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Biomedical subjects

L D Mayer

Publications and source records attributed to L D Mayer.

At least 37 records · Page 2Linked to original sources
PubMed2000

Molecular and pharmacokinetic properties associated with the therapeutics of bcl-2 antisense oligonucleotide G3139 combined with free and liposomal doxorubicin.

Bcl-2 is a key apoptosis-regulating protein that has been implicated in mechanisms of chemoresistance for a variety of malignancies by blocking programmed cell death. This study investigated the activity of the Bcl-2 antisense oligodeoxynucleotide (AS ODN) G3139 combined with free doxorubicin (F-DOX) or sterically stabilized liposomal doxorubicin (SL-DOX) to determine the role that drug pharmacodistribution properties may have on antitumor activity using a Bcl-2-expressing human breast solid tumor xenograft model. Administration of G3139 was able to delay the growth of MDA435/LCC6 cells compared with control ODN-treated animals; however, in all of the cases, tumors reestablished after AS ODN treatment. Western blot analyses of Bcl-2 levels of solid tumors showed a sequence-specific down-regulation of the Bcl-2 protein after four daily doses of G3139, which correlated with histological evidence of tumor cell death. Interestingly, the expression of Bcl-2 returned to pretreatment levels during the course of subsequent ODN administration, which suggested the development of resistance to continued Bcl-2 ODN treatment. The antitumor activity of ODN given in conjunction with either F-DOX or SL-DOX was also examined. The combination of G3139 and F-DOX was able to suppress the growth of MDA435/LCC6 cells beyond that obtained with either of the treatments given alone, indicative of synergistic action. Examination of the pharmacokinetics of F-DOX with systemic G3139 administration revealed that elevated tumor drug DOX levels were obtained compared with DOX treatment in the absence of G3139. This effect was sequence-specific and plasma DOX levels were unaffected by G3139 treatment, which indicated possible positive ODN-drug interactions at the tumor site. Combining G3139 with SL-DOX further increased the degree of antitumor activity. The improved efficacy of this combination was attributed to increased tumor drug levels that arise from the ability of SL-DOX to passively accumulate in solid tumors. These results suggest that additional benefits of Bcl-2 antisense ODN may be obtained when it is combined with liposomal formulations of anticancer drugs such as DOX.

Animals↗
PubMed1999

Intravenous pretreatment with empty pH gradient liposomes alters the pharmacokinetics and toxicity of doxorubicin through in vivo active drug encapsulation.

Liposomes have been used widely to improve the therapeutic activity of pharmaceutical agents. The traditional approach for such applications has been to formulate the pharmaceutical agent in liposomes prior to administration in vivo. In this report we demonstrate that liposomes exhibiting a transmembrane pH gradient injected intravenously (iv) can actively encapsulate doxorubicin in the circulation after iv administration of free drug. Small (110 nm) liposomes composed of phosphatidylcholine (PC)/cholesterol (Chol, 55:45 mol:mol) exhibiting a pH gradient (inside acidic) were administered iv 1 h prior to free doxorubicin, and plasma drug levels as well as toxicity and efficacy were evaluated. Predosing with egg PC/Chol pH gradient liposomes increased the plasma concentration of doxorubicin as much as 200-fold compared to free drug alone as well as to predosing with dipalmitoyl PC/Chol pH gradient liposomes or EPC/Chol liposomes without a pH gradient. The ability of the liposomes to alter the pharmacokinetics of doxorubicin was dependent on the presence of a transmembrane pH gradient and correlated with the extent of doxorubicin uptake into the liposomes at 37 degreesC in pH 7.5 buffer, indicating that doxorubicin was being actively accumulated in the circulating liposomes. This in vivo drug loading was achieved over a range of doxorubicin doses (5 mg/kg-40 mg/kg) and was dependent on the dose of EPC/Chol liposomes administered prior to free doxorubicin injection. The altered pharmacokinetic properties of doxorubicin associated with in vivo doxorubicin encapsulation were accompanied by a decrease in drug toxicity and maintained antitumor potency. These results suggest that pretreatment with empty liposomes exhibiting a pH gradient may provide a versatile and straightforward method for enhancing the pharmacological properties of many drugs that can accumulate into such vesicle systems at physiological temperatures.

Animals↗
PubMed1999

Phase I study of liposomal vincristine.

PURPOSE: A phase I study of vincristine encapsulated inside 120-nm-diameter distearoylphosphatidylcholine-cholesterol liposomes was performed. The primary objectives were to determine the maximum-tolerated dose (MTD), recommended phase II dose, toxicity, and pharmacokinetics of liposomal vincristine (ONCO-TCS). PATIENTS AND METHODS: Twenty-five patients with histologically confirmed malignancies were enrolled and assessable. Vincristine doses were increased from 0.5 mg/m2 to 1.0, 1.5, 2.0, 2.4, and 2.8 mg/m2 with cohorts of three or more patients per dose level. A total of 64 courses of ONCO-TCS were administered intravenously once every 3 weeks. The pharmacokinetics of total vincristine content in plasma were determined using a high-performance liquid chromatography method. RESULTS: Patients were treated with vincristine doses up to 2.8 mg/m2; however, 2.4 mg/m2 was defined as the MTD and 2.0 mg/m2 as the phase II recommended dose. Pain and obstipation were the dose-limiting toxicites. Other toxicities were fever, rigors, fatigue, myalgias, and peripheral neuropathy. Hematologic toxicity was mild. All patients who were treated with doses above 1.5 mg/m2 received in excess of 2.0 mg of vincristine, with doses as high as 6.2 mg. One partial response was seen in a patient with pancreatic cancer. Tumor response not meeting partial response criteria was seen in two other patients. Pharmacokinetic studies revealed significantly elevated concentrations of total vincristine, but parameters varied and were not directly correlated with toxicity or response. CONCLUSION: The ability to administer elevated doses of vincristine, as well as indications of efficacy, suggests that ONCO-TCS warrants further clinical investigation in a phase II setting.

Adult↗
PubMed1999

Doxorubicin encapsulated in sterically stabilized liposomes exhibits renal and biliary clearance properties that are independent of valspodar (PSC 833) under conditions that significantly inhibit nonencapsulated drug excretion.

Coadministration of anticancer drugs and multidrug resistance modulators directed against P-glycoprotein over-expressed in tumors also results in nonspecific blockade of this drug efflux pump in excretory tissues such as the liver and kidneys. These interactions often result in impaired renal and biliary clearance for anticancer agents such as doxorubicin (DOX). In the present investigation, we characterized the excretory processes associated with liposomal DOX administration to elucidate how liposome encapsulation may bypass adverse pharmacokinetic interactions between DOX and (3'-keto-Bmt1)-(Val2)-cyclosporin (Valspodar). Renal and biliary clearance properties of liposome-encapsulated DOX were compared with those for nonencapsulated DOX in the presence and absence of Valspodar using an instrumented rat model with implanted jugular vein and bile duct catheters for continuous sampling. Two types of liposomal DOX formulations were used, a drug-permeable egg phosphatidyl choline/cholesterol system and a sterically stabilized polyethylene glycol/1,2 distearoyl-sn-glycero-3-phosphocholine/cholesterol system to establish the relative roles of liposome-encapsulated and released drug on the pharmacokinetic and excretion alterations induced by Valspodar. DOX and its primary metabolites were quantitated using high-performance liquid chromatography. When Valspodar was coadministered with nonencapsulated DOX, 3.5- and 37.5-fold reductions in renal clearance (CLr) and biliary clearance (CLb), respectively, were observed, which resulted in increased plasma DOX concentrations and total exposure. However, Valspodar-induced alterations in CLr and CLb were less profound with egg phosphatidyl choline/cholesterol DOX (1.7- and 2.0-fold reductions, respectively) and negligible with the long-circulating polyethylene glycol-containing liposomal formulation. These results indicate that liposomes may circumvent Valspodar-induced DOX pharmacokinetic changes by reducing the rate of drug excretion in liver and kidney tissue to a level that is within the renal and biliary excretion capacity in the presence of P-glycoprotein blockade.

Animals↗
PubMed1998

Comparison of different hydrophobic anchors conjugated to poly(ethylene glycol): effects on the pharmacokinetics of liposomal vincristine.

Poly(ethylene glycol) (PEG) conjugated lipids have been used to increase the circulation longevity of liposomal carriers encapsulating therapeutic compounds. PEG is typically conjugated to distearoylphosphatidylethanolamine (DSPE) via a carbamate linkage that results in a net negative charge on the phosphate moiety at physiological pH. It was anticipated that the presence of this negative charge could have deleterious effects on liposome pharmacokinetic characteristics. We describe here the synthesis of a new class of neutrally charged PEG-lipid conjugates in which the PEG moiety was linked to ceramide (CER). These PEG-CER conjugates were compared with PEG-DSPE conjugates for their effects on the pharmacokinetics of liposomal vincristine. PEG-CER (78% palmitic acid, C16) and PEG-DSPE achieved comparable increases in the circulation lifetimes of sphingomyelin/cholesterol (SM/chol) liposomes. However, PEG-DSPE significantly increased the in vitro and in vivo leakage rates of vincristine from SM/chol-based liposomes compared to vincristine leakage observed when PEG-CER was used. The increase in drug leakage observed in vitro that was due to the presence of PEG-DSPE was likely due to the presence of a negative surface charge. Analysis of the electrophoretic mobilities of these formulations suggested that the negative surface charges were shielded by approx. 80% by the PEG layer extending from the membrane surface. In contrast, formulations containing PEG-CER had no surface charge and no electrophoretic mobility. A comparison of the effects of the ceramide acyl chain length (C8 through C24) on the pharmacokinetics of SM/chol/PEG-CER formulations of vincristine demonstrated that longer acyl chains on the PEG-CER were associated with longer circulation lifetimes of the liposomal carriers and, consequently, higher plasma vincristine concentrations. These data suggest that the short chain PEG-ceramides underwent rapid partitioning from the vesicles after i.v. administration, whereas the longer chain PEG-ceramides had stronger anchoring properties in the liposome bilayers and partitioned slowly from the administered vesicles. These data demonstrate the utility of ceramide-based steric stabilizing lipids as well as the potential for developing controlled release formulations by manipulating the retention of the PEG-ceramide conjugate in liposome bilayers.

Animals↗
PubMed1998

Pharmacokinetic behavior of vincristine sulfate following administration of vincristine sulfate liposome injection.

The pharmacokinetic behavior of vincristine sulfate (VINC) following administration of vincristine sulfate liposome injection (VSLI), 0.16 mg/ml, as an intravenous infusion over 60 min in 24 of 25 patients enrolled in a phase I clinical study of this drug is described. Plasma samples for determination of the pharmacokinetic behavior of VINC were collected during the infusion at 15, 30 and 60 min as well as at 2, 4, 8, 12, 48 and 72 h postinfusion. Total VINC concentration was determined using a validated high-performance liquid chromatographic (HPLC) assay. Patients receiving doses of 0.5 to 1.5 mg/m2 VSLI did not provide useful pharmacokinetic data at late time-points owing to the limit of quantitation of the HPLC assay (28.6 ng/ml). Sufficient concentration-time data were available for seven of the patients receiving doses of VSLI from 2.0 to 2.8 mg/m2 for compartmental modelling. A two-compartment open model (PCNONLIN Model 10) was the best fit for the observed VINC plasma data for these patients. The mean maximum observed concentration values were significantly greater for patients receiving VSLI at 2.8 mg/m2 (2260 +/- 212 ng/ml, n = 2) than for those receiving 2.0 mg/m2 and 2.4 mg/m2 (891 +/- 671 ng/ml, n = 6; 679 +/- 634 ng/ml, n = 6, respectively). No significant differences were observed in maximum concentration values between patients at 2.0 mg/m2 and those at 2.4 mg/m2. A trend towards higher parametric AUC (0 to infinity) values with increasing dose (on a milligram per meter squared basis) was observed but statistical significance was not reached. Comparison of the pharmacokinetic behavior of VSLI observed in this study with nonencapsulated VINC demonstrated that (1) the variability observed for VSLI pharmacokinetic parameters was similar to nonencapsulated VINC, (2) although variability in absolute concentration was observed between patients, the behavior of VSLI in individual patients followed a two- rather than a three-compartment open model, and (3) VINC plasma concentrations were significantly greater following administration of VSLI than described for nonencapsulated VINC. Overall, the results for patients treated with VSLI from 2.0 to 2.8 mg/m2 suggest that this formulation protects VINC from the early phase of rapid elimination seen with nonencapsulated drug, resulting in significantly elevated VINC plasma concentrations over extended periods of time.

Adult↗
PubMed1998

Preclinical pharmacology, toxicology and efficacy of sphingomyelin/cholesterol liposomal vincristine for therapeutic treatment of cancer.

PURPOSE: To establish the pharmacodynamic relationships between drug biodistribution and drug toxicity/efficacy, a comprehensive preclinical evaluation of sphingomyelin/cholesterol (SM/chol) liposomal vincristine and unencapsulated vincristine in mice was undertaken. METHODS: Pharmaceutically acceptable formulations of unencapsulated vincristine and liposomal vincristine at drug/lipid ratios of 0.05 or 0.10 (wt/wt) were evaluated for toxicity, antitumor activity and pharmacokinetics following intravenous administration. RESULTS: Mice given liposomal vincristine at 2 mg/kg vincristine had concentrations of vincristine in blood and plasma at least two orders of magnitude greater then those achieved after an identical dose of unencapsulated drug. One day after administration of the liposomal vincristine, there were at least tenfold greater drug quantities, relative to unencapsulated vincristine, in the axillary lymph nodes, heart, inguinal lymph nodes, kidney, liver, skin, small intestines and spleen. Increased plasma and tissue exposure to vincristine as a result of encapsulation in SM/chol liposomes was not associated with increased drug toxicities. Treatment of the murine P388 ascitic tumor with a single intravenous dose of unencapsulated drug at 2, 3 and 4 mg/kg, initiated 1 day after tumor cell inoculation, resulted in a 33 to 38% increase in lifespan. In contrast, long-term survival rates of 50% or more were achieved in all groups treated with the SM/chol liposomal vincristine formulations at doses of 2, 3 and 4 mg/kg. At the 4 mg/kg dose, eight of ten and nine of ten animals survived past day 60 when treated with SM/chol liposomal vincristine prepared at the 0.05 and 0.1 drug/lipid ratios, respectively. CONCLUSIONS: Overall, increased and prolonged plasma concentrations of vincristine achieved by liposomal encapsulation were correlated with dramatically increased antitumor activity in comparison with the unencapsulated drug, but no correlations could be established between pharmacokinetic parameters and toxicity.

Animals↗
PubMed1998

Future developments in the selectivity of anticancer agents: drug delivery and molecular target strategies.

In the past, our limited understanding of the processes involved in the initiation and growth of cancer hindered our ability to effectively treat most human malignancies and therapies were often associated with significant toxic side effects as well as re-emergence of disease. The development of drug delivery systems such as liposomes has improved the specificity of various conventional anticancer agents by enhancing drug accumulation in tumors while often decreasing exposure to susceptible healthy tissues. More recently, the identification of a wide range of genes and corresponding protein products that are altered in various human cancers has revealed new molecular targets for cancer therapy that may provide improved selectivity for tumor cells over traditional cytotoxic agents. This review discusses how advances in the sophistication of liposomal delivery systems may open new opportunities for combining novel molecular targeting strategies with pharmacological targeting via liposomes to optimize the therapy of many human malignancies.

Animals↗
PubMed1997

Liposomal doxorubicin circumvents PSC 833-free drug interactions, resulting in effective therapy of multidrug-resistant solid tumors.

Conventional methods that are used to overcome multidrug resistance (MDR) often involve the coadministration of chemosensitizers and anticancer drugs. The cyclosporin analogue SDZ PSC 833 [(3'-keto-Bmt1)-(Val2)-cyclosporin] (PSC 833) has been shown to possess powerful chemosensitization properties in vitro, in addition to being intrinsically nontoxic. However, coadministration of PSC 833 with anticancer drugs, such as daunorubicin, doxorubicin (DOX), and Taxol, have resulted in the exacerbation of anticancer drug toxicity, which is due to altered anticancer drug pharmacokinetics. Here, we hypothesized that optimization of the anticancer drug delivery, using liposomal carriers, may, by avoiding these adverse interactions, offer a significant advantage over nonencapsulated drugs. Toxicity studies were conducted in normal BDF1 mice, with i.v. DOX (free or liposome encapsulated) administration and p.o. PSC 833 in single and multiple dosage regimens over a 15-day study period. p.o. administration of PSC 833, at a dose of 100 mg/kg, reduced the maximum tolerated dose (MTD) of i.v administered free drug by 2.5-3-fold, in single- and multiple-dose regimens. In contrast, PSC 833 administration resulted in only a 20% reduction of the MTD for DOX encapsulated in 100-nm 1,2 distearoyl-sn-glycero-3-phosphocholine/cholesterol liposomes (55:45 molar lipid ratio) in a single-dose regimen and had no effect on the liposomal DOX MTD for the day 1, 5, and 9 treatment schedule. Modest modulation of P-glycoprotein-mediated MDR was observed in the murine P388/ADR solid tumor model when PSC 833 was administered with free DOX at the MTD. In contrast, liposomal DOX combined with PSC 833 resulted in tumor growth inhibition that was comparable to that observed for drug-sensitive P388/WT tumors. This efficacy of P388/ADR tumors treatment was dependent on PSC 833 because treatment with liposomal DOX alone provided significantly less antitumor activity. Pharmacokinetic and tissue distribution data demonstrated that DOX encapsulated in 1,2 distearoyl-sn-glycero-3-phosphocholine/cholesterol liposomes exhibited comparable plasma elimination and tissue distribution properties in the presence and absence of PSC 833, whereas free DOX displayed reduced plasma elimination rates and altered tissue distribution in the presence of PSC 833. These results provide evidence that PSC 833 can induce P-glycoprotein modulation and chemosensitize MDR tumors in the absence of altered DOX pharmacokinetics when liposomal carriers are used. This suggests that the improved tumor selectivity of anticancer drugs that are administered in liposomal formulations may avoid the complications that are associated with free drug-MDR-reversing agent combinations and enhance the therapy of multidrug-resistant tumors.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1997

Validation of a high-performance liquid chromatographic assay method for quantification of total vincristine sulfate in human plasma following administration of vincristine sulfate liposome injection.

The validation of a high performance liquid chromatographic (HPLC) assay method for quantitation of total vincristine sulfate (VINC) in human plasma is described. VINC was extracted from plasma using BondElut CBA solid phase cartridges with vinblastine as the internal standard. Chromatography was accomplished using a Waters Symmetry C8 (250 mm x 4.6 mm i.d.) analytical column, a Waters Delta-Pak ODS guard column with a mobile phase of 34.9% water-0.1% diethylamine (pH 7.0)-40% acetonitrile-25% methanol pumped isocratically at 1.0 ml min(-1) with ultraviolet detection at 297 nm. Above the limit of quantitation of 28.6 ng ml(-1), the area ratio precision (R.S.D. range 3.33-11.6%) and accuracy of predicted values (R.S.D. range 8.56-23.8% with the limit of quantitation being the only value above 20%) were acceptable. The assay was linear from 28.6-2860 ng ml(-1) VINC in plasma. Recovery of VINC from plasma and VINC from plasma spiked with vincristine sulfate liposome injection ranged from 74.9-87.1%. Stability of VINC in plasma stored at -20 degrees C for at least 49 days and of extracted plasma samples was demonstrated. Potential interference in quantitation of VINC from commonly co-administered drugs was evaluated along with day-to-day variability. The assay procedure was found suitable for evaluation of VINC clinical pharmacokinetics in plasma following administration of vincristine sulfate liposome injection prepared using distearoylphosphatidylcholine (DSPC)/cholesterol liposomes for injection.

Chromatography, High Pressure Liquid↗
PubMed1997

The role of tumor-associated macrophages in the delivery of liposomal doxorubicin to solid murine fibrosarcoma tumors.

Murine fibrosarcoma tumors arising from subcutaneous inoculation of FSa-N cells exhibit 4-fold higher tumor-associated macrophage (TAM) levels than those from the FSa-R line. These solid tumors were used to assess the role of TAMs in the accumulation of liposomal anticancer drugs. Two liposomal formulations of doxorubicin were investigated: a conventional formulation composed of distearoylphosphatidylcholine (DSPC) and cholesterol and a sterically stabilized liposomal formulation composed of DSPC/cholesterol/poly (ethylene glycol)-modified distearoylphosphatidyethanolamine (PEG-PE). Circulating concentrations of PEG-PE containing liposomes 24 h after i.v. administration were 3-fold greater than those observed after administration of conventional liposomes. No differences were observed in drug retention or tumor (FSa-R or FSa-N) drug and liposomal lipid delivery when comparisons were made between different liposomal formulations. However, tumor doxorubicin concentrations were increased as much as 4-fold for liposomal formulations relative to free drug. Further, there was a 1.5- to 2-fold increase in doxorubicin delivery to TAM-enriched FSa-N tumors compared with FSa-R tumors. Fluorescence microscopy studies revealed a poor correlation between CD11b (Mac-1) positive cells (TAMs) and the appearance of doxorubicin fluorescence. These results suggest that uptake of liposomal drugs by TAMs does not account for the enhanced accumulation of liposomal drugs in solid tumors. Rather, the increased tumor drug delivery may be related to alternative TAM-mediated processes that increase tumor vascular permeability. Therapeutic studies demonstrated that increased tumor drug uptake observed for the liposomal doxorubicin formulations led to marginal improvements in antitumor activity, and it is suggested that much of the drug delivered in liposomal form is not biologically available.

Animals↗
PubMed1995

Determination of free and liposome-associated doxorubicin and vincristine levels in plasma under equilibrium conditions employing ultrafiltration techniques.

A thorough understanding of the pharmacodynamic relationships associated with toxicity and efficacy behavior of liposome-encapsulated anticancer agents such as doxorubicin and vincristine will rely on the ability to accurately separate and quantify the free and liposome-associated drug fractions in plasma after administration. We have investigated the use of ultrafiltration as a method of isolating free doxorubicin and vincristine from liposomal drug under equilibrium conditions and compared it to previously developed nonequilibrium procedures based on solid-phase extraction. Adsorption of drugs dissolved in saline to the ultrafiltration devices resulted in concentration-dependent ultrafiltrate drug recoveries ranging from 41 to 96%. However, concentration-independent quantitative recovery of vincristine in saline solutions could be obtained by passivating the ultrafiltration devices with PEG-8000 and device drug adsorption was ameliorated for both agents by plasma. The ultrafiltration method provided a more reliable separation of free and protein-bound drug, whereas solid-phase extraction yielded artificially high free drug concentrations due to process-induced protein-bound drug complex dissocation. Also, coelution of liposomes with the free drug fraction using solid-phase extraction was 64- to 418-fold higher than observed with ultrafiltration. Taken together, these properties indicated a significantly increased degree of accuracy in measuring the amount of free doxorubicin and vincristine in samples containing liposomal formulations employing ultrafiltration compared to solid-phase extraction. The importance of this improvement was highlighted by observations that determinations of free drug concentrations in the plasma of mice injected with liposomal doxorubicin and vincristine were 3- to 12-fold higher using solid-phase extraction compared to ultrafiltration. Finally, the ultrafiltration procedure is rapid, versatile, and can be used for a wide range of drug and liposome concentrations and free drug/liposomal drug ratios.

Adsorption↗
PubMed1995

The cationic lipid stearylamine reduces the permeability of the cationic drugs verapamil and prochlorperazine to lipid bilayers: implications for drug delivery.

The therapeutic activity of a wide variety of drugs is significantly improved when their longevity in the circulation is extended by encapsulation in liposomes. To improve the retention of cationic drugs in liposomes, we have investigated the effect of the cationic lipid stearylamine on the permeability of the calcium channel blocker verapamil and the antipsychotic drug prochlorperazine, both of which are also multidrug resistance modulators. Both drugs were efficiently incorporated into liposomes composed of DSPC/cholesterol that possessed a transmembrane pH gradient (inside acidic). However, the efflux of the loaded drugs was relatively rapid (i.e., 50% of the encapsulated verapamil was released after 4 h at 37 degrees C), despite the presence of a 3 unit pH gradient (pHi = 4.0, pHo = 7.5). Drug retention within the liposomes was improved by increasing the magnitude of the transmembrane pH gradient to approx. 5 units (pHi = 2.0, pHo = 7.5). Further improvements in drug retention were achieved by the addition of 10 mol% of the cationic lipid stearylamine in the DSPC/cholesterol liposomes. The combination of the 5 unit pH gradient and stearylamine resulted in increases of the retention of verapamil and prochlorperazine by approx. 20- and 5-fold, respectively. Calculation of the permeability coefficients for the charged (cationic) and neutral forms of the drugs indicated that the neutral forms of both drugs were approx. 10(4)-fold more permeable than were the cationic forms of the drugs. Further, the presence of stearylamine reduced the permeability coefficient for the cationic species of the drugs by approximately an order of magnitude, but had no effect on the neutral species of the drugs. The efflux curves observed for both verapamil and prochlorperazine could be mathematically modeled by assuming that the primary influence of stearylamine was on the development of a positive surface charge density on the inner monolayer of the liposome. Taken in sum, these results indicate that stearylamine is effective at decreasing the leakage of cationic drugs from liposomes, and may prove to be a valuable component of liposomal drug formulations.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1995

Sphingomyelin-cholesterol liposomes significantly enhance the pharmacokinetic and therapeutic properties of vincristine in murine and human tumour models.

This study reports on the development of a liposomal formulation of vincristine with significantly enhanced stability and biological properties. The in vitro and in vivo pharmacokinetic, tumour delivery and efficacy properties of liposomal vincristine formulations based on sphingomyelin (SM) and cholesterol were compared with liposomes composed of distearoylphosphatidylcholine (DSPC) and cholesterol. SM/cholesterol liposomes had significantly greater in vitro stability than did similar DSPC/cholesterol liposomes. SM/cholesterol liposomes also had significantly improved biological properties compared with DSPC/cholesterol. Specifically, SM/cholesterol liposomes administered intravenously retained 25% of the entrapped vincristine after 72 h in the circulation, compared with 5% retention in DSPC/cholesterol liposomes. The improved retention properties of SM/cholesterol liposomes resulted in plasma vincristine levels 7-fold higher than in DSPC/cholesterol liposomes. The improved circulation lifetime of vincristine in SM/cholesterol liposomes correlated with increased vincristine accumulation in peritoneal ascitic murine P388 tumours and in subcutaneous solid A431 human xenograft tumours. Increased vincristine delivery to tumours was also accompanied by increased anti-tumour efficacy. Treatment with SM/cholesterol liposomal formulations of vincristine resulted in greater than 50% cures in mice bearing ascitic P388 tumours, an activity that could not be achieved with the DSPC/cholesterol formulation. Similarly, treatment of mice with severe combined immunodeficiency (SCID) bearing solid human A431 xenograft tumours with SM/cholesterol vincristine formulations delayed the time required for 100% increase in tumour mass to > 40 days, compared with 5 days, 7 days and 14 days for mice receiving no treatment or treatment with free vincristine or DSPC/cholesterol formulations of vincristine respectively.

Animals↗
PubMed1995

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.

Animals↗
PubMed1994

Liposomal vincristine which exhibits increased drug retention and increased circulation longevity cures mice bearing P388 tumors.

Prolonged exposure to vincristine correlates with improved therapeutic activity. In this work, two methods are used to increase the circulation longevity of liposomal formulations of vincristine. The first involves incorporation of the ganglioside GM1, which acts to increase the circulation longevity of liposomal carriers, while the second approach relies on a modification of the vincristine encapsulation procedure which enhances drug retention. It is shown that these approaches are synergistic and increase the circulation half-life of vincristine from approximately 1 h to greater than 12 h. This results in a dramatic improvement in the therapeutic activity of liposomal vincristine as measured using a murine P388 lymphocytic leukemia model. At doses above 2 mg/kg, the optimized liposomal vincristine formulation cures greater than 50% of mice bearing the P388 tumor, whereas free vincristine results in no cures.

Animals↗
PubMed1994

Transfer of liposomal drug carriers from the blood to the peritoneal cavity of normal and ascitic tumor-bearing mice.

Previously we have demonstrated that the L1210 antitumor activity of liposomal doxorubicin increased significantly as the size of the liposomal carrier was reduced from 1.0 to 0.1 micron. It is demonstrated herein that empty and drug-loaded small (0.1-micron diameter) liposomes accumulate efficiently into the peritoneal cavity of normal and ascitic L1210 tumor-bearing animals following i.v. administration. In normal mice injected with 100 nm DSPC/chol liposomal doxorubicin (drug-to-lipid ratio of 0.2; wt/wt) approximately 2.8 micrograms drug could be recovered from the peritoneal cavity following peritoneal lavage at 24 h. Although this represents only 0.7% of the injected doxorubicin dose, this level of drug is 2 orders of magnitude greater than that achieved following administration of an equivalent dose of free drug (20 mg/kg). The drug levels achieved within the peritoneal cavity are dependent on the physical characteristics (size, drug-to-lipid ratio and lipid composition) of the liposomes employed. Optimal delivery is obtained employing 100 nm DSPC/chol liposomal doxorubicin, a vesicle system that is known to retain entrapped drug following i.v. administration and exhibits extended circulation lifetimes. Analysis of drug and liposome distribution within the peritoneal cavity of normal mice indicates that as much as 50% of the measured doxorubicin and liposomal lipid is cell-associated. Flow cytometric analysis of the peritoneal cells demonstrated that cell-associated doxorubicin resides almost exclusively within resident peritoneal macrophages. The increased delivery of doxorubicin to the peritoneal cavity of normal mice following i.v. administration of small (0.1-micron) liposomal doxorubicin is correlated with a pronounced (> 90%) and prolonged (> 14-day) suppression of resident peritoneal cells. Liposomal drug accumulation increased dramatically in animals with an established L1210 ascitic tumor. More than 5% of the injected dose was found in the peritoneal cavity of these animals 24 h after treatment with DSPC/chol liposomal doxorubicin as compared with a value of 0.03% of the injected dose achieved with free drug. It is proposed that accumulation of liposomes into the peritoneal cavity of normal and tumor-bearing mice may serve as a useful model for characterizing factors mediating the transfer of liposomes from the vascular compartment to extravascular sites.

Animals↗