Antitumor reactivity induced by liposomal MTP-PE in a liver metastasis model of colon cancer in the rat (original) (raw)
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Cancer research, 1986
We investigated the in vitro activation of rat liver macrophages to a tumoricidal state with free and liposome-encapsulated immunomodulators. The cytolytic activity of liver macrophages was determined by a radioactivity release assay using murine B16 melanoma cells, labeled with [methyl-3H]thymidine. Exposure of the liver macrophages to concentrations of 50 micrograms of free, nonencapsulated, muramyl dipeptide (MDP) per ml resulted in maximal levels of tumor cell lysis of approximately 20%. Encapsulation of the MDP within liposomes (multilamellar vesicles, 0.3 to 0.5 micron in diameter, consisting of egg phosphatidylcholine, cholesterol, and dicetylphosphate, 4:5:1) not only caused a 500-fold reduction in the amount of MDP required to obtain the same levels of cytolysis but also increased the maximally obtainable level of cytolysis more than 2-fold. A synergistic effect of lipopolysaccharide and free or encapsulated MDP on cytolytic activity was observed when the macrophages were e...
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1996
Liposomes can very efficiently deliver imlnunomodulators to macrophages so as to induce tumor cytotoxicity, Liposomes most widely used I'~,r that purpose contain negatively charged lipidx, in particular phosphatidylscrine I, ps), to enhance liposome uptake by the macrophages. We investigated the eft~:ct ,,~f three negatively charged liposomal lipids Oil the in vitro activation of liver macrophages to tumor cytotoxieity by muran'tyl dipeptide (MDP) and lipopolysaccharide (LPS'L Both MDP-and LPS-induced tumor cytotoxicity towards n]urinc colon adenncarcinoma cells w~'re slrongly inhibited by PS-containing liposomes. Under comparable conditions phosl~hatidylglycerol (DPPG)-containing or dicetyl phosphate (DCP)-containing liposome~, dis not inhibit or only marginally inhibited the induction of tumor cytotoxicity. We did not observe PS-mediated inhibition of tumor cell toxicity when the exposure of the macrophages Io PS-liposomes was limited t,~ the 4-h activation period prior to addition of the tumor target cells, su~'~csting that the inhibitory effect is accomplished t~t the level of the later stages of the activation process. Previously. v,,e shorted th:n macrophages which are activated to tumor eytntoxicity during a 24-h incubation ,.,.'ith MDP become refractory to a second activation with MDP. Now we observed that simultaneous incubation with PS-containing liposomcs partially prevents Ibis refractoriness, which is also compatible with an interfering action of PS at a relatively late stage in the activation process. We conelnde thai PS, despite its, reported stimuiatory eftEct on liposome uptake by macrophages, can seriously antagonize the effectiveness of immunomodulating agents acting on macrophages. This bears relevance to the use of PS-colnaining litrosomes as a vehicle for such agents. The results are discussed in perspective of earlier reported phamlacological e fleets t~f PS and its metabolites.
We examined whether the macrophages in the liver, Kupffer cells, could be activated to a tumoricidal state in a similar way as has been described for other macrophage types. Kupffer cells were isolated by centrifugal elutriation of pronase-treated rat livers. Incubation with highly purified recombinant rat 7-interferon in combination with small amounts of lipopolysaccharide or muramyldipeptide resulted in highly cytotoxic macrophages, as measured against P815 tumor cells in a 18 h 5lCr- release assay. Incubation of Kupffer cells with the stimulators entrapped within liposomes, caused phagocytosis of the liposomes and subsequent activation to tumor cytotoxicity, provided that both rat 7-interferon and subthreshold doses of either lipopolysaccharide or muramyldipeptide were encapsulated. The minimum amount of liposomal rat 7-interferon that induced optimal activation was 0.5 I '/ml, while 6 ng/ml of liposomal lipopolysaccharide or muramyldipeptide was required. Cytotoxicity of Ku...
Role of macrophage lipids in regulating tumoricidal activity
Cellular Immunology, 1983
Peritoneal macrophages (Mb) from mice became cytotoxic after incubation with lymphokine (LK); tumoricidal activity was evident with Mg treated with LK for 4 hr, became maximal after 8-12 hr of incubation, and decreased to control levels by 24-36 hr. LK induced marked changes in M@ lipid composition: cellular content of cholesterol (CHOL) and polyunsaturated fatty acid (UFA) content of cellular lipids (especially 18:3) increased two-to threefold aher 8 hr when the cells showed maximal tumoricidal activity. Cellular lipid and fatty-acid content returned to control levels by 24 hr when the M&J had lost tumoricidal activity. These changes were not observed with equal numbers of Mg cultured in control supematants. To analyze the role of CHOL and UFA in Mb tumor cytotoxicity, casein-induced peritoneal M+ were enriched in CHOL or linolenic acid (18:3) and then tested for their ability to kill 1023 tumor cells. The 18:3-enriched cells were markedly tumoricidal, whereas controls cultured in delipidized medium alone or enriched with saturated fatty acid (18:O) were not cytotoxic. CHOL-enriched Mb were not tumoricidal; indeed, these cells were inhibited in their killing after treatment with LK compared to M& cultured in delipidized medium with LK alone. The effects of 18:3 and CHOL enrichment of the M&I on their metabolic status, inflammatory function, and tumor cell-binding capacity were tested. The 18:3-enriched Mg were depressed in their ability to synthesize protein and in phagocytic activity compared to controls; these cells showed a transient increase in superoxide release. MI#J cultured with 18:3 for 48 hr were also cytotoxic for P8 I5 tumor cells, but did not show an enhanced capacity for P8 15 binding compared to controls. CHOL-enriched Mg were similar to control cells in their protein synthesizing and phagocytic activities; these cells also showed an early transient increase in superoxide release. CHOL-enriched M4 were not cytotoxic for P8 I5 cells, but bound the tumor cells more readily than did the 18:3-enriched M&J. The data suggest that endogenous levels of 18:3 and CHOL can regulate Mb tumor cytotoxicity, but not through regulation of Mb protein synthesis, oxidative metabolism, or augmented capacity for tumor target binding.
Journal of immunology (Baltimore, Md. : 1950), 1989
We investigated the in vitro activation of rat liver macrophages to a tumor-cytotoxic state with muramyl dipeptide (MDP), rough LPS (Re-LPS) and lipid A in both a free and liposome-encapsulated form. The tumor cytotoxic state of the liver macrophages was determined with a [methyl-3H]thymidine release assay using C26 colon adenocarcinoma cells as target cells. As was shown previously, the encapsulation of MDP within multi-lamellar phospholipid vesicles greatly enhanced the activating potency of the drug; by contrast, encapsulation of Re-LPS or lipid A significantly reduced the activation of macrophages as compared to the free form of these agents. At a dose of 1 ng of free Re-LPS per ml a significant induction of tumor cell lysis was observed whereas a maximal level was obtained at a concentration of approximately 10 ng/ml. By encapsulation of Re-LPS in liposomes the activating potency diminished 20- to 100-fold. The minimal concentration required to induce detectable macrophage acti...
Cancer Immunology, Immunotherapy, 2009
Tumor cell expansion relies on nutrient supply, and oxygen limitation is central in controlling neovascularization and tumor spread. Monocytes infiltrate into tumors from the circulation along defined chemotactic gradients, differentiate into tumor-associated macrophages (TAMs), and then accumulate in the hypoxic areas. Elevated TAM density in some regions or overall TAM numbers are correlated with increased tumor angiogenesis and a reduced host survival in the case of various types of tumors. To evaluate the role of TAMs in tumor growth, we here specifically eliminated TAMs by in vivo application of dichloromethylene diphosphonate (DMDP)-containing liposomes to mice bearing various types of tumors (e.g., B16 melanoma, KLN205 squamous cell carcinoma, and 3LL Lewis lung cancer), all of which grew in the dermis of syngeneic mouse skin. When DMDP-liposomes were injected into four spots to surround the tumor on day 0 or 5 after tumor injection and every third day thereafter, both the induction of TAMs and the tumor growth were suppressed in a dose-dependent and injection number-dependent manner; and unexpectedly, the tumor cells were rejected by 12 injections of three timesdiluted DMDP-liposomes. The absence of TAMs in turn induced the invasion of inflammatory cells into or around the tumors; and the major population of effector cells cytotoxic against the target tumor cells were CD11b ? monocytic macrophages, but not CCR3 ? eosinophils or Gr-1 ? neutrophils. These results indicate that both the absence of TAMs and invasion of CD11b ? monocytic macrophages resulted in the tumor rejection.
Neoplasia, 2008
Prednisolone phosphate (PLP) encapsulated in long-circulating liposomes (LCLs) (LCL-PLP) exerts antitumor activity through the inhibition of tumor angiogenesis. It is known that tumor-associated macrophages (TAMs) play a crucial role in tumor growth as they are actively involved in promoting and maintaining tumor angiogenesis. To gain more insight into the antiangiogenic mechanisms of LCL-PLP, this study aimed to investigate the role of TAM in the antitumor mode of action of LCL-PLP in B16.F10 melanoma-bearing mice. Our results show that TAMs have a pivotal function in the growth of B16.F10 melanoma through the production of pro-angiogenic/pro-inflammatory factors. One of the major inhibitory actions of LCL-PLP on tumor growth is the reduction of the TAM-mediated production of pro-angiogenic factors, whereas production of anti-angiogenic factors by these cells is hardly affected.
Endocytic and tumoricidal heterogeneity of rat liver macrophage populations
Selective cancer therapeutics, 1989
The macrophage population of the liver has been reported to be heterogeneous with respect to endocytic and lysosomal enzyme activity. Yet we demonstrate that all liver macrophages in the rat can be activated to a tumoricidal state by the i.v. injection of liposomal muramyl dipeptide (MDP). After isolation, liver macrophages were fractionated according to size into five subfractions by means of elutriation centrifugation. Tumoricidal activity of liver macrophages, activated in vivo, was determined by an in vitro radioactivity release assay using B16 melanoma and C26 adenocarcinoma cells, labeled with [methyl-3H]thymidine, as target cells. Endocytic activity of the subpopulations both in vitro and in vivo was determined using [3H]-labeled liposome preparations. Finally, the extent to which the subpopulations become cytotoxic as a result of in vitro uptake of muramyl dipeptide-(MDP)-containing liposomes was studied employing the cytotoxicity assay described above. No significant differ...
Cancer research, 1985
The ability of a member of a new class of lipophilic muramyl dipeptide (MDP) derivative, muramyl dipeptide-glyceryldipalmitate (MDP-GDP), to induce alveolar macrophage cytotoxic activity in vitro towards B16 melanoma cells when incorporated into two types of liposome was studied. MDP-GDP incorporated into conventionally prepared liposomes formulated from distearoylphosphatidylcholine and phosphatidylserine (7:3 molar ratio) was 10-fold more effective than liposomes containing MDP, and 7000-fold more effective than free MDP in inducing macrophage cytotoxic activity. MDP-GDP incorporated into freeze-dried liposomes was 50,000- to 100,000-fold more effective than free MDP in inducing such activity. Freeze-dried liposomes containing MDP-GDP were efficiently localized in the lungs of normal mice, and induced cytotoxic activity in the alveolar macrophages. Such liposomes were able to significantly reduce the pulmonary metastatic burden of mice carrying the B16 melanoma. These data provide...