Heme oxygenase-1 protects tumor cells against photodynamic therapy-mediated cytotoxicity

Photodynamic therapy is a promising antitumor treatment modality approved for the management of both early and advanced tumors. The mechanisms of its antitumor action include generation of singlet oxygen and reactive oxygen species that directly damage tumor cells and tumor vasculature. A number of mechanisms seem to be involved in the protective responses to PDT that include activation of transcription factors, heat shock proteins, antioxidant enzymes and antiapoptotic pathways. Elucidation of these mechanisms might result in the design of more effective combination strategies to improve the antitumor efficacy of PDT. Using DNA microarray analysis to identify stress-related genes induced by Photofrin-mediated PDT in colon adenocarcinoma C-26 cells, we observed a marked induction of heme oxygenase-1 (HO-1). Induction of HO-1 with hemin or stable transfection of C-26 with a plasmid vector encoding HO-1 increased resistance of tumor cells to PDT-mediated cytotoxicity. On the other hand, zinc (II) protoporphyrin IX, an HO-1 inhibitor, markedly augmented PDT-mediated cytotoxicity towards C-26 and human ovarian carcinoma MDAH2774 cells. Neither bilirubin, biliverdin nor carbon monoxide, direct products of HO-1 catalysed heme degradation, was responsible for cytoprotection. Importantly, desferrioxamine, a potent iron chelator significantly potentiated cytotoxic effects of PDT. Altogether our results indicate that HO-1 is involved in an important protective mechanism against PDT-mediated phototoxicity and administration of HO-1 inhibitors might be an effective way to potentiate antitumor effectiveness of PDT.

Increased local vascular endothelial growth factor expression associated with antitumor activity of proteasome inhibitor

Inhibition of the proteasome, a multicatalytic proteinase complex, is an attractive approach to cancer therapy. Here we report that a selective inhibitor of the chymotrypsin-like activity of the proteasome, PSI (N-benzyloxycarbonyl-Ile-Glu(O-t-butyl)-Ala-leucinal) may inhibit growth of solid tumors not only through apoptosis induction, but also indirectly--through inhibition of angiogenesis. Two murine tumors: colon adenocarcinoma (C-26) and Lewis lung carcinoma (3LL) were chosen to study the antitumor effect of PSI. In an in vivo model of local tumor growth, PSI exerted significant antitumor effects against C-26 colon carcinoma, but not against 3LL lung carcinoma. Retardation of tumor growth was observed in mice treated with both 10 nmoles and 100 nmoles doses of PSI and in the latter group prolongation of the survival time of tumor-bearing mice was observed. PSI inhibited angiogenesis in the C-26 growing tumors with no such effect in 3LL tumors. Unexpectedly, that activity was associated with upregulation of vascular endothelial growth factor (VEGF) at the level of mRNA expression and protein production in C-26 tumors treated with PSI. C-26 cells treated with PSI produced increased amounts of VEGF in vitro in a dose- and time-dependent manner. We demonstrated that in C-26 colon adenocarcionoma higher VEGF production may render endothelial cells susceptible to the proapoptotic activity of PSI and is associated with inhibition of tumor growth.

Potentiatied antitumor effectiveness of combined chemo-immunotherapy with interleukin-12 and 5-fluorouracil of L1210 leukemia in vivo

In this study we investigated the efficacy of a combination of IL-12 and 5-FU, a chemotherapeutic exerting several immunomodulatory effects, in murine L1210 leukemia. Mice inoculated with 1 x 10(5) leukemia cells were treated with a single dose of 5-FU (50 mg/kg) and seven daily doses of IL-12 (100 ng/dose), and were observed for survival. Treatment with IL-12 or 5-FU given alone produced moderate anti-leukemic effects. However, combination of both drugs resulted in a significant prolongation of mouse survival time. Importantly, there were 70% of long-term (>60 days) survivors among mice treated with both agents simultaneously. Moreover, we observed 100% of long-term survivors when mice were treated with a minimally increased dose of IL-12 (170 ng) in combination with 5-FU (50 mg/kg). The antileukemic effects were completely abrogated in scid/scid mice and in mice depleted of peritoneal macrophages and significantly decreased after administration of anti-CD3+, anti-CD4+ or anti-CD8+ monoclonal antibodies. Administration of anti-NK1.1 antibodies did not decrease the antileukemic effects indicating that NK cells are not important effectors of this treatment regimen. Collectively, these results indicate that the combination of IL-12 and 5-FU is inducing strong antileukemic responses that are dependent on the presence and activity of macrophages and T lymphocytes and warrant further studies of combined chemo-immunotherapy with IL-12.

Augmented pro-apoptotic effects of TRAIL and proteasome inhibitor in human promonocytic leukemic U937 cells

TRAIL, Tumor necrosis factor-related apoptosis-inducing ligand), a member of the TNF family, is known to be cytotoxic for a high proportion of tumor cell lines. However, successful application of TRAIL in tumor therapy may depend on finding other agents that can potentiate its antitumor effects. The present study showed that the cytostatic/cytotoxic TRAIL activity against U937 cells could be significantly augmented by proteasome inhibitor PSI, as revealed by MTT assay. Increased cytostatic/cytotoxic effect on U937 cells by TRAIL/PSI combined treatment was caused by apoptosis, as shown by an increased PARP cleavage rate. TRAIL/PSI did not affect the level of mRNA expression for TRAIL receptors (DR4, DR5, DcR1) and other apoptosis signal transduction molecules (TRADD, caspase-8).

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

To study the antitumor activity of the combination immunotherapy with interleukin-12 (IL-12) and granulocyte-macrophage colony-stimulating factor (GM-CSF), a murine MmB 16 melanoma tumor model was used. Seven days after inoculation of MmB 16 melanoma cells into the footpad of the right hind limb, mice were treated with IL-12 and/or GM-CSF administered intratumorally for 7 consecutive days. IL-12 used both at a high (1 microg) and at a low (0.01 microg) dose per day produced retardation of tumor growth, although neither treatment resulted in any significant prolongation of the survival of tumor-bearing mice. GM-CSF did not by itself exert antitumor activity in this model; however, it potentiated antitumor effects of IL-12. In particular, survival of tumor-bearing mice treated with IL-12 (0.01 microg per day) and GM-CSF was significantly prolonged compared with that in mice treated with either IL-12 or GM-CSF alone.

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.

Interleukin 12 and indomethacin exert a synergistic, angiogenesis-dependent antitumor activity in mice

Nonsteroidal anti-inflammatory drugs have been shown to reduce the incidence and mortality from colorectal cancer. It has recently been demonstrated that these drugs are capable of suppressing the production of pro-angiogenic factors from tumor cells. The mechanisms of antitumor action of interleukin 12 include the enforced secretion of anti-angiogenic factors and stimulation of antitumor immunity. Therefore, we hypothesized that the combination of a model nonsteroidal anti-inflammatory drug--indomethacin and interleukin 12--would result in enhanced angiogenesis-dependent antitumor effects against a colon-26 carcinoma cells transplanted into syngeneic mice. As expected the combined administration of both agents simultaneously resulted in a strengthened antitumor activity that was manifested as a retardation of tumor growth and prolongation of mouse survival. Importantly some mice were completely cured after the combined treatment. As administration of interleukin 12 and indomethacin resulted in enhanced inhibition of angiogenesis it seems possible that prevention of new blood vessel formation is one of the mechanisms responsible for the observed antitumor effects.

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.

Subtherapeutic doses of interleukin-15 augment the antitumor effect of interleukin-12 in a B16F10 melanoma model in mice

Interleukin-12 (IL-12) is a potent immunoregulatory cytokine that exhibits antitumor activity in many experimental tumor models. In the present study, we investigated the ability of IL-15, a cytokine sharing many functions of IL-2, to modulate antitumor effectiveness of IL-12 against B16F10 melanoma in mice. In a model of locally growing tumor, intratumoral (i.t.) administration of IL-12, in three cycles of five consecutive daily injections (0.1 mug) followed by 2 days of rest, led to considerable delay of tumor development but no curative response was achieved. When combined with IL-12, subtherapeutic doses of IL-15 (0.4 mug) pontentiated the antitumor effects of IL-12 and induced complete tumor regressions in 50% of mice. Similar results were obtained in a model in which tumor-bearing mice were intravenously co-injected with melanoma cells to induce metastases. Combined administration of IL-12 and IL-15 yielded greater antitumor activity than injections of either cytokine alone and resulted in prolonged survival of mice bearing locally growing tumor and metastases. Studies of immunological parameters in mice treated with both IL-12 and IL-15 have shown enhanced NK activity (against YAC-1 cells) in the spleen and stimulation of both NK activity and specific anti-B16F10 cytotoxic effector cells in tumor-draining lymph nodes (LN). The strong antitumor effect of the IL-12 + IL-15 combination correlated with a high serum level of IFN-gamma in the treated mice. Moreover, increased expression of IL-15Ralpha was demonstrated in LN lymphocytes isolated from mice injected with IL-12. This result together with findings of other authors showing enhanced expression of IL-12 receptor by IL-15 [1] suggests that the augmentation of the antitumor effect during the course of IL-12/IL-15-based therapy could result from reciprocal upregulation of receptors by both cytokines and synergistic effects on IFN-gamma induction.

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.

Granulocyte colony-stimulating factor demonstrates antitumor activity in melanoma model in mice

Granulocyte colony-stimulating factor (G-CSF) was found to exert antitumor activity against murine MmB16 melanoma when administered intratumorally. However, subcutaneous administration of this cytokine at a site distant from the growing tumor did not show any antitumor effects. G-CSF did not influence the proliferative activity of MmB16 in vitro. Intraperitoneal administration of G-CSF resulted in decreased secretion of nitric oxide (NO) by peritoneal macrophages and their decreased tumoricidal activity against MmB16.

G-CSF prevents the suppression of bone marrow hematopoiesis induced by IL-12 and augments its antitumor activity in a melanoma model in mice

BACKGROUND

IL-12 has been successfully used in experimental tumor therapy. However, administration of this cytokine induces dose-dependent suppression of hematopoiesis that could potentially limit its use in clinical trials. We decided to examine whether the myelosuppressive activity of IL-12 could be corrected by the administration of G-CSF.

MATERIALS AND METHODS

In the initial experiments the influence of IL-12 and/or G-CSF on bone marrow and spleen GM-CFC was evaluated. To examine whether C-CSF could influence the antitumor activity of IL-12 the combination therapy with these agents was carried out starting on day seven following inoculation of melanoma MmB16 cells into the footpads of B6D2F1 mice. To obtain insight into the mechanism of the observed augmented antitumor activity of the combination therapy with IL-12 and G-CSF, the influence of these cytokines on macrophage activity (cytotoxicity and nitric oxide release) was analyzed.

RESULTS

In accord with our expectations, the application of G-CSF partially prevented the suppression of bone marrow myelopoiesis in IL-12 treated mice. Unexpectedly, G-CSF also showed potentiation of antitumor effects of IL-12 in this melanoma model. The augmented antitumor activity of combined IL-12/G-CSF immunotherapy could result from the enhanced stimulation of macrophage NO production and cytotoxicity.

CONCLUSION

The simultaneous administration of IL-12 and G-CSF partially prevented suppression of bone marrow myelopoiesis in IL-12-treated mice. Moreover, treatment with these cytokines also results in potentiated antitumor effects in a murine melanoma model.

Augmented antitumor effects of combination therapy with interleukin-12, cisplatin, and tumor necrosis factor-alpha in a murine melanoma model

Interleukin-12 (IL-12) has demonstrated antitumor activity in many murine tumor models. However, toxic effects resulting from treatment with IL-12 have been also described. Combining IL-12 with other antineoplastic agents could potentiate its antitumor efficacy and, furthermore, could minimize its toxicity by reducing the doses necessary to achieve the antitumor activity. We examined in a murine melanoma model the efficacy of combination tumor chemo-immunotherapy based on administration of IL-12, cisplatin (CDDP), and tumor necrosis factor-alpha (TNF-alpha). In the current study pairs of: IL-12 + CDDP and IL-12 + TNF-alpha, showed stronger antitumor activity than either agent given alone. Furthermore, combination tumor therapy with IL-12 + CDDP + TNF-alpha was more effective at retarding local tumor growth than either IL-12 + CDDP, IL-12 + TNF-alpha or CDDP + TNF-alpha combination therapies. Our observations indicate that combining of CDDP with IL-12 and IL-12 with TNF-alpha as well as using the triple combination of CDDP, IL-12 and TNF-alpha could be beneficial in tumor therapy.

Antitumor effects of the combination immunotherapy with interleukin-12 and tumor necrosis factor alpha in mice

There is strong evidence that antitumor activity of interleukin-12 (IL-12) in vivo is mediated, in part, through interferon (IFN gamma) produced by IL-12-stimulated natural killer and T cells. Since IFN gamma and tumor necrosis factor alpha (TNF alpha) have been reported to synergize in antitumor effects in a number of models, we decided to examine whether the combined treatment with recombinant mouse IL-12 and recombinant human TNF alpha would produce similar effects. The efficacy of the combined IL-12/TNF alpha immunotherapy was evaluated in three tumor models in mice: B16F10 melanoma, Lewis lung (LL/2) carcinoma and L1 sarcoma. Intratumoral daily injections of 1 microgram IL-12 in combination with 5 micrograms TNF alpha into B16F10-melanoma-bearing mice resulted in a significant retardation of the tumor growth as compared with that in controls and in mice treated with either cytokine alone. Similar effects were obtained using 0.1 microgram IL-12 and 5 micrograms TNF alpha in LL/2 carcinoma and L1 sarcoma models. Antitumor activity against L1 sarcoma was still preserved when TNF alpha at a low dose (1 microgram) was combined with 0.1 microgram IL-12 and applied for a prolonged time. Potentiation of antitumor effects, which was observed in IL-12/TNF alpha-based immunotherapy, could result from at least three different mechanisms, partly related to stimulation of IFN gamma and TNF alpha production in treated mice: (a) direct cytostatic/cytotoxic effects on tumor cells, (b) induction of antitumor activity of macrophages, and (c) inhibition of blood vessel formation in the tumor. Our studies demonstrate that combination tumor immunotherapy with IL-12 and TNF alpha may be more effective than single-cytokine treatment, and suggest possible mechanisms by which IL-12 and TNF alpha may exert potentiated therapeutic effects against locally growing tumors.

Potentiation of the anti-tumor effect of actinomycin D by tumor necrosis factor alpha in mice: correlation between in vitro and in vivo results

The anti-tumor effects of actinomycin D (Act D) and recombinant human tumor necrosis factor (TNF)-alpha have been studied on 4 established murine tumor cell lines: MmB16 melanoma, Lewis lung (LL/2) carcinoma, L1 sarcoma and L1210 leukemia. During short-term incubation (24 hr) Act D produced dose-dependent cytostatic/cytotoxic effects against MmB16, LL/2 and L1 tumor cells but did not reduce the viability of these cells even at high concentration (10 micrograms/ml), below a threshold of 30-60%. However, L1210 leukemic cells were highly susceptible to Act D, and no viable cells were detected in cultures incubated with 1 microgram/ml of Act D. TNF-alpha alone, when used under the same culture conditions, had only a negligible effect on all cell lines tested. However, the combination of this cytokine with Act D produced synergistic cytotoxic effects against MmB16, LL/2 and L1 cells but not against L1210 leukemia cells. In an in vivo model of regional therapy in which tumor-bearing mice were treated with Act D and TNF-alpha, a correlation with in vitro results was observed. In mice bearing MmB16 melanoma, LL/2 carcinoma and L1 sarcoma, the most potent anti-tumor effects were observed in mice treated with Act D and TNF-alpha together. This treatment led to a delay of tumor growth and induced complete tumor regression in some cases. On the contrary, TNF-alpha did not enhance the effect of Act D in mice injected with L1210 leukemia cells. Our results show that TNF-alpha can potentiate the anti-tumor effects of Act D against tumors weakly susceptible to Act D and may be a useful adjuvant to chemotherapy in the local treatment of neoplasia.