Nitric oxide enhancement of fludarabine cytotoxicity for B-CLL lymphocytes

Fludarabine is active but not curative in the treatment of chronic lymphocytic leukemia (B-CLL). Nitric oxide (NO) supplied from exogenous, NO-donating pro-drugs can also induce apoptosis and death of acute leukemia cells. This study investigated combinations of fludarabine with NO-donating pro-drugs for their cytotoxicity against freshly isolated B-CLL lymphocytes following a 72 h exposure in vitro. The median IC(50)for fludarabine was 2.2 microM (n = 85). The nitric oxide donors DETA-NO, PAPA-NO, and MAHMA-NO were also cytotoxic, and their effects were inversely related to rates of NO release. Neither DETA-NO depleted of NO nor DETA itself was effective, indicating that NO was required for cytotoxicity. Drug interactions were evaluated by a modified combination index method. Synergy was observed in combinations of fludarabine or nelarabine (506U78) with DETA-NO in 52% and 88% of samples, respectively. Interestingly, the combination of fludarabine and DETA-NO was more cytotoxic in B-CLL cells less sensitive to fludarabine. DETA-NO did not enhance the activity of other DNA anti-metabolites, topoisomerase I and II inhibitors, or alkylating agents. Finally, the anti-leukemic activity of fludarabine alone or in combination with DETA-NO was found to correlate with inhibition of cellular RNA synthesis. These results indicate that NO donors could enhance fludarabine therapy for B-CLL.

Dual role of glutathione in modulating camptothecin activity: depletion potentiates activity, but conjugation enhances the stability of the topoisomerase I-DNA cleavage complex

Depletion of glutathione (GSH) in MCF-7 and MDA-MB-231 cell lines by pretreatment with the GSH synthesis inhibitor buthionine sulfoximine potentiated the activity of 10,11-methylenedioxy-20(S)-camptothecin, SN-38 [7-ethyl-10-hydroxy-20(S)-camptothecin], topotecan, and 7-chloromethyl-10,11-methylenedioxy-20(S)-camptothecin (CMMDC). The greatest potentiation was observed with the alkylating camptothecin CMMDC. Buthionine sulfoximine pretreatment also increased the number of camptothecin-induced DNA-protein crosslinks, indicating that GSH affects the mechanism of action of camptothecin. We also report that GSH interacts with CMMDC to form a stable conjugate, 7-(glutathionylmethyl)-10,11-methylenedioxy-20(S)-camptothecin (GSMMDC), which is formed spontaneously in buffered solutions and in MCF-7 cells treated with CMMDC. GSMMDC was synthesized and found to be nearly as active as 10,11-methylenedioxy-20(S)-camptothecin in a topoisomerase (topo) I-mediated DNA nicking assay. The resulting topo I cleavage complexes were remarkably stable. In cell culture, GSMMDC displayed potent growth-inhibitory activity against U937 and P388 leukemia cell lines. GSMMDC was not active against a topo I-deficient P388 cell line, indicating that topo I is its cellular target. Peptide-truncated analogues of GSMMDC were prepared and evaluated. All three derivatives [7-(gamma-glutamylcysteinylmethyl)-10,11-methylenedioxy-20(S)-camptothecin, 7-(cysteinylglycylmethyl)-10,11-methylenedioxy-20(S)-camptothecin, and 7-(cysteinylmethyl)-10,11-methylenedioxy-20(S)-camptothecin] displayed topo I and cell growth-inhibitory activity. These results suggest that 7-peptidyl derivatives represent a new class of camptothecin analogues.

Induction of topoisomerase II activity after ErbB2 activation is associated with a differential response to breast cancer chemotherapy

ErbB2 (HER-2) gene amplification and overexpression have been shown to predict a better outcome with doxorubicin-based chemotherapy as opposed to alkylator-based chemotherapy in early stage breast cancer. To understand the mechanism of differential response to these two regimens, we have evaluated the effect of signaling through the ErbB2 receptor on downstream enzymes that may affect drug response, using two different models. The first system employs breast cancer cells that have high levels of endogenous ErbB2 by gene amplification (BT-474 and SKBR3 cells). The second system allows us to isolate the effect of ErbB2 receptor-mediated intracellular signaling using an epidermal growth factor receptor-ErbB2 chimeric receptor activated by epidermal growth factor. Our experiments show that the cytotoxicity of doxorubicin is inhibited in ErbB2+ breast cancer cells by the anti-ErbB2 antibody, Herceptin. This is accompanied by a decrease in topoisomerase (topo) IIalpha protein and activity, suggesting that this is the mechanism of change in doxorubicin response. In addition, a 10-100-fold (1-2 log) decrease in the LD(50) of doxorubicin is seen after ErbB2 activation using the chimeric receptor model. Furthermore, we see a 100-fold decrease in the LD(50) of etoposide, another topo II inhibitor. This increase in doxorubicin sensitivity is associated with a 4.5-fold increase in the amount of topo IIalpha protein and an increase in topo II activity as measured by DNA decatenating and unknotting activities, as well as cleavable complex formation. In contradistinction to doxorubicin, we have observed an increased resistance to cyclophosphamide chemotherapy after chimeric receptor activation. We propose that the differential benefit seen with doxorubicin- versus alkylator-based chemotherapy in ErbB2+ breast cancer is due, in some cases, to ErbB2-mediated topo IIalpha activation. These data also suggest hypotheses for the optimal sequencing of Herceptin and chemotherapy agents in ErbB2+ breast cancer.

Camptothecin analogues with enhanced antitumor activity at acidic pH

BACKGROUND

Camptothecin (CPT) is a specific inhibitor of the nuclear enzyme topoisomerase I, which is involved in cellular DNA replication and transcription. Topoisomerase I is therefore an attractive target for anticancer drug development, and two analogues of CPT, topotecan (TPT) and irinotecan (CPT-11), have demonstrated significant antitumor activity in the clinic. This activity is limited, however, by lability of the CPT E ring lactone, which forms the inactive hydroxy acid at physiological pH. The reaction is reversible at acidic pH, which provides a rationale for selectivity, because many solid tumors create an acidic extracellular environment while maintaining a normal intracellular pH.

PURPOSE

To exploit the tumor-selective pH gradient to improve the efficacy of CPT-based chemotherapy.

METHODS

CPT analogues were evaluated by growth inhibition assay in three human breast cancer cell lines that had been adapted to in vitro culture at acidic pH versus the respective cells cultured at physiological pH. The MCF-7, MDA-MB-231, and MCF-7/hc cell lines represent the hormone-dependent and hormone-independent stages of the disease, and a MCF-7 variant that is resistant to the alkylating agent 4-hydroperoxycyclophosphamide (4-HC), respectively. Antiproliferative activity of SN-38 (the active metabolite of CPT-11), and TPT was compared to that of CPT and two CPT analogues, 10,11-methylenedioxy-CPT (MDC), and the alkylating derivative, 7-chloromethyl-10,11-MDC (CMMDC).

RESULTS

In general, MDC was the most potent and TPT or CPT the least potent analogue, regardless of pH. However, if the comparison was based on magnitude of potentiation by pH, a different rank order emerged. CPT was modulated 4-fold; MDC, SN-38, and TPT were each modulated 5- to 6-fold, while the activity of CMMDC was increased 10- to 11-fold by acidic pH in MCF-7 lines, and 65-fold in MDA-MB-231 cells. Thus MDC was the superior CPT analogue based on potency, but CMMDC was the best candidate for pH modulation. Drug specificity was also observed. While the alkylating agent, 4-HC, was 2- to 3-fold more active at acidic pH, modulation was not observed for 5-fluorouracil, doxorubicin, or paclitaxel. Preliminary mechanism studies indicated that pH modulation of CPT analogues was directly correlated to intracellular levels of glutathione. In addition, protein-associated DNA strand breaks were more rapidly induced at acidic pH.

CONCLUSION

These results suggest that CPT-based drug development and resulting chemotherapy could benefit from evaluation of differential activity at acidic versus physiological pH. Analogues have been identified that could have improved therapeutic indices based on the pH gradient that selectively exists in human tumors.

Evidence for a role of chloroethylaziridine in the cytotoxicity of cyclophosphamide

A number of investigators have observed that the use of 4-hydroperoxycyclophosphamide (4-HC) in multiwell plate cytotoxicity assays can be associated with toxicity to cells in wells that contain no drug. Previous reports have implicated diffusion of 4-HC decomposition products, and acrolein in particular, as the active species.

PURPOSE

The purpose of this study was to elucidate the species responsible for the airborne cytotoxicity of 4-HC, and to devise ways to minimize such effects in chemosensitivity assays.

METHODS

To this end, analogues of 4-HC were synthesized to identify the contributions of individual cyclophosphamide metabolites to cytotoxicity. The analogues were then tested for activity against three human breast tumor cell lines (including a line resistant to 4-HC), and one non-small-cell lung carcinoma line. Cytotoxicity was evaluated by assays that quantitate cellular metabolism and nucleic acid content.

RESULTS

Didechloro-4-hydroperoxycyclophosphamide, a compound that generates acrolein and a nontoxic analogue of phosphoramide mustard, gave no cross-well toxicity. In contrast, a significant neighboring well effect was observed with phenylketophosphamide, a compound that generates phosphoramide mustard but not acrolein. Addition of authentic chloroethylaziridine reproduced the airborne toxicity patterns generated by 4-HC and phenylketophosphamide. Increasing the buffering capacity of the growth medium and sealing the microtiter plates prevented airborne cytotoxicity.

CONCLUSION

Since it is unlikely that phosphoramide mustard is volatile, these findings implicate chloroethylaziridine rather than acrolein as the volatile metabolite of 4-HC that is responsible for airborne cytotoxicity. The fact that chloroethylaziridine is generated in amounts sufficient to volatilize, diffuse across wells and cause cytotoxicity indicates that it is an important component in the overall cytotoxicity of 4-HC in vitro. Furthermore, these findings suggest that chloroethylaziridine may also contribute to the toxicity of cyclophosphamide in vivo.

Intraneoplastic polymer-based delivery of cyclophosphamide for intratumoral bioconversion by a replicating oncolytic viral vector

rRp450 is an oncolytic herpesvirus that expresses the CYP2B1 cDNA, responsible for bioconverting cyclophosphamide (CPA) into the active metabolites 4-hydroxyCPA/aldophosphamide (AP). However, formal proof of prodrug activation is lacking. We report that activation of CPA in cells infected with rRp450 generates a time-dependent increase of diffusible 4-hydroxyCPA/AP. For in vivo applications, a CPA-impregnated polymer was implanted into human tumor xenografts inoculated with rRp450. The area under the curve for 4-hydroxyCPA/AP was 806 microg/g of tumor tissue/h when CPA was administered via intraneoplastic polymer and 3 microg/g of tumor tissue/h when CPA was administered i.p. Therefore, (a) a lytic virus expressing a "suicide" gene can activate a prodrug; and (b) within rRp450-infected tumor, more prolonged and higher concentrations of activated metabolites are generated by intraneoplastic compared with systemic administration of prodrug.

Efficacy of liposomes and hyperthermia in a human tumor xenograft model: importance of triggered drug release

The tumor drug concentrations, drug distributions, and therapeutic efficacies achieved by three fundamentally different liposomes, nonthermosensitive liposome (NTSL), traditional thermosensitive liposome (TTSL), and low temperature sensitive liposome (LTSL); free doxorubicin (DOX); and saline in combination with hyperthermia (HT) were directly compared in a human tumor xenograft model. NTSL is a nonthermosensitive liposome in the physiological temperature range, TTSL is a traditional thermosensitive liposome that triggers in the range of approximately 42-45 degrees C and releases drug over approximately 30 min, and LTSL is a new low temperature sensitive liposome that triggers in the range of approximately 39-40 degrees C and releases drug in a matter of seconds. Because of the different attributes of the liposomes, it was possible to delineate the relative importance of liposome drug encapsulation, HT cytotoxicity, HT-drug interaction, HT-induced liposomal delivery, and HT-triggered liposomal drug release in achieving antitumor activity. Athymic nude mice bearing the FaDu human tumor xenograft were given a single i.v. dose of 5 mg/kg of DOX (free drug or liposome encapsulated), and the tumors were then heated to either 34 degrees C or 42 degrees C for 1 h at 34 degrees C. All treatment groups were similar, achieving low concentrations of DOX (0-4.5 ng/mg). At 42 degrees C, the LTSL (25.6 ng/mg) achieved the highest DOX concentration (P < 0.04), but all three liposomal formulations (7.3-25.6 ng/mg) were higher than saline or DOX (0-0.7 ng/mg; P < 0.02). LTSL + HT was also the only group that resulted in significant amounts of DNA-bound DOX (silver nitrate-extractable fraction; P < 0.02). Tumor tissue sections were visualized for DOX fluorescence to investigate the local distribution of the drug in the tumor and confirm the relative drug concentrations based on fluorescence intensity. There was relatively little fluorescence seen with treatment groups at 34 degrees C. At 42 degrees C, the LTSL showed the most DOX fluorescence (P < 0.01), and the fluorescence, although not homogeneous, was pervasive throughout the tumor sections. Therapeutic efficacy of treatments was determined from tumor growth time. At 34 degrees C, the only treatment group significantly better than the saline group (9.8 days) was the NTSL group, with a growth time of 20.9 days (P < 0.02). At 42 degrees C, all three liposomal formulations were more efficacious than DOX. LTSL + HT had the longest growth time (51.4 days) and the most number of local controls at 60 days (six of nine tumors). With HT, the DOX concentrations and fluorescence were tightly correlated with tumor growth delay, indicating that adequate (increased) drug delivery can be predictive of therapeutic effect. Overall, the LTSL + HT group showed the largest DOX concentration, the highest and most pervasive DOX fluorescence, and the most antitumor effect. Thus, HT-triggered liposomal drug release may account for the largest differential therapeutic effect and demonstrates the importance of rapid drug release from the drug carriers at the tumor site.

Phase I trial of carmustine plus O6-benzylguanine for patients with recurrent or progressive malignant glioma

PURPOSE

The major mechanism of resistance to alkylnitrosourea therapy involves the DNA repair protein O(6)-alkylguanine-DNA alkyltransferase (AGT), which removes chloroethylation or methylation damage from the O(6) position of guanine. O(6)-benzylguanine (O(6)-BG) is an AGT substrate that inhibits AGT by suicide inactivation. We conducted a phase I trial of carmustine (BCNU) plus O(6)-BG to define the toxicity and maximum-tolerated dose (MTD) of BCNU in conjunction with the preadministration of O(6)-BG with recurrent or progressive malignant glioma.

PATIENTS AND METHODS

Patients were treated with O(6)-BG at a dose of 100 mg/m(2) followed 1 hour later by BCNU. Cohorts of three to six patients were treated with escalating doses of BCNU, and patients were observed for at least 6 weeks before being considered assessable for toxicity. Plasma samples were collected and analyzed for O(6)-BG, 8-oxo-O(6)-BG, and 8-oxoguanine concentration.

RESULTS

Twenty-three patients were treated (22 with glioblastoma multiforme and one with anaplastic astrocytoma). Four dose levels of BCNU (13.5, 27, 40, and 55 mg/m(2)) were evaluated, with the highest dose level being complicated by grade 3 or 4 thrombocytopenia and neutropenia. O(6)-BG rapidly disappeared from plasma (elimination half-life = 0. 54 +/- 0.14 hours) and was converted to a longer-lived metabolite, 8-oxo-O(6)-BG (elimination half-life = 5.6 +/- 2.7 hours) and further to 8-oxoguanine. There was no detectable O(6)-BG 5 hours after the start of the O(6)-BG infusion; however, 8-oxo-O(6)-BG and 8-oxoguanine concentrations were detected 25 hours after O(6)-BG infusion. The mean area under the concentration-time curve (AUC) of 8-oxo-O(6)-BG was 17.5 times greater than the mean AUC for O(6)-BG.

CONCLUSION

These results indicate that the MTD of BCNU when given in combination with O(6)-BG at a dose of 100 mg/m(2) is 40 mg/m(2) administered at 6-week intervals. This study provides the foundation for a phase II trial of O(6)-BG plus BCNU in nitrosourea-resistant malignant glioma.

Intrathecal busulfan treatment of human neoplastic meningitis in athymic nude rats

The current study was designed to evaluate the toxicity and activity of Spartaject Busulfan, a microcrystalline preparation of busulfan, following its intrathecal administration into a nude rat model of human neoplastic meningitis. Animals were treated through permanent indwelling subarachnoid catheters. Human glioma D-456 MG growing in the subarachnoid space was treated with 8.1 micromol of intrathecal Spartaject Busulfan. Single-dose therapy was also subsequently compared with 4 doses of 8.1 and 2.0 micromol busulfan, respectively, against D-456 MG neoplastic meningitis. Additional experiments evaluated a saline control versus 8.1 micromol x 1, 6.2 micromol x 4 and 4.1 micromol x 4, respectively, against D-456 MG. A single dose of 8.1 micromol of intrathecal Spartaject Busulfan resulted in an increase in median survival of 61.7% compared with the saline control. In experiment 2, all busulfan treatments showed increases in median survival of 142.8% (8.1 micromol x 1), 52.3% (2.0 micromol x 4), and 23% (8.1 micromol x 4) (p < 0.001 for all groups) compared with the saline control. These results suggest that a narrow therapeutic dose range for both toxicity and activity has been defined for intrathecal busulfan in the treatment of human neoplastic meningitis in athymic nude rats. Although busulfan has only limited activity against solid tumors, the high doses achievable in the CSF following intrathecal administration coupled with the steep dose-response relationships of alkylating agents, provide rationale for further evaluation of this agent.

Pre-clinical evaluation of SN-38 and novel camptothecin analogs against human chronic B-cell lymphocytic leukemia lymphocytes

The topoisomerase I inhibitor camptothecin and its analogs have potent activity against a wide range of solid tumors and several hematologic malignancies. Previous studies with these compounds using the MTT metabolic inhibition assay have shown significant cytotoxicity against lymphocytes from patients with chronic B-cell lymphocytic leukemia (B-CLL). Yet the water soluble analogue, topotecan, which was inhibitory at > 1 microM in vitro, had no clinical activity in vivo. In the present study, we evaluated the in vitro cytotoxicities of SN-38, the active form of irinotecan, and two newer water soluble camptothecin derivatives 10,11-methylenedioxy-20(S)-camptothecin glycinate (MDCG) and 7-chloromethyl-10,11-methylenedioxy-20(S)-camptothecin glycinate (CMMDCG). These two glycinate esters are prodrugs for 10,11-methylenedioxy-20(S)-camptothecin (MDC) and 7-chloromethyl-10,11-methylenedioxy-20(S)-camptothecin (CMMDC), respectively. Effects on cellular metabolism, induction of apoptosis, and overall cell survival were used to evaluate chemosensitivity. We report that the relative cytotoxic potency for these compounds is MDC > or = CMMDC > or = SN-38 >> TPT > CPT-11, where MDC, CMMDC, and SN-38 were over an order of magnitude more cytotoxic than TPT and CPT-11. We also investigated potential mechanisms underlying the unexpected cytotoxicity of these camptothecin derivatives in B-CLL cells that are known to be arrested in G0/G1 of the cell cycle, and found that this class of compounds inhibited [3H]uridine incorporation. We therefore postulate that the inhibition of RNA rather than DNA synthesis may be responsible for the observed cytotoxicity in non-cycling B-CLL cells.

Isolation of primitive human hematopoietic progenitors on the basis of aldehyde dehydrogenase activity

Because hematopoietic stem cells are rich in aldehyde dehydrogenase (ALDH) activity, we developed a fluorescent substrate for ALDH, termed BODIPY aminoacetaldehyde (BAAA), and tested its potential for isolating primitive human hematopoietic cells. A population of cells with low orthogonal light scattering and bright fluorescence intensity (SSC(lo)ALDH(br) cells) could be readily fractionated from human umbilical cord blood cells costained with BAAA and the multidrug-resistance inhibitor verapamil. The SSC(lo)ALDH(br) population was depleted of lineage-committed cells, 40-90% pure for CD34(+)CD38(lo/-) cells, and enriched 50- to 100-fold for primitive hematopoietic progenitors detected in short- and long-term culture analyses. Together, these observations indicate that fractionating human hematopoietic stem cells on the basis of ALDH activity using BAAA is an effective method for isolating primitive human hematopoietic progenitors. This technique may be useful for isolating stem cells from other tissues as well.

An overview of cyclophosphamide development and clinical applications

In this overview of the pharmacology of the anticancer drug cyclophosphamide, a brief history of the development of this drug from the general class of nitrogen mustards is provided. The antitumor activity of cyclophosphamide and its isomer ifosfamide is discussed through considerations of metabolism, resistance, detoxification, and DNA cross-linking. Clinical uses in general chemotherapy, bone marrow transplantation and immunosuppression are presented. A review with 73 references.

Irinotecan therapy in adults with recurrent or progressive malignant glioma

PURPOSE

To determine the activity, toxicity, and pharmacokinetics of irinotecan (CPT-11, Camptosar; Pharmacia & Upjohn, Kalamazoo, MI) in the treatment of adults with progressive, persistent, or recurrent malignant glioma.

PATIENTS AND METHODS

Patients with progressive or recurrent malignant gliomas were enrolled onto this study between October 1996 and August 1997. CPT-11 was given as a 90-minute intravenous (i.v.) infusion at a dose of 125 mg/m2 once weekly for 4 weeks followed by a 2-week rest, which comprised one course. Plasma concentrations of CPT-11 and its metabolites, SN-38 and SN-38 glucuronide (SN-38G), were determined in a subset of patients.

RESULTS

All 60 patients who enrolled (36 males and 24 females) were treated with CPT-11 and all were assessable for toxicity, response, and survival. Pharmacokinetic data were available in 32 patients. Nine patients (15%; 95% confidence interval, 6% to 24%) had a confirmed partial response, and 33 patients (55%) achieved stable disease lasting more than two courses (12 weeks). Toxicity observed during the study was limited to infrequent neutropenia, nausea, vomiting, and diarrhea. CPT-11, SN-38, and SN-38G area under the plasma concentration-time curves through infinite time values in these patients were approximately 40%, 25%, and 25%, respectively, of those determined previously in patients with metastatic colorectal cancer not receiving antiepileptics or chronic dexamethasone treatment.

CONCLUSION

Response results document that CPT-11, given with a standard starting dose and treatment schedule, has activity in patients with recurrent malignant glioma. However, the low incidence of severe toxicity and low plasma concentrations of CPT-11 and SN-38 achieved in this patient population suggest that concurrent treatment with anticonvulsants and dexamethasone enhances drug clearance.

Modulation of cyclophosphamide activity by O6-alkylguanine-DNA alkyltransferase

PURPOSE

The human medulloblastoma cell line D283 Med (4-HCR), a line resistant to 4-hydroperoxycyclophosphamide (4-HC), displays enhanced repair of DNA interstrand crosslinks induced by phosphoramide mustard. D283 Med (4-HCR) cells are cross-resistant to 1,3-bis(2-chloroethyl)- -nitrosourea, but partial sensitivity is restored after elevated levels of O6-alkylguanine-DNA alkyltransferase (AGT) are depleted by O6-benzylguanine (O6-BG). Studies were conducted to define the activity of 4-HC and 4-hydroperoxydidechlorocyclophosphamide against D283 Med (4-HCR) after AGT is depleted by O6-BG.

METHODS

Limiting dilution and xenograft studies were conducted to define the activity of 4-HC and 4-hydroperoxydidechlorocyclophosphamide with or without O6-BG.

RESULTS

The activity of 4-HC and 4-hydroperoxydidechlorocyclophosphamide against D283 Med (4-HCR) was increased after AGT depletion by O6-BG preincubation. Similar studies with Chinese hamster ovary cells, with or without stable transfection with a plasmid expressing the human AGT protein, revealed that the AGT-expressing cells were significantly less sensitive to 4-HC and 4-hydroperoxydidechlorocyclophosphamide. Reaction of DNA with 4-HC, phosphoramide mustard, or acrolein revealed that only 4-HC and acrolein caused a decrease in AGT levels.

CONCLUSIONS

We propose that a small but potentially significant part of the cellular toxicity of cyclophosphamide in these cells is due to acrolein, and that this toxicity is abrogated by removal of the acrolein adduct from DNA by AGT.

Multiple DNA repair mechanisms and alkylator resistance in the human medulloblastoma cell line D-283 Med (4-HCR)

PURPOSE

We have previously reported preferential repair of DNA interstrand crosslinks in the 4-hydroperoxycyclophosphamide-resistant human medulloblastoma cell line D-283 Med (4-HCR). We now report further studies that explored the potential mechanisms underlying this repair.

METHODS

Limiting dilution assays and Western, Southern, and Northern blots were used to compare specific differences between D-283 Med (4-HCR) and its parental line D-283 Med.

RESULTS

D-283 Med (4-HCR) was cross-resistant to melphalan and 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), with O6-alkylguanine-DNA alkyltransferase (AGT) levels of 466+/-164 fmol/mg protein; AGT levels in the parental line, D-283 Med, were 76+/-96 fmol/mg. The increase in AGT activity was not a result of gene amplification. Depleting AGT with O6-benzylguanine partially restored sensitivity to BCNU. Both cell lines were deficient in the human mismatch protein MutLalpha. ERCC4 mRNA and poly(ADP-ribose) polymerase levels were similar in both cell lines, and ERCC1 mRNA levels were 2- to 2.5-fold lower in D-283 Med (4-HCR). Topoisomerase I levels were 2- to 2.5-fold higher in D-283 Med compared with D-283 Med (4-HCR).

CONCLUSION

These results, while illustrating the multiple differences between D-283 Med and D-283 Med (4-HCR), do not explain the enhanced DNA interstrand crosslink repair seen in D-283 Med (4-HCR).

DNA mismatch repair and O6-alkylguanine-DNA alkyltransferase analysis and response to Temodal in newly diagnosed malignant glioma

PURPOSE

We evaluated the response to Temodal (Schering-Plough Research Institute, Kenilworth, NJ) of patients with newly diagnosed malignant glioma, as well as the predictive value of quantifying tumor DNA mismatch repair activity and O6-alkylguanine-DNA alkyltransferase (AGT).

PATIENTS AND METHODS

Thirty-three patients with newly diagnosed glioblastoma multiforme (GBM) and five patients with newly diagnosed anaplastic astrocytoma (AA) were treated with Temodal at a starting dose of 200 mg/m2 daily for 5 consecutive days with repeat dosing every 28 days after the first daily dose. Immunochemistry for the detection of the human DNA mismatch repair proteins MSH2 and MLH1 and the DNA repair protein AGT was performed with monoclonal antibodies and characterized with respect to percent positive staining.

RESULTS

Of the 33 patients with GBM, complete responses (CRs) occurred in three patients, partial responses (PRs) occurred in 14 patients, stable disease (SD) was seen in four patients, and 12 patients developed progressive disease (PD). Toxicity included infrequent grades 3 and 4 myelosuppression, constipation, nausea, and headache. Thirty tumors showed greater than 60% cells that stained for MSH2 and MLH1, with three CRs, 12 PRs, three SDs, and 12 PDs. Eight tumors showed 60% or less cells that stained with antibodies to MSH2 and/or MLH1, with 3 PRs, 3 SDs, and 2 PDs. Eleven tumors showed 20% or greater cells that stained with an antibody to AGT, with 1 PR, 2 SDs, and 8 PDs. Twenty-five tumors showed less than 20% cells that stained for AGT, with 3 CRs, 12 PRs, 4 SDs, and 6 PDs.

CONCLUSION

These results suggest that Temodal has activity against newly diagnosed GBM and AA and warrants continued evaluation of this agent. Furthermore, pretherapy analysis of tumor DNA mismatch repair and, particularly, AGT protein expression may identify patients in whom tumors are resistant to Temodal.

Therapeutic efficacy of vinorelbine against pediatric and adult central nervous system tumors

PURPOSE

The activity of vinorellbine, a new semisynthetic vinca alkaloid, was evaluated against a battery of human tumor xenografts derived from adult and pediatric CNS malignancies.

METHODS

Tumors included adult high-grade gliomas (D-54 MG, D-245 MG), childhood high-grade gliomas (D-212 MG, D-456 MG), medulloblastomas (D-341 MED, D-487 MED), ependymomas (D-612 EP, D-528 EP), and a mismatch repair-deficient procarbazine-resistant glioma [D-245 MG (PR)]. Tumors were grown subcutaneously in athymic nude mice and vinorelbine was administered at a dose of 11 mg/kg on days 1, 5, and 9. Additionally, vinorelbine was also administered in combination with BCNU against D-54 MG.

RESULTS

Vinorelbine produced statistically significant growth delays in D-456 MG, D-245 MG, and D-245 MG (PR). No statistically significant growth delays were observed in D-54 MG, D-487 MED, D-212 MG, D-528 EP, D-341 MED or D-612 EP. The antitumor effects of the vinorelbine/BCNU combination were additive. Growth delays observed in the procarbazine-resistant line [D-245 MG (PR)] were greater than twofold the delays seen in the parent line (D-245 MG). Vincristine was equally potent against D-245 MG and D-245 MG (PR). Taxol demonstrated little activity against D-245 MG but produced 32- and 18-day growth delays in D245 MG (PR).

CONCLUSIONS

These studies indicate that vinorelbine possesses antitumor activity against several glioma tumor xenografts with marked activity in a mismatch repair deficient-tumor.

Enhancement of irinotecan (CPT-11) activity against central nervous system tumor xenografts by alkylating agents

Two major obstacles in the treatment of patients with central nervous system malignancies are drug resistance and host toxicity. The goal of combination chemotherapy is to achieve therapeutic effects that are more favorable than using a single drug alone, but without an increase in normal organ toxicity. The study reported here examined the combination of a topoisomerase I inhibitor, irinotecan (CPT-11), with three different alkylating agents: 1,3-bis(2-chloroethyl)-1-nitrosourea, busulfan, and cyclophosphamide. We evaluated the antitumor effects of these three combinations against a panel of human tumor xenografts derived from central nervous system malignancies, including adult high-grade gliomas (D-54 MG, D-245 MG) and a childhood ependymoma (D-612 EP). In replicate experiments, the alkylating agents were given on day 1 in doses varying from 10% to 75% of the dose lethal to 10% of the animals, and CPT-11 was given on days 1-5 and 8-12 in doses varying from 10% to 100% of the dose lethal to 10% of the animals. The antitumor effects of the various combinations ranged from less than additive (7.61 days below additive with 0.5 CPT-11 + 0.75 cyclophosphamide in D-54 MG) to statistically significant (P < 0.001) supraadditive effects (18.80 days above additive with 0.5 CPT-11 + 0.5 1,3-bis(2-chloroethyl)-1-nitrosourea in D-54 MG). These studies show that the combination of the topoisomerase inhibitor CPT-11 and alkylating agents may increase the antitumor effect in some cases well above additive with no increase in host toxicity (0/10 deaths in both experiments cited above) and should be considered for combination chemotherapy of central nervous system malignancies.

Pharmacokinetics of interstitial delivery of carmustine, 4-hydroperoxycyclophosphamide, and paclitaxel from a biodegradable polymer implant in the monkey brain

Polymeric interstitial chemotherapy increases survival of humans with recurrent gliomas and animals with transplanted tumors in the brain, but the relationship between rates of drug release from polymer implants and drug concentration in brain tissue is unknown. This work presents a pharmacokinetic framework for application of this new modality of chemotherapy delivery in primates. Either [3H]carmustine, 4-hydroperoxycyclophosphamide (4-HC), or paclitaxel was encapsulated in a polyanhydride pellet (28-41 microCi/animal, 40 mg/animal), which was implanted intracranially in cynomolgus monkeys (Macaca fascicularis); (n = 17) for up to 30 days. Drug concentrations in the brain, blood, and cerebrospinal fluid were measured by quantitative autoradiography, TLC, and scintillation counting. High drug concentrations (0.5-3.5 mM for carmustine, 0.3-0.4 mM for 4-HC, and 0.2-1.0 mM for paclitaxel) were measured within the first 3 mm from the polymer implant; significant (0.4 microM for carmustine, 3 microM for 4-HC, and 0.6 microM for paclitaxel) concentrations were measured up to approximately 5 cm from the implant as long as 30 days after implantation. Pharmacokinetic analysis indicated that tissue exposure to carmustine area under concentration-time curve achieved by polymeric delivery was 4-1200 times higher than that produced by i.v. administration of a higher dose.

The partitioning of phosphoramide mustard and its aziridinium ions among alkylation and P-N bond hydrolysis reactions

NMR (1H and 31P) and HPLC techniques were used to study the partitioning of phosphoramide mustard (PM) and its aziridinium ions among alkylation and P-N bond hydrolysis reactions as a function of the concentration and strength of added nucleophiles at 37 degrees C and pH 7.4. With water as the nucleophile, bisalkylation accounted for only 10-13% of the product distribution given by PM. The remainder of the products resulted from P-N bond hydrolysis reactions. With 50 mM thiosulfate or 55-110 mM glutathione (GSH), bisalkylation by a strong nucleophile increased to 55-76%. The rest of the PM was lost to either HOH alkylation or P-N bond hydrolysis reactions. Strong experimental and theoretical evidence was obtained to support the hypothesis that the P-N bond scission observed at neutral pH does not occur in the parent PM to produce nornitrogen mustard; rather it is an aziridinium ion derived from PM which undergoes P-N bond hydrolysis to give chloroethylaziridine. In every buffer studied (bis-Tris, lutidine, triethanolamine, and Tris), the decomposition of PM (with and without GSH) gave rise to 31P NMR signals which could not be attributed to products of HOH or GSH alkylation or P-N bond hydrolysis. The intensities of these unidentified signals were dependent on the concentration of buffer.

Activity of high-dose cyclophosphamide in the treatment of childhood malignant gliomas

Seventeen patients less than or equal to 20 years of age with newly diagnosed (n = 10) or recurrent (n = 7) malignant gliomas (anaplastic astrocytoma and glioblastoma multiforme) were treated with cyclophosphamide in association with hematopoietic cytokines (GM-CSF or G-CSF). Cyclophosphamide was given at a dose of 2 g/m2 daily for 2 days at 4-week intervals. Toxicity consisted of grade IV neutropenia and thrombocytopenia in 95% and 48% of cycles, respectively. There were no cyclophosphamide-related cardiac, pulmonary, or urothelial toxicities observed. Four of 10 patients with newly diagnosed disease demonstrated responses (three complete and one partial responses; one CR was only of 2 months duration). None of the seven patients with recurrent tumors demonstrated a response. We conclude that high-dose cyclophosphamide warrants further evaluation in children with newly diagnosed malignant glioma.

Drug resistance in the treatment of sarcomas

The antineoplastic action and development of drug resistance are reviewed for chemotherapeutic agents used in the treatment of sarcoma, including alkylating agents (cyclophosphamide, ifosphamide, dacarbazine), platinum compounds (cisplatin, carboplatin), the anthracycline compound doxorubicin, the topoisomerase II inhibitor etoposide, and the taxanes (paclitaxel, taxotere). Drug resistance mechanisms discussed include changes in intracellular glutathione and metallothione levels, increased aldehyde dehydrogenase levels, enhanced DNA repair and protection from apoptosis (for alkylating agents); increased 0-6 alkyltranferase levels (for dacarbazine); multidrug resistance 1- and multidrug resistance associated protein-mediated drug export from cells (anthracyclines, taxanes); and structural alteration of microtubules (taxanes).

Methylator resistance mediated by mismatch repair deficiency in a glioblastoma multiforme xenograft

A methylator-resistant human glioblastoma multiforme xenograft, D-245 MG (PR), in athymic nude mice was established by serially treating the parent xenograft D-245 MG with procarbazine. D-245 MG xenografts were sensitive to procarbazine, temozolomide, N-methyl-N-nitrosourea, 1,3-bis(2-chloroethyl)-1-nitrosourea, 9-aminocamptothecin, topotecan, CPT-11, cyclophosphamide, and busulfan. D-245 MG (PR) xenografts were resistant to procarbazine, temozolomide, N-methyl-N-nitrosourea, and busulfan, but they were sensitive to the other agents. Both D-245 MG and D-245 MG (PR) xenografts displayed no O6-alkylguanine-DNA alkyltransferase activity, and their levels of glutathione and glutathione-S-transferase were similar. D-245 MG xenografts expressed the human mismatch repair proteins hMSH2 and hMLH1, whereas D-245 MG (PR) expressed hMLH1 but not hMSH2.

Nonlinear pharmacokinetics of cyclophosphamide and 4-hydroxycyclophosphamide/aldophosphamide in patients with metastatic breast cancer receiving high-dose chemotherapy followed by autologous bone marrow transplantation

The pharmacokinetics of cyclophosphamide and 4-hydroxycyclophosphamide/aldophosphamide has been evaluated in 12 patients with metastatic breast cancer undergoing high-dose chemotherapy followed by bone marrow transplantation. Each patient received an initial dose of 4 g/m2 of cyclophosphamide over 90 min to prime peripheral blood progenitor cells (the first course), and 3 weeks later, 6 g/m2 of cyclophosphamide with 800 mg/m2 of thiotepa by 96-hr infusion before marrow stem cell infusion (the second course). Whole blood cyclophosphamide and 4-hydroxycyclophosphamide/aldophosphamide concentrations were measured by a GC-EIMS method using deuterium labeled compounds as internal standards. In addition, plasma and urine cyclophosphamide concentrations were determined by a GC assay. Whole blood concentrations of cyclophosphamide and 4-hydroxycyclophosphamide/aldophosphamide vs. time data and urinary excretion of cyclophosphamide data from the first course were co-modeled using a one-compartment model with Michaelis-Menten saturable elimination in parallel with first-order renal elimination (N = 7) or first-order metabolic and renal elimination (N = 5) for cyclophosphamide and one-compartment model with first-order elimination for 4-hydroxycyclophosphamide/aldophosphamide. The parallelism between cyclophosphamide and 4-hydroxycyclophosphamide/aldophosphamide disposition curves implies that the pharmacokinetics of 4-hydroxycyclophosphamide/aldophosphamide is formation limited; only the fractional 4-hydroxycyclophosphamide/ aldophosphamide clearance rate (Clmet/Fmet) can be estimated. The mean Vmax and Km for cyclophosphamide were 0.78 microM/min and 247 microM, respectively. The mean nonrenal clearance (Clnr) of cyclophosphamide for five patients with apparent first-order elimination of cyclophosphamide was 67 ml/min. The mean Clmet/Fmet of 4-hydroxycyclophosphamide/aldophosphamide was 2982 ml/min. The mean renal clearance (Clr) of cyclophosphamide was 29 ml/min and 24 ml/min for the first course and the second course, respectively. The correlations between cyclophosphamide AUCs and 4-hydroxycyclophosphamide/aldophosphamide AUCs were sought for both drug courses. Blood and plasma cyclophosphamide concentrations were remarkably similar, indicating that cyclophosphamide partitions equally in the red cell and plasma volume. Computer simulation of the effect of potential alterations in Michaelis-Menten saturable elimination and renal clearance on 4-hydroxycyclophosphamide/aldophosphamide has been used to illustrate the complex relationship between the exposure to parent compound and active metabolite.

Characterization of the mechanisms of busulfan resistance in a human glioblastoma multiforme xenograft

Busulfan is an alkylating agent commonly used in the treatment of chronic myelogenous leukemia and in combination with cyclophosphamide in preparation for allogeneic bone marrow transplantation. Serial treatment of a childhood high-grade glioma xenograft (D-456 MG) with busulfan resulted in a busulfan-resistant xenograft, D-456 MG(BR). Cross-resistance to 1,3-bis(2-chloroethyl)-1-nitrosourea was seen but not resistance to cyclophosphamide or CPT-11. Cytoplasmic levels of glutathione in D-456 MG(BR) were approximately one-half those found in D-456 MG. This depletion could not be explained by levels of glutathione-S-transferase, or by amplification, rearrangement, or increased levels of transcript of gamma-glutamylcysteine synthetase. Furthermore, depletion of glutathione in D-456 MG did not alter busulfan activity. Quantitation of busulfan levels in D-456 MG and D-456 MG(BR) xenografts following treatment of mice at the dose lethal to 10% of the animals demonstrated that significantly lower levels of drug were achieved in D-456 MG(BR). These studies suggest that alterations in drug transport or metabolism of busulfan may play a role in the resistance of D-456 MG(BR) to this alkylator.

Predicted and actual BCNU concentrations in normal rabbit brain during intraarterial and intravenous infusions

Normal New Zealand White rabbits were used to compare theoretical brain concentrations (based upon pharmacokinetic modeling) with actual experimental concentrations of BCNU following intraarterial (IA) or intravenous (IV) infusions. IA infusion therapy for brain tumor patients has been promising based upon theoretical predictions but of limited effectiveness clinically. Experimentally-measured rabbit carotid artery flow rates (63.9 +/- 3.4 ml/min) [mean +/- 1 sem] and BCNU systemic clearances (197 +/- 10.2 ml/min) predicted a theoretical IA advantage of 4.1 +/- 0.2. Ipsilateral brain concentrations of BCNU during and after IA infusions (20 mg/min/m2 over 15 minutes) were: 16.2 +/- 2.9, 19.0 +/- 3.9, 20.3 +/- 2.8, 4.8 +/- 2.5, 2.1 +/- 1.5, and 1.7 +/- 1.6 micrograms/gm brain at 5, 10, 15, 25, 35, and 45 minutes after infusion start. Mean concentrations at same time points in contralateral hemisphere (IA infusions) were: 7.1 +/- 1.8, 9.0 +/- 1.8, 10.3 +/- 0.7, 4.2 +/- 1.4, 2.2 +/- 1.2, 2.0 +/- 1.5 micrograms/gm brain. Concentrations in either hemisphere during IV infusions were similar to contralateral hemisphere during IA infusions. Comparison of ipsilateral: contralateral hemisphere ratios during and after IA infusions were: 3.2 +/- 0.4, 2.6 +/- 0.3, 2.2 +/- 0.3, 1.1 +/- 0.3, 1.0 +/- 0.4, and 0.9 +/- 0.3 at the same time points. Although these data show higher drug concentrations with IA infusions, actual values were considerably less than predicted by theoretical modeling. This discrepancy between theoretical and experimental results emphasizes need for further study of causes and remedies so that IA therapy can achieve better drug concentrations with less toxicity.

Cyclophosphamide and 4-Hydroxycyclophosphamide/aldophosphamide kinetics in patients receiving high-dose cyclophosphamide chemotherapy

Using a recently developed gas chromatography and mass spectrometry method to determine whole-blood cyclophosphamide (CP) and 4-hydroxycyclophosphamide/aldophosphamide (4-HO-CP/AP) concentrations, we investigated their pharmacokinetics in women receiving CP therapy. Patients (n = 18) received one or two courses of CP: (a) a 90-min i.v. infusion (4 g/m2) followed by a 96-h i.v. infusion (6 g/m2) in combination with high-dose thiotepa; or (b) a 96-h i.v. infusion (6 g/m2) in combination with high-dose thiotepa. Whole-blood exposures to CP [area under the whole blood concentration versus time curve (AUCCP)] and 4-HO-CP/AP (AUC4HOCP) between courses 1 and 2 were compared after normalization to dose (g/m2). A nonproportional increase was observed for the AUCCP between the first course [1112 micrometer. h/g/m2 +/- 14% coefficient of variation (CV)] and the second course (1579 micrometer . h/g/m2 +/- 28% CV) (P < 0.001). In contrast, the AUC4HOCP (27 micrometer . h/g/m2 +/- 25% CV) determined for the first course was 29% higher than the AUC4HOCP (21 micrometer . h/g/m2 +/- 26% CV) for the second course (P < 0.01). The interpatient whole-blood exposures to both CP and 4-HO-CP/AP were remarkably consistent in this patient population with percent CVs ranging from 14 to 28%. Because thiotepa (800 mg/m2) was administered simultaneously with CP during the second course of treatment, possible inhibition of CP metabolism by thiotepa was investigated using human liver microsomes in vitro. IC50 values determined for inhibition of CP metabolism in three individual liver donors ranged from 1.0 to 40 micrometer. However, the clinical relevance of this observation has not been established.

Characterization of mouse lymphohematopoietic stem cells lacking spleen colony-forming activity

The classical definition of lymphohematopoietic stem cells (LHSC), the most primitive progenitors of all blood cells, requires that they have the capacity for self-renewal and for the long-term production of all blood cell lineages. However, other characteristics of LHSC have been debated. Our previous data suggested that mouse LHSC are very slowly proliferating cells that generate delayed multilineage engraftment, while "radioprotection" (rapid engraftment that will prevent early death from radiation-induced marrow aplasia) results from more committed progenitors. Alternatively, some groups have reported that mouse LHSC are responsible for both radioprotection and long-term repopulation of all blood cell lineages. A possible explanation for this difference is that cells with the capacity for long-term production of all blood cell lineages are biologically heterogeneous. We now show that 10 LHSC can generate all blood cell lineages for the lifetime of the animal. However, these cells lacked radioprotection and spleen colony-forming activity. LHSC were identified and isolated by their small size, their lack of expression of antigens characteristic of mature blood cell lineages, and their high expression of aldehyde dehydrogenase. In addition, these cells were found to express undetectable or low levels of many antigens presumed to mark LHSC, including Thy-1, Ly-6A/E (Sca-1), c-kit, and CD34. There appears to be at least two classes of LHSC with the capacity for long-term production of all blood cell lineages: one that generates both radioprotection and long-term engraftment and one that produces delayed but durable engraftment. Our data suggest that this latter class may represent a very primitive class of LHSC.

Successful treatment of childhood pilocytic astrocytomas metastatic to the leptomeninges with high-dose cyclophosphamide

Leptomeningeal dissemination of childhood pilocytic astrocytoma (PA) is a rare event with little information available regarding therapy. We report here four children with disseminated PA whom we treated with high doses of cyclophosphamide with clinical benefit. The patients were aged 2.5 to 8 years. Three patients presented with PA localized in the posterior fossa, initially treated with surgical resection (n = 3) and radiotherapy (n = 1). Leptomeningeal dissemination occurred at 32, 44, and 8 months from diagnosis, respectively. The fourth patient presented with an optic pathway tumor with leptomeningeal dissemination at diagnosis. At commencement of cyclophosphamide therapy, disease was present in the subarachnoid space (intracranial, n = 2; spinal, n = 4), cerebral ventricles (n = 2), and primary site (n = 3). Histology was identical at diagnosis and recurrence in the two biopsied cases and cerebrospinal fluid was negative in all cases. Treatment was with cyclophosphamide 4-5 g/m2/cycle given every 4 weeks for a total of two cycles (n = 1) and four cycles (n = 3). One patient achieved disease stabilization (duration 27 months at the time of publication) and three patients experienced significant reductions in tumor burden. Subsequent intrathecal therapy was administered to two patients. Two patients developed disease progression at 10 and 9 months from cessation of chemotherapy. The one re-treated patient responded to further, lower dose, cyclophosphamide. This is the first report of the use of high dose cyclophosphamide for disseminated PA. The recurrence of disease in two cases with a further response to lower dose cyclophosphamide has implications for the optimal duration of therapy for these low grade, aggressive tumors.

Treatment of patients with pineoblastoma with high dose cyclophosphamide

The outcome for patients with pineoblastoma has historically been very poor, with most patients dying of disseminated disease despite irradiation. Furthermore, the low incidence of this tumor has hindered progress toward defining better treatment strategies. Here we report the activity and toxicity of cyclophosphamide administered as a single agent at a dose schedule of 2 g/m2/day for 2 successive days at monthly intervals for a maximum of four courses. Eight patients were evaluated, six newly diagnosed and two recurrent. Amongst the six newly diagnosed patients, there were three patients demonstrating partial responses, and three had stable disease throughout the cyclophosphamide treatment period. All six patients are alive and disease free after further therapy. One patient with recurrent disease demonstrated tumor progression on cyclophosphamide, and the other had stable disease throughout the cyclophosphamide treatment period. Both patients subsequently died of progressive disease. The major toxicity of high dose cyclophosphamide was hematopoietic, with one patient requiring a dose reduction after three courses due to prolonged thrombocytopenia. One patient was also withdrawn from treatment with cyclophosphamide due to impaired pulmonary function. This study demonstrates the activity of high dose cyclophosphamide in the treatment of pineoblastoma and may serve as basis for the design of future studies of this tumor.

A structural basis for a phosphoramide mustard-induced DNA interstrand cross-link at 5'-d(GAC)

Phosphoramide mustard-induced DNA interstrand cross-links were studied both in vitro and by computer simulation. The local determinants for the formation of phosphoramide mustard-induced DNA interstrand cross-links were defined by using different pairs of synthetic oligonucleotide duplexes, each of which contained a single potentially cross-linkable site. Phosphoramide mustard was found to cross-link dG to dG at a 5'-d(GAC)-3'. The structural basis for the formation of this 1,3 cross-link was studied by molecular dynamics and quantum chemistry. Molecular dynamics indicated that the geometrical proximity of the binding sites also favored a 1,3 dG-to-dG linkage over a 1,2 dG-to-dG linkage in a 5'-d(GCC)-3' sequence. While the enthalpies of 1,2 and 1,3 mustard cross-linked DNA were found to be very close, a 1,3 structure was more flexible and may therefore be in a considerably higher entropic state.

Local delivery of the topoisomerase I inhibitor camptothecin sodium prolongs survival in the rat intracranial 9L gliosarcoma model

Camptothecin, a naturally occurring inhibitor of the DNA-replicating enzyme topoisomerase I, demonstrated promising anti-tumor activity in pre-clinical testing; however, because of unexpected toxicity and low anti-tumor effects in the initial clinical trials, further testing was discontinued. We hypothesized that local controlled delivery of camptothecin sodium would achieve effective concentrations in brain tumors without the observed systemic side effects, thereby allowing this novel drug to be used to treat patients with malignant gliomas. To test this hypothesis, we evaluated the sensitivity of rat glioma lines and established human glioma lines to camptothecin in vitro. We found that the LD90 for the established rat and human lines was 0.3 to 1.4 microM after a 1 hr exposure and decreased to less than 0.1 microM after continuous exposure for 7 days. We loaded camptothecin into a controlled-release polymer (ethylene-vinyl acetate co-polymer; EVAc) and showed by high-pressure liquid chromatography that controlled release occurred over at least 21 days. We then tested camptothecin against 9L gliosarcoma, implanted into the brain of Fischer 344 rats. Five days after tumor implantation, animals were treated with camptothecin delivered either systemically or locally by release from EVAc. Local controlled delivery by the polymer significantly extended survival: 59% of the treated animals were long-term survivors (> 120 days) compared to 0% of controls. Systemic administration did not extend survival compared to controls. We compared the efficacy of camptothecin delivered locally with a polymer to camptothecin injected directly into the tumor. Camptothecin increased survival only when delivered locally by polymer.

Cyclophosphamide in combination with sargramostim for treatment of recurrent medulloblastoma

Thirteen patients with recurrent medulloblastoma were treated with cyclophosphamide in association with Sargramostim. Cyclophosphamide was given at doses ranging between 1.0-2.5 g/m2 daily for two doses. Sargramostim was given at a fixed dose of 250 micrograms/m2 subcutaneously twice a day beginning 24 hours after the second cyclophosphamide dose and continuing through the leukocyte nadir until the ANC was more than 1,000 cells/microliters for two consecutive days. A total of 33 courses were given with toxicity consisting of grade 4 neutropenia in all courses and grade 3-4 thrombocytopenia in 10 of 13 patients. There were no deaths related to infection or bleeding. Four patients were taken off study because of prolonged myelosuppression. Three of these patients were at the 2.5 g/m2 level, and of these three, two developed lung toxicity (grades 2 and 4, respectively). One patient developed an allergic reaction following the first injection of Sargramostim and was also taken off study. Of 10 evaluable patients, there were 9 PR and 1 SD. We conclude that cyclophosphamide at a dose of 2.0 g/m2/day x 2 days q 4 weeks in association with Sargramostim demonstrates marked activity with acceptable toxicity in patients with recurrent medulloblastoma.

Determination of nitrosourea compounds in brain tissue by gas chromatography and electron capture detection

A relatively simple, high-sensitivity gas chromatographic assay is described for nitrosourea compounds, such as BCNU [1,3-bis(2-chloroethyl)-1-nitrosourea] and MeCCNU [1-(2-chloroethyl)-3-(trans-4-methylcyclohexyl)-1-nitrosourea], in small biopsy samples of brain and other tissues. After extraction with ethyl acetate, secondary amines in BCNU and MeCCNU are derivatized with trifluoroacetic anhydride. Compounds are separated and quantitated by gas chromatography using a capillary column with temperature programming and an electron capture detector. Standard curves of BCNU indicate a coefficient of variance of 0.066 +/- 0.018, a correlation coefficient of 0.929, and an extraction efficiency from whole brain of 68% with a minimum detectable amount of 20 ng in 5-10 mg samples. The assay has been facile and sensitive in over 1000 brain biopsy specimens after intravenous and intraarterial infusions of BCNU.

Comparison of the protonation of isophosphoramide mustard and phosphoramide mustard

The alkylating agent isophosphoramide mustard (IPM) spontaneously forms a relatively stable aziridine derivative which can be directly observed using NMR spectroscopy. The protonations of IMP and its aziridine were probed using 1H, 31P, 15N, and 17O NMR spectroscopy. The positions of the 31P, 15N, and 17O resonances of IPM between pH 2 and 10 each exhibit a single monobasic titration curve with the same pKa of 4.31 +/- 0.02. On the basis of a comparison with other compounds and our earlier work with phosphoramide mustard, the NMR results for IPM indicate that protonation occurs at nitrogen and not oxygen. Over this same pH range, each of the 1H, 31P, and 15N resonances of IPM-aziridine also show a single monobasic titration with a pKa of 5.30 +/- 0.09. The magnitude of the change in chemical shifts suggests that the protonation of the IPM-aziridine occurs at the ring nitrogen. Theoretical gas-phase calculations of PM, IPM, and IPM-aziridine suggest O-protonation to be more likely; however, aqueous phase calculations predict the N-protonated forms to be most stable. Furthermore, for PM and IPM-aziridine, which contain nonequivalent nitrogens, the theoretical calculations and experimental data both agree as to which nitrogen undergoes protonation. These results suggest that the IMP-aziridine remains unprotonated under physiological conditions and may, in part, explain the lower alkylating activity of IPM as compared to PM.

Quantitation of 4-hydroxycyclophosphamide/aldophosphamide in whole blood

There is considerable interest in determining 4-hydroxycylcophosphamide/aldophosphamide (4-HO-CP/AP) blood levels in patients receiving the prodrug, cyclophosphamide (CP). Phosphoramide mustard (PM), the alkylating metabolite of CP, is relatively impermeable to cell membranes and it is generally believed that circulating intermediary metabolites, including aldophosphamide, the immediate precursor of PM, is transported by circulating blood to tumor tissue. Therefore, circulating 4-HO-CP/AP blood levels should more closely reflect the oncostatic and cytotoxic effects of CP than the parent drug. We have developed a gas chromatographic electron-impact mass spectrometric (GC-EIMS) method suitable for routine monitoring of 4-HO-CP/AP levels in whole blood over the range 0.085 microM (25 ng/ml) to 34 microM (10 micrograms/ml). The unstable metabolites were derivatized with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine-HCl to form a stable aldophosphamide oxime derivative (PBOX). [2H4]PBOX was used as an internal standard. For clinical samples, tubes were prepared prior to blood drawing, which contained the derivatizing reagent solution and the internal standard. These solutions were stable for up to 3 months when stored at room temperature. Following addition of blood to the reaction tubes, PBOX formation was rapid and the resulting derivative was stable under these conditions for up to 8 days at room temperature. Application of the method was demonstrated by quantitating 4-HO-CP/AP blood levels in patients receiving 4 g/m2 intravenous infusion of CP over a period of 90 min.

Noninvasive detection of elevated glutathione levels in MCF-7 cells resistant to 4-hydroperoxycyclophosphamide

Native human mammary MCF-7 adenocarcinoma cells and a subline displaying resistance to 4-hydroperoxycyclophosphamide, the chemically activated form of cyclophosphamide, were grown as multicellular spheroids or on a collagen sponge matrix and perfused for study by 31P and 13C nuclear magnetic resonance spectroscopy. The natural abundance 13C spectrum of the perfused cells exhibits well-resolved resonances due to the intracellular glutathione (GSH). The resistant cell line shows a higher intensity of the GSH 13C resonances, consistent with the increased GSH concentration determined from biochemical assays of extracts. Treatment of the resistant cell line with buthionine sulfoximine selectively diminishes the intensity of the GSH resonances in the 13C nuclear magnetic resonance spectrum.

Assessment of aldehyde dehydrogenase in viable cells

Cytosolic aldehyde dehydrogenase (ALDH), an enzyme responsible for oxidizing intracellular aldehydes, has an important role in ethanol, vitamin A, and cyclophosphamide metabolism. High expression of this enzyme in primitive stem cells from multiple tissues, including bone marrow and intestine, appears to be an important mechanism by which these cells are resistant to cyclophosphamide. However, although hematopoietic stem cells (HSC) express high levels of cytosolic ALDH, isolating viable HSC by their ALDH expression has not been possible because ALDH is an intracellular protein. We found that a fluorescent aldehyde, dansyl aminoacetaldehyde (DAAA), could be used in flow cytometry experiments to isolate viable mouse and human cells based on their ALDH content. The level of dansyl fluorescence exhibited by cells after incubation with DAAA paralleled cytosolic ALDH levels determined by Western blotting and the sensitivity of the cells to cyclophosphamide. Moreover, DAAA appeared to be a more sensitive means of assessing cytosolic ALDH levels than Western blotting. Bone marrow progenitors treated with DAAA proliferated normally. Furthermore, marrow cells expressing high levels of dansyl fluorescence after incubation with DAAA were enriched for hematopoietic progenitors. The ability to isolate viable cells that express high levels of cytosolic ALDH could be an important component of methodology for identifying and purifying HSC and for studying cyclophosphamide-resistant tumor cell populations.

Phase I and pharmacologic study of the alkylating agent modulator novobiocin in combination with high-dose chemotherapy for the treatment of metastatic breast cancer

PURPOSE

Resistance to alkylators may potentially be overcome by drugs that inhibits DNA repair, thus improving the efficacy of high-dose chemotherapy. This trial was performed to determine if novobiocin, an agent that inhibits DNA repair, could be given with high-dose alkylators. Study aims were to define the toxicities and maximal-tolerated dose (MTD) of novobiocin and the pharmacokinetics of novobiocin and high-dose cyclophosphamide and thiotepa.

PATIENTS AND METHODS

Thirty-eight women with responsive metastatic breast cancer received high-dose cyclophosphamide (3 to 6 g/m2 over 4 days), thiotepa (400 to 800 mg/m2), and novobiocin (0.5 to 5.0 g/d x 7, orally) with autologous marrow support. Toxicity was monitored. The pharmacology of novobiocin, cyclophosphamide, and thiotepa was evaluated.

RESULTS

There were no toxic deaths. The MTD of novobiocin was 4 g/d. All seven patients treated at 5 g/d developed grade III/IV mucositis and vomiting. The severity of mucositis correlated with the plasma levels of novobiocin. Other severe toxicities were not observed. Plasma novobiocin levels > or = 100 micrograms/mL, which are associated with reversal of drug resistance in animal models, were consistently seen at dose levels greater than 2 g. The dispositions of cyclophosphamide and thiotepa were not altered by novobiocin.

CONCLUSION

Novobiocin may be given with high-dose alkylators in doses that produce plasma levels that augment the activity of these cytotoxics in experimental models. The pharmacology of high-dose cyclophosphamide and thiotepa is unaffected. Novobiocin 4 g/d orally for 7 days is recommended for future study.

Dose escalation trial of cyclophosphamide with Sargramostim in the treatment of central nervous system (CNS) neoplasms

We conducted a dose escalation trial of cyclophosphamide plus Sargramostim in the therapy of patients with newly diagnosed or recurrent central nervous system tumors. Cyclophosphamide was administered at doses ranging between 1.0 and 2.5 g/m2 daily for two doses. Sargramostim was administered at a fixed dose of 250 micrograms/m2 subcutaneously twice a day beginning 24 hours after the second cyclophosphamide dose and continuing through the leukocyte nadir until the absolute neutrophil count (ANC) was > 1,000 cells/microliters for two consecutive days. The MTD for patients who had not received any prior chemotherapy and who had received either no radiotherapy or radiotherapy confined to the cranium was 2.0 g/m2 daily for two doses. The MTD for patients previously treated with chemotherapy or neuraxis radiotherapy was also 2.0 g/m2 daily for two doses. Responses were seen in patients with medulloblastoma (8/9), glioblastoma multiforme (2/13), germinoma (1/1), and pineoblastoma (1/2).

Oxime derivatives of the intermediary oncostatic metabolites of cyclophosphamide and ifosfamide: synthesis and deuterium labeling for applications to metabolite quantification

There is ongoing interest in the selective, quantitative analysis of the cyclophosphamide metabolites 4-hydroxycyclophosphamide (2a) and aldophosphamide (3a) because these tautomers are generally believed to play a key role in oncostatic selectivity and metabolite transport. O-(2,3,4,5,6-Pentafluorobenzyl)hydroxylamine (C6F5CH2ONH2, 1 equiv) provided for the complete conversion (by 31P NMR, 60% reaction within 15 min at 20 degrees C) of 2a/3a (17 mM in H2O/CH3OH) to E/Z-aldophosphamide O-(2,3,4,5,6-pentafluorobenzyl)oxime [C6F5CH2ON = CHCH2CH2OP-(O)(NH2)N(CH2CH2Cl)2; E:Z = 54:46 (+/- 3% average deviation)]. Under these conditions, the oxime exhibited little (6%) decomposition over 3 weeks. Parallel studies showed that 4-hydroxyifosfamide/aldoifosfamide reacted completely to give the analogous aldoifosfamide oxime [C6F5CH2ON = CHCH2CH2OP(O)(NHCH2CH2Cl)2; E:Z = 52:48 (+/- 1% average deviation)] with 50% reaction within 15 min at 20 degrees C with no product decomposition over 3 weeks. In aqueous methanol and with 2 equiv C6F5CH2ONH2, clinically useful 4-hydroperoxycyclophosphamide (10 mM; tau 1/2 = 10 min, 37 degrees C) and its isomer 4-hydroperoxyifosfamide (10 mM; tau 1/2 = 25 min, 20 degrees C) underwent complete conversion to the corresponding aldehyde oximes. Each oxime was synthesized with deuterium in the chloroethyl moieties for use as internal standards in GC/MS applications.

Molecular pharmacology of hepsulfam, NSC 3296801: identification of alkylated nucleosides, alkylation site, and site of DNA cross-linking

We have determined that hepsulfam, in common with its structural homologue busulfan, alkylates both free guanosine and GMP in DNA at the 7 nitrogen. Mass spectral analysis of the products of the reaction of hepsulfam with guanosine has identified the mono- and bis-alkylated guanosine adducts. UV spectrophotometry and mass spectrometry were used to confirm that alkylation occurred at the 7 nitrogen by following the formation of the formamidopyrimidyl form of the hepsulfam-guanosine adduct at high pH. We have also isolated and identified 1-guanyl,7-hydroxyheptane, 1-guanyl,7-sulfamylheptane, and 1,7-bis(guanyl)heptane from in vitro reaction mixtures of hepsulfam and calf thymus DNA. We have isolated bis-(7-formamidopyrimidyldeoxyguanosinyl)-heptane from an enzymatic digest of DNA treated with hepsulfam. Finally, we have found that hepsulfam forms interstrand cross-links at 5'-GXC-3' sites in model oligonucleotides.

Effectiveness of controlled release of a cyclophosphamide derivative with polymers against rat gliomas

Most malignant gliomas grow despite treatment by standard chemotherapeutic agents. The authors explored the use of an innovative drug, 4-hydroperoxycyclophosphamide (4HC), delivered via a controlled-release biodegradable polymer to determine whether local delivery would enhance efficacy. This drug is an alkylator-type chemotherapeutic agent derived from cyclophosphamide. Unlike the parent drug, which requires activation by hepatic microsomes, 4HC is active in vitro. Two rat glioma cell lines, 9L and F98, were treated in cell culture with medium containing 4HC. Both cell lines were more sensitive to 4HC than to a nitrosourea, BCNU, an agent of established value in the local therapy of gliomas. Ninety Fischer 344 rats implanted with 9L or F98 gliomas were treated with an intracranial polymer implant containing 0% to 50% loaded 4HC in the polymer, and it was found that 20% 4HC-loaded polymers caused minimum local brain toxicity and maximum survival. These polymers were then used to compare the in vivo efficacy of 4HC to BCNU in rats implanted with 9L glioma. Animals with brain tumors treated with 4HC had a median survival span of 77 days compared to the median survival of 21 days in BCNU-treated animals and median survival of 14 days in untreated animals. Long-term survival for more than 80 days was 40% in the 4HC-treated rats versus 30% in the BCNU-treated rats. The polymer carrier used in this study was a copolyanhydride of dimer erucic acid and sebacic acid 1:1, which was able to maintain the hydrolytically unstable 4HC in a stable state for local delivery. Thus, it is concluded that 4HC-impregnated polymers provide an effective and safe local treatment for rat glioma.

Nonlinear pharmacokinetics of cyclophosphamide in patients with metastatic breast cancer receiving high-dose chemotherapy followed by autologous bone marrow transplantation

The pharmacokinetics of cyclophosphamide has been evaluated in 15 patients with metastatic breast cancer undergoing high-dose chemotherapy with alkylating agents followed by autologous bone marrow transplantation. Each patient received two courses of chemotherapy: 4 g/m2 of cyclophosphamide by 90-min infusion prior to peripheral blood progenitor cell collection (the first course) and 6 g/m2 of cyclophosphamide with 800 mg/m2 of thiotepa by 96-h constant infusion before marrow and stem cell reinjection (the second course). In the first course, plasma cyclophosphamide concentration-time data of 9 of 15 patients were fit by a one-compartment model with Michaelis-Menten saturable elimination in parallel with first-order renal elimination. The mean (SD) Vmax and Km values were 1.47 (0.89) microM/min and 575 (347) microM, respectively. The first course data of the remaining six patients were fit using first-order elimination only. In the second drug course, plasma cyclophosphamide disposition curves of 13 of 15 patients demonstrated a decline in concentration following attainment of an initial steady state. The plasma cyclophosphamide disposition data of these patients were fit by a one-compartment pharmacokinetic model, in which the decline of plasma cyclophosphamide concentration after reaching the initial steady state was modeled as being due to an increase in the clearance rate of cyclophosphamide. The mean (SD) initial and final clearance rates were 51 (16) ml/min and 106 (48) ml/min, respectively. Michaelis-Menten elimination was not apparent in the second course because the plasma concentration of cyclophosphamide was much lower. The mean renal clearance rate was 17 ml/min in the first course and 16 ml/min in the second course. Urinary excretion of cyclophosphamide accounted for 17% and 23% of the total dose administered in the first and the second course, respectively. No change in cyclophosphamide clearance rate was apparent in a patient who was taking phenytoin, but a change was present in a patient who was taking phenobarbital. A drug interaction between cyclophosphamide and thiotepa may explain the smaller initial clearance rate for cyclophosphamide during the second drug course.

The effect of L-amino acid oxidase on activity of melphalan against an intracranial xenograft

We have previously shown that diet restriction-induced depletion of large neutral amino acids (LNAAs) in murine plasma to 46% of control significantly enhances intracranial delivery of melphalan without enhancing delivery to other organs. Studies have now been conducted to determine whether more substantial LNAA depletion could further enhance intracranial delivery of melphalan. Treatment with L-amino acid oxidase (LOX) significantly depleted murine plasma LNAAs: phenylalanine, leucine, and tyrosine (> 95%); methionine (83%); isoleucine (70%); and valine (46%). Experiments evaluating the intracellular uptake of melphalan and high-pressure liquid chromatography quantitation of melphalan metabolites revealed, however, that melphalan is rapidly degraded in the presence of LOX, and that the timing of the administration of melphalan following the use of LOX to deplete LNAAs is crucial. Conditions were found under which LOX-mediated degradation of melphalan was minimized and LNAA depletion was maximized, resulting in a potentiation of the antitumor effect of melphalan on human glioma xenografts in nude mice. Such potentiation could not be obtained using diet restriction alone.

Repair analysis of 4-hydroperoxycyclophosphamide-induced DNA interstrand crosslinking in the c-myc gene in 4-hydroperoxycyclophosphamide-sensitive and -resistant medulloblastoma cell lines

Cyclophosphamide is one of the most active agents in the treatment of medulloblastoma. However, development of resistance to this alkylator frequently occurs and is the harbinger of tumor progression and death. In order to understand the biochemical basis of this resistance, we generated a panel of medulloblastoma cell lines in our laboratory that were resistant to 4-hydroperoxycyclophosphamide (4-HC). Previously, we have shown that elevated levels of aldehyde dehydrogenase and glutathione mediate cellular resistance to 4-HC. The present study was conducted to identify the third unknown mechanism mediating the resistance of cell line D283 Med (4-HCR) to 4-HC, testing the hypothesis that this resistance is mediated by an increased repair of DNA interstrand crosslinks (ICLs). The doses of 4-HC that produced a one- and two-log cell kill of D283 Med cells were 25 and 50 microM, respectively, compared with values of 125 and 165 microM in D283 Med (4-HCR), the resistant cell line. The formation and disappearance of 4-HC-induced DNA ICLs at the c-myc gene were subsequently studied by DNA denaturing/renaturing gel electrophoresis and Southern blot analysis. 4-HC-induced DNA ICLs in the c-myc gene exhibited a dose-dependent relationship. The percentage of the c-myc gene that was crosslinked was approximately 1-3% at a dose of 100 microM. More than 50% of the DNA crosslinking in D283 Med (4-HCR) cells was removed by 6 h after drug treatment, whereas, in D283 Med cells, more than 90% of the DNA crosslinking was still present at 6 h. These findings suggest that the increased repair of DNA ICLs in D283 Med (4-HCR) may contribute significantly to its resistance to 4-HC.

Intrathecal melphalan therapy of human neoplastic meningitis in athymic nude rats

We report the activity and toxicity of intrathecal melphalan in the treatment of human neoplastic meningitis in the subarachnoid space of athymic nude rats. Animals received injections via chronic indwelling subarachnoid catheters with 5 x 10(5) or 5 x 10(6) TE-671 human rhabdomyosarcoma cells or 5 x 10(6) D-54 MG human glioma cells and were treated with melphalan on days 8, 5, or 5, respectively. Melphalan toxicity in nontumor-bearing rats was assessed at single doses of a 2.0, 3.0, 4.0, or 5.0 mM solution, with clinical and histological evidence of neurotoxicity observed at the 4.0 and 5.0 mM levels. Multiple-dose toxicity studies using a dosing schedule of twice a week for two weeks with a 0.25, 0.5, 0.75, 1.0, 1.5, or 2 mM solution revealed dose-dependent clinical and histological evidence for toxicity at all dosages. Treatment of TE-671 with a single dose of 2.0 mM intrathecal melphalan produced an increase in median survival of 442% compared with saline controls (P < 0.003). Comparison of a single dose of 1.0 or 2.0 mM melphalan with a multiple dose regimen at 0.25 or 0.5 mM melphalan in the treatment of TE-671 revealed increases in median survival of 50% for 1.0 mM, 57% for 2.0 mM, 79% for 0.5 mM, and 111% for 0.25 mM concentrations. Comparison of a single dose of 1 mM melphalan with multiple doses of 0.25 mM melphalan in the treatment of D-54 MG revealed an increase in median survival of 475+% for each of the regimens. Intrathecal melphalan may be an important new addition in the treatment of neoplastic meningitis and is currently being evaluated clinically in a Phase 1 trial.