Macrophage-mediated destruction of malignant tumor cells and new strategies for the therapy of metastatic disease

Recent advances in ultra-small fluorescent Au nanoclusters toward oncological research

Au nanoclusters possess a series of excellent properties owing to their size being comparable to the Fermi wavelength of electrons. For example, they show excellent biocompatibility, optical stability, large Stokes shift, intense size-dependent emission and monodispersion, and thus could effectively compensate for the shortcomings of traditional organic fluorescent dyes and fluorescent quantum. In this review, we detail the latest developments of Au nanoclusters employed in the field of biomedicine, especially in oncology research, by summarizing the application of imaging, sensing and drug delivery based on their excellent luminescent properties and unique structural features. We also discuss the significant work relating to Au NCs that now is being devoted in other therapeutic strategies, such as radiotherapy, photothermal therapy and photodynamic therapy, for example. It is anticipated that this review will provide new insights and theoretical guidance to allow the advantages of Au nanoclusters to be realized in oncotherapy.

A replication-incompetent CD154/40L recombinant vaccinia virus induces direct and macrophage-mediated antitumor effects in vitro and in vivo

CD40 triggering may result in antitumor effects of potentially high clinical relevance. To gain insights important for patient selection and to identify adequate targeting techniques, we investigated CD40 expression in human cancer tissues and generated a replication-incompetent recombinant vaccinia virus expressing CD40 ligand (rVV40L). Its effects were explored in vitro and in vivo upon direct CD40 targeting on malignant cells or macrophage activation. CD40 expression was analyzed by immunohistochemistry in tumor and stromal cells in a multi-tumor array including 836 specimens from 27 different tumor types. Established tumor cell lines were used to explore the capacity of rVV40L to induce malignant cell apoptosis and modulate functional profiles of polarized macrophages. CD40 expression was detectable in significantly higher numbers of stromal as compared to malignant cells in lung and breast cancers. CD40 ligation following rVV40L infection induced apoptosis in CD40(+) cancer cells, but only in the presence of intact specific signal transduction chain. Importantly, rVV40L infection promoted the induction of TNF-α-dependent antitumor activity of M1-like macrophages directed against CD40(-) targets. CD40-activated M1-like macrophages also displayed enhanced ability to CXCL10-dependently recruit CD8+ T cells and to efficiently present cancer cell intracellular antigens through cross-priming. Moreover, rVV-driven CD40L expression partially “re-educated” M2-like macrophages, as suggested by detectable CXCL10 and IL-12 production. Most importantly, we observed that intra-tumoral injection of rVV40L-infected human macrophages inhibits progression of human CD40(-) tumors in vivo. First evidences of anticancer activity of rVV40L strongly encourage further evaluations.

From the Hellstrom paradox toward cancer cure

Several decades ago we published some of the first papers showing that both murine and human cancers are recognized in vitro as immunologically foreign and that this is the case also in the presence of a growing tumor. The latter situation, sometimes referred to as the Hellstrom paradox, implies that the tumor is protected in vivo by a highly immunosuppressive environment. After many disappointments, the discovery that tumor-related immunosuppression can be counteracted by administrating monoclonal antibodies (mAbs) to checkpoint inhibitors such as CTLA-4, PD-1, and PD-L1 is now revolutionizing cancer therapy. Over the past several years we have applied mouse models in attempts to further improve the ability of such mAbs to cause long-term complete tumor rejection. This review is focused on that work and emphasizes that successful immunotherapy is associated with a shift from a tumor-promoting Th2 inflammation to a tumor-inhibiting Th1 response.

Dissemination from a Solid Tumor: Examining the Multiple Parallel Pathways

Metastasis can be generalized as a linear sequence of events whereby halting one or more steps in the cascade may reduce tumor cell dissemination and ultimately improve patient outcomes. However, metastasis is a complex process with multiple parallel mechanisms of dissemination. Clinical strategies focus on removing the primary tumor and/or treating distant metastases through chemo- or immunotherapies. Successful strategies for blocking metastasis will need to address the parallel mechanisms of dissemination and identify common bottlenecks. Here, we review the current understanding of common dissemination pathways for tumors. Understanding the complexities of metastasis will guide the design of new therapies that halt dissemination.

Macrophage-based cell therapies: The long and winding road

In the quest for better medicines, attention is increasingly turning to cell-based therapies. The rationale is that infused cells can provide a targeted therapy to precisely correct a complex disease phenotype. Between 1987 and 2010, autologous macrophages (MΦs) were used in clinical trials to treat a variety of human tumors; this approach provided a modest therapeutic benefit in some patients but no lasting remissions. These trials were initiated prior to an understanding of: the complexity of MΦ phenotypes, their ability to alter their phenotype in response to various cytokines and/or the environment, and the extent of survival of the re-infused MΦs. It is now known that while inflammatory MΦs can kill tumor cells, the tumor environment is able to reprogram MΦs into a tumorigenic phenotype; inducing blood vessel formation and contributing to a cancer cell growth-promoting milieu. We review how new information enables the development of large numbers of ex vivo generated MΦs, and how conditioning and gene engineering strategies are used to restrict the MΦ to an appropriate phenotype or to enable production of therapeutic proteins. We survey applications in which the MΦ is loaded with nanomedicines, such as liposomes ex vivo, so when the drug-loaded MΦs are infused into an animal, the drug is released at the disease site. Finally, we also review the current status of MΦ biodistribution and survival after transplantation into an animal. The combination of these recent advances opens the way for improved MΦ cell therapies.

Review of mifamurtide in the treatment of patients with osteosarcoma

Osteosarcoma is the most common primary malignant tumor of bone. The disease, however, is very rare with less than 2,000 expected patients at all age groups per year within the European Union and the United States of America. With multimodal therapy, which combines multiagent chemotherapy and complete resection of all macroscopically detectable tumors, about 60%–70% of patients with localized osteosarcoma can be cured. The prognosis, however, is still poor for patients with synchronous or metachronous metastatic or nonresectable primary disease, with reported 5-year event-free survival (EFS) rates of less than 30%. Overall, the EFS rate has been rather stable since the introduction of combination chemotherapy including doxorubicin, cisplatin, high-dose methotrexate with leukovorin rescue, and/or ifosfamide. Mifamurtide, a modulator of innate immunity, which activates macrophages and monocytes, which in turn release chemicals with potential tumoricidal effects, may help to control microscopic metastatic disease and has been safely given together with standard adjuvant chemotherapy to patients with high-grade osteosarcoma. Results of the recently published intergroup study 0133 trial from the Children’s Cancer and Pediatric Oncology Groups suggest that mifamurtide is a medicine that deserves further investigation in this orphan disease.

Tumor cells expressing anti-CD137 scFv induce a tumor-destructive environment

For immunotherapy to become more effective, there is a need to maximize the antitumor response at the tumor site as well as to eliminate tumor cell variants that lack a given tumor antigen or the ability to present it. We have previously shown that wild-type (WT) cells from the K1735 melanoma (K1735-WT) are rejected following vaccination with cells (K1735-1D8) transfected to express scFv from the anti-CD137 monoclonal antibody 1D8, and that CD4(+) T cells and natural killer (NK) cells are needed for this rejection. We now show that tumors harvested 4 to 10 days after mice had been transplanted with K1735-1D8 cells or a mixture of K1735-1D8 and K1735-WT cells contained more NK cells and that they had an increased percentage of CD4(+) T lymphocytes producing IFNgamma or tumor necrosis factor-alpha. We further show that the percentage of NK cells was higher in B16-1D8 melanomas expressing anti-CD137 scFv than in the WT tumors and that the percentage of FoxP3(+) cells was lower. Admixture of 10% K1735-1D8 cells prevented the progressive growth of transplanted K1735-WT cells in syngeneic mice and also of cells from the antigenically different sarcoma Ag104. Inhibition of WT tumor cells by tumor cells transfected to express anti-CD137 scFv was shown also with the TC1 carcinoma and B16 melanoma. Furthermore, injection of an adenovirus vector, Ad-1D8, which encodes anti-CD137 scFv into established B16 melanomas, significantly prolonged the survival of tumor-bearing mice and could induce regression. Our data suggest that targeting of anti-CD137 scFv to tumors should be explored for therapy for some human cancers.

IFN-γ- and Cell-to-Cell Contact-Dependent Cytotoxicity of Allograft-Induced Macrophages Against Syngeneic Tumor Cells and Cell Lines: An Application of Allografting to Cancer Treatment

In allogeneic tumor or skin transplantation, the rejection process that destroys the allogeneic cells leaves syngeneic cells intact by discrimination between self and nonself. Here, we examined whether the cells infiltrating into the allografts could be cytotoxic against syngeneic immortal cells in vitro and in vivo. The leukocytes (i.e., macrophages (Mφ; 55–65% of bulk infiltrates), granulocytes (20–25%), and lymphocytes (15–20%)) infiltrating into allografts, but not into autografts, in C57BL/6 mice were cytotoxic against syngeneic tumor cells and cell lines, whereas the cytotoxic activity was hardly induced in allografted, IFN-γ−/− C57BL/6 mice. Among the leukocytes, Mφ were the major population of cytotoxic cells; and the cytotoxic activity appeared to be cell-to-cell contact dependent. When syngeneic tumor cells were s.c. injected into normal C57BL/6 mice simultaneously with the Mφ-rich population or allogeneic, but not syngeneic, fibroblastic cells, tumor growth was suppressed in a cell number-dependent manner, and tumor cells were rejected either with a Mφ:tumor ratio of about 30 or with an allograft:tumor ratio of ∼200. In the case of IFN-γ−/− C57BL/6 mice, however, the s.c. injection of the allograft simultaneously with tumor cells had no effect on the tumor growth. These results suggest that allograft or allograft-induced Mφ may be applicable for use in cancer treatment and that IFN-γ induction by the allograft may be crucial for the treatment.

Liposomal muramyl tripeptide (CGP 19835A lipid) therapy for resectable melanoma in patients who were at high risk for relapse: an update

Liposome-encapsulated muramyl tripeptide-phosphatidyl ethanolamine (L-MTP-PE) was used in a pilot study for resectable melanoma patients who were at high risk for relapse. We entered 18 evaluable patients. The patient group included: (a) patients with stage III disease and clinically measurable regional metastases at presentation as confirmed by needle biopsy and (b) patients with stage IV disease presenting with measurable and resectable distant metastases confirmed by needle biopsy and limited to lungs, lymph nodes and subcutaneous tissues. L-MTP-PE was given for 4 weeks prior to surgical resection and for an additional 20 weeks postoperatively. Disease-free intervals were then determined based on the date of surgery. A preliminary report published in 1993 indicated an average disease-free interval of 18 months (range 8-33 months). This article presents an updated report on the long-term, disease-free survival status of these patients and shows that of the 18 evaluable patients, 4 remain free of disease for more than 5 years after surgical resection and therapy. The period of survival for these patients ranged from 69 months to more than 91 months (average 80.5 months). Although this was only a pilot study, we believe that the duration of survival indicates that L-MTP-PE may produce significant biologic activity in patients with melanoma, resulting in long-term benefits in terms of tumor eradication.

Osteosarcoma

Over the last several decades, significant advances have been made in our ability to understand and treat osteosarcoma. In this article we describe the diagnosis, evaluation, and treatment of patients with this disease. The surgical issues are discussed. We review the major clinical trials that have led to our current level of understanding. The current studies for the treatment of osteosarcoma are described.

Canine osteosarcoma: amputation and chemoimmunotherapy

Canine osteosarcoma is a highly metastatic cancer commonly seen in large breed dogs. At the time of diagnosis, approximately 90% to 95% of the dogs have established micrometastases. Dogs undergoing amputation alone have a median survival time of 3 to 4 months. Amputation followed by cisplatin chemotherapy increases median survival times to 9 to 11 months. When dogs are treated with amputation and cisplatin, followed by immunotherapy (with liposome-encapsulated muramyl tripeptide phosphatidylethanolamine), median survival times increase to 14.4 months, the longest reported median survival time for dogs with osteosarcoma treated by amputation and any form of adjuvant therapy.

Receptor mediated glycotargeting

Glycotargeting relies on carrier molecules possessing carbohydrates that are recognized and internalized by cell surface mammalian lectins. Numerous types of glycotargeting vehicles have been designed based on the covalent attachment of saccharides to proteins, polymers and other aglycones. These carriers have found their major applications in antiviral therapy, immunoactivation, enzyme replacement therapy and gene therapy. This review compared different types of glycotargeting agents and the lectins which have been successfully targeted to treat both model and human diseases. It may be concluded that the discovery of new mammalian lectins which endocytose their ligands will lead to the rapid development of new glycotargeting agents founded on the principles of carbohydrate-protein interactions.

Liposome-encapsulated muramyl tripeptide phosphatidylethanolamine for the treatment of feline mammary adenocarcinoma--a multicenter randomized double-blind study

Forty cats with previously untreated, histologically confirmed mammary gland adenocarcinoma received a radical mastectomy of the affected mammary chain(s). All cats were stratified according to clinical stage and randomized to receive either weekly intravenous liposome-encapsulated muramyl tripeptide phosphatidylethanolamine or placebo (lipid-equivalent) for eight consecutive weeks in this double-blind study. Thirty-six of the 40 cats were available for follow-up. No significant differences in either disease-free interval or survival were found as a result of treatment. Cats with clinical stage II disease had a statistically significantly longer disease-free interval (p < 0.02), and overall survival (p < 0.005) when compared with clinical stage III cats.

Current studies of liposome muramyl tripeptide (CGP 19835A lipid) therapy for metastasis in spontaneous tumors: a progress review

Targeted delivery of macrophage activating agents is an attractive approach to treat micrometastatic disease. Liposome-encapsulated muramyl tripeptide phosphatidylethanolamine (L-MTP-PE) is a potent activator of monocytes/macrophages in humans, mice, and dogs. We have conducted clinical trials in dogs with malignant and highly metastatic spontaneous tumors. Presented are results of our trials evaluating L-MTP-PE in combination with surgery and chemotherapy in dogs with spontaneous osteosarcoma and hemangiosarcoma, particularly relevant malignancies having having many similarities to human cancer. Osteosarcoma dogs received chemotherapy following surgery (cisplatin q 28 days x 4). At completion of chemotherapy, dogs were randomized to receive L-MTP-PE or placebo. The L-MTP-PE group had a significantly longer median survival time compared to the placebo group (p < 0.021). Dogs with splenic hemangiosarcoma received combination chemotherapy following surgery (doxorubicin and cyclophosphamide q 21 days x 4). At the first chemotherapy, dogs were randomized to receive L-MTP-PE or placebo. The L-MTP-PE group had a significantly longer median survival time compared to the placebo group (p < 0.03). These studies show that L-MTP-PE is an effective agent for treatment of metastasis and can be safely administered in combination with chemotherapy.

Liposome-encapsulated muramyl tripeptide up-regulates monocyte chemotactic and activating factor gene expression in human monocytes at the transcriptional and post-transcriptional levels

Liposome-encapsulated muramyl tripeptide phosphatidylethanolamine (L-MTP-PE) is a novel immune modulator that is now under investigation against metastatic melanoma and osteosarcoma. We have already reported that L-MTP-PE induced monocyte-mediated tumoricidal activity and up-regulation of the tumor necrosis factor and interleukin-1 (IL-1) in vivo and in vitro. We now demonstrate that L-MTP-PE also induces monocyte chemotactic and activating factor (MCAF) mRNA expression at both the transcriptional and post-transcriptional levels. Monocyte chemotactic activity was also present in the supernatants of L-MTP-PE-stimulated cells. In monocytes, the increased expression of MCAF was induced rapidly (by 2 h) but was short-lived. By 4 h, MCAF mRNA had decreased to background level. We found no change in MCAF mRNA levels in lymphocytes exposed to L-MTP-PE. We therefore conclude that L-MTP-PE selectively up-regulates MCAF expression in monocytes and that MCAF may play a role in the tumoricidal and immune-stimulating activity of L-MTP-PE.

Anti-(tumor necrosis factor) alters the response of human monocytes to liposomal muramyl tripeptide

The purpose of this study was to examine the mechanisms by which liposome-encapsulated muramyl tripeptide phosphatidylethanolamine (L-MTP-PE) stimulates monocytes to produce tumor necrosis factor (TNF) and interleukin-1 (IL-1). We have previously shown that secretion of TNF protein occurred 2-4 h following incubation of monocytes with L-MTP-PE and that this stimulation of TNF production was associated with an increase in TNF mRNA. Increased intracellular interleukin-1 alpha (IL-1 alpha) and IL-1 beta were not detected until 8 h after exposure to L-MTP-PE. To determine whether TNF played a role in the stimulation of IL-1 production by L-MTP-PE, normal human monocytes were incubated with L-MTP-PE or medium in the presence or absence of anti-TNF or anti IL-1 alpha plus anti IL-1 beta. Enhanced expression of IL-1 alpha and IL-1 beta mRNA was inhibited at 4 h but not 24 h when monocytes were incubated with L-MTP-PE plus anti-TNF compared with L-MTP-PE alone. By contrast, enhanced expression of TNF mRNA was not inhibited at any time when monocytes were incubated with L-MTP-PE and anti-IL-1 alpha plus anti-IL-1 beta. These data indicate that the up-regulation of IL-1 seen in monocytes following L-MTP-PE exposure may be due in part to the production of TNF. The up-regulation of TNF, however, appears to be independent of IL-1 production.

Cytokine production and immune cell activation in melanoma patients treated with liposomal muramyl tripeptide (CGP 19835A lipid)

We conducted a pilot study using liposome-encapsulated muramyl tripeptide phosphatidylethanolamine (L-MTP-PE) preoperatively in patients with stage III or IV resectable melanoma who were at high risk for recurrence. Patients received L-MTP-PE for 1 month before surgery and then 5 months postoperatively. Several immune parameters were monitored during preoperative therapy to search for correlations with clinical (tumor) response. The 18 patients were classified into three groups according to their responses and disease-free intervals: no evidence of disease (NED) at week 24 of therapy, relapse during therapy and progressive disease on therapy noted at the time of surgery. Six of nine patients in the NED group demonstrated increased monocyte tumoricidal activity (MTA) during week 1 of therapy. MTA increased in three of the six patients in the relapse group. MTA did not increase in the three patients who had progressive disease on therapy. Plasma neopterin levels were elevated by 72 h following the first L-MTP-PE dose in all 18 patients. Circulating levels of tumor necrosis factor were elevated in 15 of 16 patients tested, and IL-6 levels were elevated in all 18 patients. Melanoma cells from all three patients with progressive disease at the time of surgery proliferated well in vitro, whereas tumor cells from 10 of the 15 patients in the other two groups did not proliferate. There were no discernible differences among the three groups in the magnitude of IL-2-induced proliferation of tumor infiltrating lymphocytes. However, IL-2-activated TILs from the NED group exhibited cytotoxicity against autologous tumor cells in vitro. In summary, whereas L-MTP-PE stimulated several immunologic responses in all patients, the only two parameters that correlated with clinical status were MTA and the tumor proliferation assay. These two biologic assays could serve to distinguish potential responders from nonresponders early in the course of treatment.

Liposome-encapsulated muramyl tripeptide: a new biologic response modifier for the treatment of osteosarcoma

We have demonstrated that monocytes from osteosarcoma patients can be rendered tumor cytotoxic by both in vitro incubation with liposomal MTP-PE and i.v. administration of this agent. Chemotherapy did not interfere with this activation process. We have further demonstrated in phase I and phase II trials that liposomal MTP-PE can be given safely i.v. to both adults and children with minimal side effects. The findings of peripheral fibrosis with neovascularization and infiltration of the tumor with chronic inflammatory cells after liposomal MTP-PE therapy are unlike any observed following chemotherapy or surgery. Subsequent to chemotherapy, osteosarcoma lung metastases usually exhibit a zone of central necrosis, with viable tumor cells growing at the periphery of the lesion. However, in our patients following liposomal MTP-PE viable tumor cells were observed in the center of the lesion, with necrosis and fibrosis at the periphery. These changes were thus interpreted as a specific response to liposomal MTP-PE. The peripheral fibrosis observed in these tumors is reminiscent of the appearance of pulmonary tuberculosis lesions. Initially, the lesion is walled off and slow necrosis proceeds from the outside so that the lesion is replaced by fibrous tissue. Eradication of tuberculosis by chronic inflammation is a slow process. Viable bacilli can persist for months. Thus, our choice of a 3-month treatment course may have been insufficient. We have now extended our protocol to allow 6 months of therapy. Osteosarcoma appears to be an ideal disease in which to employ liposomal MTP-PE as an additional adjuvant to present chemotherapy regimens.(ABSTRACT TRUNCATED AT 250 WORDS)

Modification of reticuloendothelial function by muramyl dipeptide-encapsulated liposomes in jaundiced rats treated with biliary decompression

Rats with 2 weeks of biliary obstruction, with and without 1 week of concomitant biliary decompression relieving the jaundice, were treated with physiologic saline, free muramyl dipeptide (MDP), placebo liposomes, or liposome-encapsulated MDP. Reticuloendothelial system (RES) function was evaluated by blood clearance of intravenously injected 125I-labelled Escherichia coli. The corrected phagocytic index (alpha) after 1 week of biliary decompression returned to normal levels in animals treated with MDP liposomes, whereas RES function was impaired (P < 0.05) in all other jaundiced and biliary-decompressed groups. In the biliary-decompressed, MDP-liposome-treated group, hepatic uptake of radiolabelled bacteria was significantly higher (P < 0.05) and renal entrapment of bacteria was significantly lower (P < 0.05) than in all other jaundiced and biliary-decompressed groups. We conclude that treatment with MDP liposomes improves the otherwise impaired RES function in rats with biliary obstruction and biliary decompression.

Recent advances in antitumor vaccines

Immunization with anti-idiotypic antibodies can induce cell-mediated and humoral antitumor immunity in animal models. This immunity can sometimes cause tumor destruction. However, more needs to be learned about how best to induce the type of immune response that is responsible for tumor destruction, since the presence of anti-idiotypic antibodies has been shown occasionally to enhance, rather than to inhibit, tumor growth. There is evidence suggesting that immunization of human cancer patients with Ab2 can have therapeutic benefit, and also that patients who mount a vigorous Ab2 response following treatment with an Ab1 may do clinically better than those who do not make any Ab2. Although the generation of Ab2 related to infused antitumor Ab1 does not cause tumor rejection in the majority of patients, and although the clinical data from patients given Ab2 are scarce, the suggestion that Ab2 may cause destruction of human cancers indicates that further work in this area may become rewarding.

Preparation and characterization of polymer coated small unilamellar vesicles

Glucose oxidase was entrapped in small unilamellar vesicles composed of phosphatidylcholine, dicetyl phosphate and cholesterol. Prediction of the enzyme content of liposomes by calculations based on input concentrations of lipid and protein, dimensions of the lipids and the liposomes yielded one protein per vesicle. The entrapment efficiency was experimentally determined to be about 13%. On the other hand the entrapment efficiency for the small chromate ions was found to be significantly lower (0.1%). The liposomes were then coated with a polymer, poly(1,4-pyridinium diylethylene salt). It was possible to remove the lipoid material from underneath the polymer layer with various techniques. The effect of sonication and treatment with organic solvents (tested for this purpose) on enzyme activity were found to be very significant and Triton X-100 was chosen for this purpose. It was shown that the enzyme within the remaining net has 89% of its original activity.

Liposomal delivery of biological response modifiers to macrophages

Macrophages activated to the tumoricidal state can recognize and destroy neoplastic cells and leave normal cells unharmed. Systemic activation of macrophages can be achieved by the intravenous administration of liposomes containing various immunomodulators. Much like any particle, liposomes are cleared from the circulation by phagocytic cells. This passive but specific targeting of immunomodulators to macrophages results in their activation for in vitro and in vivo lysis of tumor cells that can be resistant to conventional therapies.

The potential importance of swainsonine in therapy for cancers and immunology

Swainsonine, an indolizidine alkaloid, was initially used in biomedical research as a tool to investigate the biosynthesis and function of asparagine-linked 'complex' type oligosaccharide moieties of glycoproteins. Recently, swainsonine has generated interest in its potential use as an anticancer agent with reports that it (i) inhibits tumor growth and metastasis, (ii) augments natural killer (NK) and macrophage-mediated tumor cell killing, and (iii) stimulates bone marrow cell proliferation. The antineoplastic activity of swainsonine can be explained at least in part by augmentation of immune effector mechanisms. The potential application of swainsonine as an anticancer agent is discussed.

Immunomodulation by propionibacteria

The ability of bacteria and bacterial products to modulate the immune response to unrelated antigens is well documented. Propionibacteria are amongst the most potent immunomodulators stimulating cell populations involved in nonspecific resistance. Generally, the activated immune system provides protection from infectious pathogens and malignancies via mechanisms of recognition and elimination. Accordingly, administration of propionibacteria could be shown to be of benefit in the treatment of neoplastic and infectious diseases. Thus, it can be recommended for further clinical investigations.

Macrophages and cancer

The uncontrolled growth of metastases resistant to conventional therapeutic modalities is a major cause of death from cancer. Data from our laboratory and others indicate that metastases arise from the nonrandom spread of specialized malignant cells that preexist within a primary neoplasm. These metastases can be clonal in their origin, and different metastases can originate from different progenitor cells. In addition, metastatic cells can exhibit an increased rate of spontaneous mutation compared with benign nonmetastatic cells. These data provide an explanation for the clinical observation that multiple metastases can exhibit different sensitivities to the same therapeutic modalities. These findings suggest that the successful therapy of disseminated metastases will have to circumvent the problems of neoplastic heterogeneity and the development of resistance. Appropriately activated macrophages can fulfill these demanding criteria. Macrophages can be activated to become tumoricidal by interaction with phospholipid vesicles (liposomes) containing immunomodulators. Tumoricidal macrophages can recognize and destroy neoplastic cells in vitro and in vivo, leaving nonneoplastic cells uninjured. Although the exact mechanism(s) by which macrophages discriminate between tumorigenic and normal cells is unknown, it is independent of tumor cell characteristics such as immunogenicity, metastatic potential, and sensitivity to cytotoxic drugs. Moreover, macrophage destruction of tumor cells apparently is not associated with the development of tumor cell resistance. Macrophages are found in association with malignant tumors in a definable pattern, suggesting that the most direct way to achieve macrophage-mediated tumor regression is in situ macrophage activation. Intravenously administered liposomes are cleared from the circulation by phagocytic cells, including macrophages, so when liposomes containing immunomodulators are endocytosed, cytotoxic macrophages are generated in situ. The administration of such liposomes in certain protocols has been shown to bring about eradication of cancer metastases. Macrophage destruction of metastases in vivo is significant, provided that the total tumor burden at the start of treatment is minimal. For this reason, we have been investigating various methods to achieve maximal cytoreduction in metastases by modalities such as chemotherapy or radiotherapy prior to macrophage-directed therapy. It is important to note that even the destruction of 99.9% of cells in a metastasis measuring 1 cm2 would leave 10(6) cells to proliferate and kill the host. The ability of tumoricidal macrophages to distinguish neoplastic from bystander nonneoplastic cells presents an attractive possibility for treatment of the few tumor cells which escape destruction by conventional treatments. Macrophage-directed therapy has been studied in several human protocols, yielding important biological information about the use of liposome-encapsulated macrophage activators in cancer patients.(ABSTRACT TRUNCATED AT 400 WORDS)

Therapy of murine liver metastases by administration of MDP encapsulated in liposomes

In a reproducible murine model of liver metastases, it was demonstrated that liposomal muramyl dipeptide (MDP) as an adjuvant therapy reduces and prevents the development of metastases. C26 colon adenocarcinoma cells were injected into the spleen (5 x 10(4) cells per mouse) of syngeneic BALB/c mice. On day 3, the spleen was removed to prevent a large tumor burden in the spleen. On day 17, 100% of the mice had developed tumor foci in the liver. Liposomal MDP treatment consisted of the i.v. or i.p. administration of 1 mumol of liposomal lipid containing 5 micrograms of MDP per mouse for ten consecutive days. When therapy was initiated two days after tumor cell inoculation, the number of metastases that had developed on day 17 was strongly reduced compared to control mice. Approximately 20% of the mice were free of liver metastases. Initiation of therapy two days prior to tumor cell inoculation enhanced the effect significantly: about 45% of the mice were free of metastases on day 17. The treatment protocol for survival studies was slightly different; liposomal MDP was administered on the first six consecutive days followed by administration twice weekly, through day 24. Control mice died between day 21 and 33 after tumor cell inoculation, whereas liposomal MDP treated mice died between day 26 and 46 with 1 out of 25 mice surviving for more than 120 days. The mortality of the liposomal MDP treated mice that were free of liver metastases was caused by a local tumor at the site of operation.(ABSTRACT TRUNCATED AT 250 WORDS)

Age-related decrease of pulmonary metastasis of rat mammary carcinoma by activated natural resistance

We found that the number of pulmonary metastatic foci of spontaneously developed rat mammary carcinoma (SST-2), when transplanted subcutaneously in spontaneously hypertensive (SH) rats, decreased with aging. In the SST-2-bearing SH rats, it was observed that T cell functions progressively declined while activities of macrophages and natural killer cells were non-specifically activated by increasing age. To examine the mechanisms of the age-related decrease of pulmonary metastasis in SH rats, we treated the SST-2-bearing rats with anti-(asialo-GM1) antibody and/or carrageenan, which are known to suppress the functions of macrophages and natural killer cells, or with poly(I).poly(C), which is a stimulator to natural killer cells. The anti-(asialo-GM1) treatment significantly increased the number of pulmonary metastatic foci in both young and old SH rats, while poly(I).poly(C) significantly decreased the lung nodules in the old SH rats. These result suggest that the decrease of pulmonary metastasis in the SH rats with aging may be closely correlated with non-specifically activated natural killer cells and macrophages, though it should be also considered that non-immunological tumor-host interactions may be involved in the differences between the young and the old SH rats.

Kupffer cells and liver metastasis. Optimization and limitation of activation of tumoricidal activity

Kupffer cells, tissue-fixed macrophages located in the sinusoids of the liver, represent the highest concentration of mononuclear phagocytes in the body. Their ability to act as scavengers of particulate material in the blood has given rise to speculation that they play a role in controlling hepatic metastases derived from blood-borne tumor cells. Circumstantial evidence for such a role has been obtained from animal studies where Kupffer cell function has been compromised or inhibited, and from anecdotal clinical observations. Current evidence suggests that Kupffer cells are capable of nonspecifically eliminating some circulating tumor cells from the circulation via phagocytosis. This surveillance mechanism would appear to be limited in capacity, and subject to a number of external factors. Recent studies have demonstrated that Kupffer cells can be activated to a tumoricidal state via the administration of biological response modifiers such as gamma interferon or muramyl peptides. The localization of liposomes within Kupffer cells after systemic administration has provided a considerable stimulus for the efficient targeting of macrophage-activating compounds to these cells. Such therapeutic intervention, while capable of inducing Kupffer cell tumoricidal activity in situ and inhibiting tumor growth, is limited with respect to the location of the tumor cells (sinusoidal versus parenchymal) and to the size of the metastatic nodule. Therapeutic intervention using liposomes containing macrophage-activating agents may only be of benefit in patients with minimal tumor load who are at risk for hepatic metastases, rather than those patients who already have clinically detectable liver tumors.

Modulation of rat bronchoalveolar lavage cell function by the intratracheal delivery of interferon-gamma

To determine if there is a rationale for compartmentalized immunostimulation, we have carried out a series of experiments to evaluate whether intratracheal delivery of interferon-gamma (rRatIFN-gamma) can activate rat bronchoalveolar lavage cells (BAL) for in vitro expression of tumoricidal activity against xenogeneic P815 tumor cells and enhanced in vitro microbicidal activity against the intracellular protozoan Toxoplasma gondii. Treatment of rat alveolar macrophages in vitro activates them for both of these activities as well as enhanced production of superoxide anion. We found that a single intratracheal dose of 5,000-10,000 units of rRatIFN-gamma activated rat BAL for both microbicidal and tumoricidal activity. To determine the duration of activation, microbicidal activity was determined 1, 2, 3, 5, and 7 days after a single intratracheal dose of 5,000 units of IFN. Enhanced microbicidal activity was maintained through day 3 but returned to control levels by day 5. Alveolar macrophages always accounted for the majority of cells in the lavage populations. However, intratracheal IFN caused an increase in the number of polymorphonuclear leukocytes and lymphocytes in the lavageable cells and, although these cells were always in the minority, they may have contributed to both the tumoricidal and microbicidal activity of the lavage cells. These studies demonstrate that local administration of an immunostimulant can activate pulmonary defense cells and may be a feasible route of drug delivery for prophylaxis against pulmonary infections.

Inhibition of liver tumor cell colonization in two animal tumor models by lectin blocking with D-galactose or arabinogalactan

Repeated administration of the hepatic lectin blocking agents D-galactose or arabinogalactan completely prevented the settling of metastatic cells of sarcoma L-1 tumor in the liver of Balb/c mice and greatly reduced the colonization process of highly metastatic ESb lymphoma cells of the liver of DBA/2 mice. Therefore, when hepatic lectins were blocked with competitive glycoconjugates, tumor cell colonization of the liver could be prevented in two different model systems.

Recombinant vaccinia virus vaccine against the human melanoma antigen p97 for use in immunotherapy

We have constructed a recombinant vaccinia virus, v-p97NY, which expresses the human melanoma-associated glycoprotein p97. Immunization with v-p97NY could induce humoral and cell-mediated immunity to p97, including delayed-type hypersensitivity, in mice and in two of two monkeys (Macaca fascicularis). The fact that an immune response was induced also in monkeys is important because normal cells from monkeys, but not from mice, express a low level of cross-reactive p97. Mice immunized with v-p97NY rejected transplants of syngeneic mouse melanoma expressing p97. A rejection response could be detected also when immunization was started 2 days after tumor transplantation, irrespective of whether the transplanted cells grew subcutaneously or as lung metastases. Evidence was obtained that melanoma cells lacking p97 may be killed as "bystanders" at the site of an immune response to melanoma cells expressing p97.

Characterization of a recombinant vaccinia virus expressing human melanoma-associated antigen p97

p97 is a cell surface glycoprotein expressed at high levels in most human melanomas but present only in trace amounts in normal adult tissues. We are interested in exploring the possibility of using recombinant vaccinia virus to express a specific tumor-associated antigen as a vaccine against human cancer. To this end, we constructed a recombinant virus, v-p97NY, which contains the entire coding sequence for p97 under the control of the vaccinia virus 7.5K promoter. Upon infection of tissue culture cells, v-p97NY expressed high levels of a membrane-bound glycoprotein immunoreactive with a p97-specific monoclonal antibody. Immunization of mice with this recombinant elicited high-titered antibodies against p97. Spleen cells isolated from these mice proliferated in vitro when stimulated either with purified p97 protein or with syngeneic cells expressing p97 antigen. Delayed-type hypersensitivity was also observed in immunized mice after challenge with p97-expressing cells. These findings indicate the potential usefulness of v-p97NY and similar recombinants in tumor immunotherapy.

Lysis of natural killer-sensitive and -resistant tumor cells by natural killer cytotoxic factors (NKCF)-containing liposomes

The lethal hit stage in NK cell-mediated lysis requires a complex series of events involving the release of NKCF, subsequent binding of these factors to the target cell, and susceptibility of the target cell to lysis by NKCF. Binding of NKCF alone is not sufficient because a number of tumor cells are able to bind NKCF without being lysed, suggesting the need for an additional processing step active on susceptible target cells. In the present study, we show that the interaction with liposome-incorporated NKCF renders NK resistant target cells sensitive to NKCF-mediated lysis. These results suggest that NKCF may mediate their cytotoxic effects through internalization of these factors into the cytosol.

Drug delivery to macrophages for the therapy of cancer and infectious diseases

The mechanisms by which mononuclear phagocytes discriminate between self and nonself, recognize foreign materials, senescent, damaged, old, or effete cells, and tumor cells are unknown. However, regardless of the mechanism(s) involved, once activated by the appropriate signal(s), macrophages are able to selectively recognize and destroy neoplastic cells in vitro and in vivo. Liposomes injected intravenously, in common with other particulate or polymeric matrices, localize preferentially in organs with high mononuclear phagocyte activity and in circulating blood monocytes. This behavior allows microparticulates to serve as a convenient system for the selective delivery of encapsulated drugs to cells of the mononuclear phagocyte series in vivo. Liposomes are a particularly attractive experimental system because of their capacity to incorporate a wide variety of water-soluble and lipid-soluble drugs. At this time, however, there is no reason to assume that a liposome-based drug delivery system will offer any significant therapeutic advantage compared to other microparticulate drug delivery systems. As in commercial development of any pharmaceutical preparation, considerations of cost-of-goods, shelf life, and acceptance of the formulation and dosing regimen by both physicians and patients will be of major importance in determining success and widespread clinical use. Liposomes containing macrophage-activating agents are highly effective at augmenting macrophage-mediated tumoricidal activity in vitro eradicating tumor metastasis in vivo, as well as protecting animals from a wide variety of microbial and viral infections. Although the demands of solving the scientific and technical problems associated with liposome development are substantial, the rapid rate of progress in biology and in pharmaceutical sciences enhances the prospect of success for at least several aspects of liposome-mediated drug delivery. The next few years will be crucial in determining whether the commercial development of liposomes is feasible or whether they will join the ranks of other drug carrier designs that have failed to fulfill their initial promise.

Combined immunostimulation (Propionibacterium avidum KP 40) and anticoagulation (heparin) prevents metastatic lung and liver colonization in mice

The antineoplastic activity of Propionibacterium avidum KP-40 and its enhancement by anticoagulation with heparin was studied. In Balb/c mice syngeneic sarcoma L-1 exclusively caused tumor colonization of the lungs. After neuraminidase treatment the organotropism of this tumor was changed, with tumor nodules developing in lung and liver. After single systemic application of Propionibacterium avidum KP-40 the number of lung and liver colonies decreased evidently. Combination of this immunomodulating therapy with temporary anticoagulation resulted in further reduction of tumor colonies in lung and liver.