Regional muramyl tripeptide phosphatidylethanolamine administration enhances hepatic immune function and tumor surveillance

Mifamurtide: a review of its use in the treatment of osteosarcoma

Mifamurtide (liposomal muramyl tripeptide phosphatidyl ethanolamine; Mepact) is an immunomodulator with antitumor effects that appear to be mediated via activation of monocytes and macrophages. In the EU, mifamurtide is indicated in children, adolescents, and young adults for the treatment of high-grade, resectable, non-metastatic osteosarcoma after macroscopically complete surgical resection; it is administered by intravenous infusion in conjunction with postoperative multiagent chemotherapy. In the US, mifamurtide is currently an investigational agent that holds orphan drug status for the treatment of osteosarcoma. In a large, randomized, open-label, multicenter, phase III trial, the addition of adjuvant (postoperative) mifamurtide to three- or four-drug combination chemotherapy (doxorubicin, cisplatin, and high-dose methotrexate with, or without, ifosfamide) was associated with a statistically significant improvement in overall survival in patients with newly diagnosed, high-grade, non-metastatic, resectable osteosarcoma. The pattern of outcome was generally similar in a small cohort of patients with metastatic disease who were enrolled in this trial. Mifamurtide is generally well tolerated; adverse events attributed to administration of the drug include chills, fever, headache, nausea, and myalgias. Based on the available data, mifamurtide can be considered for inclusion in treatment protocols for localized osteosarcoma.

Role of Kupffer cells in the outgrowth of colorectal cancer liver metastases

Colorectal cancer is one of the commonest malignancies in the "developed" world. The liver constitutes the main host organ for its distant metastases which, when present, augur a bad prognosis for the disease. Kupffer cells (KCs) are macrophages that constantly reside within the liver and form an effective first line defence against multiple harmful agents which reach the hepatic sinusoids via the portal circulation. KCs remove chemical compounds and dead or damaged cells, eliminate bacteria and protect against invading tumour cells. They may play a crucial tumouricidal role, exerting cytotoxic and cytostatic functions through the release of multiple cytokines and chemokines. Subsequently, colorectal metastasising cells are destroyed either by KC-performed phagocytosis or via the stimulation of other immune cells which migrate into the sinusoids and act accordingly. On the contrary, KC products, including cytokines, growth factors and matrix-degrading enzymes may promote liver metastasis, supporting tumour cell extravasation, motility and invasion. Current research aims to exploit the antineoplastic properties of KCs in new therapeutic approaches of colorectal cancer liver metastasis. Numerous agents, such as the granulocyte macrophage-colony stimulating factor, interferon gamma, muramyl peptide analogues and various antibody based treatments, have been tested in experimental models with promising results. Future trials may investigate their use in everyday clinical practice and compare their therapeutic value with current treatment of the disease.

Muramyl tripeptide (mifamurtide) for the treatment of osteosarcoma

Osteosarcoma is an ultraorphan disease. There are approximately 1000 new patients diagnosed with osteosarcoma each year in the USA and Europe. Current treatment for osteosarcoma utilizes multiagent chemotherapy and surgical resection of all clinically detectable disease. Current treatments for osteosarcoma achieve 60-70% event-free survival (EFS) for patients with localized disease and approximately 20% EFS for patients who present with metastasis. These results have been stable for two decades. The addition of muramyl tripeptide (mifamurtide) to chemotherapy resulted in a trend towards improved EFS and a one-third reduction in the risk of death from osteosarcoma. Mifamurtide has been approved in Europe for the treatment of newly diagnosed osteosarcoma in combination with chemotherapy.

Imunomodulative effect of liposomized muramyltripeptide phosphatidylethanolamine (L-MTP-PE) on mice with alveolar echinococcosis and treated with albendazole

The effect of liposomized muramyltripeptide phosphatidylethanolamine (L-MTP-PE) administered separately or with anthelmintic albendazole (ABZ) on cellular immunity of mice with alveolar echinococcosis was studied. The proliferative activity of splenic T and B lymphocytes was the most stimulated after combined L-MTP-PE + ABZ therapy [from weeks 8 to 14 post-infection (p.i.)] that also induced a long-term development of protective Th1 response (the highest serum concentration of IFN-gamma from weeks 8 to 18 p.i.). On the contrary, Th2 response (cytokine IL-5) in infected mice treated with L-MTP-PE was inhibited since week 8 p.i., but a significant long-term decrease in IL-5 concentration was found after combined L-MTP-PE+ABZ therapy until the end of the experiment (until week 26 p.i.). L-MTP-PE stimulated the production of superoxide anion (O2-) by peritoneal macrophages from weeks 8 to 12 p.i., but the highest O2- production was accordingly recorded after therapy L-MTP-PE+ABZ from weeks 8 to 18 p.i. Stimulation of cellular immunity of mice with alveolar echinococcis with L-MTP-PE and an interaction with ABZ's anti-parasitic effect resulted in the greatest and long-term reduction of growth of Echinococcus multilocularis cysts in the host from week 10 p.i. until the end of the experiment.

Hepatic colorectal cancer metastases: imaging initial steps of formation in mice

PURPOSE

To prospectively use optical imaging to study the cell-specific mechanisms of entrapment and subsequent growth of two human colon cancer cell lines differing in their propensity to form hepatic metastases.

MATERIALS AND METHODS

In this Animal Care Committee-approved study, intravital optical imaging was performed in exteriorized livers of three groups of mice after intrasplenic inoculation of human colon cancer cells. Group 1 mice (control group; n=12) received a cell-maintaining solution only. Groups 2 and 3 (n=12 in each) were administered poorly (MIP-101 colon cancer cells) or highly (CX-1 colon cancer cells) metastatic cells. Imaging was performed on postinoculation days 0, 1, 3, and 6 to document sites and mechanisms of tumor cell entrapment and presence and sites of endothelial cell activation and of tumor cell interactions with systemic macrophages and Kupffer cells. Fluorescence intensity of Kupffer cells was compared by using the Mann-Whitney test. Immunohistochemistry served as the reference standard for all in vivo observations.

RESULTS

Whereas both MIP-101 and CX-1 colon cancer cells adhered to periportal Kupffer cells, the CX-1 cells resulted in Kupffer cell activation, evidenced in vivo by increased visible peroxidase activity (P<.05). Only CX-1 cells were associated with subsequent downstream endothelial cell activation, evidenced by in vivo expression of E-selectin. By day 6, regression of periportal MIP-101 tumor growth correlated with ingrowth of systemic macrophages, while CX-1 tumor growth, originating in the outflow venous regions, correlated with translobular migration and ingrowth of activated Kupffer cells.

CONCLUSION

Formation of hepatic colon cancer metastases is cancer cell-type specific, with cell lines differing in their mechanisms and intrahepatic locations of initial entrapment and Kupffer cell activation and subsequent growth.

Role of Kupffer cells in host defense and liver disease

Kupffer cells (KC) constitute 80-90% of the tissue macrophages present in the body. They reside within the lumen of the liver sinusoids, and are therefore constantly exposed to gut-derived bacteria, microbial debris and bacterial endotoxins, known to activate macrophages. Upon activation KC release various products, including cytokines, prostanoides, nitric oxide and reactive oxygen species. These factors regulate the phenotype of KC themselves, and the phenotypes of neighboring cells, such as hepatocytes, stellate cells, endothelial cells and other immune cells that traffic through the liver. Therefore, KC are intimately involved in the liver's response to infection, toxins, ischemia, resection and other stresses. This review summarizes established basic concepts of KC function as well as their role in the pathogenesis of various liver diseases.

Macrophage inflammatory protein-2 contributes to liver resection-induced acceleration of hepatic metastatic tumor growth

AIM: To study the role of macrophage inflammatory protein (MIP)-2 in liver resection-induced acceleration of tumor growth in a mouse model of hepatic metastasis.

METHODS: After a 50% hepatectomy, 1×10⁵ CT26.WT cells were implanted into the left liver lobe of syngeneic balb/c mice (PHx). Additional animals were treated with a monoclonal antibody (MAB452) neutralizing MIP-2 (PHx+mAB). Non-resected and non-mAB-treated mice (Con) served as controls. After 7 d, tumor angiogenesis and microcirculation as well as cell proliferation, tumor growth, and CXCR-2 expression were analyzed using intravital fluorescence microscopy, histology, immunohistochemistry, and flow cytometry.

RESULTS: Partial hepatectomy increased (P < 0.05) the expression of the MIP-2 receptor CXCR-2 on tumor cells when compared with non-resected controls, and markedly accelerated (P < 0.05) angiogenesis and metastatic tumor growth. Neutralization of MIP-2 by MAB452 treatment significantly (P < 0.05) depressed CXCR-2 expression. Further, the blockade of MIP-2 reduced the angiogenic response (P < 0.05) and inhibited tumor growth (P < 0.05). Of interest, liver resection-induced hepatocyte proliferation was not effected by anti-MIP-2 treatment.

CONCLUSION: MIP-2 significantly contributes to liver resection-induced acceleration of colorectal CT26.WT hepatic metastasis growth.

Therapeutic potential of Kupffer cells in prevention of liver metastases outgrowth

Development of liver metastases is a frequent complication in the course of gastro-intestinal malignancies. After entering the liver via the portal circulation, blood-borne tumor cells that have been seeded from primary colorectal cancer, are first encountered by Kupffer cells (KC), which line the liver sinusoids. KC represent approximately 10% of all liver cells, and have the ability to kill tumor cells. As such, they may play an important intrinsic role in the protection against outgrowth of hepatic metastases. Furthermore, the cytotoxic function of KC is increased upon stimulation with various biological response modifiers, such as interferon-gamma, granulocyte macrophage-colony stimulating factor, antibodies and muramyl dipeptides. Therefore, enhancement of KC cytotoxic functions may represent an attractive treatment modality to prevent development of liver metastases in the clinical setting.

Efficacy of multiagent herpes simplex virus amplicon-mediated immunotherapy as adjuvant treatment for experimental hepatic cancer

OBJECTIVE

To evaluate the use of herpes simplex viral (HSV) amplicon vectors for production of tumor vaccines and to determine if such vaccines expressing combinations of immunostimulatory agents may be effective in the treatment of experimental liver cancer.

METHODS

A hepatic metastatic tumor model using CT-26 colorectal cancer in syngeneic Balb/C mice was utilized. Tumor vaccines were produced by brief (20 minutes) exposure of irradiated tumor cells to herpes amplicon vectors carrying the transgene for RANTES, B7.1, or GM-CSF. The antitumor efficacy of vaccination using tumor cells secreting GM-CSF (single agent) or a combination of RANTES/B7.1/GM-CSF (multiagent) was tested. The effect of 60% hepatectomy or T-cell depletion was also tested in this model.

RESULTS

In vitro assays confirmed high-level cytokine or costimulatory molecule production by cells transduced with amplicons. Antitumor efficacy was observed with single-agent or multiagent treatment. Without hepatectomy, immunization with single-agent or multiagent vaccine therapy appears equivalent. When administered in the setting of hepatectomy, multiagent regimens produced a higher cure rate than single-agent therapy (50% vs. 12.5%, =.03). Animals treated with GM-CSF alone had an average nodule count of 40 +/- 19 ( <.006 vs. Hep control 232 +/- 30), while animals treated with multiagent therapy had an average nodule count of 11 +/- 7 ( <.0004 vs. control). CD4 and CD8 lymphocyte blockade abrogated observed efficacy, confirming a lymphocyte-mediated response.

CONCLUSIONS

Tumor vaccines produced using HSV amplicon-mediated gene transfer may be useful in the treatment of liver malignancies. In the setting of hepatectomy, multiagent vaccine therapy offers an advantage over single-agent therapy. These data encourage consideration of such HSV-based neoadjuvant immunotherapy for treatment of liver malignancies.