Synthesis of epothilones A and B in solid and solution phase

Convergent Total Synthesis of Ixabepilone and Its Analogues Enabled by Highly Efficient Asymmetric Hydrogenations

The convergent total synthesis of ixabepilone and its analogues in a 13-step longest linear sequence is reported. The crucial chiral centers at challenging C3-O, C8-C and C15-N positions on the scaffold of the ixabepilone were installed via highly efficient asymmetric hydrogenations (up to 95 % yield and up to 99 % e.e.) and all three fragments could be prepared on gram scale. The key aldol reaction bridges the aldehyde and keto fragments with high yield and exquisite diastereo control (8 : 1 d.r.). Finally, a novel RCM reaction conformationally controlled by a bulky silyl group was reported, which allows the facile synthesis of ixabepilone and its analogues.

Advances, opportunities, and challenges in methods for interrogating the structure activity relationships of natural products

Time span in literature: 1985-early 2024Natural products play a key role in drug discovery, both as a direct source of drugs and as a starting point for the development of synthetic compounds. Most natural products are not suitable to be used as drugs without further modification due to insufficient activity or poor pharmacokinetic properties. Choosing what modifications to make requires an understanding of the compound's structure-activity relationships. Use of structure-activity relationships is commonplace and essential in medicinal chemistry campaigns applied to human-designed synthetic compounds. Structure-activity relationships have also been used to improve the properties of natural products, but several challenges still limit these efforts. Here, we review methods for studying the structure-activity relationships of natural products and their limitations. Specifically, we will discuss how synthesis, including total synthesis, late-stage derivatization, chemoenzymatic synthetic pathways, and engineering and genome mining of biosynthetic pathways can be used to produce natural product analogs and discuss the challenges of each of these approaches. Finally, we will discuss computational methods including machine learning methods for analyzing the relationship between biosynthetic genes and product activity, computer aided drug design techniques, and interpretable artificial intelligence approaches towards elucidating structure-activity relationships from models trained to predict bioactivity from chemical structure. Our focus will be on these latter topics as their applications for natural products have not been extensively reviewed. We suggest that these methods are all complementary to each other, and that only collaborative efforts using a combination of these techniques will result in a full understanding of the structure-activity relationships of natural products.

Recent applications of solid-phase strategy in total synthesis of antibiotics

Antibiotics produced by soil microorganisms have been widespread and have cured the most prevalent diseases since 1940s. However, recent bacterial resistance to existing antibacterial drugs is causing a public health crisis. The structure-activity relationship of antibiotics needs to be established to search for existing antibiotics-based next-generation drug candidates that can conquer the challenge of bacterial resistance preparedness, which relies on the development of highly efficient total synthesis strategies. The solid-phase strategy has become important to circumvent tedious intermediate isolation and purification procedures with simple filtrations. This review will give a brief overview of recent applications of solid-phase strategy in the total synthesis of antibiotics.

Automated synthesis of prexasertib and derivatives enabled by continuous-flow solid-phase synthesis

Recent advances in end-to-end continuous-flow synthesis are rapidly expanding the capabilities of automated customized syntheses of small-molecule pharmacophores, resulting in considerable industrial and societal impacts; however, many hurdles persist that limit the number of sequential steps that can be achieved in such systems, including solvent and reagent incompatibility between individual steps, cumulated by-product formation, risk of clogging and mismatch of timescales between steps in a processing chain. To address these limitations, herein we report a strategy that merges solid-phase synthesis and continuous-flow operation, enabling push-button automated multistep syntheses of active pharmaceutical ingredients. We demonstrate our platform with a six-step synthesis of prexasertib in 65% isolated yield after 32 h of continuous execution. As there are no interactions between individual synthetic steps in the sequence, the established chemical recipe file was directly adopted or slightly modified for the synthesis of twenty-three prexasertib derivatives, enabling both automated early and late-stage diversification.

A Bayesian machine learning approach for drug target identification using diverse data types

Drug target identification is a crucial step in development, yet is also among the most complex. To address this, we develop BANDIT, a Bayesian machine-learning approach that integrates multiple data types to predict drug binding targets. Integrating public data, BANDIT benchmarked a ~90% accuracy on 2000+ small molecules. Applied to 14,000+ compounds without known targets, BANDIT generated ~4,000 previously unknown molecule-target predictions. From this set we validate 14 novel microtubule inhibitors, including 3 with activity on resistant cancer cells. We applied BANDIT to ONC201—an anti-cancer compound in clinical development whose target had remained elusive. We identified and validated DRD2 as ONC201’s target, and this information is now being used for precise clinical trial design. Finally, BANDIT identifies connections between different drug classes, elucidating previously unexplained clinical observations and suggesting new drug repositioning opportunities. Overall, BANDIT represents an efficient and accurate platform to accelerate drug discovery and direct clinical application.

Drug target identification is a crucial step in drug development. Here, the authors introduce a Bayesian machine learning framework that integrates multiple data types to predict the targets of small molecules, enabling identification of a new set of microtubule inhibitors and the target of the anti-cancer molecule ONC201.

Total Synthesis in Search of Potent Antibody-Drug Conjugate Payloads. From the Fundamentals to the Translational

The emergence and evolution of antibody-drug conjugates (ADCs) as targeted cancer therapies in recent years is a living example of the "magic bullet" concept of Paul Ehrlich, introduced by him more than a century ago. Consisting of three components, the antibody serving as the delivery system, the payload drug that kills the cancer cell, and the chemical linker through which the payload is attached to the antibody, ADCs represent a currently hotly pursued paradigm of targeted cancer therapies. While the needed monoclonal antibody falls in the domains of biology and biochemistry, the potent payload and the linker belong to the realm of chemistry. Naturally occurring molecules and their derivatives endowed with high cytotoxic properties have proven to be useful payloads for the first approved ADCs (i.e., Mylotarg, Adcetris, Kadcyla, and Besponsa). The latest approaches and intensifying activities in this new paradigm of cancer therapy demands a variety of payloads with different mechanisms of action in order to address the medical needs for the various types of cancers, challenging synthetic organic chemists to enrich the library of potential payloads. Total synthesis of natural and designed molecules not only provides a powerful avenue to replicate rare naturally occurring compounds in the laboratory but also offers a unique opportunity to rationally design and synthesize analogues thereof for biological evaluation and optimization of ADC payloads. In this Account, we describe our efforts in this area highlighting a number of total synthesis endeavors through which we rendered scarce naturally occurring molecules readily available for biological evaluations and, most importantly, employed the developed synthetic strategies and methods to construct, otherwise unavailable or difficult to reach, designed analogues of these molecules. Specifically, we summarize the total syntheses of natural and designed molecules of the calicheamicin, uncialamycin, tubulysin, trioxacarcin, epothilone, shishijimicin, namenamicin, thailanstatin, and disorazole families of compounds and demonstrate how these studies led to the discovery of analogues of higher potencies, yet some of them possessing lower complexities than their parent compounds as potential ADC payloads. The highlighted examples showcase the continuing impact of total synthesis of natural products and their analogues on modern medicine, including the so-called biologics and should prove useful and inspirational in advancing both the fields of total synthesis and biomedical research and the drug discovery and development process.

"One-Pot" Protection, Glycosylation, and Protection-Glycosylation Strategies of Carbohydrates

Carbohydrates, which are ubiquitously distributed throughout the three domains of life, play significant roles in a variety of vital biological processes. Access to unique and homogeneous carbohydrate materials is important to understand their physical properties, biological functions, and disease-related features. It is difficult to isolate carbohydrates in acceptable purity and amounts from natural sources. Therefore, complex saccharides with well-defined structures are often most conviently accessed through chemical syntheses. Two major hurdles, regioselective protection and stereoselective glycosylation, are faced by carbohydrate chemists in synthesizing these highly complicated molecules. Over the past few years, there has been a radical change in tackling these problems and speeding up the synthesis of oligosaccharides. This is largely due to the development of one-pot protection, one-pot glycosylation, and one-pot protection-glycosylation protocols and streamlined approaches to orthogonally protected building blocks, including those from rare sugars, that can be used in glycan coupling. In addition, new automated strategies for oligosaccharide syntheses have been reported not only for program-controlled assembly on solid support but also by the stepwise glycosylation in solution phase. As a result, various sugar molecules with highly complex, large structures could be successfully synthesized. To summarize these recent advances, this review describes the methodologies for one-pot protection and their one-pot glycosylation into the complex glycans and the chronological developments associated with automated syntheses of oligosaccharides.

MacroEvoLution: A New Method for the Rapid Generation of Novel Scaffold-Diverse Macrocyclic Libraries

Macrocycles are a structural class bearing great promise for future challenges in medicinal chemistry. Nevertheless, there are few flexible approaches for the rapid generation of structurally diverse macrocyclic compound collections. Here, an efficient method for the generation of novel macrocyclic peptide‐based scaffolds is reported. The process, named here as “MacroEvoLution”, is based on a cyclization screening approach that gives reliable access to novel macrocyclic architectures. Classification of building blocks into specific pools ensures that scaffolds with orthogonally addressable functionalities are generated, which can easily be used for the generation of structurally diverse compound libraries. The method grants rapid access to novel scaffolds with scalable synthesis (multi gram scale) and the introduction of further diversity at a late stage. Despite being developed for peptidic systems, the approach can easily be extended for the synthesis of systems with a decreased peptidic character.

Stabilized Polymer Micelles for the Development of IT-147, an Epothilone D Drug-Loaded Formulation

Epothilones have demonstrated promising potential for oncology applications but suffer from a narrow therapeutic window. Epothilone D stabilizes microtubules leading to apoptosis, is active against multidrug-resistant cells, and is efficacious in animal tumor models despite lack of stability in rodent plasma. Clinical development was terminated in phase II due to dose limiting toxicities near the efficacious dose. Taken together, this made epothilone D attractive for encapsulation in a stabilized polymer micelle for improved safety and efficacy. We have designed a library of triblock copolymers to develop IT-147, a lead formulation of epothilone D that extends plasma circulation for accumulation in the tumor environment, and potentially decrease systemic exposure to reduce dose limiting toxicities. The drug loading efficiency for IT-147 exceeds 90%, is 75 nm in diameter, and demonstrates pH-dependent release of epothilone D without chemical conjugation or enzymatic activation. Administration of IT-147 at 20 mg/kg increases exposure of epothilone D to the plasma compartment over 6-fold compared to free drug. At the same dose, 20 mg/kg epothilone D from IT-147 is considered the no observed adverse effect level (NOAEL) but is the maximum tolerated dose for free drug. Consequently, IT-147 is positioned to be a safer, more effective means to deliver epothilone D.

Synthesis, Biological Profiling and Determination of the Tubulin-Bound Conformation of 12-Aza-Epothilones (Azathilones)

12-Aza-epothilones (azathilones) incorporating quinoline side chains and bearing different N12-substituents have been synthesized via highly efficient RCM-based macrocyclizations. Quinoline-based azathilones with the side chain N-atom in the meta-position to the C15 atom in the macrocycle are highly potent inhibitors of cancer cell growth in vitro. In contrast, shifting the quinoline nitrogen to the position para to C15 leads to a ca. 1000-fold loss in potency. Likewise, the desaturation of the C9-C10 bond in the macrocycle to an E double bond produces a substantial reduction in antiproliferative activity. This is in stark contrast to the effect exerted by the same modification in the natural epothilone macrocycle. The conformation of a representative azathilone bound to α/β-tubulin heterodimers was determined based on TR-NOE measurements and a model for the posture of the compound in its binding site on β-tubulin was deduced through a combination of STD measurements and CORCEMA-ST calculations. The tubulin-bound, bioactive conformation of azathilones was found to be overall similar to that of epothilones A and B.

Strategies for the Discovery and Development of New Antibiotics from Natural Products: Three Case Studies

Natural products continue to be a predominant source for new anti-infective agents. Research at the Helmholtz Institute for Pharmaceutical Research Saarland (HIPS) and the Helmholtz Centre for Infection Research (HZI) is dedicated to the development of new lead structures against infectious diseases and, in particular, new antibiotics against hard-to-treat and multidrug-resistant bacterial pathogens. In this chapter, we introduce some of the concepts currently being employed in the field of antibiotic discovery. In particular, we will exemplarily illustrate three approaches: (1) Current sources for novel compounds are mainly soil-dwelling bacteria. In the course of our antimicrobial discovery program, a biodiverse collection of myxobacterial strains has been established and screened for antibiotic activities. Based on this effort, one successful example is presented in this chapter: Antibacterial cystobactamids were discovered and their molecular target, the DNA gyrase, was identified soon after the analysis of myxobacterial self-resistance making use of the information found in the respective biosynthesis gene cluster. (2) Besides our focus on novel natural products, we also apply strategies to further develop either neglected drugs or widely used antibiotics for which development of resistance in the clinical setting is an issue: Antimycobacterial griselimycins were first described in the 1960s but their development and use in tuberculosis therapy was not further pursued. We show how a griselimycin derivative with improved pharmacokinetic properties and enhanced potency against Mycobacterium tuberculosis revealed and validated a novel target for antibacterial therapy, the DNA sliding clamp. (3) In a third approach, biosynthetic engineering was used to modify and optimize natural products regarding their pharmaceutical properties and their production scale: The atypical tetracycline chelocardin is a natural product scaffold that was modified to yield a more potent derivative exhibiting activity against multidrug-resistant pathogens. This was achieved by genetic engineering of the producer strain and the resulting compound is now subject to further optimization by medicinal chemistry approaches.

Epothilones in epithelial ovarian, fallopian tube, or primary peritoneal cancer: a systematic review

Ovarian cancer is the most lethal gynecologic malignancy; consequently, there is a need for effective therapies. Epothilones are microtubule-stabilizing agents that inhibit cell growth. Currently, patupilone and its four synthetic derivatives ixabepilone, BMS-310705, sagopilone, 20-desmethyl-20-methylsulfanyl epothilone B and epothilone D, as well as its derivative KOS-1584, are under clinical evaluation. This is the first systematic review conducted in accordance with the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines that synthesizes all available data emerging from trials and evaluates the efficacy and safety of epothilones in epithelial ovarian, primary fallopian tube, and primary peritoneal cancer. Despite the fact that epothilones have proven active in taxane-resistant settings in preclinical models, it is not yet clear from Phase II/III studies reviewed here that their clinical activity is superior to that of taxanes. Nevertheless, responses to epothilones have been observed in platinum-refractory/resistant ovarian cancer patients. Moreover, despite the shared mechanism of action of epothilones, their clinical profile seems clearly different, with diarrhea being the most common dose-limiting toxicity encountered with patupilone, whereas neutropenia and sensory neuropathy are the most common toxic effects observed with the other epothilones. In any case, randomized trials comparing epothilones with standard treatments seem warranted to define further the role of these agents, whereas biomarker analysis might further optimize patient selection.

Divergent solid-phase synthesis of natural product-inspired bipartite cyclodepsipeptides: total synthesis of seragamide A

Macrocyclic natural products (NPs) and analogues thereof often show high affinity, selectivity, and metabolic stability, and methods for the synthesis of NP-like macrocycle collections are of major current interest. We report an efficient solid-phase/cyclorelease method for the synthesis of a collection of macrocyclic depsipeptides with bipartite peptide/polyketide structure inspired by the very potent F-actin stabilizing depsipeptides of the jasplakinolide/geodiamolide class. The method includes the assembly of an acyclic precursor chain on a polymeric carrier, terminated by olefins that constitute complementary fragments of the polyketide section and cyclization by means of a relay-ring-closing metathesis (RRCM). The method was validated in the first total synthesis of the actin-stabilizing cyclodepsipeptide seragamide A and the synthesis of a collection of structurally diverse bipartite depsipeptides.

Reusable manganese compounds containing pyrazole-based ligands for olefin epoxidation reactions

New robust and effective Mn-pyrazolyl catalysts for olefin epoxidation in [bmim]PF₆ : CH₃CN, with good activity even after several reuses, are described. The cis → trans isomerization in the epoxidation of cis-β-methylstyrene is confirmed through computational calculations.

Trial watch: Chemotherapy with immunogenic cell death inducers

It is now clear that the immune system plays a critical role not only during oncogenesis and tumor progression, but also as established neoplastic lesions respond to therapy. Selected cytotoxic chemicals can indeed elicit immunogenic cell death, a functionally peculiar type of apoptosis that stimulates tumor-specific cognate immune responses. Such immunogenic chemotherapeutics include cyclophosphamide, doxorubicin and oxaliplatin (which are approved by FDA for the treatment of various hematological and solid malignancies), mitoxantrone (which is currently employed both as an anticancer agent and against multiple sclerosis) and patupilone (a microtubular poison in clinical development). One year ago, in the second issue of OncoImmunology, we discussed the scientific rationale behind immunogenic chemotherapy and reviewed the status of recent clinical trials investigating the off-label use of cyclophosphamide, doxorubicin, oxaliplatin and mitoxantrone in cancer patients. Here, we summarize the latest developments in this area of clinical research, covering both high-impact studies that have been published during the last 13 months and clinical trials that have been initiated in the same period to assess the antineoplastic profile of immunogenic chemotherapeutics.

Epothilones

Epothilones A and B are naturally occurring microtubule stabilizers with nanomolar or even sub-nanomolar activity against human cancer cells in vitro and potent in vivo antitumor activity against multidrug-resistant tumors. Over the last decade, ten epothilonetype agents have entered clinical trials in humans; of these, the epothilone B lactam ixabepilone (BMS-247550; Ixempra®) was approved by the FDA for breast cancer treatment in 2007. Numerous synthetic and semisynthetic analogs of epothilones have been prepared and their in vitro and (in selected cases) in vivo biological activity has been determined, producing a wealth of SAR information on this compound family. This chapter will provide a brief summary of the in vitro and in vivo biological properties of epothilone B (Epo B). The major part of the discussion will then be organized around those epothilone analogs that have entered clinical development. For each analog the underlying synthetic chemistry and the most important preclinical features will be reviewed, together with the properties of some important related structures.

Gold-catalyzed 1,2-acyloxy migration/intramolecular [3+2] 1,3-dipolar cycloaddtion cascade reaction: an efficient strategy for syntheses of medium-sized-ring ethers and amines

A highly efficient strategy for the formation of medium-sized-ring ethers and amines based on a gold-catalyzed cascade reaction, involving enynyl ester isomerization and intramolecular [3+2] cyclization, has been developed. Various multisubstituted medium-sized-ring unsaturated ethers and amines were obtained through this transformation. This method represents one of the relatively few transition metal catalyzed intramolecular cycloaddition reactions for medium-sized ring synthesis.

Antimalarial activity of the myxobacterial macrolide chlorotonil a

Myxobacteria are Gram-negative soil-dwelling bacteria belonging to the phylum Proteobacteria. They are a rich source of promising compounds for clinical application, such as epothilones for cancer therapy and several new antibiotics. In the course of a bioactivity screening program of secondary metabolites produced by Sorangium cellulosum strains, the macrolide chlorotonil A was found to exhibit promising antimalarial activity. Subsequently, we evaluated chlorotonil A against Plasmodium falciparum laboratory strains and clinical isolates from Gabon. Chlorotonil A was highly active, with a 50% inhibitory concentration between 4 and 32 nM; additionally, no correlations between the activities of chlorotonil A and artesunate (rho, 0.208) or chloroquine (rho, -0.046) were observed. Per os treatment of Plasmodium berghei-infected mice with four doses of as little as 36 mg of chlorotonil A per kg of body weight led to the suppression of parasitemia with no obvious signs of toxicity. Chlorotonil A acts against all stages of intraerythrocytic parasite development, including ring-stage parasites and stage IV to V gametocytes, and it requires only a very short exposure to the parasite to exert its antimalarial action. Conclusively, chlorotonil A has an exceptional and unprecedented profile of action and represents an urgently required novel antimalarial chemical scaffold. Therefore, we propose it as a lead structure for further development as an antimalarial chemotherapeutic.

Mononuclear complexes of amide-based ligands containing appended functional groups: role of secondary coordination spheres on catalysis

Coordination complexes of amide-based ligands with appended heterocyclic rings create a hydrogen bonding cavity that effectively binds the substrate(s). Such cavity-based complexes function as reusable and heterogeneous catalysts for various organic transformations.

Macrolide-based microtubule-stabilizing agents - chemistry and structure-activity relationships

This article provides an overview on the chemistry and structure-activity relationships of macrolide-based microtubule-stabilizing agents. The primary focus will be on the total synthesis or examples thereof, but a brief summary of the current state of knowledge on the structure-activity relationships of epothilones, laulimalide, dictyostatin, and peloruside A will also be given. This macrolide class of compounds, over the last decade, has become the subject of growing interest due to their ability to inhibit human cancer cell proliferation through a taxol-like mechanism of action.

Phase I clinical, pharmacokinetic, and pharmacodynamic study of KOS-862 (Epothilone D) in patients with advanced solid tumors and lymphoma

PURPOSE

To determine the maximum tolerated dose and safety of the epothilone, KOS-862, in patients with advanced solid tumors or lymphoma.

PATIENTS AND METHODS

Patients were treated weekly for 3 out of 4 weeks (Schedule A) or 2 out of 3 weeks (Schedule B) with KOS-862 (16-120 mg/m(2)). Pharmacokinetic (PK) sampling was performed during cycles 1 and 2; pharmacodynamic (PD) assessment for microtubule bundle formation (MTBF) was performed after the 1st dose, only at or above 100 mg/m(2).

RESULTS

Thirty-two patients were enrolled, and twenty-nine completed ≥1 cycle of therapy. Dose limiting toxicity [DLT] was observed at 120 mg/m(2). PK data were linear from 16 to 100 mg/m(2), with proportional increases in mean C(max) and AUC(tot) as a function of dose. Full PK analysis (mean ± SD) at 100 mg/m(2) revealed the following: half-life (t (½)) = 9.1 ± 2.2 h; volume of distribution (V(z)) = 119 ± 41 L/m(2); clearance (CL) = 9.3 ± 3.2 L/h/m(2). MTBF (n = 9) was seen in 40% of PBMCs within 1 h and in 15% of PBMC at 24-hours post infusion at 100 mg/m(2). Tumor shrinkage (n = 2, lymphoma), stable disease >3 months (n = 5, renal, prostate, oropharynx, cholangiocarcinoma, and Hodgkin lymphoma), and tumor marker reductions (n = 1, colorectal cancer/CEA) were observed.

CONCLUSION

KOS-862 was well tolerated with manageable toxicity, favorable PK profile, and the suggestion of clinical activity. The maximum tolerated dose was determined to be 100 mg/m(2) weekly 3-on/1-off. MTBF can be demonstrated in PBMCs of patients exposed to KOS-862.

Constructing molecular complexity and diversity: total synthesis of natural products of biological and medicinal importance

The advent of organic synthesis and the understanding of the molecule as they occurred in the nineteenth century and were refined in the twentieth century constitute two of the most profound scientific developments of all time. These discoveries set in motion a revolution that shaped the landscape of the molecular sciences and changed the world. Organic synthesis played a major role in this revolution through its ability to construct the molecules of the living world and others like them whose primary element is carbon. Although the early beginnings of organic synthesis came about serendipitously, organic chemists quickly recognized its potential and moved decisively to advance and exploit it in myriad ways for the benefit of mankind. Indeed, from the early days of the synthesis of urea and the construction of the first carbon-carbon bond, the art of organic synthesis improved to impressively high levels of sophistication. Through its practice, today chemists can synthesize organic molecules--natural and designed--of all types of structural motifs and for all intents and purposes. The endeavor of constructing natural products--the organic molecules of nature--is justly called both a creative art and an exact science. Often called simply total synthesis, the replication of nature's molecules in the laboratory reflects and symbolizes the state of the art of synthesis in general. In the last few decades a surge in total synthesis endeavors around the world led to a remarkable collection of achievements that covers a wide ranging landscape of molecular complexity and diversity. In this article, we present highlights of some of our contributions in the field of total synthesis of natural products of biological and medicinal importance. For perspective, we also provide a listing of selected examples of additional natural products synthesized in other laboratories around the world over the last few years.

Stereoselective synthesis of Z-alkenes

This chapter offers a general review of the evolvement of methods for the stereoselective synthesis of Z-alkenes, with a focus on the development of catalytic systems towards this goal in recent years.

C6-C8 bridged epothilones: consequences of installing a conformational lock at the edge of the macrocycle

A series of conformationally restrained epothilone analogues with a short bridge between the methyl groups at C6 and C8 was designed to mimic the binding pose assigned to our recently reported EpoA-microtubule binding model. A versatile synthetic route to these bridged epothilone analogues has been successfully devised and implemented. Biological evaluation of the compounds against A2780 human ovarian cancer and PC3 prostate cancer cell lines suggested that the introduction of a bridge between C6-C8 reduced potency by 25-1000 fold in comparison with natural epothilone D. Tubulin assembly measurements indicate these bridged epothilone analogues to be mildly active, but without significant microtubule stabilization capacity. Molecular mechanics and DFT energy evaluations suggest the mild activity of the bridged epo-analogues may be due to internal conformational strain.

A phase 1 study of KOS-862 (Epothilone D) co-administered with carboplatin (Paraplatin®) in patients with advanced solid tumors

PURPOSE

To determine the maximally tolerated dose (MTD) and pharmacokinetics of carboplatin plus KOS-862 (Epothilone D) a novel cytotoxic macrolide capable of causing mitotic arrest, in patients with advanced solid malignancies.

EXPERIMENTAL DESIGN

Patients who have progressed on standard regimens were treated at four different levels of KOS-862(mg/m(2))/Carboplatin(AUC): 50/5,75/5, 75/6 and 100/6 in a "3 + 3" phase I study study design to determine MTD. Patients received KOS-862 on Days 1 and 8, and carboplatin on day 1, of 3-week cycles. Pharmacokinetics of KOS-862 and Carboplatin were studied.

RESULTS

Twenty-seven patients enrolled in the study. At the top dose level, 2 out of the 9 patients experienced Dose Limiting Toxicity. (grade 3 peripheral motor neuropathy in both patients) Twenty-seven patients had sufficient plasma data points for pharmacokinetic analysis Both the parent drug, KOS-862, and the major inactive metabolite Seco-D KOS-862 (KOS-1965) were quantified in plasma. Kinetics of KOS-862 were the same as seen in monotherapy studies using the same route and time of administration. Two patients had tumor response after study treatment. Ten of 20 evaluable patients had stable disease after 2 cycles of study treatment. The MTD in the present study was KOS-862 100 mg/m(2) + carboplatin AUC = 6.

CONCLUSIONS

The pharmacokinetics of KOS-862 were similar in this combination study to those seen in previous monotherapy studies using the same route and time of administration. We have described the MTD of this schedule. The neurotoxicity seen with this regimen should be considered prior to its administration in unselected populations.

Ixabepilone for the treatment of breast cancer

Patients with breast cancer that becomes resistant to taxanes and anthracyclines experience considerable morbidity and mortality. The Food and Drug Administration has approved the use of ixabepilone for the treatment of patients with locally advanced or metastatic breast cancer that is refractory or resistant to taxanes and anthracyclines. The purpose of this review is to summarize the evidence from published studies on the pharmacological data and clinical activity of ixabepilone in patients with breast cancer. The conclusion of this review is that ixabepilone demonstrated a high efficacy in combination with capecitabine and as a single agent in breast cancer refractory to taxanes and anthracyclines. The clinical activity of ixabepilone combined with bevacizumab for advanced breast cancer was very promising.

Diversity through semisynthesis: the chemistry and biological activity of semisynthetic epothilone derivatives

Epothilones are myxobacterial natural products that inhibit human cancer cell growth through the stabilization of cellular microtubules (i.e., a "taxol-like" mechanism of action). They have proven to be highly productive lead structures for anticancer drug discovery, with at least seven epothilone-type agents having entered clinical trials in humans over the last several years. SAR studies on epothilones have included a large number of fully synthetic analogs and semisynthetic derivatives. Previous reviews on the chemistry and biology of epothilones have mostly focused on analogs that were obtained by de novo chemical synthesis. In contrast, the current review provides a comprehensive overview on the chemical transformations that have been investigated for the major epothilones A and B as starting materials, and it discusses the biological activity of the resulting products. Many semisynthetic epothilone derivatives have been found to exhibit potent effects on human cancer cell growth and several of these have been advanced to the stage of clinical development. This includes the epothilone B lactam ixabepilone (Ixempra(®), which has been approved by the FDA for the treatment of advanced and metastatic breast cancer.

Phase I trial of ixabepilone plus pegylated liposomal doxorubicin in patients with adenocarcinoma of breast or ovary

BACKGROUND

Ixabepilone is a semisynthetic epothilone B analogue that is active in taxane-resistant cell lines and has shown activity in patients with refractory breast and ovarian cancer. We carried out a phase I trial of ixabepilone plus pegylated liposomal doxorubicin (PLD) in patients with advanced taxane-pretreated ovarian and breast cancer.

METHODS

Patients with recurrent ovarian or breast carcinoma received PLD every 3 or 4 weeks plus five different dose schemas of ixabepilone in cohorts of three to six patients.

RESULTS

Thirty patients received a total of 142 treatment cycles of the PLD-ixabepilone combination. The recommended phase II dose and schedule of ixabepilone was 16 mg/m(2) on days 1, 8, and 15 plus PLD 30 mg/m(2) given on day 1, repeated every 4 weeks. Hand-foot syndrome and mucositis were dose limiting when both ixabepilone and PLD were given every 3 or 4 weeks. Objective responses were observed in 3 of 13 patients (23%) with breast cancer and 5 of 17 patients (29%) with ovarian cancer.

CONCLUSION

Ixabepilone may be safely combined with PLD, but tolerability is highly dependent upon the scheduling of both agents. This combination demonstrated efficacy in patients with breast and ovarian cancer and merits further evaluation in these settings.