivity relationships are also discussed.

β-Lactams with antiproliferative and antiapoptotic activity in breast and chemoresistant colon cancer cells

A series of novel 1,4-diaryl-2-azetidinone analogues of combretastatin A-4 (CA-4) have been designed, synthesised and evaluated in vitro for antiproliferative activity, antiapoptotic activity and inhibition of tubulin polymerisation. Glucuronidation of CA-4 by uridine 5-diphosphoglucuronosyl transferase enzymes (UGTs) has been identified as a mechanism of resistance in cancer cells. Potential sites of ring B glucuronate conjugation are removed by replacing the B ring meta-hydroxy substituent of selected series of β-lactams with alternative substituents e.g. F, Cl, Br, I, CH₃. The 3-phenyl-β-lactam 11 and 3-hydroxy-β-lactam 46 demonstrate improved activity over CA-4 in CA-4 resistant HT-29 colon cancer cells (IC₅₀ = 9 nM and 3 nM respectively compared with IC₅₀ = 4.16 μM for CA-4), while retaining potency in MCF-7 breast cancer cells (IC₅₀ = 17 nM and 22 nM respectively compared with IC₅₀ = for 4 nM for CA-4). Compound 46 binds at the colchicine site of tubulin, and strongly inhibits tubulin assembly at micromolar concentrations comparable to CA-4. In addition, compound 46 induced mitotic arrest at low concentration in both cell lines MCF-7 and HT-29 together with downregulation of expression of antiapoptotic proteins Mcl-1, Bcl-2 and survivin in MCF-7 cells. These novel antiproliferative and antiapoptotic β-lactams are potentially useful scaffolds in the development of tubulin-targeting agents for the treatment of breast cancers and chemoresistant colon cancers.

3-Vinylazetidin-2-Ones: Synthesis, Antiproliferative and Tubulin Destabilizing Activity in MCF-7 and MDA-MB-231 Breast Cancer Cells

Microtubule-targeted drugs are essential chemotherapeutic agents for various types of cancer. A series of 3-vinyl-β-lactams (2-azetidinones) were designed, synthesized and evaluated as potential tubulin polymerization inhibitors, and for their antiproliferative effects in breast cancer cells. These compounds showed potent activity in MCF-7 breast cancer cells with an IC₅₀ value of 8 nM for compound 7s 4-[3-Hydroxy-4-methoxyphenyl]-1-(3,4,5-trimethoxyphenyl)-3-vinylazetidin-2-one) which was comparable to the activity of Combretastatin A-4. Compound 7s had minimal cytotoxicity against both non-tumorigenic HEK-293T cells and murine mammary epithelial cells. The compounds inhibited the polymerisation of tubulin in vitro with an 8.7-fold reduction in tubulin polymerization at 10 μM for compound 7s and were shown to interact at the colchicine-binding site on tubulin, resulting in significant G2/M phase cell cycle arrest. Immunofluorescence staining of MCF-7 cells confirmed that β-lactam 7s is targeting tubulin and resulted in mitotic catastrophe. A docking simulation indicated potential binding conformations for the 3-vinyl-β-lactam 7s in the colchicine domain of tubulin. These compounds are promising candidates for development as antiproiferative microtubule-disrupting agents.

Harnessing the Properties of Natural Products

Natural products (NPs) have been used as traditional medicines since antiquity. With more than 10⁶⁰ estimated compounds with molecular weights less than 500 Da representing chemical space, NPs occupy a very small percentage; however, they are significantly overrepresented in biologically relevant chemical space. The classical approach concentrates on identifying one or more NPs with biological activity from a source organism. There is much more to be learned from NPs than we can discover this narrow view. In this review, we discuss ways to harness the global properties of NPs.

Current Management Strategies in Breast Cancer by Targeting Key Altered Molecular Players

Breast cancer is the second largest disease affecting women worldwide. It remains the most frequently reported and leading cause of death among women in both developed and developing countries. Tamoxifen and raloxifene are commonly used selective estrogen receptor modulators for treatment of breast cancer in women with high risk, although resistance occurs by tamoxifen after 5 years of therapy and both drugs cause uterine cancer and thromboembolic events. Aromatase inhibitors (AIs) are one of the optional modes used for breast cancer treatment. The combination of AIs along with tamoxifen can also be beneficial. Various therapeutic agents from different sources are being studied, which further need to be improved for potential outcome. For this, clinical trials based on large number of patients with optimal dose and lesser side effects have to be more in practice. Despite the clinical trials going on, there is need of better molecular models, which can identify high risk population, new agents with better benefit having less side effects, and improved biomarkers for treating breast cancer.

Effect of CPU-XT-008, a combretastatin A-4 analogue, on the proliferation, apoptosis and expression of vascular endothelial growth factor and basic fibroblast growth factor in human umbilical vein endothelial cells

The present study investigated the effect of the combretastatin A-4 analogue CPU-XT-008 on the proliferation, apoptosis and expression of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (FGF-2) in human umbilical vein endothelial cells (HUVECs). The proliferation capacity of HUVECs was analyzed with a cell viability assay, while their apoptosis and migration abilities were evaluated via flow cytometry and monolayer denudation assay, respectively. The mRNA and protein expression levels of VEGF and FGF-2 in these cells were determined by reverse transcription-polymerase chain reaction, and cell-based ELISA, western blotting and immunocytochemistry, respectively. The results demonstrated that CPU-XT-008 inhibited proliferation and migration, and induced apoptosis in HUVECs in a dose-dependent manner. In addition, CPU-XT-008 downregulated the mRNA and protein expression levels of VEGF and FGF-2 in these cells. These findings suggest that CPU-XT-008 exerts anti-angiogenic effects in HUVECs, which may explain the inhibition of cell proliferation and migration, induction of apoptosis, and reduction in the mRNA and protein expression levels of VEGF and FGF-2 observed in the present study.

Novel Etoposide Analogue Modulates Expression of Angiogenesis Associated microRNAs and Regulates Cell Proliferation by Targeting STAT3 in Breast Cancer

Tumor microenvironment play role in angiogenesis and carcinogenesis. Etoposide, a known topoisomerase II inhibitor induces DNA damage resulting in cell cycle arrest. We developed a novel Etoposide analogue, Quinazolino-4β-amidopodophyllotoxin (C-10) that show better efficacy in regulating cell proliferation and angiogenesis. We evaluated its role on expression of microRNAs-15, 16, 17 and 221 and its targets Bcl-2, STAT3 and VEGF that dictate cell proliferation and angiogenesis. Docking studies clearly demonstrated the binding of Etoposide and C-10 to STAT3. We conclude that combination of Etoposide or C-10 with miR-15, 16, 17 and 221 as a new approach to induce apoptosis and control angiogenesis in breast cancer.

Combretastatins: more than just vascular targeting agents?

Several prodrugs of the naturally occurring combretastatins have undergone extensive clinical evaluation as vascular targeting agents (VTAs). Their increased selectivity toward endothelial cells together with their innate ability to rapidly induce vascular shutdown and inhibit tumor growth at doses up to 10-fold less than the maximum tolerated dose led to the clinical evaluation of combretastatins as VTAs. Tubulin is well established as the molecular target of the combretastatins and the vast majority of its synthetic derivatives. Furthermore, tubulin is a highly validated molecular target of many direct anticancer agents routinely used as front-line chemotherapeutics. The unique vascular targeting properties of the combretastatins have somewhat overshadowed their development as direct anticancer agents and the delineation of the various cell death pathways and anticancer properties associated with such chemotherapeutics. Moreover, the ongoing clinical trial of OXi4503 (combretastatin-A1 diphosphate) together with preliminary preclinical evaluation for the treatment of refractory acute myelogenous leukemia has successfully highlighted both the indirect and direct anticancer properties of combretastatins. In this review, we discuss the development of the combretastatins from nature to the clinic. The various mechanisms underlying combretastatin-induced cell cycle arrest, mitotic catastrophe, cell death, and survival are also reviewed in an attempt to further enhance the clinical prospects of this unique class of VTAs.

Insights into drug discovery from natural products through structural modification

Natural products (NPs) have played a key role in drug discovery and are still a prolific source of novel lead compounds or pharmacophores for medicinal chemistry. Pharmacological activity and druggability are two indispensable components advancing NPs from leads to drugs. Although naturally active substances are usually good lead compounds, most of them can hardly satisfy the demands for druggability. Hence, these structural phenotypes have to be modified and optimized to overcome existing deficiencies and shortcomings. This review illustrates druggability optimization of NPs through structural modification with some successful examples.

Combretastatin (CA)-4 and its novel analogue CA-432 impair T-cell migration through the Rho/ROCK signalling pathway

The capacity of T-lymphocytes to migrate and localise in tissues is important in their protective function against infectious agents, however, the ability of these cells to infiltrate the tumour microenvironment is a major contributing factor in the development of cancer. T-cell migration requires ligand (ICAM-1)/integrin (LFA-1) interaction, activating intracellular signalling pathways which result in a distinct polarised morphology, with an actin-rich lamellipodium and microtubule (MT)-rich uropod. Combretastatin (CA)-4 is a MT-destabilising agent that possesses potent anti-tumour properties. In this study, the effect of CA-4 and its novel analogue CA-432 on human T-cell migration was assessed. Cellular pretreatment with either of CA compounds inhibited the migration and chemotaxis of the T-cell line HuT-78 and primary peripheral blood lymphocyte (PBL) T-cells. This migration-inhibitory effect of CA compounds was due to the disruption of the MT network of T-cells through tubulin depolymerisation, reduced tubulin acetylation and decreased MT stability. In addition, both CA compounds induced the RhoA/RhoA associated kinase (ROCK) signalling pathway, leading to the phosphorylation of myosin light chain (MLC). Furthermore, the siRNA-mediated depletion of GEF-H1, a MT-associated nucleotide exchange factor that activates RhoA upon release from MTs, in T-cells prevented CA-induced phosphorylation of MLC and attenuated the formation of actin-rich membrane protrusions and cell contractility. These results suggest an important role for a GEF-H1/RhoA/ROCK/MLC signalling axis in mediating CA-induced contractility of T-cells. Therapeutic agents that target cytoskeletal proteins and are effective in inhibiting cell migration may open new avenues in the treatment of cancer and metastasis.

Combretastatin A-4 inspired novel 2-aryl-3-arylamino-imidazo-pyridines/pyrazines as tubulin polymerization inhibitors, antimitotic and anticancer agents

Novel 2-aryl-3-arylamino-imidazo-pyridines/pyrazines that exhibit potent tubulin polymerization inhibition, anticancer activity, anti-migration of cancer cells, chromosomal damage, and apoptosis have been developed.