Novel second generation analogs of eribulin. Part I: Compounds containing a lipophilic C32 side chain overcome P-glycoprotein susceptibility

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.

A unified strategy for the total syntheses of eribulin and a macrolactam analogue of halichondrin B

A unified synthetic route for the total syntheses of eribulin and a macrolactam analog of halichondrin B is described. The key to the success of the current synthetic approach includes the employment of our reverse approach for the construction of cyclic ether structural motifs and a modified intramolecular cyclization reaction between alkyl iodide and aldehyde functionalities to establish the all-carbon macrocyclic framework of eribulin. These syntheses, together with our previous work on the total syntheses of halichondrin B and norhalichondrin B, demonstrate and validate the powerful reverse approach in the construction of cyclic ether structural motifs. On the other hand, the unified synthetic strategy for the synthesis of the related macrolactam analog provides inspiration and opportunities in the halichondrin field and related polycyclic ether areas.

A Highly Convergent Total Synthesis of Norhalichondrin B

A new synthetic strategy for the total synthesis of norhalichondrin B featuring a highly convergent approach and our recently disclosed reverse approach for the synthesis of cyclic ether structural motifs is disclosed. Resulting in the shortest route to norhalichondrin B disclosed thus far, the reported total synthesis was achieved through the synthesis of two almost equally complex fragments whose coupling and short elaboration sequence featured an essential epimerization of the C16 stereocenter occurring concurrently with a simple acid-induced deprotection, a tactic based on a prior study along the synthetic route. This unprecedented strategy within the halichondrin family of natural products could find practical application to the synthesis of other more or less complex natural or designed halichondrin analogues.

A Reverse Approach to the Total Synthesis of Halichondrin B

A new strategy is described for the total synthesis of halichondrin B featuring reversal of the sequential construction of a number of its cyclic ethers from the classical approach by instead forming C-O bonds first followed by C-C bond formation. Employing the Nicholas reaction to generate linear ethers as precursors for the total synthesis of halichondrin B and other members of the halichondrin and eribulin families of compounds, this novel approach provides new opportunities for the development of improved syntheses of these complex and valuable compounds. In this Article, we report the syntheses of defined fragments I, MN, EFG, and A. Fragments I and MN were then coupled and elaborated to advanced intermediate IJKLMN, which was joined with fragment EFG to afford, after appropriate elaboration and macrolactonization, the more advanced polycyclic intermediate EFGHIJKLMN. Elaboration of the latter and coupling with fragment A followed by further functionalization completed the total synthesis of halichondrin B through a short and convergent pathway.

Marine Natural Products as Models to Circumvent Multidrug Resistance

Multidrug resistance (MDR) to anticancer drugs is a serious health problem that in many cases leads to cancer treatment failure. The ATP binding cassette (ABC) transporter P-glycoprotein (P-gp), which leads to premature efflux of drugs from cancer cells, is often responsible for MDR. On the other hand, a strategy to search for modulators from natural products to overcome MDR had been in place during the last decades. However, Nature limits the amount of some natural products, which has led to the development of synthetic strategies to increase their availability. This review summarizes the research findings on marine natural products and derivatives, mainly alkaloids, polyoxygenated sterols, polyketides, terpenoids, diketopiperazines, and peptides, with P-gp inhibitory activity highlighting the established structure-activity relationships. The synthetic pathways for the total synthesis of the most promising members and analogs are also presented. It is expected that the data gathered during the last decades concerning their synthesis and MDR-inhibiting activities will help medicinal chemists develop potential drug candidates using marine natural products as models which can deliver new ABC transporter inhibitor scaffolds.

Eribulin in Cancer Treatment

Halichondrin B is a complex, natural, polyether macrolide derived from marine sponges. Eribulin is a structurally-simplified, synthetic, macrocyclic ketone analogue of Halichondrin B. Eribulin was approved by United States Food and Drug Administration in 2010 as a third-line therapy for metastatic breast cancer patients who have previously been treated with an anthracycline and a taxane. It has a unique microtubule dynamics inhibitory action. Phase III studies have either been completed or are currently ongoing in breast cancer, soft tissue sarcoma, and non-small cell lung cancer. Phase I and II studies in multiple cancers and various combinations are currently ongoing. This article reviews the available information on eribulin with respect to its clinical pharmacology, pharmacokinetics, pharmacodynamics, mechanism of action, metabolism, preclinical studies, and with special focus on clinical trials.

New horizons for old drugs and drug leads

There is mounting urgency to find new drugs for the treatment of serious infectious diseases and cancer that are rapidly developing resistance to previously effective drugs. One approach to addressing this need is through drug repurposing, which refers to the discovery of new useful activities for "old" clinically used drugs through screening them against relevant disease targets. A large number of potential drug that, for various reasons, have failed to advance to clinical and commercial use can be added to the candidates available for such purposes. The application of new techniques and methodology developed through the impressive progress made in multidisciplinary, natural product-related research in recent years should aid substantially in expediting the discovery and development process. This review briefly outlines some of these developments as applied to a number of selected natural product examples, which may also include advances in chemical synthesis of derivatives with extended biological activities.

Atom-based enumeration: new eribulin analogues with low susceptibility to P-glycoprotein-mediated drug efflux

A series of eribulin analogues was evolved in silico through iterative atom-based enumeration employing a genetic algorithm-derived survival function to minimize predicted PgP-mediated drug efflux. Representatives of the virtual series were subsequently synthesized in the laboratory and tested in vitro for PgP-susceptibility. These new computer-inspired derivatives were found to exhibit high cell growth inhibitory activity and to be among the least sensitive to P-glycoprotein-mediated drug efflux in the eribulin series, thereby validating this approach to in silico molecular design.

Identification of the protease inhibitor miraziridine A in the Red sea sponge Theonella swinhoei

BACKGROUND

Miraziridine A, a natural peptide isolated from a marine sponge, is a potent cathepsin B inhibitor with a second-order rate constant of 1.5 × 10(4) M(-1) s(-1). In the present study, miraziridine A was isolated from the Red Sea sponge Theonella swinhoei on the basis of chromatographic and spectrometric techniques. We conclude that T. swinhoei from the Red Sea represents an alternative source of the aziridinylpeptide miraziridine A to the previously identified Theonella mirabilis from Japan. We confirmed that the metabolite is produced by marine sponges from different geographical locations.

CONTEXT

Marine sponges have been proven to be a rich source of secondary metabolites exhibiting a huge diversity of biological activities, including antimicrobial, antitumor and immunomodulatory activities. Theonella species (order Lithistida, Demospongiae) have been shown to be a source of anti-protease and anti-HIV secondary metabolites.

AIMS

To identify the protease inhibitor mirazirine A in the marine sponge Theonella swinhoei.

MATERIAL AND METHODS

The marine sponge Theonella swinhoei was collected by SCUBA diving in the Red Sea in Eilat (Israel). Sponge material was lyophilized and further extracted successively with cyclohexane, dichloromethane and methanol to obtain three crude extracts. LC-MS analysis was performed to confirm the presence of Miraziridine A in the dichloromethane fraction.

RESULTS

In the present study, miraziridine A was isolated from the Red Sea sponge T. swinhoei on the basis of chromatographic and spectrophotometric techniques.

CONCLUSIONS

We conclude that T. swinhoei from the Red Sea represents an alternative source of the aziridinylpeptide miraziridine A to the previously identified Theonella mirabilis from Japan.

Eribulin: A Novel Cytotoxic Chemotherapy Agent

OBJECTIVE:

To review the chemistry, pharmacology, pharmacokinetics, safety, and efficacy of eribulin (Halaven).

DATA SOURCES:

A literature search (up to December 2011) using the terms eribulin, Halaven, ER-086526, and E7389 was performed with PubMed, Google Scholar, selected Ovid bibliography searches, and the abstract search tool from the American Society of Clinical Oncology Annual Meetings and the San Antonio Breast Cancer Symposia. Additional references from the bibliographies of these articles were also assessed.

DATA EXTRACTION:

English-language preclinical and clinical studies on the chemistry, pharmacology, pharmacokinetics, safety, and efficacy of eribulin were reviewed.

DATA SYNTHESIS:

Eribulin is a novel microtubule inhibitor with a unique mechanism of action, which involves interaction with a distinct binding site on β-tubulin leading to G2/M phase cell-cycle arrest and apoptosis. Eribulin has been approved by the Food and Drug Administration for the treatment of metastatic breast cancer in patients who have been previously treated with an anthracycline and a taxane. In a pivotal Phase 3 study conducted in patients with metastatic breast cancer, eribulin 1.4 mg/m2, administered over 2-5 minutes as an intravenous infusion on days 1 and 8 of 21-day cycles, was associated with a significantly increased median overall survival of 13.1 months compared to the median overall survival of 10.6 months in the therapy of physician's choice. Eribulin has also shown activity in Phase 2 studies in other types of cancers, such as non–small cell lung cancer, prostate cancer, urothelial cancer, soft tissue sarcomas, and platinum-susceptible ovarian, fallopian tube, or peritoneal cancers. The most severe (grade 3/4) adverse effects associated with eribulin include neutropenia, leukopenia, and peripheral neuropathy. Common toxicities include fatigue, neutropenia, alopecia, anemia, and peripheral neuropathy.

CONCLUSIONS:

Eribulin is a promising new cytotoxic chemotherapy agent due to its ability to treat cancers that are refractory or resistant to other drugs as well as its manageable toxicity profile.

Potential clinical applications of halichondrins in breast cancer and other neoplasms

Halichondrin B is a large polyether macrolide found in a rare Japanese sponge, Halichondria okadai and has been shown to have anticancer activity. Eribulin mesylate is a completely synthetic analog of halichondrin B with a unique mechanism of action relative to other antimicrotubule agents. This new agent has demonstrated activity in preclinical studies, and it is being developed for the treatment of different tumor types. Eribulin has been approved by the United States Food and Drug Administration and the European Medicines Agency as late-line therapy for metastatic breast cancer patients previously treated with an anthracycline and a taxane. It has demonstrated superiority over other treatments in overall survival (OS) (hazard ratio: 0.81, P = 0.041), leading to its regulatory approbation for clinical practice use. Median OS for the eribulin-treated group was 13.1 months versus 10.6 months in the physician's treatment-of-choice group. Eribulin demonstrated a manageable toxicity profile. Most common adverse events associated with treatment were mild neutropenia and fatigue, mainly of grade 1 or 2. In contrast to other antimicrotubule agents, eribulin has a relatively low incidence of peripheral neuropathy and alopecia. Eribulin has been extensively studied in breast cancer and is currently being developed for treatment of other cancer types. Eribulin has demonstrated activity in Phase II trials in non-small cell lung cancer, pancreatic cancer, urothelial tract cancer, and sarcomas. Further studies in these cancers are ongoing. This article reviews pharmacology, mechanism of action, pharmacokinetics and efficacy of eribulin in breast cancer and other neoplasms.

Novel second generation analogs of eribulin. Part I: Compounds containing a lipophilic C32 side chain overcome P-glycoprotein susceptibility

Eribulin mesylate (Halaven™), a totally synthetic analog of the marine polyether macrolide halichondrin B, has recently been approved in the United States as a treatment for breast cancer. It is also currently under regulatory review in Japan and the European Union. Our continuing medicinal chemistry efforts on this scaffold have focused on oral bioavailability, brain penetration and efficacy against multidrug resistant (MDR) tumors by lowering the susceptibility of these compounds to P-glycoprotein (P-gp)-mediated drug efflux. Replacement of the 1,2-amino alcohol C32 side chain of eribulin with fragments neutral at physiologic pH led to the identification of analogs with significantly lower P-gp susceptibility. The analogs maintained low- to sub-nM potency in vitro against both sensitive and MDR cell lines. Within this series, increasing lipophilicity generally led to decreased P-gp susceptibility. In addition to potency in cell culture, these compounds showed in vivo activity in mouse xenograft models.