Mechanistic aspects of the cytotoxic activity of glufosfamide, a new tumour therapeutic agent

Targeting Pivotal Hallmarks of Cancer for Enhanced Therapeutic Strategies in Triple-Negative Breast Cancer Treatment-In Vitro, In Vivo and Clinical Trials Literature Review

This literature review provides a comprehensive overview of triple-negative breast cancer (TNBC) and explores innovative targeted therapies focused on specific hallmarks of cancer cells, aiming to revolutionize breast cancer treatment. TNBC, characterized by its lack of expression of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2), presents distinct features, categorizing these invasive breast tumors into various phenotypes delineated by key elements in molecular assays. This article delves into the latest advancements in therapeutic strategies targeting components of the tumor microenvironment and pivotal hallmarks of cancer: deregulating cellular metabolism and the Warburg effect, acidosis and hypoxia, the ability to metastasize and evade the immune system, aiming to enhance treatment efficacy while mitigating systemic toxicity. Insights from in vitro and in vivo studies and clinical trials underscore the promising effectiveness and elucidate the mechanisms of action of these novel therapeutic interventions for TNBC, particularly in cases refractory to conventional treatments. The integration of targeted therapies tailored to the molecular characteristics of TNBC holds significant potential for optimizing clinical outcomes and addressing the pressing need for more effective treatment options for this aggressive subtype of breast cancer.

Metabolic tricks of cancer cells

One of the characteristics of cancer cells important for tumorigenesis is their metabolic plasticity. Indeed, in various stress conditions, cancer cells can reshape their metabolic pathways to support the increased energy request due to continuous growth and rapid proliferation. Moreover, selective pressures in the tumor microenvironment, such as hypoxia, acidosis, and competition for resources, force cancer cells to adapt by complete reorganization of their metabolism. In this review, we highlight the characteristics of cancer metabolism and discuss its clinical significance, since overcoming metabolic plasticity of cancer cells is a key objective of modern cancer therapeutics and a better understanding of metabolic reprogramming may lead to the identification of possible targets for cancer therapy.

Dual Action of Acidic Microenvironment on the Enrichment of the Active Metabolite of Disulfiram in Tumor Tissues

Disulfiram, an antialcoholism drug, could potentially be repurposed as an anticancer drug because of the formation of copper(II) diethyldithiocarbamate (CuET) from dithiocarb (DTC, a reduced metabolite of disulfiram) and Cu²⁺ CuET exhibited preferential distribution to tumor tissues. This study investigated the mechanism of CuET accumulation in tumor tissues by employing MDA-MB-231 human breast cancer cells. The concentration of CuET in cells treated with DTC and Cu²⁺ in acidic culture medium (pH 6.8) was significantly higher than that of the control group (pH 7.4). Subsequently, the effects of pH on the uptake of DTC, Cu²⁺, and CuET were investigated separately. The acidic environment significantly increased the uptake rate of DTC and Cu²⁺ but had no effect on CuET. MDA-MB-231 cells overexpressing copper transporter hCTR1 were constructed to evaluate its intermediate role in CuET accumulation. After treatment with CuCl₂ followed by DTC for 15 minutes, the levels of CuET and Cu²⁺ in hCTR1-overexpressed cells were 2.5 times as much as those of vector group. In the tumors of cancer xenograft models constructed by hCTR1-MDA-MB-231 cells, the concentrations of CuET and Cu were also significantly higher than those of control group. In conclusion, the acidic microenvironment of tumors can promote the enrichment of CuET in tumors through dual action. On the one hand, it can promote transmembrane transport of DTC by converting ionic DTC into molecular state. On the other hand, it enhances Cu²⁺ uptake by activating hCTR1, which ultimately leads to the enrichment of CuET. SIGNIFICANCE STATEMENT: Increasing evidence suggests that the antitumor activity of disulfiram is related to the formation of a copper(II) diethyldithiocarbamate (CuET) of its reducing metabolite dithiocarb with copper(II) ion, which is preferentially distributed in tumor tissues. We showed that the acidic microenvironment, a common feature of many solid tumor tissues, could promote intracellular CuET accumulation through dual action without changing CuET uptake. This result is helpful for the formulation of clinical dosage regimens of disulfiram in cancer treatment.

Anti-cancer agents and reactive oxygen species modulators that target cancer cell metabolism

Traditionally the perspective on reactive oxygen species (ROS) has centered on the role they play as carcinogenic or cancer-causing radicals. Over the years, characterization and functional studies have revealed the complexity of ROS as signaling molecules that regulate various physiological cellular responses or whose levels are altered in various diseases. Cancer cells often maintain high basal level of ROS and are vulnerable to any further increase in ROS levels beyond a certain protective threshold. Consequently, ROS-modulation has emerged as an anticancer strategy with synthesis of various ROS-inducing or responsive agents that target cancer cells. Of note, an increased carbohydrate uptake and/or induction of death receptors of cancer cells was exploited to develop glycoconjugates that potentially induce cellular stress, ROS and apoptosis. This mini review highlights the development of compounds that target cancer cells by taking advantage of redox or metabolic alteration in cancer cells.

d- Versus l-Glucose Conjugation: Mitochondrial Targeting of a Light-Activated Dual-Mode-of-Action Ruthenium-Based Anticancer Prodrug

Light-activated ruthenium polypyridyl anticancer prodrugs often suffer from poor water solubility, poor selectivity, and/or ill-defined intracellular targets. Coordination of the d- or l-glucose thioether ligand 3 (2-(2-(2-(methylthio)ethoxy)ethoxy)ethyl-β-glucopyranoside) to the highly lipophilic ruthenium complex [Ru(tpy)(dppn)(H2 O)]2+ ([1]2+ ; dppn=benzo[i]dipyrido-[3,2-a:2',3'-c]phenazine, tpy=2,2':6',2''-terpyridine) solved all these problems at once. The two enantiomers of [Ru(tpy)(dppn)(3)][PF6 ]2 , [d-2][PF6 ]2 and [l-2][PF6 ]2 , were soluble in water, which allowed the influence of the chirality of the glucose moiety on uptake, toxicity, and intracellular localization of the prodrug to be probed without changing any other physicochemical properties. Both compounds showed mild, but different, cytotoxicity in A549 (human lung carcinoma) and MCF-7 (human breast adenocarcinoma) cancer cells in the dark, whereas following low doses of visible light irradiation (3.1 J cm-2 at λ = 454 nm), a similar, but high cytotoxicity (EC50 < 1 μm), was observed. Irrespective of the chirality, both slightly emissive Ru complexes were found in the mitochondria, and two modes of action may contribute to light-induced cell death: 1) the glucose thioether ligand is photosubstituted by water, thus [1]2+ , which interacts with DNA at an exceptionally high 400:1 base pair/Ru ratio, is released; 2) both [1]2+ and [2]2+ produce massive amounts of singlet oxygen, which leads to very efficient photodynamic DNA cleavage.

The chemomodulatory effects of glufosfamide on docetaxel cytotoxicity in prostate cancer cells

Background. Glufosfamide (GLU) is a glucose conjugate of ifosfamide in which isophosphoramide mustard is glycosidically linked to the β-D-glucose molecule. Based on GLU structure, it is considered a targeted chemotherapy with fewer side effects. The main objective of the current study is to assess the cytotoxic potential of GLU for the first time in prostate cancer (PC) cells representing different stages of the tumor. Furthermore, this study examined the potential synergistic activity of GLU in combination with docetaxel (DOC).

Methods. Two different cell lines were used, LNCaP and PC-3. Concentration-response curves were assessed. The tested groups per cell line were, control, GLU, DOC and combination. Treatment duration was 72 h. Cytotoxicity was assessed using sulforhodamine B (SRB) assay and half maximal inhibitory concentration (IC50) was calculated. Synergy analyses were performed using Calcusyn^®software. Subsequent mechanistic studies included β-glucosidase activity assay, glucose uptake and apoptosis studies, namely annexin V-FITC assay and the protein expression of mitochondrial pathway signals including Bcl-2, Bax, Caspase 9 and 3 were assessed. Data are presented as mean ± SD; comparisons were carried out using one way analysis of variance (ANOVA) followed by Tukey-Kramer’s test for post hoc analysis.

Results. GLU induced cytotoxicity in both cell lines in a concentration-dependent manner. The IC50 in PC-3 cells was significantly lower by 19% when compared to that of LNCaP cells. The IC50 of combining both drugs showed comparable effect to DOC in PC-3 but was tremendously lowered by 49% compared to the same group in LNCaP cell line. β-glucosidase activity was higher in LNCaP by about 67% compared to that determined in PC-3 cells while the glucose uptake in PC-3 cells was almost 2 folds that found in LNCaP cells. These results were directly correlated to the efficacy of GLU in each cell line. Treatment of PC cells with GLU as single agent or in combination with DOC induced significantly higher apoptosis as evidenced by Annexin V-staining. Apoptosis was significantly increased in combination group by 4.9 folds and by 2.1 Folds when compared to control in LNCaP cells and PC-3 cells; respectively. Similarly, the expression of Bcl-2 was significantly decreased while Bax, caspase 9 and 3 were significantly increased in the combined treatment groups compared to the control.

Conclusion. GLU has a synergistic effect in combination with DOC as it increases the cell kill which can be attributed at least partially to apoptosis in both the tested cell lines and it is suggested as a new combination regimen to be considered in the treatment of the prostate cancer. Further experiments and clinical investigations are needed for assessment of that regimen.

Small Molecules for Active Targeting in Cancer

For the purpose of this review, active targeting in cancer research encompasses strategies wherein a ligand for a cell surface receptor expressed on tumor cells is used to deliver a cytotoxic or imaging cargo. This area of research is more than two decades old, but in those 20 and more years, how many receptors have been studied extensively? What kinds of the ligands are used for active targeting? Are they mostly naturally occurring molecules such as folic acid, or synthetic substances developed in campaigns for medicinal chemistry efforts? This review outlines the most important receptor or ligand combinations that have been used in active targeting to answer these questions, and therefore to address the most important one of all: is research in active targeting affording diminishing returns, or is this an area for which the potential far exceeds progress made so far?

Sulfur and nitrogen mustards induce characteristic poly(ADP-ribosyl)ation responses in HaCaT keratinocytes with distinctive cellular consequences

Mustard agents are potent DNA alkylating agents with mutagenic, cytotoxic and vesicant properties. They include bi-functional agents, such as sulfur mustard (SM) or nitrogen mustard (mustine, HN2), as well as mono-functional agents, such as "half mustard" (CEES). Whereas SM has been used as a chemical warfare agent, several nitrogen mustard derivatives, such as chlorambucil and cyclophosphamide, are being used as established chemotherapeutics. Upon induction of specific forms of genotoxic stimuli, several poly(ADP-ribose) polymerases (PARPs) synthesize the nucleic acid-like biopolymer poly(ADP-ribose) (PAR) by using NAD(+) as a substrate. Previously, it was shown that SM triggers cellular poly(ADP-ribosyl) ation (PARylation), but so far this phenomenon is poorly characterized. In view of the protective effects of PARP inhibitors, the latter have been proposed as a treatment option of SM-exposed victims. In an accompanying article (Debiak et al., 2016), we have provided an optimized protocol for the analysis of the CEES-induced PARylation response in HaCaT keratinocytes, which forms an experimental basis to further analyze mustard-induced PARylation and its functional consequences, in general. Thus, in the present study, we performed a comprehensive characterization of the PARylation response in HaCaT cells after treatment with four different mustard agents, i.e., SM, CEES, HN2, and chlorambucil, on a qualitative, quantitative and functional level. In particular, we recorded substance-specific as well as dose- and time-dependent PARylation responses using independent bioanalytical methods based on single-cell immuno-fluorescence microscopy and quantitative isotope dilution mass spectrometry. Furthermore, we analyzed if and how PARylation contributes to mustard-induced toxicity by treating HaCaT cells with CEES, SM, and HN2 in combination with the clinically relevant PARP inhibitor ABT888. As evaluated by a novel immunofluorescence-based protocol for the detection of N7-ETE-guanine DNA adducts, the excision rate of CEES-induced DNA adducts was not affected by PARP inhibition. Furthermore, while CEES induced moderate changes in cellular NAD(+) levels, annexin V/PI flow cytometry analysis revealed that these changes did not affect CEES-induced short-term cytotoxicity 24h after treatment. In contrast, PARP inhibition impaired cell proliferation and clonogenic survival, and potentiated micronuclei formation of HaCaT cells upon CEES treatment. Similarly, PARP inhibition affected clonogenic survival of cells treated with bi-functional mustards such as SM and HN2. In conclusion, we demonstrate that PARylation plays a functional role in mustard-induced cellular stress response with substance-specific differences. Since PARP inhibitors exhibit therapeutic potential to treat SM-related pathologies and to sensitize cancer cells for mustard-based chemotherapy, potential long-term effects of PARP inhibition on genomic stability and carcinogenesis should be carefully considered when pursuing such a strategy.

Oxazaphosphorine bioactivation and detoxification The role of xenobiotic receptors

Oxazaphosphorines, with the most representative members including cyclophosphamide, ifosfamide, and trofosfamide, constitute a class of alkylating agents that have a broad spectrum of anticancer activity against many malignant ailments including both solid tumors such as breast cancer and hematological malignancies such as leukemia and lymphoma. Most oxazaphosphorines are prodrugs that require hepatic cytochrome P450 enzymes to generate active alkylating moieties before manifesting their chemotherapeutic effects. Meanwhile, oxazaphosphorines can also be transformed into non-therapeutic byproducts by various drug-metabolizing enzymes. Clinically, oxazaphosphorines are often administered in combination with other chemotherapeutics in adjuvant treatments. As such, the therapeutic efficacy, off-target toxicity, and unintentional drug-drug interactions of oxazaphosphorines have been long-lasting clinical concerns and heightened focuses of scientific literatures. Recent evidence suggests that xenobiotic receptors may play important roles in regulating the metabolism and clearance of oxazaphosphorines. Drugs as modulators of xenobiotic receptors can affect the therapeutic efficacy, cytotoxicity, and pharmacokinetics of coadministered oxazaphosphorines, providing a new molecular mechanism of drug-drug interactions. Here, we review current advances regarding the influence of xenobiotic receptors, particularly, the constitutive androstane receptor, the pregnane X receptor and the aryl hydrocarbon receptor, on the bioactivation and detoxification of oxazaphosphorines, with a focus on cyclophosphamide and ifosfamide.

Glufosfamide as a new oxazaphosphorine anticancer agent

Glufosfamide (β-D-glucose-isophosphoramide mustard, D-19575) belongs to the oxazaphosphorine class. Glufosfamide is a novel glucose conjugate of ifosfamide in which isophosphoramide mustard, the alkylating metabolite of ifosfamide, is glycosidically linked to the β-D-glucose molecule. Glufosfamide represents an attractive new agent for cancer therapy. Its mode of action on normal and pathological cells is still under experimental and clinical investigations. An assessment of the anticancer potential of glufosfamide is of key importance in therapy. The researchers reviewed the current knowledge available on glufosfamide tested in the preclinical studies/clinical trials, based on a collection of the original papers and conference abstracts published and relevant articles searched in the SCOPUS and MEDLINE database and websites.

Preclinical investigation of tolerance and antitumour activity of new fluorodeoxyglucose-coupled chlorambucil alkylating agents

Our strategy is to increase drug accumulation in target tumour cells using specific "vectors" tailored to neoplastic tissue characteristics, which ideally are not found in healthy tissues. The aim of this work was to use 2-fluoro-2-deoxyglucose (FDG) as a drug carrier, in view of its well-known accumulation by most primary and disseminated human tumours. We had previously selected two FDG-cytotoxic conjugates of chlorambucil (CLB), i.e. compounds 21a and 40a, on the basis of their in vitro profiles. Here we investigated the antitumour profile and tolerance of these compounds in vitro and in vivo in two murine cell lines of solid tumours. In vitro, we found that micromolar concentrations of compounds 21a and 40a inhibited proliferation of B16F0 and CT-26 cell lines. Interestingly, compounds 21a and 40a were found to act at different levels in the cell cycle: S and subG1 accumulation for 21a and G2 accumulation for 40a. In vivo, a single-dose-finding study to select the Maximum Tolerated Dose (MTD) by the intraperitoneal route (IP) showed that the two peracetylated glucoconjugates of CLB were less toxic than CLB itself. When given to tumour-bearing mice (melanoma and colon carcinoma models), according to a "q4d × 3" schedule (i.e., three doses at 4-day intervals) both compounds demonstrated a promising antitumour activity, with Log Cell Kill (LCK) values higher than 1.3 in both B16F0 and CT-26 models. Hence compounds 21a and 40a are good candidates for further works to develop new highly active antineoplastic compounds.

The tumor suppressor function of mitochondria: translation into the clinics

Recently, the inevitable metabolic reprogramming experienced by cancer cells as a result of the onset of cellular proliferation has been added to the list of hallmarks of the cancer cell phenotype. Proliferation is bound to the synchronous fluctuation of cycles of an increased glycolysis concurrent with a restrained oxidative phosphorylation. Mitochondria are key players in the metabolic cycling experienced during proliferation because of their essential roles in the transduction of biological energy and in defining the life-death fate of the cell. These two activities are molecularly and functionally integrated and are both targets of commonly altered cancer genes. Moreover, energetic metabolism of the cancer cell also affords a target to develop new therapies because the activity of mitochondria has an unquestionable tumor suppressor function. In this review, we summarize most of these findings paying special attention to the opportunity that translation of energetic metabolism into the clinics could afford for the management of cancer patients. More specifically, we emphasize the role that mitochondrial beta-F1-ATPase has as a marker for the prognosis of different cancer patients as well as in predicting the tumor response to therapy.

Synthesis and cytotoxic properties of new fluorodeoxyglucose-coupled chlorambucil derivatives

Frequently used in the treatment of malignant cells, alkylating agents, like most anticancer substances, produce adverse side effects caused by the toxicity of the agents toward normal tissues and lose efficiency through poor distribution to target sites. Our approach to developing more selective drugs with low systemic toxicity is based on the premise that the body distribution and cell uptake of a drug can be altered by attaching a neoplastic cell-specific uptake enhancer, such as 2-fluoro-2-deoxyglucose (FDG), the radiotracer most frequently used in PET for tumor imaging. Two properties of deoxyglucose, namely preferential accumulation in neoplastic cells and inhibition of glycolysis, underpin this targeting approach. Here, we report the synthesis of 19 new chlorambucil glycoconjugates in which the alkylating drug is attached to the C-1 position of FDG, directly or via different linkages. This set of compounds was evaluated for in vitro cytotoxicity against different human normal and tumor cell lines. There was a significant improvement in the in vitro cytotoxicity of peracetylated glucoconjugates compared with the free substance. Four compounds were finally selected for further in vivo studies owing to their lack of oxidative stress-inducing properties.

Outpatient Chemotherapy plus Radiotherapy in Sarcomas: Improving Cancer Control with Radiosensitizing Agents

Background

Cancer control by radiotherapy (RT) can be improved with concurrent chemotherapy. Outpatient strategies for sarcomas that combine chemotherapy and RT are possible since supportive care and RT techniques have improved.

Methods

The current status of non-anthracycline chemotherapy in combination with radiation for high-risk sarcoma is reviewed.

Results

Ifosfamide with mesna and newer activated ifosfamide agents (ZIO-201 and glufosfamide) have high potential to improve sarcoma cancer control. In Ewing's sarcoma and osteosarcoma, high-dose ifosfamide with mesna (2.8 g/m2/day of each x 5 days; mesna day 6) can be safely given to outpatients using continuous infusion. Reducing ifosfamide nephrotoxicity and central nervous system side effects are discussed. Other outpatient radiosensitization regimens include gemcitabine (600–1000 mg/m2/dose IV over 1 hour weekly x 2–3 doses), temozolomide (75 mg/m2/daily x 3–6 weeks), or temozolomide (100 mg/m2/dose daily x 5) + irinotecan (10 mg/m2/dose daily x 5 x 2 weeks). In osteosarcoma with osteoblastic metastases on bone scan, samarium (1 mCi/kg; day 3 of RT) and gemcitabine (600 mg/m2 IV over 1 hour day 9 of RT) is a radiosensitization strategy. Future drugs for radiosensitization include beta-D-glucose targeted activated ifosfamide (glufosfamide) and sapacitabine, an oral nucleoside with in vitro activity against solid tumors including sarcomas.

Conclusions

The potential to treat major causes of sarcoma treatment failure (local recurrence and distant metastases) with concurrent chemotherapy during radiation should be considered in high-grade sarcomas.

Glucosylated heparin derivatives as non-toxic anti-cancer drugs

Heparin, which has been widely used as an anti-coagulant agent, has potential anti-tumor effects; in particular, low molecular weight heparin (LMWH) may inhibit tumor angiogenesis and/or metastasis with reduced toxicity. For decades, it has been known that malignant cancer cells display abnormally enhanced glucose uptake rates and overexpress glucose transporters (GLUTs) compared to normal cells. With these findings in mind, we introduced a glucose moiety to heparin for the purpose of increasing the concentration of heparin at the tumor site by targeting GLUTs. Three glucosylated heparin (GH) derivatives were prepared by conjugation of glucosamine and heparin in different mole ratios. To evaluate the potential of GH derivatives as anti-cancer drugs, their anti-coagulant activities, inhibitory effects on glucose analog uptake, cellular interactions, tumor growth inhibitory effects and sub-acute toxicities were investigated. The anti-coagulant activities of GH derivatives decreased proportionally to the degree of glucosylation. In vitro, GH derivatives inhibited HUVEC proliferation to a greater extent than heparin. GH derivatives mainly existed outside of cells and interacted with GLUTs on the cell surface, thereby inhibiting glucose uptake into cells. In vivo, GH derivatives significantly suppressed tumor growth compared to control, without systemic toxicity. Therefore, GH derivatives are proposed as potent non-toxic anti-cancer drugs.

A novel alkylating agent, glufosfamide, enhances the activity of gemcitabine in vitro and in vivo

Glufosfamide is an alkylating agent consisting of iphosphoramide mustard conjugated to glucose that is currently included in clinical studies of pancreatic cancer. We studied the effects of glufosfamide, in combination with gemcitabine, on in vitro and in vivo models of pancreatic cancer. In proliferation assays, glufosfamide and gemcitabine inhibited the growth of MiaPaCa-2, H766t, and PANC-1 cells, but the combination of the two agents provided greater effects. Apoptosis of MiaPaCa-2 cells, measured by fluorescence-activated cell sorting, was enhanced by the combination of the two drugs, compared to single-agent treatment. Glufosfamide alone inhibited the growth of red fluorescent protein-expressing MiaPaCa-2 tumors in an orthotopic nude mouse model in a dose-dependent manner. Combining glufosfamide (30 mg/kg) with gemcitabine resulted in enhanced inhibition of tumor growth and significantly prolonged survival. Immunohistochemistry of excised tumors revealed that both glufosfamide and gemcitabine increased levels of apoptosis (measured by terminal deoxynucleotidyl transferase-mediated nick end labeling staining) and reduced proliferation (measured by proliferating cell nuclear antigen staining). No effects on microvessel density were observed. These results support the use of the alkylating agent glufosfamide and the DNA synthesis inhibitor gemcitabine, rather than the use of either agent alone, to provide greater benefits and demonstrate that this combination treatment should be useful in the clinical treatment of pancreatic carcinoma.

Antirestenotic effects of a novel polymer-coated d-24851 eluting stent. Experimental data in a rabbit iliac artery model

Experimental and clinical data suggest that stents eluting antiproliferative agents can be used for the prevention of in-stent restenosis. Here we investigate in vitro the antiproliferative and apoptotic effect of D-24851 and evaluate the safety and efficacy of D-24851-eluting polymer-coated stents in a rabbit restenosis model (n = 53). Uncoated stents (n = 6), poly (DL: -lactide-co-glycolide) (PLGA)-coated stents (n = 7), and PLGA-coated stents loaded with 0.08 +/- 0.0025 microM (31 +/- 1 mug; low dose; n = 7), 0.55 +/- 0.02 microM (216 +/- 8 mug; high dose; n = 6), and 4.55 +/- 0.1 microM (1774 +/- 39 mug; extreme dose; n = 5) of D-24851 were randomly implanted in New Zealand rabbit right iliac arteries and the animals were sacrificed after 28 days for histomorphometric analysis. For the assessment of endothelial regrowth in 90 days, 12 rabbits were subjected to PLGA-coated (n = 3), low-dose (n = 3), high-dose (n = 3), and extreme-dose (n = 3) stent implantation. In vitro studies revealed that D-24851 exerts its growth inhibitory effects via inhibition of proliferation and induction of apoptosis without increasing the expression of heat shock protein-70, a cytoprotective and antiapoptotic protein. Treatment with low-dose D-24851 stents was associated with a significant reduction in neointimal area and percentage stenosis only compared with bare metal stents (38% [P = 0.029] and 35% [P = 0.003] reduction, respectively). Suboptimal healing, however, was observed in all groups of D-24851-loaded stents in 90 days in comparison with PLGA-coated stents. We conclude that low-dose D-24851-eluting polymer-coated stents significantly inhibit neointimal hyperplasia at 28 days through inhibition of proliferation and enhancement of apoptosis. In view of the suboptimal re-endothelialization, longer-term studies are needed in order to establish whether the inhibition of intimal growth is maintained.

Glycolysis inhibition for anticancer treatment

Most cancer cells exhibit increased glycolysis and use this metabolic pathway for generation of ATP as a main source of their energy supply. This phenomenon is known as the Warburg effect and is considered as one of the most fundamental metabolic alterations during malignant transformation. In recent years, there are significant progresses in our understanding of the underlying mechanisms and the potential therapeutic implications. Biochemical and molecular studies suggest several possible mechanisms by which this metabolic alteration may evolve during cancer development. These mechanisms include mitochondrial defects and malfunction, adaptation to hypoxic tumor microenvironment, oncogenic signaling, and abnormal expression of metabolic enzymes. Importantly, the increased dependence of cancer cells on glycolytic pathway for ATP generation provides a biochemical basis for the design of therapeutic strategies to preferentially kill cancer cells by pharmacological inhibition of glycolysis. Several small molecules have emerged that exhibit promising anticancer activity in vitro and in vivo, as single agent or in combination with other therapeutic modalities. The glycolytic inhibitors are particularly effective against cancer cells with mitochondrial defects or under hypoxic conditions, which are frequently associated with cellular resistance to conventional anticancer drugs and radiation therapy. Because increased aerobic glycolysis is commonly seen in a wide spectrum of human cancers and hypoxia is present in most tumor microenvironment, development of novel glycolytic inhibitors as a new class of anticancer agents is likely to have broad therapeutic applications.

Metabolism and transport of oxazaphosphorines and the clinical implications

The oxazaphosphorines including cyclophosphamide (CPA), ifosfamide (IFO), and trofosfamide represent an important group of therapeutic agents due to their substantial antitumor and immuno-modulating activity. CPA is widely used as an anticancer drug, an immunosuppressant, and for the mobilization of hematopoetic progenitor cells from the bone marrow into peripheral blood prior to bone marrow transplantation for aplastic anemia, leukemia, and other malignancies. New oxazaphosphorines derivatives have been developed in an attempt to improve selectivity and response with reduced toxicity. These derivatives include mafosfamide (NSC 345842), glufosfamide (D19575, beta-D-glucosylisophosphoramide mustard), NSC 612567 (aldophosphamide perhydrothiazine), and NSC 613060 (aldophosphamide thiazolidine). This review highlights the metabolism and transport of these oxazaphosphorines (mainly CPA and IFO, as these two oxazaphosphorine drugs are the most widely used alkylating agents) and the clinical implications. Both CPA and IFO are prodrugs that require activation by hepatic cytochrome P450 (CYP)-catalyzed 4-hydroxylation, yielding cytotoxic nitrogen mustards capable of reacting with DNA molecules to form crosslinks and lead to cell apoptosis and/or necrosis. Such prodrug activation can be enhanced within tumor cells by the CYP-based gene directed-enzyme prodrug therapy (GDEPT) approach. However, those newly synthesized oxazaphosphorine derivatives such as glufosfamide, NSC 612567 and NSC 613060, do not need hepatic activation. They are activated through other enzymatic and/or non-enzymatic pathways. For example, both NSC 612567 and NSC 613060 can be activated by plain phosphodiesterase (PDEs) in plasma and other tissues or by the high-affinity nuclear 3'-5' exonucleases associated with DNA polymerases, such as DNA polymerases and epsilon. The alternative CYP-catalyzed inactivation pathway by N-dechloroethylation generates the neurotoxic and nephrotoxic byproduct chloroacetaldehyde (CAA). Various aldehyde dehydrogenases (ALDHs) and glutathione S-transferases (GSTs) are involved in the detoxification of oxazaphosphorine metabolites. The metabolism of oxazaphosphorines is auto-inducible, with the activation of the orphan nuclear receptor pregnane X receptor (PXR) being the major mechanism. Oxazaphosphorine metabolism is affected by a number of factors associated with the drugs (e.g., dosage, route of administration, chirality, and drug combination) and patients (e.g., age, gender, renal and hepatic function). Several drug transporters, such as breast cancer resistance protein (BCRP), multidrug resistance associated proteins (MRP1, MRP2, and MRP4) are involved in the active uptake and efflux of parental oxazaphosphorines, their cytotoxic mustards and conjugates in hepatocytes and tumor cells. Oxazaphosphorine metabolism and transport have a major impact on pharmacokinetic variability, pharmacokinetic-pharmacodynamic relationship, toxicity, resistance, and drug interactions since the drug-metabolizing enzymes and drug transporters involved are key determinants of the pharmacokinetics and pharmacodynamics of oxazaphosphorines. A better understanding of the factors that affect the metabolism and transport of oxazaphosphorines is important for their optional use in cancer chemotherapy.

Insights into oxazaphosphorine resistance and possible approaches to its circumvention

The oxazaphosphorines cyclophosphamide, ifosfamide and trofosfamide remain a clinically useful class of anticancer drugs with substantial antitumour activity against a variety of solid tumors and hematological malignancies. A major limitation to their use is tumour resistance, which is due to multiple mechanisms that include increased DNA repair, increased cellular thiol levels, glutathione S-transferase and aldehyde dehydrogenase activities, and altered cell-death response to DNA damage. These mechanisms have been recently re-examined with the aid of sensitive analytical techniques, high-throughput proteomic and genomic approaches, and powerful pharmacogenetic tools. Oxazaphosphorine resistance, together with dose-limiting toxicity (mainly neutropenia and neurotoxicity), significantly hinders chemotherapy in patients, and hence, there is compelling need to find ways to overcome it. Four major approaches are currently being explored in preclinical models, some also in patients: combination with agents that modulate cellular response and disposition of oxazaphosphorines; antisense oligonucleotides directed against specific target genes; introduction of an activating gene (CYP3A4) into tumor tissue; and modification of dosing regimens. Of these approaches, antisense oligonucleotides and gene therapy are perhaps more speculative, requiring detailed safety and efficacy studies in preclinical models and in patients. A fifth approach is the design of novel oxazaphosphorines that have favourable pharmacokinetic and pharmacodynamic properties and are less vulnerable to resistance. Oxazaphosphorines not requiring hepatic CYP-mediated activation (for example, NSC 613060 and mafosfamide) or having additional targets (for example, glufosfamide that also targets glucose transport) have been synthesized and are being evaluated for safety and efficacy. Characterization of the molecular targets associated with oxazaphosphorine resistance may lead to a deeper understanding of the factors critical to the optimal use of these agents in chemotherapy and may allow the development of strategies to overcome resistance.

Glufosfamide

Glufosfamide [D 19575, beta-D-Glc-IPM] is a next-generation glucose conjugate of ifosfamide that is under development with Threshold Pharmaceuticals for the treatment of cancer. It is an alkylating agent in which isophosphoramide mustard, the alkylating metabolite of ifosfamide, is glycosidically linked to beta-D-glucose. Cellular uptake of glufosfamide is mediated by a sodium-dependent transmembrane transporter protein of glucose and possibly also by other transporter proteins. Threshold is using its Metabolic Targeting technology to exploit unique aspects of tumour metabolism, particularly the elevated glucose utilisation of tumour cells to selectively target glufosfamide to the tumour site. Glufosfamide was originally developed from a research collaboration between Asta Medica (Degussa) and the Cancer Research Centre (DKFZ) in Heidelberg, Germany. In October 2001, Baxter International acquired the oncology division of ASTA Medica, and renamed it Baxter Oncology GmbH. According to its 2002 Annual Report, Baxter announced that it was terminating development of glufosfamide. Subsequently, Baxter and Threshold Pharmaceuticals entered into an exclusive licensing and development agreement in August 2003. Threshold has responsibility for the development and commercialisation of glufosfamide, primarily for use as an antitumour agent. In addition, Baxter manufactures glufosfamide on Threshold's behalf. Threshold received fast-track status for glufosfamide from the US FDA in the treatment of metastatic pancreatic cancer refractory to gemcitabine in November 2004. In December 2004, Threshold initiated a phase I/II trial (TH-CR-301 Study) investigating glufosfamide in combination with gemcitabine as a first-line treatment of pancreatic cancer or advanced solid tumours. The phase I portion of the study may enroll up to 15 patients. The maximum tolerable dose combination determined will then be used in the phase 2 portion of the study. Up to 42 patients with advanced pancreatic cancer will be enrolled at various sites in the US, Latin America and Brazil.Previously, glufosfamide had been in phase II trials among patients with pancreatic carcinoma in Germany with Baxter Oncology and with the EORTC in the UK as well as Greece. However, development has been discontinued.

DNA intrastrand cross-link at the 5'-GA-3' sequence formed by busulfan and its role in the cytotoxic effect

Busulfan (1,4-butanediol dimethanesulfonate) has been used widely for the treatment of patients with chronic myelogenous leukemia. Busulfan is bifunctional and thus may effectively induce DNA damage, which may play an important role in the cytotoxicity. In this study, we compared the cytotoxicity of bifunctional busulfan with that of monofunctional ethyl methanesulfonate (EMS) in human promyelocytic leukemia HL-60 cells. Busulfan showed a significant inhibitory effect on cell growth, whereas the cells grew in the presence of EMS. To clarify the mechanism of cytotoxicity of busulfan, we investigated DNA damage induced by busulfan using 32P-5'-end-labeled DNA fragments obtained from the human p16 tumor suppressor gene. Busulfan induced DNA damage dose-dependently, whereas EMS caused little DNA damage. DNA-sequencing experiments using piperidine and 3-methyladenine DNA glycosylase indicated that busulfan caused double-base lesions mainly at 5'-GA-3' and, to a lesser extent, at 5'-GG-3' sequences. Time of flight mass spectrometry confirmed that busulfan forms an intrastrand cross-link at the 5'-GA-3' sequence, in addition to mono-alkylation. The mechanism and the role of cross-linking at the 5'-GA-3' sequence are discussed in relation to the cytotoxicity induced by busulfan.

The role of new agents in the treatment of non-small cell lung cancer

Lung cancer is one of the most frequent causes of cancer deaths worldwide. Non-small cell lung cancer (NSCLC) accounts for approximately 80% of cases and no curative treatment is available for the advanced stages of disease (stages III and IV), which comprise the majority of cases. Current treatment regimens with standard chemotherapy offer only a limited survival benefit, and, therefore, the development of new therapeutic strategies is needed. Novel chemotherapeutic drugs such as the epothilones, MEN 10755 and S-1 are being studied in patients with advanced stages of disease. Furthermore, a large number of therapies targeted against critical biological abnormalities in NSCLC are being investigated in clinical trials. The latter approach includes inhibition of growth factors, interference with abnormal signal transduction, inhibition of angiogenesis and gene replacement therapy. Promising results have thus far been obtained with some of these therapies. This review describes the role of new therapeutic agents in the treatment of NSCLC.

Induction of DNA breaks and apoptosis in crosslink-hypersensitive V79 cells by the cytostatic drug beta-D-glucosyl-ifosfamide mustard

To study molecular aspects of cytotoxicity of the anticancer drug beta-D-glucose-ifosfamide mustard we investigated the potential of the agent to induce apoptosis and DNA breakage. Since beta-D-glucose-ifosfamide mustard generates DNA interstrand crosslinks, we used as an in vitro model system a pair of isogenic Chinese hamster V79 cells differing in their sensitivity to crosslinking agents. CL-V5B cells are dramatically more sensitive (30-fold based on D(10) values) to the cytotoxic effects of beta-D-glucose-ifosfamide mustard as compared to parental V79B cells. After 48 h of pulse-treatment with the agent, sensitive cells but not the resistant parental line undergo apoptosis and necrosis, with apoptosis being the predominant form of cell death (70 and 20% of apoptosis and necrosis, respectively). Apoptosis increased as a function of dose and was accompanied by induction of DNA double-strand breaks in the hypersensitive cells. Furthermore, a strong decline in the level of Bcl-2 protein and activation of caspases-3, -8 and -9 were observed. The resistant parental cells were refractory to all these parameters. Bcl-2 decline in the sensitive cells preceded apoptosis, and transfection-mediated overexpression of Bcl-2 protected at least in part from apoptosis. From the data we hypothesize that non-repaired crosslinks induced by beta-D-glucose-ifosfamide mustard are transformed into double-strand breaks which trigger apoptosis via a Bcl-2 dependent pathway.

Clinical pharmacokinetics and pharmacodynamics of ifosfamide and its metabolites

This review discusses several issues in the clinical pharmacology of the antitumour agent ifosfamide and its metabolites. Ifosfamide is effective in a large number of malignant diseases. Its use, however, can be accompanied by haematological toxicity, neurotoxicity and nephrotoxicity. Since its development in the middle of the 1960s, most of the extensive metabolism of ifosfamide has been elucidated. Identification of specific isoenzymes responsible for ifosfamide metabolism may lead to an improved efficacy/toxicity ratio by modulation of the metabolic pathways. Whether ifosfamide is specifically transported by erythrocytes and which activated ifosfamide metabolites play a key role in this transport is currently being debated. In most clinical pharmacokinetic studies, the phenomenon of autoinduction has been observed, but the mechanism is not completely understood. Assessment of the pharmacokinetics of ifosfamide and metabolites has long been impaired by the lack of reliable bioanalytical assays. The recent development of improved bioanalytical assays has changed this dramatically, allowing extensive pharmacokinetic assessment, identifying key issues such as population differences in pharmacokinetic parameters, differences in elimination dependent upon route and schedule of administration, implications of the chirality of the drug and interpatient pharmacokinetic variability. The mechanisms of action of cytotoxicity, neurotoxicity, urotoxicity and nephrotoxicity have been pivotal issues in the assessment of the pharmacodynamics of ifosfamide. Correlations between the new insights into ifosfamide metabolism, pharmacokinetics and pharmacodynamics will rationalise the further development of therapeutic drug monitoring and dose individualisation of ifosfamide treatment.

The clinical pharmacology of alkylating agents in high-dose chemotherapy

Alkylating agents are widely used in high-dose chemotherapy regimens in combination with hematological support. Knowledge about the pharmacokinetics and pharmacodynamics of these agents administered in high doses is critical for the safe and efficient use of these regimens. The aim of this review is to summarize the clinical pharmacology of the alkylating agents (including the platinum compounds) in high-dose chemotherapy. Differences between conventional and high doses will be discussed.