Nuclear delivery of doxorubicin via folate-targeted liposomes with bypass of multidrug-resistance efflux pump.

Folic acid, attached to polyethyleneglycol-derivatized, distearoyl-phosphatidylethanolamine, was used to target in vitro liposomes to folate receptor (FR)-overexpressing tumor cells. Confocal fluorescence microscopic observations demonstrated binding and subsequent internalization of rhodamine-labeled liposomes by a high FR-expressing, murine lung carcinoma line (M109-HiFR cells), with inhibition by free folic acid. Additional experiments tracking doxorubicin (DOX) fluorescence with DOX-loaded, folate-targeted liposomes (FTLs) indicate that liposomal DOX is rapidly internalized, released in the cytoplasmic compartment, and, shortly thereafter, detected in the nucleus, the entire process lasting 1-2 h. FR-mediated cell uptake of targeted liposomal DOX into a multidrug-resistant subline of M109-HiFR cells (M109R-HiFR) was unaffected by P-glycoprotein-mediated drug efflux, in sharp contrast to uptake of free DOX, based on verapamil-blockade experiments with quantitation of cell-associated DOX and flow cytometry analysis. Delivery of DOX by FTLs to M109R-HiFR cells increased continuously with time of exposure, reaching higher drug concentrations in whole cells and nuclei compared with exposure to free DOX. The in vitro cytotoxic activity obtained with DOX-loaded FTLs was 10-fold greater than that of the nontargeted liposome formulation, but was not improved over that of free DOX despite the higher cellular drug levels obtained with the targeted liposomes in M109R-HiFR cells. However, if M109R-HiFR cells were exposed to drugs in vitro and tested in an in vivo adoptive assay for tumor growth in syngeneic mice along a 5-week time span, FTL DOX was significantly more tumor inhibitory than free DOX. It is suggested that the biological activity of liposomal DOX released inside the cellular compartment is reduced in vitro due to the aggregated state of DOX, resulting from the liposome drug-loading process, and requires a long period of time and/or an in vivo environment for full expression.

Targeting folate receptor with folate linked to extremities of poly(ethylene glycol)-grafted liposomes: in vitro studies.

Conjugates of three components, folic acid-poly(ethylene glycol)-distearoylphosphatidylethanolamine (FA-PEG-DSPE), derived from PEG with molecular masses of 2000 and 3350 Da were synthesized by a carbodiimide-mediated coupling of FA to H2N-PEG-DSPE. The conjugates were characterized by 1H NMR, MALDI-TOF, and HPLC analysis of enzymatic cleavage with carboxypeptidase G. As a prototype of a folate receptor (FR)-targeted system, the conjugates were formulated at 0.5 mol % phospholipid in hydrogenated phosphatidylcholine/cholesterol liposomes with or without additional methoxyPEG2000-DSPE. In vitro binding studies were performed with sublines of M109 (murine lung carcinoma) and KB (human epidermal carcinoma) cells each containing high and low densities of FR. FA-PEG-DSPE significantly enhanced liposome binding to tumor cells. The best binding was observed when FA-PEG liposomes contained no additional mPEG-lipid. In fact, our experiments showed that the presence of mPEG on liposomal surfaces significantly inhibited FA-PEG-liposome binding to FR. Increasing the molecular mass of the PEG tether from 2000 to 3350 Da improved the FR binding, particularly in the case of mPEG-coated liposomes. The FA-PEG liposomes bound to M109-HiFR cells very avidly as demonstrated by the inability of free FA (used in a 700-fold excess either at the beginning or at the end of the incubation) to prevent the cell binding. This is in contrast to the 5-10-fold lower cell binding activity of mPEG-FA compared to that of free FA, and likely to be related to the multivalent nature of the liposome-bound FA. Only 22% of FA-PEG3350 and 32% of FA-PEG3350/mPEG cell-associated liposomes could be removed by exposure to pH 3, conditions that dissociate FA-FR, suggesting that more than two-thirds of the bound liposomes were internalized during incubation for 24 h at 37 degrees C. FA-targeted liposomes also show enhanced nonspecific binding to extracellular tissue culture components, a phenomenon especially relevant in short incubation time experiments.

Comparative study of the antitumor activity of free doxorubicin and polyethylene glycol-coated liposomal doxorubicin in a mouse lymphoma model.

Here, we investigate various factors affecting the therapeutic efficacy of free doxorubicin (Free-Dox) and polyethylene glycol (PEG)-coated (PEGylated) liposomal doxorubicin (referred to as Doxil) in the ascitic J6456 lymphoma model of BALB/c mice. Free drug and liposomal drug were affected differently by the tumor burden and route of treatment administration. A delay in start of treatment from day 1 to day 5 almost completely abolished the efficacy of Free-Dox, whereas that of Doxil was only minimally reduced. Contrasting effects on the therapeutic efficacy of Free-Dox and Doxil were obtained by changing treatment administration from the i.v. to the i.p. route; the efficacy of free drug was relatively enhanced, whereas that of liposomal drug was relatively diminished. Overall, Doxil given by the systemic i.v. route was the most effective treatment in prolonging median survival and obtaining cures. Variations in the dose-schedule treatment regime confirm the superior therapeutic profile and reduced dependence on tumor burden of the PEGylated liposomal formulation over free drug. In addition, these experiments indicate that, at equal dose intensity, the dose level is more important than the frequency of administration for therapeutic activity.

Targeting of stealth liposomes to erbB-2 (Her/2) receptor: in vitro and in vivo studies.

Long-circulating (stealth) liposomes coated with polyethylene glycol (PEG), which show reduced uptake by the reticuloendothelial system (RES) and enhanced accumulation in tumours, were used for conjugation to monoclonal antibodies (MAbs) as a drug-targeting device. A MAb (N-12A5) directed against erbB-2 oncoprotein, a functional surface antigen, was used. Amplification and overexpression of the erbB-2 gene product, being unique to malignancy, confer onto this antibody-mediated therapy high tumour specificity. In vitro binding of [3H]cholesteryl ether ([3H]Chol ether) labelled anti-erbB-2 conjugated liposomes to N-87 cells (erbB-2-positive human gastric carcinoma) was compared with the binding of non-targeted liposomes and indicated a 16-fold increase in binding for the targeted liposomes. No difference in binding to OV1063 cells (erbB-2-negative human ovary carcinoma) was observed. These results indicate highly selective binding of antibody-targeted liposomes to erbB-2-overexpressing cells. Despite increased cell binding, doxorubicin (DOX) loaded in anti-erbB-2-conjugated liposomes did not cause increased in vitro cytotoxicity against N-87 cells, suggesting lack of liposome internalisation. In vivo, the critical factor needed to decrease the non-specific RES uptake and prolong the circulation time of antibody-conjugated liposomes is a low protein to phospholipid ratio ( < 60 micrograms mumol-1). Using these optimised liposome preparations loaded with DOX and by monitoring the drug levels and the [3H]Chol ether label, biodistribution studies in nude mice bearing subcutaneous implants of N-87 tumours were carried out. No significant differences in liver and spleen uptake between antibody-conjugated and plain liposomes were observed. Nevertheless, there was no enhancement of tumour liposome levels over plain liposomes. Both liposome preparations considerably enhanced DOX concentration in the tumour compared with free drug administration. Therapeutic experiments with N-87 tumour-bearing nude mice indicated that anti-tumour activity of targeted and non-targeted liposomes was similar, although both preparations had an increased therapeutic efficacy compared with the free drug. These studies suggest that efficacy is dependent on drug delivery to the tumour and that the rate-limiting factor of liposome accumulation in tumours is the liposome extravasation process, irrespective of liposome affinity or targeting to tumour cells.

Liposome longevity and stability in circulation: effects on the in vivo delivery to tumors and therapeutic efficacy of encapsulated anthracyclines.

The effect of liposome composition on drug delivery to tumors and therapeutic efficacy of liposome-encapsulated anthracyclines was investigated in two murine tumor models: an ascitic tumor (J6456 lymphoma) and a solid carcinoma (M-109). Longevity in circulation correlated positively with high drug levels in the extracellular (ascitic) tumor fluid and with delayed peak tumor levels. Using polyethylene-glycol(PEG)-coated liposomes, liposome stability (drug retention) was found to be an important determinant of therapeutic efficacy, as indicated by the superior survival conferred by high Tm phosphatidylcholines (hydrogenated, dipalmitoyl) over low Tm (egg phosphatidyl-choline). Replacing PEG with another negatively-charged surface headgroup (phosphatidyl-glycerol, phosphatidyl-inositol) resulted in relatively shorter longevity in circulation of the liposome-associated drug, but no detectable differences in anti-tumor efficacy. When neither the surface charged headgroup nor the PEG coating are present, the resulting drug formulation was significantly less effective than PEG and phosphatidylinositol-based formulations in both tumor models. In conclusion, longevity in circulation, as obtained with PEG coating, tends to improve the therapeutic efficacy of liposome-encapsulated anthracyclines. The current therapeutic models were however unable to detect differences between the therapeutic activity of PEG and other liposome formulations with relatively small differences in circulation longevity.

In vitro cytotoxicity of liposome-encapsulated doxorubicin: dependence on liposome composition and drug release.

We have investigated the in vitro cytotoxicity of free doxorubicin (DOX) and liposome-entrapped DOX (L-DOX) against a human ovarian carcinoma cell line (OV-1063) using a colorimetric assay. DOX was encapsulated in the inner water phase of liposomes by an ammonium sulfate-generated proton gradient. Liposomes varied in phospholipid composition but were of a similar size. It was found that the cytotoxic activity of L-DOX is substantially decreased when liposomes containing phospholipids of high phase-transition temperature (Tm) are used. The type of negatively charged headgroup did not have any significant influence on the cytotoxicity observed. Experiments using resin beads that bind free and protein-bound DOX, but do not interact with L-DOX, indicated that the cytotoxic effect is mediated by the release of drug from the liposomes into the extracellular medium; no evidence was found for direct cellular uptake of liposome-encapsulated drug. The use of the ionophore nigericin to induce the release of DOX from high-Tm liposomes increased cytotoxicity to a level comparable to free DOX, suggesting that 'remote release' techniques may substantially improve the efficiency of liposome-mediated drug delivery and allow for the full exploitation of the favorable pharmacokinetic properties of specific high-Tm formulations.

Maintenance on extracellular matrix and expression of heparanase activity by human ovarian carcinoma cells from biopsy specimens.

A routine procedure has been developed for the isolation and maintenance in culture of human ovarian carcinoma cells derived from biopsy specimens. Cell attachment, plating efficiency and initial outgrowth were greatly improved by seeding the cells on a basement-membrane-like extracellular matrix (ECM) deposited by cultured corneal endothelial cells. These effects were most significant in serum-free conditions which markedly reduced the rate of cell attachment and growth on regular tissue culture plastic. In 60-80% of the cases and regardless of the patient's age, cells cultured on ECM in the absence of serum divided actively and formed a tightly packed epithelial cell monolayer. Fibroblast overgrowth and cell detachment often occurred on ECM in the presence of serum. Incubation of the human ovarian carcinoma cells with sulfate-labelled ECM, resulted in the release of heparan sulfate degradation fragments, 4- to 7-fold smaller than intact heparan sulfate side chains. This degradation was brought about by endoglycosidase (heparanase) activity expressed to a higher extent by cells that were first maintained in primary cultures as compared with cell aggregates taken directly from the biopsy specimen. In most cases, cells derived from metastatic tumors expressed a higher heparanase activity than cells from the primary ovarian tumor. This result corroborates previous studies, performed with cell lines, on the possible involvement of heparanase in tumor cell invasion and metastasis.

Oncogenous osteomalacia: a case study.

A case of oncogenous osteomalacia due to a fibrosarcoma of the maxilla is reported, with a 19 year course before treatment. Metabolic studies of calcium and phosphorus were performed 3 and 19 years after the first symptomology. There was a negative balance for both phosphorus and calcium with low serum levels of 1,25-dihydroxyvitamin D which were corrected by resection of the tumor. Portions of the tumor were cultured and the supernatant did not affect phosphorus transport by a proximal tubule kidney cell line. Other portions were injected into athymic nude mice where they resulted in hypophosphatemia and phosphaturia, thus confirming the endocrine nature of the oncogenous osteomalacia factor.

Involvement of heparanase in tumor metastasis and angiogenesis.

The capacity of various blood-borne cells, whether normal or malignant, to extravasate was found to correlate with heparanase-mediated degradation of HS in subendothelial ECM. This degradation was stimulated by proteases or plasminogen and inhibited by native heparin and by various modified nonanticoagulant species of heparin. These heparins also induced a marked reduction in tumor cell metastasis and autoimmune diseases in experimental animals. Heparanase-mediated degradation of HS in ECM also released EC growth factors that are stored in ECM, most likely by high affinity binding to HS. Such growth factors were extracted from subendothelial ECM synthesized in vitro and from basement membranes of the cornea in vivo, and are structurally and functionally related to bFGF;bFGF binds to ECM and is readily released by incubation with either HS, heparin or low MW heparin fragments as well as by various normal and malignant cells and by heparanase-mediated degradation of ECM HS. In contrast, there was little or no release of growth-promoting activity upon incubation of ECM with hyaluronic acid, chondroitin sulfate or chondroitinase ABC. A model is proposed suggesting that regulation of capillary growth and neovascular response may result from displacement of an angiogenic protein (bFGF) from its storage sites within basement membranes.

Prevention of human bladder tumor cell implantation in an in vitro assay.

The high recurrence rate of bladder tumors can be reduced by prevention of tumor cell reimplantation on denuded urothelium following transurethral resection. This can be achieved by intravesical chemotherapy immediately after the resection of the bladder tumors. We have demonstrated, in an in-vitro system, the process of human bladder tumor cell implantation on a naturally produced extracellular matrix (ECM) which simulates the exposed bladder basement membrane and submucosa. Using this model we examined the efficacy of various cytotoxic agents in preventing tumor cell adhesion to the ECM. Human bladder tumor cell implantation was prevented following exposure of the cells to distilled water, epodyl or mitomycin C, and significantly reduced following one hour incubation in cisplatinum and doxorubicin. The maximal effect for each of these cytotoxic agents was reached within 30 to 60 minutes of treatment. Mitomycin C reached maximal effect within 10 minutes. In contrast, thiotepa did not cause a significant reduction in cell adherence to ECM as compared to untreated control cells.

Growth of human mammary carcinoma cells from biopsy specimens in serum-free medium on extracellular matrix.

A method developed for the initiation and maintenance in primary culture of human normal mammary epithelial cells was adopted for the growth of epithelial cells from 45 primary human breast tumors. The cells were grown on a naturally produced extracellular matrix (ECM) or on regular tissue culture plastic in a serum-free medium containing growth supplements and high-density lipoprotein (HDL). Successful enzymatic dissociation of the tumor biopsy into organoid structures and cell aggregates was crucial for subsequent cell attachment and growth. Fifty-five percent of the biopsy specimens were successfully dissociated and 87% of these gave rise to actively dividing epithelial cells forming monolayer cultures. In contrast, only 21% of the biopsies which were not optimally dissociated yielded growing cultures. Variations in sample size, duration of enzymatic digestion, and tumor composition affected the outcome of tumor dissociation. Omission of serum from the culture medium prevented the growth of fibroblasts, while plating on ECM greatly improved and in some cases was essential for cell attachment and subsequent outgrowth. The epithelial nature of the cells was verified by their cuboidal and closely apposed morphology and positive staining with antikeratin antibodies. The growth and subculture requirements and the expression of the B38.1 tumor marker were compared in human mammary epithelial cells derived from solid tumors, pleural effusion and normal breast tissue.

The mechanism of human bladder tumor implantation in an in vitro model.

Implantation of tumor cells in the bladder following transurethral resection of superficial bladder tumors is believed to be one factor in the etiology of bladder tumor recurrences. Using an in vitro model system we have studied the initial interaction between bladder carcinoma cells and a naturally produced basement membrane-like substrate. Minced explants of superficial low grade human bladder tumors from 10 patients were plated into culture dishes coated with a naturally produced extracellular matrix (ECM). This ECM has been shown to resemble the human urothelial basement membrane and submucosa in its macromolecular composition and ultrastructural appearance. It was found that a firm attachment of the human bladder tumor cells occurred within one hour, reached a maximal value within 24 hours and was followed by flattening and proliferation of the plated cells. These results indicate that prevention of tumor implantation should be initiated in the first hour after transurethral resection of the bladder tumors. This assay can be used for the investigation of various treatments to prevent tumor implantation.

Immunofluorescent characterization of fibronectin, laminin, and keratin in normal and neoplastic human mammary epithelial cells in culture and in breast tissue sections.

Employing indirect immunofluorescent staining, primary and secondary serum-free cultures and frozen sections of human mammary tissue, normal and neoplastic, were examined for the presence and distribution of fibronectin (FN) and keratin, and frozen sections also for laminin (LM). The epithelial cell purity of the cultures was confirmed by the observation that all cells stained with anti-keratin antibody. In confluent cultures, FN was absent at the apical cell surface, and was seen as a fibrillar matrix exclusively beneath the epithelial monolayer, at the cell-substratum interface. No differences were noted between normal and neoplastic cells in vitro. In sections of normal breast tissue, FN was localized in the basement membrane zone (BMZ) and in the connective tissue stroma. A distinguishing feature of the neoplastic tissue was the considerably more intensive anti-FN immunofluorescence of the stroma. In normal tissue sections, LM was present exclusively in the BMZ, where it formed a continuous, well-delineated, smooth line; this line was found to be distorted, interrupted, and sometimes entirely absent in the neoplastic tissue. The cytoplasm of all cultured cells, neoplastic as well as normal, exhibited a dense network of keratin filaments that was especially prominent around the nucleus. In the sections, keratin was ubiquitously present in the epithelial cells, predominantly along the interior border of the surface membrane; in the neoplastic tissue, this pattern was markedly disorganized, and some of the cells failed to express the substance.

A new human ovarian carcinoma cell line: establishment and analysis of tumor-associated markers.

In the present study we describe the establishment and characteristics of a new human tumor cell line (OV-1063) positive for carcinoembryonic antigen (CEA) originating from ovarian metastatic tumor cells. Analysis of the cultured cells during their in vitro adaptation period revealed while the primary culture exhibited a low proportion of CEA-positive cells, this proportion increased with culture passages and eventually more than 90% of the cells in the established line were CEA-positive. Thus, during the period of adaptation to in vitro growth, a selection for CEA-positive cells took place but the amount of CEA secreted per each positive cell seemed to be constant. Several tumor-associated characteristics were found positive on the established OV-1063 cell line. The in vitro growing cell line exhibited an abnormal chromosome pattern with a near-trisomy karyotype for some chromosomes, colony formation in soft agar as well as positive staining with a monoclonal antibody B38.1. Culture supernatants of the OV-1063 cells contained significant amounts of CEA as well as CA-125 antigen which is an ovarian-carcinoma-associated antigen.

High-density lipoprotein and extracellular matrix promotes growth and plating efficiency of normal human mammary epithelial cells in serum-free medium.

A routine procedure has been developed for the establishment in culture of normal primary and secondary human mammary epithelial cells. The high (80-100%) rate of success resulted from the combined use of a serum-free medium supplemented with high-density lipoprotein (HDL) and of cell plating on a naturally produced extracellular matrix (ECM). Plating on ECM greatly improved cell attachment, plating efficiency and initial outgrowth. HDL supported epithelial cell proliferation and prevented their detachment and degeneration while the omission of serum prevented the growth of stromal fibroblasts. Under these conditions we obtained from each specimen, and regardless of the patient's age, pure and actively dividing epithelial cell cultures forming a tightly packed and non-overlapping cell monolayer covering the entire area of the culture dish. These epithelial cultures could be easily dissociated and subcultured at a split ratio of 1:10. The described procedure will promote studies on the role of hormones and growth factors in the proliferation and differentiation of human mammary epithelial cells and on the susceptibility of human breast epithelial cells to various transforming agents and anti-cancer treatments.

The use of carcinoembryonic antigen for identification of human tumor cells in malignant effusions.

A specific anti-carcinoembryonic antigen (CEA) antiserum was used to identify CEA-positive tumor cells in peritoneal and pleural effusions obtained from patients with various malignant neoplasia. In 7 out of 10 fluids in which tumor cells were detected by cytological examinations, cytoplasmic CEA-positive cells were also detected by an indirect immunofluorescence test. In addition, out of 11 fluid samples cytologically negative for tumor cells, CEA-positive cells were found in 8 cases. When both staining for cytoplasmic CEA and soluble fluid CEA levels were considered in combination, 81% of the samples were found to be positive by either one or both of these markers, whereas only 54% were positive by using cytological criteria. The data suggest that CEA marker may be used to identify tumor cells and to assess malignancy in pleural and peritoneal effusions in patients with certain types of cancer. The CEA marker was also used for identifying tumor cells grown in tissue cultures and for separating viable CEA-positive and CEA-negative cells from a mixed cell population using the fluorescence-activated cell sorter.

No activation of new initiation points for deoxyribonucleic acid replication in BALB/c 3T3 cells transformed by Kirsten sarcoma virus.

BALB/c 3T3 cells were transformed by Kirsten sarcoma virus, and five clones were isolated in soft agar. Average replicon sizes of the transformed cell lines were estimated by the method of fiber-autoradiography (J. A. Huberman and A. D. Riggs, J. Mol. Biol.32:327-341, 1968) and found to be the same size as the nontransformed 3T3 cells, analyzed in parallel. The results indicate that, unlike simian virus 40 and Epstein-Barr virus, Kirsten sarcoma virus does not activate new initiation points for cellular deoxyribonucleic acid replication in murine sarcoma virus-transformed BALB/c 3T3 cells.

Growth cycle of predacious Bdellovibrios in a host-free extract system and some properties of the host extract.

Host-free growth and reproduction of a host-dependent strain of Bdellovibrio bacteriovorus incubated with an extract from host cells were studied. The morphological changes occurring in the cells were correlated with deoxyribonucleic acid (DNA) synthesis as measured by labeled nucleotide or orthophosphate incorporation. The host-free developmental cycle of Bdellovibrio is similar to that of the two-membered system; the early loss of flagella, the elongation into filaments, and multiple fission into flagellated progeny are typical for both host-free and intraperiplasmic development of bdellovibrios. Filament length and time of division appear to depend on the concentration of the host extract. Host extract was found to be heat stable and DNase stable, and Pronase sensitive and RNase sensitive. Addition of ribonucleic acid to the extract medium at various times during the Bdellovibrio growth cycle demonstrated that host extract is required continuously during the cycle for growth. The observations reported give a unified picture of Bdellovibrio development and allow for the suggestion that wild-type bdellovibrios depend upon the presence of some host factor for induction of DNA synthesis, whereas depletion of host factor triggers division. The ecological implications of such host dependence are discussed.