Showing papers on "Doxorubicin published in 1988"

Effect of Granulocyte Colony-Stimulating Factor on Neutropenia and Associated Morbidity Due to Chemotherapy for Transitional-Cell Carcinoma of the Urothelium

Abstract: We evaluated the ability of human recombinant granulocyte colony-stimulating factor (rhG-CSF) to prevent chemotherapy-induced neutropenia or to accelerate recovery from this complication and thus allow patients to receive full doses of antineoplastic agents on time, according to protocol design. Twenty-seven patients with transitional-cell carcinoma of the urothelium who were undergoing treatment with methotrexate, doxorubicin, vinblastine, and cisplatin were given rhG-CSF (up to 60 micrograms per kilogram of body weight per day) before their first cycle of combination chemotherapy, during the first cycle, or at both points. Treatment with rhG-CSF before chemotherapy resulted in a dose-dependent increase in the absolute neutrophil count. Treatment with rhG-CSF after chemotherapy significantly reduced the number of days (91 percent) per patient on which the absolute neutrophil count was 1000 per microliter or less (P = 0.0039), reduced the number of days (1 vs. 35) on which antibiotics were used to treat fever and neutropenia, and significantly increased the percentage (100 vs. 29 percent) of patients qualified to receive planned chemotherapy on day 14 of the treatment cycle (P = 0.0015). In addition, the incidence of mucositis was significantly decreased (11 vs. 44 percent, P = 0.041), as was its severity. These findings demonstrate that rhG-CSF is a potent stimulus of normal neutrophil proliferation and maturation. In addition, its administration can reduce both the hematopoietic and oral toxicity of chemotherapy.

Clinical Pharmacokinetics of Doxorubicin

Abstract: Doxorubicin (adriamycin) has a very wide antitumour spectrum, compared with other anticancer drugs; however, except for Hodgkin’s disease, it is not associated with curative chemotherapy. Doxorubicin has been in clinical use for more than 2 decades, and only recently has it been recognised that the cytotoxic effect is produced at the cellular level by multiple mechanisms which have not yet been conclusively identified. Key factors are a combination of doxorubicin-induced free radical formation due to metabolic activation, deleterious actions at the level of the membrane, and drug-intercalation into DNA.

Doxorubicin cardiotoxicity may be caused by its metabolite, doxorubicinol.

Abstract: Doxorubicin (former generic name, adriamycin), a highly effective anticancer drug, produces cardiotoxicity, which limits its therapeutic potential. The mechanism of this cardiotoxicity has remained elusive. Our data suggest that this toxicity could involve doxorubicinol, the primary circulating metabolite of doxorubicin. Doxorubicinol was markedly more potent than doxorubicin at compromising both systolic and diastolic cardiac function. Similarly, doxorubicinol was much more potent than doxorubicin at inhibiting the calcium pump of sarcoplasmic reticulum [ATP phosphohydrolase (Ca2+-transporting), EC 3.6.1.38], the Na+/K+ pump of sarcolemma [ATP phosphohydrolase (Na+/K+-transporting), EC 3.6.1.37], and the F0F1 proton pump of mitochondria [ATP phosphohydrolase (H+-transporting, EC 3.6.1.34]. Our finding that this highly toxic metabolite was produced by cardiac tissue exposed to doxorubicin suggests that doxorubicinol could accumulate in the heart and contribute significantly to the chronic cumulative cardiotoxicity of doxorubicin therapy. Our observation that doxorubicin was more potent than doxorubicinol in inhibiting tumor cell growth in vitro suggests that the cardiotoxicity of doxorubicin is dissociable from its anticancer activity.

Adjuvant chemotherapy for patients with high-grade soft-tissue sarcomas of the extremity.

Abstract: We have previously reported the results of a randomized trial that demonstrated the survival benefit of adjuvant chemotherapy in the treatment of patients with high-grade extremity sarcomas compared with no chemotherapy. This regimen included doxorubicin, cyclophosphamide, and methotrexate. This report updates and extends our experience. The median follow-up of this trial is now 7.1 years and reveals a 5-year disease-free survival of 75% and 54% for chemotherapy and no chemotherapy groups, respectively (two-sided P [P2] = .037). The 5-year overall survival for patients in this trial was 83% and 60% for the chemotherapy and no chemotherapy groups, respectively, with a trend towards improved survival in the chemotherapy arm (P2 = .124). Because of doxorubicin-induced cardiomyopathy we performed a subsequent randomized trial comparing this high-dose regimen to reduced cumulative doses of doxorubicin and cyclophosphamide without methotrexate. Eighty-eight patients were entered into this trial which has a medi...

Adjuvant cyclophosphamide, doxorubicin, and cisplatin chemotherapy for bladder cancer: an update.

Abstract: Seventy-one patients received adjuvant Cytoxan (cyclophosphamide; Bristol-Myers Co, Evansville, IN), Adriamycin (doxorubicin; Adria Laboratories, Columbus, OH), and cisplatin (CISCA) chemotherapy between March 1981 and March 1986. Patients received adjuvant CISCA chemotherapy if they had pathological findings that were thought to predict for high likelihood of relapse. These included the presence of resected nodal metastases, extravesicular involvement of tumor, lymphatic/vascular permeation of the primary tumor, or pelvic visceral invasion. Sixty-two patients at a similar high risk for recurrence did not receive adjuvant CISCA chemotherapy because they refused, had medical contraindications to therapy, or were not referred for chemotherapy. Two-hundred six patients had a cystectomy performed during the same study period but had none of the poor prognostic features suggesting a high risk for relapse. Sixty-two percent of the patients receiving adjuvant chemotherapy are alive and disease-free for a mean fo...

Clinical modulation of doxorubicin resistance by the calmodulin-inhibitor, trifluoperazine: a phase I/II trial.

Abstract: Drug resistance to chemotherapy agents such as doxorubicin appears to be an important cause of therapeutic failure in cancer treatment. Based on preclinical information demonstrating that the phenothiazine calmodulin-inhibitor trifluoperazine can enhance retention and cytotoxicity of doxorubicin in resistant cells, a phase I/II trial of the combination was performed to determine the maximally tolerated dose (MTD) of trifluoperazine that could be administered with doxorubicin. Patients with intrinsic (no previous response) and acquired (previous response with relapse) doxorubicin resistance were eligible. Doxorubicin was administered as a 96-hour continuous infusion (60 mg/m2) on days 2 through 5. Trifluoperazine was administered in divided doses orally on days 1 through 6, with dose escalation from 20 to 100 mg/d. Thirty-six patients were evaluable. The MTD of trifluoperazine was 60 mg/d, with dose-limiting toxicity being extrapyramidal side effects. No alteration of doxorubicin toxicity was observed. Sev...

Advanced ovarian cancer: long-term results of treatment with intensive cisplatin-based chemotherapy of brief duration.

Abstract: Study Objective:To determine the efficacy of a 6-month course of combination chemotherapy with hexamethylmelamine, cyclophosphamide, doxorubicin, and cisplatin (H-CAP) in the treatment of ...

Verapamil Reversal of Doxorubicin Resistance in Multidrug-resistant Human Myeloma Cells and Association with Drug Accumulation and DNA Damage

Abstract: Verapamil reversed resistance to doxorubicin in a human multiple myeloma cell line selected for multiple drug resistance. The drug-resistant cell line 8226/DOX40 is known to have reduced intracellular drug accumulation associated with the overexpression of P-glycoprotein when compared to the sensitive parent cell line 8226/S. Verapamil alone was minimally cytotoxic in both cell lines, but reversed doxorubicin resistance in a dose-related manner in 8226/DOX40. A similar dose-response relationship was observed for verapamil in increasing net intracellular doxorubicin accumulation. This increased net accumulation was secondary to block of enhanced doxorubicin efflux by verapamil from resistant cells. In contrast, verapamil did not alter initial doxorubicin accumulation over the first 60 s when incubated with resistant cells. Addition of verapamil to the 8226/DOX40 cells enhanced the formation of doxorubicin-induced DNA single strand breaks, double strand breaks, and DNA-protein cross-links. Verapamil had no effect on these lesions in the drug-sensitive cells. In addition, verapamil did not affect chemotherapeutic cytotoxicity or transport in the drug-sensitive cell line. Verapamil appears to reverse doxorubicin resistance in this human myeloma cell line by blocking enhanced drug efflux, leading to increased drug accumulation and enhanced DNA damage.

Combined effects of chemotherapy and interleukin 2 in the therapy of mice with advanced pulmonary tumors.

Abstract: We have evaluated the effects of chemotherapeutic agents on the toxicity and antitumor benefit of therapy of established murine tumors by high-dose interleukin 2 (IL-2). Cyclophosphamide (Cy), doxorubicin, and bischloroethylnitrosourea were given to normal mice prior to IL-2 administration to test the effects of these agents on IL-2-induced toxicity. Cy at doses of 100 mg/kg and 150 mg/kg completely protected mice from a 100% lethal dose of IL-2, and doses of 50 mg/kg and 150 mg/kg allowed the administration of a median of 4.5 and 10.0 more doses of IL-2, respectively, before death from IL-2 toxicity occurred. Doxorubicin at 8 mg/kg and bischloroethylnitrosourea at 20 mg/kg did not impact on toxicity in IL-2-treated mice. In mice bearing pulmonary metastases of the weakly immunogenic MCA-105 sarcoma, IL-2 increased median survival time from 33 (no IL-2) to >60 days for all doses of IL-2 tested when combined with a single injection of Cy at 75 mg/kg ( P in vivo generated lymphokine-activated killer cells, but these lymphokine-activated killer cells are still lytic for fresh tumor targets in vitro . Thus, the mechanism of this synergy does not appear to involve stimulation of lymphokine-activated killer cell activity, but may in part involve reduction of tumor burden by the chemotherapeutic agent, an increase in susceptibility of tumor to cellular immune lysis, and/or a decrease in suppressor cell activity mediated by the chemotherapy.

Reversal of drug-resistance in multiple myeloma with verapamil.

Abstract: Summary In vitro testing with a new doxorubicin resistant myeloma cell line revealed the reversal of drug resistance with as little as 100 ng/ml of verapamil (a calcium channel blocker), a dose easily achievable in humans. A first patient with IgGk Myeloma is presented in whom resistance to VAD (vincristine/doxorubicin infusion plus dexamethasone) chemotherapy was reversed with the administration of verapamil. A subsequent clinical study has been initiated. The potential for further evaluation of calcium channel blockers in multiple myeloma is discussed.

Combination cytotoxic chemotherapy with cisplatin or doxorubicin and photodynamic therapy in murine tumors.

Abstract: This study was designed to evaluate the interaction of photodynamic therapy (PDT) and chemotherapy in an animal model. PDT is based on the interaction of hematoporphyrin derivative and red light of the appropriate wavelength (630 nm) and intensity. Two tumor models were utilized: C3H/Km mice bearing the RIF-1 tumor and BALB/c mice bearing the EMT-6 tumor. Tumor-bearing mice were treated with either cisplatin (DDP), doxorubicin (ADM), PDT, or a combination of drug and PDT. It was demonstrated that the RIF-1 tumor was sensitive to DDP and insensitive to both PDT and ADM. There was no additional antitumor effect when either drug was combined with PDT. The EMT-6 tumor was moderately sensitive to PDT and mildly sensitive to both DDP and ADM. Although the addition of DDP did not potentiate tumor destruction, the addition of ADM significantly enhanced the effect of PDT (P = .01). The enhanced activity of the combination of PDT and ADM appeared to be the result of increased activity of ADM alone, when illuminated with red (630 nm) light. This potentiation may be due to a photochemical process or may be secondary to the mild hyperthermia generated by illumination with the laser. This study demonstrates that PDT combined with cytotoxic chemotherapy is well tolerated in these animals and that certain combinations of PDT and chemotherapy may result in an enhanced tumoricidal effect.

Estrogen-induced Potentiation of DNA Damage and Cytotoxicity in Human Breast Cancer Cells Treated with Topoisomerase II-interactive Antitumor Drugs

Abstract: Hormone stimulation of responsive neoplasms is a potential strategy for improving the target selectivity of cancer chemotherapy. Using an alkaline DNA-unwinding technique to detect drug-induced DNA strand breakage, we have shown that estrogen stimulation of T-47D human breast cancer cells enhances induction of DNA cleavage by etoposide (VP-16), 4',9-acridinylaminomethanesulfon-m-anisidide (m-AMSA), mitoxantrone, and doxorubicin, drugs known to interact with the DNA-modifying enzyme topoisomerase II. No enhancement of DNA cleavage or cytotoxicity was seen in estrogen-treated cells exposed to X-rays or bleomycin. Novobiocin (an inhibitor of topoisomerase II) markedly antagonized the enhancing effect of estrogen on VP-16-induced DNA cleavage, while neutral nucleoid sedimentation detected less than 10% of such strand breaks revealed in estrogen-treated cells by alkaline unwinding. Estrogen did not affect DNA repair of lesions induced by X-rays, VP-16, or ultraviolet radiation. Enhancement of DNA cleavage was accompanied by a corresponding enhancement of cytotoxicity in cells treated with VP-16 or m-AMSA, but only minimal enhancement of cytotoxicity was seen following treatment with mitoxantrone or doxorubicin. Estrogen-treated and control cells treated with VP-16 and m-AMSA sustained similar levels of DNA cleavage for equivalent levels of cytotoxicity. These findings suggest that estrogen potentiates the cytotoxicity of VP-16 and m-AMSA by enhancing topoisomerase II-mediated DNA damage but that such "damage" does not contribute significantly to cytotoxicity induced by mitoxantrone or doxorubicin. Estrogen stimulation of receptor-positive breast cancer may prove to be a clinically relevant strategy for improving the selectivity and cytotoxicity of some, but not all, topoisomerase II-interactive drugs.

Mitoxantrone: A Novel Anthracycline Derivative

Abstract: The chemistry, pharmacology, pharmacokinetics, clinical efficacy, dosage and administration, and adverse effects of mitoxantrone are reviewed. Mitoxantrone, an aminoanthraquinone that was synthesized in 1979, belongs to a new chemical class of agents known as the anthracenediones. It possesses antiviral, antibacterial, immunomodulatory, and antitumor activity. The drug's antitumor activity is attributed to its interaction with DNA topoisomerase II, and its interaction with human cells may also involve nonintercalary, electrostatic interactions. Mitoxantrone is poorly absorbed orally and is most commonly administered intravenously. The drug is rapidly distributed into the red blood cells, white blood cells, and platelets, followed by deep-tissue sequestration. Mitoxantrone has demonstrated clinical efficacy in the treatment of leukemia, lymphoma, and breast cancer. As a single agent, mitoxantrone has a response rate of roughly 30% in acute nonlymphocytic leukemia or acute myeloid leukemia. In combination with other standard agents (cytarabine, vincristine, and prednisone), the response rate may reach 60%. In breast cancer, mitoxantrone's response rate as a single agent is 25-30%, while combination regimens produce response rates of 60% or more. The drug can cause cardiotoxicity with cumulative doses. Other adverse effects include myelosuppression, nausea and vomiting, stomatitis, mucositis, and alopecia. The cost of mitoxantrone is comparable to that of doxorubicin, but it is substantially more expensive than daunorubicin. Mitoxantrone is an important new agent with antitumor activity in leukemia, lymphoma, and breast cancer. In most situations, mitoxantrone will be considered second-line treatment or a restricted-use item because of its high cost and because of the lack of FDA approval for indications other than acute nonlymphocytic leukemia.

Chemotherapy versus chemotherapy plus radiotherapy in the treatment of tonsillar squamous cell carcinoma in the dog.

Abstract: The effect of adjuvant chemotherapy and combined chemotherapy and radiotherapy in 22 dogs with advanced canine tonsillar carcinoma (World Health Organization [WHO], T2-3 primary tumor with infiltration into surrounding tissues) was evaluated. There were four treatment groups of at least five dogs each. Combinations of chemotherapeutic drugs reported to have activity against squamous cell carcinoma in humans and dogs (doxorubicin, cisplatin, vinblastine, and cyclophosphamide) were administered after tonsillectomy. Radiation therapy (orthovoltage type, external beam) was combined with chemotherapy in one treatment group. The dogs that had combination radiation therapy and chemotherapy had higher response rates and significantly longer survival times. However, most dogs died of progression of disease.

Reduction of doxorubicin cytotoxicity by ouabain: correlation with topoisomerase-induced DNA strand breakage in human and hamster cells.

Abstract: The cardiac glycoside ouabain, which is a specific inhibitor of the Na+, K+-pump, confers dramatic protection from the cytotoxic effects of doxorubicin (Adriamycin). This effect was documented in cultured A549 cells (human lung adenocarcinoma). CCL210 cells (human fibroblasts), and V79 cells (hamster fibroblasts). Maximum protection from doxorubicin cytotoxicity was achieved using 1 µm ouabain for A549 and CCL210 cells and 300 µm ouabain for V79 cells. These concentrations correlated well with the concentrations of ouabain required to induce Na+, K+-pump blockade, which was assessed using the K+ analogue 86Rb+. This suggests that protection is mediated by pump blockade. Addition of ouabain at the same time as doxorubicin was just as protective as preincubation with ouabain for an hour, demonstrating that the ouabain acts rapidly. Ouabain treatment affected neither influx nor efflux of doxorubicin. Ouabain also had no effect on verapamil-induced inhibition of doxorubicin efflux. However, ouabain partially blocked the verapamil-induced potentiation of the cytotoxic effects of doxorubicin. Therefore, ouabain does not protect by affecting intracellular doxorubicin levels. Fluorescence microscopy showed that the ability of doxorubicin to reach the nucleus was not influenced by ouabain. Alkaline elution studies demonstrated that ouabain greatly decreased doxorubicin-induced DNA strand breakage. Protection from cytotoxicity correlated closely with this decrease in strand breakage. These studies suggest that the stabilization of DNA-topoisomerase II complexes is closely linked to the mechanism of doxorubicin cytotoxicity and that this stabilization is influenced by the intracellular ionic milieu.

In Vitro Rat Myocyte Cardiotoxicity Model for Antitumor Antibiotics Using Adenosine Triphosphate/Protein Ratios

Abstract: Cumulative cardiotoxicity consistently limits the use of antitumor anthracyclines such as doxorubicin (DOX). Several in vivo and in vitro model systems have been developed for screening cardiotoxic agents. Problems with these models include excessive time and nonquantitative toxicity end points. We describe an in vitro system for culturing cardiac myocytes which overcomes these problems. Optimal myocyte cultures were obtained using serial 0.2% crude trypsin digestions of hearts from 1-2-day-old rats. Three-day-old myocyte cultures were treated with DOX for 6 h at concentrations of 0.1 to 10 micrograms/ml (0.18 to 18 microM). Electron microscopy performed on control and DOX-treated cultures showed characteristic histopathological signs of anthracycline damage. These changes included mitochondrial swelling, nuclear pleomorphism, chromatin clumping, and a diffuse loss of membrane integrity. Intracellular ATP, quantitated by the luciferase bioluminescence method, was shown to provide a simple and consistent quantitative biochemical marker of myocyte viability over the range of DOX concentrations used. The results showed both time- and dose-dependent decrements in ATP/protein ratios 72 h following exposure to DOX at concentrations greater than 0.1 microgram/ml. Leakage of lactate dehydrogenase activity, trypan blue uptake, and myocyte beating rates were variable and not as sensitive as ATP levels for evaluation of myocyte viability. Other cytotoxic agents which are not known to be cardiotoxic (dactinomycin, 1-beta-D-arabinofuranosylcytosine, fluorouracil, melphalan, and vincristine), required extremely high concentrations to produce myocyte damage in vitro. Tests with anthracycline analogues also demonstrated the ability of the assay to rank-order cardiotoxic agents on a weight basis: idarubicin greater than DOX greater than daunomycin greater than aclarubicin. When the in vitro drug concentrations required to lower ATP/protein ratios to 50% of controls were related to clinically achievable concentration x time products, DOX and daunomycin proved to be the most cardiotoxic in this series. These results suggest that comparative cardiotoxic screening studies may be performed in vitro using ATP levels in beating neonatal myocytes.

Direct relation of DNA lesions in multidrug-resistant human myeloma cells to intracellular doxorubicin concentration.

Abstract: Using a human myeloma cell line selected for resistance to doxorubicin (8226/DOX), which expresses the multidrug resistance phenotype, we studied the effects of drug accumulation on DNA damage and cytotoxicity in multidrug-resistant cells. The resistant 8226 subline showed a decrease in [14C]doxorubicin accumulation as compared to the sensitive (8226/S) subline at all time points investigated. DNA alkaline elution techniques were used to examine the formation of single and double strand breaks and DNA-protein cross-links following exposure to doxorubicin in both sensitive and resistant sublines. When 8226/S and 8226/DOX40 cells were exposed to the same extracellular concentration of doxorubicin there was a difference in the quantity of DNA lesions occurring, with the 8226/DOX40 line exhibiting less DNA damage. However, when the extracellular concentration of drug was adjusted to yield equivalent intracellular concentrations these differences were removed and both lines exhibited the same degree of damage for all three DNA lesions. The same DNA lesions were also studied in isolated nuclei from sensitive and resistant cells. Such a model removes any confounding factors due to drug accumulation such as altered cytosolic distribution and/or metabolism of drug. We observed no difference in the formation of single or double strand breaks, or DNA-protein cross-links when the nuclei were exposed to the same concentration of doxorubicin. Results from colony-forming assays have shown that when resistant and sensitive 8226 cells were exposed to high concentrations of doxorubicin, there was a good correlation between DNA damage, drug accumulation, and cytotoxicity. This relationship did not hold for lower concentrations of doxorubicin, for which there was a lack of correlation between drug accumulation and cytotoxicity. Such findings may possibly be due to a prolonged retention of drug by the sensitive cell line as compared to the resistant cells. Further studies are under way to examine this possibility.

Chemotherapy of Advanced Soft Tissue Sarcomas

Abstract: Doxorubicin (Adriamycin) and ifosfamide are the most active single agents in soft tissue sarcoma, with response rates of 15–35% in various trials. Dacarbazine (DTIC), frequently used in combinations, has a response rate as a single agent of 16%.

DNA Cross-linking and Cytotoxicity of the Alkylating Cyanomorpholino Derivative of Doxorubicin in Multidrug-Resistant Cells

Abstract: The cyanomorpholino derivative of doxorubicin (MRA-CN) is an anthracycline that is extremely potent and non-cross-resistant with doxorubicin (DOX) in multidrug-resistant cells. MRA-CN binds to and cross-links DNA and thus has been proposed to act as a targeted alkylating agent. In our study, the number of DNA interstrand and DNA-protein cross-links produced by MRA-CN was identical in multidrug-resistant Dx5 and parental MES-SA cells, as shown by alkaline elution analysis. The amount of cross-linking was directly proportional to drug concentration at concentrations from 10(-11) to 10(-7) M MRA-CN. Extensive DNA cross-linking was evident within 30 minutes of drug exposure. After 1 hour of drug exposure, the number of DNA cross-links increased for 90 minutes, reached a plateau, and then began to decrease after 120 minutes. Loss of cell viability was also observed as early as 3 hours after exposure to MRA-CN. The finding of the same number of DNA cross-links in MES-SA and Dx5 cells indicates that similar amounts of MRA-CN are likely to enter the nuclei of multidrug-resistant and sensitive cells. Other anthracyclines have major differences in nuclear distribution in sensitive and resistant cells. Several factors may contribute to the non-cross-resistance of MRA-CN in multidrug-resistant cells. (a) The lipophilicity of MRA-CN facilitates cell entry. (b) The substitution and loss of basicity at the amino nitrogen may reduce the affinity of the drug for the P-glycoprotein efflux pump, compared with that of DOX. (c) The detoxification function of P-glycoprotein may be less effective for drugs that produce rapid and irreversible cell damage, such as the DNA-targeted alkylation caused by MRA-CN.

Schwann cell degeneration induced by doxorubicin (adriamycin)

Abstract: Doxorubicin is an anthracycline antineoplastic antibiotic that acts at the cell nucleus by intercalating between base pairs of DNA, thus inhibiting DNA-directed mRNA synthesis. Intraneural micro-injection of 0.19-0.38 micrograms of this substance into rat sciatic nerve results in a delayed subacute demyelination that is secondary to focal Schwann cell degeneration. Remyelination eventually occurs but is not complete until at least days 60-75 postinjection. Toxic Schwann cell disorders produced by agents such as doxorubicin may serve as useful models in understanding the pathogenesis of human demyelinative neuropathies.

Induction of lymphokine-activated killer-like cells by cancer chemotherapy.

Abstract: Natural cell-mediated cytotoxicity against NK-resistant target tumor cells was found in the peripheral blood of tumor-bearing patients approximately 1 mo after combined chemotherapy. The recognition specificity of these effector cells was broad and had no restriction. From the experiments of negative selection with mAbs and complements, these newly developed killer cells after chemotherapy were thought to be LAK-like cells. Contribution of these LAK-like cells to the mechanism of action of anticancer drugs remains to be clarified.

Uptake and Intracellular Distribution of Doxorubicin Metabolites in B-Lymphocytes of Chronic Lymphocytic Leukemia

Abstract: The toxicity of doxorubicin metabolites was evaluated on lymphocytes of B-cell chronic lymphocytic leukemia. Only doxorubicinol was found to be cytotoxic for these lymphocytes, whereas exposure to aglycones at concentrations as high as 5 microM for 1 h had no effect on the proliferative capacity of these cells. After exposure of cells to isomolar concentrations of doxorubicin or its metabolites, uptake/retention of doxorubicinol was 23% of doxorubicin, and uptake/retention of aglycones was 5 to 13% of doxorubicin. Seventy to 90% of doxorubicin and 60 to 90% of doxorubicinol taken up/retained by the cells were detected in the cell nuclear fraction, whereas only 20 to 40% of the aglycones were localized in the cell nucleus. Cytotoxicity of metabolites was generally related to the proportion of drug taken up/retained by the cells and localized to the nuclei. The low uptake and nuclear localization may be at least partially responsible for the lack of cytotoxicity of aglycones on B-lymphocytes from chronic lymphocytic leukemia.

Partial reversal of doxorubicin resistance by forskolin and 1,9-dideoxyforskolin in murine sarcoma S180 variants.

Abstract: Acquired resistance to chemotherapeutic agents is an important clinical problem One preclinical model, termed multidrug resistance (MDR), is characterized by a complex phenotype of cross-resistance to biochemically unrelated antineoplastic agents, the presence of a high-molecular-weight membrane glycoprotein, and impaired accumulation of drug To determine whether MDR is mediated in part by altered cyclic 3′,5′-adenosine monophosphate (cAMP) levels, the effect of incubation with the adenylate cyclase agonist, forskolin, was investigated in the murine sarcoma S180 cell line and two MDR variants (A5–8, A5–25) Basal cAMP levels in sensitive and MDR lines were not significantly different (range, 015 ± 005 to 031 ± 009 pmol/mg protein); however, 1-h incubation with forskolin, 10 µm, elevated intracellular cAMP 2-fold in the parent line and 43- and 35-fold in the variants The adenylate cyclase agonists, prostaglandin E2 and cholera toxin, and the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine had no significant effect on cAMP levels To determine the effect of forskolin on doxorubicin-induced cell lethality, S180 and MDR lines were incubated with doxorubicin plus forskolin for 1 h and cloned in soft agar Coincubation with forskolin partially reversed doxorubicin resistance in the MDR lines in a dose-dependent fashion To determine whether this effect was mediated solely by elevation of intracellular cAMP, the inactive 1,9-dideoxy analogue of forskolin (DF) was used Incubation with DF resulted in no elevation of cAMP levels in the sensitive or resistant cell lines; however, DF also partially reversed doxorubicin resistance in the MDR variants Furthermore, coincubation of the A5–25 cell line with doxorubicin and 8-bromo cAMP, 1 mm, did not result in reversal of resistance to doxorubicin To determine whether the reversal of resistance by the diterpenes was associated with alteration of doxorubicin transport, uptake and efflux of [14C]doxorubicin were measured Coincubation with both forskolin and DF, 10 µm, enhanced [14C]doxorubicin uptake in the resistant cells, while drug efflux was significantly affected only in the cell line exhibiting intermediate resistance Since both forskolin and its inactive analogue are effective in partially reversing resistance to doxorubicin and augmenting anthracycline uptake, a mechanism other than elevation of cAMP is most likely responsible