Zampanolide, a Microtubule-Stabilizing Agent, Is Active in Resistant Cancer Cells and Inhibits Cell Migration

In Vivo Evaluation of (-)-Zampanolide Demonstrates Potent and Persistent Antitumor Efficacy When Targeted to the Tumor Site

Microtubule-stabilizing agents (MSAs) are a class of compounds used in the treatment of triple-negative breast cancer (TNBC), a subtype of breast cancer where chemotherapy remains the standard-of-care for patients. Taxanes like paclitaxel and docetaxel have demonstrated efficacy against TNBC in the clinic, however new classes of MSAs need to be identified due to the rise of taxane resistance in patients. (−)-Zampanolide is a covalent microtubule stabilizer that can circumvent taxane resistance in vitro but has not been evaluated for in vivo antitumor efficacy. Here, we determine that (−)-zampanolide has similar potency and efficacy to paclitaxel in TNBC cell lines, but is significantly more persistent due to its covalent binding. We also provide the first reported in vivo antitumor evaluation of (−)-zampanolide where we determine that it has potent and persistent antitumor efficacy when delivered intratumorally. Future work on zampanolide to further evaluate its pharmacophore and determine ways to improve its systemic therapeutic window would make this compound a potential candidate for clinical development through its ability to circumvent taxane-resistance mechanisms.

Challenges in Discovering Drugs That Target the Protein-Protein Interactions of Disordered Proteins

Protein–protein interactions (PPIs) outnumber proteins and are crucial to many fundamental processes; in consequence, PPIs are associated with several pathological conditions including neurodegeneration and modulating them by drugs constitutes a potentially major class of therapy. Classically, however, the discovery of small molecules for use as drugs entails targeting individual proteins rather than targeting PPIs. This is largely because discovering small molecules to modulate PPIs has been seen as extremely challenging. Here, we review the difficulties and limitations of strategies to discover drugs that target PPIs directly or indirectly, taking as examples the disordered proteins involved in neurodegenerative diseases.

Microtubule Targeting Agents in Disease: Classic Drugs, Novel Roles

Microtubule-targeting agents (MTAs) represent one of the most successful first-line therapies prescribed for cancer treatment. They interfere with microtubule (MT) dynamics by either stabilizing or destabilizing MTs, and in culture, they are believed to kill cells via apoptosis after eliciting mitotic arrest, among other mechanisms. This classical view of MTA therapies persisted for many years. However, the limited success of drugs specifically targeting mitotic proteins, and the slow growing rate of most human tumors forces a reevaluation of the mechanism of action of MTAs. Studies from the last decade suggest that the killing efficiency of MTAs arises from a combination of interphase and mitotic effects. Moreover, MTs have also been implicated in other therapeutically relevant activities, such as decreasing angiogenesis, blocking cell migration, reducing metastasis, and activating innate immunity to promote proinflammatory responses. Two key problems associated with MTA therapy are acquired drug resistance and systemic toxicity. Accordingly, novel and effective MTAs are being designed with an eye toward reducing toxicity without compromising efficacy or promoting resistance. Here, we will review the mechanism of action of MTAs, the signaling pathways they affect, their impact on cancer and other illnesses, and the promising new therapeutic applications of these classic drugs.

Liposomal paclitaxel induces apoptosis, cell death, inhibition of migration capacity and antitumoral activity in ovarian cancer

The main goal of this study is to evaluate the efficacy of the paclitaxel (PTX) drug formulated with a liposomal nanosystem (L-PTX) in a peritoneal carcinomatosis derived from ovarian cancer. In vitro cell viability studies with the human ovarian cancer line A2780 showed a 50% decrease in the inhibitory concentration for L-PTX compared to free PTX. A2780 cells treated with the L-PTX formulation demonstrated a reduced capacity to form colonies in comparison to those treated with PTX. Cell death following L-PTX administration hinted at apoptosis, with most cells undergoing initial apoptosis. A2780 cells exhibited an inhibitory migration profile when analyzed by Wound Healing and real-time cell analysis (xCELLigence) methods after L-PTX administration. This inhibition was related to decreased expression of the zinc finger E-box-binding homeobox 1 (ZEB1) and transforming growth factor 2 (TGF-β2) genes. In vivoL-PTX administration strongly inhibited tumor cell proliferation in ovarian peritoneal carcinomatosis derived from ovarian cancer, indicating higher antitumor activity than PTX. L-PTX formulation did not show toxicity in the mice model. This study demonstrated that liposomal paclitaxel formulations are less toxic to normal tissues than free paclitaxel and are more effective in inhibiting tumor cell proliferation/migration and inducing ZEB1/TGF-β2 gene expression.

Microtubule destabilization is a critical checkpoint of chemotaxis and transendothelial migration in melanoma cells but not in T cells

Microtubules (MTs) control cell shape and intracellular cargo transport. The role of MT turnover in the migration of slow-moving cells through endothelial barriers remains unclear. To irreversibly interfere with MT disassembly, we have used the MT-stabilizing agent zampanolide (ZMP) in Β16F10 melanoma as amodel of slow-moving cells. ZMP-treated B16 cells failed to follow chemotactic gradients across rigid confinements and could not generate stable sub-endothelial pseudopodia under endothelial monolayers. In vivo, ZMP-treated Β16 cells failed to extravasate though lung capillaries. In contrast to melanoma cells, the chemotaxis and transendothelial migration of ZMP-treated Tcells were largely conserved. This is afirst demonstration that MT disassembly is akey checkpoint in the directional migration of cancer cells but not of lymphocytes.

An amide mimic of desTHPdactylolide: Total synthesis and antiproliferative evaluation

(-)-Zampanolide is a unique microtubule stabilizing agent (MSA) with covalent-binding mechanism and low nanomolar anitproliferative potency towards multi-drug resistant cancer cells. MSAs have a special connection with prostate cancer by inhibiting androgen receptor nuclear translocation. Zampanolide and the structurally related dactylolide have thus been sought after by us as lead compounds for development of anti-prostate cancer agents. DesTHPdactylolide is a simplified mimic of dactylolide and has previously been synthesized by us in both configurations, with the (17R) configuration being more potent in suppressing prostate cancer cell proliferation. The current study aims to synthesize an amide mimic of (17R) desTHPdactylolide that was anticipated to be metabolically more stable than (17R) desTHPdactylolide. To this end, the amide mimic has been successfully synthesized through a 26-step transformation from 2-butyn-1-ol. Our WST-1 cell proliferation assay in five human prostate cancer cell models indicated that the lactam moiety can serve as a bioisostere for the lactone in desTHPdactylolide.

Taxanes in cancer treatment: Activity, chemoresistance and its overcoming

Since 1984, when paclitaxel was approved by the FDA for the treatment of advanced ovarian carcinoma, taxanes have been widely used as microtubule-targeting antitumor agents. However, their historic classification as antimitotics does not describe all their functions. Indeed, taxanes act in a complex manner, altering multiple cellular oncogenic processes including mitosis, angiogenesis, apoptosis, inflammatory response, and ROS production. On the one hand, identification of the diverse effects of taxanes on oncogenic signaling pathways provides opportunities to apply these cytotoxic drugs in a more rational manner. On the other hand, this may facilitate the development of novel treatment modalities to surmount anticancer drug resistance. In the latter respect, chemoresistance remains a major impediment which limits the efficacy of antitumor chemotherapy. Taxanes have shown impact on key molecular mechanisms including disruption of mitotic spindle, mitosis slippage and inhibition of angiogenesis. Furthermore, there is an emerging contribution of cellular processes including autophagy, oxidative stress, epigenetic alterations and microRNAs deregulation to the acquisition of taxane resistance. Hence, these two lines of findings are currently promoting a more rational and efficacious taxane application as well as development of novel molecular strategies to enhance the efficacy of taxane-based cancer treatment while overcoming drug resistance. This review provides a general and comprehensive picture on the use of taxanes in cancer treatment. In particular, we describe the history of application of taxanes in anticancer therapeutics, the synthesis of the different drugs belonging to this class of cytotoxic compounds, their features and the differences between them. We further dissect the molecular mechanisms of action of taxanes and the molecular basis underlying the onset of taxane resistance. We further delineate the possible modalities to overcome chemoresistance to taxanes, such as increasing drug solubility, delivery and pharmacokinetics, overcoming microtubule alterations or mitotic slippage, inhibiting drug efflux pumps or drug metabolism, targeting redox metabolism, immune response, and other cellular functions.

Recent advances in the development of protein-protein interactions modulators: mechanisms and clinical trials

Protein-protein interactions (PPIs) have pivotal roles in life processes. The studies showed that aberrant PPIs are associated with various diseases, including cancer, infectious diseases, and neurodegenerative diseases. Therefore, targeting PPIs is a direction in treating diseases and an essential strategy for the development of new drugs. In the past few decades, the modulation of PPIs has been recognized as one of the most challenging drug discovery tasks. In recent years, some PPIs modulators have entered clinical studies, some of which been approved for marketing, indicating that the modulators targeting PPIs have broad prospects. Here, we summarize the recent advances in PPIs modulators, including small molecules, peptides, and antibodies, hoping to provide some guidance to the design of novel drugs targeting PPIs in the future.

Intrinsic and Extrinsic Factors Affecting Microtubule Dynamics in Normal and Cancer Cells

Microtubules (MTs), highly dynamic structures composed of α- and β-tubulin heterodimers, are involved in cell movement and intracellular traffic and are essential for cell division. Within the cell, MTs are not uniform as they can be composed of different tubulin isotypes that are post-translationally modified and interact with different microtubule-associated proteins (MAPs). These diverse intrinsic factors influence the dynamics of MTs. Extrinsic factors such as microtubule-targeting agents (MTAs) can also affect MT dynamics. MTAs can be divided into two main categories: microtubule-stabilizing agents (MSAs) and microtubule-destabilizing agents (MDAs). Thus, the MT skeleton is an important target for anticancer therapy. This review discusses factors that determine the microtubule dynamics in normal and cancer cells and describes microtubule–MTA interactions, highlighting the importance of tubulin isoform diversity and post-translational modifications in MTA responses and the consequences of such a phenomenon, including drug resistance development.

Targeting and extending the eukaryotic druggable genome with natural products: cytoskeletal targets of natural products

Covering: 2014-2019We review recent progress on natural products that target cytoskeletal components, including microtubules, actin, intermediate filaments, and septins and highlight their demonstrated and potential utility in the treatment of human disease. The anticancer efficacy of microtubule targeted agents identified from plants, microbes, and marine organisms is well documented. We highlight new microtubule targeted agents currently in clinical evaluations for the treatment of drug resistant cancers and the accumulating evidence that the anticancer efficacy of these agents is not solely due to their antimitotic effects. Indeed, the effects of microtubule targeted agents on interphase microtubules are leading to their potential for more mechanistically guided use in cancers as well as neurological disease. The discussion of these agents as more targeted drugs also prompts a reevaluation of our thinking about natural products that target other components of the cytoskeleton. For instance, actin active natural products are largely considered chemical probes and non-selective toxins. However, studies utilizing these probes have uncovered aspects of actin biology that can be more specifically targeted to potentially treat cancer, neurological disorders, and infectious disease. Compounds that target intermediate filaments and septins are understudied, but their continued discovery and mechanistic evaluations have implications for numerous therapeutic indications.

Microtubule-targeting agents and their impact on cancer treatment

Microtubule-targeting agents (MTAs) constitute a diverse group of chemical compounds that bind to microtubules and affect their properties and function. Disruption of microtubules induces various cellular responses often leading to cell cycle arrest or cell death, the most common effect of MTAs. MTAs have found a plethora of practical applications in weed control, as fungicides and antiparasitics, and particularly in cancer treatment. Here we summarize the current knowledge of MTAs, the mechanisms of action and their role in cancer treatment. We further outline the potential use of MTAs in anti-metastatic therapy based on inhibition of cancer cell migration and invasiveness. The two main problems associated with cancer therapy by MTAs are high systemic toxicity and development of resistance. Toxic side effects of MTAs can be, at least partly, eliminated by conjugation of the drugs with various carriers. Moreover, some of the novel MTAs overcome the resistance mediated by both multidrug resistance transporters as well as overexpression of specific β-tubulin types. In anti-metastatic therapy, MTAs should be combined with other drugs to target all modes of cancer cell invasion.

Tubulin heterogeneity regulates functions and dynamics of microtubules and plays a role in the development of drug resistance in cancer

Microtubules, composed of αβ-tubulin heterodimers, exhibit diverse structural and functional properties in different cell types. The diversity in the microtubule structure originates from tubulin heterogeneities, namely tubulin isotypes and their post-translational modifications (PTMs). These heterogeneities confer differential stability to microtubules and provide spatial cues for the functioning of the cell. Furthermore, the altered expressions of tubulin isotypes and PTMs are prominent factors for the development of resistance against some cancer drugs. In this review, we summarize our current knowledge of the tubulin isotypes and PTMs and how, together, they control the cellular functions of the microtubules. We also describe how cancer cells use this tubulin heterogeneity to acquire resistance against clinical agents and discuss existing attempts to counter the developed resistance.

Crystal Structure of the Cyclostreptin-Tubulin Adduct: Implications for Tubulin Activation by Taxane-Site Ligands

It has been proposed that one of the mechanisms of taxane-site ligand-mediated tubulin activation is modulation of the structure of a switch element (the M-loop) from a disordered form in dimeric tubulin to a folded helical structure in microtubules. Here, we used covalent taxane-site ligands, including cyclostreptin, to gain further insight into this mechanism. The crystal structure of cyclostreptin-bound tubulin reveals covalent binding to βHis229, but no stabilization of the M-loop. The capacity of cyclostreptin to induce microtubule assembly compared to other covalent taxane-site agents demonstrates that the induction of tubulin assembly is not strictly dependent on M-loop stabilization. We further demonstrate that most covalent taxane-site ligands are able to partially overcome drug resistance mediated by βIII-tubulin (βIII) overexpression in HeLa cells, and compare their activities to pironetin, an interfacial covalent inhibitor of tubulin assembly that displays invariant growth inhibition in these cells. Our findings suggest a relationship between a diminished interaction of taxane-site ligands with βIII-tubulin and βIII tubulin-mediated drug resistance. This supports the idea that overexpression of βIII increases microtubule dynamicity by counteracting the enhanced microtubule stability promoted by covalent taxane-site binding ligands.

Anti-tubulin agents of natural origin: Targeting taxol, vinca, and colchicine binding domains

Microtubules are a protein which is made of α- and β-heterodimer. It is one of the main components of the cell which play a vital role in cell division especially in G2/M-phase. It exists in equilibrium dynamic of polymerization and depolymerization of α- and β-heterodimer. It is one of the best targets for developing anti-cancer drugs. Various natural occurring molecules are well known for their anti-tubulin effect such as vinca, paclitaxel, combretastatin, colchicine etc. These microtubule-targeted drugs are acted through two processes (i) inhibiting depolymerization of tubulin (tubulin stabilizing agents) and (ii) inhibiting polymerization of tubulin (tubulin destabilizing agents). Now days, various binding domains have been explore through which these molecules are binding to tubulin but the three major binding domain of tubulin are taxol, vinca and colchicine binding domain. The present article mainly focus on the classification of various naturally occurring compounds on the basis of their inhibition processes (depolymerization and polymerization) and the site of interaction (targets taxol, vinca and colchicine binding domain) which has been hitherto reported. By placing all the naturally occurring taxol, vinca and colchicine binding site analogues at one place makes a better understanding of the tubulin interactions with known natural tubulin binders that would helps in the discovery of new and potent natural, semi-synthetic and synthetic analogues for treating cancer.

Zampanolides B-E from the Marine Sponge Cacospongia mycofijiensis: Potent Cytotoxic Macrolides with Microtubule-Stabilizing Activity

Four new compounds (2-5) structurally related to the microtubule-stabilizing agent (-)-zampanolide (1) have been isolated from the Tongan marine sponge Cacospongia mycofijiensis. Three of these new structures, zampanolides B-D (2-4), exhibit nanomolar cytotoxicity toward the HL-60 cell line, are antimitotic, and induce in vitro tubulin polymerization at levels comparable to 1. Zampanolide E (5), saturated at C-8/C-9, was significantly less potent and does not stabilize purified tubulin, even at 10-fold higher concentrations. The structural differences across these compounds reveal a plasticity of the zampanolide pharmacophore. While unsaturation is required at Δ⁸, the configuration of this alkene and those of Δ⁴ and Δ^4' have little effect on tubulin polymerization. The first natural co-occurrence of 1 and (-)-dactylolide (6) from the same sponge extract is also noted.

Antitubulin sulfonamides: The successful combination of an established drug class and a multifaceted target

Tubulin, the microtubules and their dynamic behavior are amongst the most successful antitumor, antifungal, antiparasitic, and herbicidal drug targets. Sulfonamides are exemplary drugs with applications in the clinic, in veterinary and in the agrochemical industry. This review summarizes the actual state and recent progress of both fields looking from the double point of view of the target and its drugs, with special focus onto the structural aspects. The article starts with a brief description of tubulin structure and its dynamic assembly and disassembly into microtubules and other polymers. Posttranslational modifications and the many cellular means of regulating and modulating tubulin's biology are briefly presented in the tubulin code. Next, the structurally characterized drug binding sites, their occupying drugs and the effects they induce are described, emphasizing on the structural requirements for high potency, selectivity, and low toxicity. The second part starts with a summary of the favorable and highly tunable combination of physical-chemical and biological properties that render sulfonamides a prototypical example of privileged scaffolds with representatives in many therapeutic areas. A complete description of tubulin-binding sulfonamides is provided, covering the different species and drug sites. Some of the antimitotic sulfonamides have met with very successful applications and others less so, thus illustrating the advances, limitations, and future perspectives of the field. All of them combine in a mechanism of action and a clinical outcome that conform efficient drugs.

Therapeutic potential of patupilone in epithelial ovarian cancer and future directions

Ovarian cancer is the most lethal gynecologic malignancy worldwide with extremely poor patient prognosis. Elucidation of the detailed mechanisms of action of drugs targeting this cancer type is necessary to optimize treatment efficacy. Epothilones, a new class of microtubule-stabilizing anticancer drugs, show strong cytotoxic properties in vitro and in vivo and are additionally effective in taxane-resistant cells. In this report, we focus on inhibitors of microtubule depolymerization, taxanes, and the novel antimicrotubule agents, epothilones. Current knowledge regarding the effects of epothilone B on ovarian tumor cell metabolism is reviewed, along with recent advances in therapeutic strategies, such as novel agents and biologic drug combinations containing epothilone that target aberrant pathways in ovarian cancer.

Marine Invertebrate Natural Products that Target Microtubules

Marine natural products as secondary metabolites are a potential major source of new drugs for treating disease. In some cases, cytotoxic marine metabolites target the microtubules of the eukaryote cytoskeleton for reasons that will be discussed. This review covers the microtubule-targeting agents reported from sponges, corals, tunicates, and molluscs and the evidence that many of these secondary metabolites are produced by bacterial symbionts. The review finishes by discussing the directions for future development and production of clinically relevant amounts of these natural products and their analogues through aquaculture, chemical synthesis, and biosynthesis by bacterial symbionts.

Design and Antiproliferative Evaluation of Novel Sulfanilamide Derivatives as Potential Tubulin Polymerization Inhibitors

A series of sulfanilamide-1,2,3-triazole hybrids were designed by a molecular hybridization strategy and evaluated for antiproliferative activity against three selected cancer cell lines (MGC-803, MCF-7 and PC-3). The detailed structure-activity relationships for these sulfanilamide-1,2,3-triazole hybrids were investigated. All these sulfanilamide-1,2,3-triazole hybrids exhibited moderate to potent activity against all cell lines. In particular 4-methyl-N-((1-(3-phenoxybenzyl)-1H-1,2,3-triazol-4-yl)methyl)benzenesulfonamide (11f) showed the most potent inhibitory effect against PC-3 cells, with an IC₅₀ value of 4.08 μM. Furthermore, the tubulin polymerization inhibitory activity in vitro of compound 11f was 2.41 μM. These sulfanilamide hybrids might serve as bioactive fragments for developing more potent antiproliferative agents.