Showing papers on "Doxorubicin published in 1986"

Characterization of a new drug-resistant human myeloma cell line that expresses P-glycoprotein.

Abstract: Multiple myeloma is a disease with a high initial chemotherapeutic response but virtually no cures due to emergence of drug resistance. A doxorubicin-resistant human myeloma cell line (8226/Dox) has been selected from the myeloma cell line RPMI8226 by continuously exposing cells to gradually increasing doses of doxorubicin. The resistant phenotype has been retained for over 2 months despite growth in drug-free medium. The resistant subline was cross-resistant to mitoxantrone, acronycine, etoposide, and vincristine. The 8226/Dox cell line remained sensitive to melphalan but acquired collateral sensitivity to dexamethasone. Intracellular doxorubicin accumulation, as measured by [14C]doxorubicin and high-performance liquid chromatography, was decreased by 54% at 1 h for 8226/Dox compared to the sensitive line. Efflux of doxorubicin was significantly greater in the resistant subline as compared to the sensitive parent cell line. Membrane analysis using immunoblotting techniques detected increased expression of the integral membrane protein P-glycoprotein (Mr 170,000) in the resistant subline. Cytogenetic analysis of 8226/Dox revealed a 7q-anomaly not seen in the parent cell line. No double minutes or homogeneously staining regions were observed. The drug sensitivity/resistance pattern of the resistant cell line correlates well with clinical observations indicating the potential of this cell line as a model for resistance in multiple myeloma.

Epirubicin: a review of the pharmacology, clinical activity, and adverse effects of an adriamycin analogue.

Abstract: Epirubicin (4'-epidoxorubicin) is an antineoplastic agent derived from doxorubicin. The compounds differ in the configuration of the hydroxyl group at the 4' position. Epirubicin, like doxorubicin, exerts its antitumor effects by interference with the synthesis and function of DNA and is most active during the S phase of the cell cycle. Epirubicin is administered by intravenous (IV) injection. It is metabolized by the liver and primarily eliminated in the bile. About 10% of the drug is eliminated in the urine. Dosage adjustments are recommended for patients with liver metastases or elevated liver function tests. The elimination half-life of epirubicin is 30 to 40 hours. Clinical studies indicate activity in breast cancer, non-Hodgkin's lymphomas, ovarian cancer, soft-tissue sarcomas, and pancreatic cancer. There is also evidence of activity against gastric cancer, small-cell lung cancer, and acute leukemia. Epirubicin has limited activity as a single agent against head and neck tumors or non-small-cell lung cancer, but may be beneficial in combination with other agents. The overall activity of epirubicin appears to be comparable with that of doxorubicin. However, more studies are needed to define its role in combination chemotherapeutic regimens. The acute dose-limiting toxicity of epirubicin is myelosuppression. Nausea, vomiting, and alopecia are also common. Epirubicin may cause transient cardiac arrhythmias and alterations of the electrocardiogram. Chronic therapy is limited, but available data indicate that epirubicin can be administered in higher cumulative doses than doxorubicin before cardiotoxicity limits further therapy.

Comparative Pharmacokinetics of Free Doxorubicin and Doxorubicin Entrapped in Cardiolipin Liposomes

Abstract: The comparative pharmacokinetics of free doxorubicin and doxorubicin entrapped in cardiolipin liposomes was evaluated in rats at a dose of 6 mg/kg i.v. Doxorubicin was entrapped in cardiolipin liposomes by using 11.2 mumol of drug, 5.6 mumol of cardiolipin, 28.5 mumol of phosphatidylcholine, 19.5 mumol of cholesterol, and 11.1 mumol of stearylamine. The peak plasma concentration with free doxorubicin at 5 min was 1.7 micrograms/ml which was reduced to 0.3 micrograms/ml by 1 h. With cardiolipin liposomes, the peak plasma concentration of doxorubicin achieved at 5 min was 20.9 micrograms/ml. The plasma levels of doxorubicin decreased gradually and by 1 h the drug concentration in plasma was 10 micrograms/ml. The plasma levels of free doxorubicin and doxorubicin entrapped in liposomes were fitted to a 3-compartment computer model. The terminal half-life with free doxorubicin in plasma was 17.3 h whereas it was 69.3 h with drug entrapped in liposomes. The area under the plasma concentration curve with liposomal doxorubicin was 81.4 micrograms X h X ml-1 compared to 1.95 micrograms X h X ml-1 observed with free doxorubicin. The steady state volume of distribution with free doxorubicin was about 23-fold higher than liposomal doxorubicin. The terminal half-life with free doxorubicin in cardiac tissue was 17.9 h compared to 12.6 h with drug encapsulated in liposomes. The terminal half-lives in liver and spleen following administration of liposomal doxorubicin were 15- and 2.3-fold higher, respectively, compared to free drug; furthermore, the concentration X time values of liposomal doxorubicin in liver were 26-fold higher and in spleen 6-fold higher than the free drug. Free doxorubicin and doxorubicin entrapped in liposomes demonstrated 17 and 20% excretion in bile of the injected dose, respectively, in rats. The present studies demonstrate that liposomal encapsulation of doxorubicin significantly alters its pharmacokinetics in plasma and tissues compared to free drug.

Phase II evaluation of doxorubicin plus cisplatin in advanced thyroid cancer: a Southeastern Cancer Study Group Trial.

Abstract: Twenty-two evaluable patients with all cell types of advanced thyroid cancer were treated with the combination of doxorubicin (60 mg/m2) plus cisplatin (60 mg/m2). There were two brief partial remissions (9.1%). There was considerable toxicity, with one drug-related death. Combination chemotherapy as given in this study was not effective for this patient population.

Comparative Long-Term Study of the Toxicities of Free and Liposome-Associated Doxorubicin in Mice After Intravenous Administration

Abstract: The toxicities of free doxorubicin (F-DOX) and liposome-associated doxorubicin (L-DOX) were investigated in inbred BALB/c and outbred Sabra mice treated iv with 5, 7.5, and 10 mg doxorubicin (DOX)/kg body weight every 2 weeks up to 8 injections and observed for 6 months. Sonicated liposomes containing phosphatidylcholine, phosphatidylglycerol, and cholesterol were used. The lethal effect was reduced in mice treated with L-DOX as compared to mice treated with F-DOX. At a dose of 7.5 mg DOX/kg, 100% of mice receiving the L-DOX survived a cumulative dose of 60 mg/kg administered over 98 days, while 92% of mice receiving the F-DOX died. Two distinct patterns of death were observed: an acute phase type occurring early after injection of high doses of DOX and apparently related to gastrointestinal toxicity and a delayed phase type requiring a long latency after initial drug exposure and characterized by a complex pattern of abnormalities. Delivery of DOX by liposomes effectively protected against both types of lethal effects. Reduced toxicity of L-DOX resulted in reduced body and organ weight losses, reduced severity of pathologic changes, and fewer blood biochemical alterations. The pathological damage to the heart muscle found in mice treated with L-DOX was less severe than with F-DOX, and in some cases it was reversible. Nephrotoxicity was extremely frequent and severe among F-DOX-treated mice, while it was totally insignificant among L-DOX-treated mice. Hyperlipidemia, hypoglycemia, and glycogen-depleted hepatocytes were characteristic findings in mice treated with F-DOX. Altogether, the data obtained in this study indicate that liposomes significantly diminish the toxicity of DOX with the use of an intermittent schedule of chemotherapy. In addition to changes in tissue distribution as a mechanism of reduced toxicity, it is proposed that DOX associated with liposomal lipids interacts less efficiently than the free drug with target intracellular phospholipids.

Enhanced in vitro selective toxicity of chemotherapeutic agents for human cancer cells based on a metabolic defect.

Abstract: A metabolic defect that is prevalent in human cancer cell lines was exploited to selectively kill these cells without killing cocultured normal human fibroblasts. Methionine dependence, a metabolic defect seen only in cancer cells or immortalized cell lines in vitro, precludes the cells from growing in media in which methionine is replaced by its immediate precursor, homocysteine, a condition that allows the growth of all normal cell strains tested. The methionine-dependent cells become reversibly blocked in late S-G2 (i.e., late-S and G2 phases) under the above condition, a block that was exploited for selective chemotherapy against these cells. In cultures that were initiated with equal amounts of cancer cells and human diploid fibroblasts, substitution of homocysteine and doxorubicin for methionine in the culture medium followed by methionine repletion with vincristine was totally effective at selectively eliminating a methionine-dependent human sarcoma and 3 methionine-dependent human carcinomas. The above protocol was nearly totally effective against a partially methionine-independent revertant of the sarcoma. The chemotherapeutic procedure used was not lethal to normal cells growing alongside the tumor cells and was ineffective when conducted totally in methionine-containing medium. The optimal procedure was 10(-10) M doxorubicin in methionine-free, homocysteine-containing medium for 10 days followed by 2 x 10(-7) M vincristine in methionine-containing, homocysteine-free medium for 1 day, in turn followed by drug-free methionine-containing, homocysteine-free medium. These results demonstrate the potential for treatment of solid tumors with chemotherapy based on metabolic differences between normal and tumor cells.

Verapamil-mediated sensitization of doxorubicin-selected pleiotropic resistance in human sarcoma cells: selectivity for drugs which produce DNA scission.

Abstract: The effects of verapamil on the cytotoxicity and accumulation of multiple drugs were studied in a model of pleiotropic resistance generated by doxorubicin (DOX) selection of the human sarcoma cell line MES-SA. The in vitro sensitivity of the DOX-resistant variant (named Dx5), which is 50- to 100-fold resistant to DOX compared to MES-SA, was enhanced approximately 7-fold by verapamil (3 micrograms/ml). In addition, the cytotoxicity of several agents to which the Dx5 line displays cross-resistance, i.e., daunorubicin, dactinomycin, mitoxantrone, and etoposide, was also enhanced 2- to 14-fold by verapamil. These agents share the properties of DNA intercalation and/or interaction with topoisomerase II. In contrast, verapamil did not alter the sensitivity of Dx5 to several other agents to which cross-resistance had been demonstrated, i.e., vincristine, vinblastine, colchicine, mitomycin C, and melphalan; nor did verapamil enhance the cytotoxicity of DOX or other agents against the DOX-sensitive parent, MES-SA. The sensitizing effect of verapamil did not correlate well with its effects on intracellular drug accumulation. [14C]DPX accumulation was increased by 30-40% in Dx5 but not in MES-SA cells in the presence of verapamil. [3H]Vinblastine accumulation was increased by 24-72% in both MES-SA and Dx5 cells in the presence of verapamil, although cytotoxicity of the Vinca alkaloids was not affected. In this human sarcoma model of DOX-selected pleiotropic resistance, verapamil partially reversed the resistance to DOX, as well as four of the nine drugs for which cross-resistance had been demonstrated in Dx5. The potentiation by verapamil of the cytotoxicity of some but not all of these antitumor agents suggests that factors other than altered drug transport may be responsible. The pattern of sensitization, restricted to agents which produce DNA strand scission by interaction with topoisomerase II, suggests that verapamil may be acting to promote the formation or inhibit the repair of such DNA strand breaks.

Preclinical trials with combinations and conjugates of T101 monoclonal antibody and doxorubicin.

Abstract: We investigated the potential for additive therapy for malignancy using an anti-human T-cell monoclonal antibody, T101, and the chemotherapy agent doxorubicin (DOX). We compared the efficacy of T101 alone, DOX alone, T101 and DOX covalently linked to dextran to form an immunoconjugate, T101 plus DOX mixed together and injected, T101 and DOX injected separately, and nonspecific murine IgG2A plus DOX mixed together. Inhibition of [3H]thymidine was examined in vitro, and the clinical efficacy of each treatment was tested on human T-cell tumors growing in athymic mice. In vitro experiments confirmed retention of immunoreactivity and cytotoxicity by the immunoconjugate, but it was not superior to DOX alone. In efficacy experiments, all therapeutic arms were superior to placebo treatment (P less than 0.05). However, the best results in the animal tumor model were obtained with T101 mixed with DOX, perhaps because of formation of weak complexes via hydrophobic bonds. This mixture was superior to all other treatments, both by growth curve analysis (P less than 0.05) and by analysis of complete regression of tumor (P less than 0.01). T101 mixed with DOX was superior to a mixture of nonspecific mouse immunoglobulin and DOX and superior to a combination of T101 injected i.v. and DOX injected i.p. The antitumor effect of T101 mixed with DOX was blocked by premodulating the target antigen with T101. These data suggest that further exploration into monoclonal antibody-anthracycline complexes is warranted.

Amiodarone-induced Enhancement of Doxorubicin and 4′-Deoxydoxorubicin Cytotoxicity to Rat Colon Cancer Cells in Vitro and in Vivo

Abstract: The mechanisms of the resistance of intestinal cancer to anthracyclines were studied on an experimental model of rat colon cancer cells. The accumulation of anthracyclines in the nucleus of living cancer cells was observed by fluorescence microscopy. This accumulation depended on both the capacity of anthracyclines to penetrate into the cell and the activity of an efflux mechanism extruding the drug from the cell. We found that 4'-deoxydoxorubicin was superior to 4 other anthracyclines in its capacity to penetrate into confluent colon cancer cells. Amiodarone, an antiarrhythmic agent used in cardiology, inhibited the efflux mechanism efficiently and increased the toxicity of anthracyclines to the colon cancer cells. Association of amiodarone and 4'-deoxydoxorubicin was able to cure 5 of 13 rats that had been inoculated i.p. previously with syngeneic colon cancer cells. This association could be of interest in the treatment of human colon cancer.

Primary or delayed debulking surgery and chemotherapy consisting of cisplatin, doxorubicin, and cyclophosphamide in stage III-IV epithelial ovarian carcinoma.

Abstract: Eighty-eight previously untreated patients with stage III and IV epithelial ovarian carcinoma were treated with primary or delayed (secondary) optimal debulking surgery unless impossible, and combination chemotherapy consisting of cisplatin, doxorubicin, and cyclophosphamide intravenously (IV) on day 1, every 4 weeks (CAP-I). In patients with no evidence of disease after six cycles of chemotherapy, a second-look laparotomy was performed. A pathologically confirmed complete response (CR) was obtained in 39% of the patients. The median progression-free survival period of all patients was 18 months and the median survival time 24 months. CAP-I is an effective chemotherapy schedule that can be administered with moderate toxicity and appears to enhance the cure rate in advanced ovarian carcinoma. The role of secondary surgery must be further defined.

Antitumor and toxicity evaluation of free doxorubicin and doxorubicin entrapped in cardiolipin liposomes.

Abstract: The antitumor activity of free doxorubicin and doxorubicin entrapped in cardiolipin liposomes was evaluated in P388 ascitic leukemia, disseminated Gross leukemia, and advanced mammary carcinoma. In P388 leukemia, free drug and drug entrapped in liposomes demonstrated equivalent antitumor activity at doses of 2.2 and 4.4 mg/kg, demonstrating 52% and 69% ILS (increase in life-span), respectively. Free doxorubicin at a dose of 10 mg/kg was superior, producing a 185% ILS against 82% with liposomal doxorubicin. With an increase in administered dose the antitumor response with liposomal doxorubicin was much more pronounced; at doses of 20 and 25 mg/kg the ILS was in excess of 376%, with five of ten mice surviving tumor-free. In Gross leukemia, the optimum dose of free doxorubicin, 10 mg/kg, brought about 186% T/C (median survival in treated mice over that in controls, x100), whereas with liposomal doxorubicin the optimum dose was 16.9 mg/kg, which yielded 214% T/C. In advanced mammary carcinoma, the maximum tumor regression with free doxorubicin was at a dose of 7.5 mg/kg, with two of six mice dying of toxicity. Liposomal doxorubicin caused maximum tumor regression at 10.8 mg/kg dose with no toxic deaths. Doxorubicin entrapped in cardiolipin liposomes was much less toxic than free drug at high doses in normal mice.

Intravesical chemotherapy: Studies on the relationship between ph and cytotoxicity

Abstract: The influence of pH on the antitumor activity of drugs used for intravesical chemotherapy was studied. A human continuous cell line derived from a transitional cell carcinoma of the bladder was exposed to 6 drugs (Adriamycin [doxorubicin], cisplatin, epirubicin, epodyl, mitomycin C, and thiotepa) for 1 hour at 11 pH values ranging from 5.2 to 9.7, and cytotoxicity was measured by inhibition of colony formation. pH had a marked influence on drug activity: cisplatin, mitomycin C, and thiotepa were most cytotoxic in acid media, Adriamycin, and epirubicin in alkaline media, while epodyl was the only drug whose cytotoxicity was unaffected by pH. In addition to these in vitro studies, comparisons were made of the pH of urine samples obtained from patients immediately before and at the completion of intravesical chemotherapy. Changes in pH up to a maximum of +/- 1.6 units were observed, although in most cases, values were similar before and after therapy. All the drugs used were acidic in solution, with the exception of thiotepa. It is concluded that by adjusting solvent and urine pH to the optimum value for each drug, the effectiveness of intravesical chemotherapy might be enhanced.

Use of Growth-stimulatory Hormones to Improve the in Vitro Therapeutic Index of Doxorubicin for Human Breast Tumors

Abstract: Tumor-specific growth factors that increase the proliferative rate of tumor cells should, in theory, enhance the efficacy of cytotoxic drugs that have cell-cycle-dependent activity To test this hypothesis, we measured the cytotoxicity of doxorubicin for clonogenic breast tumor cells in the presence and the absence of hormones that stimulate their in vitro growth (17β-estradiol, epidermal growth factor, hydrocortisone, and insulin) These growth factors increased the sensitivity to doxorubicin of the clonogenic cell populations from 20 of 25 breast tumors Their effect was greatest on tumors from hormone-responsive patients In contrast, these hormones increased the clonogenicity and sensitivity to doxorubicin of bone marrow progenitor cells to a much lesser degree Hence, under the effect of these growth factors, the in vitro therapeutic index of doxorubicin improved for most of the tumors tested, while tamoxifen citrate, a tumor growth-inhibitory hormone, had the opposite effect We conclude that tumor tissue-specific growth-stimulatory hormones can improve the in vitro efficacy of cell cycle-active anticancer drugs

Comparison of doxorubicin-induced DNA damage in doxorubicin-sensitive and -resistant P388 murine leukemia cells.

Abstract: Doxorubicin-induced DNA damage was studied in the P388 leukemia cell line and in a doxorubicin-resistant subline by alkaline elution techniques. DNA single-strand breaks and DNA-protein cross-links were determined. Whereas, in the sensitive line, 1 hr exposure to drug induced DNA damage in a concentration-dependent manner, in the resistant line only a marginal effect was observed at high drug concentrations. In contrast, elution kinetics of DNAs from cells irradiated with X-rays were similar in both lines. Although a reduced intracellular drug accumulation was found in resistant cells, this difference could not account for the marked reduction in doxorubicin-induced DNA damage. The degree of resistance of the P388 subline was reduced about 7-fold by verapamil, whereas the extent of DNA damage was unaffected. These results suggest the presence of alternative modes of resistance, independent of membrane changes, in highly resistant cells.

Doxorubicin Chemotherapy in the Treatment of Soft-Tissue Sarcoma: Combined Results of Two Randomized Trials

Abstract: • In 1978, there were initiated two independent randomized, prospective trials of adjuvant doxorubicin hydrochloride (Adriamycin) following primary therapy for soft-tissue sarcoma. The virtual identity of these two protocols permits their combination for analysis. A total of 75 patients (42 men, 33 women) with soft-tissue sarcoma (stages IIB to IVA) were randomized, after receiving optimal regional therapy, to receive either doxorubicin hydrochloride (450 mg/m 2 ) (37 patients) or observation (38 patients). Follow-up has ranged from 16 to 80 months (median, 49 months). Twenty-five patients (33%) died, and two patients receiving doxorubicin developed cardiotoxicity. No significant differences in local control, metastasis-free survival, disease-free survival, and overall survival were observed for the two treatment arms. Despite temporary prolongation of disease-free survival with doxorubicin in some subgroups, we conclude that there is no advantage to the use of adjuvant doxorubicin in the treatment of soft-tissue sarcoma. ( Arch Surg 1986;121:1354-1359)

Intensely potent anthracycline antibiotic oxaunomycin produced by a blocked mutant of the daunorubicin-producing microorganism.

Abstract: A new potent anthracycline antibiotic oxaunomycin was isolated from the culture broth of a blocked mutant derived from a baumycin producer and was identified as 7-O-(α-L-daunosaminyl)-β-rhodomycinone. It exhibited about 100 times more strongly cytotoxic activity against leukemic L1210 cell culture than doxorubicin.

Phase I and II agents in cancer therapy: I. Anthracyclines and related compounds.

Abstract: Anthracycline antibiotics remain among the most potent anticancer drugs, but their efficacy is limited by the development of a dose-dependent irreversible cardiomyopathy and by the emergence of clones of tumor cells resistant to the effects of the drug. Modifications of the basic anthracycline structure have resulted in molecules that may share the activity of the parent compound, with amelioration of some toxicities, absence of cross-resistance, or activity against tumors insensitive to the parent drug. Epirubicin has a unique metabolic pathway, glucuronidation, that may result in more rapid plasma clearance and reduced toxicity as compared with doxorubicin. Epirubicin has demonstrated comparable activity to doxorubicin in breast cancer, with possibly reduced toxicity. Idarubicin is of interest because of its cytotoxic activity when given orally. Idarubicin has prolonged retention in the plasma and has equal cytotoxic activity to the parent compound. Idarubicin has demonstrated activity against acute leukemia and breast cancer; in the latter tumor category, some doxorubicin-resistant tumors have responded. Esorubicin is of interest because of its nearly absent cardiac toxicity. This agent has some activity against solid tumors and is currently being clinically tested. Aclacinomycin A is an anthracycline in which a trisaccharide is substituted for the aminosugar. Aclacinomycin A and the related compound marcellomycin are of interest as both cytotoxic and differentiating agents. Menogaril is an anthracycline with the aminosugar on the D ring; it does not exhibit cross-resistance with doxorubicin or cardiotoxicity. Mitoxantrone is a compound that is related to the anthracyclines but has a different mechanism of action. This agent has significant activity against acute leukemia and breast cancer and is currently being compared with doxorubicin. Amsacrine is another compound related to the anthracyclines that possesses major activity against acute leukemias. Minor modifications of the anthracycline molecule have had major impact on the biologic activity of these drugs. New anthracycline analogues with up to 100 times the potency of currently available anthracyclines are being developed for clinical testing, and these complex molecules retain a nearly unlimited potential for structural modification.

Prospective Study of Cardiomyopathy Induced by Adjuvant Doxorubicin Therapy in Patients With Soft-Tissue Sarcomas

Abstract: • Since a combination of surgery and adjuvant high-dose doxorubicin therapy can prolong survival in patients with extremity sarcomas, but at the expense of significant cardiomyopathic changes, we prospectively studied the differences in cardiotoxicity in 118 patients with sarcomas treated with high- vs low-dose doxorubicin therapy following surgery. Cardiac function, as assessed by left ventricular ejection fraction (EF), was determined by standard radionuclide angiography during rest and exercise. No patients in this study developed congestive heart failure. While both regimens produced net decreases in EF during rest and exercise, the high-dose doxorubicin regimen resulted in significantly greater declines in EF than the low-dose protocol. Of patients with normal baseline values, a greater percentage of patients receiving the high-dose regimen developed an abnormal EF than did those receiving the low-dose regimen, even after separating younger from older individuals. Thus, treatment-induced cardiomyopathy appears to be a significant clinical problem after both high- and low-dose doxorubicin therapy. The use of the low-dose regimen decreases the magnitude of the cardiomyopathic changes. ( Arch Surg 1986;121:1445-1451)

Single-Strand DNA Breaks Induced by Chromophore-modified Anthracyclines in P388 Leukemia Cells

Abstract: Single-strand DNA breaks induced by chromophore-modified anthracyclines related to doxorubicin (including 11-deoxydaunorubicin, 4-demethoxydaunorubicin, 4-demethoxy-11-deoxy-4′- epi -daunorubicin, 4-demethyl-6- O -methyldoxorubicin) in cultured P388 leukemia cells were determined by the filter alkaline elution method. The tested analogues differed markedly in their cytotoxic potency. In the range of cytotoxic concentrations, 11-deoxydaunorubicin produced single-strand DNA break frequency of the same order of magnitude as that produced by doxorubicin, while other derivatives caused much more marked damage on DNA than doxorubicin. Since DNA breaks were found to be protein associated, the type of DNA damage produced by all tested derivatives presumably resulted by action of DNA topoisomerases II, as proposed for doxorubicin and other intercalating agents. Although the “potent” (with respect to DNA damage) derivatives, except 4-demethyl-6- O -methyldoxorubicin, showed an increased cellular drug accumulation as compared to doxorubicin, this did not account for the marked differences in ability to damage DNA. 4-Demethyl-6- O -methyldoxorubicin was the most efficient derivative, producing DNA breaks in a lower range of cellular drug content. A striking biphasic dose-response curve was observed for the 4-demethoxy derivatives, suggesting a complex mechanism of interaction among drug, DNA, and enzyme. A lack of correlation was noted among DNA binding affinity, induction of strand breaks, and cytotoxic activity of these chromophore-modified derivatives. From these observations, it is suggested that multiple actions of anthracyclines at the DNA level are responsible for their cytotoxic activity, which is not simply related to inhibition of a specific DNA-dependent enzyme and/or function.

Characterization of a doxorubicin-resistant murine melanoma line: studies on cross-resistance and its circumvention.

Abstract: A B16 mouse melanoma cell line resistant to doxorubicin was obtained by continuous in vitro exposure to the drug. The ID50 for this line was 200 times higher than that for the parental cell line. The resistant cell line had some biological characteristics similar to those of the sensitive parental cell line, like saturation density and protein content. Differences were found in doubling time which was longer, cloning efficiency which was lower and DNA content which was higher in the resistant as compared to the parental line. Intracellular distribution of doxorubicin was also different having a nuclear-cytoplasmic ratio higher in sensitive than in resistant cells. Melanin content was an unstable feature in the sensitive cell line, whereas melanin was always present in resistant cells. Resistance to doxorubicin was maintained during 50 in vitro passages in the absence of the drug. Cross-resistance was found with vincristine and other anthracyclines, like daunorubicin and 4'-epi-doxorubicin but not with cis-platinum, and a new doxorubicin derivative, 4'-deoxy-4'-iodio-doxorubicin. The B16 line showed a lower resistance index to 4'-deoxy-doxorubicin and 4-demethoxy-daunorubicin (30 and 3 respectively), as compared to doxorubicin. Doxorubicin-resistance was partially circumvented by pretreatment of resistant cells with verapamil, a calcium chelating agent, and by trifluoperazine, a calmodulin-antagonist.

Synergistic activity of doxorubicin and the bisdioxopiperazine (+)-1,2-bis(3,5-dioxopiperazinyl-1-yl)propane (ICRF 187) against the murine sarcoma S180 cell line.

Abstract: The bisdioxopiperazine (+)-1,2-bis(3,5-dioxopiperazinyl-1-yl)propane (ICRF 187) abrogates doxorubicin cardiotoxicity in every mammalian species tested, but its effect on doxorubicin antitumor activity remains poorly understood. In order to better define the anthracycline-bisdioxopiperazine interaction, the ability of murine sarcoma S180 cells to form colonies in soft agar and their capability to proliferate in microtiter wells were assayed after exposure to drug at varying doses and schedules. Incubation of cell suspensions for 1 h with doxorubicin, 0.1 µg/ml, with or without (+)-1,2-bis(3,5-dioxopiperazinyl-1-yl)propane, 80 µg/ml, produces additive cytotoxicity for the combination. Prolonged incubation (24 h) with the same drugs produces synergistic cytotoxic and antiproliferative effects at 1- and 2-log order reductions in dose. These studies indicate that the antineoplastic activity of the single agents doxorubicin and (+)-1,2-bis(3,5-dioxopiperazinyl-1-yl)propane is enhanced when the drugs are used in combination, and that this phenomenon is highly dose and schedule dependent.

Immunotoxicity of multiple dosing regimens of free doxorubicin and doxorubicin entrapped in cardiolipin liposomes.

Abstract: We have shown that doxorubicin entrapped in cardiolipin liposomes retain antitumour efficacy in mice but had diminished cardiac uptake and cardiotoxicity. Such liposomes are preferentially taken up by spleen. In a previous study we showed that a single dose of liposomal doxorubicin is not more toxic than free doxorubicin with regard to immunologic parameters including generation of cytotoxicity for histocompatibility alloantigens and mitogenic responsiveness. In the present study, we have explored clinically relevant multiple dosing at weekly intervals, 2, 3, or 4 times. Again, despite splenic localization of liposomal doxorubicin, the depressive effect on these immunological parameters is not greater than the effect of free drug, and, in addition, the damage is repaired earlier.