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High-dose melphalan with autotransplantation for refractory multiple myeloma: results of a Southwest Oncology Group phase II trial.

PURPOSE: To evaluate high-dose melphalan followed by autologous stem-cell transplantation in patients with refractory multiple myeloma. PATIENTS AND METHODS: Multiple myeloma patients with alkylating agent or vincristine/doxorubicin/dexamethasone-refractory disease were eligible for the phase II multi-institutional Southwest Oncology Group trial S8993. Patients up to age 70 years were enrolled between April 15, 1991, and May 1, 1996. Patients without prior stem-cell collection were primed with high-dose cyclophosphamide (HD-CTX; 6 g/m(2)) and granulocyte-macrophage colony-stimulating factor. After stem-cell procurement, patients received melphalan 200 mg/m(2) with autologous transplantation. Upon recovery from melphalan, patients were to receive interferon alfa-2b until relapse. RESULTS: Seventy-two patients were enrolled onto S8993; five were ineligible and one received no therapy. Of the 66 assessable patients, 56 patients underwent the transplant procedure; 54 were assessable for response and 56 for toxicity. The response to HD-CTX (n = 37) included three complete remissions (CRs; 8%) and five partial remissions (PR; 14%); response to melphalan (n = 54) included 16 CRs (30%) and 19 PRs (35%), for an overall CR and >/= PR (n = 66; intent-to-treat) of 27% and 58%, respectively. Toxicities included six treatment-related deaths: two during HD-CTX and four during transplantation. The median progression-free survival (PFS) and overall survival (OS) durations on an intent-to-treat basis from transplant registration was 11 months and 19 months (95% confidence interval, 14 to 29 months), respectively. The 3-year actuarial PFS and OS rates were 25% and 31%, respectively. CONCLUSION: High-dose therapy with melphalan 200 mg/m(2) is feasible with high response rates (58% overall) and an OS of 19 months in patients with refractory multiple myeloma.

Adult↗

Sensitization to the cytotoxicity of melphalan by ethacrynic acid and hyperthermia in drug-sensitive and multidrug-resistant Chinese hamster ovary cells.

The ability of physical and pharmacological modulators to increase the cytotoxicity of melphalan was investigated in Chinese hamster ovary cells using a clonogenic cell survival assay. Hyperthermia has potential for use in cancer treatment, particularly as an adjuvant to chemotherapy or radiotherapy. Ethacrynic acid is a glutathione S-transferase inhibitor and also undergoes conjugation with glutathione. Interactions between hyperthermia (41-43 degrees C), ethacrynic acid and melphalan were evaluated in multidrug-resistant (CH(R)C5) cells with overexpression of P-glycoprotein (33.69-fold), and in drug-sensitive (AuxB1) cells. GST alpha was expressed at a higher level (3.65-fold) in CH(R)C5 cells than in sensitive cells, whereas levels of isoforms pi and mu were the same. GST pi was the most highly expressed isoform in the two cell populations. Ethacrynic acid was cytotoxic at elevated temperatures, while it caused little or no cytotoxicity at 37 degrees C. This effect occurred in drug-resistant and drug-sensitive cells, and attributes thermosensitizing properties to ethacrynic acid. Ethacrynic acid (20 microM) alone did not alter the cytotoxicity of melphalan at 37 degrees C. Hyperthermia potentiated drug cytotoxicity in cells, both with and without ethacrynic acid treatment. Ethacrynic acid could be useful in cancer treatment by acting as a thermosensitizer when combined with heat and by enhancing the cytotoxicity of melphalan at elevated temperatures. A major advantage arising from the use of regional hyperthermia is the ability to target drug cytotoxicity to the tumor volume. A useful finding is that ethacrynic acid, heat and/or melphalan are also effective against multidrug-resistant cells with overexpression of P-glycoprotein.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

Cost-effectiveness of a transplantation strategy compared to melphalan and prednisone in younger patients with multiple myeloma.

High dose chemotherapy with autologous stem cell transplantation (ASCT) improves outcomes in patients 65 years of age or less with multiple myeloma. Survival and costs in a cohort of 16 patients who received melphalan and prednisone as part of a clinical trial were compared with those of 36 patients referred to our centre for consideration of ASCT. In the transplant group, survival and costs were extrapolated to match the period of observation in the melphalan and prednisone group. Patient-specific and average costs were calculated from the perspective of the Ontario Ministry of Health. Costs and survival were varied by 50% in the sensitivity analysis. Transplantation improved life expectancy by 19.3 months with a cost difference of 30,517 Canadian dollars. The incremental cost-effectiveness of transplantation compared with melphalan and prednisone was 25,710 Canadian dollars per life-year gained when additional pamidronate and follow-up costs were considered. Discounting costs and survival at 3 and 5% did not result in important differences. The sensitivity analysis resulted in best and worse case scenarios for transplantation compared with melphalan and prednisone of 13,049 dollars and 63,954 dollars per life-year gained respectively. In comparison with melphalan and prednisone, ASCT appears to be cost-effective in patients 65 years old or younger with myeloma.

Adult↗

High-dose melphalan and autologous stem-cell transplantation in patients with AL amyloidosis: an 8-year study.

BACKGROUND: AL amyloidosis is a fatal disease resulting from tissue deposition of amyloid fibrils derived from monoclonal immunoglobulin light chains. Treatment with oral chemotherapy is minimally effective. OBJECTIVE: To test survival and organ response in a large sample of patients treated with high-dose intravenous melphalan (100 to 200 mg/m2) and autologous blood stem-cell transplantation. DESIGN: 8-year longitudinal analysis of clinical effectiveness. SETTING: University-affiliated specialty referral clinic. PATIENTS: 701 consecutive new patients with AL amyloidosis. INTERVENTION: High-dose chemotherapy and autologous stem-cell transplantation for patients who met eligibility requirements based on organ involvement and clinical status. MEASUREMENTS: Survival analysis of all patients evaluated and a detailed analysis of treatment outcome in the subgroup that received high-dose melphalan and stem-cell transplantation. RESULTS: Among 701 patients with AL amyloidosis, 394 (56%) were eligible for high-dose melphalan and stem-cell transplantation; 82 did not proceed with treatment because of patient choice or disease progression. Median survival of the 312 patients who initiated treatment was 4.6 years. A complete hematologic response, defined as no evidence of an underlying plasma cell dyscrasia 1 year after treatment, was achieved in 40% of patients and was associated with prolonged survival. Statistically significant improvements occurred in end-organ disease and were greater in patients with a complete hematologic response. Mortality rate within 100 days of treatment with high-dose melphalan and stem-cell transplantation was 13%; patients with cardiomyopathy had the highest mortality rates. CONCLUSIONS: Treatment of selected patients with AL amyloidosis by using high-dose melphalan and stem-cell transplantation resulted in hematologic remission, improved 5-year survival, and reversal of amyloid-related disease in a substantial proportion.

Aged↗

Dose-intensive melphalan with stem cell support (CM regimen) is effective and well tolerated in elderly myeloma patients.

BACKGROUND AND OBJECTIVE: Multiple myeloma (MM) typically afflicts elderly patients. High-dose therapy has recently been shown to lead to a better outcome than standard treatment, mainly in younger patients. The extent to which older subjects can benefit from intensified approaches without excessive toxicity is examined in this study. DESIGN AND METHODS: Between December 1994 and May 1997, 12 Italian Multiple Myeloma Study Group institutions entered 68 patients at diagnosis (median age 65) into an intensified chemotherapy regimen: cyclophosphamide (CY) 3 g/m(2) plus melphalan 60 mg/m(2) followed by peripheral blood progenitor cells (PBPC) and G-CSF (CM regimen). CY (day 0) and G-CSF were used to mobilize PBPC harvested by a single leukapheresis on day 10. Melphalan was infused on day 11. PBPC were kept unprocessed at 4 degrees C for 48 hours and reinfused on day 12. Three CM regimens were delivered at 6-month intervals. RESULTS: Sufficient PBPC to support the first CM cycle were available (median CD34(+) harvest: 4.9x10(6)/kg), but dropped significantly after the second (median CD34(+) harvest: 2x10(6)/kg) and the third (median CD34(+) harvest: 0.9x10(6)/kg). The median durations of severe neutropenia (absolute neutrophil count < 500 microL) were 3, 4, and 3 days, and those of severe thrombocytopenia (platelets < 25,000/microL) were 2.5, 2, and 1 days, after the first, second and third courses, respectively. The frequency of extramedullary toxicities was low. Treatment-related mortality (TRM) was 3% after the first CM, only. Complete remission (CR) was 14% after the first, 16% after the second and 27% after the third CM. After a median follow-up of 34 months (range 19-49 months), median event-free survival was 35.6 months. INTERPRETATION AND CONCLUSIONS: These results indicate that dose-intensity of melphalan can be increased by reinfusing PBPC with acceptable low toxicity. The combination of CY and melphalan followed by PBPC is an effective chemotherapy for elderly myeloma patients. Repeated melphalan infusion hampered subsequent CD34(+) harvests.

Aged↗

Melphalan versus adriamycin in the treatment of advanced carcinoma of the ovary.

The therapeutic effects of adriamycin and of melphalan in patients with advanced carcinoma of the ovary were tested in a prospective randomized study. Complete and partial remission occurred in eight of 19 patients treated with adriamycin and in four of 20 patients given melphalan. The difference, however, is not statistically significant. The median duration of complete and partial remissions was slightly longer after treatment with melphalan than with adriamycin. The number of cycles required to produce the initial regression state was less in the patients in the group given adriamycin as compared with those in the group treated with melphalan. No cross resistance was observed between the two drugs. These data indicate that, in patients with carcinoma of the ovary, the therapeutic efficacy of adriamycin is competitive with that of the most effective conventional agents, such as melphalan.

Adenocarcinoma↗

Interleukin-6 affects melphalan-induced DNA damage and repair in human multiple myeloma cells.

In addition to signaling proliferation, growth factors may contribute to the persistence of hematopoietic tumors upon chemotherapeutical challenge. In multiple myeloma, malignant growth is mediated either by paracrine interleukin-6 (IL-6) elaborated by bone marrow stromal cells or via autocrine loops by malignant myeloma cells themselves. Although melphalan is one of the most active drugs in this tumor entity, the development of drug resistance frequently impedes cure of patients by attenuating melphalan-induced DNA-damage. We analyzed whether IL-6 protects XG-1 cells and plasma cells of a patient suffering from end-stage multiple myeloma (plasma cell leukemia) from melphalan with respect to DNA damage and DNA repair. Investigating the housekeeping gene glucose-6-phosphate dehydrogenase (G6PD) by using a PCR-stop assay, we found that there was more DNA damage in the G6PD gene of IL-6 deprived XG-1 and the patient's plasma cells, respectively, than in those with IL-6 supplementation. After cessation of melphalan exposure and 24 hours post-incubation in melphalan-free medium, DNA repair was observed in the patient's plasma cells but not in XG-1 cells. There was more DNA repair with IL-6 addition than without IL-6 addition. Similarly, the apoptotic cell fractions, as measured by flow cytometry, were lower if IL-6 was added to the medium. These results indicate that IL-6 may contribute to drug resistance in multiple myeloma.

Aged↗

Efficacy and toxicity of low-dose melphalan in myelodysplastic syndromes and acute myeloid leukemia with multilineage dysplasia.

Effective therapy of myelodysplatic syndromes and acute myeloid leukemia originating from myelodysplastic syndrome has remained an unresolved problem. Advanced age of the patients and persistent pancytopenia make the treatment difficult. Despite large number of therapeutic options none of them is satisfactory. Recently palliative treatment with low-dose melphalan has been reported to have certain activity. The aim of the study was to evaluate the efficacy of low-dose melphalan in high-risk myelodysplastic syndromes (MDS) and acute myeloid leukemia with multilineage dysplasia (AML). Twenty three patients were eligible for the study: 8 with MDS and 15 with AML with multilineage dysplasia. All of them received oral melphalan in a daily dose of 2 mg. Median total dose of the drug was 120 mg (40-840 mg). Ten patients responded to the therapy. We observed complete remission (CR) in 4, partial remission (PR) in 3 and stabilization of the disease in 3 patients. Thirteen patients did not respond to the therapy. The survival time of the patients from the day of diagnosis and from the beginning of the treatment with melphalan was longer in patients responding to the therapy (median 15 and 10 months, respectively) than in non-responders (4.5 and 4 months, p=0.003 and p=0.008, respectively). Low-dose melphalan shows significant activity in high-risk MDS and AML with multilineage dysplasia with acceptable toxicity.

Acute Disease↗

Genotypic and phenotypic comparisons of de novo and acquired melphalan resistance in an isogenic multiple myeloma cell line model.

Cancer cell adhesion confers a transient, de novo drug-resistant phenotype referred to as cell adhesion-mediated drug resistance (CAM-DR). In this report, we extend the CAM-DR phenotype to primary specimens from patients with myeloma, providing further evidence that CAM-DR is a viable clinical form of drug resistance. To examine mechanisms of cellular resistance to melphalan, we compared genotypic and phenotypic profiles of acquired and de novo melphalan resistance in an isogenic human myeloma cell line. Acquired melphalan resistance (8226/LR5) was associated with decreased drug-induced DNA damage and a complex gene expression profile showing that genes involved in the Fanconi anemia DNA repair pathway are increased in the LR5 cells compared with drug-sensitive or adherent cells. In contrast, cells adhered to fibronectin accumulate similar amounts of DNA damage compared with drug-sensitive cells but are protected from melphalan-induced mitochondrial perturbations and caspase activation. Levels of the proapoptotic protein Bim were significantly reduced in adherent cells. Gene expression changes associated with de novo resistance were significantly less complex compared with acquired resistance, but a significant overlap in gene expression was noted involving cholesterol synthesis. We propose that myeloma cell adhesion promotes a form of de novo drug resistance by protecting cells from melphalan-induced cytotoxic damage and that this transient protection allows cells to acquire a more permanent and complex drug resistance phenotype associated with a reduction in drug induced DNA damage.

Antineoplastic Agents, Alkylating↗

Direct measurement of melphalan conjugation with glutathione: studies with human melanoma cells and mammalian liver.

The rate of formation of the major glutathione conjugate of the antitumor alkylating agent melphalan can be directly measured by high pressure liquid chromatography. Rates of melphalan-glutathione conjugate formation were determined in the presence and in the absence of human melanoma cell homogenates, or cell fractions from various tissue sources, and the relative contributions of enzyme-catalyzed and nonenzymatic conjugate formation to the overall rates of conjugation were determined. Significant rates of conjugation were observed in the absence of any enzyme-containing cell fractions. These rates were not increased by the addition of melanoma cell homogenates, animal liver microsomes or human liver cytosol or microsomes, even though these preparations all enhanced the rate of conjugation of 1-chloro-2,4-dinitrobenzene. Animal liver cytosol contains enzymes that provided a significant contribution to the overall rate of melphalan conjugate formation. We conclude that although liver cytosol contains enzymes that significantly enhance the rate of glutathione conjugation with melphalan, in the case of the tumor cells studied, cellular glutathione S-transferase-catalyzed activity appears to be, at best, a very minor determinant of the overall rate of melphalan-glutathione conjugate formation.

Animals↗

Effect of melphalan against self-renewal capacity of leukemic progenitors in acute myeloblastic leukemia.

This study aimed to evaluate the effect of melphalan on both terminal divisions and self-renewal capacity of acute myeloblastic leukemia (AML) progenitors (colony-forming units, CFU-L) grown in methylcellulose. Terminal divisions and self-renewal were assayed by primary (PE1) and secondary (PE2) colony formation, respectively. Thirteen cases of AML, were tested. Melphalan induced a negative exponential dose-effect on CFU-L survival. Moreover, melphalan was equally effective in inhibiting CFU-L growth in both PE1 and PE2 assays, with D10 values of 1.53 +/- 0.17 micrograms/ml and 1.59 +/- 0.21 micrograms/ml for PE1 and PE2, respectively (p = 0.48). Cytotoxicity of melphalan on CFU-L did not differ significantly from that observed for normal hemopoietic granulocyte-macrophage colony-forming units, erythroid burst-forming units, and granulocyte-erythroid-macrophage-megakaryocyte progenitors. Mafosfamide-lysine, a stable cyclophosphamide congener, strongly inhibited primary colony formation (PE1) with a D10 value of 14.46 +/- 1.76 micrograms/ml, but was much less efficient in the PE2 assay. Our findings suggest that the self-renewal capacity of AML progenitors can be differentially affected by alkylating agents. Moreover, since it is now considered that chemotherapy should be preferentially directed against the self-renewal of leukemic progenitors, melphalan might offer a greater potential than cyclophosphamide or cyclophosphamide derivatives in the therapy of AML.

Antineoplastic Agents↗

Phase II study of melphalan as a single-agent infused over a 24-hour period with individual adapted dosing in patients with recurrent epithelial ovarian cancer.

The current study was performed to evaluate the efficacy and toxicity of a chemotherapy treatment using melphalan administered over a 24-h period with individual adapted dosing in advanced ovarian cancer. Melphalan was infused intravenously with an automatic infusion pump over a 24-h period. The schedule was repeated every 28 days for a maximum of 6 cycles. The initial administered dose was 25 mg/m(2). Drug adjustment was then made using a population approach, with the aim of constraining the overall area under the plasma concentration-time curve within 2.0-2.5 mg . h/l. A total of 96 courses of chemotherapy was administered. The toxicity profile did not differ greatly from that reported after a 1-h infusion and was acceptable in such a heavily pretreated patient population. Twenty-five patients were assessable for response and survival. Four (16%) partial responses were observed, which lasted 9, 10, 13 and 37 months, respectively. Three patients experienced stable disease during 8, 14 and 22 months, respectively. The 1- and 2-year survival rates were 18% and 6%, respectively. At the time of analysis, two patients remained alive with progressive disease at 22 and 37 months, respectively. In conclusion, melphalan administered over a 24-h period in platinum- and taxane-resistant ovarian cancer patients appeared to provide some clinical benefits with manageable toxicity. Based on these results, future studies comparing melphalan administered over a 24-h period and oral melphalan administrations will be scheduled.

Adult↗

[Relationship between anti-tumor effects of melphalan and IFN-gamma].

AIM: To investigate the relationship between IFN-gamma and anti-tumor effects of melphalan in vivo. METHODS: Different gene-type mice (IFN-gamma(+/+), IFN-gamma(+/-) and IFN-gamma(-/-)), which had the same genetic background of C57BL/6, were used in this experiment. Murine lymphoma EL4 cells were inoculated subcutaneously into different gene-type mice simultaneously. Twelve days later, 7.5 mg/kg melphalan was used intraperitoneally to treat all these IFN-gamma(+/+), IFN-gamma(+/-) and IFN-gamma(-/-) tumor-bearing mice. Tumor size was observed and recorded every one to three days in these different gene-type mice subsequently. RESULTS: After melphalan (7.5 mg/kg) treatment, tumor size decreased at a similar rate in IFN-gamma(-/-), IFN-gamma(+/-) and IFN-gamma(+/+) mice within the first 3 d. Tumors shrank further or completely disappeared in most of IFN-gamma(+/-) and IFN-gamma(+/+) mice, whereas tumors grew gradually in all IFN-gamma(-/-) mice. CONCLUSION: 7.5 mg/kg melphalan has obvious anti-tumor effects on tumor-bearing IFN-gamma(+/+) and IFN-gamma(+/-) mice, but little effects on IFN-gamma(-/-) mice. These data suggest that IFN-gamma is required for the anti-tumor effects of melphalan on tumor-bearing mice in vivo.

Animals↗

Therapeutic analysis of melphalan-resistant human rhabdomyosarcoma xenograft TE-671 MR.

Investigations with the melphalan-resistant human rhabdomyosarcoma xenograft TE-671 MR were carried out to identify patterns of cross-resistance and collateral sensitivity and to define the mechanism(s) mediating melphalan resistance. TE-671 MR was cross-resistant to thio-TEPA, mitomycin, vincristine, and cisplatin, and partially resistant to chlorambucil and cyclophosphamide. TE-671 MR and the parent line TE-671 were both resistant to 1,3-bis(2-chloroethyl)-nitrosourea and expressed similar levels of O6-alkylguanine-DNA alkyltransferase. TE-671 MR retained full sensitivity to actinomycin D and demonstrated enhanced sensitivity to VP-16 compared to TE-671. Treatment of TE-671 MR with melphalan plus VP-16 resulted in greater than additive growth delays. The frequency of hypoxic regions was similar in TE-671 MR and TE-671, respectively. Measurement of tumor-to-plasma levels at 180 min following i.p. administration of melphalan at 0.5 of the 10% lethal dosage showed mean tumor-to-plasma ratios of 3.81 in TE-671 MR and 7.38 in TE-671, respectively. The lower drug levels in TE-671 MR may be contributing to the resistance to melphalan and thus indicate the need for further studies to define the reasons for these differences in tumor drug level.

Animals↗

Pharmacokinetics of buthionine sulfoximine (NSC 326231) and its effect on melphalan-induced toxicity in mice.

Intravenous doses of buthionine sulfoximine (BSO, NSC 326231), an inhibitor of glutathione synthesis, were eliminated rapidly from mouse plasma in a biexponential manner. The initial phase of the plasma concentration versus time curve had a half-life of 4.9 min and accounted for 94% of the total area under the curve. The half-life of the terminal phase of the curve was 36.7 min and the area accounted for only 6% of the total area under the curve. Plasma clearance of BSO was 28.1 ml/min/kg and the steady state volume of distribution was 280 ml/kg. The oral bioavailability of BSO, based on plasma BSO levels, was extremely low. However, comparable glutathione depletion was apparent after i.v. and p.o. doses of BSO, suggesting a rapid tissue uptake and/or metabolism of BSO. Therefore, due to the rapid elimination of BSO from mouse plasma, plasma drug levels do not directly correlate with BSO-induced tissue glutathione depletion. Administration of multiple i.v. doses of BSO to male and female mice resulted in a marked 88% depletion of liver glutathione at doses of 400-1600 mg/kg/dose. Toxicity of i.v. administered BSO was limited to a transient depression of peripheral WBC levels in female mice given six doses of 1600 mg/kg. Multiple i.v. doses of BSO of up to 800 mg/kg/dose (every 4 h for a total of six doses) did not alter the toxicity of i.v. administered melphalan. However, multiple doses of 1600 mg/kg/dose of BSO did potentiate histopathological evidence of melphalan-induced bone marrow toxicity in 30% of the mice and, additionally, the combination of BSO and melphalan produced renal tubular necrosis in 80% of the male mice. The potentiation of melphalan induced toxicity did not appear to be related to GSH depletion, since: quantitatively similar amount of GSH depletion occurred at lower dose of BSO without any increase in melphalan toxicity.

Administration, Oral↗

[A case report of acute renal failure induced by melphalan in a patient with ovarian cancer].

Melphalan is widely used in the chemotherapeutic treatment of an ovarian cancer. Bone marrow depression, nail change, hypersensitivity, chronic pulmonary fibrosis, and nausea and vomiting, are the side effects reported as a result of the toxicity of Melphalan. So far as we know, renal toxicity caused by Melphalan has not been reported in the past literature. A case of acute renal failure induced by Melphalan in a patient with 3rd stage ovarian cancer is presented in this paper. This therefore is the first report of renal toxicity caused by Melphalan.

Acute Kidney Injury↗

Unexpected toxicity associated with use of body surface area for dosing melphalan in the dog.

A multiinstitutional Phase I study using i.v. melphalan was conducted in dogs with spontaneously occurring neoplasia. Melphalan was administered at 7.5, 10, 11.25, 12.5, and 20 mg/m2 of body surface area. Disproportionately greater toxicity was observed in small dogs. Seven of the eight dogs (88%) weighing less than 14 kg experienced severe myelosuppression (neutropenia, less than 1500/mm3; and/or thrombocytopenia, less than 80,000/mm3), whereas only three of 13 dogs (23%) weighing greater than 14 kg developed severe myelosuppression (P = 0.016). We concluded that small dogs are at greater risk of developing bone marrow toxicity from i.v. melphalan than large dogs if body surface area is used to calculate the dose. Although both body surface area and weight were found to be significantly correlated with severity of toxicity, melphalan-induced toxicity in dogs can be more accurately estimated by body weight than by surface area, P = 0.008 versus P = 0.022, respectively. It may be necessary to prescribe antineoplastic agents that are eliminated by processes not primarily under metabolic influence or that produce side effects on tissue not correlated to basal metabolic rate on a parameter other than body surface area. In dogs, melphalan should be dosed on a weight basis, and treatment groups should be stratified by weight in randomized clinical studies, particularly when the weight range of treated subjects is great.

Animals↗

Formation and removal of DNA cross-links induced by melphalan and nitrogen mustard in relation to drug-induced cytotoxicity in human melanoma cells.

The formation and removal of nitrogen mustard (HN2)- and melphalan-induced DNA cross-links (DNA interstrand and DNA-protein cross-links) in a human melanoma cell line (RPMI 8322), as determined by alkaline elution of DNA, was compared and related to the cytotoxic effect of each drug. HN2 was considerably more cytotoxic than melphalan as determined by inhibition of colony formation. Immediately following exposure to HN2 maximum levels of DNA cross-links were found. Melphalan, in contrast, caused a protracted induction of DNA cross-links with maximum levels obtained 6-12 h following drug exposure. HN2 induced approximately 13 times higher peak levels of DNA cross-links compared to equal concentrations of melphalan. Removal of DNA cross-links following exposure to both drugs followed an exponential time course. The rate of removal of HN2-induced DNA cross-links was, however, 1.5-2.4 times more rapid than that of melphalan-induced cross-links. A strong correlation was obtained between the cytotoxicity of both drugs and the total area under the curve for DNA interstrand cross-links, indicating that both the initial induction of as well as the rate of removal of DNA interstrand cross-links are important for the cytotoxic effects of bifunctional alkylating agents.

Cell Line↗