Organ distribution and tumor uptake of annamycin, a new anthracycline derivative with high affinity for lipid membranes, entrapped in multilamellar vesicles

Lipid-Based Drug Delivery Systems in Cancer Therapy: What Is Available and What Is Yet to Come

Cancer is a leading cause of death in many countries around the world. However, the efficacy of current standard treatments for a variety of cancers is suboptimal. First, most cancer treatments lack specificity, meaning that these treatments affect both cancer cells and their normal counterparts. Second, many anticancer agents are highly toxic, and thus, limit their use in treatment. Third, a number of cytotoxic chemotherapeutics are highly hydrophobic, which limits their utility in cancer therapy. Finally, many chemotherapeutic agents exhibit short half-lives that curtail their efficacy. As a result of these deficiencies, many current treatments lead to side effects, noncompliance, and patient inconvenience due to difficulties in administration. However, the application of nanotechnology has led to the development of effective nanosized drug delivery systems known commonly as nanoparticles. Among these delivery systems, lipid-based nanoparticles, particularly liposomes, have shown to be quite effective at exhibiting the ability to: 1) improve the selectivity of cancer chemotherapeutic agents; 2) lower the cytotoxicity of anticancer drugs to normal tissues, and thus, reduce their toxic side effects; 3) increase the solubility of hydrophobic drugs; and 4) offer a prolonged and controlled release of agents. This review will discuss the current state of lipid-based nanoparticle research, including the development of liposomes for cancer therapy, different strategies for tumor targeting, liposomal formulation of various anticancer drugs that are commercially available, recent progress in liposome technology for the treatment of cancer, and the next generation of lipid-based nanoparticles.

Modifications in high-density lipoprotein lipid composition and structure alter the plasma distribution of free and liposomal annamycin

Recent studies have shown that changes in lipoprotein cholesterol and triglyceride concentration alters the plasma distribution of free (Ann.) and liposomal annamycin (LAnn) and that the majority of Ann. is associated with high-density lipoproteins (HDL) following the incubation in plasma of LAnn. To demonstrate that alterations in HDL lipid composition and HDL structure may influence the plasma distribution of Ann. and LAnn, Ann. and LAnn (20 micrograms/mL) were incubated in plasma pretreated with dithionitrobenzoate (DTNB, a compound which inhibits the conversion of free cholesterol to esterified cholesterol) 18 h prior to the experiment or in untreated plasma for 60 min at 37 degrees C. In addition, Ann. and LAnn were co-incubated with DTNB in plasma for 60 min at 37 degrees C. Following incubation the plasma was separated into its HDL, low-density lipoprotein (LDL), very-low-density lipoprotein (VLDL), and lipoprotein-deficient plasma (LPDP) fractions by ultracentrifugation and assayed for Ann. by fluorimetry. The HDL plasma cholesterol:triglyceride concentration ratio was significantly decreased following 18 h of DTNB pretreatment compared to untreated plasma controls. No significant differences in LDL/VLDL plasma cholesterol:triglyceride concentration ratio following 18 h of DTNB pretreatment was observed. An increased number of discoidal HDL particles were observed following 18 h of DTNB pretreatment. When Ann. was incubated in plasma pretreated with DTNB for 18 h the percentage of Ann. recovered in the HDL, LDL, and VLDL fractions significantly increased. However, the percentage of Ann. recovered within the LPDP fraction was significantly decreased. When LAnn was incubated in plasma pretreated with DTNB for 18 h the percentage of Ann. recovered in the HDL fraction significantly decreased. The percentage of Ann. recovered in the LPDP fraction significantly increased when LAnn was incubated in plasma pretreated with DTNB for 18 h. No significant differences in Ann. lipoprotein distribution were observed when Ann. and LAnn were co-incubated with DTNB in plasma for 1 h. These findings suggest that the cholesterol:triglyceride concentration ratio and physical structure of HDL maybe important in defining the capacity of HDL to sequester Ann.

Blood and plasma lipoprotein distribution and gender differences in the plasma pharmacokinetics of lipid-associated annamycin

The objectives of this study were to determine the lipoprotein distribution of unbound annamycin and liposomal annamycin within human and rabbit blood and plasma and to evaluate the plasma pharmacokinetics of liposomal annamycin in male and female rabbits following a single intravenous bolus of the compound. Annamycin and liposomal annamycin were incubated in human and rabbit blood and plasma for 60 min. at 37 degrees C. Following incubation blood and plasma samples were assayed by HPLC for drug in each of the lipoprotein and lipoprotein-deficient plasma fractions. To evaluate the plasma pharmacokinetics of liposomal annamycin in male versus female rabbits, a single intravenous bolus dose (5 mg/kg) of liposomal annamycin was administered to male and female rabbits. Sequential blood samples were obtained from the animals following the dose, analyzed for drug, and the pharmacokinetics determined using multicompartmental methods. The incorporation of annamycin into liposomes composed of dimyristoylphosphatidylcholine and dimyristoylphosphatidylglycerol resulted in no significant differences in blood versus plasma lipoprotein drug distribution. Furthermore, no differences in the plasma distribution of liposomal annamycin were observed when the drug was either incubated in vitro for 1 hr or 1 hr following intravenous administration into New Zealand male white rabbits. The plasma clearance and volume of distribution of liposomal annamycin were decreased and a increase in plasma AUC in female as compared to male rabbits following a single intravenous bolus of liposomal annamycin was observed. These findings suggest that the lipoprotein distribution of liposomal annamycin is not different when incubated in blood or plasma and that in vitro liposomal annamycin plasma distribution is similar to in vivo. Furthermore, it appears that the pharmacokinetics of liposomal annamycin are different following administration to male versus female rabbits.

Differences in lipoprotein concentration and composition modify the plasma distribution of free and liposomal annamycin

PURPOSE

The purpose of these studies were to determine the distribution of a lipophilic antineoplastic agent, annamycin (Ann), and its liposomal counterpart (LAnn) in plasma which had been altered in its lipoprotein concentration and lipid composition.

METHODS

Ann, LAnn, and doxorubicin (a hydrophilic control) were incubated in human plasma for 1 hour at 37 degrees C. Following incubation plasma samples were assayed by fluorimetry for drug in each of the lipoprotein and lipoprotein-deficient plasma (LPDP) fractions. To assess the influence of modified lipoprotein concentrations and lipid composition on plasma distribution of Ann and LAnn, either Ann or LAnn were incubated in human plasma which had been supplemented with very low density lipoproteins (VLDL) or low density lipoproteins (LDL).

RESULTS

When unbound Ann or doxorubicin was incubated in plasma for 1 hour at 37 degrees C, the majority of drug was found in the LPDP fraction. However, when Ann was incorporated into liposomes composed of dimyristoylphosphatidylcholine and dimyristoylphosphatidylglycerol (LAnn) the majority of Ann was recovered in the high-density lipoprotein (HDL) fraction. Elevation of plasma LDL-cholesterol or VLDL-triglyceride concentrations increased the amounts of Ann and LAnn associated with these lipoprotein classes. Alterations in HDL composition decreased the amount of Ann, but increased the amount of L-Ann within the HDL fraction. Lipid transfer protein (LTP) activity did not significantly modify the plasma distribution of Ann and LAnn in short-term experiments, but the modified lipoprotein composition that LTP facilitates in long-term incubations reduced the capacity of VLDL and LDL to accept drug.

CONCLUSIONS

These findings suggest that lipoprotein concentration and composition alter the plasma distribution of Ann and LAnn and may help to explain the discrepancies observed in the pharmacokinetics of Ann and LAnn when they are administered to healthy versus cancer patients.

Distribution of free and liposomal annamycin within human plasma is regulated by plasma triglyceride concentrations but not by lipid transfer protein

Annamycin (Ann) is a lipophilic and non-cross-resistant anthracycline antibiotic currently in clinical development as a liposomal formulation (L-Ann) composed of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylglycerol (DMPG). Previous studies have demonstrated that the incorporation of Ann into these liposomes prolongs its terminal serum half-life and increases the tumor levels of the drug. However, an explanation for the altered pharmacokinetics and pharmacodynamics of doxorubicin and Ann when entrapped into these multilamellar lipid vesicles remains unknown. Since the distribution of lipophilic compounds within plasma lipoproteins has been shown to influence the pharmacokinetics and organ distribution of a number of lipophilic compounds and this distribution appears to be regulated by lipid transfer protein (LTP), we studied the distribution of Ann and L-Ann among plasma lipoproteins and the influence of LTP on the distribution of Ann and L-Ann among plasma lipoproteins. Our results concluded that when Ann was incorporated into liposomes composed of DMPC and DMPG, over 65% of the initial Ann concentration would distribute into the high density lipoprotein (HDL) fraction and that free Ann and L-Ann distribution within human plasma was independent of LTP activity. In addition, we observed that the increase in total plasma triglyceride (TG) concentrations (through the increase of very low-density lipoproteins (VLDL)) resulted in the increase distribution of Ann and L-Ann within the TG-rich VLDL fraction. However, increasing the VLDL core TG/cholesterol ratio decreased Ann distribution into VLDL. These findings suggest that initial Ann distribution is regulated by a mechanism that does not involve LTP, but through its interaction with plasma VLDL-TG.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of vesicle size and lipid composition on the in vivo tumor selectivity and toxicity of the non-cross-resistant anthracycline annamycin incorporated in liposomes

Annamycin (Ann) is a non-cross-resistant lipophilic anthracycline antiobiotic optimally suited for liposome delivery. We studied how vesicle size and presence of phospholipids with a high phase transition temperature and monosialoganglioside (GM I) in the liposome bilayers affect the pharmacokinetics, tumor selectivity and toxicity of Ann. Entrapment of Ann in multilamellar vesicles (L-Ann) resulted in a 20% lower heart AUC and a 30-40% higher tumor and liver AUC. Reduction of the liposome size from 1.6 to 0.03 microns increased Ann plasma circulation time and tumor AUC by 2-fold, enhanced Ann tumor selectivity and decreased Ann subacute toxicity by 2-fold. The presence of phospholipids with a high phase transition temperature and GMI in the liposome bilayers further prolonged Ann plasma circulation time by 2- to 4-fold, did not increase Ann tumor AUC and moderately increased Ann subacute toxicity. The anti-tumor activity of Ann correlated with the tumor AUC achieved with each particular formulation. Our results strongly suggest that vesicle size may be an important determinant of the therapeutic index of liposomal Ann, but they fail to demonstrate a beneficial tumor-targeting effect of liposomes composed of GMI and phospholipids with a high phase transition temperature, as has been reported for the hydrophilic parent compound doxorubicin.

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.

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

The in vitro cytotoxicity, cellular pharmacology, and DNA lesions induced by the lipophilic anthracycline annamycin (Ann) were studied in KB and KB-V1 (multidrug-resistant) cells. Ann was tested in suspension in saline and 10% dimethylsulfoxide (DMSO: final concentration, 0.05%-0.5%) or entrapped in multilamellar liposomes (median size, 1.57 microns). Doxorubicin (Dox) was about twice as cytotoxic as Ann or liposome-entrapped Ann (L-Ann) against KB cells. Both Ann and L-Ann displayed a partial lack of cross-resistance with Dox (resistance indices: > 60 for Dox, 4.7 for Ann, 4.0 for L-Ann). Accumulation of Ann in KB and KB-V1 cells was consistently about 2-3 and 10-20 times higher, respectively, than that of Dox. Cellular retention of Ann in KB and KB-V1 cells was about 2 and 30 times higher, respectively, than that of Dox as a result of the different efflux patterns of the two drugs: Dox was not effluxed from KB cells but was significantly effluxed from KB-V1 cells (66% at 1 h, whereas Ann efflux was similar in both cell lines (about 50% at 1 h). Dox retention in KB-V1 cells was increased by a factor of 2 in the presence of verapamil or cyclosporine A, but Ann retention was not. In addition, accumulation of Dox in KB-V1 cells was enhanced by the metabolic inhibitor deoxyglucose/azide and the membrane carboxylic ionophore monensin, whereas accumulation of Ann was not affected by either agent. All these findings indicate significant differences in the cellular transmembrane transport systems between Dox and Ann and suggest that Ann efflux is not mediated by P-glycoprotein. Liposome entrapment reduced by a factor of 1.3-2.0 the cellular accumulation of Ann without affecting its cytotoxicity. As compared with Dox, both Ann and L-Ann induced 3 times more DNA double- and single-strand breaks in KB cells. In KB-V1 cells, Dox did not induce DNA damage, whereas the extent of DNA breaks induced by both Ann and L-Ann was similar to that induced by Dox in KB cells. Our results indicate (1) that the lack of cross-resistance between Ann and Dox is associated with a markedly enhanced accumulation and retention of Ann in KB-V1 cells and (2) that the type of liposomes used does not significantly affect the cellular effects of Ann.

Design and tumor targeting of anthracyclines able to overcome multidrug resistance: a double-advantage approach

A novel, 'double-advantage approach' to developing more effective chemotherapies will be reviewed. This approach is based on a presumption that analogs designed on a sound hypothesis, and combined with a rationally selected drug delivery system, will optimize antitumor activity by creating drugs that are more active and that can be more specifically targeted to tumors. In the design of drugs superior to doxorubicin, we have focused on typical multidrug resistance and new anthracycline analogs, whose uptake is not affected by P-glycoprotein. Analysis of structural elements of anthracyclines affecting activity against multidrug resistant tumors and affinity for liposomes will be discussed. Annamycin, a lipophilic anthracycline analog, was selected for further preclinical development as a liposomal formulation and demonstrated, in the initial biological evaluation, high activity against tumors resistant to doxorubicin.