A Synthetic Dolastatin 10 Analogue Suppresses Microtubule Dynamics, Inhibits Cell Proliferation, and Induces Apoptotic Cell Death

Identification of the potential Pan-CDK antagonists: tracing the path of virtual screening and inhibitory activity on lung cancer cells

Cyclin-dependent kinases (CDKs) are overexpressed in tumor cells, and their aberrant activation can promote the progression of non-small-cell lung cancer (NSCLC). We utilized structure-based virtual screening and experimental validation to screen for potential CDKs antagonists among TargetMol natural products. Molecular docking and molecular dynamics simulation results indicate that Dolastatin 10 exhibits strong interactions with multiple subtypes of CDKs (CDK1, CDK2, CDK3, CDK4, and CDK6), forming stable CDKs-Dolastatin 10 complex compounds. Furthermore, in vitro experiments demonstrate that Dolastatin 10 significantly inhibits the viability, migration, and invasion of H1299 cells in a concentration-dependent manner, arresting the cell cycle at the G2/M phase by inducing cell senescence. These findings suggest that Dolastatin 10 may serve as a potential CDKs antagonist deserving further investigation.

Antibody-drug conjugates for targeted cancer therapy: Recent advances in potential payloads

Antibody-drug conjugates (ADCs) represent a promising cancer therapy modality which specifically delivers highly toxic payloads to cancer cells through antigen-specific monoclonal antibodies (mAbs). To date, 15 ADCs have been approved and more than 100 ADC candidates have advanced to clinical trials for the treatment of various cancers. Among these ADCs, microtubule-targeting and DNA-damaging agents are at the forefront of payload development. However, several challenges including toxicity and drug resistance limit the potential of this modality. To tackle these issues, multiple innovative payloads such as immunomodulators and proteolysis targeting chimeras (PROTACs) are incorporated into ADCs to enable multimodal cancer therapy. In this review, we describe the mechanism of ADCs, highlight the importance of ADC payloads and summarize recent progresses of conventional and unconventional ADC payloads, trying to provide an insight into payload diversification as a key step in future ADC development.

CEP41, a ciliopathy-linked centrosomal protein, regulates microtubule assembly and cell proliferation

Centrosomal proteins play pivotal roles in orchestrating microtubule dynamics, and their dysregulation leads to disorders, including cancer and ciliopathies. Understanding the multifaceted roles of centrosomal proteins is vital to comprehend their involvement in disease development. Here, we report novel cellular functions of CEP41, a centrosomal and ciliary protein implicated in Joubert syndrome. We show that CEP41 is an essential microtubule-associated protein with microtubule-stabilizing activity. Purified CEP41 binds to preformed microtubules, promotes microtubule nucleation and suppresses microtubule disassembly. When overexpressed in cultured cells, CEP41 localizes to microtubules and promotes microtubule bundling. Conversely, shRNA-mediated knockdown of CEP41 disrupts the interphase microtubule network and delays microtubule reassembly, emphasizing its role in microtubule organization. Further, we demonstrate that the association of CEP41 with microtubules relies on its conserved rhodanese homology domain (RHOD) and the N-terminal region. Interestingly, a disease-causing mutation in the RHOD domain impairs CEP41-microtubule interaction. Moreover, depletion of CEP41 inhibits cell proliferation and disrupts cell cycle progression, suggesting its potential involvement in cell cycle regulation. These insights into the cellular functions of CEP41 hold promise for unraveling the impact of its mutations in ciliopathies.

Development of QTMP: A promising anticancer agent through NP-Privileged Motif-Driven structural modulation

In this study of creating new molecules from clinical trial agents, an approach of Combretastatin structural modulation with the installation of NP-privileged motifs was considered, and a series of trimethoxyphenyl-2-aminoimidazole with functionalized quinolines and isoquinolines was investigated. An exciting method of quinoline C3-H iodination coupled with imidazopyridine-C3-H arylation and hydrazine-mediated fused-ring cleavage enabled synthesizing a class of compounds with two specific unsymmetric aryl substitutions. Interestingly, three compounds (6, 11, and 13) strongly inhibited HeLa cell proliferation with a half-maximal inhibitory concentration (10-46 nM). Among the compounds, compound 6 (QTMP) showed stronger antiproliferative ability than CA-4 (a clinical trial agent) in various cancer cell lines, including cervical, lung, breast, highly metastatic breast, and melanoma cells. QTMP inhibited the assembly of purified tubulin, depolymerized microtubules of A549 lung carcinoma cells, produced defective spindles, and arrested the cells in the G2/M phase. Further, QTMP binds to the colchicine site in tubulin with a dissociation constant of 5.0 ± 0.6 µM. QTMP displayed higher aqueous stability than CA-4 at 37 °C. Further, in silico analysis of QTMP indicated excellent drug-like properties, including good aqueous solubility, balanced hydrophilicity-lipophilicity, and high GI-absorption ability. The results together suggest that QTMP has anticancer potential.

New opportunities and challenges of natural products research: When target identification meets single-cell multiomics

Natural products, and especially the active ingredients found in traditional Chinese medicine (TCM), have a thousand-year-long history of clinical use and a strong theoretical basis in TCM. As such, traditional remedies provide shortcuts for the development of original new drugs in China, and increasing numbers of natural products are showing great therapeutic potential in various diseases. This paper reviews the molecular mechanisms of action of natural products from different sources used in the treatment of inflammatory diseases and cancer, introduces the methods and newly emerging technologies used to identify and validate the targets of natural active ingredients, enumerates the expansive list of TCM used to treat inflammatory diseases and cancer, and summarizes the patterns of action of emerging technologies such as single-cell multiomics, network pharmacology, and artificial intelligence in the pharmacological studies of natural products to provide insights for the development of innovative natural product-based drugs. Our hope is that we can make use of advances in target identification and single-cell multiomics to obtain a deeper understanding of actions of mechanisms of natural products that will allow innovation and revitalization of TCM and its swift industrialization and internationalization.

Discovery and Development of Dolastatin 10-Derived Antibody Drug Conjugate Anticancer Drugs

Dolastatin 10 is an extremely potent broad-spectrum antitubulin anticancer pentapeptide isolated from Dolabella auricularia. The two-dimensional structure was elucidated by NMR and mass spectrometric analyses. The absolute configuration was determined by a convergent total synthesis. SAR studies established that modifications at C- and N-terminals were tolerated for cytotoxic activity. Human clinical trials of dolastatin 10 and auristatin PE (a C-terminal analog) showed occasional signs of efficacy but failed due to lack of separation of toxicity and efficacy. Nanomolar cytotoxicity helped transition this class of pentapeptides to the next phase of development as antibody drug conjugates (ADCs) by reducing systemic toxicity. Four ADC drugs (Adcetris, Padcev, Polivy, and Blenrep) carrying monomethyl auristatin E (MMAE, vedotin) and monomethyl auristatin F (MMAF, mafodotin) payloads have been approved for treatment of a number of cancers expressing antibody-specific antigens. More than 36 ADCs carrying a variety of pentapeptide analogues are undergoing preclinical and clinical developments. They are being evaluated in more than 200 human trials. A comprehensive review of the discovery, total synthesis of dolastatin 10 and new amino acids, SAR studies of dolastatin 10 and auristatins, conjugations to antibodies, and preclinical and clinical development of ADCs have been presented.

Inhibition of the HIF-1 Survival Pathway as a Strategy to Augment Photodynamic Therapy Efficacy

Photodynamic therapy (PDT) is a non-to-minimally invasive treatment modality that utilizes photoactivatable drugs called photosensitizers to disrupt tumors with locally photoproduced reactive oxygen species (ROS). Photosensitizer activation by light results in hyperoxidative stress and subsequent tumor cell death, vascular shutdown and hypoxia, and an antitumor immune response. However, sublethally afflicted tumor cells initiate several survival mechanisms that account for decreased PDT efficacy. The hypoxia inducible factor 1 (HIF-1) pathway is one of the most effective cell survival pathways that contributes to cell recovery from PDT-induced damage. Several hundred target genes of the HIF-1 heterodimeric complex collectively mediate processes that are involved in tumor cell survival directly and indirectly (e.g., vascularization, glucose metabolism, proliferation, and metastasis). The broad spectrum of biological ramifications culminating from the activation of HIF-1 target genes reflects the importance of HIF-1 in the context of therapeutic recalcitrance. This chapter elaborates on the involvement of HIF-1 in cancer biology, the hypoxic response mechanisms, and the role of HIF-1 in PDT. An overview of inhibitors that either directly or indirectly impede HIF-1-mediated survival signaling is provided. The inhibitors may be used as pharmacological adjuvants in combination with PDT to augment therapeutic efficacy.

Marine-derived pipeline anticancer natural products: a review of their pharmacotherapeutic potential and molecular mechanisms

Background

Cancer is a complex and most widespread disease and its prevalence is increasing worldwide, more in countries that are witnessing urbanization and rapid industrialization changes. Although tremendous progress has been made, the interest in targeting cancer has grown rapidly every year. This review underscores the importance of preventive and therapeutic strategies.

Main text

Natural products (NPs) from various sources including plants have always played a crucial role in cancer treatment. In this growing list, numerous unique secondary metabolites from marine sources have added and gaining attention and became potential players in drug discovery and development for various biomedical applications. Many NPs found in nature that normally contain both pharmacological and biological activity employed in pharmaceutical industry predominantly in anticancer pharmaceuticals because of their enormous range of structure entities with unique functional groups that attract and inspire for the creation of several new drug leads through synthetic chemistry. Although terrestrial medicinal plants have been the focus for the development of NPs, however, in the last three decades, marine origins that include invertebrates, plants, algae, and bacteria have unearthed numerous novel pharmaceutical compounds, generally referred as marine NPs and are evolving continuously as discipline in the molecular targeted drug discovery with the inclusion of advanced screening tools which revolutionized and became the component of antitumor modern research.

Conclusions

This comprehensive review summarizes some important and interesting pipeline marine NPs such as Salinosporamide A, Dolastatin derivatives, Aplidine/plitidepsin (Aplidin®) and Coibamide A, their anticancer properties and describes their mechanisms of action (MoA) with their efficacy and clinical potential as they have attracted interest for potential use in the treatment of various types of cancers.

Antibody-Drug Conjugate Payloads; Study of Auristatin Derivatives

Auristatins are important payloads used in antibody drug conjugates (ADCs), and the most well-known compound family member, monomethyl auristatin (MMAE), is used in two Food and Drug Administration (FDA)-approved ADCs, Adcetris^® and Polivy^®. Multiple other auristatin-based ADCs are currently being evaluated in human clinical trials and further studies on this class of molecule are underway by several academic and industrial research groups. Our group's main focus is to investigate the structure-activity relationships (SAR) of novel auristatins with the goal of applying these to next generation ADCs. Modifications of the auristatin backbone scaffold have been widely reported in the chemical literature focusing on the terminal subunits: P1 (N-terminus) and P5 (C-terminus). Our approach was to modulate the activity and hydrophilic character through modifications of the central subunits P2-P3-P4 and thorough SAR study on the P5 subunit. Novel hydrophilic auristatins were observed to have greater potency in vitro and displayed enhanced in vivo antitumor activity when conjugated via protease-cleavable linkers and delivered intracellularly. Analysis of ADC aggregation also indicated that novel hydrophilic payloads enabled the synthesis of high-drug-to-antibody ratio (DAR) ADCs that were resistant to aggregation. Modification of the central peptide subunits also resulted in auristatins with potent cytotoxic activity in vitro and these azide-modified auristatins contain a handle for linker attachment from the central portion of the auristatin backbone.

A diastereoselective approach to amino alcohols and application for divergent synthesis of dolastatin 10

A diastereoselective approach to obtain amino alcohols through SmI₂-induced radical addition and divergent synthesis of dolastatin 10 are described.

Indibulin dampens microtubule dynamics and produces synergistic antiproliferative effect with vinblastine in MCF-7 cells: Implications in cancer chemotherapy

Indibulin, a synthetic inhibitor of tubulin assembly, has shown promising anticancer activity with a minimal neurotoxicity in preclinical animal studies and in Phase I clinical trials for cancer chemotherapy. Using time-lapse confocal microscopy, we show that indibulin dampens the dynamic instability of individual microtubules in live breast cancer cells. Indibulin treatment also perturbed the localization of end-binding proteins at the growing microtubule ends in MCF-7 cells. Indibulin reduced inter-kinetochoric tension, produced aberrant spindles, activated mitotic checkpoint proteins Mad2 and BubR1, and induced mitotic arrest in MCF-7 cells. Indibulin-treated MCF-7 cells underwent apoptosis-mediated cell death. Further, the combination of indibulin with an anticancer drug vinblastine was found to exert synergistic cytotoxic effects on MCF-7 cells. Interestingly, indibulin displayed a stronger effect on the undifferentiated neuroblastoma (SH-SY5Y) cells than the differentiated neuronal cells. Unlike indibulin, vinblastine and colchicine produced similar depolymerizing effects on microtubules in both differentiated and undifferentiated SH-SY5Y cells. The data indicated a possibility that indibulin may reduce chemotherapy-induced peripheral neuropathy in cancer patients.

Synthesis and Evaluation of Linear and Macrocyclic Dolastatin 10 Analogues Containing Pyrrolidine Ring Modifications

Because of their potent cytotoxic activity, members of the auristatin family (synthetic analogues of the naturally occurring dolastatin 10) have remained a target of significant research, most notably in the context of antibody drug conjugate payloads. Typically, modifications of the backbone scaffold of dolastatin 10 have focused on variations of the N-terminal (P1) and C-terminal (P5) subunits. Scant attention has been paid thus far to the P4 subunit in the scientific literature. In this paper, we introduce an azide functional group at the P4 subunit, resulting in potent cytotoxic activity seen in vitro. Another highly active compound in this study contained azide functional groups in both the P2 and P4 subunits and required dolavaline as the P1 subunit and a phenylalanine as the P5 subunit. Furthermore, these two azide groups served not only as modifiers of cytotoxicity but also as handles for linker attachment or as a tether for use in the synthesis of a macrocyclic analogue.

Antitumour bioactive peptides isolated from marine organisms

Marine organisms are an important source of antitumour active substances. Thus, pharmaceutical research in recent years has focused on exploring new antitumour drugs derived from marine organisms, and, many peptide drugs with strong antitumour activities have been successfully extracted. Based on different mechanisms, this paper reviews the research on several typical antitumour bioactive peptides in marine drugs and the latest progress therein. Additionally, the development prospects for these antitumour bioactive peptide-based drugs are discussed so as to provide a reference for future research in this field.

Synthesis, SAR and biological studies of sugar amino acid-based almiramide analogues: N-methylation leads the way

Leishmaniasis, caused by the protozoan parasites of the genus Leishmania, is one of the most neglected diseases endemic in many continents posing enormous global health threats and therefore the discovery of new antileishmanial compounds is of utmost urgency. The antileishmanial activities of a library of sugar amino acid-based linear lipopeptide analogues were examined with the aim to identify potential drug candidates to treat visceral leishmaniasis. It was found that among the synthesized analogues, most of the permethylated compounds exhibited more activity in in vitro studies against intra-macrophagic amastigotes than the non-methylated analogues. SAR and NMR studies revealed that introduction of the N-methyl groups inhibited the formation of any turn structure in these molecules, which led to their improved activities.

The synthetic diazonamide DZ-2384 has distinct effects on microtubule curvature and dynamics without neurotoxicity

Microtubule-targeting agents (MTAs) are widely used anticancer agents, but toxicities such as neuropathy limit their clinical use. MTAs bind to and alter the stability of microtubules, causing cell death in mitosis. We describe DZ-2384, a preclinical compound that exhibits potent antitumor activity in models of multiple cancer types. It has an unusually high safety margin and lacks neurotoxicity in rats at effective plasma concentrations. DZ-2384 binds the vinca domain of tubulin in a distinct way, imparting structurally and functionally different effects on microtubule dynamics compared to other vinca-binding compounds. X-ray crystallography and electron microscopy studies demonstrate that DZ-2384 causes straightening of curved protofilaments, an effect proposed to favor polymerization of tubulin. Both DZ-2384 and the vinca alkaloid vinorelbine inhibit microtubule growth rate; however, DZ-2384 increases the rescue frequency and preserves the microtubule network in nonmitotic cells and in primary neurons. This differential modulation of tubulin results in a potent MTA therapeutic with enhanced safety.

Anticancer potential of bioactive peptides from animal sources (Review)

Cancer is the most common cause of human death worldwide. Conventional anticancer therapies, including chemotherapy and radiation, are associated with severe side effects and toxicities as well as low specificity. Peptides are rapidly being developed as potential anticancer agents that specifically target cancer cells and are less toxic to normal tissues, thus making them a better alternative for the prevention and management of cancer. Recent research has focused on anticancer peptides from natural animal sources, such as terrestrial mammals, marine animals, amphibians, and animal venoms. However, the mode of action by which bioactive peptides inhibit the proliferation of cancer cells remains unclear. In this review, we present the animal sources from which bioactive peptides with anticancer activity are derived and discuss multiple proposed mechanisms by which these peptides exert cytotoxic effects against cancer cells.

In situ generation of N-unsubstituted imines from alkyl azides and their applications for imine transfer via copper catalysis

Although azides have been widely used in nitrene transfer reactions, in situ generation of N-H imines from azides for downstream transformations has rarely been explored. We report copper-mediated formation of N-unsubstituted aliphatic imines from easily available aliphatic azides using a customized phenanthroline-based ligand (L₁*). Through trapping in situ-generated N-H imines, multisubstituted pyridines or indoles were readily synthesized. ¹³C-labeled azide was used as part of an isotope labeling study, which suggests that the construction of pyridine derivatives involves a three-component dehydrogenative condensation. The construction of 2,3,5-triaryl pyridines using this method provided evidence supporting a proposed pathway involving both imine formation and abnormal Chichibabin pyridine synthesis. The generation of N-unsubstituted imine intermediates was also confirmed by formation of indole derivatives from alkyl azides.

Novel organotin(iv) complexes derived from 4-fluorophenyl-selenoacetic acid: synthesis, characterization and in vitro cytostatic activity evaluation

A cluster of novel organotin(iv) complexes were designed, synthesized, and characterized by elemental analysis, FT-IR, and NMR (¹H, ¹³C, and ¹¹⁹Sn) spectroscopy as well as single-crystal X-ray diffraction.

Intracellular interactions of electrostatically mediated layer-by-layer assembled polyelectrolytes based sorafenib nanoparticles in oral cancer cells

In this paper, we report the preparation of LbL-nanoSraf (100-300nm) comprising of layer-by-layer (LbL) assembled polyelectrolytes dextran-sulfate/poly-l-arginine, with a multikinase inhibitor sorafenib (Sraf) encapsulated calcium carbonate (CaCO3) nanoparticles for oral cancer therapy in vitro. The zeta potential of LbL-nanoSraf exhibited a negative charge of the polyanionic dextran sulfate, which alternated with a positive charge of polycationic poly-l-arginine indicating a successful LbL assembly of the two polyelectrolyte bilayers on the CaCO3 nanoparticles. The LbL-nanoSraf exhibited an encapsulation efficiency of 61±4%. The LbL-nanoSraf was characterized using field-emission gun scanning electron microscopy, X-ray powder diffraction, atomic force microscopy and confocal laser scanning microscopy. Confocal laser scanning microscopy, flow cytometry and transmission electron microscopic investigations showed the internalization of LbL-nanoSraf in human oral cancer (KB) cells. The LbL-nanoSraf exhibited more potent antiproliferative, apoptotic and antimigratory activities in KB cells than the free drug Sraf. The findings could promote the application of nano-sized LbL assembled polyelectrolytes for the delivery of Raf-kinase inhibitors and provide mechanistic insights for oral cancer therapy.

C1, a highly potent novel curcumin derivative, binds to tubulin, disrupts microtubule network and induces apoptosis

C1 is one of the most potent curcumin analogues identified till date which inhibits proliferation of various cancer cell lines. C1 binds to tubulin and depolymerized microtubules of MCF-7 cells. C1 altered the expression of apoptotic proteins and induces p53-dependent apoptosis.

We have synthesized a curcumin derivative, 4-{5-(4-hydroxy-3-methoxy-phenyl)-2-[3-(4-hydroxy-3-methoxy-phenyl)-acryloyl]-3-oxo-penta-1,4-dienyl}-piperidine-1-carboxylic acid tert-butyl ester (C1) that displays much stronger antiproliferative activity against various types of cancer cells including multidrug resistance cells than curcumin. C1 depolymerized both interphase and mitotic microtubules in MCF-7 cells and also inhibited the reassembly of microtubules in these cells. C1 inhibited the polymerization of purified tubulin, disrupted the lattice structure of microtubules and suppressed their GTPase activity in vitro. The compound bound to tubulin with a dissociation constant of 2.8±1 μM and perturbed the secondary structures of tubulin. Further, C1 treatment reduced the expression of Bcl2, increased the expression of Bax and down regulated the level of a key regulator of p53, murine double minute 2 (Mdm2) (S166), in MCF-7 cells. C1 appeared to induce p53 mediated apoptosis in MCF-7 cells. Interestingly, C1 showed more stability in aqueous buffer than curcumin. The results together showed that C1 perturbed microtubule network and inhibited cancer cells proliferation more efficiently than curcumin. The strong antiproliferative activity and improved stability of C1 indicated that the compound may have a potential as an anticancer agent.

Cyanobacterial Metabolite Calothrixins: Recent Advances in Synthesis and Biological Evaluation

The marine environment is host to unparalleled biological and chemical diversity, making it an attractive resource for the discovery of new therapeutics for a plethora of diseases. Compounds that are extracted from cyanobacteria are of special interest due to their unique structural scaffolds and capacity to produce potent pharmaceutical and biotechnological traits. Calothrixins A and B are two cyanobacterial metabolites with a structural assembly of quinoline, quinone, and indole pharmacophores. This review surveys recent advances in the synthesis and evaluation of the biological activities of calothrixins. Due to the low isolation yields from the marine source and the promise this scaffold holds for anticancer and antimicrobial drugs, organic and medicinal chemists around the world have embarked on developing efficient synthetic routes to produce calothrixins. Since the first review appeared in 2009, 11 novel syntheses of calothrixins have been published in the efforts to develop methods that contain fewer steps and higher-yielding reactions. Calothrixins have shown their potential as topoisomerase I poisons for their cytotoxicity in cancer. They have also been observed to target various aspects of RNA synthesis in bacteria. Further investigation into the exact mechanism for their bioactivity is still required for many of its analogs.

Microtubule targeted therapeutics loaded polymeric assembled nanospheres for potentiation of antineoplastic activity

Polymeric nanoassemblies represent an attractive strategy for efficient cellular internalization of microtubule targeted anticancer drugs. Using dynamic light scattering, zeta potential, transmission electron microscopy and scanning electron microscopy, the physical properties and surface morphology of microtubule-binding PEGylated PLGA assembled nanospheres (100–200 nm) were analyzed. The present approach leads to strong internalization as observed by confocal laser scanning microscopy and transmission electron microscopy in hepatocarcinoma cells. The effect of these nanoassemblies on microtubules and mitosis were explored using immunofluorescence microscopy. The effects of these nanoassemblies on cancer cell proliferation and cell death revealed their antitumor enhancing effects. Perturbation of the microtubule assembly, mitosis and nuclear modulations potentiated the antineoplastic effects delivered via nanospheres in hepatocarcinoma cells. The extensive biomolecular and physical characterizations of the synthesized nanoassemblies will help to design potent therapeutic materials and the present approach can be applied to deliver microtubule-targeted drugs for liver cancer therapy.

A Chimeric Cetuximab-Functionalized Corona as a Potent Delivery System for Microtubule-Destabilizing Nanocomplexes to Hepatocellular Carcinoma Cells: A Focus on EGFR and Tubulin Intracellular Dynamics

In this study, we have developed microtubule destabilizing agents combretastatin A4 (CA4) or 2-methoxyestradiol (2ME) encapsulated poly(d,l-lactide-co-glycolide)-b-poly(ethylene glycol) (PLGA-b-PEG) nanocomplexes for targeted delivery to human hepatocellular carcinoma (HCC) cells. An epidermal growth factor receptor (EGFR) is known to be overexpressed in HCC cells. Therefore, the targeting moiety cetuximab (Cet), an anti-EGFR chimeric monoclonal antibody, is functionalized on the surface of these diblock copolymeric coronas. Cetuximab is associated with the extracellular domain of the EGFR; therefore, the uptake of the cetuximab conjugated nanocomplexes occurred efficiently in EGFR overexpressing HCC cells indicating potent internalization of the complex. The cetuximab targeted-PLGA-b-PEG nanocomplexes encapsulating CA4 or 2ME strongly inhibited phospho-EGFR expression, depolymerized microtubules, produced spindle abnormalities, stalled mitosis, and induced apoptosis in Huh7 cells compared to the free drugs, CA4 or 2ME. Further, the combinatorial strategy of targeted nanocomplexes, Cet-PLGA-b-PEG-CA4 NP and Cet-PLGA-b-PEG-2ME NP, significantly reduced the migration of Huh7 cells, and markedly enhanced the anticancer effects of the microtubule-targeted drugs in Huh7 cells compared to the free drugs, CA4 or 2ME. The results indicated that EGFR receptor-mediated internalization via cetuximab facilitated enhanced uptake of the nanocomplexes leading to potent anticancer efficacy in Huh7 cells. Cetuximab-functionalized PLGA-b-PEG nanocomplexes possess a strong potential for the targeted delivery of CA4 or 2ME in EGFR overexpressed HCC cells, and the strategy may be useful for selectively targeting microtubules in these cells.

Recent advances in the development of new auristatins: structural modifications and application in antibody drug conjugates

Dolastatin 10 is a powerful antineoplastic agent and microtubule inhibitor that was discovered by Pettit et al. and published in 1987. Since then, many research groups have engaged in SAR studies of synthetic analogues, termed "auristatins". It was eventually discovered that auristatins are of great value as payloads in antibody drug conjugates (ADCs), which led to the FDA-approved ADC brentuximab vedotin (Seattle Genetics). Currently, over 30 ADCs in clinical trials employ auristatins as payloads, and there is a great interest in the research community, both on academic and industrial sides, to further study these analogues. This review will provide an overview of the recent advancements in auristatin development spanning a time frame of about the past ten years. The main focus will be to describe structural changes made to the auristatin peptide and their resulting biological activities in tumor cell proliferation assays. Selected ADC examples will also be described.

Discovery of cytotoxic dolastatin 10 analogues with N-terminal modifications

Auristatins, synthetic analogues of the antineoplastic natural product Dolastatin 10, are ultrapotent cytotoxic microtubule inhibitors that are clinically used as payloads in antibody-drug conjugates (ADCs). The design and synthesis of several new auristatin analogues with N-terminal modifications that include amino acids with α,α-disubstituted carbon atoms are described, including the discovery of our lead auristatin, PF-06380101. This modification of the peptide structure is unprecedented and led to analogues with excellent potencies in tumor cell proliferation assays and differential ADME properties when compared to other synthetic auristatin analogues that are used in the preparation of ADCs. In addition, auristatin cocrystal structures with tubulin are being presented that allow for the detailed examination of their binding modes. A surprising finding is that all analyzed analogues have a cis-configuration at the Val-Dil amide bond in their functionally relevant tubulin bound state, whereas in solution this bond is exclusively in the trans-configuration. This remarkable observation shines light onto the preferred binding mode of auristatins and serves as a valuable tool for structure-based drug design.

Dinuclear Cu(I) complexes of pyridyl-diazadiphosphetidines and aminobis(phosphonite) ligands: synthesis, structural studies and antiproliferative activity towards human cervical, colon carcinoma and breast cancer cells

The copper(i) complexes containing phosphorus donor ligands such as diazadiphosphetidine, cis-{(o-OCH2C5H4N)P(μ-N(t)Bu)}2 (1) and aminobis(phosphonite), C6H5N{P(OC6H3(OMe-o)(C3H5-p))2}2 (2, PNP), have been synthesized. Treatment of 1 with copper iodide afforded the 1D coordination polymer [{Cu(μ-I)}2{(o-OCH2C5H4N)P(μ-N(t)Bu)}2]n (3). Treatment of 3 with 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen) produced mixed-ligand complexes [(L)2Cu2{(o-OCH2C5H4N)P(μ-N(t)Bu)}2][I]2 (4 L = bpy; 5 L = phen) in good yields. The reaction of 2 with copper iodide yielded a rare tetranuclear copper complex [(CuI)2C6H5N(PR2)2]2 (6), which on subsequent treatment with various pyridyl ligands produced binuclear complexes [{Cu(μ-I)(py)}2(μ-PNP)] (7), [Cu2(μ-I)(bpy)2(μ-PNP)]I (8), [Cu2(μ-I)I(bpy)(μ-PNP)] (9), [Cu2(phen)(bpy)(μ-PNP)](OTf)2 (10), [Cu2(μ-I)I(phen)(μ-PNP)] (11) and [Cu2(μ-I)(phen)2(μ-PNP)]I (12), in an almost quantitative yield. The new copper(i) complexes (4, 5 and 7-12) were tested for anti-cancer activity against three human tumor cell lines. Compounds 5, 10 and 12 showed in vitro antitumor activity 5-7 fold higher than cisplatin, the most used anticancer drug. These three most potent compounds (5, 10 and 12) were chosen for detailed study to understand their mechanism of action. The copper(i) compounds studied in the present investigation were found to inhibit tumor cell growth by arresting cells at the S-phase of the cell cycle. The characteristic nuclear morphology of treated cells showed signs of DNA damage. The experimental evidence clearly indicated that these compounds initiated apoptosis, which is mediated through the p53 pathway.

Diverse synthesis of marine cyclic depsipeptide lagunamide A and its analogues

The asymmetric total synthesis of lagunamide A (3.0%, 20 steps longest linear sequence) and its five analogues, including the structure dehydrated at the C37 position, are detailed in this report. The key feature in this diverse synthesis includes the elaboration of four consecutive chiral centers at C37-40 and the final macrocyclization. Starting from chiral aldehyde 10, we synthesized both 1,3-anti and 1,3-syn homoallylic alcohols 20a and 20b through asymmetric aldol condensation and stereoselective allylation. The following esterification to introduce the L-N-Me-Ala unit resulted in significant epimerization. This problem was finally overcome by coupling the alcohols with the corresponding acid chloride of the L-alanine derivative. The key α,β-unsaturated carboxylic acid unit was produced by cross-metathesis (CM) of methacrylaldehyde and related olefins. Interestingly, we found that the C7 configuration dramatically affected the ring closure. Natural lagunamide A (1a), its 39-epimer (1c), and its 2-epimer (1d) were obtained through macrolactamization between alanine and isoleucine moieties.

Ansamitocin P3 depolymerizes microtubules and induces apoptosis by binding to tubulin at the vinblastine site

Maytansinoid conjugates are currently under different phases of clinical trials and have been showing promising activity for various types of cancers. In this study, we have elucidated the mechanism of action of ansamitocin P3, a structural analogue of maytansine for its anticancer activity. Ansamitocin P3 potently inhibited the proliferation of MCF-7, HeLa, EMT-6/AR1 and MDA-MB-231 cells in culture with a half-maximal inhibitory concentration of 20±3, 50±0.5, 140±17, and 150±1.1 pM, respectively. Ansamitocin P3 strongly depolymerized both interphase and mitotic microtubules and perturbed chromosome segregation at its proliferation inhibitory concentration range. Treatment of ansamitocin P3 activated spindle checkpoint surveillance proteins, Mad2 and BubR1 and blocked the cells in mitotic phase of the cell cycle. Subsequently, cells underwent apoptosis via p53 mediated apoptotic pathway. Further, ansamitocin P3 was found to bind to purified tubulin in vitro with a dissociation constant (K_d) of 1.3±0.7 µM. The binding of ansamitocin P3 induced conformational changes in tubulin. A docking analysis suggested that ansamitocin P3 may bind partially to vinblastine binding site on tubulin in two different positions. The analysis indicated that the binding of ansamitocin P3 to tubulin is stabilized by hydrogen bonds. In addition, weak interactions such as halogen-oxygen interactions may also contribute to the binding of ansamitocin P3 to tubulin. The study provided a significant insight in understanding the antiproliferative mechanism of action of ansamitocin P3.