Phase I and Pharmacokinetic Study of the Dolastatin 10 Analogue TZT-1027, Given on Days 1 and 8 of a 3-Week Cycle in Patients with Advanced Solid Tumors

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.

Therapeutic potential of marine peptides in cervical and ovarian cancers

Cervical and ovarian cancers contribute significantly to female morbidity and mortality worldwide. The current standard of treatment, including surgical removal, radiation therapy, and chemotherapy, offers poor outcomes. There are many side effects to traditional chemotherapeutic agents and treatment-resistant types, and often the immune response is depressed. As a result, traditional approaches have evolved to include new alternative remedies, such as natural compounds. Aquatic species provide a rich supply of possible drugs. The potential anti-cancer peptides are less toxic to normal cells and can attenuate multiple drug resistance by providing an efficacious treatment approach. The physiological effects of marine peptides are described in this review focusing on various pathways, such as apoptosis, microtubule balance disturbances, suppression of angiogenesis, cell migration/invasion, and cell viability. The review also highlights the potential role of marine peptides as safe and efficacious therapeutic agent for the treatment of cervical and ovarian cancers.

Bacterial proteolytic activity improves drug delivery in tumors in a size, pharmacokinetic, and binding affinity dependent manner - A mechanistic understanding

Motile bacteria are able to penetrate in the distal areas of blood vessel, which makes bacteria attractive to researchers as a drug delivery vehicle carrying anti-cancer drugs to tumors. Not only therapeutic bacteria show wide anti-tumor effect but also the combination of therapeutic bacteria and conventional chemotherapy leads to dramatically large synergetic effect. We provide a mechanistic understanding of enhanced drug delivery in tumors by co-administration of chemotherapeutic agents and therapeutic bacteria. In this work, simultaneous delivery of C. novyi-NT and chemotherapeutic agents in tumors is mathematically modeled. Simulated doxorubicin concentration in tumors after Doxil administration with or without bacteria agreed reasonably well with experimental literature. Simulated doxorubicin concentration in tumors by the combination of Doxil and C. novyi-NT is over twice higher than that of Doxil alone. This enhanced doxorubicin concentration in tumors is due to the degradation of extracellular matrix of collagen by bacterial proteolytic activity, which increases hydraulic conductivity of interstitium, reduces interstitial fluid pressure, and thus increases convection through vessel walls. Additionally, it alleviates solid stress, which decompresses blood vessels, and thus increases vessel density. On the other hand, simulated doxorubicin concentration in tumors for non-liposomal free-doxorubicin is not enhanced by C. novyi-NT because vascular permeability of free-doxorubicin is larger than Doxil, and thus increased but relatively small convection across vessel walls is offset by the efflux due to increased interstitial flow. A strategy to further enhance this combination therapy is discussed along with sensitivity analysis.

Vascular Disrupting Agents in cancer treatment: Cardiovascular toxicity and implications for co-administration with other cancer chemotherapeutics

Destruction of the established tumour vasculature by a class of compound termed Vascular Disrupting Agents (VDAs) is showing considerable promise as a viable approach for the management of solid tumours. VDAs induce a rapid shutdown and collapse of tumour blood vessels, leading to ischaemia and consequent necrosis of the tumour mass. Their efficacy is hindered by the persistence of a viable rim of tumour cells, supported by the peripheral normal vasculature, necessitating their co-administration with additional chemotherapeutics for maximal therapeutic benefit. However, a major limitation for the use of many cancer therapeutics is the development of life-threatening cardiovascular toxicities, with significant consequences for treatment response and the patient's quality of life. The aim of this review is to outline VDAs as a cancer therapeutic approach and define the mechanistic basis of cardiovascular toxicities of current chemotherapeutics, with the overall objective of discussing whether VDA combinations with specific chemotherapeutic classes would be good or bad in terms of cardiovascular toxicity.

A high-specificity immunoassay for the therapeutic drug monitoring of cyclophosphamide

Personalized medicine is pushing forward new diagnostic techniques to aid in controlling drug therapeutic levels and their toxic effects.

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 and Evaluation of Dolastatin 10 Analogues Containing Heteroatoms on the Amino Acid Side Chains

Synthetic analogues of the natural occurring dolastatin 10 are of great interest in cancer due to their potent in vitro activity and their uses as payloads in antibody drug conjugates (ADCs). Modification of the dolastatin 10 core scaffold has mainly focused on modifications of the P1, N-terminus, and P5, C-terminus, with minimal attention to the P2 subunit. In this paper we discuss the introduction of heteroatoms to the P2 side chain, which results in potent activity in vitro. The most active compounds contained azides in the P2 unit and required a phenylalanine-derived P5 subunit.

Dose-banding of carboplatin: rationale and proposed banding scheme

Background. In dose-banding (DB) prescribed doses of cancer chemotherapy are fitted to doseranges or ‘bands’ and standard doses for each band are provided using a selection of pre-filled infusions or syringes, either singly or in combination. DB is used for several drugs where dose is based on body surface area. No DB-scheme has been reported for carboplatin, which, in clinical practice, is routinely dosed according to renal function.

Study objective. To assess the rationale for DB of carboplatin with regards to factors that influence dosing accuracy, develop a DB scheme, and discuss its potential use and limitations.

Methods. Prospective evaluations of carboplatin area under the plasma concentration – time curve (AUC) following application of the Calvert-formula were identified by a literature search. A relevant carboplatin dose range for construction of a DB-scheme with Calvert-formula based doses was obtained from published glomerular filtration rate distributions for patients receiving carboplatin.

Results. A DB-scheme was developed for individually calculated carboplatin doses of 358–1232 mg, with 35 mg increments between each standard dose and a maximum deviation of 4.7% from prescribed dose. The proposed DB-scheme covers the GFR-ranges 47–221 mL/min and 26–151 mL/min for patients receiving doses based on the target AUCs of 5 and 7 mg/mL/min, respectively.

Conclusion. There is a strong scientific rationale to support DB of carboplatin. The proposed banding scheme could introduce benefits to patients and healthcare staff but, as with other DB schemes, should be validated with prospective clinical and pharmacokinetic studies to confirm safety and efficacy.

Stabilizing versus destabilizing the microtubules: a double-edge sword for an effective cancer treatment option?

Microtubules are dynamic and structural cellular components involved in several cell functions, including cell shape, motility, and intracellular trafficking. In proliferating cells, they are essential components in the division process through the formation of the mitotic spindle. As a result of these functions, tubulin and microtubules are targets for anticancer agents. Microtubule-targeting agents can be divided into two groups: microtubule-stabilizing, and microtubule-destabilizing agents. The former bind to the tubulin polymer and stabilize microtubules, while the latter bind to the tubulin dimers and destabilize microtubules. Alteration of tubulin-microtubule equilibrium determines the disruption of the mitotic spindle, halting the cell cycle at the metaphase-anaphase transition and, eventually, resulting in cell death. Clinical application of earlier microtubule inhibitors, however, unfortunately showed several limits, such as neurological and bone marrow toxicity and the emergence of drug-resistant tumor cells. Here we review several natural and synthetic microtubule-targeting agents, which showed antitumor activity and increased efficacy in comparison to traditional drugs in various preclinical and clinical studies. Cryptophycins, combretastatins, ombrabulin, soblidotin, D-24851, epothilones and discodermolide were used in clinical trials. Some of them showed antiangiogenic and antivascular activity and others showed the ability to overcome multidrug resistance, supporting their possible use in chemotherapy.

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.

Phase I study of TZT-1027, a novel synthetic dolastatin 10 derivative and inhibitor of tubulin polymerization, given weekly to advanced solid tumor patients for 3 weeks

TZT-1027 is a novel synthetic dolastatin 10 derivative that inhibits tubulin polymerization. A phase I study was conducted to determine the maximum tolerated dose (MTD) of TZT-1027, and to assess its pharmacokinetic profile in Japanese patients with advanced solid tumors following administration of the drug weekly for 3 weeks. Eligible patients had advanced solid tumors that failed to respond to standard therapy or for which no standard therapy was available, and met the following criteria: performance status ≤2 and acceptable organ function. The MTD was defined as the highest dose at which more than two-thirds of the patients experienced grade 4 hematological toxicity or grade 3/4 non-hematological toxicity during weekly TZT-1027 administration for 3 weeks. Forty patients were enrolled in the present study. Twelve doses between 0.3 and 2.1 mg/m2 were evaluated. Grade 4 neutropenia was the principal dose-limiting toxicity (DLT). At a dose of 2.1 mg/m2, two patients developed DLT: one patient developed grade 4 neutropenia, grade 3 myalgia, and grade 4 constipation, and the other one developed grade 4 neutropenia and grade 3 constipation. At a dose level of 1.8 mg/m2, toxicity was acceptable and no DLT was observed. The area under the curve and maximum concentration of TZT-1027 tended to increase linearly with the dose. The DLT observed were neutropenia, myalgia, and constipation, and the MTD was 2.1 mg/m2. The recommended dose for a phase II study was determined to be 1.8 mg/m2 for the drug administered weekly for 3 weeks.

Drug development from marine natural products

Drug discovery from marine natural products has enjoyed a renaissance in the past few years. Ziconotide (Prialt; Elan Pharmaceuticals), a peptide originally discovered in a tropical cone snail, was the first marine-derived compound to be approved in the United States in December 2004 for the treatment of pain. Then, in October 2007, trabectedin (Yondelis; PharmaMar) became the first marine anticancer drug to be approved in the European Union. Here, we review the history of drug discovery from marine natural products, and by describing selected examples, we examine the factors that contribute to new discoveries and the difficulties associated with translating marine-derived compounds into clinical trials. Providing an outlook into the future, we also examine the advances that may further expand the promise of drugs from the sea.

Dose calculation of anticancer drugs

BACKGROUND

Anticancer drugs are characterized by a narrow therapeutic window and significant inter-patient variability in therapeutic and toxic effects. Current body surface area (BSA)-based dosing fails to standardize systemic anticancer drug exposure and other alternative dosing strategies also have their limitations. Just as important as the initial dose selection is the subsequent dose revision to ensure the dose is correct.

OBJECTIVE

To provide an insight into the different dose individualization and dose adjustment methods, their feasibility and applicability in daily oncology practice and to suggest a practical framework for dose calculation and a basis for future research.

METHODS

Review of relevant literature related to dose calculation of anticancer drugs.

RESULTS

Strategies using clinical parameters, genotype and phenotype markers, and therapeutic drug monitoring all have potential and each has a role for specific drugs. However, no one method is a practical dose calculation strategy for many or all drugs.

CONCLUSION

Given that BSA-dosing leads to significant underdosing it is not reasonable to use this as the sole method of dose calculation. Because of wide disparity in individual patient characteristics and elimination mechanisms, we are unlikely to find the 'Holy Grail' of a single individualized dosing strategy for every patient and anticancer drug in the near future. We propose a pragmatic, although invalidated system for initial dose calculation using dose clusters and structured subsequent dose revision based on treatment-related toxicities and therapeutic drug monitoring. These models need to be tested in clinical trials.

Marine pharmacology in 2005-2006: antitumour and cytotoxic compounds

During 2005 and 2006, marine pharmacology research directed towards the discovery and development of novel antitumour agents was reported in 171 peer-reviewed articles. The purpose of this article is to present a structured review of the antitumour and cytotoxic properties of 136 marine natural products, many of which are novel compounds that belong to diverse structural classes, including polyketides, terpenes, steroids and peptides. The organisms yielding these bioactive marine compounds included invertebrate animals, algae, fungi and bacteria. Antitumour pharmacological studies were conducted with 42 structurally defined marine natural products in a number of experimental and clinical models which further defined their mechanisms of action. Particularly potent in vitro cytotoxicity data generated with murine and human tumour cell lines were reported for 94 novel marine chemicals with as yet undetermined mechanisms of action. Noteworthy is the fact that marine anticancer research was sustained by a global collaborative effort, involving researchers from Australia, Belgium, Benin, Brazil, Canada, China, Egypt, France, Germany, India, Indonesia, Italy, Japan, Mexico, the Netherlands, New Zealand, Panama, the Philippines, Slovenia, South Korea, Spain, Sweden, Taiwan, Thailand, United Kingdom (UK) and the United States of America (USA). Finally, this 2005-2006 overview of the marine pharmacology literature highlights the fact that the discovery of novel marine antitumour agents continued at the same active pace as during 1998-2004.

Epothilones and new analogues of the microtubule modulators in taxane-resistant disease

BACKGROUND

Microtubule-stabilising agents typified by the epothilone class of drug have demonstrated promising activity in Phase II and III clinical trials.

OBJECTIVE

Data supporting the efficacy of these agents are reviewed and their potential use in taxane-refractory disease assessed.

METHODS

Preclinical evidence assessing the role of the spindle assembly checkpoint in determining the cellular response to microtubule stabilization are presented together with clinical data documenting the efficacy of non-taxane microtubule modulators.

RESULTS/CONCLUSIONS

Evidence suggests that microtubule-stabilising agents prolong activation of the spindle assembly checkpoint which may promote cancer cell death in mitosis or following mitotic exit. A weakened spindle assembly checkpoint is associated with altered sensitivity to agents targeting the microtubule and therefore pathways of drug resistance may be shared by these cytotoxic therapies. Preliminary clinical trial data do suggest modest activity of epothilones in truly taxane-resistant patient cohorts, indicating the potential niche for these agents in a molecularly undefined patient group, potentially implicating the role of P-glycoprotein in the acquisition of taxane-resistant disease. Trial data of these antimitotic agents will be presented together with their potential role in taxane-resistant disease and the implications for future clinical trial design.

Efficacy of selected natural products as therapeutic agents against cancer

With emerging sophistication in the exploration of ocean environment, a number of marine bioactive products have been identified with promising anticancer activity. Many of these are in active phase I or phase II clinical trials or have been terminated because of adverse side effects, mainly hematological in nature. Nonetheless, the information derived has aided enormously in providing leads for laboratory synthesis with modifications in the parent structure affecting compound solubility, absorption, and toxicity, resulting in less severe toxicity while achieving maximum efficacy in smaller doses. We describe herein, a few of the compounds obtained from marine and terrestrial sources [bryostatin 1 ( 1), dolastatin 10 ( 2), auristatin PE ( 3), and combretastatin A4 ( 4)] that have been extensively investigated in our laboratory and continue to be investigated for their sensitization effects with other cytotoxic agents in several different site-specific tumors employing murine models or human subjects.

Phase I study of TZT-1027, a novel synthetic dolastatin 10 derivative, for the treatment of patients with non-small cell lung cancer

PURPOSE

The purpose of this phase I study was to evaluate the maximum-tolerated dose (MTD), dose-limiting toxicity (DLT), the recommended dose for phase II study, pharmacokinetics, and antitumor activity of TZT-1,027 (soblidotin) in patients with non-small cell lung cancer (NSCLC) when administered every 3-4 weeks.

METHODS

Eligible patients had the following characteristics: stage III/b or IV NSCLC that was refractory to conventional therapy or for which no standard therapy was available; Eastern Cooperative Oncology Group (ECOG) performance status (PS) <or=2; adequate organ function; and age >or=20 and <75 years. The patients were administered TZT-1,027 in escalating doses from 0.5 to 5.6 mg/m(2). Pharmacokinetic samples were collected during each treatment course.

RESULTS

Forty-nine patients were enrolled. Three patients had DLTs, including neutropenia, neutropenia complicated by fever, myalgia, and neuropathic pain. The common toxicities included constipation, anorexia, alopecia, nausea, leukopenia, and neutropenia. One complete response and three partial responses were observed. The pharmacokinetic parameters (AUC and C (max)) of TZT-1,027 tended to increase linearly with dose.

CONCLUSIONS

DLTs included neutropenia, neutropenia complicated by fever, myalgia, and neuropathic pain. The MTD was 4.8 mg/m(2). The recommended phase II study dose of TZT-1027 is 4.8 mg/m(2) administered every 3-4 weeks.

Comparison of the antivascular and cytotoxic activities of TZT-1027 (Soblidotin) with those of other anticancer agents

TZT-1027 (Soblidotin), a microtubule-depolymerizing agent exerts both a direct cytotoxic activity against cancer cells and an indirect antivascular activity against tumor vascular endothelial cells. We compared both activities of TZT-1027 with those of various anticancer agents having different mechanisms of action, including vinca alkaloids, a vascular targeting agent, a taxane and nonmicrotubule-binding agents. In the MTT assay, TZT-1027 most potently inhibited the growth of both murine colon C26 cancer cells and human umbilical vein endothelial cells, implying its potent antivascular activity against tumor vasculature in addition to its cytotoxic activity against cancer cells. Treatment with 0.1 microg/ml TZT-1027 significantly enhanced vascular permeability in human umbilical vein endothelial cell monolayers and a single intravenous administration of 2 mg/kg TZT-1027 significantly reduced the perfusion of Colon26 tumors implanted into mice, with efficacies superior to vinca alkaloids and comparable to a known vascular targeting agent. These results strongly suggest that TZT-1027 exerts marked antivascular activity. Next, to clarify the mechanism of the antivascular activity, we have taken a novel approach, and analyzed the relationships among human umbilical vein endothelial cells cytotoxicity, vascular permeability and tumor perfusion, on the basis of efficacies of each agent. Analyses revealed strong and significant correlations, and indicated that the vascular endothelial cell damage leads to endothelial barrier dysfunction and, thereby, tumor vascular shutdown. In summary, TZT-1027 was verified to have not only an excellent cytotoxic activity, but also an attractive antivascular activity through the induction of damage to vascular endothelial cells. We believe that these dual activities may make TZT-1027 useful for treating solid tumors.

Population pharmacokinetics of the BEACOPP polychemotherapy regimen in Hodgkin's lymphoma and its effect on myelotoxicity

BACKGROUND AND OBJECTIVE

The BEACOPP (bleomycin, etoposide, doxorubicin, cyclophosphamide, vincristine, procarbazine and prednisone) chemotherapy regimen for the treatment of advanced Hodgkin's lymphoma has a superior outcome, but its toxicity (mainly haematotoxicity) is pronounced and highly variable. The present study was conducted to address the role of pharmacokinetics in individual toxicity.

STUDY DESIGN

Three plasma samples and a 24-hour urine collection for day 1 of the first three cycles of chemotherapy were analysed in 30 patients, and the pharmacokinetic parameters of the respective drugs were estimated by population pharmacokinetic methods (nonlinear mixed-effects model [NONMEM] software). Demographic data, doses and durations of infusion were also recorded. The effect of these parameters on platelet counts was estimated by analysis of covariance using a general linear model.

RESULTS

The pharmacokinetic parameters and respective covariates were similar to the published data. The body surface area, peak concentrations of etoposide, urinary recovery of dechloroethylcyclophosphamide (formed by cytochrome P450 [CYP] 3A4) relative to the cyclophosphamide dose and number of cycles had a significant effect on toxicity. These factors explained 37% of the interindividual variability in the change in platelet counts from day 1 to day 8 of each cycle.

CONCLUSION

The results show that the individual pharmacokinetics of BEACOPP drugs are an important link between dosage and toxicity. Accordingly, individualisation of treatment based on pharmacokinetics may result in more uniform toxicity. Individualisation may also allow escalation of the mean dose, which is probably related to better efficacy. As a consequence of the present study, infusion rates should be standardised, and the potential of a dose reduction in the first cycle and of CYP3A4 phenotyping should be addressed in clinical studies.

The novel microtubule-interfering agent TZT-1027 enhances the anticancer effect of radiation in vitro and in vivo

TZT-1027 is a novel anticancer agent that inhibits microtubule polymerisation and manifests potent antitumour activity in preclinical models. We have examined the effect of TZT-1027 on cell cycle progression as well as the anticancer activity of this drug both in vitro and in vivo. With the use of tsFT210 cells, which express a temperature-sensitive mutant of Cdc2, we found that TZT-1027 arrests cell cycle progression in mitosis, the phase of the cell cycle most sensitive to radiation. A clonogenic assay indeed revealed that TZT-1027 increased the sensitivity of H460 cells to gamma-radiation, with a dose enhancement factor of 1.2. Furthermore, TZT-1027 increased the radiosensitivity of H460 and A549 cells in nude mice, as revealed by a marked delay in tumour growth and an enhancement factor of 3.0 and 2.2, respectively. TZT-1027 also potentiated the induction of apoptosis in H460 cells by radiation both in vitro and in vivo. Histological evaluation of H460 tumours revealed that TZT-1027 induced morphological damage to the vascular endothelium followed by extensive central tumour necrosis. Our results thus suggest that TZT-1027 enhances the antitumour effect of ionising radiation, and that this action is attributable in part to potentiation of apoptosis induction and to an antivascular effect. Combined treatment with TZT-1027 and radiation therefore warrants investigation in clinical trials as a potential anticancer strategy.

Simultaneous quantification of cyclophosphamide and its active metabolite 4-hydroxycyclophosphamide in human plasma by high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (LC-MS/MS)

Cyclophosphamide is a cytotoxic prodrug with a very narrow therapeutic index. To study the clinical pharmacology of cyclophosphamide in a large cohort of patients a previously published method for the simultaneous quantitative determination of cyclophosphamide and 4-hydroxycyclophosphamide in human plasma using liquid chromatography tandem mass spectrometry (LC-MS/MS) was optimized. Addition of an isotopically labelled internal standard and adaptation of the gradient resulted in a fast, robust and sensitive assay. Because 4-hydroxycyclophosphamide is not stable in plasma, the compound is derivatized with semicarbazide immediately after sample collection. Sample preparation was carried out by protein precipitation with methanol-acetonitrile (1:1, v/v), containing isotopically labelled cyclophosphamide and hexamethylphosphoramide as internal standards. The LC separation was performed on a Zorbax Extend C18 column (150 mm x 2.1 mm ID, particle size 5 microm) with 1 mM ammonium hydroxide in water-acetonitrile (90:10, v/v) as the starting gradient, at a flow-rate of 0.40 mL/min with a total run time of 6 min. The lower limit of quantification (LLQ, using a 100 microL sample volume) was 200 ng/mL and the linear dynamic range extended to 40,000 ng/mL for cyclophosphamide and 50-5000 ng/mL for 4-hydroxycyclophosphamide. Accuracies as well as precisions were lower than 20% at the LLQ concentration and lower than 15% for all other concentrations. This method has been successfully applied in our institute to support ongoing studies into the pharmacokinetics and pharmacogenetics of cyclophosphamide.

Vascular disrupting agents in clinical development

Growth of human tumours depends on the supply of oxygen and nutrients via the surrounding vasculature. Therefore tumour vasculature is an attractive target for anticancer therapy. Apart from angiogenesis inhibitors that compromise the formation of new blood vessels, a second class of specific anticancer drugs has been developed. These so-called vascular disrupting agents (VDAs) target the established tumour vasculature and cause an acute and pronounced shutdown of blood vessels resulting in an almost complete stop of blood flow, ultimately leading to selective tumour necrosis. As a number of VDAs are now being tested in clinical studies, we will discuss their mechanism of action and the results obtained in preclinical studies. Also data from clinical studies will be reviewed and some considerations with regard to the future development are given.

Tumor-specific antivascular effect of TZT-1027 (Soblidotin) elucidated by magnetic resonance imaging and confocal laser scanning microscopy

TZT-1027 (soblidotin), an antimicrotubule agent, has previously been evaluated in terms of its antivascular effects. In this study, Evans blue perfusion, magnetic resonance imaging (MRI), and confocal laser scanning microscopy (CLSM) were utilized to further elucidate the antivascular effect of TZT-1027 in female nude mice and rats bearing human breast tumor MX-1, as well as in female Sprague-Dawley rats that developed breast tumors induced by dimethylbenz(a)anthracene (DMBA). Therapeutic doses of TZT-1027 caused nearly complete regression of implanted MX-1 tumors in nude mice and rats as well as DMBA-induced tumors in rats. The perfusion in MX-1 tumor implanted in nude mice was drastically reduced within 30 min after TZT-1027 administration and was completely inhibited after 6 h or more, although not reduced in normal tissue of kidney. The study using MRI demonstrated that rich blood flow within tumors was remarkably reduced 1-3 h after TZT-1027 administration both in nude rats bearing MX-1 tumors and in rats with DMBA-induced tumors. Furthermore, the study with CLSM in nude mice bearing MX-1 tumors revealed a disruption of tumor microvessels at 1 h and a destruction of tumor microvessel network at 3 h after TZT-1027 administration. In contrast, these types of vascular disorders were not observed in heart and kidney. These results suggest that TZT-1027 specifically damages tumor vasculatures, leading to extensive tumor necrosis within tolerable dose range, and confirms earlier observations that TZT-1027 exerts a considerable antivascular effect in addition to an excellent cytotoxic effect.

Drug insight: vascular disrupting agents and angiogenesis--novel approaches for drug delivery

Vascular disrupting agents (VDAs), or endothelial disrupting agents, attempt to exploit the vascular endothelium that supplies rapidly dividing neoplasms. Unlike antiangiogenesis agents (e.g. the monoclonal antibody bevacizumab; and tyrosine kinase inhibitors sorafenib and sunitinib) that disrupt endothelial cell survival mechanisms and the development of a new tumor blood supply, VDAs are designed to disrupt the already established abnormal vasculature that supports tumors, by targeting their dysmorphic endothelial cells. Tumor vascular endothelium is characterized by its increased permeability, abnormal morphology, disorganized vascular networks, and variable density. VDAs induce rapid shutdown of tumor blood supply, causing subsequent tumor death from hypoxia and nutrient deprivation. The safety profile of this class of compounds is more indicative of agents that are indeed 'vascularly' active. For example, VDAs can cause: acute coronary and other thrombophlebitic syndromes; alterations in blood pressure, heart rate, and ventricular conduction; transient flush and hot flashes; neuropathy; and tumor pain. Despite these cardiovascular concerns some patients have benefited from VDAs in early clinical trials. Further drug development of VDAs must include the combination of these agents with other novel biological agents, cytotoxic chemotherapy, and radiotherapy. Close monitoring of patients receiving VDAs for any cardiovascular toxicity is imperative.

Vascular disrupting agents

A clear definition for vascular targeting agents (VTAs) and vascular disrupting agents (VDAs) has separated the two as distinct methods of cancer treatment. VDAs differ from VTAs (antiangiogenesis drugs) in their mechanism of action. VTAs attempt to keep new blood vessels from forming and do not act on blood vessels that already feed existing tumors. In contrast, VDAs cause the vascular structure inside a solid tumor to collapse, depriving the tumor of blood and oxygen it needs to survive. Therefore, VDAs are an attractive way to approach the cancer problem by combating developed tumors. The following review discusses six small molecule VDAs, namely DMXAA, ZD6126, TZT1027, CA4P, AVE8062, and Oxi4503, their synthesis, biological mechanism of action, and current clinical status.

Phase I study of TZT-1027, a novel synthetic dolastatin 10 derivative and inhibitor of tubulin polymerization, which was administered to patients with advanced solid tumors on days 1 and 8 in 3-week courses

PURPOSE

To determine the maximum tolerated dose (MTD), dose-limiting toxicity (DLT), and pharmacokinetics of TZT-1027 (soblidotin), a dolastatin 10 analogue, in Japanese patients with advanced solid tumors when administered on days 1 and 8 in 3-week courses.

METHODS

Eligible patients had advanced solid tumors that failed to respond to standard therapy or for which no standard therapy was available, and also met the following criteria: prior chemotherapy < or = 2 regimens, Eastern Cooperative Oncology Group (ECOG) performance status < or = 1, and acceptable organ function. The MTD was defined as the highest dose at which no more than one of six patients experienced a DLT during course 1. Pharmacokinetic samples were collected in courses 1 and 2.

RESULTS

Eighteen patients were enrolled in the present study. Three doses (1.5, 1.65, and 1.8 mg/m(2)) were evaluated. Neutropenia was the principal DLT at doses of 1.65 and 1.8 mg/m(2). In addition, one patient also experienced grade 3 pneumonia with neutropenia, and another patient experienced grade 3 constipation, neuropathy, grade 4 neutropenia, and hyponatremia as DLTs at 1.65 mg/m(2). Phlebitis, the most frequent nonhematological toxicity, was improved by administration of additional saline after TZT-1027 administration. The MTD was 1.5 mg/m(2), at which DLT was not observed in a total of nine patients. The pharmacokinetic profile did not differ from that for the European population. One patient with metastatic esophageal cancer achieved partial response, and each of two patients with non-small cell lung cancer had a minor response.

CONCLUSIONS

When TZT-1027 was administered on days 1 and 8 in 3-week courses to Japanese patients, the MTD was 1.5 mg/m(2) and was lower than the value of 2.4 mg/m(2) in European patients. However, antitumor activity was observed at low doses. TZT-1027 was tolerated well at the MTD, without grade 3 nonhematological toxicities or neutropenia up to grade 2. TZT-1027 is a promising new tubulin polymerization inhibitor that requires further investigation in phase II studies.

A phase 2 study of TZT-1027, administered weekly to patients with advanced non-small cell lung cancer following treatment with platinum-based chemotherapy

INTRODUCTION

: TZT-1027, a derivative of dolastatin-10, has a wide spectrum of in vitro activity against cancer cell lines. We conducted a phase 2 trial of TZT-1027 in patients with previously treated non-small cell lung cancer (NSCLC).

PATIENTS AND METHODS

Patients with stage IV or recurrent NSCLC who had received one prior platinum-based chemotherapy regimen were eligible. Patients received 2.4mg/m(2) of TZT-1027 on days 1 and 8 of a 21-day cycle. The primary endpoint was response rate as measured by RECIST.

RESULTS

Thirty-two patients were enrolled (16 women, 16 men). The most common grade 3/4 adverse effects were leukopenia and neutropenia. Four patients died within 30 days of receiving TZT-1027, three from progressive disease and one with pneumonia and neutropenia. No objective response was observed (0% observed rate, 95% confidence interval 0-11%). The median time to progression was 1.5 months. The median overall survival was 8.5 months.

CONCLUSIONS

This phase 2 trial showed that TZT-1027 administered on days 1 and 8 of a 21-day cycle had no anticancer activity. Further development of TZT-1027 in patients with previously treated NSCLC is not warranted.

Colchitaxel, a coupled compound made from microtubule inhibitors colchicine and paclitaxel

BACKGROUND

Tumor promoters enhance tumor yield in experimental animals without directly affecting the DNA of the cell. Promoters may play a role in the development of cancer, as humans are exposed to them in the environment. In work based on computer-assisted microscopy and sophisticated classification methods, we showed that cells could be classified by reference to a database of known normal and cancerous cell phenotypes. Promoters caused loss of properties specific to normal cells and gain of properties of cancer cells. Other compounds, including colchicine, had a similar effect. Colchicine given together with paclitaxel, however, caused cells to adopt properties of normal cells. This provided a rationale for tests of microtubule inhibitor combinations in cancer patients. The combination of a depolymerizing and a stabilizing agent is a superior anti-tumor treatment. The biological basis of the effect is not understood.

RESULTS

A single compound containing both colchicine and paclitaxel structures was synthesized. Colchicine is an alkaloid with a trimethoxyphenyl ring (ring A), a ring with an acetamide linkage (ring B), and a tropolone ring (ring C). Although rings A and C are important for tubulin-binding activity, the acetamide linkage on ring B could be replaced by an amide containing a glutamate linker. Alteration of the C-7 site on paclitaxel similarly had little or no inhibitory effect on its biological activity. The linker was attached to this position. The coupled compound, colchitaxel (1), had some of the same effects on microtubules as the combination of starting compounds. It also caused shortening and fragmentation of the + end protein cap.

CONCLUSION

Since microtubule inhibitor combinations give results unlike those obtained with either inhibitor alone, it is important to determine how such combinations affect cell shape and growth. Colchitaxel shows a subset of the effects of the inhibitor combination. Thus, it may be able to bind the relevant cellular target of the combination. It will be useful to determine the basis of the shape reversal effect and possibly, the reasons for therapeutic efficacy of microtubule inhibitor combinations.

A phase I study of intravenous TZT-1027 administered on day 1 and day 8 of a three-weekly cycle in combination with carboplatin given on day 1 alone in patients with advanced solid tumours

BACKGROUND

TZT-1027 is a tubulin-binding drug and synthetic derivative of dolastatin-10 with cytotoxic and antivascular activity in vitro and in vivo. Studies have demonstrated anti-tumour activity in several tumour types.

METHODS

Patients were treated with escalating doses of TZT-1027 and carboplatin at doses from 1.6 to 2.0 mg/m2 and AUC 4 and 5 respectively. For pharmacokinetic analysis, plasma sampling was done during the first course using a high-performance liquid chromatographic assay.

RESULTS

14 patients received a total of 55 cycles at three dose levels. Dose limiting toxicities (DLTs) were first observed with 1.6 mg/m2 TZT-1027 and carboplatin AUC 5; 1 patient had grade 4 neutropenia and a delay in day 8 treatment occurred in two patients (gr 2 fatigue, gr 3 diarrhoea). At TZT-1027 2 mg/m2 and carboplatin AUC 5, one patient experienced grade 3 paralytic ileus. The most frequent toxicities were neutropenia, anaemia, fatigue, constipation, infection and vomiting. Peripheral neuropathy was reported in 36% of patients. One patient (pancreatic adenocarcinoma) achieved a partial response lasting 181 days. Pharmacokinetic analysis did not demonstrate any interaction between TZT-1027 and carboplatin.

CONCLUSIONS

The recommended phase II dose is TZT-1027 1.6 mg/m2 and carboplatin AUC 5. No evidence of a PK interaction between these agents was observed.

Reference profiling of the genomic response induced by an antimicrotubule agent, TZT-1027 (Soblidotin), in vitro

TZT-1027 is an antimicrotubule agent targeting beta-tubulin that is undergoing clinical development. The genomic response of cancer cells to TZT-1027 was profiled to evaluate its biochemical activity. A lung cancer cell line, PC-14, was exposed to antimicrotubule agents including dolastatins, Vinca alkaloids and taxanes at an equivalent toxicity level. Alterations in the TZT-1027-induced gene expression of approximately 600 genes were then examined using microarray technology and the resulting gene profiles were compared with those for cells exposed to the other antimicrotubule agents. A principle component analysis using the whole gene set demonstrated that TZT-1027 produced similar gene profiles to those produced by dolastatin 10, but that these gene profiles differed from those produced by other agents. The agents were classified according to their induced genomic response in a molecular structure-dependent manner. Genes whose expression profiles differed according to drug class included intermediate filaments, extracellular matrix protein and Rho regulatory genes that may be involved in cytoskeletal and angiogenesis processes that are regulated by microtubule dynamics. TZT-1027 produces a unique genomic response profile distinct from that of Vinca alkaloids and taxanes, suggesting that this agent has a different mechanism of action. The selected genes may act as pharmacodynamic biomarkers allowing the unique mode of action of TZT-1027 to be discriminated from those of other antimicrotubule agents.

Phase II study of intravenous TZT-1027 in patients with advanced or metastatic soft-tissue sarcomas with prior exposure to anthracycline-based chemotherapy

BACKGROUND

TZT-1027, a novel chemotherapeutic agent, is derived from dolastatin 10, and blocks cells during G2/M-phase by interfering with microtubule assembly and stability. TZT-1027 has exhibited potential cytotoxic activity in several human cancer cell lines (in vitro) and also demonstrated antitumor activity in human xenografts (in vivo). In addition, Phase I clinical investigations suggested activity in STS (soft-tissue sarcoma).

METHODS

Eligible patients were those who had histologic evidence of locally advanced or metastatic STS and who had received 1 prior treatment regimen with an anthracycline-based chemotherapy for metastatic disease. Subjects received intravenous infusions of TZT-1027 over 1 hour on Day 1 and Day 8 of each 21-day treatment course. Efficacy was evaluated per Response Evaluation Criteria in Solid Tumors (RECIST) criteria.

RESULTS

Twenty-nine patients were enrolled and 28 patients received at least 1 course of study drug and were eligible for efficacy and safety evaluation. The median age of the patients was 48 years (range, 23-73 years) and the median baseline Eastern Cooperative Oncology Group (ECOG) performance status was 1 (range, 0-2). A total of 67 courses (range, 1-9 courses; median, 2 courses) of TZT-1027 were administered. No patient in the study demonstrated an objective response to treatment. Of 6 patients (21.4%) who experienced disease stabilization, 1 continued to have stable disease for 9.3 months. The median time to tumor progression was 44 days (95% confidence interval [95% CI], 43.0-54.0) and the median survival was 178 days (95% CI, 134.0-317.0). The most commonly reported toxicities were neutropenia, fatigue, and constipation.

CONCLUSIONS

TZT-1027 was found to be safe and well tolerated, and the hematologic toxicities observed were consistent with preclinical toxicology and Phase I study findings. No confirmed responses were seen in the current study.

Vascular disrupting agents

It has been well established that a functioning vascular supply is essential for solid tumor growth and metastases. In the absence of a viable vascular network, tumors are unable to grow beyond a few millimeters and therefore remain dormant. Initiation of angiogenesis allows for continued tumor growth and progression. Targeting tumor vasculature, either by inhibiting growth of new tumor blood vessels (antiangiogenic agents) or by destroying the already present tumor vessels (vascular disrupting agents; VDA), is an area of extensive research in the development of new antitumor agents. These two groups differ in their direct physiological target, the type or extent of disease that is likely to be susceptible, and the treatment schedule. VDAs target the established tumor blood vessels, resulting in tumor ischemia and necrosis. These agents show more immediate effects compared to antiangiogenic agents and may have more efficacy against advanced bulky disease. VDAs can be divided into two groups--ligand-bound and small molecule agents. Both VDA groups have demonstrated antitumor effects and tumor core necrosis, but consistently leave a thin rim of viable tumor cells at the periphery of the tumor. More evidence suggests VDAs will have their greatest effect in combination with conventional chemotherapy or other modes of treatment that attack this outer rim of cells.