Eddy Pasquier

Metronomic chemotherapy: new rationale for new directions

Tumor angiogenesis is recognized as a major therapeutic target in the fight against cancer. The key involvement of angiogenesis in tumor growth and metastasis has started to redefine chemotherapy and new protocols have emerged. Metronomic chemotherapy, which is intended to prevent tumor angiogenesis, is based on more frequent and low-dose drug administrations compared with conventional chemotherapy. The potential of metronomic chemotherapy was revealed in animal models a decade ago and the efficacy of this approach has been confirmed in the clinic. In the past 5 years, multiple clinical trials have investigated the safety and efficacy of metronomic chemotherapy in a variety of human cancers. While the results have been variable, clinical studies have shown that these new treatment protocols represent an interesting alternative for either primary systemic therapy or maintenance therapy. We review the latest clinical trials of metronomic chemotherapy in adult and pediatric cancer patients. Accumulating evidence suggests that the efficacy of such treatment may not only rely on anti-angiogenic activity. Potential new mechanisms of action, such as restoration of anticancer immune response and induction of tumor dormancy are discussed. Finally, we highlight the research efforts that need to be made to facilitate the optimal development of metronomic chemotherapy.

Class III β-tubulin mediates sensitivity to chemotherapeutic drugs in non-small cell lung cancer

First line therapy for non–small cell lung carcinoma (NSCLC) commonly includes combination therapy with a tubulin-binding agent (TBA) and a DNA-damaging agent. TBAs suppress microtubule dynamics by binding to the β-tubulin subunit of α/β-tubulin, inducing mitotic arrest and apoptosis. Up-regulation of class III β-tubulin (βIII-tubulin) has been implicated in clinical resistance in NSCLC, ovarian and breast tumors treated in combination with a TBA and DNA-damaging agent. To investigate the functional significance of βIII-tubulin in resistance to both these classes of agents, small interfering RNA (siRNA) was used to silence the expression of this isotype in two NSCLC cell lines, NCI-H460 and Calu-6. Reverse transcription-PCR and immunoblotting showed that βIII-siRNA potently inhibited the expression of βIII-tubulin, without affecting the expression of other major β-tubulin isotypes. Clonogenic assays showed that βIII-siRNA cells were significantly more sensitive to TBAs, paclitaxel, vincristine, and vinorelbine, and for the first time, DNA-damaging agents, cisplatin, doxorubicin, and etoposide compared with controls. Cell cycle analysis of H460 βIII-siRNA cells showed reduced accumulation at the G2-M boundary and an increase in the sub-G1 population in response to TBA treatment compared with control cells. Importantly, βIII-siRNA cells displayed a significant dose-dependent increase in Annexin V staining when treated with either paclitaxel or cisplatin, compared with controls. These findings have revealed a novel role for βIII-tubulin in mediating response to both TBA and DNA-damaging agent therapy and may have important implications for improving the targeting and treatment of drug-refractory NSCLC. [Cancer Res 2007;67(19):9356–63]

Metronomics: towards personalized chemotherapy?

Since its inception in 2000, metronomic chemotherapy has undergone major advances as an antiangiogenic therapy. The discovery of the pro-immune properties of chemotherapy and its direct effects on cancer cells has established the intrinsic multitargeted nature of this therapeutic approach. The past 10 years have seen a marked rise in clinical trials of metronomic chemotherapy, and it is increasingly combined in the clinic with conventional treatments, such as maximum-tolerated dose chemotherapy and radiotherapy, as well as with novel therapeutic strategies, such as drug repositioning, targeted agents and immunotherapy. We review the latest advances in understanding the complex mechanisms of action of metronomic chemotherapy, and the recently identified factors associated with disease resistance. We comprehensively discuss the latest clinical data obtained from studies performed in both adult and paediatric populations, and highlight ongoing clinical trials. In this Review, we foresee the future developments of metronomic chemotherapy and specifically its potential role in the era of personalized medicine.

Antiangiogenic Concentrations of Paclitaxel Induce an Increase in Microtubule Dynamics in Endothelial Cells but Not in Cancer Cells

Microtubule-targeted drugs such as paclitaxel exhibit potent antiangiogenic activity at very low concentrations, but the mechanism underlying such an effect remains unknown. To understand the involvement of microtubules in angiogenesis, we analyzed the dynamic instability behavior of microtubules in living endothelial cells [human microvascular endothelial cells (HMEC-1) and human umbilical vascular endothelial cells (HUVEC)] following 4 hours of paclitaxel treatment. Unexpectedly, antiangiogenic concentrations of paclitaxel (0.1-5 nmol/L) strongly increased microtubule overall dynamicity in both HMEC-1 (86-193%) and HUVEC (54-83%). This increase was associated with increased microtubule growth and shortening rates and extents and decreased mean duration of pauses. The enhancement of microtubule dynamics by paclitaxel seemed to be specific to antiangiogenic concentrations and to endothelial cells. Indeed, cytotoxic concentration (100 nmol/L) of paclitaxel suppressed microtubule dynamics by 40% and 54% in HMEC-1 and HUVECs, respectively, as observed for all tested concentrations in A549 tumor cells. After 4 hours of drug incubation, antiangiogenic concentrations of paclitaxel that inhibited endothelial cell proliferation without apoptosis (1-5 nmol/L) induced a slight decrease in anaphase/metaphase ratio, which was more pronounced and associated with increased mitotic index after 24 hours of incubation. Interestingly, the in vitro antiangiogenic effect also occurred at 0.1 nmol/L paclitaxel, a concentration that did not alter mitotic progression and endothelial cell proliferation but was sufficient to increase interphase microtubule dynamics. Altogether, our results show that paclitaxel mediates antiangiogenesis by an increase in microtubule dynamics in living endothelial cells and suggest that the impairment of interphase microtubule functions is responsible for the inhibition of angiogenesis.

Microtubules: a dynamic target in cancer therapy.

The tubulin/microtubule system is an important target for anticancer therapy. Two of the most clinically valuable groups of these agents are the vinca alkaloids and taxanes. In recent years, new tubulin‐binding agents have been under preclinical or clinical development. One of these classes of agents, epothilones, has shown great promise in phase III clinical trials. What all these agents share in common, is that they bind to β‐tubulin and disrupt microtubule function during mitosis which in turn leads to mitotic arrest and cell death. In addition, these agents can inhibit angiogenesis. Not withstanding their effectiveness, drug resistance can pose a major clinical problem. This review provides an overview of the mechanisms mediating resistance to tubulin‐binding agents related to the cellular target and discusses strategies to overcome this important clinical problem.

Targeting microtubules to inhibit angiogenesis and disrupt tumour vasculature: implications for cancer treatment.

Anticancer agents that interfere with tubulin functions are widely used in the clinic and have a broad spectrum of activity against both haematological malignancies and solid tumours. These Microtubule-Targeting Agents (MTAs), such as the taxanes and Vinca alkaloids, bind to the beta subunit of alpha/beta tubulin and disrupt microtubule dynamics in tumour cells, ultimately leading to mitotic block and subsequent cell death. Recently, MTAs have received considerable interest as potential tumour-selective anti-angiogenic and vascular-disrupting agents. Angiogenesis is a keystone of tumour progression and metastasis and targeting the formation of new blood vessels within the tumour is therefore regarded as a promising strategy for cancer therapy. In this regard, conventional MTAs can be given on daily schedules at non-toxic doses (metronomic dosing) to disturb tumour angiogenesis. Some MTAs can also act as vascular-disrupting agents. After briefly reviewing the classical mechanisms involved in the anti-tumour action of MTAs, we will focus on the latest studies investigating the molecular and cellular processes underlying the anti-angiogenic and the vascular-disrupting properties of these agents. We will also review and discuss the potential clinical development and the limitations of MTAs used as tumour-specific anti-vascular molecules.

Has the time come for metronomics in low-income and middle-income countries?

In 2008, 72% of cancer deaths occurred in low-income and middle-income countries, where, although there is a lower incidence of cancer than in high-income countries, survival rates are also low. Many patients are sent home to die, and an even larger number of patients do not have access to treatment facilities. New constraint-adapted therapeutic strategies are therefore urgently needed. Metronomic chemotherapy--the chronic administration of chemotherapy at low, minimally toxic doses on a frequent schedule of administration, with no prolonged drug-free breaks--has recently emerged as a potential strategy to control advanced or refractory cancer and represents an alternative for patients with cancer living in developing countries. This low-cost, well-tolerated, and easy to access strategy is an attractive therapeutic option in resource-limited countries. Moreover, combined with drug repositioning, additional anticancer effects can be achieved, ultimately resulting in improved cancer control while maintaining minimum cost of treatment. In this Personal View, we will briefly review the rationale behind the combination of metronomic chemotherapy and drug repositioning-an approach we term metronomics. We assess the clinical experience obtained with this kind of anticancer treatment and describe potential new developments in countries with limited resources. We also highlight the need for adapted clinical study endpoints and innovative models of collaboration between for-profit and non-profit organisations, to address the growing problem of cancer in resource-limited countries.

Antiangiogenic Concentrations of Vinflunine Increase the Interphase Microtubule Dynamics and Decrease the Motility of Endothelial Cells

Angiogenesis is a key event in tumor progression and metastasis. This complex process, which constitutes a potent target for cancer therapy, is inhibited by very low concentrations of microtubule-targeting drugs (MTD). However, the intimate mechanisms of the antiangiogenic activity of MTDs remain unclear. Recently, we have shown that low antiangiogenic and noncytotoxic concentrations of paclitaxel induced an unexpected increase in microtubule dynamics in endothelial cells. In this study, we showed that vinflunine, the newest Vinca alkaloid, increased microtubule dynamic instability in human endothelial cells after 4-hour incubation at low concentrations (29% and 54% at 0.1 and 2 nmol/L). The growth and shortening rates were increased, and the percentage of time spent in pause and the mean duration of pauses were decreased, as previously observed with paclitaxel. As opposed to paclitaxel, the transition frequencies were not significantly disturbed by vinflunine. Moreover, low concentrations of vinflunine did not affect mitotic index and anaphase/metaphase ratio. Interestingly, these low vinflunine concentrations that increased microtubule dynamics exhibited an antiangiogenic effect through the inhibition of both morphogenesis and random motility. Capillary tube formation on Matrigel was decreased up to 44%. The cell speed and the random motility coefficient were decreased (13% and 19% and 13% and 33% at 0.1 and 2 nmol/L, respectively) and the persistent time was statistically increased. Altogether, our results confirm that the increase in microtubule dynamics is involved in MTD antiangiogenic activity and highlight the crucial role of interphase microtubule dynamics in angiogenesis.

ENMD-1198, a New Analogue of 2-Methoxyestradiol, Displays Both Antiangiogenic and Vascular-Disrupting Properties

The formation of a new vascular network by angiogenesis is a key driver in tumor growth and metastasis, making this an attractive therapeutic target. Different strategies are being developed to either prevent tumor angiogenesis or disrupt the tumor vasculature already in place. In this in vitro study, we investigated the antivascular properties of ENMD-1198, a new anticancer drug currently in clinical trials. ENMD-1198 is a new analogue of 2-methoxyestradiol, a microtubule-targeting agent that has shown promising results in the treatment of multiple myeloma and hormone-refractory prostate cancer. Using both bone marrow–derived and dermal microvascular endothelial cell lines, we analyzed the effect of ENMD-1198 on the different functions of endothelial cells involved in angiogenesis. In both cell lines, ENMD-1198 was more potent than 2-methoxyestradiol at inhibiting endothelial cell proliferation, motility, migration, and morphogenesis. In addition, ENMD-1198 induced a significant decrease in vascular endothelial growth factor receptor-2 protein expression in endothelial cells. Furthermore, videomicroscopy experiments showed that ENMD-1198 was able to completely disrupt preformed vascular structures within 2 hours. This vascular-disrupting activity was associated with extensive depolymerization of the microtubule network and accumulation of actin stress fibers and large focal adhesions in vascular endothelial cells. Collectively, our results show that this new compound displays potent antivascular properties, and this study provides important insights into the mechanism of action of this promising new anticancer drug. Mol Cancer Ther; 9(5); 1408–18. ©2010 AACR.

Concentration- and schedule-dependent effects of chemotherapy on the angiogenic potential and drug sensitivity of vascular endothelial cells.

The anti-angiogenic activity of chemotherapy is both dose- and schedule-dependent. While conventional maximum tolerated dose (MTD) chemotherapy exerts only mild and reversible anti-angiogenic effects, low-dose metronomic (LDM) chemotherapy was developed to specifically target tumour angiogenesis. However, the long-term effects of either MTD or LDM chemotherapy on vascular endothelial cells have never been investigated. Here, we demonstrated that repeated exposure to MTD and LDM chemotherapy differentially impact on the angiogenic potential and chemosensitivity of immortalized endothelial cells. Repeated MTD vinblastine treatment of vascular endothelial cells led to an increased proliferation rate and resistance to paclitaxel. In contrast, repeated LDM treatment with vinblastine or etoposide impaired the angiogenic potential of endothelial cells and increased their chemosensitivity. This effect was associated with a significant decrease in βII- and βIII-tubulin expression. Functional analysis using siRNA showed that silencing the expression of βIII-tubulin in endothelial cells significantly decreased their capacity to form vascular structures and increased their sensitivity to the anti-angiogenic and vascular-disrupting effects of chemotherapy, whereas silencing βII-tubulin expression had no effect. Collectively our results show that LDM chemotherapy impairs the angiogenic potential of endothelial cells while increasing their chemosensitivity—an effect at least in part mediated by the down-regulation of βIII-tubulin expression. Furthermore, our study suggests that βIII-tubulin represents an attractive therapeutic target to increase the anti-angiogenic effects of chemotherapy and overall anti-tumour efficacy.