Cellular pharmacology of the partially non-cross-resistant anthracycline annamycin entrapped in liposomes in KB and KB-V1 cells

Topoisomerase II inhibitors in AML: past, present, and future

Introduction: Topoisomerase II inhibitors have long been used in the frontline and as salvage therapy for AML, with daunorubicin and idarubicin being prototypical agents in this therapeutic class, classically in combination with nucleoside analogs, e.g. cytarabine. Most recently, several other compounds from this drug class have or are being investigated. Areas covered: The current paper reviews older and newer topoisomerase II inhibitors in clinical development for the treatment of AML. The authors discuss the clinical use of these agents, current trials involving them as well as their safety profile. Important side effects of these medications including therapy-related AML (t-AML) are also covered. Expert opinion: Topoisomerase II inhibitors have helped improve outcomes in AML. Recently, the FDA approved several agents including CPX-351 for the treatment of secondary and t-AML. CPX-351 may have applicability in other high-risk myeloid diseases. Future directions include a combination of these agents with other targeted therapies. Finally, the authors believe that small molecule inhibitors, such as venetoclax and possibly immunotherapy options could also be incorporated to our treatment paradigm in selected patients.

Improving intracellular doxorubicin delivery through nanoliposomes equipped with selective tumor cell membrane permeabilizing short-chain sphingolipids

PURPOSE

To improve nanoliposomal-doxorubicin (DoxNL) delivery in tumor cells using liposome membrane-incorporated short-chain sphingolipids (SCS) with selective membrane-permeabilizing properties. DoxNL bilayers contained synthetic short-chain derivatives of known membrane microdomain-forming sphingolipids; C₈-glucosylceramide (C₈-GluCer), C₈-galactosylceramide (C₈-GalCer) or C₈-lactosylceramide (C₈-LacCer).

METHODS

DoxNL enriched with C₈-GluCer or C₈-GalCer were developed, optimized and characterized with regard to size, stability and drug retention. In vitro cytotoxic activity was studied in a panel of human tumor cell lines and normal cells. Intracellular Dox delivery was measured by flow cytometry and visualized by fluorescence microscopy. For a further understanding of the involved drug delivery mechanism confocal microscopy studies addressed the cellular fate of the nanoliposomes, the SCS and Dox in living cells.

RESULTS

C₈-LacCer-DoxNL aggregated upon Dox loading. In tumor cell lines SCS-DoxNL with C₈-GluCer or C₈-GalCer demonstrated strongly increased Dox delivery and cytotoxicity compared to standard DoxNL. Surprisingly, this effect was much less pronounced in normal cells. Nanoliposomes were not internalized, SCS however transfered from the nanoliposomal bilayer to the cell membrane and preceded cellular uptake and subsequent nuclear localization of Dox.

CONCLUSION

C₈-GluCer or C₈-GalCer incorporated in DoxNL selectively improved intracellular drug delivery upon transfer to tumor cell membranes by local enhancement of cell membrane permeability.

Enhanced topoisomerase II targeting by annamycin and related 4-demethoxy anthracycline analogues

Targeting topoisomerase II (topo II) is regarded as an important component of the pleiotropic mechanism of action of anthracycline drugs. Here, we show that 4-demethoxy analogues of doxorubicin, including annamycin, exhibit a greater ability to trap topo II cleavage complexes than doxorubicin and some other 4-methoxy analogues. In leukemic CEM cells with wild-type topo II, annamycin induced substantial levels of topo II–mediated DNA-protein cross-links (15-37% of total DNA for 0.5-50 μmol/L drug), whereas doxorubicin-induced DNA-protein cross-links were marginal (0-4%). In CEM/VM-1 cells that harbor mutated, drug-resistant topo II, both 4-methoxy and 4-demethoxy drugs produced marginal DNA-protein cross-links. Annamycin, but not doxorubicin, formed topo II–mediated DNA-protein cross-links also in isolated CEM nuclei. In disparity with the unequal DNA-protein cross-link induction, both drugs induced comparable levels of DNA strand breaks in CEM cells. Compared with CEM, drug cytotoxicity against CEM/VM-1 cells was reduced 10.5- to 13.8-fold for 4-demethoxy analogues but only 3.8- to 5.5-fold for 4-methoxy drugs. Hence, growth inhibition by 4-demethoxy analogues seems more dependent on the presence of wild-type topo II. The enhanced topo II targeting by 4-demethoxy analogues was accompanied by a profound induction of apoptotic DNA fragmentation in leukemic CEM cells. Normal WI-38 fibroblasts, however, were markedly more resistant to annamycin-induced DNA-protein cross-links, apoptosis, and growth inhibition. The enhanced topo II targeting by 4-demethoxy doxorubicin analogues underscores the mechanistic diversity of anthracycline drugs. This diversity needs to be recognized as a factor in responses to drugs such as annamycin and doxorubicin.

Effects of liposome-entrapped annamycin in human breast cancer cells: interference with cell cycle progression and induction of apoptosis

The effects of liposome-encapsulated annamycin (L-Ann) were investigated in two human breast cancer cell lines, MCF7 and MDA-MB-435. For comparative purposes, doxorubicin (Dx) was used throughout the study. A 4-hour treatment with L-Ann was significantly more active in MDA-MB-435 than in MCF7 cells (IC(50) values of 0.03 and 0.08 microg/ml, respectively), whereas Dx was equally active in the two cell lines (IC(50) 0.12 microg/ml). L-Ann induced an accumulation of cells in G2M phases which was dose-dependent in MDA-MB-435 but not in MCF7 cells. Dx also caused a dose-dependent increase of G2M cell fraction in MDA-MB-435 cells, whereas a G2M cell accumulation was observed only after treatment with the highest Dx concentration in MCF7 cells. G2M phase cell accumulations induced in MCF7 cells by L-Ann or Dx were accompanied by a decrease in cdc2 kinase activity and in cyclin B1 and cdc2 expression. Conversely, in MDA-MB-435 cells exposed to L-Ann or Dx, cdc2 kinase activity, cyclin B1 and cdc2 expression increased in parallel to the increase in the number of cells accumulated in the G2M phase. L-Ann and Dx induced apoptosis in MDA-MB-435 but not in MCF7 cells. In MDA-MB-435 cells exposed to L-Ann or Dx, no change was observed in the expression of bax, but there was a p53-independent increase in p21(waf1) expression. In MCF7 cells, treatment with L-Ann or Dx induced an increase in p53 expression with a consequent transactivation of p21(waf1) and bax. Our results indicate that L-Ann is more cytotoxic than Dx in breast cancer cells and is able to induce apoptosis through p53-independent mechanisms.

Annamycin circumvents resistance mediated by the multidrug resistance-associated protein (MRP) in breast MCF-7 and small-cell lung UMCC-1 cancer cell lines selected for resistance to etoposide

Annamycin (Ann) is a highly lipophilic anthracycline antibiotic that has been shown to circumvent MDR-1 both in vitro and in vivo. A liposomal formulation of Ann is currently in phase I clinical trials. The multidrug resistance-associated protein (MRP) has been found to be over-expressed in some human leukemias at relapse and to be a poor prognostic factor in neuroblastoma. We studied the in vitro cytotoxicity and the cellular uptake and efflux of Ann and doxorubicin (Dox) in 2 pairs of human cell lines, breast carcinoma MCF7 and small-cell lung cancer UMCC-1, and their MRP-expressing counterparts, MCF-7/VP and UMCC-1/VP. Resistance indexes were 1.1 and 1.4 for Ann vs. 6.9 and 11.6 for Dox. Ann cellular accumulation was 3- to 5-fold higher than that of Dox in both sensitive and resistant cells. No changes in drug efflux between sensitive and resistant cells were observed in the case of Ann, while Dox efflux at 1 hr was 20-25% higher in resistant than in sensitive cells. By confocal microscopy, the subcellular distribution of Ann was identical in sensitive and resistant cells, localizing mostly in the perinuclear structures, while that of Dox was exclusively nuclear in sensitive cells and nuclear and in the cell membrane in resistant cells. There was a good correlation between the extent of DNA breaks induced by each drug in the different cell lines and cytotoxic effect. Our results indicate that Ann may be effective in the treatment of malignancies in which MRP is a relevant mechanism of clinical resistance.

Recent advances in liposomal drug-delivery systems

Liposomal drug-delivery systems have come of age in recent years, with several liposomal drugs currently in advanced clinical trials or already on the market. It is clear from numerous pre-clinical and clinical studies that drugs, such as antitumor drugs, packaged in liposomes exhibit reduced toxicities, while retaining, or gaining enhanced, efficacy. This results, in part, from altered pharmacokinetics, which lead to drug accumulation at disease sites, such as tumors, and reduced distribution to sensitive tissues. Fusogenic liposomal systems that are under development have the potential to deliver drugs intracellularly, and this is expected to markedly enhance therapeutic activity. Advances in liposome design are leading to new applications for the delivery of new biotechnology products, such as recombinant proteins, antisense oligonucleotides and cloned genes.

Partial circumvention of multi-drug resistance by annamycin is associated with comparable inhibition of DNA synthesis in the nuclear matrix of sensitive and resistant cells

We studied the subcellular and subnuclear distributions of the partially cross-resistant anthracycline Annamycin (Ann) in KB-3-1 and multi-drug resistant KB-VI cells. Subcellular drug localization was assessed qualitatively by fluorescence microscopy and quantitatively by cell fractionation and fluorescence measurements. Doxorubicin (Dox) localized predominantly in the nucleus in KB-3-1 cells and in the membranes in KB-VI cells. In contrast, the subcellular distribution of Ann was identical in both cell lines, with preferential drug localization in the perinuclear region, Golgi apparatus, endoplasmic reticulum and endosomes. Dox rate of efflux from the nucleus was negligible in KB-3-1 cells but markedly enhanced in KB-VI cells, whereas Ann was lost at a similar rate from the nucleus in both cell lines. In KB-3-1 cells Dox levels in the nuclear non-matrix were about 2-fold higher than those of Ann, while in the matrix the inverse relationship was observed. In spite of these differences, Dox and Ann had a similar inhibitory effect on new DNA synthesis in the nuclear matrix and non-matrix of KB-3-1 cells. Dox levels were reduced by 10-fold in the nuclear non-matrix and 2-fold in the matrix in KB-VI cells compared with KB-3-1 cells, whereas Ann levels were reduced by about 2- to 3-fold in the non-matrix and were unchanged in the matrix. In correlation with these findings, Dox did not cause inhibition of new DNA synthesis in either nuclear fraction in KB-VI cells, whereas inhibition of new DNA synthesis in the matrix by Ann was similar in both cell lines. Our results indicate that Ann's partial circumvention of multi-drug resistance is associated with its ability to cause comparable new DNA synthesis inhibition in the nuclear matrix of sensitive and resistant cells.

Pharmacology of liposomal vincristine in mice bearing L1210 ascitic and B16/BL6 solid tumours

Vincristine pharmacokinetic, tumour uptake and therapeutic characteristics were investigated here in order to elucidate the processes underlying the enhanced efficacy observed for vincristine entrapped in small (120 nm) distearoylphosphatidylcholine/cholesterol liposomes. Plasma vincristine levels after intravenous (i.v.) injection are elevated more than 100-fold in the liposomal formulation compared with free drug in tumour-bearing as well as non-tumour-bearing mice over 24 h. Biodistribution studies demonstrate that the extent and duration of tumour exposure to vincristine is dramatically improved when the drug is administered i.v. in liposomal form. Specifically, 72 h trapezoidal area under the curve values for liposomal vincristine in the murine L1210 ascitic and B16/BL6 solid tumours are 12.9- to 4.1-fold larger, respectively, than observed for free drug. Similar to previous results with the L1210 model, increased drug delivery to the B16 tumour results in significant inhibition of tumour growth, whereas no anti-tumour activity is observed with free vincristine. Comparisons of drug and liposomal lipid accumulation in tumour and muscle tissue indicate that the enhanced efficacy of liposomal vincristine is related predominantly to drug delivered by liposomes to the tumour site rather than drug released from liposomes in the circulation. Consequently, improvements in liposomal vincristine formulations must focus on factors that increase uptake of liposomes into tumour sites as well as enhance liposomal drug retention in the circulation.