Anti-angiogenesis immunotherapy

New advances in the research of clinical treatment and novel anticancer agents in tumor angiogenesis

In 1971, Folkman proposed that tumors could be limited to very small sizes by blocking angiogenesis. Angiogenesis is the generation of new blood vessels from pre-existing vessels, considered to be one of the important processes in tumor growth and metastasis. Angiogenesis is a complex process regulated by various factors and involves many secreted factors and signaling pathways. Angiogenesis is important in the transport of oxygen and nutrients to the tumor during tumor development. Therefore, inhibition of angiogenesis has become an important strategy in the clinical management of many solid tumors. Combination therapies of angiogenesis inhibitors with radiotherapy and chemotherapy are often used in clinical practice. In this article, we will review common targets against angiogenesis, the most common and up-to-date anti-angiogenic drugs and clinical treatments in recent years, including active ingredients from chemical and herbal medicines.

PD-1 inhibitor combined with apatinib for advanced gastric or esophagogastric junction cancer: a retrospective study

BACKGROUND

Nivolumab and pembrolizumab were approved as immune checkpoint inhibitors for third-line treatment of advanced gastric or esophagogastric junction cancer (GC/EGJC) in 2017. However, immunotherapy monotherapy has low efficacy. Apatinib has been proven effective in advanced GC/EGJC. Numerous studies have shown that immunotherapy has a synergistic effect when combined with targeted drug therapy. Based on these facts and to assess the efficacy and safety of programmed death 1 (PD-1) inhibitor and apatinib as combination therapy in patients (pts) with unresectable locally advanced or metastatic GC/EGJC, a retrospective clinical research study was carried out.

METHODS

Pts (n=24) received PD-1 inhibitor and apatinib (250 mg once daily) as second- or third-line therapy in this observational, retrospective study. The primary objectives were efficacy and safety.

RESULTS

At data cut-off (December 31, 2019), 24 pts were enrolled. Of the 19 pts who were evaluable, the objective response rate (ORR) was 26.3% (5/19), the median progression-free survival (PFS) was 3.0 (95% CI: 1.3 to 4.7) months, and the median overall survival (OS) was not reached. Grade 3 or 4 treatment-related adverse events (TRAEs) occurred in 3 (15.8%) of the 19 pts. These adverse events (AEs) included pruritus, rash, hand-foot syndrome, and increased aspartate aminotransferase (AST) or alanine aminotransferase (ALT). No treatment-related deaths occurred.

CONCLUSIONS

Combination therapy of PD-1 inhibitor and apatinib showed encouraging clinical activity and demonstrated tolerable toxicity in pts with advanced GC/EGJC. Hence, our work provide rationale for the combination of PD-1 inhibitor and apatinib in advanced GC/EGJC.

IL-18 immunoadjuvanted xenogeneic canine MMP-7 DNA vaccine overcomes immune tolerance and supresses the growth of murine mammary tumor

The development of the tumorigenesis and angiogenesis through proteolytic cleavage of extracellular matrix protein and basement membranes is promoted by Matrix metelloproteinases-7 (MMP-7). Consequently, MMP-7 is presumed as potential target for mammary cancer immunotherapy. However, MMP-7 is an endogenous tumor associated antigen (TAA); therefore, immunization is challenging. In current study, a potent anti-tumor immune response has been elicited through recombinant bivalent plasmid pVIVO2.IL18.cMMP7 which subside the highly metastatic 4 T1 cell line induced mammary tumors and efficiently negate the existing challenge of using MMP-7 as immunotherapeutic target. Balb/c mice were immunized with canine MMP-7 (cMMP-7) using interleukine-18 (IL-18), as an immunoadjuvant, to explore the potential of the combination regarding elicitation of a potent anti-tumor immune response. Mice vaccinated with pVIVO2.IL18.cMMP7 DNA plasmid reduced the tumor growth significantly along with augmentation of the immune response to fight against tumor antigen as depicted by substantial enrichment of CD4+ and CD8+ population in splenocytes, infiltration of immune system cells in tumor tissue and enhanced survival time of mice. Further, splenocyte supernatant examination of the cytokines revealed that Th1 cytokines (IFN-γ and IL-2) were remarkably up-regulated demonstrating the stimulation of cell-mediated immune response. Thus the current observations vividly portray that administration of xenogeneic MMP-7 DNA vaccine bypasses the tolerance barrier.

Antiangiogenic Vascular Endothelial Growth Factor-Blocking Peptides Displayed on the Capsid of an Infectious Oncolytic Parvovirus: Assembly and Immune Interactions

As many tumor cells synthetize vascular endothelial growth factors (VEGF) that promote neo-vascularization and metastasis, frontline cancer therapies often administer anti-VEGF (α-VEGF) antibodies. To target the oncolytic parvovirus minute virus of mice (MVM) to the tumor vasculature, we studied the functional tolerance, evasion of neutralization, and induction of α-VEGF antibodies of chimeric viruses in which the footprint of a neutralizing monoclonal antibody within the 3-fold capsid spike was replaced by VEGF-blocking peptides: P6L (PQPRPL) and A7R (ATWLPPR). Both peptides allowed viral genome replication and nuclear translocation of chimeric capsid subunits. MVM-P6L efficiently propagated in culture, exposing the heterologous peptide on the capsid surface, and evaded neutralization by the anti-spike monoclonal antibody. In contrast, MVM-A7R yielded low infectious titers and was poorly recognized by an α-A7R monoclonal antibody. MVM-A7R showed a deficient assembly pattern, suggesting that A7R impaired a transitional configuration that the subunits must undergo in the 3-fold axis to close up the capsid shell. The MVM-A7R chimeric virus consistently evolved in culture into a mutant carrying the P6Q amino acid substitution within the A7R sequence, which restored normal capsid assembly and infectivity. Consistent with this finding, anti-native VEGF antibodies were induced in mice by a single injection of MVM-A7R empty capsids, but not by MVM-A7R virions. This fundamental study provides insights to endow an infectious parvovirus with immune antineovascularization and evasion capacities by replacing an antibody footprint in the capsid 3-fold axis with VEGF-blocking peptides, and it also illustrates the evolutionary capacity of single-stranded DNA (ssDNA) viruses to overcome engineered capsid structural restrictions.IMPORTANCE Targeting the VEGF signaling required for neovascularization by vaccination with chimeric capsids of oncolytic viruses may boost therapy for solid tumors. VEGF-blocking peptides (VEbp) engineered in the capsid 3-fold axis endowed the infectious parvovirus MVM with the ability to induce α-VEGF antibodies without adjuvant and to evade neutralization by MVM-specific antibodies. However, these properties may be compromised by structural restraints that the capsid imposes on the peptide configuration and by misassembly caused by the heterologous peptides. Significantly, chimeric MVM-VEbp resolved the structural restrictions by selecting mutations within the engineered peptides that restored efficient capsid assembly. These data show the promise of antineovascularization vaccines using chimeric VEbp-icosahedral capsids of oncolytic viruses but also raise safety concerns regarding the genetic stability of manipulated infectious parvoviruses in cancer and gene therapies.

Combined antiangiogenic and anti-PD-L1 therapy stimulates tumor immunity through HEV formation

Inhibitors of VEGF (vascular endothelial growth factor)/VEGFR2 (vascular endothelial growth factor receptor 2) are commonly used in the clinic, but their beneficial effects are only observed in a subset of patients and limited by induction of diverse relapse mechanisms. We describe the up-regulation of an adaptive immunosuppressive pathway during antiangiogenic therapy, by which PD-L1 (programmed cell death ligand 1), the ligand of the negative immune checkpoint regulator PD-1 (programmed cell death protein 1), is enhanced by interferon-γ-expressing T cells in distinct intratumoral cell types in refractory pancreatic, breast, and brain tumor mouse models. Successful treatment with a combination of anti-VEGFR2 and anti-PD-L1 antibodies induced high endothelial venules (HEVs) in PyMT (polyoma middle T oncoprotein) breast cancer and RT2-PNET (Rip1-Tag2 pancreatic neuroendocrine tumors), but not in glioblastoma (GBM). These HEVs promoted lymphocyte infiltration and activity through activation of lymphotoxin β receptor (LTβR) signaling. Further activation of LTβR signaling in tumor vessels using an agonistic antibody enhanced HEV formation, immunity, and subsequent apoptosis and necrosis in pancreatic and mammary tumors. Finally, LTβR agonists induced HEVs in recalcitrant GBM, enhanced cytotoxic T cell (CTL) activity, and thereby sensitized tumors to antiangiogenic/anti-PD-L1 therapy. Together, our preclinical studies provide evidence that anti-PD-L1 therapy can sensitize tumors to antiangiogenic therapy and prolong its efficacy, and conversely, antiangiogenic therapy can improve anti-PD-L1 treatment specifically when it generates intratumoral HEVs that facilitate enhanced CTL infiltration, activity, and tumor cell destruction.

Trimming the Vascular Tree in Tumors: Metabolic and Immune Adaptations

Angiogenesis, the formation of new blood vessels, has become a well-established hallmark of cancer. Its functional importance for the manifestation and progression of tumors has been further validated by the beneficial therapeutic effects of angiogenesis inhibitors, most notably ones targeting the vascular endothelial growth factor (VEGF) signaling pathways. However, with the transient and short-lived nature of the patient response, it has become evident that tumors have the ability to adapt to the pressures of vascular growth restriction. Several escape mechanisms have been described that adapt tumors to therapy-induced low-oxygen tension by either reinstating tumor growth by vascular rebound or by altering tumor behavior without the necessity to reinitiate revascularization. We review here two bypass mechanisms that either instigate angiogenic and immune-suppressive polarization of intratumoral innate immune cells to facilitate VEGF-independent angiogenesis or enable metabolic adaptation and reprogramming of endothelial cells and tumor cells to adapt to low-oxygen tension.

Tumor rim cells: From resistance to vascular targeting agents to complete tumor ablation

Current vascular targeting strategies pursue two main goals: anti-angiogenesis agents aim to halt sprouting and the formation of new blood vessels, while vascular disrupting agents along with coaguligands seek to compromise blood circulation in the vessels. The ultimate goal of such therapies is to deprive tumor cells out of oxygen and nutrients long enough to succumb cancer cells to death. Most of vascular targeting agents presented promising therapeutic potential, but the final goal which is cure is rarely achieved. Nevertheless, in both preclinical and clinical settings, tumors tend to grow back, featuring a highly invasive, metastatic, and extremely resistant form. This review highlights the critical significance of tumor rim cells as the main factor, determining therapy success with vascular targeting agents. We present an overview of different single and combination treatments with vascular targeting agents that enable efficient targeting of tumor rim cells and long-lasting tumor cure. Understanding the nature of tumor rim cells, how they establish, how they manage to survive of vascular targeting agents, and how they contribute in tumor refractoriness, may open new avenues to the development of beneficial strategies, capable to eliminate residual rim cells, and enable tumor ablation once and forever.

Targeted vaccination against the bevacizumab binding site on VEGF using 3D-structured peptides elicits efficient antitumor activity

Therapeutic targeting of the VEGF signaling axis by the VEGF-neutralizing monoclonal antibody bevacizumab has clearly demonstrated clinical benefit in cancer patients. To improve this strategy using a polyclonal approach, we developed a vaccine targeting VEGF using 3D-structured peptides that mimic the bevacizumab binding site. An in-depth study on peptide optimization showed that the antigen's 3D structure is essential to achieve neutralizing antibody responses. Peptide 1 adopts a clear secondary, native-like structure, including the typical cysteine-knot fold, as evidenced by CD spectroscopy. Binding and competition studies with bevacizumab in ELISA and surface plasmon resonance analysis revealed that peptide 1 represents the complete bevacizumab binding site, including the hairpin loop (β5-turn-β6) and the structure-supporting β2-α2-β3 loop. Vaccination with peptide 1 elicited high titers of cross-reactive antibodies to VEGF, with potent neutralizing activity. Moreover, vaccination-induced antisera displayed strong angiostatic and tumor-growth-inhibiting properties in a preclinical mouse model for colorectal carcinoma, whereas antibodies raised with peptides exclusively encompassing the β5-turn-β6 loop (peptides 15 and 20) did not. Immunization with peptide 1 or 7 (murine analog of 1) in combination with the potent adjuvant raffinose fatty acid sulfate ester (RFASE) showed significant inhibition of tumor growth in the B16F10 murine melanoma model. Based on these data, we conclude that this vaccination technology, which is currently being investigated in a phase I clinical trial (NCT02237638), can potentially outperform currently applied anti-VEGF therapeutics.

Endostatin enhances antitumor effect of tumor antigen-pulsed dendritic cell therapy in mouse xenograft model of lung carcinoma

Objective

To investigate the antitumor effect of endostatin combined with tumor antigen-pulsed dendritic cell (DC)-T cell therapy on lung cancer.

Methods

Transplanted Lewis lung cancer (LLC) models of C57BL/6 mice were established by subcutaneous injection of LLC cells in left extremity axillary. Tumor antigen-pulsed DC-T cells from spleen cells and bone of mice were cultured in vitro. Tumor-bearing mice were randomly divided into three groups, including DC-T+endostatin group, DC-T group, and phosphate-buffered saline (PBS) control group. Microvessel density (MVD) of tumor tissue in tumor-bearing mice was determined by immunohistochemistry (IHC). The expressions of vascular endothelial growth factor (VEGF) and hypoxia-inducible factor-1α (HIF-1α) were determined by Western blotting and IHC staining. The proportions of CD8+ T cells, mature dendritic cells (mDC), tumor-associated macrophages [TAM (M1/M2)], and myeloid-derived suppressor cells (MDSC) in suspended cells of tumor tissue were determined by flow cytometry. The expressions of interleukin (IL)-6, IL-10, IL-17, transforming growth factor-β (TGF-β) and interferon-γ (IFN-γ) in suspended cells of tumor tissue were detected by enzyme-linked immune sorbent assay (ELISA).

Results

DC-T cells combined with endostatin remarkably suppressed tumor growth. MVD of mice in DC-T+endostatin group was significantly lower than that of the control group and DC-T monotherapy group. The expressions of VEGF, IL-6 and IL-17 in tumors were markedly decreased, but IFN-γ and HIF-1α increased after treating with DC-T cells combined with endostatin, compared to control group and DC-T group. In the DC-T+endostatin group, the proportions of MDSC and TAM (M2 type) were significantly decreased, mDC and TAM (M1 type) were up-regulated, and CD8+ T cells were recruited to infiltrate tumors, in contrast to PBS control and DC-T monotherapy. DC-T cells combined with endostatin potently reduced the expressions of IL-6, IL-10, TGF-β and IL-17 in tumor tissue, and enhanced the expression of IFN-γ.

Conclusions

The study indicated the synergic antitumor effects between endostatin and tumor antigen-pulsed DC-T cells, which may be a prospective therapy strategy to achieve potent antitumor effects on lung cancer.

Therapeutic vaccination against fibronectin ED-A attenuates progression of metastatic breast cancer

Therapeutic vaccination targeting self-molecules is an attractive alternative to monoclonal antibody-based therapies for cancer and various inflammatory diseases. However, development of cancer vaccines targeting self-molecules has proven difficult. One complicating factor is that tumor cells have developed strategies to escape recognition by the immune system. Antigens specifically expressed by the tumor vasculature can therefore provide alternative targets. The alternatively spliced extra domain-A and B (ED-A and ED-B) of fibronectin are expressed during vasculogenesis in the embryo, but essentially undetectable under normal conditions in the adult. However, these domains are re-expressed during tumor angiogenesis and matrix remodeling, which renders them highly interesting for targeted cancer therapies.

Using the MMTV-PyMT transgenic model of metastatic mammary carcinoma, we show that tumor burden can be significantly decreased by immunization against ED-A in a therapeutic setting. Furthermore, we found that in mice carrying anti-ED-A antibodies the number of metastases was reduced. ED-A immunization increased infiltration of macrophages and compromised tumor blood vessel function. These findings implicate an attack of the tumor vasculature by the immune system, through a polyclonal antibody response. We conclude that tumor vascular antigens are promising candidates for development of therapeutic vaccines targeting growth of primary tumors as well as disseminated disease.

Intratumoral myeloid cells regulate responsiveness and resistance to antiangiogenic therapy

Antiangiogenic therapy is commonly used in the clinic, but its beneficial effects are short-lived, leading to tumor relapse within months. Here, we found that the efficacy of angiogenic inhibitors targeting the VEGF/VEGFR pathway was dependent on induction of the angiostatic and immune-stimulatory chemokine CXCL14 in mouse models of pancreatic neuroendocrine and mammary tumors. In response, tumors reinitiated angiogenesis and immune suppression by activating PI3K signaling in all CD11b+ cells, rendering tumors nonresponsive to VEGF/VEGFR inhibition. Adaptive resistance was also associated with an increase in Gr1+CD11b+ cells, but targeting Gr1+ cells was not sufficient to further sensitize angiogenic blockade because tumor-associated macrophages (TAMs) would compensate for the lack of such cells and vice versa, leading to an oscillating pattern of distinct immune-cell populations. However, PI3K inhibition in CD11b+ myeloid cells generated an enduring angiostatic and immune-stimulatory environment in which antiangiogenic therapy remained efficient.

Vaccines targeting self-antigens: mechanisms and efficacy-determining parameters

We recently showed that it is possible to compromise tumor vessel function and, as a consequence, suppress growth of aggressive preclinical tumors by immunizing against the tumor vascular markers extra domain-A (ED-A) or -B (ED-B) of fibronectin, using a fusion protein consisting of the ED-A or ED-B peptide fused to bacterial thioredoxin. To address the mechanism behind fusion protein-induced immunization and the specific contribution of the different vaccine constituents to elicit an anti-self-antibody response, we immunized mice with modified or unmodified self-antigens, combined with different adjuvant components, and analyzed antibody responses by ELISA in sera. Several essential requirements to circumvent tolerance were identified: (1) a potent pattern recognition receptor agonist like an oligonucleotide containing unmethylated cytosine and guanine dinucleotides (CpG); (2) a depot adjuvant to keep the CpG at the site of injection; and (3) the presence of foreign sequences in the vaccine protein. Lack of either of these factors abolished the anti-self-response (P = 0.008). In mice genetically deficient for type I IFN signaling, there was a 60% reduction in the anti-self-response compared with wild-type (P = 0.011), demonstrating a key role of this pathway in CpG-induced circumvention of self-tolerance. Identification of these mechanistic requirements to generate a potent anti-self-immune response should significantly aid the design of efficient, specific, and safe therapeutic cancer vaccines.

Intertwined regulation of angiogenesis and immunity by myeloid cells

Angiogenesis is a hallmark of cancer because its induction is indispensable to fuel an expanding tumor. The tumor microenvironment contributes to tumor vessel growth, and distinct myeloid cells recruited by the tumor have been shown not only to support angiogenesis but also to foster an immune suppressive environment that supports tumor expansion and progression. Recent findings suggest that the intertwined regulation of angiogenesis and immune modulation can offer therapeutic opportunities for the treatment of cancer. We review the mechanisms by which distinct myeloid cell populations contribute to tumor angiogenesis, discuss current approaches in the clinic that are targeting both angiogenic and immune suppressive pathways, and highlight important areas of future research.

Angiogenic cytokines are antibody targets during graft-versus-leukemia reactions

PURPOSE

The graft-versus-leukemia (GVL) reaction is an important example of immune-mediated tumor destruction. A coordinated humoral and cellular response accomplishes leukemia cell killing, but the specific targets remain largely uncharacterized. To learn more about the antigens that elicit antibodies during GVL reactions, we analyzed patients with advanced myelodysplasia (MDS) and acute myelogenous leukemia (AML) who received an autologous, granulocyte-macrophage colony-stimulating factor (GM-CSF)-secreting tumor cell vaccine early after allogeneic hematopoietic stem cell transplantation (HSCT).

EXPERIMENTAL DESIGN

A combination of tumor-derived cDNA expression library screening, protein microarrays, and antigen-specific ELISAs were used to characterize sera obtained longitudinally from 15 patients with AML/MDS who were vaccinated early after allogeneic HSCT.

RESULTS

A broad, therapy-induced antibody response was uncovered, which primarily targeted intracellular proteins that function in growth, transcription/translation, metabolism, and homeostasis. Unexpectedly, antibodies were also elicited against eight secreted angiogenic cytokines that play critical roles in leukemogenesis. Antibodies to the angiogenic cytokines were evident early after therapy, and in some patients manifested a diversification in reactivity over time. Patients that developed antibodies to multiple angiogenic cytokines showed prolonged remission and survival.

CONCLUSIONS

These results reveal a potent humoral response during GVL reactions induced with vaccination early after allogeneic HSCT and raise the possibility that antibodies, in conjunction with natural killer cells and T lymphocytes, may contribute to immune-mediated control of myeloid leukemias.

Vaccination approach to anti-angiogenic treatment of cancer

Improvement of patient survival by anti-angiogenic therapy has proven limited. A vaccination approach inducing an immune response against the tumor vasculature combines the benefits of immunotherapy and anti-angiogenesis, and may overcome the limitations of current anti-angiogenic drugs. Strategies to use whole endothelial cell vaccines and DNA- or protein vaccines against key players in the VEGF signaling axis, as well as specific markers of tumor endothelial cells, have been tested in preclinical studies. Current clinical trials are now testing the promise of this specific anti-cancer vaccination approach. This review will highlight the state-of-the-art in this exciting field of cancer research.

The multifaceted activity of VEGF in angiogenesis - Implications for therapy responses

Vascular endothelial growth factor (VEGF) is a key growth factor driving angiogenesis (i.e. the formation of new blood vessels) in health and disease. Pharmacological blockade of VEGF signaling to inhibit tumor angiogenesis is clinically approved but the survival benefit is limited as patients invariably acquire resistance. This is partially mediated by the intrinsic flexibility of tumor cells to adapt to VEGF-blockade. However, it has become clear that tumor stromal cells also contribute to the resistance. Originally, VEGF was thought to specifically target endothelial cells (ECs) but it is now clear that many stromal cells also respond to VEGF signaling, making anti-VEGF therapy more complex than initially anticipated. A more comprehensive understanding of the complex responses of stromal cells to VEGF-blockade might inform the design of improved anti-angiogenic agents.