A Phase I Study of the Dolastatin-15 Analogue Tasidotin (ILX651) Administered Intravenously Daily for 5 Consecutive Days Every 3 Weeks in Patients with Advanced Solid Tumors

Marine-Derived Leads as Anticancer Candidates by Disrupting Hypoxic Signaling through Hypoxia-Inducible Factors Inhibition

The inadequate vascularization seen in fast-growing solid tumors gives rise to hypoxic areas, fostering specific changes in gene expression that bolster tumor cell survival and metastasis, ultimately leading to unfavorable clinical prognoses across different cancer types. Hypoxia-inducible factors (HIF-1 and HIF-2) emerge as druggable pivotal players orchestrating tumor metastasis and angiogenesis, thus positioning them as prime targets for cancer treatment. A range of HIF inhibitors, notably natural compounds originating from marine organisms, exhibit encouraging anticancer properties, underscoring their significance as promising therapeutic options. Bioprospection of the marine environment is now a well-settled approach to the discovery and development of anticancer agents that might have their medicinal chemistry developed into clinical candidates. However, despite the massive increase in the number of marine natural products classified as 'anticancer leads,' most of which correspond to general cytotoxic agents, and only a few have been characterized regarding their molecular targets and mechanisms of action. The current review presents a critical analysis of inhibitors of HIF-1 and HIF-2 and hypoxia-selective compounds that have been sourced from marine organisms and that might act as new chemotherapeutic candidates or serve as templates for the development of structurally similar derivatives with improved anticancer efficacy.

Microtubule associated proteins as targets for anticancer drug development

The dynamic equilibrium of tubulin-microtubule is an essential aspect of cell survivality. Modulation of this dynamics has become an important target for the cancer drug development. Tubulin exists in the alpha-beta dimer form which polymerizes to form microtubule and further depolymerizes back to tubulin dimer. The microtubule plays an essential role in mitosis and cell multiplication. Antitubulin drugs disturb the microtubule dynamics which is essentially required for DNA segregation and cell division during mitosis so killing the cancerous cells. Microtubule Associated Proteins (MAPs) interact with cellular cytoskeletal microtubules. MAPs bind to the either polymerized or depolymerized tubulin dimers within the cell and mostly causing stabilization of microtubules. Some of the tubulin binding drugs are in clinical use and others in clinical trial. MAPs inhibitors are also in clinical trial. Post-translational modification of lysine-40 either in histone or in alpha tubulin has an important role in gene expression and is balanced between histone deacetylases (HDACs) and histone acetyltransferases (HATs). HDAC inhibitors have the anticancer properties to form a drug for the treatment of cancer. They act by inducing cell cycle arrest and cell death. Some of the HDAC inhibitors are approved to be used as anticancer drug while others are under different phases of clinical trial. The present review updates on various MAPs, their role in cancer progression, MAPs inhibitors and their future prospects.

Biosynthetic strategies for tetramic acid formation

Covering: up to the end of 2020Natural products bearing tetramic acid units as part of complex molecular architectures exhibit a broad range of potent biological activities. These compounds thus attract significant interest from both the biosynthetic and synthetic communities. Biosynthetically, most of the tetramic acids are derived from hybrid polyketide synthase (PKS) and nonribosomal peptide synthetase (NRPS) machineries. To date, over 30 biosynthetic gene clusters (BGCs) involved in tetramate formation have been identified, from which different biosynthetic strategies evolved in Nature to assemble this intriguing structural unit were characterized. In this Highlight we focus on the biosynthetic concepts of tetramic acid formation and discuss the molecular mechanism towards selected representatives in detail, providing a systematic overview for the development of strategies for targeted tetramate genome mining and future applications of tetramate-forming biocatalysts for chemo-enzymatic synthesis.

Recent Advances in Small Peptides of Marine Origin in Cancer Therapy

Cancer is one of the leading causes of death in the world, and antineoplastic drug research continues to be a major field in medicine development. The marine milieu has thousands of biological species that are a valuable source of novel functional proteins and peptides, which have been used in the treatment of many diseases, including cancer. In contrast with proteins and polypeptides, small peptides (with a molecular weight of less than 1000 Da) have overwhelming advantages, such as preferential and fast absorption, which can decrease the burden on human gastrointestinal function. Besides, these peptides are only connected by a few peptide bonds, and their small molecular weight makes it easy to modify and synthesize them. Specifically, small peptides can deliver nutrients and drugs to cells and tissues in the body. These characteristics make them stand out in relation to targeted drug therapy. Nowadays, the anticancer mechanisms of the small marine peptides are still largely not well understood; however, several marine peptides have been applied in preclinical treatment. This paper highlights the anticancer linear and cyclic small peptides in marine resources and presents a review of peptides and the derivatives and their mechanisms.

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.

Targeting HER2-positive cancer with dolastatin 15 derivatives conjugated to trastuzumab, novel antibody-drug conjugates

PURPOSE

Targeting tubulin binders to cancer cells using antibody-drug conjugates (ADCs) has great potential to become an effective cancer treatment with low normal tissue toxicity. The nature of the linker used to tether the tubulin binder to the antibody and the conjugation sites on the antibody and the small molecule are important factors in the ADC stability and effectiveness.

METHODS

We explored the use of tubulin-targeting dolastatin 15 derivatives (Dol15) tethered covalently to a representative antibody, trastuzumab, via cleavable and non-cleavable linkers at varying antibody reactive sites (i.e., lysine residues, partially reduced hinge region disulfide bonds) and drug coupling sites (i.e., C-terminus, N-terminus), to investigate which constructs were more effective in killing HER2-positive cells in vitro and in vivo.

RESULTS

We found that Dol15 conjugated to trastuzumab via lysine residues at the drug C-terminus using a non-cleavable linker (trastuzumab-amide-C-term-Dol15) produced target-dependent growth inhibition of cells endogenously expressing high HER2 levels (i.e., SK-BR-3, SK-OV-3) in vitro. This ADC was effective at varying doses (i.e., 10 and 20 mg/kg) in the SK-OV-3 human ovarian cancer xenograft.

CONCLUSIONS

Tethering Dol15 via partially reduced disulfide bonds at the drug C-terminus via a non-cleavable linker (trastuzumab-MC-C-term-Dol15) resulted in an equally effective ADC in vitro, showing that site of antibody conjugation did not influence ADC activity. However, tethering Dol15 at the drug N-terminus using non-cleavable and cleavable linkers (trastuzumab-MC-N-term-Dol15 and trastuzumab-MC-VC-PABC-N-term-Dol15, respectively) resulted in ineffective ADCs. Thus, Dol15 tethered at the C-terminus may be a useful tubulin-targeting agent for conjugation at various antibody reactive sites.

Eribulin mesylate, a novel microtubule inhibitor in the treatment of breast cancer

BACKGROUND

Microtubule-targeted agents are one of the most common classes of chemotherapeutic drug for the treatment of breast cancer. Limitations of current microtubule-targeted agents such as primary or secondary resistance of cancer cells and side effects like neuropathy prompted the discovery and introduction of newer more effective drugs. This review aims to provide a summary of the novel halichondrin B analog eribulin mesylate (E7389) and illustrate where it is placed in the treatment arena versus other agents that are approved or are currently in various stages of clinical development.

METHODS

Preclinical and clinical trial (phases I-III) data for eribulin were obtained from scientific journals and meeting abstracts, posters, and oral presentations. The use of current and other emerging microtubule inhibiting agents in breast cancer was also surveyed and briefly reviewed.

RESULTS

Eribulin mesylate at a dose of 1.4 mg/m(2) given on days 1 and 8 of a 21-day cycle increased overall survival in patients with metastatic breast cancer (MBC). Neutropenia, fatigue, alopecia, nausea and anemia were common adverse events (AEs) associated with eribulin in clinical studies. A low incidence of peripheral neuropathy was also associated with eribulin in clinical studies (21-26%). Other emerging microtubule targeted agents, such as vinflunine and larotaxel, also reported efficacy in patients with MBC who had received prior chemotherapy, with grade 3/4 neutropenia being the most common AEs for both agents.

CONCLUSIONS

Eribulin mesylate offers clinical activity in advanced breast cancer through improved overall survival, its favorable side-effect profile and convenience of preparation and administration.

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.

The expanding role of marine microbes in pharmaceutical development

Marine microbes have received growing attention as sources of bioactive metabolites and offer a unique opportunity to both increase the number of marine natural products in clinical trials as well as expedite their development. This review focuses specifically on those molecules currently in the clinical pipeline that are established or highly likely to be produced by bacteria based on expanding circumstantial evidence. We also include an example of how compounds from harmful algal blooms may yield both tools for measuring environmental change as well as leads for pharmaceutical development. An example of the karlotoxin class of compounds isolated from the dinoflagellate Karlodinium veneficum reveals a significant environmental impact in the form of massive fish kills, but also provides opportunities to construct new molecules for the control of cancer and serum cholesterol assisted by tools associated with rational drug design.

Bone marrow CFU-GM and human tumor xenograft efficacy of three tubulin binding agents

PURPOSE

The dynamic instability of microtubules in cells is one of the key targets of anticancer therapeutics. Microtubule-disrupting agents such as vinca alkaloids and microtubule-stabilizing agents such as taxanes are important antitumor agents. The bone marrow toxicity and human tumor xenograft activity of three tubulin-binding compounds, vincristine, paclitaxel, and tasidotin were compared.

METHODS

Mouse and human bone marrow were subjected to colony-forming (CFU-GM) assays over a 5-log concentration range in culture. In vivo, a range of tasidotin doses was compared with vincristine, paclitaxel, and docetaxel for efficacy in several human tumor xenografts.

RESULTS

The IC(90) concentrations for vincristine and paclitaxel for mouse CFU-GM were 30 and 27 nM, and for human CFU-GM were 3 and 9 nM, giving mouse to human differentials of ten- and threefold. Tasidotin produced IC(90)s of >300 nM in mouse and 65 nM in human CFU-GM, thus a >4.6-fold differential between species. In vivo, tasidotin resulted in a dose-dependent increase in tumor growth delay in the RL lymphoma, the RPMI 8226 multiple myeloma, and MX-1 breast carcinoma models. Vincristine and tasidotin were also very effective against these tumors. The PC-3 prostate carcinoma was very responsive to full-dose paclitaxel and docetaxel while tasidotin generated a dose dependent effect.

CONCLUSIONS

Bringing together bone marrow toxicity data, pharmacokinetic parameters, and human tumor xenograft efficacy provides valuable information for the translation of preclinical findings to the clinic.

Toxins affecting actin filaments and microtubules

Actin and tubulin are the two major proteins of the cytoskeleton in eukaryotic cells and both display a common property to reversibly assemble into long and flexible polymers, actin filaments and microtubules, respectively. These proteins play important roles in a variety of cellular functions and are also involved in numbers of diseases. An emerging number of marine-derived cytotoxins have been found to bind either actin or tublin, resulting in either inhibition or enhancement of polymerization. Thus, these toxins are valuable molecular probes for solving complex mechanisms of biological processes. This chapter describes actin- and tubulin-targeting marine natural products and their modes of action, with reference to their use as research tools and their clinical applications.

Plasma and cerebrospinal fluid pharmacokinetics of tasidotin (ILX-651) and its metabolites in non-human primates

PURPOSE

To evaluate the plasma and cerebrospinal fluid (CSF) pharmacokinetics and CSF penetration of tasidotin and metabolites in a nonhuman primate model.

METHODS

Tasidotin 0.75 mg/kg was administered intravenously. The plasma and CSF concentrations of tasidotin and its metabolites were determined. Pharmacokinetic parameters were estimated using model-independent and model-dependent methods.

RESULTS

The mean (+/-SD) CSF:plasma AUC ratio for tasidotin was 1.1 +/- 0.4. For tasidotin, tasidotin-C-carboxylate and desprolyl-tasidotin-C-carboxylate the plasma AUCs (mean +/- SD) were 30 +/- 10, 54 +/- 19 and 12 +/- 2 microM min, and apparent plasma half-lives were 27 +/- 4, 229 +/- 73 and 100 +/- 29 min. The plasma clearance of tasidotin was 44 +/- 14 ml/min/kg. The CSF AUC and half-life of tasidotin was 28 +/- 10 microM min and 96 +/- 40 min. The model-dependent plasma clearance was 35 ml/min/kg for tasidotin and 2 ml/min/kg for tasidotin-C-carboxylate.

CONCLUSIONS

Tasidotin penetrates into the CSF well and further evaluation of its activity in the treatment of central nervous system malignancies should be considered.

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.

Pharmacokinetics in mice implanted with xenografted tumors after intravenous administration of tasidotin (ILX651) or its carboxylate metabolite

The pharmacokinetics of tasidotin (ILX651), a depsipeptide currently in phase II for the treatment of advanced solid tumors, and tasidotin-C-carboxylate, the main metabolite, were characterized in male nude mice implanted with LOX tumors, which are sensitive to tasidotin, or H460 tumors, which are resistant to tasidotin. The pharmacokinetics of tasidotin and its metabolites were characterized after single-dose administration of tasidotin (20 and 120 mg/kg), tasidotin-C-carboxylate (150 mg/kg), or tasidotin (53 mg/kg) in the presence and absence of Z-prolyl prolinal (5 mg/kg administered 1 hour prior to tasidotin administration), a competitive antagonist of prolyl oligopeptidase, the enzyme responsible for the metabolism of tasidotin to tasidotin-C-carboxylate. A secondary study was done comparing tumor growth in tasidotin-treated mice with implanted LOX tumors in the presence and absence of Z-prolyl-prolinal. After tasidotin administration, the pharmacokinetics of tasidotin and tasidotin-C-carboxylate were similar in plasma and tumors in LOX- and H460-implanted mice, indicating the resistance was not due to pharmacokinetic factors. Tumor carboxylate concentrations were much higher than in plasma after tasidotin administration. The metabolite appeared to contribute approximately 17% to 33% to the total exposure in LOX tumors and 20% to 49% in H460 tumors but <5% in plasma. Less than 5% of the administered tasidotin dose was converted to tasidotin-C-carboxylate, with no apparent differences between LOX- and H460-treated animals. The presence of Z-prolyl-prolinal decreased the amount of tasidotin converted to tasidotin-C-carboxylate from 5.5% to 0.90%, a reduction of almost 80%. After tasidotin-C-carboxylate administration, the half-life was on the order of minutes compared with hours when observed after tasidotin administration. Tasidotin-C-carboxylate elimination was not dependent on tasidotin pharmacokinetics, suggesting that the rate of efflux from cells into plasma was the rate-limiting step in its elimination. Tasidotin-C-carboxylate was also further metabolized to desprolyl-tasidotin-C-carboxylate, although the metabolite ratios were <10%. Pretreatment with Z-prolyl-prolinal completely abolished the antitumor activity of tasidotin, indicating that the metabolite is the main moiety responsible for activity and that, despite tasidotin itself having activity in vitro, tasidotin is acting mainly as a prodrug.

Preclinical analysis of tasidotin HCl in Ewing's sarcoma, rhabdomyosarcoma, synovial sarcoma, and osteosarcoma

PURPOSE

Dolastatins are a group of structurally unique peptides originally isolated from a sea hare, Dolabella auricularia, which seem to inhibit tubulin polymerization and mitosis. Tasidotin hydrochloride (tasidotin), a novel synthetic analogue of dolastatin 15, is evaluated in preclinical models of pediatric tumors.

EXPERIMENTAL DESIGN

The cytotoxicity of tasidotin was evaluated in a panel of pediatric sarcoma cell lines in vitro and in vivo.

RESULTS

The IC(50) in Ewing's sarcoma, rhabdomyosarcoma, osteosarcoma, and synovial sarcoma lines ranged from 0.002 micro to 0.32 micromol/L. In the SK-ES1 and RH30 cell lines, tasidotin induced a G(2)-M arrest that persisted for 48 h after the drug was washed from the cells. In vitro, more than half the cells were in the early or late phase of apoptosis 48 h after treatment with tasidotin. In vivo, a significant increase in apoptotic nuclei was apparent in xenograft tumors harvested within 24 h after a 5-day course of tasidotin. In vivo response was determined in severe combined immunodeficient xenograft models of pediatric sarcomas implanted heterotopically. Significant antitumor activity was observed in all tumor lines tested. A complete response was observed in 2 synovial sarcoma lines, 1 osteosarcoma line, 1 rhabdomyosarcoma line, and 1 Ewing's sarcoma line. A partial response was observed in 1 rhabdomyosarcoma and 1 Ewing's sarcoma.

CONCLUSIONS

Tasidotin induces a G(2)-M block in treated cells ultimately resulting in apoptosis. Antitumor activity is confirmed in vivo in preclinical xenograft models of pediatric sarcomas.

Cytotoxic polyketides containing tetramic acid moieties isolated from the fungus Myceliophthora Thermophila: elucidation of the relationship between cytotoxicity and stereoconfiguration

Five new polyketides that contain tetramic acids, myceliothermophins A-E, were isolated from the thermophilic fungus Myceliophthora thermophila. Two sets of 5-alkyl-5-hydroxyl (or 5-methoxyl)-1H-pyrrol-2(5H)-one diastereomers, myceliothermophins A/B and C/D, were separated as pure compounds by using silica-gel column chromatography and recycling reverse-phase high-performance liquid chromatography (RP-HPLC). The relative configurations of the chiral centers in 5-alkyl-5-hydroxyl (or 5-methoxyl)-1H-pyrrol-2(5H)-one moieties were deduced from NOESY correlations. In the cytotoxic assay, the 5-(2-methylpropyldiene)-1H-pyrrol-2(5H)-one analogue (myceliothermophin E) exhibited inhibition against four cancer cell lines. In addition, the significant inhibitory effect of myceliothermophins A and C and the inactivity of myceliothermophins B and D revealed the importance of the relative configurations of 5-alkyl-5-hydroxyl (or 5-methoxyl)-1H-pyrrol-2(5H)-one moieties on their cytotoxicity potency against cancer cells.

Mechanism of action of the microtubule-targeted antimitotic depsipeptide tasidotin (formerly ILX651) and its major metabolite tasidotin C-carboxylate

Tasidotin (ILX-651), an orally active synthetic microtubule-targeted derivative of the marine depsipeptide dolastatin-15, is currently undergoing clinical evaluation for cancer treatment. Tasidotin inhibited proliferation of MCF7/GFP breast cancer cells with an IC(50) of 63 nmol/L and inhibited mitosis with an IC(50) of 72 nmol/L in the absence of detectable effects on spindle microtubule polymer mass. Tasidotin inhibited the polymerization of purified tubulin into microtubules weakly (IC(50) approximately 30 micromol/L). However, it strongly suppressed the dynamic instability behavior of the microtubules at their plus ends at concentrations approximately 5 to 10 times below those required to inhibit polymerization. Its major actions were to reduce the shortening rate, the switching frequency from growth to shortening (catastrophe frequency), and the fraction of time the microtubules grew. In contrast with all other microtubule-targeted drugs thus far examined that can inhibit polymerization, tasidotin did not inhibit the growth rate. In contrast to stabilizing plus ends, tasidotin enhanced microtubule dynamic instability at minus ends, increasing the shortening length, the fraction of time the microtubules shortened, and the catastrophe frequency and reducing the rescue frequency. Tasidotin C-carboxylate, the major intracellular metabolite of tasidotin, altered dynamic instability of purified microtubules in a qualitatively similar manner to tasidotin but was 10 to 30 times more potent. The results suggest that the principal mechanism by which tasidotin inhibits cell proliferation is by suppressing spindle microtubule dynamics. Tasidotin may be a relatively weak prodrug for the functionally active tasidotin C-carboxylate.

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.

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.