Granulocyte-macrophage colony-stimulating factor potentiates antitumor activity of interleukin-12 in melanoma model in mice

Interleukin 12: still a promising candidate for tumor immunotherapy?

Interleukin 12 (IL-12) seemed to represent the ideal candidate for tumor immunotherapy, due to its ability to activate both innate (NK cells) and adaptive (cytotoxic T lymphocytes) immunities. However, despite encouraging results in animal models, very modest antitumor effects of IL-12 in early clinical trials, often accompanied by unacceptable levels of adverse events, markedly dampened hopes of the successful use of this cytokine in cancer patients. Recently, several clinical studies have been initiated in which IL-12 is applied as an adjuvant in cancer vaccines, in gene therapy including locoregional injections of IL-12 plasmid and in the form of tumor-targeting immunocytokines (IL-12 fused to monoclonal antibodies). The near future will show whether this renewed interest in the use of IL-12 in oncology will result in meaningful therapeutic effects in a select group of cancer patients.

Direct stimulation of macrophages by IL-12 and IL-18--a bridge too far?

A novel pathway of autocrine macrophage activation based on a positive feedback loop involving interleukin (IL)-12, IL-18 and IFN-gamma has recently been suggested. However, the macrophage isolation technique employed to describe the above phenomenon does not allow obtaining a pure population of macrophages casting some doubt to its existence. In the present study, we show that even minor contamination with lymphoid cells of a pure population of macrophage-like cells (Raw 264.7) results in a marked production of nitric oxide after stimulation with both IL-12 and IL-18. Neither macrophage-like cells nor lymphoid cells were capable of secreting high amounts of nitric oxide after stimulation with IL-12 and/or IL-18. Based on these observations we hypothesize that proposed autocrine feedback loop of macrophage activation is rather paracrine in nature and involves direct stimulation of residual lymphoid cells to secrete IFN-gamma that is then capable of activating macrophages.

Potentiation of the anti-tumour effects of Photofrin-based photodynamic therapy by localized treatment with G-CSF

Photofrin-based photodynamic therapy (PDT) has recently been approved for palliative and curative purposes in cancer patients. It has been demonstrated that neutrophils are indispensable for its anti-tumour effectiveness. We decided to evaluate the extent of the anti-tumour effectiveness of PDT combined with administration of granulocyte colony-stimulating factor (G-CSF) as well as the influence of Photofrin and G-CSF on the myelopoiesis and functional activity of neutrophils in mice. An intensive treatment with G-CSF significantly potentiated anti-tumour effectiveness of Photofrin-based PDT resulting in a reduction of tumour growth and prolongation of the survival time of mice bearing two different tumours: colon-26 and Lewis lung carcinoma. Moreover, 33% of C-26-bearing mice were completely cured of their tumours after combined therapy and developed a specific and long-lasting immunity. The tumours treated with both agents contained more infiltrating neutrophils and apoptotic cells then tumours treated with either G-CSF or PDT only. Importantly, simultaneous administration of Photofrin and G-CSF stimulated bone marrow and spleen myelopoiesis that resulted in an increased number of neutrophils demonstrating functional characteristics of activation. Potentiated anti-tumour effects of Photofrin-based PDT combined with G-CSF observed in two murine tumour models suggest that clinical trials using this tumour therapy protocol would be worth pursuing.

The potentiated antileukemic effects of doxorubicin and interleukin-12 combination are not dependent on nitric oxide production

In our recent study we described a significant antileukemic efficacy of a combination therapy with interleukin-12 (IL-12) and doxorubicin (DOX) in the L1210 leukemia model. This therapeutic effect was abrogated by elimination of activated macrophages. Activated macrophages produce a variety of factors that can contribute to the elimination of tumor cells in vivo, including proteases, TNF, reactive oxygen intermediates, and nitric oxide (NO). Based on the results of previous reports, the contribution of NO in potentiated antileukemic effects of IL-12 + DOX combination seemed to be highly possible. Both DOX and IL-12 given alone increased the production of NO by peritoneal macrophages, however, macrophages derived from the mice treated with the combination of those agents produced significantly less NO than macrophages from IL-12-alone-treated mice. Production of NO by spleen macrophages after IL-12 + DOX treatment was higher than it was in controls, IL-12-alone or DOX-alone-treated groups. In serum, concentrations of NOx- in IL-12- or IL-12 + DOX-treated mice were significantly higher in comparison with controls, however not significantly different from each other. Addition of L-NAME treatment to the IL-12 + DOX therapy in leukemia-bearing mice did not significantly change the antileukemic efficacy of this therapy. Thus, our results indicate that the augmented antileukemic effects of IL-12 + DOX combination therapy in L1210 model are NO-independent. Therefore, further studies on the possible mechanisms of potentiated antileukemic activity of combination of IL-12 and DOX would be worth pursuing.

Effective chemo-immunotherapy of L1210 leukemia in vivo using interleukin-12 combined with doxorubicin but not with cyclophosphamide, paclitaxel or cisplatin

It has been well established that chemo-immunotherapy using cytotoxic drugs and appropriate cytokines offers a new approach to increasing the therapeutic index in the treatment of neoplastic diseases. This study investigates the efficacy of combinations of interleukin-12 with cyclophosphamide, paclitaxel, cisplatin or doxorubicin in the murine L1210 leukemia model. Mice inoculated i.p. with 1 x 10(3) or 1 x 10(5) leukemia cells were treated with interleukin-12 and/or chemotherapeutics, and were observed daily for survival. Immunosuppression with X-irradiation or macrophage depletion with injections of silica were used to examine the dependence of the therapeutic effects on the efficiency of the immune system. Treatment with interleukin-12 or one of the studied chemotherapeutics given alone resulted in moderate antileukemic effects. Combination of interleukin-12 with cyclophosphamide or paclitaxel produced no augmentation of anti-leukemic effects in comparison with these agents given alone. Combination of interleukin-12 with cisplatin resulted in prolongation of the survival time; however, in the experiment with mice inoculated with 1 x 10(5) leukemia cells, no long-term survivors (>60 days) were observed; on the contrary, combination of interleukin-12 with doxorubicin resulted in 100% long-term survivors. This effect was completely abrogated either by X-irradiation of mice or by macrophage depletion. We also found that doxorubicin augments IL-12-stimulated production of interferon-gamma in vivo. Our observations demonstrating potentiation of the antileukemic effects of the IL-12 and doxorubicin combination suggest that the combined use of these 2 agents could be beneficial in leukemia therapy.