Ifosfamide/carboplatin/etoposide (ICE) as front-line, topotecan/cyclophosphamide as second-line and oral temozolomide as third-line treatment for advanced neuroblastoma over one year of age

Venetoclax-based Rational Combinations are Effective in Models of MYCN-amplified Neuroblastoma

Venetoclax is a small molecule inhibitor of the prosurvival protein BCL-2 that has gained market approval in BCL-2-dependent hematologic cancers including chronic lymphocytic leukemia and acute myeloid leukemia. Neuroblastoma is a heterogenous pediatric cancer with a 5-year survival rate of less than 50% for high-risk patients, which includes nearly all cases with amplified MYCN We previously demonstrated that venetoclax is active in MYCN-amplified neuroblastoma but has limited single-agent activity in most models, presumably the result of other pro-survival BCL-2 family protein expression or insufficient prodeath protein mobilization. As the relative tolerability of venetoclax makes it amenable to combining with other therapies, we evaluated the sensitivity of MYCN-amplified neuroblastoma models to rational combinations of venetoclax with agents that have both mechanistic complementarity and active clinical programs. First, the MDM2 inhibitor NVP-CGM097 increases the prodeath BH3-only protein NOXA to sensitize p53-wild-type, MYCN-amplified neuroblastomas to venetoclax. Second, the MCL-1 inhibitor S63845 sensitizes MYCN-amplified neuroblastoma through neutralization of MCL-1, inducing synergistic cell killing when combined with venetoclax. Finally, the standard-of-care drug cocktail cyclophosphamide and topotecan reduces the apoptotic threshold of neuroblastoma, thus setting the stage for robust combination efficacy with venetoclax. In all cases, these rational combinations translated to in vivo tumor regressions in MYCN-amplified patient-derived xenograft models. Venetoclax is currently being evaluated in pediatric patients in the clinic, including neuroblastoma (NCT03236857). Although establishment of safety is still ongoing, the data disclosed herein indicate rational and clinically actionable combination strategies that could potentiate the activity of venetoclax in patients with amplified MYCN with neuroblastoma.

Novel Therapies for Relapsed and Refractory Neuroblastoma

While recent increases in our understanding of the biology of neuroblastoma have allowed for more precise risk stratification and improved outcomes for many patients, children with high-risk neuroblastoma continue to suffer from frequent disease relapse, and despite recent advances in our understanding of neuroblastoma pathogenesis, the outcomes for children with relapsed neuroblastoma remain poor. These children with relapsed neuroblastoma, therefore, continue to need novel treatment strategies based on a better understanding of neuroblastoma biology to improve outcomes. The discovery of new tumor targets and the development of novel antibody- and cell-mediated immunotherapy agents have led to a large number of clinical trials for children with relapsed neuroblastoma, and additional clinical trials using molecular and genetic tumor profiling to target tumor-specific aberrations are ongoing. Combinations of these new therapeutic modalities with current treatment regimens will likely be needed to improve the outcomes of children with relapsed and refractory neuroblastoma.

Hydroxylation and N-dechloroethylation of Ifosfamide and deuterated Ifosfamide by the human cytochrome p450s and their commonly occurring polymorphisms

The hydroxylation and N-dechloroethylation of deuterated ifosfamide (d4IFO) and ifosfamide (IFO) by several human P450s have been determined and compared. d4IFO was synthesized with deuterium at the alpha and alpha' carbons to decrease the rate of N-dechloroethylation and thereby enhance hydroxylation of the drug at the 4' position. The purpose was to decrease the toxic and increase the efficacious metabolites of IFO. For all of the P450s tested, hydroxylation of d4IFO was improved and dechloroethylation was reduced as compared with nondeuterated IFO. Although the differences were not statistically significant, the trend favoring the 4'-hydroxylation pathway was noteworthy. CYP3A5 and CYP2C19 were the most efficient enzymes for catalyzing IFO hydroxylation. The importance of these enzymes in IFO metabolism has not been reported previously and warrants further investigation. The catalytic ability of the common polymorphisms of CYP2B6 and CYP2C9 for both reactions were tested with IFO and d4IFO. It was determined that the commonly expressed polymorphisms CYP2B6*4 and CYP2B6*6 had reduced catalytic ability for IFO compared with CYP2B6*1, whereas CYP2B6*7 and CYP2B6*9 had enhanced catalytic ability. As with the wild-type enzymes, d4IFO was more readily hydroxylated by the polymorphic variants than IFO, and d4IFO was not dechloroethylated by any of the polymorphic forms. We also assessed the use of specific inhibitors of P450 to favor hydroxylation in human liver microsomes. We were unable to separate the pathways with these experiments, suggesting that multiple P450s are responsible for catalyzing both metabolic pathways for IFO, which is not observed with the closely related drug cyclophosphamide.

Local control in metastatic neuroblastoma in children over 1 year of age

BACKGROUND

Local control is always considered in metastatic neuroblastoma (NBL). The aim of this study is to evaluate the impact of radical surgery on survival in children over 1 year of age.

METHODS

Fifty-eight patients older than 1 year of age with metastatic NBL were treated with conventional plus high-dose chemotherapy with or without addition of local radiotherapy (RT, 21Gy). Surgery was classified as radical surgery (complete resection and gross total resection) or non-radical surgery. The Kaplan-Meier method and the Cox proportional hazard model were used to calculate the probability of progression free and overall survival (PFS and OS) and for multivariate analysis.

RESULTS

The 5-year PFS and OS for patients with radical surgery were 26% (95% CI 14-40%) and 38% (95% CI 23-53%) respectively, while the PFS and OS for patients without radical surgery were 33% (95% CI 10-59%) and 31% (95% CI 10-55%) (respectively, P 0.85 and P 0.42). The 5-year PFS and OS for patients who received RT were 36% (95% CI 19-53%) and 46% (95% CI 26-64%) respectively, while the 5-year PFS and OS for patients who did not receive RT were 22% (95% CI 9-38%) and 27% (95% CI 13-42%) respectively (P 0.02 for PFS). Multivariate analysis confirmed the role of well-known prognostic factors, such as the presence of MYCN amplification, age and response before high-dose chemotherapy.

CONCLUSIONS

Our data suggest that the degree of resection does not influence survival in metastatic NBL patients treated with high-dose chemotherapy; local RT contributes to local disease control.

Efficacy and toxicity of second-course ophthalmic artery chemosurgery for retinoblastoma

OBJECTIVE

Assess the usefulness of second-course ophthalmic artery chemosurgery (OAC) for patients with intraocular retinoblastoma that recurred after prior OAC. This study evaluated the efficacy and toxicity of second-course OAC.

DESIGN

Single-arm retrospective study of 29 eyes of 30 patients treated with second-course OAC at Memorial Sloan Kettering Cancer Center between May 2006 and July 2013, with a median follow-up of 25.9 months.

PARTICIPANTS

Retinoblastoma patients who underwent a course of OAC, with a minimum of 2 months of progression-free follow-up at monthly examinations, but who subsequently received additional OAC for recurrent tumor.

METHODS

To determine efficacy, Kaplan-Meier survival estimates were generated and the Mantel-Cox test was used to compare curves. To determine toxicity, electroretinography (ERG) amplitudes were measured in response to 30-Hz photopic flicker stimulation before and after OAC treatment; systemic adverse events were graded according to the Common Terminology Criteria for Adverse Events version 4.0 (CTCAE 4.0).

MAIN OUTCOME MEASURES

For efficacy, ocular progression-free survival, ocular event-free survival (e.g., enucleation, external-beam radiation, or intravitreal melphalan), and ocular survival. For toxicity, peak-to-peak comparisons between ERG studies before and after OAC treatment and CTCAE 4.0-graded systemic adverse events.

RESULTS

Fifty percent of all recurrences were within 4.4 months and 90% were within 16 months of completion of the first course of OAC. The 2-year Kaplan-Meier ocular survival, event-free survival, and progression-free survival estimates after second-course OAC were 82.8% (95% confidence interval [CI], 60.1%-93.2%), 57.3% (95% CI, 36.1%-73.7%), and 26.5% (95% CI, 11.0%-45.0%), respectively. All eyes without vitreous seeding were progression free, whereas eyes with vitreous seeding were associated significantly with worse ocular survival after second-course OAC (P = 0.03). After second-course OAC, 90% of eyes had stable or improved ERG responses. Of all evaluable cases, there was no increased risk of systemic toxicity during the second course compared with the initial course of OAC.

CONCLUSIONS

Retinoblastoma eyes requiring second-course OAC after initial OAC treatment have good salvage rates, and the treatment has an acceptable ocular and systemic toxicity profile. However, these eyes often require additional (third- or fourth-course) OAC or other treatment methods because of progression of disease after second-line OAC, particularly if vitreous seeds are present at the time of initial OAC failure.

Pre-Clinical Evaluation of rHDL Encapsulated Retinoids for the Treatment of Neuroblastoma

Despite major advances in pediatric cancer research, there has been only modest progress in the survival of children with high risk neuroblastoma (NB) (HRNB). The long term survival rates of HRNB in the United States are still only 30-50%. Due to resistance that often develops during therapy, development of new effective strategies is essential to improve the survival and overcome the tendency of HRNB patients to relapse subsequent to initial treatment. Current chemotherapy regimens also have a serious limitation due to off target toxicity. In the present work, we evaluated the potential application of reconstituted high density lipoprotein (rHDL) containing fenretinide (FR) nanoparticles as a novel approach to current NB therapeutics. The characterization and stability studies of rHDL-FR nanoparticles showed small size (<40 nm) and high encapsulation efficiency. The cytotoxicity studies of free FR vs. rHDL/FR toward the NB cell lines SK-N-SH and SMS-KCNR showed 2.8- and 2-fold lower IC50 values for the rHDL encapsulated FR vs. free FR. More importantly, the IC50 value for retinal pigment epithelial cells (ARPE-19), a recipient of off target toxicity during FR therapy, was over 40 times higher for the rHDL/FR as compared to that of free FR. The overall improvement in in vitro selective therapeutic efficiency was thus about 100-fold upon encapsulation of the drug into the rHDL nanoparticles. These studies support the potential value of this novel drug delivery platform for treating pediatric cancers in general, and NB in particular.

New aspects of neuroblastoma treatment: ASPHO 2011 symposium review

Neuroblastoma is the most common extracranial solid tumor of childhood, and the outcomes for children with high-risk and relapsed disease remain poor. However, new international strategies for risk stratification and for treatment based on novel tumor targets and including immunotherapy are being employed in attempts to improve the outcomes of children with neuroblastoma. A new international neuroblastoma risk classification system has been developed which is being incorporated into cooperative group clinical trials in North America, Japan, and Europe, resulting in standardized approaches for the initial evaluation and treatment stratification of neuroblastoma patients. Furthermore, novel treatment regimens are being developed based on improved understanding of neuroblastoma biology and on the recruitment of the immune system to specifically target neuroblastoma tumors. These approaches will lead to new therapeutic strategies that likely will improve the outcomes for children with neuroblastoma worldwide.

Short topotecan-based induction regimen in newly diagnosed high-risk neuroblastoma

PURPOSE

Topotecan is an active drug in relapsed neuroblastoma. We investigated the efficacy and toxicity of a topotecan-based induction regimen in newly diagnosed neuroblastoma.

METHODS

Patients older than 1 year with either metastatic or localised stage 2-3 MYCN-amplified neuroblastoma received 2 courses of high-dose topotecan (HD-TPT) 6mg/m(2) and high-dose cyclophosphamide (HD-CPM) 140 mg/kg, followed by 2 courses of ifosfamide, carboplatin and etoposide (ICE) every 28 days. After surgery on primary tumour, a fifth course with vincristine, doxorubicin and CPM was given, followed by high-dose chemotherapy with stem cell support. Response was assessed in accordance with the International Neuroblastoma Response Criteria.

RESULTS

Of 35 consecutive patients, 33 had metastatic disease. The median length of induction phase was 133 days (range 91-207) and time to high-dose chemotherapy was 208 days (range 156-285). The median tumour volume reduction was 55% after two HD-TPT/HD-CPM courses and 80% after four courses. Radical surgery was performed in 16/27 patients after chemotherapy. After the fifth course, 29/34 patients (85%) had achieved a partial remission (12) or a CR/very good partial remission (17). CR of metastases was achieved in 13/32 (41%) and bone marrow was in complete remission in 16/24 patients (67%). Grade 4 neutropenia and/or thrombocytopenia occurred in 100% of HD-TPT/HD-CPM and in 95% of ICE courses, while non-haematological toxicities were manageable.

CONCLUSIONS

These data indicate that our induction regimen is feasible and well tolerated. A major response rate of 85% with 41% complete metastatic response confirms this regimen as effective induction in high-risk neuroblastoma.

The combination of the novel glycolysis inhibitor 3-BrOP and rapamycin is effective against neuroblastoma

Children with high-risk and recurrent neuroblastoma have poor survival rates, and novel therapies are needed. Many cancer cells have been found to preferentially employ the glycolytic pathway for energy generation, even in the presence of oxygen. 3-BrOP is a novel inhibitor of glycolysis, and has demonstrated efficacy against a wide range of tumor types. To determine whether human neuroblastoma cells are susceptible to glycolysis inhibition, we evaluated the role of 3-BrOP in neuroblastoma model systems. Neuroblastoma tumor cell lines demonstrated high rates of lactate accumulation and low rates of oxygen consumption, suggesting a potential susceptibility to inhibitors of glycolysis. In all ten human tested neuroblastoma tumor cell lines, 3-BrOP induced cell death via apoptosis in a dose and time dependent manner. Furthermore, 3-BrOP-induced depletion of ATP levels correlated with decreased neuroblastoma cell viability. In a mouse neuroblastoma xenograft model, glycolysis inhibition with 3-BrOP demonstrated significantly reduced final tumor weight. In neuroblastoma tumor cells, treatment with 3-BrOP induced mTOR activation, and the combination of 3-BrOP and mTOR inhibition with rapamycin demonstrated synergistic efficacy. Based on these results, neuroblastoma tumor cells are sensitive to treatment with inhibitors of glycolysis, and the demonstrated synergy with rapamycin suggests that the combination of glycolysis and mTOR inhibitors represents a novel therapeutic approach for neuroblastoma that warrants further investigation.

A novel therapeutic combination for neuroblastoma: the vascular endothelial growth factor receptor/epidermal growth factor receptor/rearranged during transfection inhibitor vandetanib with 13-cis-retinoic acid

BACKGROUND

High-risk cases of neuroblastoma have poor survival rates, and novel therapies are needed. Vandetanib (ZD6474, Zactima) is an inhibitor of the vascular endothelial growth factor receptor, epidermal growth factor receptor, and rearranged during transfection (RET) tyrosine kinases, which have each been implicated in neuroblastoma pathogenesis. The authors hypothesized that vandetanib combined with 13-cis-retinoic acid (CRA), a differentiating agent used in most current neuroblastoma treatment regimens, would be effective against neuroblastoma tumor models.

METHODS

The authors evaluated the effects of vandetanib with and without CRA on RET phosphorylation and on the proliferation and survival of human neuroblastoma cell lines in vitro. Using a subcutaneous mouse xenograft model of human neuroblastoma, they analyzed tumors treated with CRA, vandetanib, and the combination of vandetanib plus CRA for growth, gross and histologic appearance, vascularity, and apoptosis.

RESULTS

Vandetanib treatment inhibited RET phosphorylation and resulted in induction of apoptosis in the majority of neuroblastoma cell lines in vitro, whereas CRA treatment induced morphologic differentiation and cell-cycle arrest. Treatment with vandetanib plus CRA resulted in more significant reduction in neuroblastoma cell viability than either alone. In a mouse xenograft model, the combination of vandetanib with CRA demonstrated significantly more growth inhibition than either alone, via both reduction in tumor vascularity and induction of apoptosis.

CONCLUSIONS

Vandetanib induces neuroblastoma tumor cell death in vitro and reduces tumor growth and vascularity in vivo. The combination of vandetanib with CRA was more effective in reducing tumor growth than either treatment alone. The antitumor effects of vandetanib plus CRA suggest a novel combination for use in neuroblastoma patients.

New approaches to pharmacotherapy of tumors of the nervous system during childhood and adolescence

Tumors of the nervous system are among the most common and most chemoresistant neoplasms of childhood and adolescence. Malignant tumors of the brain collectively account for 21% of all cancers and 24% of all cancer-related deaths in this age group. Neuroblastoma, a peripheral nervous system tumor, is the most common extracranial solid tumor of childhood, and 65% of children with this tumor have only a 10 or 15% chance of living 5 years beyond the time of initial diagnosis. Novel pharmacological approaches to nervous system tumors are urgently needed. This review presents the role of and current challenges to pharmacotherapy of malignant tumors of the nervous system during childhood and adolescence and discusses novel approaches aimed at overcoming these challenges.

Parents' views of cancer-directed therapy for children with no realistic chance for cure

PURPOSE

Previous literature suggests that parents often wish to continue cancer-directed therapy for their children with incurable cancer. We assessed parents' experiences with treatment for their children with cancer and no realistic chance of cure.

PATIENTS AND METHODS

We administered questionnaires to 141 parents of children with cancer who died after receiving care at one of two cancer centers. Parents were asked whether the child benefited and suffered from treatment administered after the parent recognized that cure was not a realistic expectation, and whether they would recommend cancer-directed therapy to other families of children with advanced cancer.

RESULTS

Fifty-three (38%) of 141 children received cancer-directed therapy after the parent recognized that the child had no realistic chance for cure. Most of these parents felt that their child had experienced at least some suffering resulting from the therapy (61%, 31 of 51) and little to no benefit (57%, 29 of 51). Fifty-one (38%) of 135 parents overall would recommend standard chemotherapy and 46 (33%) of 140 would recommend experimental chemotherapy to families of children with advanced cancer. Even parents who would not recommend standard chemotherapy generally felt the physician should offer it (91%, 88 of 97). Parents who reported that their children experienced suffering resulting from cancer-directed therapy (odds ratio = 0.46; P = .02) were less likely to recommend standard chemotherapy to other families.

CONCLUSION

Although many parents choose treatment for their children with incurable cancer, bereaved parents often would not recommend such therapy. Parents who felt their children suffered as a result of cancer treatment were particularly unlikely to recommend it.

Flow cytometry analysis of single-strand DNA damage in neuroblastoma cell lines using the F7-26 monoclonal antibody

The F7-26 monoclonal antibody (Mab) has been reported to be specific for single-strand DNA damage (ssDNA) and to also identify cells in apoptosis. We carriedout studies to determine if F7-26 binding measured by flow cytometry was able to specifically identify exogenous ssDNA as opposed to DNA damage from apoptosis. Neuroblastoma cells were treated with melphalan (L-PAM), fenretinide, 4-hydroperoxycyclophosphamide (4-HC)+/-pan-caspase inhibitor BOC-d-fmk, topotecan or with 10Gy gamma radiation+/-hydrogen peroxide (H2O2) and fixed immediately postradiation. Cytotoxicity was measured by DIMSCAN digital imaging fluorescence assay. The degree of ssDNA damage was analyzed by flow cytometry using Mab F7-26, with DNA visualized by propidium iodide counterstaining. Flow cytometry was used to measure apoptosis detected by terminal deoxynucleotidyltransferase (TUNEL) assay and reactive oxygen species (ROS) by carboxy-dichlorofluorescein diacetate. Irradiated and immediately fixed neuroblastoma cells showed increased ssDNA, but not apoptosis by TUNEL (TUNEL-negative). 4-HC or L-PAM+/-BOC-d-fmk increased ssDNA (F7-26-positive), but BOC-d-fmk prevented TUNEL staining. Fenretinide increased apoptosis by TUNEL but not ssDNA damage detected with F7-26. Enhanced ssDNA in neuroblastoma cells treated with radiation+H2O2 was associated with increased ROS. Topotecan increased both ssDNA and cytotoxicity in 4-HC-treated cells. These data demonstrate that Mab F7-26 recognized ssDNA due to exogenous DNA damage, rather than apoptosis. This assay should be useful to characterize the mechanism of action of antineoplastic drugs.

Targeting methylguanine-DNA methyltransferase in the treatment of neuroblastoma

PURPOSE

The combination of temozolomide and irinotecan has preclinical schedule-dependent synergy against neuroblastoma but is not curative for relapsed high-risk patients. We hypothesized that the DNA repair protein methylguanine-DNA methyltransferase (MGMT) is an important resistance factor, and that inactivation of MGMT would sensitize neuroblastoma cells to these agents.

EXPERIMENTAL DESIGN

MGMT protein expression was assessed in 74 primary neuroblastoma tumors. Growth inhibition assays were done to determine the IC(50) and the extent of synergy observed with various concentrations of temozolomide, irinotecan, and the MGMT-inactivating agent O(6)-benzylguanine, using cultured syngeneic neuroblastoma cells with either low or high levels of MGMT expression. We then assessed efficacy in a mouse xenograft model of metastatic neuroblastoma.

RESULTS

MGMT was expressed by all 74 tumors evaluated. Pretreatment of neuroblastoma cells with O(6)-benzylguanine reduced the IC(50) of temozolomide by 10-fold regardless of level of MGMT expression, and pretreatment with BG followed by temozolomide + irinotecan further reduced the IC(50) in cells with high MGMT expression another 10-fold, to well below clinically achievable concentrations. The combination index was 0.27 to 0.30 for all three drugs in both cell lines, indicating strong synergy. Survival at 100 days for mice with metastatic neuroblastoma was 56% with three-drug treatment, compared with untreated controls (0%, P < 0.001) or temozolomide + irinotecan (10%, P = 0.081).

CONCLUSIONS

MGMT is widely expressed in primary neuroblastoma tumors, and is a relevant therapeutic target. Both in vitro and in vivo studies suggest inactivation of MGMT with O(6)-benzylguanine may increase the activity of temozolomide and irinotecan against neuroblastoma.

Proapoptotic compound ARC targets Akt and N-myc in neuroblastoma cells

We have previously described the identification of a nucleoside analog transcriptional inhibitor ARC (4-amino-6-hydrazino-7-beta-D-ribofuranosyl-7H-pyrrolo[2,3-d]-pyrimidine-5-carboxamide) that was able to induce apoptosis in cancer cell lines of different origin. Here, we report the characterization of ARC on a panel of neuroblastoma cell lines. We found that these cell lines were more than 10-fold sensitive to ARC than to the well-known nucleoside analog DRB (5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole), and that ARC-induced apoptosis proceeds through mitochondrial injury. Also, we observed that ARC-mediated cell death was accompanied by caspase-3 cleavage and repression of antiapoptotic proteins such as Mcl-1 and survivin. Conversely, we found that overexpression of Mcl-1-protected neuroblastoma cell line NB-1691 from ARC-induced apoptosis. Furthermore, we found that while ARC inhibited the phosphorylation of Akt Ser-473 in multiple cancer cell lines, forced expression of myristoylated Akt promoted resistance to ARC-induced apoptosis in neuroblastoma cells. In addition, we observed that ARC was able to downregulate the protein levels of N-myc, a commonly amplified oncogene in neuroblastomas, and Akt protected N-myc from ARC-induced downregulation. These data suggest that ARC may antagonize different antiapoptotic pathways and induce apoptosis in neuroblastoma cells via multiple mechanisms. Overall, ARC could represent an attractive candidate for anticancer drug development against neuroblastomas.

Irinotecan Plus Temozolomide for Relapsed or Refractory Neuroblastoma

Purpose

To report on an irinotecan and temozolomide regimen for neuroblastoma (NB). Quality of life and minimizing toxicity were major considerations.

Patients and Methods

The plan stipulated 5-day courses of irinotecan 50 mg/m2 (1-hour infusion) and temozolomide 150 mg/m2 (oral) every 3 to 4 weeks, with a pretreatment platelet count more than 30,000/μL. Granulocyte colony-stimulating factor was used when the absolute neutrophil count was less than 1,000/μL.

Results

Forty-nine NB patients received 1 to 15 courses (median, 5). Gastrointestinal and myelosuppressive toxicities were readily managed. Lymphocyte responses to phytohemagglutinin after 2 to 10 courses (median, 3.5) were normal in 10 of 10 patients treated after nonimmunosuppressive therapy, and normalized in five of seven patients first treated less than 2 months after high-dose alkylators. Of 19 patients treated for refractory NB and assessable for response, nine showed evidence of disease regression, including two complete responses and seven objective responses. Of 17 patients treated for progressive disease, three showed evidence of disease regression, including one partial response and two objective responses. Multiple courses entailed no cumulative toxicity and controlled disease for prolonged periods in many patients, including some who were unable to complete prior treatments because of hematologic, infectious, cardiac, or renal problems.

Conclusion

This regimen has anti-NB activity, spares vital organs, is feasible with poor bone marrow reserve, causes limited immunosuppression, and allows good quality of life.

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.