A pilot study of amiodarone with infusional doxorubicin or vinblastine in refractory breast cancer

Microfluidic production of amiodarone loaded nanoparticles and application in drug repositioning in ovarian cancer

Amiodarone repositioning in cancer treatment is promising, however toxicity limits seem to arise, constraining its exploitability. Notably, amiodarone has been investigated for the treatment of ovarian cancer, a tumour known for metastasizing within the peritoneal cavity. This is associated with an increase of fatty acid oxidation, which strongly depends on CPT1A, a transport protein which has been found overexpressed in ovarian cancer. Amiodarone is an inhibitor of CPT1A but its role still has to be explored. Therefore, in the present study, amiodarone was tested on ovarian cancer cell lines with a focus on lipid alteration, confirming its activity. Moreover, considering that drug delivery systems could lower drug side effects, microfluidics was employed for the development of drug delivery systems of amiodarone obtaining simultaneously liposomes with a high payload and amiodarone particles. Prior to amiodarone loading, microfluidics production was optimized in term of temperature and flow rate ratio. Moreover, stability over time of particles was evaluated. In vitro tests confirmed the efficacy of the drug delivery systems.

Drug transporters in breast cancer: response to anthracyclines and taxanes

Despite the advances that have taken place in the past decade, including the development of novel molecular targeted agents, cytotoxic chemotherapy remains the mainstay of cancer treatment. In breast cancer, anthracyclines and taxanes are the two main chemotherapeutic options used on a routine basis. Although effective, their usefulness is limited by the inevitable development of resistance, a lack of response to drug-induced cancer cell death. A large body of research has resulted in the characterization of a plethora of mechanisms involved in resistance; ATP-binding cassette transporter proteins, through their function in xenobiotic clearance, play an important role in resistance. We review here the current evidence for drug transporters as biomarkers and the benefit of adding drug transporter modulators to conventional chemotherapy.

Targeting MDR in breast and lung cancer: discriminating its potential importance from the failure of drug resistance reversal studies

This special issue of Drug Resistance Updates is dedicated to multidrug resistance protein 1 (MDR-1), 35 years after its discovery. While enormous progress has been made and our understanding of drug resistance has become more sophisticated and nuanced, after 35 years the role of MDR-1 in clinical oncology remains a work in progress. Despite clear in vitro evidence that P-glycoprotein (Pgp), encoded by MDR-1, is able to dramatically reduce drug concentrations in cultured cells, and that drug accumulation can be increased by small molecule inhibitors, clinical trials testing this paradigm have mostly failed. Some have argued that it is no longer worthy of study. However, repeated analyses have demonstrated MDR-1 expression in a tumor is a poor prognostic indicator leading some to conclude MDR-1 is a marker of a more aggressive phenotype, rather than a mechanism of drug resistance. In this review we will re-evaluate the MDR-1 story in light of our new understanding of molecular targeted therapy, using breast and lung cancer as examples. In the end we will reconcile the data available and the knowledge gained in support of a thesis that we understand far more than we realize, and that we can use this knowledge to improve future therapies.

Modulation of the sensitivity in Chinese hamster cells to photons and fast neutrons by cisplatin, vinblastine, and bleomycin

Normal tissue toxicity resulting from chemoradiotherapy is of significant clinical concern. This study used normal Chinese hamster fibroblasts from lung (V79) and ovary (CHO-K1) to assess the modulation of cellular response to photons and neutrons by cisplatin, vinblastine, and bleomycin. Based on the colony formation assay, the drug concentration corresponding to 50% cell survival (EC50) of V79 cells was 1.50 ± 0.21 µmol/L for cisplatin, 0.97 ± 0.06 nmol/L for vinblastine, and 1.68 ± 0.11 µmol/L for bleomycin. The corresponding values for CHO-K1 cells were significantly lower for vinblastine (0.54 ± 0.02 nmol/L) and bleomycin (0.49 ± 0.13 µmol/L), but not for cisplatin (1.57 ± 0.20 µmol/L). No radiosensitivity enhancement was apparent when cells were exposed to p(66)/Be neutrons or photons (60Co γ-rays) in the presence of these drugs at EC50 concentrations. These data suggest that concurrent use of these drugs with radiation for the treatment of lung and ovarian diseases radiation does not exacerbate radiation-induced normal tissue toxicity, regardless of the quality of radiation. The relatively higher sensitivity of the ovarian cells to vinblastine and bleomycin might constitute a limitation in the use of these drugs for the treatment of lung lesions.

Novel amiodarone-doxorubicin cocktail liposomes enhance doxorubicin retention and cytotoxicity in DU145 human prostate carcinoma cells

We have developed novel cocktail liposomes bearing doxorubicin in their hydrophilic cores, and amiodarone, a potent multidrug resistance inhibitor, in their lipid bilayers. The efficacy of these liposomes was studied in DU145 human prostate carcinoma cells. Intracellular calcein retention, which is inversely proportional to multidrug resistance activity, significantly increased following cell incubation with amiodarone loaded liposomes. Fluorescence confocal microscopy on cells incubated with the cocktail liposomes revealed enhanced intranuclear doxorubicin accumulation. Two liposomal drug concentration combinations were employed to assess the differential cytotoxicity of the cocktail liposomes, doxorubicin (1.4 microM)-amiodarone (15 microM) and doxorubicin 3 (microM)-amiodarone (45 microM), and two incubation times, 5 and 19 h. Cell toxicity was determined by XTT assays at 24, 48, and 72 h following incubation and was significantly enhanced for incubation with the cocktail liposomes. On the whole, we believe that these liposomes will greatly contribute to the cancer chemotherapy arena.

Approaches to multidrug resistance reversal

Multidrug resistance (MDR) is characterised by cross-resistance between unrelated anticancer drugs and is associated with the overexpression of a membrane bound high-molecular weight glycoprotein, named P-glycoprotein, which is able to actively expel the drugs out of the cells. In vitro, numerous compounds have demonstrated the ability to inhibit the transport activity of P-glycoprotein, resulting in enhanced intracellular drug accumulation and MDR reversal. Such compounds include drugs of current use in other therapeutic areas, such as verapamil, cyclosporin A, quinidine or tamoxifen. Clinical trials have been performed on these drugs with the aim of reversing drug-resistance, but their toxicity was often too high. Therefore pharmaceutical firms have preferred to evaluate either analogues of these drugs, or compounds specifically designed for resistance reversal. Drugs that have clearly shown a potential for sensitisation of resistant cancers with acceptable toxicity include dexverapamil one of the two enantiomers constituting verapamil, valspodar (PSC-833), an analogue of cyclosporine A, and original compounds, named VX-710 and GF-120918. Positive results have most often been obtained in haematological malignancies (myelomas, lymphomas and acute myeloblastic leukaemias), but sometimes also in solid tumours (breast and ovarian carcinomas). Randomised Phase III studies are ongoing for compounds showing a definite activity in Phase II studies, with the aim of analysing the benefits of the combination of an MDR reverter and conventional chemotherapy, in terms of patients' survival. However, drug-resistance is a multifactorial phenomenon, with MDR constituting only part of it. In addition, a rigorous clinical evaluation of MDR will have to be performed, which has not always been the case in early trials.

A Phase I study of infusional vinblastine in combination with the P-glycoprotein antagonist PSC 833 (valspodar)

BACKGROUND

PSC 833 is a second-generation P-glycoprotein (Pgp) antagonist developed to reverse multidrug resistance (MDR). The authors conducted a Phase I study of orally administered PSC 833 in combination with vinblastine administered as a 5-day continuous infusion.

METHODS

Seventy-nine patients with advanced malignant disease were enrolled in the trial and treated with escalating doses of PSC 833. Pharmacokinetic interactions between PSC 833 and vinblastine were anticipated. Accordingly, when dose limiting toxicities were observed, the dose of vinblastine was reduced as PSC 833 was escalated. Three schedules and two formulations of PSC 833 were used in the study.

RESULTS

The maximum tolerated doses of PSC 833 were 12.5 mg/kg orally every 12 hours for 8 days for the liquid formulation in combination with 0.9 mg/m(2) per day vinblastine as a continuous intravenous infusion (CIV) for 5 days; and 4 mg/kg orally every 6 hours for 8 days for the microemulsion formulation in combination with 0.6 mg/m(2) per day vinblastine CIV for 5 days. The principal toxicities for PSC 833 were ataxia and paresthesias and for the combination, constipation, fever. and neutropenia. Increased oral bioavailability and increased peak and trough concentrations were observed with the microemulsion formulation. Significant interpatient variability in pharmacokinetic parameters was observed. Ten patients studied at the MTD for PSC 833 (4 mg/kg orally every 6 hours for 8 days) had inhibition of rhodamine efflux from CD56 positive peripheral lymphocytes as a surrogate for Pgp antagonism. Among 43 evaluable patients with clear cell carcinoma of the kidney, 3 patients had complete responses, and 1 patient had a partial response.

CONCLUSIONS

PSC 833 in combination with vinblastine can be administered safely to patients provided the vinblastine dose is adjusted for pharmacokinetic interactions. The high interpatient variability is a significant confounding factor. Surrogate studies with CD56 positive cells suggest that Pgp inhibition in the clinical setting is achievable. Improved methods for predicting pharmacokinetic interactions should improve future studies.

Pharmacokinetic and pharmacodynamic implications of P-glycoprotein modulation

P-glycoprotein (P-gp) is a cell membrane-associated protein that transports a variety of drug substrates. Although P-gp has been studied extensively as a mediator of multidrug resistance in cancer, only recently has the role of P-gp expressed in normal tissues as a determinant of drug pharmacokinetics and pharmacodynamics been examined. P-glycoprotein is present in organ systems that influence drug absorption (intestine), distribution to site of action (central nervous system and leukocytes), and elimination (liver and kidney), as well as several other tissues. Many marketed drugs inhibit P-gp function, and several compounds are under development as P-gp inhibitors. Similarly, numerous drugs can induce P-gp expression. While P-gp induction does not have a therapeutic role, P-gp inhibition is an attractive therapeutic approach to reverse multidrug resistance. Clinicians should recognize that P-gp induction or inhibition may have a substantial effect on the pharmacokinetics and pharmacodynamics of concomitantly administered drugs that are substrates for this transporter.

Current options in treatment of anthracycline-resistant breast cancer

Breast cancer is a chemosensitive tumour and anthracyclines are one of the most active cytotoxic agents in chemotherapy treatment. Failure after anthracycline-containing chemotherapy is a poor prognostic factor because of low response rate to salvage chemotherapy. Several factors like P-glycoprotein mediated drug resistance (MDR-1 or MRP), glutathione or amplification of topoisomerase II have been found to be involved in anthracycline resistance. No clear benefit for patients treated with 'resistance-modifier' agents like verapamil, dexverapamil or quinidine has yet been demonstrated. Most clinical studies with non-cross resistant cytotoxic agents are lacking a strict definition of anthracycline resistance. A strict definition of anthracycline resistance implies progressive disease during anthracycline chemotherapy. Among the cytotoxic drugs only 5-Fluorouracil (given as 24 h continuous infusion with folinic acid) and the taxanes produce more than 20% objective remission (RR) in case of anthracycline resistance, whereas the highest response rate was reported for docetaxel (32-57%). Only few randomized studies were performed: docetaxel showed higher anti-tumor activity than methotrexat/5-FU (RR: 42% vs 19%, P<0.001) or mitomycin/vinblastine (RR: 30% vs 12%;P<0.001) and treatment with paclitaxel (175 mg/m(2)) was in favour to mitomycin (RR 17% vs 6%). In combination chemotherapy most activity have been reported for paclitaxel plus high-dose 5-fluorouracil (given as 24 h continuous infusion with folinic acid) (RR: 58%) or for docetaxel plus cisplatinum (RR: 46%). High-dose regimens with growth factor or stem cell support seems to be active in anthracycline-resistant disease but the toxicity is considerable. In conclusion, the taxanes, especially docetaxel as single agent or paclitaxel plus high-dose 5-FU, are the most promising therapeutic options in treatment of anthracycline resistant disease. Further clinical phase II/III studies in breast cancer should include exact definition of anthracycline pretreatment and resistance.

Phase II trial of dexverapamil and epirubicin in patients with non-responsive metastatic breast cancer

Agents capable of reversing P-glycoprotein-associated multidrug resistance have usually failed to enhance chemotherapy activity in patients with solid tumours. Based on its toxicity profile and experimental potency, dexverapamil, the R-enantiomer of verapamil, is considered to be promising for clinical use as a chemosensitizer. The purpose of this early phase II trial was to evaluate the effects of dexverapamil on epirubicin toxicity, activity and pharmacokinetics in patients with metastatic breast cancer. A two-stage design was applied. Patients first received epirubicin alone at 120 mg m(-2) i.v. over 15 min, repeated every 21 days. Patients with refractory disease continued to receive epirubicin at the same dose and schedule but supplemented with oral dexverapamil 300 mg every 6 h x 13 doses. The Gehan design was applied to the dexverapamil/epirubicin cohort of patients. Thirty-nine patients were entered on study, 25 proceeded to receive epirubicin plus dexverapamil. Dexverapamil did not increase epirubicin toxicity. The dose intensity of epirubicin was similar when used alone or with dexverapamil. In nine intrapatient comparisons, the area under the plasma concentration-time curve (AUC) of epirubicin was significantly reduced by dexverapamil (mean 2968 vs 1901 microg ml[-1] h[-1], P= 0.02). The mean trough plasma levels of dexverapamil and its major metabolite nor-dexverapamil were 1.2 and 1.5 microM respectively. The addition of dexverapamil to epirubicin induced partial responses in 4 of 23 patients evaluable for tumour response (17%, CI 5-39%, s.e.P 0.079). The remissions lasted 3, 8, 11 and 11+ months. These data suggest that the concept of enhancing chemotherapy activity by adding chemosensitizers may function not only in haematological malignancies but also in selected solid tumours. An increase in the AUC and toxicity of cytotoxic agents does not seem to be a prerequisite for chemosensitizers to enhance anti-tumour activity.

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 verapamil's 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 other's 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.

Mutually co-operative interactions between modulators of P-glycoprotein

We measured the effects of combinations of verapamil, vinblastine, mefloquine, and tamoxifen, all being modulators of the multidrug resistance pump, P-glycoprotein, on the accumulation of labelled daunomycin into multidrug-resistant P388 leukemia cells at 37 degrees C. We found that, contrary to our initial expectations (based on Ayesh, Shao and Stein (1996) Biochim. Biophys. Acta 1316, 8), vinblastine, mefloquine, and tamoxifen all appeared to interact with one another synergistically, i.e. by the kinetics of a non-competitive interaction. A simple kinetic analysis showed that pairs of co-operating modulators can give apparent non-competitive behaviour, but refined kinetic analysis enables the two types of interaction to be distinguished. The modulators vinblastine, mefloquine, and tamoxifen thus appear to co-operate with one another in pairs to bring about reversal of P-glycoprotein. This may have important implications for the design of new modulators of P-glycoprotein.

Clinical reversal of multidrug resistance

Reversal of drug resistance offers the hope of increasing the efficacy of conventional chemotherapy. We tested dexverapamil as a P-glycoprotein antagonist in combination with EPOCH chemotherapy in refractory non-Hodgkin's lymphoma. In a cross-over design, dexverapamil was added to EPOCH after disease stabilization or progression occurred. Objective responses were observed in 10 of 41 assessable patients. Biopsies for mdr-1 were obtained before EPOCH treatment and at the time of cross-over to dexverapamil. Levels of mdr-1 were low before EPOCH, but increased four-fold or more in 42% of patients in whom serial samples were obtained. Pharmacokinetic analysis revealed median peak concentrations of dexverapamil and its metabolite, nor-dexverapamil, of 1.66 mumol/l and 1.58 mumol/l, respectively. Since both are comparable antagonists, a median peak total reversing concentration of 3.24 mumol/l was achieved. Pharmacokinetic analysis of doxorubicin and etoposide levels confirmed a delay in the clearance of doxorubicin ranging from 5% to 24%; no change in the pharmacokinetics of etoposide was observed. This study provides sufficient rationale for testing dexverapamil in a randomized clinical trial.

Downregulation of mdr-1 expression by 8-Cl-cAMP in multidrug resistant MCF-7 human breast cancer cells

8-Cl-cAMP, a site-selective analogue of cAMP, decreased mdr-1 expression in multidrug-resistant human breast cancer cells. A sixfold reduction of mdr-1 mRNA expression by 8-Cl-cAMP began within 8 h of treatment and was associated with a decrease in the synthesis of P-glycoprotein and with an increase in vinblastine accumulation. A reduction in mdr-1 expression after 8-Cl-cAMP treatment was also observed in multidrug-resistant human ovarian cancer cell lines. 8-Cl-cAMP is known to change the ratio between the two regulatory subunits, RI and RII, of protein kinase A (PKA). We observed that RI alpha decreased within 24 h of 8-Cl-cAMP treatment, that RII beta increased after as few as 3 h of treatment, and that PKA catalytic activity remained unchanged during 48 h of 8-Cl-cAMP treatment. The results are consistent with the hypothesis that mdr-1 expression is regulated in part by changes in PKA isoenzyme levels. Although 8-Cl-cAMP has been used to differentiate cells in other model systems, the only differentiating effect that could be detected after 8-Cl-cAMP treatment in the MCF-7TH cells was an increase in cytokeratin expression. Evidence that the reduction of mdr-1 mRNA occurred at the level of gene transcription was obtained by measuring chloramphenicol acetyltransferase (CAT) mRNA in MCF-7TH cells transfected with an mdr-1 promoter-CAT construct prior to 8-Cl-cAMP treatment. Thus, 8-Cl-cAMP is able to downregulate mdr-1 expression and suggests a new approach to reversal of drug resistance in human breast cancer.