Glen M. Miller

Liposome-Encapsulated Tumor Necrosis Factor-α Enhances the Effects of Radiation Against Human Colon Tumor Xenografts

Recent reports have shown that tumor necrosis factor-alpha (TNF-alpha) can augment the effects of radiation against certain tumor types. However, the high concentrations of intravenous infusion of TNF-alpha needed to cause tumor regression can induce many systemic side effects. The aims of this study were to determine if TNF-alpha encapsulated in sterically stabilized (Stealth, ALZA Corporation, Mountain View, CA), PEGylated liposomes (SL) augments the antitumor effects of radiation and to compare its efficacy and possible toxicity with free TNF-alpha in the LS174T human colon tumor xenograft model. Nude mice were injected subcutaneously (s.c.) with LS174T cells and treated intravenously (i.v.) with Stealth-liposomal TNF-alpha (SL-TNF-alpha) with and without radiation or TNF-alpha with or without radiation when tumor size was approximately 200 mm(3). In phase 1, a significant decrease (p = 0.047) in tumor growth was observed with radiation at day 21 but not with SL-TNF-alpha or free TNF-alpha alone. By the end of phase 1 (day 27) with continued treatments, the SL-TNF-alpha plus radiation group had significantly smaller tumors (p = 0.044) than those in the free TNF-alpha plus radiation group. In phase 2, where a similar tumor growth reduction pattern was observed, the addition of TNF-alpha to radiation, either as free protein or within SL, increased lymphocyte activation and natural killer (NK) cell numbers in both blood and spleen. The effect was generally more pronounced with SL-TNF-alpha. Systemic toxicity, based on hematologic analyses and body weight, was absent or minimal. Collectively, the data show that pretreatment with SL-TNF-alpha can enhance more effectively, and possibly more safely, the effects of radiation against human colon tumor xenografts than can free TNF-alpha and that the increased antitumor action may involve upregulation of lymphocytes.

Changes in the activation and reconstitution of lymphocytes resulting from total-body irradiation correlate with slowed tumor growth

Alterations in cytokine secretion, activation marker expression, and immune cell concentrations were investigated at sequential time points following delivery of total-body irradiation (TBI) to C57BL/6 mice (n = 64) in the Lewis lung tumor model. Significantly slower tumor growth was observed when a 3-Gy dose of TBI was administered 2 h prior to tumor implantation (p < 0.05). The antitumor effect was correlated with an increased CD4:CD8 T cell ratio and heightened leukocyte blastogenesis. TBI was also found to induce an expansion of natural killer (NK) cells in the blood and spleen of tumor-bearing animals 10 days after irradiation (2.8 × 106 NK cells/spleen in test mice compared to 8.9 × 105 NK cells/spleen in normal control animals). However, no significant differences were found in NK cell levels within the tumor tissue. Enhanced production of interleukin (IL)-12 and IL-18 from spleen supernatants was consistent with an augmentation of the NK cell response. Significant reductions in transforming growth factor-β1 (TGF-β1) and vascular endothelial growth factor, both of which are associated with immune suppression, were also noted. Furthermore, TBI induced changes in expression of CD25 and CD71 activation markers, suggesting that radiation may alter tumor surveillance. Taken together, the relative percentages and activation status of immune cell compartments support the conclusion that these TBI-induced changes function to slow tumor progression.

Radiation Enhances the Anti-tumor Effects of Vaccinia-p53 Gene Therapy in Glioma

The overall goal of this study was to analyze the effect and mechanism of radiation in combination with vaccinia viruses (VV) carrying the p53 gene against glioma. Comparison of two alternative treatments of cultured C6 (p53+) and 9L (p53−) rat glioma cells showed significantly reduced survival for both cell lines, especially 9L, when radiation was applied prior to virus versus radiation alone. High p53 protein expression mediated by VV-TK-p53 was measured in infected cells. Single modality treatment of C6 cells with psoralen and UV (PUV)-inactivated VV-TK-p53 (PUV-VV-TK-53) or radiation significantly decreased survival compared with PUV-inactivated L-15 (PUV-L-15) control virus. However, no difference was observed between radiation and combination treatments of C6 cells. In contrast, radiation followed by PUV-VV-TK-53 resulted in dramatic reduction of 9L cell viability, compared to single modality treatment. Flow cytometry analysis of Annexin-V-stained 9L cells showed that radiation and PUV-VV-TK-53 caused a significant decrease in live cells (17.2%) as compared to other treatments and control (61.6–98.3%). Apoptosis was observed in 37.2% of cells, while the range was 0.7–7.8% in other treatment groups; maximal p53 level was measured on day 7 post-infection. In athymic mice bearing C6 tumors, VV-TK-53 plus radiation in both single and multiple therapies resulted in significantly smaller tumors by day 30 compared to the agents given only once. Immunohistochemical analysis of tumor sections demonstrated p53 protein expression over 20 days after VV-TK-53 treatment. Analysis of blood and spleen cells of mice given multiple combination treatments showed significant splenomegaly, leukocytosis, and increased DNA synthesis and response to mitogen. Multiple combination treatments were also associated with significantly elevated natural killer and B cells in the spleen. There were no overt toxicities, although depression in red blood cell and thrombocyte parameters was noted. Collectively, the data demonstrate that radiation significantly improves the efficacy of VV-mediated tumor suppressor p53 therapy and may be a promising strategy for glioma treatment. Furthermore, the results support the conclusion that the mechanisms underlying the enhanced anti-tumor effect of combination treatment include apoptosis/necrosis and upregulation of innate immune defenses.

Proton Radiation and TNF-α/Bax Gene Therapy for Orthotopic C6 Brain Tumor in Wistar Rats

High-grade tumors of the brain remain virtually incurable with current therapeutic regimens, new approaches to augment existing therapies need to be explored. The major goal of this pilot study was to evaluate the feasibility of gene therapy using plasmid DNA encoding tumor necrosis factor-α and bax together with proton radiation in an immunocompetent animal model with orthotopic brain tumor. C6 glioma cells were stereotactically implanted into the left hemibrain of Wistar rats (day 0). On day 5, the appropriate groups received intratumoral pGL1-TNF-α and pGL1-Bax (10 μg each), parental plasmid pWS4 (20 μg), or PBS. Hemibrain proton irradiation (10 Gy, 90 MeV, single fraction) was delivered 18–20 hr later. Rats were euthanized when signs of illness appeared. In addition, a subset of animals from each group was euthanized on day 9 for immune and other assays. By day 9, 25%, 20%, and 10% of rats treated with PBS, pWS4, or pGL1-TNF-μ/pGL1-Bax, respectively, had been euthanized due to weight loss or other signs of illness, whereas all rats treated with pGL1-TNF-μ/pGL1-Bax + radiation or radiation alone were healthy (P<0.05). At this same time, the pGL1-TNF-μ/pGL1-Bax + radiation group had significantly elevated lymphocyte percentages (P<0.005 or less) and a relatively high level of lymphocytic infiltrate within tumors. Although the rats treated with pGL1-TNF-μ/pGL1-Bax had the highest levels of activated T helper (CD4+/CD71+) and T cytotoxic (CD8+/CD71+) cells, the values were not significantly different compared to the pWS4-injected control group. Splenocytes in all tumor cell-injected groups had higher mean values for DNA and protein synthesis compared to the non-tumor cell injected control group, whereas oxygen radical production by phagocytes was consistently higher in groups injected with plasmid or treated with radiation. Body, hemibrain, and spleen masses, white blood cell, red blood cell and platelet counts, hemoglobin, hematocrit, and transforming growth factor-β1 levels in plasma were similar among groups. The results demonstrate that treatment with pGL1-TNF-α/pGL1-Bax combined with proton hemibrain irradiation is safe under the conditions used. Overall, these data support further investigation of this unique combination therapy.

Evaluation of TNF-α/Bax Gene Therapy and Radiation against C6 Glioma Xenografts

Successful therapy of high-grade tumors of the brain is likely to require a combination of new therapeutic approaches. The major goal of the present study was to construct a plasmid-based bax gene vector (pGL1-Bax) and evaluate its expression in vitro and in vivo using athymic mice with subcutaneously growing C6 glioma. Preliminary experiments of efficacy and safety were also performed using pGL1-Bax alone and in combination with previously constructed pGL1-TNF-α, as well as with radiation. pGL1-Bax was expressed by C6 cells and was correlated with apoptosis, indicating that the construct and the bax protein were functional. Although intratumoral injections of pGL1-Bax alone, up to total doses of 450 μg, did not significantly affect tumor growth, consistently smaller tumors were obtained when pGL1-TNF-α plus pGL1-Bax were injected 16–18 hr prior to tumor irradiation. Furthermore, in mice with two tumors, one treated and one untreated, progression of the untreated tumor was delayed in the animals receiving all three modalities. No prohibitive toxicities were noted, based on mouse body weights and in vitro assays of blood and spleen. Significant increases in spleen mass, total leukocyte counts, percentage of granulocytes, spontaneous blastogenesis, and CD71-expressing B cells were primarily associated with tumor presence and not treatment type. Overall, the results are promising and suggest that TNF-α/Bax gene therapy may be beneficial against highly malignant tumors of the brain. To our knowledge, this is the first report of bax gene therapy used together with radiation in an in vivo glioma model.

Dose and timing of total-body irradiation mediate tumor progression and immunomodulation.

The major goal of this study was to examine the effects of total-body irradiation (TBI) on lung carcinoma progression and determine if changes in tumor growth could be correlated with radiation-induced alterations of immune system parameters. Lewis lung tumor cells were injected subcutaneously into syngeneic C57BL/6 mice that had been irradiated with a single 3.0 Gy dose of gamma-rays (60Co) at four time points either before or after tumor cell implantation. Subsequently, a second group of mice was irradiated 2 h prior to tumor injection with sequential doses of gamma-rays (0.46-2.66 Gy range). Assays were performed on blood and spleen from mice euthanized 16 days postimplantation. Tumor growth was consistently slower regardless of the timing of radiation exposure. However, dose of radiation influenced tumor growth delay. The preirradiated tumor-bearing mice had high CD4/CD8 T lymphocyte ratios along with increasing percentages of NKT cells in the blood supply with dose. Tumor-induced immunomodulation was also present, as evidenced by splenomegaly, low proliferative response to mitogens, and decreased spontaneous blastogenesis of leukocytes within the blood compared with normal values (P < or = 0.01). Anemia and thrombocytopenia were not observed with either tumor presence or irradiation. The present study demonstrates that a modest dose of TBI prior to tumor cell implantation resulted in a beneficial antitumor effect. A selective radiation-induced depletion of CD8+ T lymphocytes and changes in NKT cell percentages, correlated with findings from cytotoxicity assays, were indicative of a protumoricidal immune environment.