Andreas G. Niethammer

A DNA vaccine against VEGF receptor 2 prevents effective angiogenesis and inhibits tumor growth

Tumor cells are elusive targets for immunotherapy due to their heterogeneity and genetic instability. Here we describe a novel, oral DNA vaccine that targets stable, proliferating endothelial cells in the tumor vasculature rather than tumor cells. Targeting occurs through upregulated vascular-endothelial growth factor receptor 2 (FLK-1) of proliferating endothelial cells in the tumor vasculature. This vaccine effectively protected mice from lethal challenges with melanoma, colon carcinoma and lung carcinoma cells and reduced growth of established metastases in a therapeutic setting. CTL-mediated killing of endothelial cells indicated breaking of peripheral immune tolerance against this self antigen, resulting in markedly reduced dissemination of spontaneous and experimental pulmonary metastases. Angiogenesis in the tumor vasculature was suppressed without impairment of fertility, neuromuscular performance or hematopoiesis, albeit with a slight delay in wound healing. Our strategy circumvents problems in targeting of genetically unstable tumor cells. This approach may provide a new strategy for the rational design of cancer therapies.

Targeting tumor-associated fibroblasts improves cancer chemotherapy by increasing intratumoral drug uptake

Tumor-associated fibroblasts are key regulators of tumorigenesis. In contrast to tumor cells, which are genetically unstable and mutate frequently, the presence of genetically more stable fibroblasts in the tumor-stromal compartment makes them an optimal target for cancer immunotherapy. These cells are also the primary source of collagen type I, which contributes to decreased chemotherapeutic drug uptake in tumors and plays a significant role in regulating tumor sensitivity to a variety of chemotherapies. To specifically kill tumor-associated fibroblasts, we constructed an oral DNA vaccine targeting fibroblast activation protein (FAP), which is specifically overexpressed by fibroblasts in the tumor stroma. Through CD8+ T cell-mediated killing of tumor-associated fibroblasts, our vaccine successfully suppressed primary tumor cell growth and metastasis of multidrug-resistant murine colon and breast carcinoma. Furthermore, tumor tissue of FAP-vaccinated mice revealed markedly decreased collagen type I expression and up to 70% greater uptake of chemotherapeutic drugs. Most importantly, pFap-vaccinated mice treated with chemotherapy showed a 3-fold prolongation in lifespan and marked suppression of tumor growth, with 50% of the animals completely rejecting a tumor cell challenge. This strategy opens a new venue for the combination of immuno- and chemotherapies.

T cell homeostatic proliferation elicits effective antitumor autoimmunity

Development of tumor immunotherapies focuses on inducing autoimmune responses against tumor-associated self-antigens primarily encoded by normal, unmutated genes. We hypothesized that such responses could be elicited by T cell homeostatic proliferation in the periphery, involving expansion of T cells recognizing self-MHC/peptide ligands. Herein, we demonstrate that sublethally irradiated lymphopenic mice transfused with autologous or syngeneic T cells showed tumor growth inhibition when challenged with melanoma or colon carcinoma cells. Importantly, the antitumor response depended on homeostatic expansion of a polyclonal T cell population within lymph nodes. This response was effective even for established tumors, was characterized by CD8(+) T cell-mediated tumor-specific cytotoxicity and IFN-gamma production, and was associated with long-term memory. The results indicate that concomitant induction of the physiologic processes of homeostatic T cell proliferation and tumor antigen presentation in lymph nodes triggers a beneficial antitumor autoimmune response.

Randomized Phase III Trial of Temsirolimus Versus Sorafenib As Second-Line Therapy After Sunitinib in Patients With Metastatic Renal Cell Carcinoma

PURPOSE This international phase III trial (Investigating Torisel As Second-Line Therapy [INTORSECT]) compared the efficacy of temsirolimus (mammalian target of rapamycin inhibitor) and sorafenib (vascular endothelial growth factor receptor [VEGFR] tyrosine kinase inhibitor) as second-line therapy in patients with metastatic renal cell carcinoma (mRCC) after disease progression on sunitinib. PATIENTS AND METHODS In total, 512 patients were randomly assigned 1:1 to receive intravenous temsirolimus 25 mg once weekly (n = 259) or oral sorafenib 400 mg twice per day (n = 253), with stratification according to duration of prior sunitinib therapy (≤ or > 180 days), prognostic risk, histology (clear cell or non-clear cell), and nephrectomy status. The primary end point was progression-free survival (PFS) by independent review committee assessment. Safety, objective response rate (ORR), and overall survival (OS) were secondary end points. RESULTS Primary analysis revealed no significant difference between treatment arms for PFS (stratified hazard ratio [HR], 0.87; 95% CI, 0.71 to 1.07; two-sided P = .19) or ORR. Median PFS in the temsirolimus and sorafenib arms were 4.3 and 3.9 months, respectively. There was a significant OS difference in favor of sorafenib (stratified HR, 1.31; 95% CI, 1.05 to 1.63; two-sided P = .01). Median OS in the temsirolimus and sorafenib arms was 12.3 and 16.6 months, respectively. Safety profiles of both agents were consistent with previous studies. CONCLUSION In patients with mRCC and progression on sunitinib, second-line temsirolimus did not demonstrate a PFS advantage compared with sorafenib. The longer OS observed with sorafenib suggests sequenced VEGFR inhibition may benefit patients with mRCC.

A dual-function DNA vaccine encoding carcinoembryonic antigen and CD40 ligand trimer induces T cell-mediated protective immunity against colon cancer in carcinoembryonic antigen-transgenic mice.

A carcinoembryonic Ag (CEA)-based DNA vaccine encoding both CEA and CD40 ligand trimer achieved effective tumor-protective immunity against murine colon carcinoma in CEA-transgenic mice by activating both naive T cells and dendritic cells. Peripheral T cell tolerance to CEA was broken in a prophylactic model by this novel, dual-function DNA vaccine, whose efficacy was further enhanced by boosts with a recombinant Ab-IL-2 fusion protein (huKS1/4-IL-2). These conclusions are supported by four lines of evidence. First, a lethal challenge of MC38-CEA-KS Ag murine colon carcinoma cells was for the first time completely rejected in 100% of experimental animals treated by oral gavage of this DNA vaccine carried by attenuated Salmonella typhimurium, followed by five boosts with huKS1/4-IL-2. Second, specific activation of dendritic cells was indicated by their marked up-regulation in expression of costimulatory molecules B7.1 (CD80), B7.2 (CD86), and ICAM-1. Third, a decisive increase over control values was observed in both MHC class I Ag-restricted cytotoxicity of CTLs from successfully vaccinated mice and secretion of proinflammatory cytokines IFN-γ and IL-12. Fourth, activation of CTLs was augmented, as indicated by up-regulation of activity markers LFA-1, CD25, CD28, and CD69. Taken together, these results suggest that a dual-function DNA vaccine encoding CEA and CD40 ligand trimer combined with tumor-targeted IL-2 may be a promising strategy for the rational development of DNA-based cancer vaccines for future clinical applications.

Randomized Phase III Trial of Temsirolimus and Bevacizumab Versus Interferon Alfa and Bevacizumab in Metastatic Renal Cell Carcinoma: INTORACT Trial

PURPOSE To prospectively determine the efficacy of combination therapy with temsirolimus plus bevacizumab versus interferon alfa (IFN) plus bevacizumab in metastatic renal cell carcinoma (mRCC). PATIENTS AND METHODS In a randomized, open-label, multicenter, phase III study, patients with previously untreated predominantly clear-cell mRCC were randomly assigned, stratified by prior nephrectomy and Memorial Sloan-Kettering Cancer Center prognostic group, to receive the combination of either temsirolimus (25 mg intravenously, weekly) or IFN (9 MIU subcutaneously thrice weekly) with bevacizumab (10 mg/kg intravenously, every 2 weeks). The primary end point was independently assessed progression-free survival (PFS). RESULTS Median PFS in patients treated with temsirolimus/bevacizumab (n = 400) versus IFN/bevacizumab (n = 391) was 9.1 and 9.3 months, respectively (hazard ratio [HR], 1.1; 95% CI, 0.9 to 1.3; P = .8). There were no significant differences in overall survival (25.8 ν 25.5 months; HR, 1.0; P = .6) or objective response rate (27.0% ν 27.4%) with temsirolimus/bevacizumab versus IFN/bevacizumab, respectively. Patients receiving temsirolimus/bevacizumab reported significantly higher overall mean scores in the Functional Assessment of Cancer Therapy-Kidney Symptom Index (FKSI) -15 and FKSI-Disease Related Symptoms subscale compared with IFN/bevacizumab (indicating improvement); however, no differences in global health outcome measures were observed. Treatment-emergent all-causality grade ≥ 3 adverse events more common (P < .001) with temsirolimus/bevacizumab were mucosal inflammation, stomatitis, hypophosphatemia, hyperglycemia, and hypercholesterolemia, whereas neutropenia was more common with IFN/bevacizumab. Incidence of pneumonitis with temsirolimus/bevacizumab was 4.8%, mostly grade 1 or 2. CONCLUSION Temsirolimus/bevacizumab combination therapy was not superior to IFN/bevacizumab for first-line treatment in clear-cell mRCC.

Multicenter, Phase II Study of Axitinib, a Selective Second-Generation Inhibitor of Vascular Endothelial Growth Factor Receptors 1, 2, and 3, in Patients with Metastatic Melanoma

Purpose: This multicenter, open-label, phase II study evaluated the safety and clinical activity of axitinib, a potent and selective second-generation inhibitor of vascular endothelial growth factor receptors (VEGFR)–1, 2, and 3, in patients with metastatic melanoma. Experimental Design: Thirty-two patients with a maximum of one prior systemic therapy received axitinib at a starting dose of 5 mg twice daily. The primary endpoint was objective response rate. Results: Objective response rate was 18.8% [95% confidence interval (CI), 7.2–36.4], comprising one complete and five partial responses with a median response duration of 5.9 months (95% CI, 5.0–17.0). Stable disease at 16 weeks was noted in six patients (18.8%), with an overall clinical benefit rate of 37.5%. Six-month progression-free survival rate was 33.9%, 1-year overall survival rate was 28.1%, and median overall survival was 6.6 months (95% CI, 5.2–9.0). The most frequently (>15%) reported nonhematologic, treatment-related adverse events were fatigue, hypertension, hoarseness, and diarrhea. Treatment-related fatal bowel perforation, a known class effect, occurred in one patient. Axitinib selectively decreased plasma concentrations of soluble VEGFR (sVEGFR)-2 and sVEGFR-3 compared with soluble stem cell factor receptor (sKIT). No significant association was noted between plasma levels of axitinib and response. However, post hoc analyses indicated potential relationships between efficacy endpoints and diastolic blood pressure of 90 mm Hg or higher as well as baseline serum lactate dehydrogenase levels. Conclusions: Axitinib was well tolerated, showed a selective VEGFR-inhibitory profile, and showed single-agent activity in metastatic melanoma. Further evaluations of axitinib, alone and combined with chemotherapy, are ongoing. Clin Cancer Res; 17(23); 7462–9. ©2011 AACR.

An oral DNA vaccine against human carcinoembryonic antigen (CEA) prevents growth and dissemination of Lewis lung carcinoma in CEA transgenic mice

A DNA vaccine encoding human carcinoembryonic antigen (CEA) broke peripheral T-cell tolerance toward this tumor self-antigen expressed by Lewis lung carcinoma stably transduced with CEA in C57BL/6J mice transgenic for CEA. This vaccine, delivered by oral gavage with an attenuated strain of Salmonella typhimurium (SL7207), and boosted with an antibody-IL2 fusion protein, induced tumor-protective immunity mediated by MHC class I antigen-restricted CD8(+) T cells, resulting in eradication of subcutaneous tumors in 100% of mice and prevention of experimental pulmonary metastases in 75% of experimental animals. Both CTL and antigen-presenting dendritic cells were activated as indicated by a decisive increase in their respective activation markers CD2, CD25, CD28 as well as CD48 and CD80. The antitumor effects of this CEA-based DNA vaccine obtained in prophylactic settings, suggest that this approach could lead to the rational design of effective treatment modalities for human lung cancer.

Vaccination Against VEGFR2 Attenuates Initiation and Progression of Atherosclerosis

Objective—Vascular endothelial growth factor receptor 2 (VEGFR2)–overexpressing cells may form an interesting target for the treatment of atherosclerosis because of their involvement in processes that contribute to this disease, such as angiogenesis. Methods and Results—We vaccinated mice against VEGFR2 by an orally administered DNA vaccine, comprising a plasmid, encoding murine VEGFR2, carried by live attenuated Salmonella typhimurium. This vaccine induces cellular immunity against cells that overexpress VEGFR2. Vaccination of hypercholesterolemic mice against VEGFR2 resulted in a marked induction of CD8+ cytotoxic T cells specific for VEGFR2 and led to an inhibition of angiogenesis in a hindlimb ischemia model. Interestingly, VEGFR2 vaccination attenuated the progression of preexisting advanced atherosclerotic lesions in the brachiocephalic artery of apoE−/− mice. Furthermore, VEGFR2 vaccination strongly reduced the initiation of collar-induced atherosclerosis in the carotid arteries of LDLr−/− mice. In addition, denudation of the carotid artery, as a model for postinterventional lesion formation, resulted in delayed endothelial replacement and significantly increased neointima formation on VEGFR2 vaccination. Conclusions—These data indicate the prominent role of VEGFR2+ cells in cardiovascular diseases and show that induction of cellular immunity against atherosclerosis-associated cells by means of DNA vaccination may contribute to the development of novel therapies against atherosclerosis.

Oral DNA vaccines target the tumor vasculature and microenvironment and suppress tumor growth and metastasis

Summary: Four novel oral DNA vaccines provide protection against melanoma, colon, breast, and lung carcinoma in mouse models. Vaccines are delivered by attenuated Salmonella typhimurium to secondary lymphoid organs and respectively target vascular endothelial growth factor receptor‐2, transcription factor Fos‐related antigen‐1, anti‐apoptosis protein survivin and Legumain, an asparaginyl endopeptidase specifically overexpressed on tumor‐associated macrophages (TAMs) in the tumor microenvironment (TME). These vaccines are all capable of inducing potent cell‐mediated protective immunity against self‐antigens, resulting in marked suppression of tumor growth and dissemination. Key mechanisms induced by these DNA vaccines include efficient suppression of angiogenesis in the tumor vasculature and marked activation of cytotoxic T cells, natural killer cells, and antigen‐presenting dendritic cells. The vaccine targeting Legumain establishes the new paradigm whereby a reduction in the density of TAMs in the TME decreases the release of factors potentiating tumor growth and angiogenesis. This, in turn, remodels the TME and decreases its immunosuppressive milieu and thereby potentiates the DNA vaccines ability to effectively suppress tumor cell proliferation, vascularization, and metastasis. It is anticipated that such research efforts will lead to novel DNA‐based vaccines that will be effective for the treatment of cancer.