Glutathione conjugation with phosphoramide mustard and cyclophosphamide. A mechanistic study using tandem mass spectrometry

The conjugations of cyclophosphamide and of phosphoramide mustard with glutathione are shown to be catalyzed by hepatic cytosolic glutathione-S-transferases. Cyclophosphamide conjugation is also catalyzed by microsomal glutathione-S-transferases, both in intact microsomes and after solubilization and immobilization. Deuterium isotope labels are used to test whether chloride is directly displaced by glutathione in the enzyme-catalyzed conjugations, or whether conjugation takes place via symmetrical cyclic aziridinium ions. Tandem mass spectrometry with high energy collisional activation is shown to provide reliable analysis of the isotope-labeling patterns in the conjugated products. This experiment leads to the conclusion that the aziridinium ion is opened in the conjugation of phosphoramide mustard in both the enzyme-catalyzed and the chemical reactions. Cyclophosphamide, on the other hand, is shown to be conjugated through direct displacement of chloride.

NMR studies of the conjugation of mechlorethamine with glutathione

Many cancer cells are resistant to chemotherapeutic treatment with mechlorethamine and other alkylating agents. These drug-resistant cells often show an increase in the intracellular concentration of glutathione and an increase in the activity of glutathione-S-transferase when compared to the sensitive cells. Both of these components are thought to be involved with inactivation of the drug either through conjugation with glutathione or by hydrolysis. NMR spectroscopy was used to monitor the nonenzymatic conjugation of mechlorethamine with glutathione. Several intermediates along the pathway to the doubly glutathione substituted mustard, including both mustard-aziridinium adducts, can be observed. The assignment of the 1H NMR spectrum of these adducts are presented. At 30 degrees C, pH 7.0, no hydrolyzed mustard was detectable. With the use of 13C-labeled mustard, the conjugation reaction can be shown to proceed through an aziridinium intermediate rather than by direct nucleophilic substitution.

Autologous bone marrow transplantation with 4-hydroperoxycyclophosphamide purged marrows for acute nonlymphocytic leukemia in late remission or early relapse

Twenty-four patients with acute nonlymphocytic leukemia (ANLL) were treated with high-dose chemotherapy or chemoradiotherapy followed by infusion of autologous marrow purged with 100 micrograms/mL of 4-hydroperoxycyclophosphamide (4HC). The marrow harvests were performed when there were less than 5% blasts in the marrow. Seven patients were transplanted in second complete remission (CR), eight in third CR, one in fourth CR, and eight in early relapse. The median time to achieve 500 neutrophils/microL or 1,000 leukocytes/microL was 30 days. A platelet count of 20,000/microL and 50,000/microL was achieved at a median of 67 and 91 days, respectively. One patient failed to engraft by day 58. There were five other transplant-related deaths: sepsis (one), intracerebral hemorrhage (one), veno-occlusive disease (one), and interstitial pneumonia (two). Four of seven evaluable patients transplanted in early relapse obtained a CR lasting 112, 143, 189, and greater than 615 days. Eight of 11 evaluable patients transplanted in CR have relapsed at a median of 153 days (range, 104 to 311). The actuarial survival for all patients was 19%. There was a trend toward improved relapse-free survival for patients transplanted in remission as opposed to those transplanted in relapse (P = .11).

Role for aldehyde dehydrogenase in survival of progenitors for murine blast cell colonies after treatment with 4-hydroperoxycyclophosphamide in vitro

We have studied the effects of 4-hydroperoxycyclophosphamide (4-HC) on murine hemopoietic progenitors. We found dose-dependent killing and differential sensitivities of colony forming cells with burst forming units-erythrocyte being most sensitive and colony-forming units-granulocyte/erythrocyte/macrophage/megakaryocyte most resistant. We also tested the effects of 4-HC on more primitive murine progenitors which were identifiable in our assay system when the addition of interleukin-3 was delayed until Day 7. We found that the sensitivities of the progenitors for blast cell colonies are similar to those of colony-forming units-granulocyte/erythrocyte/macrophage/megakaryocyte and that late-appearing blast cell colonies were particularly resistant to 4-HC. In order to study the mechanism of differential sensitivities of murine progenitors to 4-HC, we examined the sensitivities of murine progenitors to 4-HC after brief incubation with diethylaminobenzaldehyde, an inhibitor of aldehyde dehydrogenase. Progenitors for granulocyte/macrophage colonies, granulocyte/erythrocyte/macrophage/megakaryocyte colonies, and blast cell colonies became more sensitive to 4-HC and the differential sensitivities of the progenitors disappeared following this treatment. We also tested the sensitivities of the progenitors to phenylketophosphamide, an analogue of 4-HC which is resistant to inactivation by aldehyde dehydrogenase. Various colony-forming units exhibited a similar dose response to this compound. These data indicate that intracellular levels of aldehyde dehydrogenase might play an important role in differential sensitivities of murine colony-forming units to 4-HC.

Enzymatic mechanisms of resistance to alkylating agents in tumor cells and normal tissues

The presence in tumor cells and in normal cells of enzymes which metabolize and inactive alkylating agents appears to play a major role in determining the effectiveness of alkylating agents against human tumors and the toxicities of these agents to normal tissues. The enzyme aldehyde dehydrogenase appears to protect bone marrow and the gastrointestinal tract against toxicity from cyclophosphamide and other closely related oxazophosphorine agents. The presence of this enzyme in bone marrow stem cells facilitates the elimination of tumor cells from bone marrow suspensions, with preservation of the ability of the marrow suspension to reconstitute normal hematopoiesis in a patient. A variety of mouse and human tumors has been shown to be resistant to cyclophosphamide on the basis of an elevated aldehyde dehydrogenase content. The clinical significance of this type of resistance is currently being explored. Increased levels of glutathione-S-transferase have been shown to be associated with cellular resistance to a variety of alkylating agents. We have identified and characterized the conjugates of nitrogen mustards with glutathione. The formation of these conjugates is catalyzed by glutathione-S-transferase. The further study and characterization of these specific reactions should contribute to the understanding and quantitation of this type of alkylating agent resistance.

Tumoricidal and immunomodulatory activities of drugs and implications for therapy of mice bearing a late stage MOPC-315 plasmacytoma

The effectiveness of a relatively low dose of cyclophosphamide (15 mg/kg CY), melphalan (2.5 mg/kg L-PAM) or the monofunctional form of CY (150 mg/kg MoCY) for the cure of mice bearing a large primary s.c. MOPC-315 tumor and extensive metastases has been shown to be dependent on the cooperation of the drugs' tumoricidal activity with T-cell-dependent antitumor immunity, the latter facilitated by the drug's immunomodulatory activity. Here, we have compared the curative effectiveness of three additional drugs: methyl nitrosourea (MNU), hydroxyurea (OH-urea) and bis-chloroethyl nitrosourea (BCNU). Among these drugs, only a relatively low dose of BCNU (15-20 mg/kg) was effective in curing most mice (85%) bearing a large, late stage tumor. A higher dose of BCNU (40 mg/kg, LD10) was much less effective. After an optimal dose of BCNU, the proliferative capacity of the tumor cells 24 h after therapy was reduced by greater than 97%. However, viable tumorigenic cells were still present in the primary tumor and enhanced T-cell-dependent antitumor immunity was necessary for their eradication. The cured mice were resistant to tumor rechallenge. When a low curative dose of L-PAM was followed by OH-urea, the therapeutic effectiveness was not affected, but when this dose of L-PAM was followed by a high nontoxic dose of MNU (100-150 mg/kg), the therapeutic effectiveness was diminished even though MNU was highly tumoricidal (i.e. greater than 99% inhibition of proliferative activity). Thus, BCNU appears to be similar to CY, L-PAM and MoCY in its mechanism of MOPC-315 tumor eradication. The alkylating activity of CY, L-PAM, MoCY and BCNU appears to be critical for their combined tumoricidal and immunomodulatory effects. Since BCNU is the simplest of these four drugs with respect to metabolic pathway, a further study with BCNU and related constructs may shed some light on the biochemical mechanisms of their mode of action. At least one reason for the ineffectiveness of OH-urea or MNU at either low or nontoxic high doses was poor tumoricidal or immunomodulatory activity, respectively. Thus, it seems important to consider both the tumoricidal and immunomodulatory activities of drugs when developing regimens for effective chemotherapy.

Marrow purging in autologous bone marrow transplantation for T-lineage acute lymphoblastic leukemia: efficacy of ex vivo treatment with immunotoxins and 4-hydroperoxycyclophosphamide against fresh leukemic marrow progenitor cells

A lymphoblast progenitor cell assay was used to evaluate the antileukemic efficacy of marrow-purging protocols that employed intact ricin immunotoxins (IT) and 4-hydroperoxycyclophosphamide (4-HC) against clonogenic primary T-lineage marrow blasts freshly obtained from 12 T-lineage acute lymphoblastic leukemia (ALL) patients. Residual T-lineage blast colonies were observed after treatment with 1 micrograms/mL T101 (anti-CD5)-Ricin (R) + G3.7 (anti-CD7)-R in eight of 12 cases and after 100 micrograms/mL 4-HC in six of nine cases. By comparison, a combination of IT and 4-HC proved very effective against T-lineage leukemic progenitor cells, and no residual blast colonies were observed in any of the eight cases studied. We conclude that future trials should consider combined treatment protocols such as IT + 4-HC for more effective purging of autologous marrow grafts.

Comparative cytotoxicity of various drug combinations for human leukemic cells and normal hematopoietic precursors

The development of suitable methods for purging the malignant cells contaminating the bone marrow of patients with cancer may offer a better chance of success for autologous bone marrow transplantation. In this paper, we further describe our efforts at purging acute myelogenous leukemia cells. HL-60, a promyelocytic leukemia cell line, was used as a model. 4-Hydroperoxycyclophosphamide (4-HC), VP-16-213 (VP-16), and Adriamycin were used alone or in combination to develop the best method to purge HL-60 cells. The cytotoxicity of 29.2 micrograms/ml (100 microM) of 4-HC was 99.8 +/- 0.12% (SD) on HL-60 cells and 82.5% on colony forming units-granulocyte, macrophage. Ninety-nine % of HL-60 cells and 72.7% of colony forming units-granulocyte, macrophage were inhibited by VP-16 at a concentration of 25 micrograms/ml (42.5 microM). The cytotoxicity of 1.5 micrograms/ml (2.76 microM) of Adriamycin on HL-60 cells was 98.6 +/- 0.8% and inhibited colony forming units-granulocyte, macrophage by 50.8%. The cytotoxicity and interactions of any two drug combinations at different combination ratios and the different effect levels were quantitatively determined by median effect plot and the multiple drug effect equation (T-C. Chou and P. Talalay. Adv. Enzyme Regul. 22: 27-55, 1984). The combination of 4-HC and VP-16 at a 4-HC:VP-16 drug ratio of 1:0.342 was found to be the best for selective toxicity towards HL-60 cells and was superior to the 4-HC-Adriamycin or VP-16 Adriamycin combination for usefulness in purging bone marrow.

High-performance liquid chromatographic assay for taxol in human plasma and urine and pharmacokinetics in a phase I trial

Taxol is a unique antineoplastic agent which appears to exert its cytotoxic action as a result of interference with microtubular structure and function. Clinical development of this drug will be facilitated by the availability of sensitive and specific methods for its quantitation in biological fluids. We have developed a reverse-phase high-performance liquid chromatographic assay for taxol capable of detecting concentrations as low as 50 nM, which can be automated using readily available equipment. With this assay we have performed pharmacologic studies of taxol during the conduct of a phase I trial of this compound at The Johns Hopkins Oncology Center. Following a 60- to 360-minute infusion, the plasma disappearance is biexponential, with harmonic mean alpha half-life and beta half-life values of 16.2 minutes and 6.4 hours, respectively. Volumes of distribution for the theoretical central compartment (VDc) and at steady state (VDss) were 8.6 and 67.1 L/m2. Mean plasma clearance was 253 ml/minute/m2. Urinary clearance was 29.3 ml/minute/m2 and 5.9% +/- 8.8% of the drug was identified in 48-hour urine collections. No metabolites have been identified. Over the 18-fold dose range studied, there was no evidence of nonlinearity or dose-dependent behavior. A rough correlation between area under the plasma disappearance curve and hematologic toxicity was observed.

Ability of cyclophosphamide in the absence of cross-linking activity to exert the immunomodulatory effect required for the cure of mice bearing a large MOPC-315 tumor

We have previously shown that mice bearing a late-stage, large primary MOPC-315 plasmacytoma and extensive metastases can be cured by a low dose of the bifunctional alkylating drug, cyclophosphamide (BiCY) (J.C.D. Hengst et al., Cancer Res., 40: 2135-2141, 1980). Here we show that therapy with the monofunctional form of cyclophosphamide (MoCY) can also cure such mice. However, a dose of at least 150 mg of MoCY per kg is required to approximate the curative effectiveness of the lowest curative dose of BiCY, i.e., 15 mg/kg. This need for a 10-fold higher dose of MoCY is due, at least in part, to the 10-fold lower direct tumoricidal and/or tumoristatic activity of MoCY compared to BiCY. Consequently, a 10-fold higher dose of MoCY is required to directly reduce the tumor burden to the level reduced by 15 mg of BiCY per kg. Other than dose, the therapy of the mice with 150 mg of MoCY per kg was similar in its essential features to that shown previously for therapy with 15 mg of BiCY per kg (J.C.D. Hengst et al., Cancer Res., 40: 2135-2141, 1980; J.C.D. Hengst et al., Cancer Res., 41:2163-2167, 1981; Q-W. Ye et al., Cancer Immunol. Immunother., 16:162-169, 1984; Q-W. Ye and M.B. Mokyr, Cancer Res., 44: 3873-3879, 1984; M.B. Mokyr and S. Dray, Cancer Res., 43: 3112-3119, 1983), namely: (a) the drug does not directly eradicate all tumor cells; (b) host T-cell-dependent antitumor immunity is also required for the curative effect; (c) the therapy of tumor bearers leads to the rapid appearance of an augmented antitumor immune potential in their hitherto immunosuppressed spleen; and (d) the cured mice are resistant to a subsequent challenge with at least 300-fold the minimal lethal tumor dose. Thus, cross-linking is not an essential property for the immunomodulatory activity of BiCY nor for its direct antitumor effect. However, in the presence of cross-linking activity, a much lower dose of drug is effective.

Hypersensitivity reaction to a metabolite of cyclophosphamide

Generalized urticaria and fever were noted in a patient with IgA (kappa) myeloma after intravenous cyclophosphamide. Intradermal skin testing revealed no reaction to cyclophosphamide and its analog, isophosphamide. However, phosphoramide mustard, a principle metabolite of cyclophosphamide, evoked an immediate wheal-and-flare response. Subsequent therapy with isophosphamide was well tolerated. These findings suggest that acute hypersensitivity reactions to cyclophosphamide are due to its metabolites and can be delineated with skin testing.

Synergistic effect of 4-hydroperoxycyclophosphamide and etoposide on a human promyelocytic leukemia cell line (HL-60) demonstrated by computer analysis

Autologous stem cell transplantation using cryopreserved bone marrow offers the opportunity to rescue patients from hematopoietic toxicity caused by intensive chemotherapy. This approach is potentially useful for high-risk leukemias as well as for other cancers. The development of suitable methods for purging malignant cells from the bone marrow will offer a better chance of success for autologous stem cell transplantation. In this paper, we describe our efforts at purging myeloid cells. HL-60, a promyelocytic leukemia cell line, was used as a model. 4-Hydroperoxycyclophosphamide (4-HC) and VP-16-213 (VP-16) (either alone or in combination) were used to treat HL-60 cells and normal bone marrow. The cytotoxic effect of 4-HC (29.2 micrograms/ml; 100 microM) upon the HL-60 cell line was 99.8 +/- 0.12% (SE), and the colony-forming units-granulocyte, macrophage (CFU-cs) of normal bone marrow was inhibited by 82.5%. VP-16, at a concentration of 25 micrograms/ml (42.5 microM), can kill 99% of HL-60 cells and inhibit 72.7% of the CFU-cs. A drug mixture containing 4-HC (29.2 micrograms/ml) and VP-16 (10 micrograms/ml) (combination ratio, 1:0.342) reduces HL-60 cells to an undetectable number, and the CFU-cs were inhibited by 87.2%. The laboratory data were further analyzed for the synergistic effect of these two drugs by quantitative determination of the median effect plot and the multiple drug equation recently described by Chou and Talalay (Adv. Enz. Regul., 22: 27-55, 1984). Interactions of two drugs at different effect levels and at different combination ratios were then determined by computer simulation. At high effect levels, 4-HC and VP-16 in combination gave a synergistic cytocidal effect on HL-60 leukemic cells and gave an antagonistic inhibitory effect on normal bone marrow CFU-cs. This combination greatly increases the safety margin. Computer simulation of a dose effect relationship has also shown that the 4-HC:VP-16 combination ratio of 1:0.342 yields a better selective effect than a ratio of 1:0.856. This quantitative analysis suggests that the combination of these two drugs at the selected dose level offers a good method for purging nonlymphoblastic leukemia cells.

Dose-response effects of 4-hydroperoxycyclophosphamide on human T and B cell function in vitro

4-Hydroperoxycyclophosphamide (4-OOH-CYP) is spontaneously converted in aqueous solution to 4-hydroxycyclophosphamide (4-OH-CYP), the major active metabolic of cyclophosphamide. We studied the dose related effects of in vitro treatment with 4-OOH-CYP on human T- and B cell-mediated immune responses. T-cell proliferation to mitogens and alloantigens was only partially inhibited even relatively high-doses of 4-OOH-CYP (greater than 6-12 micrograms/ml). In contrast cytotoxic functions of activated T-cells and natural killer (NK) cells were inhibited at lower doses (3-6 micrograms/ml). PWM induced in vitro synthesis of IgG by B-cells was inhibited at less than 3 micrograms/ml of 4-OOH-CYP. These data indicate that 4-HOO-CYP has selective, dose-dependent effects on human T and B cells in vitro.

Cyclophosphamide-mediated enhancement of antitumor immune potential of immunosuppressed spleen cells from mice bearing a large MOPC-315 tumor

We have utilized 4-hydroperoxycyclophosphamide (4-HP-CY) as a probe for the immunomodulatory activity of the metabolites of cyclophosphamide (CY) since 4-HP-CY hydrolyzes spontaneously in aqueous solution to the same metabolites as those formed after in vivo conversion of CY by microsomal enzymes. Exposure of immunosuppressed MOPC-315 tumor bearer spleens to a low concentration of 4-HP-CY (0.1-3.0 micron) resulted in augmented antitumor immune potential. The level of antitumor immune potential exhibited by 4-HP-CY-treated tumor bearer spleen cells was not further augmented but was actually reduced by depletion of glass-adherent cells, a procedure which is effective in removing the cells known to have immunosuppressive activity (i.e. metastatic tumor cells and macrophages) from the spleen of untreated MOPC-315 tumor-bearing mice. In fac, 4-HP-CY was superior to depletion of glass-adherent cells in augmenting the antitumor immune potential of immunosuppressed tumor bearer spleen cells. When cells from the primary tumor nodule were incubated with a low concentration of 4-HP-CY which only marginally inhibited their proliferation, the drug completely abolished the suppressive activity of the cells for in vitro generation of antitumor cytotoxicity by normal spleen cells. Moreover, a high level of antitumor cytotoxicity developed when normal spleen cells were cultured in vitro with 4-HP-CY-treated tumor cells at a wide range of ratios of spleen cells to tumor cells. Thus, in the MOPC-315 tumor model, metabolites of CY eliminate the inhibitory effectiveness of splenic suppressor cells and induce the appearance of immunopotentiating activity. The results obtained with 4-HP-CY in vitro provide support for the hypothesis that low-dose CY therapy of mice bearing a large MOPC-315 tumor leads to the appearance of augmented antitumor immune potential in their hitherto immunosuppressed spleen cells as a result of the in situ immunomodulatory effect of the drug on cells in the spleen.

In vitro effects of 4-hydroperoxycyclophosphamide on the morphology and function of human peripheral blood mononuclear phagocytic cells (macrophages)

Human peripheral blood mononuclear cells were incubated for 1 hr in 4-hydroperoxycyclophosphamide (0.5 to 10.0 micrograms/ml), and the adherent, esterase-positive cells (macrophages) were studied. At 2 hr, a reduction was noted in both latex particle ingestion and Fc gamma receptor binding and phagocytosis. At 24 hr, spreading and pinocytosis were reduced, and cytoplasmic vacuoles developed. This vacuolization represented dilatation of the rough endoplasmic reticulum. These morphological and functional changes occurred with 4-hydroperoxycyclophosphamide concentrations which did not reduce viability or produce detectable DNA alkylation. This effect on macrophages may offer a mechanism whereby low-dosage cyclophosphamide could modify the immune response.

In vitro alteration of canine renal allografts with cyclophosphamide metabolites

4-Hydroxycyclophosphamide (4-HCY) is generated spontaneously in cryoprecipitated plasma from synthesized 4-hydroperoxycyclophosphamide (4-HPCY); its immunosuppressive and cytotoxic effects seem to depend on milieu, temperature, time, and dosage. Our preliminary results suggest that prolonged canine renal allograft survival can be achieved with grafts exposed to CY metabolites (4-HPCY and PM) in vitro for 24 hr. Further studies with larger dosages (greater than or equal to 100 micrograms/ml of 4-HPCY) are indicated to test these suggestions conclusively.

Vomiting induced by cyclophosphamide and phosphoramide mustard in cats

Cyclophosphamide and phosphoramide mustard produce significant vomiting. Cyclophosphamide is metabolized to phosphoramide mustard, which may ultimately contribute to vomiting after cyclophosphamide administration. The role of the chemoreceptor trigger zone (CTZ) in vomiting caused by these agents is unknown. We studied the emetic syndromes produced by iv and intracerebroventricular cyclophosphamide and phosphoramide mustard in unanesthetized normal and CTZ-ablated cats. Iv cyclophosphamide produced vomiting unpredictably, with a mean latency of 54 +/- 9 mins (mean +/- SE) in cats that vomited. A dose-response relationship was found for phosphoramide mustard-induced emesis. A dose of 200 mg/kg was consistently effective, with a mean latency of 127 +/- 6 mins. Neither agent produced predictable emesis by the intracerebroventricular route of administration. One of four CTZ-ablated cats vomited after 300 mg/kg of cyclophosphamide. Since cyclophosphamide was an unpredictable emetic stimulus, it was not possible to further evaluate the effect of CTZ ablation on cyclophosphamide-induced vomiting. However, CTZ-ablated cats given 200 mg/kg of phosphoramide mustard vomited significantly less frequently (P = 0.05 by chi-square test) and with a longer latency than nonablated animals. A temporary, severe neurotoxic reaction was observed in cats receiving greater than or equal to 3400 mg/kg of cyclophosphamide, which may have had an inhibitory effect on emesis. Phosphoramide mustard was found to be a potent emetic stimulus in cats and may contribute to the emetic response following cyclophosphamide administration. Analysis of latency data suggests that in the cat other cyclophosphamide metabolites may also contribute to the emetic syndrome.

Cyclophosphamide plasma and cerebrospinal fluid kinetics with and without dimethyl sulfoxide

Ten patients with brain tumors and indwelling ventricular reservoirs were pretreated with 5% to 10% dimethyl sulfoxide (DMSO) (intravenous, oral, or both) and were then treated with 1.0 to 1.25 gm/m2 cyclophosphamide (CYC). All patients were also on anticonvulsants and dexamethasone. CYC and alkylating activity (alk act) in plasma and concomitant ventricular cerebrospinal fluid (CSF) were measured by gas chromatography and p-nitrobenzyl pyridine assay. CYC entered the CSF without difficulty and was lost from CSF more slowly than from plasma. Alk act did not enter CSF as well as did CYC. DMSO did not alter any measured aspect of CYC or alk act disposition. Specifically, it did not alter the CYC plasma half-life (t1/2), CSF t1/2, peak CSF: peak plasma CYC concentration ratio, or the urinary excretion of CYC. DMSO did not alter the plasma t1/2 or urinary excretion of alk act or the peak CSF:peak plasma concentration ratio of alk act. Our data show reduced plasma t1/2 of CYC and increased plasma and urinary alk act. This may reflect tht effect of long-term therapy with anticonvulsants or steroids.