The history of the oxazaphosphorine cytostatics

DNA Adducts in Cancer Chemotherapy

DNA adducting drugs, including alkylating agents and platinum-containing drugs, are prominent in cancer chemotherapy. Their mechanisms of action involve direct interaction with DNA, resulting in the formation of DNA addition products known as DNA adducts. While these adducts are well-accepted to induce cancer cell death, understanding of their specific chemotypes and their role in drug therapy response remain limited. This perspective aims to address this gap by investigating the metabolic activation and chemical characterization of DNA adducts formed by the U.S. FDA-approved drugs. Moreover, clinical studies on DNA adducts as potential biomarkers for predicting patient responses to drug efficacy are examined. The overarching goal is to engage the interest of medicinal chemists and stimulate further research into the use of DNA adducts as biomarkers for guiding personalized cancer treatment.

Association between CYP2B6 genetic variability and cyclophosphamide therapy in pediatric patients with neuroblastoma

Cyclophosphamide, an oxazaphosphorine prodrug is frequently used in treatment of neuroblastoma, which is one of the most prevalent solid organ malignancies in infants and young children. Cytochrome P450 2B6 (CYP2B6) is the major catalyst and CYP2C19 is the minor enzyme in bioactivation and inactivation pathways of cyclophosphamide. CYP-mediated metabolism may contribute to the variable pharmacokinetics of cyclophosphamide and its toxic byproducts leading to insufficient response to the therapy and development of clinically significant side effects. The aim of the study was to reveal the contribution of pharmacogenetic variability in CYP2B6 and CYP2C19 to the treatment efficacy and cyclophosphamide-induced side effects in pediatric neuroblastoma patients under cyclophosphamide therapy (N = 50). Cyclophosphamide-induced hematologic toxicities were pivotal in all patients, whereas only moderate hepatorenal toxicity was developed. The patients' CYP2B6 metabolizer phenotypes were associated with the occurrence of lymphopenia, thrombocytopenia, and monocytopenia as well as of liver injury, but not with kidney or urinary bladder (hemorrhagic cystitis) toxicities. Furthermore, the patients' age (< 1.5 years, P = 0.03) and female gender (P ≤ 0.02), but not CYP2B6 or CYP2C19 metabolizer phenotypes appeared as significant prognostic factors in treatment outcomes. Our results may contribute to a better understanding of the impact of CYP2B6 variability on cyclophosphamide-induced side effects.

Sulfated glycosaminoglycans in bladder tissue and urine of rats after acute exposure to paraoxon and cyclophosphamide

Glycosaminoglycans (GAGs) in the urine of Wistar rats, and on the surface of the epithelium and lamina propria of the bladder, were quantitatively assessed before and after acute intoxication with paraoxon or cyclophosphamide. Paraoxon was administered subcutaneously (s.c.) twice with an interval of 1h to a final dose of 275mg/kg; cyclophosphamide was administered intraperitoneally (i.p.) with a single dose of 100mg/kg or to a final dose of 240mg/kg (three times per 80mg/kg every 12h). GAGs on the surface of the epithelium and lamina propria of the urinary bladder of rats were quantitatively determined by Alcian blue dye staining. GAGs in the urine were determined spectrophotometrically with 1-9-dimethyl methylene blue. By 48-96h after intoxication with either paraoxon or cyclophosphamide, statistically significant increases in the concentration of GAGs were obtained both for the tissues of the bladder and the urine of rats. Cyclophosphamide, in contrast to paraoxon, caused the development of hemorrhagic cystitis in the animals. The synthesis of GAGs is considered to be compensatory response to the toxic xenobiotics.

Antineoplastic drugs and their analysis: a state of the art review

We provide an overview of the analytical methods available for the quantification of antineoplastic drugs in pharmaceutical formulations, biological and environmental samples.

Murine model of chemotherapy-induced extraintestinal pathogenic Escherichia coli translocation

Escherichia coli is a major cause of life-threatening infections in patients with neutropenia, particularly those receiving chemotherapy for the treatment of cancer. In most cases, these infections originate from opportunistic strains living within the patient's gastrointestinal tract which then translocate to major organ systems. There are no animal models that faithfully recapitulate these infections, and, as such, the host or bacterial factors that govern this process remain unidentified. We present here a novel model of chemotherapy-induced bacterial translocation of E. coli. Oral gavage of BALB/c mice with a clinical isolate of extraintestinal pathogenic E. coli (ExPEC) leads to stable and long-term colonization of the murine intestine. Following the induction of neutropenia with the chemotherapeutic drug cyclophosphamide, ExPEC translocates from the intestine to the lungs, liver, spleen, and kidneys with concomitant morbidity in infected animals. Translocation can also occur in mice bearing mammary tumors, even in the absence of chemotherapy. Translocation of ExPEC is also associated with an increase of the diversity of bacterial DNA detected in the blood. This is the first report of a chemotherapy-based animal model of ExPEC translocation in cancerous mice, a system that can be readily used to identify important virulence factors for this process.

Targeted prodrug approaches for hormone refractory prostate cancer

Due to the propensity of relapse and resistance with prolonged androgen deprivation therapy (ADT), there is a growing interest in developing non-hormonal therapeutic approaches as alternative treatment modalities for hormone refractory prostate cancer (HRPC). Although the standard treatment for HRPC consists of a combination of ADT with taxanes and anthracyclines, the clinical use of chemotherapeutics is limited by systemic toxicity stemming from nondiscriminatory drug exposure to normal tissues. In order to improve the tumor selectivity of chemotherapeutics, various targeted prodrug approaches have been explored. Antibody-directed enzyme prodrug therapy (ADEPT) and gene-directed enzyme prodrug therapy (GDEPT) strategies leverage tumor-specific antigens and transcription factors for the specific delivery of cytotoxic anticancer agents using various prodrug-activating enzymes. In prostate cancer, overexpression of tumor-specific proteases such as prostate-specific antigen (PSA) and prostate-specific membrane antigen (PSMA) is being exploited for selective activation of anticancer prodrugs designed to be activated through proteolysis by these prostate cancer-specific enzymes. PSMA- and PSA-activated prodrugs typically comprise an engineered high-specificity protease peptide substrate coupled to a potent cytotoxic agent via a linker for rapid release of cytotoxic species in the vicinity of prostate cancer cells following proteolytic cleavage. Over the past two decades, various such prodrugs have been developed and they were effective at inhibiting prostate tumor growth in rodent models; several of these prodrug approaches have been advanced to clinical trials and may be developed into effective therapies for HRPC.

The influence of pemirolast on autonomic imbalance in rat cystitis model

Cyclophosphamide (CP) treatment is associated with the risk of haemorrhagic cystitis (HC). Moreover, CP-induced HC is complicated by autonomic nervous system (ANS) dysfunction. Pemirolast is thought to be a mast cell stabiliser that inhibits the release of many inflammatory mediators and sensory neuropeptides, and thus, it may be considered a potential chemoprotective HC agent. The aim of the study was to indirectly estimate the effect of pemirolast in experimental HC by measuring ANS activity with the heart rate variability (HRV) method. In CP-treated rats, we found a decreasing trend of overall autonomic activity, together with an imbalance between the main components, and a dominant very low frequency (VLF) power component. Pemirolast treatment did not improve the total HRV power value or the main non-normalized HRV components. Moreover, CP-HC animals treated with pemirolast displayed a different disproportion of normalized spectral components as compared to both control and CP-HC animals without pemirolast treatment, with the balance between normalized low frequency (nLF) and normalized high frequency (nHF) shifted towards nLF. This finding, together with a relatively high VLF tension, indicates that the pemirolast treatment resulted in high sympathetic activity that may contribute to HC exacerbation; thus, this agent seems to be ineffective in CP-induced HC.

Analysis of a novel protocol of pulsed intravenous cyclophosphamide for recalcitrant or severe ocular inflammatory disease

PURPOSE

To analyze the success rate of pulsed intravenous (IV) cyclophosphamide (CyP) for noninfectious ocular inflammatory disease and to identify risk factors for failure of therapy.

DESIGN

Retrospective, interventional, noncomparative cohort study.

PARTICIPANTS

One hundred ten eyes of 65 patients.

METHODS

Through a computer search of the Massachusetts Eye Research and Surgery Institution's database, we identified patients who were treated with IV CyP between May 2005 and April 2012. We obtained demographic and clinical information through review of the electronic health record of each patient.

MAIN OUTCOMES MEASURES

Clinical response, corticosteroid-sparing effect, recurrence rate, calculated "risk factors" for failure, visual acuity, and adverse reactions.

RESULTS

Pulsed IV CyP achieved complete remission of inflammation (for ≥ 2 visits) in 54 patients (84.4%). Sustained remission of inflammation occurred in 70% of patients within 3 months, 86.6% of patients within 6 months, and 91.7% within 9 months. The mean time to achieving quiescence was 3.5 months. The success rate in reducing corticosteroid to prednisone ≤ 10 mg/d within 6 months, while maintaining control of ocular inflammation, was 89.7% (95% confidence interval [CI], 81.1-93.5%). The mean duration of clinical remission for those patients who had a positive response to CyP was 32.67 months (95% CI, 25.91-39.43). Relapse of vasculitis was observed in 1 patient (1.5%) after completing the course of therapy. Early initiation of therapy during the course of the disease was correlated with a lesser rate of recurrence (P = 0.028). The most common adverse effects were nausea (29%) and transient lymphopenia (26%). The mean best-corrected visual acuity (BCVA) improved from 0.59 ± 0.66 at baseline to 0.30 ± 0.54 at 6 months of follow-up (P<0.001). The mean follow-up period was 31.61 ± 20.47 months.

CONCLUSIONS

Pulsed IV CyP employing our protocol results in an extremely high rate of sustained complete remission in patients with recalcitrant and fulminant, vision-threatening ocular inflammatory disorders, with an excellent safety profile in the hands of physicians trained and skilled in the art of this therapy. It also allows tapering and discontinuing corticosteroids in most patients. Early initiation of therapy may decrease the risk of relapses.

FINANCIAL DISCLOSURE(S)

The authors have no proprietary or commercial interest in any materials discussed in this article.

Expression of myoferlin in human and murine carcinoma tumors: role in membrane repair, cell proliferation, and tumorigenesis

Cancer cells are often characterized by high proliferation rates, a consequence of increased mitotic signaling coupled with unchecked cellular growth. We recently demonstrated that vascular endothelial cells unexpectedly express ferlins, a family of muscle-specific proteins capable of regulating the fusion of lipid patches to the plasma membrane, and that these highly regulated membrane fusion events are essential to endothelial cell proliferation and homeostasis. Here, we show that human and mouse breast cancer cell lines also express myoferlin at various levels, and that the processes of transformation, epithelial-mesenchymal transition, and metastasis do not appear to have any effect on myoferlin expression in vitro. In vivo, we observed that solid mouse and human carcinoma tissues also express high levels of myoferlin protein. Loss-of-function studies performed in mice revealed that myoferlin gene knockdown can attenuate cancer cell proliferation in vitro and decrease tumor burden, and that accelerated tumor cell growth appears to rely on intact myoferlin-dependent membrane repair and signaling under exponential growth conditions. To our knowledge, these data provide the first evidence of myoferlin expression in solid human and mouse tumors. We have thus identified a novel membrane repair process that likely helps sustain the high growth rates characteristic of tumors, and we suggest that interfering with normal myoferlin expression and/or membrane repair and remodeling may provide therapeutically relevant antiproliferative effects.

Cytochrome P450-activated prodrugs

A prodrug is a compound that has negligible, or lower, activity against a specified pharmacological target than one of its major metabolites. Prodrugs can be used to improve drug delivery or pharmacokinetics, to decrease toxicity, or to target the drug to specific cells or tissues. Ester and phosphate hydrolysis are widely used in prodrug design because of their simplicity, but such approaches are relatively ineffective for targeting drugs to specific sites. The activation of prodrugs by the cytochrome P450 system provides a highly versatile approach to prodrug design that is particularly adaptable for targeting drug activation to the liver, to tumors or to hypoxic tissues.

Use of whole sheep red blood cells in ELISA to assess immunosuppression in vivo

An enzyme-linked immunosorbent assay (ELISA) using whole sheep red blood cells (SRBC) has been reported as one of the methods for detecting a T-lymphocyte-dependent antibody response. However, it has not been widely used because of SRBC problems such as the weak attachment to ELISA plates, specificity and short-term stability. The objectives of this study were to address these issues and to validate the SRBC-specific antibody response assay. Male Sprague-Dawley rats were bled after 6 days of SRBC immunization. In our new procedure, glutaraldehyde was added before discarding the supernatant of inoculated SRBC suspension to attach SRBC firmly to the plate, while in the original method it was added after discarding. As a result, the attached SRBC was maintained throughout the ELISA procedures. No interference was observed in the titration curve of IgM and IgG antibodies in rats and IgM-antibody in mice when control sera were analyzed to evaluate specificity of this method. The short-term stability of SRBC was overcome by using the different lots of SRBC. They provided antibody titers, which were consistent with those measured using the same lot for immunization. In addition, cyclophosphamide, cyclosporine, prednisolone and methotrexate, well-known immunosuppressive agents, were tested to confirm the applicability of the improved ELISA method to detect the T-lymphocyte-dependent antibody response. All four compounds inhibited the IgM antibody responses dose-dependently. These results demonstrate that the improved whole SRBC-ELISA method provides reproducible and reliable results in the T-lymphocyte-dependent antibody response assay.

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.

Cyclophosphamide inhibits the generation and function of CD8(+) regulatory T cells

CD8(+) regulatory T cells (Treg) and CD4(+)CD25(+) Treg infiltrate human cancers, thus favoring tumor immune escape. Therefore, in the setting of antitumor therapeutic protocols, it is important to associate antitumor treatment with agents that are able to inhibit Treg function. Cyclophosphamide (CY) has been demonstrated to be effective in counteracting CD4(+)CD25(+) Treg activity. Hence, we tested its inhibitory efficacy on human CD8(+) Treg. Because CY is a prodrug, 4-hydroperoxycyclophosphamide (4-HC), a derivative of CY that in aqueous solution is converted to 4-hydroxycyclophosphamide, an active metabolite of CY, was used. 4-HC significantly inhibited CD8(+) Treg generation and function but only at the higher tested concentration (0.5 μg/mL), that is, in the therapeutic range of the drug. The lower 4-HC concentration tested (0.1 μg/mL) was almost ineffective. 4-HC inhibitory effects were related to apoptosis/necrosis induction. When CD8(+)CD28(+) non-Treg were analyzed for comparative purposes, significantly lower cytotoxic rates among these cells were observed than among CD8(+) Treg, which were differentiated because they did not express the CD28 molecule. These data demonstrate that CD8(+) Treg are inhibited through cytotoxic phenomena by CY, thus supporting the use of this drug at adequate concentrations and schedules of administration as a Treg inhibitor in combinatorial chemo- or immunotherapeutic anticancer protocols.

Versican G3 domain modulates breast cancer cell apoptosis: a mechanism for breast cancer cell response to chemotherapy and EGFR therapy

Overexpression of EGFR and versican has been reported in association with breast cancers. Considered oncogenic, these molecules may be attractive therapeutic targets. Possessing anti-apoptotic and drug resistant properties, overexpression of these molecules is accompanied by selective sensitization to the process of apoptosis. In this study, we exogenously expressed a versican G3 construct in breast cancer cell lines and analyzed the effects of G3 on cell viability in fetal bovine serum free conditioned media and evaluated the effects of apoptotic agent C2-ceramide, and chemotherapeutic agents including Docetaxel, Doxorubicin, and Epirubicin. Versican G3 domain enhanced tumor cell resistance to apoptosis when cultured in serum free medium, Doxorubicin, or Epirubicin by up-regulating pERK and GSK-3β (S9P). However, it could be prevented by selective EGFR inhibitor AG 1478 and selective MEK inhibitor PD 98059. Both AG 1478 and PD 98059 enhanced expression of pSAPK/JNK, while selective JNK inhibitor SP 600125 enhanced expression of GSK-3β (S9P). Versican G3 promoted cell apoptosis induced by C2-ceramide or Docetaxel by enhancing expression of pSAPK/JNK and decreasing expression of GSK-3β (S9P), an observation blocked by AG 1478 or SP 6000125. Inhibition of endogenous versican expression by siRNA or reduction of versican G3's expression by linking G3 with 3'UTR prevented G3 modulated cell apoptosis. The dual roles of G3 in modulating breast cancer cell resistance to chemotherapeutic agents may in part explain a potential mechanism for breast cancer cell resistance to chemotherapy and EGFR therapy. The apoptotic effects of chemotherapeutics depend upon the activation and balance of down stream signals in the EGFR pathway. GSK-3β (S9P) appears to function as a key checkpoint in this balance of apoptosis and anti-apoptosis. Investigation and potential consideration of targeting GSK-3β (S9P) merits further study.

Greater than the sum of their parts: combination strategies for immune regeneration following allogeneic hematopoietic stem cell transplantation

Cytoreductive conditioning regimes designed to allow for successful allogeneic hematopoietic stem cell transplantation (allo-HSCT) paradoxically are also detrimental to recovery of the immune system in general but lymphopoiesis in particular. Post-transplant immune depletion is particularly striking within the T cell compartment which is exquisitely sensitive to negative regulation, evidenced by the profound decline in thymic function with age. As a consequence, regeneration of the immune system remains a significant unmet clinical need. Over the past decade studies have revealed several promising therapeutic strategies to address ineffective lymphopoiesis and post-transplant immune deficiency. These include the use of cytokines such as IL-7, IL-12 and IL-15; growth factors and hormones like keratinocyte growth factor (KGF), insulin-like growth factor (IGF)-1 and growth hormone (GH); adoptive transfer of ex vivo-generated precursor T cells (pre-T) and sex steroid ablation (SSA). Moreover, recently several novel approaches have been proposed to generate whole thymii ex vivo using stem cell technologies and bioscaffolds. Increasingly, however, when transferred to the clinic, these strategies alone are not sufficient to restore thymopoiesis in all patients leading to the potential of combination strategies as a way to reign in non-responders. Synergistic enhancement in combination may be due to differential targets may therefore be effective in improving clinical outcomes in the transplant settings as well as in other lymphopenic states induced by high dose chemotherapy/radiation therapy or HIV, and may also be useful in improving responses to vaccination and augmenting anti-tumor immunotherapy.

Immunomodulatory effects of cyclophosphamide and implementations for vaccine design

Drug repositioning refers to the utilization of a known compound in a novel indication underscoring a new mode of action that predicts innovative therapeutic options. Since 1959, alkylating agents, such as the lead compound cyclophosphamide (CTX), have always been conceived, at high dosages, as potent cytotoxic and lymphoablative drugs, indispensable for dose intensity and immunosuppressive regimen in the oncological and internal medicine armamentarium. However, more recent work highlighted the immunostimulatory and/or antiangiogenic effects of low dosing CTX (also called "metronomic CTX") opening up novel indications in the field of cancer immunotherapy. CTX markedly influences dendritic cell homeostasis and promotes IFN type I secretion, contributing to the induction of antitumor cytotoxic T lymphocytes and/or the proliferation of adoptively transferred T cells, to the polarization of CD4(+) T cells into TH1 and/or TH17 lymphocytes eventually affecting the Treg/Teffector ratio in favor of tumor regression. Moreover, CTX has intrinsic "pro-immunogenic" activities on tumor cells, inducing the hallmarks of immunogenic cell death on a variety of tumor types. Fifty years after its Food and Drug Administration approval, CTX remains a safe and affordable compound endowed with multifaceted properties and plethora of clinical indications. Here we review its immunomodulatory effects and advocate why low dosing CTX could be successfully combined to new-generation cancer vaccines.

Sex steroid ablation enhances hematopoietic recovery following cytotoxic antineoplastic therapy in aged mice

Cytotoxic antineoplastic therapy is widely used in the clinic as a treatment for malignant diseases. The treatment itself, however, leads to long-term depletion of the adaptive immune system, which is more pronounced in older patients, predominantly due to thymic atrophy. We and others have previously shown that withdrawal of sex steroids is able to regenerate the aged thymus and enhance recovery from autologous and allogeneic hematopoietic stem cell transplant. In this study we have examined the effects of sex steroid ablation (SSA) on the recovery of lymphopoiesis in the bone marrow (BM) and thymus following treatment with the chemotherapeutic agent cyclophosphamide (Cy) in middle-aged and old mice. Furthermore, we have also examined the impact of this regeneration on peripheral immunity. SSA enhanced the recovery of BM resident hematopoietic stem cells and lymphoid progenitors and promoted lymphopoiesis. Interestingly, Cy alone caused a profound increase in the recently described common lymphoid progenitor 2 (CLP-2) population in the BM. In the thymus, SSA caused a profound increase in cellularity as well as all intrathymic T-lineage progenitors including early T-lineage progenitors (ETPs) and non-canonical T cell progenitors such as the CLP-2. We also found that these transferred into numerical increases in the periphery with enhanced B and T cell numbers. Furthermore, these lymphocytes were found to have an enhanced functional capacity with no perturbation of the TCR repertoire. Taken together, these results provide the basis for the use of SSA in the clinic to enhance treatment outcomes from cytotoxic antineoplastic therapy.

Recent prognostic factors in diffuse large B-cell lymphoma indicate NF-kappaB pathway as a target for new therapeutic strategies

The diffuse large B-cell lymphoma (DLBCL) is the most common type of lymphoid cancer. The classical chemotherapy regimen given to these patients was the CHOP (Cyclophosphamide, Hydroxydaunorubicin or Adriamycin, Oncovin or Vincristine, Prednisone or Prednisolone), but recently rituximab with CHOP (R-CHOP) increased the number of cases responding to first line therapy. DLBCL classification identified three principle subgroups. The first one, named germinal centre B cell-like (GCB), responds to both CHOP and R-CHOP treatment and it is mainly characterised by the expression of markers like Bcl-6 and CD10. The second, the activated B-cell like (ABC), has a worse prognosis in comparison with GCB, and is mainly characterised by the expression of IRF-4, PRDM1 and NF-kappaB. It is interesting to notice that IRF-4 and PRDM1 are under the transcriptional control of NF-kappaB, whose high activation level is associated with a worse prognosis. The third one, mediastinal large B-cell lymphoma (PMBCL) is an uncommon subtype characteristically found in young females. Gene expression profiling suggests that this disease resembles Hodgkin lymphoma more than other types of DLBCL. The impact of rituximab on the outcome of patients with PMBCL has still not been fully assessed. It was seen that rituximab inhibits NF-kappaB pathway in vitro. However, the clinical significance of this finding is still unknown, because both ABC and GCB DLBCL show a significant improvement of overall survival after R-CHOP treatment. In this review, the NF-kappaB pathway is suggested as a target for new chemotherapy strategies based on the association of CHOP with molecules more effective than rituximab in this pathway inhibition.

Strategies for reconstituting and boosting T cell-based immunity following haematopoietic stem cell transplantation: pre-clinical and clinical approaches

Poor immune recovery is characteristic of bone marrow transplantation and leads to high levels of morbidity and mortality. The primary underlying cause is a compromised thymic function, resulting from age-induced atrophy and further compounded by the damaging effects of cytoablative conditioning regimes on thymic epithelial cells (TEC). Several strategies have been proposed to enhance T cell reconstitution. Some, such as the use of single biological agents, are currently being tested in clinical trials. However, a more rational approach to immune restoration will be to leverage the evolving repertoire of new technologies. Specifically, the combined targeting of TEC, thymocytes and peripheral T cells, together with the bone marrow niches, promises a more strategic clinical therapeutic platform.

Cyclophosphamide for the treatment of systemic lupus erythematosus

Aggressive immunosuppressive therapy with cyclophosphamide has improved the outcome of major organ disease in lupus patients. Controlled trials have shown that pulse cyclophosphamide is the treatment of choice for patients with moderate to severe proliferative nephritis. Long-term follow-up of patients participating in these controlled trials suggests that combining pulse cyclophoshamide with pulse methylprednisolone increases efficacy but not toxicity. Retrospective case series have also shown that pulse cyclophosphamide therapy may be effective for the management of severe or refractory to standard therapy neuropsychiatric, pulmonary, cardiovascular and hematologic disease. Pulse cyclophosphamide is associated with an increased risk for herpes zoster infections in the short term and with sustained amenorrhea in the long-term. Recent studies have also drawn attention to the lack of response (or incomplete response) and flare of lupus after an initial response. In an effort to circumvent these limitations, current investigations explore the therapeutic potential of high-dose, immunoablative cyclophosphamide therapy or low-dose cyclophosphamide in combination with nucleoside analogs or biologic response modifiers.

Modulation of P450-dependent ifosfamide pharmacokinetics: a better understanding of drug activation in vivo

The anti-cancer prodrug ifosfamide (IF) is metabolized by liver P450 enzymes by two alternative pathways. IF is activated to 4-hydroxy IF (4-OH-IF), which ultimately yields the alkylating mustard isophosphoramide, whereas IF N-dechlororethylation inactivates the drug and produces the neurotoxic metabolite chloroacetaldehyde (CA). Both reactions are catalysed by multiple liver P450 enzymes in vitro in isolated rat liver microsomes. The present pharmacokinetic study investigates the potential for modulation of these alternative pathways of IF metabolism in vivo using the adult male Fischer 344 rat model. Rats were treated with IF alone or in conjunction with various P450 inducers and inhibitors in an effort to improve the balance between drug activation and drug inactivation. Plasma concentrations, areas under the curve (AUC) and half-lives were calculated for 4-OH-IF and CA, allowing estimations of the extent of IF activation and deactivation/toxification. Induction of liver P450 2B enzymes by 4-day high-dose phenobarbital (PB) pretreatment significantly decreased the fraction of IF undergoing 4-hydroxylation (AUC(4-OH-IF)/AUC(4-OH-IF)+AUC(CA)), from 37% to 22% of total metabolism (P < 0.05), consistent with in vitro findings that the PB-inducible P450 enzyme 2B1 plays a major role in IF N-dechloroethylation. Pretreatment with the P450 3A inducer dexamethasone proportionally decreased the AUC for both IF metabolites, without any net impact on the fraction of IF undergoing metabolic activation. By contrast, the P450 2B1 inhibitor metyrapone preferentially increased the AUC for the 4-hydroxylation pathway in 3-day low-dose PB-induced rats, thereby increasing the total fraction of IF metabolized via the activation pathway from 36% to 54% (P < 0.05), whereas the P450 inhibitors orphenadrine and troleandomycin had no significant affect on AUC values. These findings demonstrate specific roles for P450 2B and 3A enzymes in catalysing these pathways of IF metabolism in vivo, and demonstrate the potential for modulation of IF's alternative metabolic pathways in a therapeutically useful manner. These studies also highlight several clinically relevant drug interactions that may occur during concomitant administration of IF with drugs and other compounds that modulate hepatic P450 enzyme levels.