Eribulin: A Novel Cytotoxic Chemotherapy Agent

Targeting Molecular Mechanisms Underlying Treatment Efficacy and Resistance in Osteosarcoma: A Review of Current and Future Strategies

Osteosarcoma is the most common primary malignant bone tumour in children and adolescents. Due to micrometastatic spread, radical surgery alone rarely results in cure. Introduction of combination chemotherapy in the 1970s, however, dramatically increased overall survival rates from 20% to approximately 70%. Unfortunately, large clinical trials aiming to intensify treatment in the past decades have failed to achieve higher cure rates. In this review, we revisit how the heterogenous nature of osteosarcoma as well as acquired and intrinsic resistance to chemotherapy can account for stagnation in therapy improvement. We summarise current osteosarcoma treatment strategies focusing on molecular determinants of treatment susceptibility and resistance. Understanding therapy susceptibility and resistance provides a basis for rational therapy betterment for both identifying patients that might be cured with less toxic interventions and targeting resistance mechanisms to sensitise resistant osteosarcoma to conventional therapies.

A phase II study of eribulin in recurrent or refractory osteosarcoma: A report from the Children's Oncology Group

BACKGROUND

Patients with recurrent or refractory osteosarcoma have a poor prognosis with less than 30% surviving two years. Eribulin is a synthetic analog of halichondrin B, has a novel mechanism of action when compared with other microtubule inhibitors, and may have antitumor activity in osteosarcoma.

METHODS

A prospective study was designed to assess the disease control success at four months and objective response rates in patients with recurrent or refractory osteosarcoma treated with eribulin. Eligible patients were between 12 and 50 years of age, had measurable tumor, and met standard organ function requirements. Patients were given eribulin 1.4 mg/m² /dose on days 1 and 8 of each 3-week cycle for up to 24 months if there was no progressive disease. Response to therapy was assessed using RECIST 1.1 criteria after cycles 2 and 5 and every fourth cycle thereafter.

RESULTS

Nineteen patients enrolled on the AOST1322 study. The median age of enrollment was 16 years (range, 12-25 years). Twelve patients were male and seven female. Eribulin was well tolerated, with neutropenia identified as the most common toxicity. The median progression-free survival was 38 days and no patients reached the four-month time point without progression. No objective responses were seen in any patient.

CONCLUSION

This study rapidly assessed the clinical activity of a novel agent in this patient population. Eribulin was well tolerated, but there were no patients who demonstrated objective response, and all patients had progression prior to four months.

Managing sarcoma: where have we come from and where are we going?

Sarcomas are a heterogeneous group of neoplasms of mesenchymal origin. Approximately 80% arise from soft tissue and 20% originate from bone. To date more than 100 sarcoma subtypes have been identified and they vary in molecular characteristics, pathology, clinical presentation and response to treatment. While sarcomas represent <1% of adult cancers, they account for approximately 21% of paediatric malignancies and thus pose some of the greatest risks of mortality and morbidity in children and young adults. Metastases occur in one-third of all patients and approximately 10-20% of sarcomas recur locally. Surgery in combination with preoperative and postoperative therapies is the primary treatment for localized sarcoma tumours and is the most promising curative possibility. Metastasized sarcomas, on the other hand, are treated primarily with single-agent or combination chemotherapy, but this rarely leads to a complete and robust response and often becomes a palliative form of treatment. The heterogeneity of sarcomas results in variable responses to current generalized treatment strategies. In light of this and the lack of curative strategies for metastatic and unresectable sarcomas, there is a need for novel subtype-specific treatment strategies. With the more recent understanding of the molecular mechanisms underlying the pathogenesis of some of these tumours, the treatment of sarcoma subtypes with targeted therapies is a rapidly evolving field. This review discusses the current management of sarcomas as well as promising new therapies that are currently underway in clinical trials.

Marine Antibody-Drug Conjugates: Design Strategies and Research Progress

Antibody-drug conjugates (ADCs), constructed with monoclonal antibodies (mAbs), linkers, and natural cytotoxins, are innovative drugs developed for oncotherapy. Owing to the distinctive advantages of both chemotherapy drugs and antibody drugs, ADCs have obtained enormous success during the past several years. The development of highly specific antibodies, novel marine toxins' applications, and innovative linker technologies all accelerate the rapid R&D of ADCs. Meanwhile, some challenges remain to be solved for future ADCs. For instance, varieties of site-specific conjugation have been proposed for solving the inhomogeneity of DARs (Drug Antibody Ratios). In this review, the usages of various natural toxins, especially marine cytotoxins, and the development strategies for ADCs in the past decade are summarized. Representative ADCs with marine cytotoxins in the pipeline are introduced and characterized with their new features, while perspective comments for future ADCs are proposed.

Microtubule destabilising agents: far more than just antimitotic anticancer drugs

Vinca alkaloids have been approved as anticancer drugs for more than 50 years. They have been classified as cytotoxic chemotherapy drugs that act during cellular mitosis, enabling them to target fast growing cancer cells. With the evolution of cancer drug development there has been a shift towards new "targeted" therapies to avoid the side effects and general toxicities of "cytotoxic chemotherapies" such as the vinca alkaloids. Due to their original classification, many have overlooked the fact that vinca alkaloids, taxanes and related drugs do have a specific molecular target: tubulin. They continue to be some of the most effective anticancer drugs, perhaps because their actions upon the microtubule network extend far beyond the ability to halt cells in mitosis, and include the induction of apoptosis at all phases of the cell cycle. In this review, we highlight the numerous cellular consequences of disrupting microtubule dynamics, expanding the textbook knowledge of microtubule destabilising agents and providing novel opportunities for their use in cancer therapy.

Recent advances in isolation, synthesis, and evaluation of bioactivities of bispyrroloquinone alkaloids of marine origin

The ocean continues to provide a plethora of unique scaffolds capable of remarkable biological applications. A large number of pyrroloiminoquinone alkaloids, including discorhabdins, epinardins, batzellines, makaluvamines, and veiutamine, have been isolated from various marine organisms. A class of pyrroloiminoquinone-related alkaloids, known as bispyrroloquinones, is the focus of this review article. This family of marine alkaloids, which contain an aryl substituted bispyrroloquinone ring system, includes three subclasses of alkaloids namely, wakayin, tsitsikammamines A-B, and zyzzyanones A-D. Both wakayin and the tsitsikammamines contain a tetracyclic fused bispyrroloiminoquinone ring system, while zyzzyanones contain a fused tricyclic bispyrroloquinone ring system. The unique chemical structures of these marine natural products and their diverse biological properties, including antifungal and antimicrobial activity, as well as the potent, albeit generally nonspecific and universal cytotoxicities, have attracted great interest of synthetic chemists over the past three decades. Tsitsikammamines, wakayin, and several of their analogs show inhibition of topoisomerases. One additional possible mechanism of anticancer activity of tsitsikammamines analogs that has been discovered recently is through the inhibition of indoleamine 2, 3-dioxygenase, an enzyme involved in tumoral immune resistance. This review discusses the isolation, synthesis, and evaluation of bioactivities of bispyrroloquinone alkaloids and their analogs.

Practical stereoselective synthesis of eribulin fragment toward building a hybrid macrocyclic toolbox

A practical stereoselective synthesis to obtain the substituted furan ring as the substructure of eribulin is developed. An asymmetric syn-aldol and intramolecular oxy-Michael were two key steps in our approach. The functionalized furan derivatives were then utilized further to build the 14- and 12-membered macrocyclic diversity as trans- and cis-fused (C-29 and C-30) compounds. This is the first report of building a chemical toolbox with macrocyclic small molecules having trans- or cis-fused 14- or 12-membered rings containing the substructure of eribulin and its diastereomer.

Clinical impact of eribulin in the treatment of breast cancer

SUMMARY 

Metastatic breast cancer is considered incurable, with a 5-year survival of approximately 23%. However, sequential chemotherapy regimens produce clinical benefit for patients, including prolonged progression-free and overall survival times. Eribulin is a convenient (<5 min infusion) and novel treatment that has shown activity and efficacy and tolerability in advanced breast cancer patients in Phase II and Phase III trials. Eribulin has also shown encouraging results as first-line treatment, either alone in patients with HER2- disease or in combination with trastuzumab in patients with HER2+ disease, in Phase II trials.

Eribulin: a new-generation antimicrotubule agent in lung cancer therapy

ABSTRACT 

Microtubule antagonists are highly active agents for treatment of metastatic lung cancer, but can lead to significant toxicities and tumor resistance. Eribulin mesylate is a novel antimicrotubule agent that binds at a different site of the microtubule chain, and has been shown to be effective against many tumor types in several Phase II trials. Studies revealed many potential mechanisms beyond disruption of microtubule machinery that may be linked to its superior efficacy and less degree of toxicities. To date, only Phase III evidence to support eribulin use is in breast cancer, but the ongoing Phase III trial testing its efficacy in metastatic lung cancer against treatment of physician's choice will prove its merits in this setting.

Leptomeningeal carcinomatosis from breast cancer treated with intrathecal topotecan with concomitant intravenous eribulin

We present a patient with leptomeningeal carcinomatosis from breast cancer treated with intrathecal topotecan and intravenous eribulin. The regimen was well tolerated and provided clinical stability in a patient with progression on a prior intrathecal chemotherapy regimen.

RNA-binding protein RBM8A (Y14) and MAGOH localize to centrosome in human A549 cells

RBM8A (Y14) is carrying RNA-binding motif and forms the tight heterodimer with MAGOH. The heterodimer is known to be a member of exon junction complex on exporting mRNA and is required for mRNA metabolisms such as splicing, mRNA export and nonsense-mediated mRNA decay. Almost all RBM8A-MAGOH complexes localize in nucleoplasm and shuttle between nuclei and cytoplasm for RNA metabolism. Recently, the abnormality of G2/M transition and aberrant centrosome regulation in RBM8A- or MAGOH-deficient cells has been reported. These results prompt us to the reevaluation of the localization of RBM8A-MAGOH in human cells. Interestingly, our immunostaining experiments showed the localization of these proteins in centrosome in addition to nuclei. Furthermore, the transiently expressed eYFP-tagged RBM8A and Flag-tagged MAGOH also co-localized with centrosome signals. In addition, the proximity ligation in situ assay was performed to detect the complex formation in centrosome. Our experiments clearly showed that Myc-tagged RBM8A and Flag-tagged MAGOH formed a complex in centrosome. GFP-tagged PLK1 also co-localized with Myc-RBM8A. Our results show that RBM8A-MAGOH complex is required for M-phase progression via direct localization to centrosome rather than indirect effect.

Initial testing (stage 1) of eribulin, a novel tubulin binding agent, by the pediatric preclinical testing program

BACKGROUND

Antimitotic agents are essential components for curative therapy of pediatric acute leukemias and many solid tumors. Eribulin is a novel agent that differs from both Vinca alkaloids and taxanes in its mode of binding to tubulin polymers.

PROCEDURES

Eribulin was tested against the PPTP in vitro cell line panel at concentrations from 0.1 nM to 1.0 μM and against the PPTP in vivo xenograft panels at a dose of 1 mg/kg (solid tumors) or 1.5 mg/kg (ALL models) using a q4dx3 schedule repeated at Day 21.

RESULTS

In vitro eribulin demonstrated cytotoxic activity, with a median relative IC50 value of 0.27 nM, (range <0.1-14.8 nM). Eribulin was well tolerated in vivo, and all 43 xenograft models were considered evaluable for efficacy. Eribulin induced significant differences in event-free survival (EFS) distribution compared to control in 29 of 35 (83%) of the solid tumors and in 8 of 8 (100%) of the ALL xenografts. Objective responses were observed in 18 of 35 (51%) solid tumor xenografts. Complete responses (CR) or maintained CR were observed in panels of Wilms tumor, Ewing sarcoma, rhabdomyosarcoma, glioblastoma, and osteosarcoma xenografts. All eight ALL xenografts achieved CR or MCR.

CONCLUSIONS

The high level of activity observed for eribulin against the PPTP preclinical models makes this an interesting agent to consider for pediatric evaluation. The activity pattern observed for eribulin in the solid tumor panels is equal or superior to that observed previously for vincristine.

Tubulin-targeted agents including docetaxel and cabazitaxel

Microtubules are dynamic filamentous cytoskeletal proteins that are responsible for cellular integrity and architecture, mitosis, intracellular transport, cell signaling, and gene expression. Tubulin exists in the cell as dimers of α and β subunits, which complexes with a variety of regulatory proteins. There is a dynamic equilibrium between free and polymerized tubulin causing a state called "dynamic instability," which is a target of anticancer drugs, which inhibit tubulin through polymerization (taxanes, epothilones) or depolymerization (vinca alkaloids). Docetaxel-based therapy was the first such treatment to demonstrate a survival benefit in men with castration-resistant prostate cancer. Cabazitaxel, an antitubulin agent, which demonstrates activity in multidrug- and docetaxel-resistant cancer cell lines, demonstrates a survival benefit over mitoxantrone and prednisone in patients who have failed docetaxel-based chemotherapy. This article reviews the use of antitubulin agents in patients with castration-resistant prostate cancer.