Relationships between resistance to cross-linking agents and glutathione metabolism, aldehyde dehydrogenase isozymes and adenovirus replication in human tumour cell lines

Immunosuppression enhances oncolytic adenovirus replication and antitumor efficacy in the Syrian hamster model

We recently described an immunocompetent Syrian hamster model for oncolytic adenoviruses (Ads) that permits virus replication in tumor cells as well as some normal tissues. This model allows exploration of interactions between the virus, tumor, normal organs, and host immune system that could not be examined in the immunodeficient or nonpermissive animal models previously used in the oncolytic Ad field. Here we asked whether the immune response to oncolytic Ad enhances or limits antitumor efficacy. We first determined that cyclophosphamide (CP) is a potent immunosuppressive agent in the Syrian hamster and that CP alone had no effect on tumor growth. Importantly, we found that the antitumor efficacy of oncolytic Ads was significantly enhanced in immunosuppressed animals. In animals that received virus therapy plus immunosuppression, significant differences were observed in tumor histology, and in many cases little viable tumor remained. Notably, we also determined that immunosuppression allowed intratumoral virus levels to remain elevated for prolonged periods. Although favorable tumor responses can be achieved in immunocompetent animals, the rate of virus clearance from the tumor may lead to varied antitumor efficacy. Immunosuppression, therefore, allows sustained Ad replication and oncolysis, which leads to substantially improved suppression of tumor growth.

Hexadecyloxypropyl-cidofovir, CMX001, prevents adenovirus-induced mortality in a permissive, immunosuppressed animal model

Adenoviruses (Ads) cause a wide array of end-organ and disseminated diseases in severely immunosuppressed patients. For example, approximately 20% of pediatric allogeneic hematopoietic stem cell transplant recipients develop disseminated Ad infection, and the disease proves fatal in as many as 50-80% of these patients. Ad infections are a serious problem for solid-organ transplant recipients and AIDS patients as well. Unfortunately, there are no antiviral drugs approved specifically to treat these infections. A suitable animal model that is permissive for Ad replication would help in the discovery process. Here we identify an animal model to study Ad pathogenesis and the efficacy of antiviral compounds. We show that human serotype 5 Ad (Ad5) causes severe systemic disease in immunosuppressed Syrian hamsters that is similar to that seen in immunocompromised patients. We also demonstrate that hexadecyloxypropyl-cidofovir (CMX001) rescues the hamsters from a lethal challenge with Ad5. The antiviral drug provided protection both prophylactically and when given up to 2 days after i.v. exposure to Ad5. CMX001 acts by reducing Ad replication in key target organs. Thus, the immunosuppressed Syrian hamster is a powerful model to evaluate anti-Ad drugs, and its use can facilitate the entry of drugs such as CMX001 into clinical trials.

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.

No correlation between GSH levels in human cancer cell lines and the cell growth inhibitory activities of platinum diamine complexes

Increases in the intracellular levels of glutathione (GSH) in cancer cells have been implicated in the development of acquired resistance to platinum antitumor agents. On the other hand, little information is available on the relationships between intracellular GSH levels in non-treated cancer cells and their response to platinum complexes. The present work investigated for possible correlations between concentrations of intracellular GSH/GSSG in 14 human cancer cell lines growing in vitro and the cell growth inhibitory activities of cisplatin, carboplatin, oxaliplatin, and d,l-trans-1,2-diaminocyclohexane-dichloro-platinum(II) (DACH-Pt). No statistically significant correlation between GSH levels and the activities of any of the four Pt-complexes could be found.

Dependence of aldehyde dehydrogenase-mediated oxazaphosphorine resistance on soluble thiols: importance of thiol interactions with the secondary metabolite acrolein

Acrolein is a highly reactive and cytotoxic by-product released during activation of oxazaphosphorine (OAP) anticancer alkylating agents. Previously, we demonstrated that transfected human aldehyde dehydrogenase (ALDH, EC 1.2.1.3) isozymes (class 1 or 3) protect V79/SD1 cells from mafosfamide (MAF) cytotoxicity, but protection from 4-hydroperoxy-cyclophosphamide (4-hpCPA) was weaker. Acrolein, an ALDH inhibitor, may be detoxified by conjugation with the nucleophilic thiol 2-mercaptoethanesulfonate (MESNA), which is released from MAF but not from 4-hpCPA. We examined the effect of acrolein or acrolein/thiol conjugates on ALDH activity in vitro. We found that both ALDH isozymes were inhibited by acrolein, with IC50 values of 35 and 144 microM for ALDH-1 or ALDH-3, respectively. Both isozymes were partially protected by NAD+ cofactor, being at least five-fold more sensitive to acrolein if added before cofactor. In contrast, thiol conjugates of acrolein did not inhibit ALDH-3 activity, but were substrates only for ALDH-1. Further, acrolein was shown to be oxidized by ALDH-3, but not by ALDH-1. The effect of acrolein on ALDH-mediated resistance to OAP agents in intact cells was also examined. In control cells (without ALDH expression), acrolein and 4-hpCPA rapidly depleted intracellular GSH levels, whereas the effect of MAF was much less. Depletion of GSH by preincubation of V79/SD1 cells with a low concentration of acrolein (2 microM) before MAF exposure caused a two-fold reduction in ALDH-mediated resistance. Conversely, protection from 4-hpCPA cytotoxicity was enhanced by the addition of thiols (GSH, 2-mercaptoethanesulfonate, or N-acetylcysteine) during the drug exposure. These results suggest 1) that thiol content is an important determinant of the OAP resistance conferred by ALDH isoenzymes; and 2) a new mechanism whereby thiol modulation could increase the therapeutic index of OAP chemotherapy.

Serine protease inhibition and mitochondrial dysfunction associated with cisplatin resistance in human tumor cell lines: targets for therapy

Indicators of mitochondrial function were studied in two different cell culture models of cis-diamminedichloroplatinum-II (CDDP) resistance: the intrinsically resistant human ovarian cancer cell line CI-80-13S, and resistant clones (HeLa-S1a and HeLa-S1b) generated by stable expression of the serine protease inhibitor-plasminogen activator inhibitor type-2 (PAI-2), in the human cervical cancer cell line HeLa. In both models, CDDP resistance was associated with sensitivity to killing by adriamycin, etoposide, auranofin, bis[1,2-bis(diphenylphosphino)ethane]gold(I) chloride ([Au(DPPE)2]Cl), CdCl2 and the mitochondrial inhibitors rhodamine-123 (Rh123), dequalinium chloride (DeCH), tetraphenylphosphonium (TPP), and ethidium bromide (EtBr) and with lower constitutive levels of ATP. Unlike the HeLa clones, CI-80-13S cells were additionally sensitive to chloramphenicol, 1-methyl-4-phenylpyridinium ion (MPP+), rotenone, thenoyltrifluoroacetone (TTFA), and antimycin A, and showed poor reduction of 1-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT), suggesting a deficiency in NADH dehydrogenase and/or succinate dehydrogenase activities. Total platinum uptake and DNA-bound platinum were slightly lower in CI-80-13S than in sensitive cells. The HeLa-S1a and HeLa-S1b clones, on the other hand, showed poor reduction of triphenyltetrazolium chloride (TTC), indicative of low cytochrome c oxidase activity. Total platinum uptake by HeLa-Sla was similar to HeLa, but DNA-bound platinum was much lower than for the parent cell line. The mitochondria of CI-80-13S and HeLa-S1a showed altered morphology and were fewer in number than those of JAM and HeLa. In both models, CDDP resistance was associated with less platinum accumulation and with mitochondrial and membrane defects, brought about one case with expression of a protease inhibitor which is implicated in tumor progression. Such markers may identify tumors suitable for treatment with gold phosphine complexes or other mitochondrial inhibitors.

Molecular dynamics simulations of chlorambucil/DNA adducts. A structural basis for the 5'-GNC interstrand DNA crosslink formed by nitrogen mustards

The alkylation of DNA by chlorambucil has been studied using a computational approach. Molecular dynamics simulations were performed on the fully solvated non-covalent complex, two monoadducts and a crosslinked diadduct of chlorambucil with the d(CGG3G2CGC).-d(GCG1CCCG) duplex, in which the N7 atoms of G1, G2 and G3 are potential alkylation sites. The results provide a structural basis for the preference of nitrogen mustards to crosslink DNA duplexes at a 5'-GNC site (a 1,3 crosslink, G1-G3) rather than at a 5'-GC sites (a 1,2 crosslink, G1-G2). In the non-covalent complex simulation the drug reoriented from a non-interstrand crosslinking location to a position favorable for G1-G3 diadduct formation. It proved possible to construct a G1-G3 diadduct from a structure from the non-covalent simulation, and continue the molecular dynamics calculation without further disruption of the DNA structure. A crosslinked diadduct developed with four BII conformations on the 3' side of each alkylated guanine and of their respective complementary cytosine. In the first monoadduct simulation the starting point was the same DNA conformation used in the crosslinked diadduct simulation with alkylation at G1. In this simulation the DNA deformation was reduced, with the helix returning to a more canonical form. A second monoadduct simulation was started from a canonical DNA conformation alkylated at G3. Here, no significant motion towards a potential crosslinking conformation occurred. Collectively, the results suggest that crosslink formation is dependent upon the drug orientation prior to alkylation and the required deformation of the DNA to permit 1,3 crosslinking can largely be achieved in the non-covalent complex.

Pharmacokinetics, metabolism and clinical effect of ifosfamide in breast cancer patients

Ifosfamide (IFO) at a dose of 5 g/m2, was administered as a 24-h infusion to 15 patients with metastatic (12) or locally advanced (3) breast cancer (age range 33-59 years, median 46). Concurrent chemotherapy was doxorubicin (40 mg/m2) or epirubicin (60 mg/m2). Ifosfamide and its metabolites were measured in plasma and urine during and for 24 h after the infusion using a high performance thin layer chromatography (HPTLC) technique. Patients' haematological toxicity and biochemistry were monitored during treatment and patients were followed for up to 2 years after therapy. At the time of evaluation, 5 of the patients were alive, 2 of whom had not relapsed. A marked variation was observed in the pharmacokinetics and metabolism of ifosfamide in the evaluable patients. Clearance, volume of distribution and half-life of the drug were 3.48 +/- 0.88 1/h/m2, 0.56 +/- 0.22 l/kg and 4.68 +/- 2.01 h, respectively. There was no apparent correlation between these pharmacokinetic variables and patient age, weight or renal function. AUCs of the ultimate alkylating species isophosphoramide mustard (IPM) varied over 6-fold, as did those of the inactivated metabolite carboxyifosfamide (CX). AUCs of dechloroethylated metabolites varied 4-fold (3-dechloroethylifosfamide, 3-DCI) or 8-fold (2-DCI), while that of the parent compound varied only 2.5-fold. Variation in recovery of the metabolites in urine varied over an even wider range, total recovery varying from 17.5 to 81.8% of the dose administered. There was little apparent correlation between pharmacokinetic and metabolite parameters of IFO and haematological toxicity. However, there was a marked negative correlation between both progression-free interval and survival and the AUCs of the products of IFO activation (IPM and CX). In addition, the recovery of IPM in urine was higher in patients experiencing a partial response compared to those with progressive or stable disease. Recovery of dechloroethylated metabolites correlated positively with survival, if 1 poor prognosis patient was excluded. Although far from conclusive, these results give some insight into a possible mechanism of action of ifosfamide and indicate that some species other than IPM, as measured systemically, is responsible for the pharmacological effects of this drug.

Histopathology of melanocytic lesions in goats and establishment of a melanoma cell line: a potential model for human melanoma

Melanocytic cells from white Angora goats were studied in vivo and in vitro. The histopathology of pigmented areas of skin from the most common sites of melanoma (solar-exposed areas of the ear, face, and perineum) resembled that of the epidermal melanocytes in Hutchinson's melanotic freckle in humans. Seven melanoma biopsies from 6 Angora goats showed histopathological features in common with human melanoma. A melanoma cell line, GM-1, was established in culture from a lymph node metastasis obtained from an animal that had a primary tumor excised and later developed extensive metastatic disease. GM-1 cells were mainly diploid, amelanotic, proliferated rapidly, spontaneously formed vacuolated cells, and were tumorigenic in nude mice. The species of origin of the GM-1 line was confirmed by isozyme profiles. GM-1 cultured cells and the original biopsy both expressed S-100 protein and tyrosinase antigen. Using GM-1 cells as the immunogen, a monoclonal antibody (MoAb 1F1) was derived that reacted strongly with a 116 kDa antigen in 50% of the GM-1 cells, but had little activity with goat fibroblasts (GM-F) or with human melanoma cells. GM-F, on the other hand, yielded more intense staining than GM-1 with an intermediate filament antibody (IFA), reacting with a 58 kDa antigen in both cell lines. The sensitivity of GM-1 to anticancer agents was similar to that of human melanoma cells. The pathology of caprine melanoma and its association with sun-exposed sites in relatively young animals suggest that it may be a suitable model for studying induction of melanoma by natural sunlight.