Activation of cytolytic activity in peripheral blood monocytes of renal cancer patients against non-cultured autologous tumor cells

Harnessing the untapped potential of nucleotide-binding oligomerization domain ligands for cancer immunotherapy

In the last decade, cancer immunotherapy has emerged as an effective alternative to traditional therapies such as chemotherapy and radiation. In contrast to the latter, cancer immunotherapy has the potential to distinguish between cancer and healthy cells, and thus to avoid severe and intolerable side‐effects, since the cancer cells are effectively eliminated by stimulated immune cells. The cytosolic nucleotide‐binding oligomerization domains 1 and 2 receptors (NOD1 and NOD2) are important components of the innate immune system and constitute interesting targets in terms of strengthening the immune response against cancer cells. Many NOD ligands have been synthesized, in particular NOD2 agonists that exhibit favorable immunostimulatory and anticancer activity. Among them, mifamurtide has already been approved in Europe by the European Medicine Agency for treating patients with osteosarcoma in combination with chemotherapy after complete surgical removal of the primary tumor. This review is focused on NOD receptors as promising targets in cancer immunotherapy as well as summarizing current knowledge of the various NOD ligands exhibiting antitumor and even antimetastatic activity in vitro and in vivo.

In Vitro Synergic Effect of Interferon Gamma Combined with Liposomes Containing Muramyl Tripeptide on Human Monocyte Cytotoxicity Against Fresh Allogeneic and Autologous Tumor Cells

Aims

The purpose of the present study was to investigate whether human recombinant interferon- γ (hrIFN - γ) can act synergically with various activators in increasing the cytotoxicity of cancer patient monocytes against fresh autologous and allogeneic tumor cells.

Methods

Fresh target cells were obtained by means on the mechanical and enzymatic dissociation of human renal carcinomas. A 375 and SW 626 cell lines were used as positive controls. Monocytes from renal cancer patients and normal volunteers were activated in vitro with lipopolysaccharide, muramyl tripeptide (MTP-PE) or liposomes containing MTP-PE (MTP-PE liposomes), with or without a pre-incubation with hrIFN- γ and were tested for cytotoxicity by means of a 72-hr 111indium-release assay. All of the patients were tumor free at the time of the study.

Results

Cancer patient peripheral blood monocytes were activated in vitro by different immunomodulators and became cytotoxic to freshly dissociated autologous or allogeneic tumor cells. A synergic effect producing maximal cytotoxicity was obtained with an appropriately scheduled combination of hrIFN- γ (10 U/ml) and MTP-PE liposomes (50 nm/ml), free lipopolysaccharide (10 μg/ml) or MTP-PE (100 μg/ml). The synergic cytotoxicity was observed against fresh allogeneic and autologous tumor cells, as well as against cultured cells.

Conclusions

All of these data support the possibility of a combined treatment using hrIFN- γ and MTP-PE liposomes in human studies, particularly when it is borne in mind that liposomes can prevent the direct toxicity of many immunomodulators and that the low levels of hrIFN- γ required for the synergic activation are not toxic in vivo.

Soluble Intercellular Adhesion Molecule-1 and Serum Cytokines in Melanoma Patients Treated with Liposomes Containing Muramyl Tripeptide

Aims and Background

A soluble form of intercellular adhesion molecule-1 (sICAM-1) has been recently identified in patients with malignant melanoma. It has been demonstrated that inflammatory cytokines can modulate the cellular expression of ICAM-1 and the shedding of this molecule by cells. To our knowledge, few data exist on serum sICAM-1 levels in cancer patients treated with immunomodulators. Liposomes containing muramyl tripeptide (MLV MTP-PE) can activate monocytes from cancer patients in vitro and in vivo, making them cytotoxic such as tumor necrosis factor- α (TNF-α) and Interleukin-6 (IL-6). The purpose of the present study was to evaluate the levels of sICAM-1 and their possible correlation with serum inflammatory cytokine levels in melanoma patients treated with MLV MTP-PE.

Methods

The sera from 9 patients with metastatic melanoma treated with MLV MTP-PE, 4 mg i.v. twice a week for 12 weeks, were tested in ELISA system to detect sICAM-1, TNF-α, IL-6, Interleukin-1 β (IL- β) and Interferon-γ (IFN-γ) before, and 2 and 24 h after the 1st, 12th and 24th infusion of MLV MTP-PE.

Results

Baseline levels of sICAM-1 were elevated in all patients (median 540 ng/ml: range 400-1030 ng/ml). Twenty-four h after the 1st infusion of MLV MTP-PE, we observed 6 increases in sICAM-1 levels, 1 decrease and 2 stable values (median 720 ng/ml: range 410-1820; P = 0.060). Twenty-four h after the 12th infusion, sICAM-1 increased in 3 patients and did not change in 4 (median 790 ng/ml: range 495-1650 ng/ml; P = 0.069). At the 24th infusion, sICAM-1 increased in 4 of 6 evaluable patients and remained stable in 2 (median 802 ng/ml: range 510-1450 ng/ml; P = 0.045). To better analyze the variations in sICAM-1, the patients were arbitrarily divided into two groups according to their clinical behavior: 4 presented stabilization (all lesions, n = 2; some lesions, n = 2) (Group A); 5 presented progressive disease (Group B). In Group A, sICAM-1 levels remained stable or showed a modest increase during treatment (except in 1 patient, who exhibited a substantial variation after the 12th infusion). In contrast, in Group B very high levels of sICAM-1 were observed at the beginning of the study therapy in 1 patient and after the 1st infusion in 3 patients; these values remained high until the 24th infusion. In most of the patients, TNF-α and IL-6 increased after the 1st infusion, but not thereafter. IFN-γ was never detected; IL-1 β was detectable in a few cases, but only before the infusions.

Conclusions

baseline levels of sICAM-1 were elevated in all patients and further increased during treatment only in patients with more aggressive disease. No correlation was found between sICAM-1 and inflammatory cytokines. It would therefore seem that in patients with advanced disease, higher levels and a progressive increase in sICAM-1 may be unfavorable prognostic factors.

Macrophages inhibit human osteosarcoma cell growth after activation with the bacterial cell wall derivative liposomal muramyl tripeptide in combination with interferon-γ

Background

In osteosarcoma, the presence of tumor-infiltrating macrophages positively correlates with patient survival in contrast to the negative effect of tumor-associated macrophages in patients with other tumors. Liposome-encapsulated muramyl tripeptide (L-MTP-PE) has been introduced in the treatment of osteosarcoma patients, which may enhance the potential anti-tumor activity of macrophages. Direct anti-tumor activity of human macrophages against human osteosarcoma cells has not been described so far. Hence, we assessed osteosarcoma cell growth after co-culture with human macrophages.

Methods

Monocyte-derived M1-like and M2-like macrophages were polarized with LPS + IFN-γ, L-MTP-PE +/− IFN-γ or IL-10 and incubated with osteosarcoma cells. Two days later, viable tumor cell numbers were analyzed. Antibody-dependent effects were investigated using the therapeutic anti-EGFR antibody cetuximab.

Results

M1-like macrophages inhibited osteosarcoma cell growth when activated with LPS + IFN-γ. Likewise, stimulation of M1-like macrophages with liposomal muramyl tripeptide (L-MTP-PE) inhibited tumor growth, but only when combined with IFN-γ. Addition of the tumor-reactive anti-EGFR antibody cetuximab did not further improve the anti-tumor activity of activated M1-like macrophages. The inhibition was mediated by supernatants of activated M1-like macrophages, containing TNF-α and IL-1β. However, specific blockage of these cytokines, nitric oxide or reactive oxygen species did not inhibit the anti-tumor effect, suggesting the involvement of other soluble factors released upon macrophage activation. While LPS + IFN-γ–activated M2-like macrophages had low anti-tumor activity, IL-10–polarized M2-like macrophages were able to reduce osteosarcoma cell growth in the presence of the anti-EGFR cetuximab involving antibody-dependent tumor cell phagocytosis.

Conclusion

This study demonstrates that human macrophages can be induced to exert direct anti-tumor activity against osteosarcoma cells. Our observation that the induction of macrophage anti-tumor activity by L-MTP-PE required IFN-γ may be of relevance for the optimization of L-MTP-PE therapy in osteosarcoma patients.

Interleukin-6 and soluble intercellular adhesion molecule-1 in renal cancer patients and cultured renal cancer cells

Serum interleukin-6 (IL-6) and soluble intercellular adhesion molecule-1 (sICAM-1) levels were measured by enzyme-linked immunosorbent assay in 62 renal cancer patients: 30 were tumor-free after radical nephrectomy and 32 presented with metastatic disease. Serum IL-6 was undetectable in all but one of the tumor-free patients, whereas 41% (13 of 32) of the metastatic patients presented serum IL-6 levels. Furthermore, there was a significant correlation between serum IL-6 levels and a shorter overall survival (p = 0.009). Moreover, serum sICAM-1 levels were significantly higher (p = 0.05) in the metastatic patients with detectable serum IL-6 than in those without IL-6, suggesting a possible link between IL-6 and sICAM-1. The probability of a shorter overall survival was greater in the metastatic patients with both serum IL-6 and elevated sICAM-1 levels (>635 ng/ml), than in those with elevated sICAM-1 but without IL-6 (p = 0.01). The production of IL-6 by 16 freshly dissociated renal cancer cells cultured in vitro was also observed. It appeared that IL-6 levels did not correlate with the expression and release of ICAM-1 by cultured cells, although the highest values of ICAM-1 release were found in cultures synthesizing the highest values of IL-6. In conclusion, in vivo presence of serum IL-6 and elevated sICAM-1 levels is related to an unfavorable prognosis; it can be speculated that the cells capable of releasing high levels of sICAM-1 and IL-6 may negatively influence the antitumor response.

Potent antitumor effects of combination therapy with IFNs and monocytes in mouse models of established human ovarian and melanoma tumors

Interferon-activated monocytes are known to exert cytocidal activity against tumor cells in vitro. Here, we have examined whether a combination of IFN-α2a and IFN-γ and human monocytes mediate significant antitumor effects against human ovarian and melanoma tumor xenografts in mouse models. OVCAR-3 tumors were treated i.t. with monocytes alone, IFN-α2a and IFN-γ alone or combination of all three on day 0, 15 or 30 post-tumor implantation. Mice receiving combination therapy beginning day 15 showed significantly reduced tumor growth and prolonged survival including complete regression in 40% mice. Tumor volumes measured on day 80 in mice receiving combination therapy (206 mm(3)) were significantly smaller than those of mice receiving the IFNs alone (1,041 mm(3)), monocytes alone (1,111 mm(3)) or untreated controls (1,728 mm(3)). Similarly, combination therapy with monocytes and IFNs of much larger tumor also inhibited OVCAR-3 tumor growth. Immunohistochemistry studies showed a large number of activated macrophages (CD31(+)/CD68(+)) infiltrating into OVCAR-3 tumors and higher densities of IL-12, IP10 and NOS2, markers of M1 (classical) macrophages in tumors treated with combination therapy compared to the controls. Interestingly, IFNs-activated macrophages induced apoptosis of OVCAR-3 tumor cells as monocytes alone or IFNs alone did not mediate significant apoptosis. Similar antitumor activity was observed in the LOX melanoma mouse model, but not as profound as seen with the OVCAR-3 tumors. Administration of either mixture of monocytes and IFN-α2a or monocytes and IFN-γ did not inhibit Lox melanoma growth; however, a significant inhibition was observed when tumors were treated with a mixture of monocytes, IFN-α2a and IFN-γ. These results indicate that monocytes and both IFN-α2a and IFN-γ may be required to mediate profound antitumor effect against human ovarian and melanoma tumors in mouse models.

Mifamurtide for the treatment of nonmetastatic osteosarcoma

INTRODUCTION

The standard treatment for osteosarcoma requires both macroscopic surgical wide resection and postoperative multi-drug chemotherapy in neoadjuvant and adjuvant settings. However, the 5-year event-free survival has remained at a plateau of 60-70% of patients with nonmetastatic osteosarcoma for more than 30 years.

AREAS COVERED

Mifamurtide (liposomal muramyl tripeptide phosphatidylethanolamine; L-MTP-PE) is a new agent. L-MTP-PE is a nonspecific immunomodulator, which is a synthetic analog of a component of bacterial cell walls. L-MTP-PE activates macrophages and monocytes as a potent activator of immune response in addition to standard chemotherapy. It also improves the overall survival from 70 to 78% and results in a one-third reduction in the risk of death from osteosarcoma. This review summarizes the most recent findings about L-MTP-PE and its therapeutic application for nonmetastatic osteosarcoma.

EXPERT OPINION

Recently, L-MTP-PE has been approved in Europe for the treatment of nonmetastatic osteosarcoma with chemotherapy. L-MTP-PE in combination with traditional treatment is expected to go mainstream and to be beneficial for patients with osteosarcoma. Information about potential benefit regarding mifamurtide use in the neoadjuvant setting (i.e., before surgery) and/or usefulness of L-MTP-PE in metastatic in relapsed and metastatic osteosarcoma requires analysis of expanded access and/or future clinical trials of L-MTP-PE in high-burden and low-burden situations.

Near eradication of clinically relevant concentrations of human tumor cells by interferon-activated monocytes in vitro

We have previously reported that low concentrations of interferon (IFN)-activated monocytes exert near-eradicative cytocidal activity against low concentrations of several human tumor cells in vitro. In the present study, we examined 7 human tumor cell lines and 3 diploid lines in the presence or absence of 10 ng/mL IFNα2a and monocytes. The results confirmed strong cytocidal activity against 4 of 7 tumor lines but none against 3 diploid lines. To model larger in vivo tumors, we increased the target cell concentration and determined the concentration of IFNα2a and monocytes, required for cell death. We found that increasing the tumor cell concentration from 10- to 100-fold (10(5) cells/well) required an increase in the concentration of IFNs by over 100-fold and monocytes by 10-fold. High concentrations of monocytes could sometimes kill tumor or diploid cells in the absence of IFN. We may conclude that killing of high concentrations of tumor or diploid cells required high concentrations of monocytes that could sometimes kill in the absence of IFN. Thus, high concentrations of tumor cells required high concentrations of IFN and monocytes to cause near eradication of tumor cells. These findings may have clinical implications.

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.

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.

IL-2 signaling in human monocytes involves the phosphorylation and activation of p59hck

The activating properties of IL-2 and the structure of the IL-2R on human monocytes are well characterized. However, relatively little is known about the biochemical mechanisms involved in IL-2 signal transduction in these cells. We investigated the role of protein tyrosine kinases (PTKs) in the activation of monocytes by IL-2. Incubation of monocytes with the PTK inhibitor herbimycin A (HA) resulted in the dose-dependent suppression of IL-2-induced monocyte tumoricidal activity. This inhibition was rather potent, as a concentration of HA as low as 0.5 microM caused a complete abrogation of cytolytic activity. Furthermore, HA markedly suppressed the ability of IL-2 to induce IL-1 beta, TNF-alpha, IL-6, and IL-8 mRNA expression and protein secretion by monocytes. Anti-phosphotyrosine immunoblotting demonstrated that IL-2 induced a rapid and time-dependent increase in tyrosine phosphorylation of several cellular proteins of molecular masses ranging from 35 to 180 kDa. Interestingly, IL-2 caused a significant up-regulation of the constitutive levels of hck PTK mRNA and protein relative to medium-treated cells as well as an increase in p59hck tyrosine phosphorylation. Finally, we demonstrated by in vitro kinase assay that the specific activity of p59hck PTK was also induced by IL-2 in monocytes. Thus, these data show that the activation of PTKs is required for the triggering of monocyte effector and secretory functions by IL-2 and strongly suggest that p59hck is a key participant in IL-2 signaling in human monocytes.

Induction of reactive oxygen intermediates in human monocytes by tumour cells and their role in spontaneous monocyte cytotoxicity

The present study examined the ability of human monocytes to produce reactive oxygen intermediates after a contact with tumour cells. Monocytes generated oxygen radicals, as measured by luminol-enhanced chemiluminescence and superoxide anion production, after stimulation with the tumour, but not with untransformed, cells. The use of specific oxygen radical scavengers and inhibitors, superoxide dismutase, catalase, dimethyl sulphoxide and deferoxamine as well as the myeloperoxidase inhibitor 4-aminobenzoic acid hydrazide, indicated that chemiluminescence was dependent on the production of superoxide anion and hydroxyl radical and the presence of myeloperoxidase. The tumour cell-induced chemiluminescent response of monocytes showed different kinetics from that seen after activation of monocytes with phorbol ester. These results indicate that human monocytes can be directly stimulated by tumour cells for reactive oxygen intermediate production. Spontaneous monocyte-mediated cytotoxicity towards cancer cells was inhibited by superoxide dismutase, catalase, deferoxamine and hydrazide, implicating the role of superoxide anion, hydrogen peroxide, hydroxyl radical and hypohalite. We wish to suggest that so-called 'spontaneous' tumoricidal capacity of freshly isolated human monocytes may in fact be an inducible event associated with generation of reactive oxygen intermediates and perhaps other toxic mediators, resulting from a contact of monocytes with tumour cells.

Expression of heat shock protein 72 in renal cell carcinoma: possible role and prognostic implications in cancer patients

Renal cancer cells from 43 patients and normal renal cells from 10 of them were studied for the expression of highly stress-inducible heat shock protein 72 (HSP72) by means of immunoperoxidase analysis. It was found that HSP72 was expressed in a significantly higher percentage of renal cancer cells than normal renal cells (P = 0.0001), the mean percentage of positive cells being 33.1 +/- 18% and 8 +/- 5%, respectively. Moreover, a percentage of HSP72-positive cells that was less than the cut-off point (18%, mean value of normal cells +2 S.D.) significantly correlated with shorter disease-free survival (P = 0.002). The renal cancer cell populations taken from the 21 patients who relapsed after a median time of 13 months (range 3-73 months) had a significantly lower percentage of HSP72-positive cells (mean value 25.1 +/- 17%) than the cells taken from the patients who remained tumour-free (mean value 40.8 +/- 15%) after a median period of 72 months (range 19-96 months, P = 0.003). It was also demonstrated that HSP72 expression can be significantly increased by 48-h in vitro incubation with rIFN-gamma (P = 0.007). These data suggest that HSP72 may represent a favourable prognostic factor regardless of stage and histological grade and its expression may be increased by treatment with rIFN-gamma. Further studies are needed in order to investigate the relationship between HSP72 and the immunoeffector cells.

Phase I/II trial of autologous activated macrophages in advanced colorectal cancer

Autologous activated macrophage (AAM) therapy is an adoptive cellular therapy based on ex vivo differentiation and activation of autologous peripheral blood monocytes. This study was undertaken to evaluate the tolerance, efficiency and biological effects of AAMs in chemoresistant progressive colorectal cancers. From January 1993 to May 1995, 15 patients were treated. Mononuclear cells were collected six times by weekly apheresis, cultured for 7 days, and activated with interferon-gamma. AAMs were then separated by elutriation and re-infused intravenously, with a mean total of 7.95 x 10(9) macrophages per patient. Clinical tolerance was good: toxicity consisted only of a World Health Organisation grade 2 fever after 28% of the infusions. Responses were not seen in the 14 evaluable patients, as expected with very bulky tumours: in 11, the tumours continued to progress, but disease was stabilised in 3 patients who experienced progression-free survival for 14, 12 and 12 weeks, respectively.

Expression and release of intercellular adhesion molecule-1 in renal-cancer patients

We examined ICAM-1 expression in 37 freshly dissociated renal-cancer cell populations. Immunoperoxidase analysis revealed that 31 of the 37 renal tumors expressed ICAM-1 to various degrees; ICAM-1 expression was significantly lower in tumor cells obtained from patients remaining tumor-free after a median follow-up of 60 months (mean value 24.4% +/- 21) than in tumor cells obtained from the relapsed patients (mean value 40.8% +/- 22), and the low expression of this molecule on the cell surface seemed to correlate with favorable clinical behavior. In 41 patients, the mean level of sICAM-I was 551 +/- 260 ng/ml, significantly higher than normal. However, sICAM-1 levels were significantly lower in the 20 tumor-free (mean 467 +/- 158 ng/ml) than in the 21 metastatic patients (mean 631 +/- 318 ng/ml). Eleven renal-cancer cell populations were cultured in order to examine the expression and release of ICAM-1. All of these cells were positive for ICAM-1 expression, which was elevated in 6 cases (> 50%) and low in the remaining 5 cases (18-35%). However, only the 5 cell populations expressing low levels of ICAM-1 released this molecule, showing an inverse correlation with cellular expression. Five of the cell populations were treated for 48 hr with rIFN-gamma, in these cells, both ICAM-1 expression and sICAM-1 levels increased, although sICAM-1 levels in the supernatants of the cell populations with constitutive high ICAM-1 expression remained very low.