Torben Skovsgaard

In vivo electroporation of skeletal muscle: threshold, efficacy and relation to electric field distribution

In vivo electroporation is increasingly being used to deliver small molecules as well as DNA to tissues. The aim of this study was to quantitatively investigate in vivo electroporation of skeletal muscle, and to determine the threshold for permeabilization. We designed a quantitative method to study in vivo electroporation, by measuring uptake of (51)Cr-EDTA. As electrode configuration influences electric field (E-field) distribution, we developed a method to calculate this. Electroporation of mouse muscle tissue was investigated using either external plate electrodes or internal needle electrodes placed 4 mm apart, and eight pulses of 99 micros duration at a frequency of 1 Hz. The applied voltage to electrode distance ratio was varied from 0 to 2.0 kV/cm. We found that: (1) the threshold for permeabilization of skeletal muscle tissue using short duration pulses was at an applied voltage to electrode distance ratio of 0.53 kV/cm (+/-0.03 kV/cm), corresponding to an E-field of 0.45 kV/cm; (2) there were two phases in the uptake of (51)Cr-EDTA, the first indicating increasing permeabilization and the second indicating beginning irreversible membrane damage; and (3) the calculated E-field distribution was more homogeneous for plate than for needle electrodes, which was reflected in the experimental results.

Epirubicin cardiotoxicity: an analysis of 469 patients with metastatic breast cancer.

PURPOSE To evaluate the influence of cumulative dose, dose-intensity, single-dose level, and schedule of epirubicin on the risk of developing congestive heart failure (CHF) in patients with advanced breast cancer. PATIENTS AND METHODS Four hundred sixty-nine consecutive anthracyline-naive patients with metastatic breast cancer were included. Only patients with cardiac failure according to New York Heart Association (NYHA) function class II or more were recorded as having CHF. For each patient, the following were calculated: the cumulative dose of epirubicin, mean dose-intensity (cumulative dose of epirubicin/duration of treatment), and single-dose level (cumulative dose of epirubicin/number of injections). RESULTS Thirty-four patients (7.2%) developed CHF. The cumulative risk of cardiotoxicity was 4% at 900 mg/m2 and increased exponentially to 15% at 1,000 mg/m2. Irradiation against the mediastinum and thoracic spine increased the risk of CHF (P=.025), but dose-intensity, single-dose level, and schedule had no influence on the risk of developing CHF. Age, previous adjuvant irradiation (to the left or right hemithorax), and previous chemotherapy (cyclophosphamide, methotrexate, and fluorouracil [CMF]) were not risk factors. The median time to onset of CHF following the last dose of epirubicin was 57 days (range, 0 to 853). Among patients with CHF, 13 (38.2%) died of cardiac failure. The median survival time for all patients with CHF was 162 days (range, 0 to +1,957). Previous irradiation directly against the heart increased the risk of death due to cardiac failure and decreased the median survival time to 125 days (range, 0 to 336). CONCLUSION The present large retrospective study of 469 patients substantiates previous results concerning the cardiotoxicity of epirubicin. A significantly increasing risk of CHF in patients who receive cumulative doses greater than 950 mg/m2 was established. The future recommended maximum cumulative dose of epirubicin should be 900 mg/m2 in patients with metastatic breast cancer. Previous irradiation against the heart leads to an increased risk of developing CHF with an accelerated course to death, which indicates an additive cardiotoxic effect of irradiation and epirubicin.

Randomized Comparative Study of Tegafur/Uracil and Oral Leucovorin Versus Parenteral Fluorouracil and Leucovorin in Patients With Previously Untreated Metastatic Colorectal Cancer

PURPOSE This phase III study compared the time to progression (TTP) of an oral regimen of dihydropyrimidine dehydrogenase inhibitory fluoropyrimidine composed of a fixed combination of tegafur and uracil in a 1:4 molar ratio (UFT) and leucovorin (LV) to intravenous (IV) fluorouracil (5-FU) and LV in previously untreated metastatic colorectal carcinoma (CRC) patients. Secondary end points were survival, tumor response, safety, and quality of life. PATIENTS AND METHODS Between May 1996 and July 1997, 380 patients were randomized to receive either UFT (300 mg/m(2)/d) and LV (90 mg/d), administered for 28 days every 35 days, or 5-FU (425 mg/m(2)/d) and LV (20 mg/m(2)/d), given IV for 5 days every 35 days. RESULTS No statistically significant difference in TTP was observed between treatments. With 320 events assessed, the median TTP was 3.4 months (95% Confidence interval [CI], 2.6 to 3.8) on UFT/LV and 3.3 months (95% CI, 2.5 to 3.7) on 5-FU/LV (P =.591, stratified log-rank test). There were no statistically significant differences in survival, tumor response, duration of response, and time to response. Substantial safety benefits were observed in patients treated with UFT/LV. They experienced significantly less stomatitis/mucositis (P <.001) and myelosuppression, resulting in fewer episodes of febrile neutropenia (P <.001) and less documented infection (P =.04). Concomitant medication usage was significantly greater on 5-FU/LV (P =.010). With respect to quality of life, after correcting for baseline imbalances, there were no significant differences between treatments for any scale, except diarrhea. CONCLUSION The oral UFT/LV regimen failed to achieve improved TTP; however, the study confirms significant safety improvements compared with bolus IV 5-FU/LV for the first-line treatment of metastatic CRC.

Vascular reactions to in vivo electroporation: characterization and consequences for drug and gene delivery.

In vivo electroporation (EP) is gaining momentum for drug and gene delivery. In particular, DNA transfer by EP to muscle tissue can lead to highly efficient long-term gene expression. We characterized a vascular effect of in vivo EP and its consequences for drug and gene delivery. Pulses of 10-20,000 micros and 0.1-1.6 kV/cm were applied over hind- and forelimb of mice and perfusion was examined by dye injection. The role of a sympathetically mediated vasoconstrictory reflex was investigated by pretreatment with reserpine. Expression of a transferred gene (luciferase), permeabilization (determined using (51)Cr-EDTA), membrane resealing and effects on perfusion were compared to assess the significance of the vascular effects. Above the permeabilization threshold, a sympathetically mediated Raynaud-like phenomenon with perfusion delays of 1-2 min was observed. Resolution of this phase followed kinetics of membrane resealing. Above a second threshold, irreversible permeabilization led to long perfusion delays. These vascular reactions (1) affect kinetics of drug delivery, (2) predict efficient DNA transfer, which is optimal during short perfusion delays, and (3) might explain electrocardiographic ST segment depressions after defibrillation as being caused by vascular effects of EP of cardiac muscle.

Structure-activity relationships of P-glycoprotein interacting drugs: kinetic characterization of their effects on ATPase activity

We have determined the kinetic parameters for stimulation and inhibition by 34 drugs of the P-glycoprotein ATPase in membranes derived from CR1R12 Chinese hamster ovary cells. The drugs chosen were sets of calmodulin antagonists, steroids, hydrophobic cations, hydrophobic peptides, chemotherapeutic substrates of P-glycoprotein, and some other drugs with lower affinity for P-glycoprotein. We studied how these kinetic parameters correlated with the partition coefficient and the Van der Waals surface area of the drugs. The maximum velocity of ATPase stimulation decreased with surface area and showed a suggestion of a maximum with increasing partition coefficient. The affinity of these drugs for P-glycoprotein showed no significant correlation with partition coefficient but was highly correlated with the surface area suggesting that binding between modulators and P-glycoprotein takes place across a wide interaction surface on the protein.

Transport and binding of daunorubicin, adriamycin, and rubidazone in ehrlich ascites tumour cells

Abstract The determinants of cellular net uptake of three anthracyclines—daunorubicin, adriamycin, and rubidazone—were studied in Ehrlich ascites tumour cells in vitro. A striking finding was the marked effect of the pH on net uptake in the way that lowering of the pH decreased the rate of uptake and steady-state level. As pKA of the drugs proved to be 8.15–8.45, this finding suggests a penetration of the drugs by passive transport of the unionized form of the molecules. Several findings indicated an uphill efflux of the drugs from the cells. (1) The estimate of the cytoplasm/medium concentration ratio at steady-state for daunorubicin and rubidazone was considerably below that predicted when assuming passive distribution. (2) The cellular accumulation of the drugs was significantly enhanced by sodium azide. (3) The cellular release of the drugs was inhibited by sodium azide. Together these findings suggest a membrane transport of the drugs as a “leak-and-pump” system. Studies of the intracellular binding showed that the affinity of adriamycin for isolated nuclei and for total cellular homogenate was about 50 per cent higher than that of daunorubicin; rubidazone possessed the lowest affinity for cellular binding sites. The affinity of the drugs for intracellular binding sites was not influenced by the pH. The results indicate that the net uptake of anthracycline derivatives in these tumour cells is determined by: (1) the permeability of the membrane to the unionized form of the molecule ; (2) the specificity of the drug for the mechanism of active efflux; (3) the relationship between intracellular and extracellular pH; (4) the pKA, value of the drug; (5) the affinity of the drug for the intracellular binding sites.

Enhancement of cytotoxicity by electropermeabilization: an improved method for screening drugs.

Electropermeabilization (EPN), also termed electroporation, is a physical method to overcome the barrier of the cell membrane by applying short and intense electric pulses. It is the basis for a new cancer treatment modality, electrochemotherapy, where uptake of chemotherapeutics is enhanced by EPN. Preclinical and clinical trials have shown that application of electric pulses in vivo is feasible and that electrochemotherapy is highly efficient. The aim of this study was to develop an improved method of screening drugs on electropermeabilized versus non-electropermeabilized cells. In this study we describe an easy protocol which gives high cell viability, good reproducibility and a high rate of cell permeabilization. Cell cytotoxicity is simply determined by the MTT assay. Cell death due to the EPN procedure was less than 4% and more than 90% of cells were permeabilized. For daunorubicin, doxorubicin, etoposide and paclitaxel, no effect of EPN was found. For carboplatin and cisplatin the effect of EPN was a factor 3 and 2.3, respectively, on the IC50 (inhibitory concentration 50%). For bleomycin we found a dramatic effect of EPN of the magnitude of a factor 300 on the IC50. In conclusion, we have established a new, easy and reliable protocol to test new drugs for cytotoxicity with or without the limitations of the cell membrane. Our data support the role of bleomycin as the drug of choice for electrochemotherapy.

A phase II study of the vitamin D analogue Seocalcitol in patients with inoperable hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a common malignant tumour, which has a poor prognosis. Surgical resection can be curative but most patients are inoperable and most chemotherapy agents have minimal activity in this disease. Seocalcitol, a vitamin D analogue, induces differentiation and inhibits growth in cancer cell lines and in vivo. The vitamin D receptor is expressed in hepatocytes and more abundantly in HCC cells. In total, 56 patients with inoperable advanced HCC were included in an uncontrolled study of oral Seocalcitol treatment for up to 1 year (with possible extension for responders). The dose was titrated according to serum calcium levels. The treatment effect was evaluated by regular CT scans. Out of 33 patients evaluable for tumour response, two had complete response (CR), 12 stable disease and 19 progressive disease. The CRs appeared after 6 and 24 months of treatment, and lasted for 29 and at least 36 months (patient still in remission when data censored). Seocalcitol was well tolerated; the most frequent toxicity was hypercalcaemia and related symptoms. Most patients tolerated a daily dose of 10 μg of Seocalcitol. This is the first study showing activity, by reduction in tumour dimensions, of a differentiating agent in patients with an advanced bulky, solid tumour. Seocalcitol may have an effect in the treatment of HCC, especially in early disease when a prolonged treatment can be instituted. The survival benefit with or without tumour response should be determined in controlled studies.

COMPETITIVE, NON-COMPETITIVE AND COOPERATIVE INTERACTIONS BETWEEN SUBSTRATES OF P-GLYCOPROTEIN AS MEASURED BY ITS ATPASE ACTIVITY

We have studied the interaction between verapamil and other modulators of the P-glycoprotein ATPase from membranes of CR1R12 Chinese hamster ovary cells. Four major categories of interaction were identified. (i) Non-competitive inhibition of verapamils stimulation of enzyme activity was found with vanadate. (ii) Competitive inhibition of the ATPase was found for the pair verapamil and cyclosporin A. (iii) Allosteric inhibition with an increase in the Hill number for verapamil was found in the cases of daunorubicin, epirubicin, gramicidin S and D, vinblastine, amiodarone, and colchicine. (iv) Cooperative stimulation of verapamil-induced ATPase activity was found with progesterone, diltiazem, amitriptyline, and propranolol. At high levels, progesterone and verapamil mutually enhanced each others inhibitory action on the ATPase. Our data show that the substrate binding behavior of P-glycoprotein is complex with more than one binding site being present. This information could form the basis for the development of improved modulators of P-glycoprotein.

P-glycoprotein as multidrug transporter: a critical review of current multidrug resistant cell lines.

MDR has been studied extensively in mammalian cell lines. According to usual practice, the MDR phenotype is characterized by the following features: cross resistance to multiple chemotherapeutic agents (lipophilic cations), defective intracellular drug accumulation and retention, overexpression of P-gp (often accompanied by gene amplification), and reversal of the phenotype by addition of calcium channel blockers. An hypothesis for the function of P-gp has been proposed in which P-gp acts as a carrier protein that actively extrudes MDR compounds out of the cells. However, basic questions, such as what defines the specificity of the pump and how is energy for active efflux transduced, remain to be answered. Furthermore, assuming that P-gp acts as a drug transporter, one will expect a relationship between P-gp expression and accumulation defects in MDR cell lines. A review of papers reporting 97 cell lines selected for resistance to the classical MDR compounds has revealed that a connection exists in most of the reported cell lines. However, several exceptions can be pointed out. Furthermore, only a limited number of well characterized series of sublines with different degrees of resistance to a single agent have been reported. In many of these, a correlation between P-gp expression and transport properties can not be established. Co-amplification of genes adjacent to the mdr1 gene, mutations [122], splicing of mdr1 RNA [123], modulation of P-gp by phosphorylation [124] or glycosylation [127], or experimental conditions [26,78] could account for some of the complexity of the phenotype and the absence of correlation in some of the cell lines. However, both cell lines with overexpression of P-gp without increased efflux [i.e., 67,75] and cell lines without P-gp expression and accumulation defects/increased efflux [i.e., 25,107] have been reported. Thus, current results from MDR cell lines contradict--but do not exclude--that P-gp acts as multidrug transporter. Other models for the mechanism of resistance have been proposed: (1) An energy-dependent permeability barrier working with greater efficacy in resistant cells. This hypothesis is supported by studies of influx which, although few, all except one demonstrate decreased influx in resistant cells; (2) Resistant cells have a greater endosomal volume, and a greater exocytotic activity accounts for the efflux.(ABSTRACT TRUNCATED AT 400 WORDS)