Monoclonal Antibody TB-403: A First-in-Human, Phase I, Double-Blind, Dose Escalation Study Directed Against Placental Growth Factor in Healthy Male Subjects

FLT1 activation in cancer cells promotes PARP-inhibitor resistance in breast cancer

Acquired resistance to PARP inhibitors (PARPi) remains a treatment challenge for BRCA1/2-mutant breast cancer that drastically shortens patient survival. Although several resistance mechanisms have been identified, none have been successfully targeted in the clinic. Using new PARPi-resistance models of Brca1- and Bard1-mutant breast cancer generated in-vivo, we identified FLT1 (VEGFR1) as a driver of resistance. Unlike the known role of VEGF signaling in angiogenesis, we demonstrate a novel, non-canonical role for FLT1 signaling that protects cancer cells from PARPi in-vivo through a combination of cell-intrinsic and cell-extrinsic pathways. We demonstrate that FLT1 blockade suppresses AKT activation, increases tumor infiltration of CD8+ T cells, and causes dramatic regression of PARPi-resistant breast tumors in a T-cell-dependent manner. Moreover, PARPi-resistant tumor cells can be readily re-sensitized to PARPi by targeting Flt1 either genetically (Flt1-suppression) or pharmacologically (axitinib). Importantly, a retrospective series of breast cancer patients treated with PARPi demonstrated shorter progression-free survival in cases with FLT1 activation at pre-treatment. Our study therefore identifies FLT1 as a potential therapeutic target in PARPi-resistant, BRCA1/2-mutant breast cancer.

Placental growth factor promotes neural invasion and predicts disease prognosis in resectable pancreatic cancer

BACKGROUND

Surgery represents the only curative treatment option for pancreatic ductal adenocarcinoma (PDAC), but recurrence in more than 85% of patients limits the success of curative-intent tumor resection. Neural invasion (NI), particularly the spread of tumor cells along nerves into extratumoral regions of the pancreas, constitutes a well-recognized risk factor for recurrence. Hence, monitoring and therapeutic targeting of NI offer the potential to stratify recurrence risk and improve recurrence-free survival. Based on the evolutionary conserved dual function of axon and vessel guidance molecules, we hypothesize that the proangiogenic vessel guidance factor placental growth factor (PlGF) fosters NI. To test this hypothesis, we correlated PlGF with NI in PDAC patient samples and functionally assessed its role for the interaction of tumor cells with nerves.

METHODS

Serum levels of PlGF and its soluble receptor sFlt1, and expression of PlGF mRNA transcripts in tumor tissues were determined by ELISA or qPCR in a retrospective discovery and a prospective validation cohort. Free circulating PlGF was calculated from the ratio PlGF/sFlt1. Incidence and extent of NI were quantified based on histomorphometric measurements and separately assessed for intratumoral and extratumoral nerves. PlGF function on reciprocal chemoattraction and directed neurite outgrowth was evaluated in co-cultures of PDAC cells with primary dorsal-root-ganglia neurons or Schwann cells using blocking anti-PlGF antibodies.

RESULTS

Elevated circulating levels of free PlGF correlated with NI and shorter overall survival in patients with PDAC qualifying for curative-intent surgery. Furthermore, high tissue PlGF mRNA transcript levels in patients undergoing curative-intent surgery correlated with a higher incidence and greater extent of NI spreading to tumor-distant extratumoral nerves. In turn, more abundant extratumoral NI predicted shorter disease-free and overall survival. Experimentally, PlGF facilitated directional and dynamic changes in neurite outgrowth of primary dorsal-root-ganglia neurons upon exposure to PDAC derived guidance and growth factors and supported mutual chemoattraction of tumor cells with neurons and Schwann cells.

CONCLUSION

Our translational results highlight PlGF as an axon guidance factor, which fosters neurite outgrowth and attracts tumor cells towards nerves. Hence, PlGF represents a promising circulating biomarker of NI and potential therapeutic target to improve the clinical outcome for patients with resectable PDAC.

The Anti-Vascular Endothelial Growth Factor Receptor 1 (VEGFR-1) D16F7 Monoclonal Antibody Inhibits Melanoma Adhesion to Soluble VEGFR-1 and Tissue Invasion in Response to Placenta Growth Factor

Placenta growth factor (PlGF) is a member of the vascular endothelial growth factor (VEGF) family involved in tumor-associated angiogenesis and melanoma invasion of the extra-cellular matrix (ECM) through activation of membrane VEGF receptor 1 (VEGFR-1). A soluble VEGFR-1 (sVEGFR-1) form is released in the ECM, where it sequesters proangiogenic factors and stimulates endothelial or tumor cell adhesion and chemotaxis through interaction with α5β1 integrin. The anti-VEGFR-1 monoclonal antibody (D16F7 mAb) inhibits VEGF-A or PlGF-mediated signal transduction without affecting ligand interaction, thus preserving sVEGFR-1 decoy function. The aim of this study was to investigate whether D16F7 mAb hampers melanoma spread by in vitro analysis of cell adhesion to sVEGFR-1, ECM invasion, transmigration through an endothelial cell monolayer and in vivo evaluation of tumor infiltrative potential in a syngeneic murine model. Results indicate that D16F7 mAb significantly inhibits melanoma adhesion to sVEGFR-1 and ECM invasion, as well as transmigration in response to PlGF. Moreover, treatment of melanoma-bearing mice with the anti-VEGFR-1 mAb not only inhibits tumor growth but also induces a significant reduction in bone infiltration associated with a decrease in PlGF-positive melanoma cells. Furthermore, D16F7 mAb reduces PlGF production by melanoma cells. Therefore, blockade of PLGF/VEGFR-1 signaling represents a suitable strategy to counteract the metastatic potential of melanoma.

A Phase I Trial of TB-403 in Relapsed Medulloblastoma, Neuroblastoma, Ewing Sarcoma, and Alveolar Rhabdomyosarcoma

PURPOSE

Placental growth factor (PlGF) and its receptor neuropilin 1 are elevated in malignant embryonal tumors and mediate tumor progression by promoting cell proliferation, survival, and metastasis. TB-403 is a blocking monoclonal antibody against PlGF that inhibits tumor growth and increases survival in orthotopic medulloblastoma models.

PATIENTS AND METHODS

We conducted a phase I, open-label, multicenter, dose-escalation study of TB-403 in pediatric subjects with relapsed or refractory cancers. The study involved four dose levels (20 mg/kg, 50 mg/kg, 100 mg/kg, 175 mg/kg) using a 3 + 3 dose-escalation scheme. Subjects received two doses of TB-403 (days 1 and 15) per cycle. After cycle 1, temozolomide or etoposide could be added. The primary objective was to determine the maximum tolerated dose (MTD) of TB-403 monotherapy during a dose-limiting toxicity assessment period. The secondary and exploratory objectives included efficacy, drug pharmacokinetics, and detection of pharmacodynamic biomarkers.

RESULTS

Fifteen subjects were treated in four dose levels. All subjects received two doses of TB-403 in cycle 1. Five serious treatment-emergent adverse events were reported in 3 subjects, but MTD was not reached. While no complete nor partial responses were observed, 7 of 11 relapsed subjects with medulloblastoma experienced stable disease, which persisted for more than 100 days in 4 of 7 subjects.

CONCLUSIONS

TB-403 was safe and well tolerated at all dose levels. No MTD was reached. The results look encouraging and therefore warrant further evaluation of efficacy in pediatric subjects with medulloblastoma.

Hepatopulmonary Syndrome and Portopulmonary Hypertension: Pulmonary Vascular Complications of Liver Disease

Pulmonary vascular disease is a frequent complication of chronic liver disease and portal hypertension, affecting up to 30% of patients. There are two distinct pulmonary vascular complications of liver disease: hepatopulmonary syndrome (HPS) and portopulmonary hypertension (POPH). HPS affects 25% of patients with chronic liver disease and is characterized by intrapulmonary vasodilatation and abnormal arterial oxygenation. HPS negatively impacts quality of life and is associated with a 2-fold increased risk of death compared to controls with liver disease without HPS. Angiogenesis, endothelin-1 mediated endothelial dysfunction, monocyte influx, and alveolar type 2 cell dysfunction seem to play important roles in disease pathogenesis but there are currently no effective medical therapies. Fortunately, HPS resolves following liver transplant (LT) with improvements in hypoxemia. POPH is a subtype of pulmonary arterial hypertension (PAH) characterized by an elevated mean pulmonary arterial pressure and pulmonary vascular resistance in the setting of normal left-sided filling pressures. POPH affects 5% to 6% of patients with chronic liver disease. Although the pathogenesis has not been fully elucidated, endothelial dysfunction, inflammation, and estrogen signaling have been identified as key pathways involved in disease pathogenesis. POPH is typically treated with PAH targeted therapy and may also improve with liver transplantation in selected patients. This article highlights what is currently known regarding the diagnosis, management, pathobiology, and outcomes of HPS and POPH. Ongoing research is needed to improve understanding of the pathophysiology and outcomes of these distinct and often misunderstood pulmonary vascular complications of liver disease. © 2021 American Physiological Society. Compr Physiol 11:1-22, 2021.

Paracrine Placental Growth Factor Signaling in Response to Ionizing Radiation Is p53-Dependent and Contributes to Radioresistance

Placental growth factor (PlGF) is a pro-angiogenic, N-glycosylated growth factor, which is secreted under pathologic situations. Here, we investigated the regulation of PlGF in response to ionizing radiation (IR) and its role for tumor angiogenesis and radiosensitivity. Secretion and expression of PlGF was induced in multiple tumor cell lines (medulloblastoma, colon and lung adenocarcinoma) in response to irradiation in a dose- and time-dependent manner. Early upregulation of PlGF expression and secretion in response to irradiation was primarily observed in p53 wild-type tumor cells, whereas tumor cells with mutated p53 only showed a minimal or delayed response. Mechanistic investigations with genetic and pharmacologic targeting of p53 corroborated regulation of PlGF by the tumor suppressor p53 in response to irradiation under normoxic and hypoxic conditions, but with so far unresolved mechanisms relevant for its minimal and delayed expression in tumor cells with a p53-mutated genetic background. Probing a paracrine role of IR-induced PlGF secretion in vitro, migration of endothelial cells was specifically increased towards irradiated PlGF wild type but not towards irradiated PlGF-knockout (PIGF-ko) medulloblastoma cells. Tumors derived from these PlGF-ko cells displayed a reduced growth rate, but similar tumor vasculature formation as in their wild-type counterparts. Interestingly though, high-dose irradiation strongly reduced microvessel density with a concomitant high rate of complete tumor regression only in the PlGF-ko tumors. IMPLICATIONS: Our study shows a strong paracrine vasculature-protective role of PlGF as part of a p53-regulated IR-induced resistance mechanism and suggest PlGF as a promising target for a combined treatment modality with RT.

Development of a Recombinant Monospecific Anti-PLGF Bivalent Nanobody and Evaluation of it in Angiogenesis Modulation

During the past two decades, tumor therapy based on monoclonal antibody has been found as a confident therapeutic approach in solid tumors and hematologic malignancies. Nanobodies are the smallest fragment of an antigen-binding domain in heavy chain-only antibody originated from the Camelidae family. Accordingly, they are being recently developed rapidly as diagnostic and therapeutic agents. In this regard, targeting of angiogenic factors like Placenta growth factor (PLGF) via nanobodies show a high effectiveness. In the current study, we developed a recombinant anti-PLGF bivalent nanobody based on the affinity enhancement mutant form of anti-PLGF nanobody to suppress the angiogenesis progression. Thereafter, the bivalent nanobody (bi-Nb) was cloned and then expressed into a bacterial system. Afterward, the purity was authorized using western blot assay and the affinity was assessed using ELISA. In this regard, proliferation, 3D capillary tube formation, and migration assays were employed as functional assays. The obtained data were analyzed using t-test and P < 0.05 was considered as statistically significant. The results indicate that the bivalent nanobody could inhibit proliferation, mobility, and formation of endothelial cell capillary-like structure. Moreover, the EC50 was estimated for endothelial cell's proliferation and capillary tube's formation to be about 100 ng/ml and 65 ng/ml, respectively. Migration of MCF-7 was inhibited as about 69%, rather than the control. Accumulation of data have shown that targeting of angiogenic factors like VEGF via monoclonal antibodies or nanobodies can be useful in the suppression of tumor progression. Also, the inhibition of PLGF with monoclonal antibody indicated that it is significant in angiogenesis suppression. However, due to intrinsic properties of nanobodies, they are suggested to be used. Since the small size is rapidly removed through liver or kidney system, so it is important to use bivalent or polymeric forms for extending the half-life. Our findings indicated that the inhibition of PLGF can prevent growth and proliferation of endothelial cells and tumor cells through the bivalent nanobody. So, it is suggested as a novel therapeutic agent for angiogenesis suppression.

Role of VEGFs/VEGFR-1 Signaling and its Inhibition in Modulating Tumor Invasion: Experimental Evidence in Different Metastatic Cancer Models

The vascular endothelial growth factor (VEGF) family members, VEGF-A, placenta growth factor (PlGF), and to a lesser extent VEGF-B, play an essential role in tumor-associated angiogenesis, tissue infiltration, and metastasis formation. Although VEGF-A can activate both VEGFR-1 and VEGFR-2 membrane receptors, PlGF and VEGF-B exclusively interact with VEGFR-1. Differently from VEGFR-2, which is involved both in physiological and pathological angiogenesis, in the adult VEGFR-1 is required only for pathological angiogenesis. Besides this role in tumor endothelium, ligand-mediated stimulation of VEGFR-1 expressed in tumor cells may directly induce cell chemotaxis and extracellular matrix invasion. Furthermore, VEGFR-1 activation in myeloid progenitors and tumor-associated macrophages favors cancer immune escape through the release of immunosuppressive cytokines. These properties have prompted a number of preclinical and clinical studies to analyze VEGFR-1 involvement in the metastatic process. The aim of the present review is to highlight the contribution of VEGFs/VEGFR-1 signaling in the progression of different tumor types and to provide an overview of the therapeutic approaches targeting VEGFR-1 currently under investigation.

Multifaceted Role of the Placental Growth Factor (PlGF) in the Antitumor Immune Response and Cancer Progression

The sharing of molecules function that affects both tumor growth and neoangiogenesis with cells of the immune system creates a mutual interplay that impairs the host’s immune response against tumor progression. Increasing evidence shows that tumors are able to create an immunosuppressive microenvironment by recruiting specific immune cells. Moreover, molecules produced by tumor and inflammatory cells in the tumor microenvironment create an immunosuppressive milieu able to inhibit the development of an efficient immune response against cancer cells and thus fostering tumor growth and progression. In addition, the immunoediting could select cancer cells that are less immunogenic or more resistant to lysis. In this review, we summarize recent findings regarding the immunomodulatory effects and cancer progression of the angiogenic growth factor namely placental growth factor (PlGF) and address the biological complex effects of this cytokine. Different pathways of the innate and adaptive immune response in which, directly or indirectly, PlGF is involved in promoting tumor immune escape and metastasis will be described. PlGF is important for building up vascular structures and functions. Although PlGF effects on vascular and tumor growth have been widely summarized, its functions in modulating the immune intra-tumoral microenvironment have been less highlighted. In agreement with PlGF functions, different antitumor strategies can be envisioned.

Potential Clinical Targets in Hepatopulmonary Syndrome: Lessons From Experimental Models

Hepatopulmonary syndrome (HPS) is a relatively common and potentially severe pulmonary complication of cirrhosis with increased risk of mortality. In experimental models, a complex interaction between pulmonary endothelial cells, monocytes, and the respiratory epithelium, which produces chemokines, cytokines, and angiogenic growth factors, causes alterations in the alveolar microvasculature, resulting in impaired oxygenation. Model systems are critical for evaluating mechanisms and for preclinical testing in HPS, due to the challenges of evaluating the lung in the setting of advanced liver disease in humans. This review provides an overview of current knowledge and recent findings in the rodent common bile duct ligation model of HPS, which recapitulates many features of human disease. We focus on the concepts of endothelial derangement, monocyte infiltration, angiogenesis, and alveolar type II cell dysfunction as main contributors and potential targets for therapy.

The role of placental growth factor (PlGF) and its receptor system in retinal vascular diseases

Placental growth factor (PlGF) is a member of the vascular endothelial growth factor (VEGF) family. Upon binding to VEGF- and neuropilin-receptor sub-types, PlGF modulates a range of neural, glial and vascular cell responses that are distinct from VEGF-A. As PlGF expression is selectively associated with pathological angiogenesis and inflammation, its blockade does not affect the healthy vasculature. PlGF actions have been extensively described in tumor biology but more recently there has been accumulating preclinical evidence that indicates that this growth factor could have an important role in retinal diseases. High levels of PlGF have been found in aqueous humor, vitreous and/or retina of patients exhibiting retinopathies, especially those with diabetic retinopathy (DR) and neovascular age-related macular degeneration (nvAMD). Expression of this growth factor seems to correlate closely with many of the key pathogenic features of early and late retinopathy in preclinical models. For example, studies using genetic modification and/or pharmacological treatment to block PlGF in the laser-induced choroidal neovascularization (CNV) model, oxygen-induced retinopathy model, as well as various murine diabetic models, have shown that PlGF deletion or inhibition can reduce neovascularization, retinal leakage, inflammation and gliosis, without affecting vascular development or inducing neuronal degeneration. Moreover, an inhibitory effect of PlGF blockade on retinal scarring in the mouse CNV model has also been recently demonstrated and was found to be unique for PlGF inhibition, as compared to various VEGF inhibition strategies. Together, these preclinical results suggest that anti-PlGF therapy might have advantages over anti-VEGF treatment, and that it may have clinical applications as a standalone treatment or in combination with anti-VEGF. Additional clinical studies are clearly needed to further elucidate the role of PlGF and its potential as a therapeutic target in ocular diseases.

Therapeutic implication of vascular endothelial growth factor receptor-1 (VEGFR-1) targeting in cancer cells and tumor microenvironment by competitive and non-competitive inhibitors

The vascular endothelial growth factor receptor-1 (VEGFR-1) is a tyrosine kinase receptor for VEGF-A, VEGF-B, and placental growth factor (PlGF) ligands that is expressed in endothelial, myelomonocytic and tumor cells. VEGF-B and PlGF exclusively bind to VEGFR-1, whereas VEGF-A also binds to VEGFR-2. At variance with VEGFR-2, VEGFR-1 does not play a relevant role in physiological angiogenesis in the adult, while it is important in tumor-associated angiogenesis. VEGFR-1 and PlGF are expressed in a variety of tumors, promote invasiveness and contribute to resistance to anti-VEGF-A therapy. The currently approved antiangiogenic therapies for the treatment of a variety of solid tumors hamper VEGF-A signaling mediated by both VEGFR-2 and VEGFR-1 [i.e., the monoclonal antibody (mAb) anti-VEGF-A bevacizumab, the chimeric molecule aflibercept and several small molecule tyrosine kinase inhibitors] or exclusively by VEGFR-2 (i.e., the mAb anti-VEGFR-2 ramucirumab). However, molecules that interfere with VEGF-A/VEGFR-2 signaling determine severe adverse effects due to inhibition of physiological angiogenesis and their efficacy is hampered by tumor infiltration of protumoral myeloid cells. Blockade of VEGFR-1 may exert anti-tumor activity by multiple mechanisms: a) inhibition of tumor-associated angiogenesis; b) reduction of myeloid progenitor mobilization and tumor infiltration by VEGFR-1 expressing M2 macrophages, which contribute to tumor progression and spreading; c) inhibition of invasiveness, vasculogenic mimicry and survival of VEGFR-1 positive tumor cells. As a consequence of these properties, molecules targeting VEGFR-1 are expected to produce less adverse effects and to counteract resistance towards anti-VEGF-A therapies. More interestingly, selective VEGFR-1 inhibition might enhance the efficacy of immunotherapy with immune checkpoint inhibitors. In this review, we will examine the experimental evidence available so far that supports targeting VEGFR-1 signal transduction pathway for cancer treatment by competitive inhibitors that prevent growth factor interaction with the receptor and non-competitive inhibitors that hamper receptor activation without affecting ligand binding.

Placental growth factor inhibition targets pulmonary angiogenesis and represents a therapy for hepatopulmonary syndrome in mice

Hepatopulmonary syndrome (HPS) is a severe complication of cirrhosis with increased risk of mortality. Pulmonary microvascular alterations are key features of HPS; but underlying mechanisms are incompletely understood, and studies on HPS are limited to rats. Placental growth factor (PlGF), a proangiogenic molecule that is selectively involved in pathological angiogenesis, may play an important role in HPS development; however, its role has never been investigated. In this study, we validated an HPS model by common bile duct ligation (CBDL) in mice, investigated the kinetic changes in pulmonary angiogenesis and inflammation during HPS development, and provide evidence for a novel therapeutic strategy by targeting pathological angiogenesis. Mice with CBDL developed hypoxemia and intrapulmonary shunting on a background of liver fibrosis. Pulmonary alterations included increased levels of proangiogenic and inflammatory markers, which was confirmed in serum of human HPS patients. Increased PlGF production in HPS mice originated from alveolar type II cells and lung macrophages, as demonstrated by immunofluorescent staining. Dysfunctional vessel formation in CBDL mice was visualized by microscopy on vascular corrosion casts. Both prophylactic and therapeutic anti-PlGF (αPlGF) antibody treatment impeded HPS development, as demonstrated by significantly less intrapulmonary shunting and improved gas exchange. αPlGF treatment decreased endothelial cell dysfunction in vivo and in vitro and was accompanied by reduced pulmonary inflammation. Importantly, αPlGF therapy did not affect liver alterations, supporting αPlGF's ability to directly target the pulmonary compartment.

CONCLUSION

CBDL in mice induces HPS, which is mediated by PlGF production; αPlGF treatment improves experimental HPS by counteracting pulmonary angiogenesis and might be an attractive therapeutic strategy for human HPS. (Hepatology 2017).

Blockade of placental growth factor reduces vaso-occlusive complications in murine models of sickle cell disease

Vaso-occlusive crisis (VOC) is the most common and debilitating complication of sickle cell disease (SCD); recurrent episodes cause organ damage and contribute to early mortality. Plasma placental growth factor (PlGF) levels are elevated in SCD and can further increase under hypoxic conditions in SCD mice. Treatment with a PlGF-neutralizing antibody (anti-PlGF Ab) in SCD mice reduced levels of monocyte chemoattractant protein-3, eotaxin, macrophage colony-stimulating factor, and plasminogen activator inhibitor-1 significantly, and of macrophage-derived chemokine and macrophage inflammatory protein-3β moderately; this may contribute to inhibition of leukocyte recruitment, activation, and thrombosis. In subsequent experiments, anti-PlGF Ab treatment significantly reduced plasma lactate dehydrogenase levels, indicating possible reduction in cellular destruction and/or hemolysis. Histopathology studies revealed decreased incidence and severity of congestion in the lungs and spleen with repeated anti-PlGF Ab treatment. Furthermore, anti-PlGF Ab significantly reduced vaso-occlusion events under hypoxic conditions in a modified dorsal skinfold chamber model in SCD mice. Therefore, elevated PlGF levels may contribute to recruitment and activation of leukocytes. This can subsequently lead to increased pathology of affected organs in addition to mediating acute hypoxia/reoxygenation-triggered vaso-occlusion under SCD conditions. Thus, targeting PlGF may offer a therapeutic approach to reduce acute VOC and possibly alleviate long-term vascular complications in patients with SCD.

Nanobodies As Novel Agents for Targeting Angiogenesis in Solid Cancers

Solid cancers are dependent on angiogenesis for sustenance. The FDA approval of Bevacizumab in 2004 inspired many scientists to develop more inhibitors of angiogenesis. Although several monoclonal antibodies (mAbs) are being administered to successfully combat various pathologies, the complexity and large size of mAbs seem to narrow the therapeutic applications. To improve the performance of cancer therapeutics, including those blocking tumor angiogenesis, attractive strategies such as miniaturization of the antibodies have been introduced. Nanobodies (Nbs), small single-domain antigen-binding antibody fragments, are becoming promising therapeutic and diagnostic proteins in oncology due to their favorable unique structural and functional properties. This review focuses on the potential and state of the art of Nbs to inhibit the angiogenic process for therapy and the use of labeled Nbs for non-invasive in vivo imaging of the tumors.

An apparent clinical pharmacokinetic drug-drug interaction between bevacizumab and the anti-placental growth factor monoclonal antibody RO5323441 via a target-trapping mechanism

PURPOSE

RO5323441 is a humanized anti-placental growth factor (PlGF) monoclonal antibody that has shown preclinical activity in several cancer models. The objective of this analysis is to examine the pharmacokinetic (PK) results from four Phase I studies that have been conducted with RO5323441 (n = 61) and to report an apparent drug-drug interaction observed when RO5323441 was administered in combination with bevacizumab.

METHODS

The four Phase I studies were a multiple-ascending dose study in 23 patients with solid tumors (Study 1), an open-label study in seven patients with colorectal/ovarian cancer (Study 2), a sorafenib combination study in nine patients with hepatocellular carcinoma (Study 3), and a bevacizumab combination study in 22 patients with recurrent glioblastoma (Study 4). A two-compartment linear population PK model was developed from these four studies to characterize the PK of RO5323441 in patients with cancer.

RESULTS

The PK properties of RO5323441 were similar in the first three studies. However, substantially higher RO5323441 exposures were observed in Study 4 when RO5323441 was administered in combination with bevacizumab. A linear two-compartmental population PK model indicated that the co-administration of bevacizumab would decrease the clearance of RO5323441 by 53%. Clinical data suggested that the decrease in RO5323441 clearance was inversely associated with bevacizumab exposure.

CONCLUSIONS

The exact reason for the increase in RO5323441 exposure following bevacizumab co-administration is not currently known. One possibility is a drug-drug interaction via a target-trapping mechanism that is mediated by the vascular endothelial growth factor receptor-1 (VEGFR-1).

Determination of the starting dose in the first-in-human clinical trials with monoclonal antibodies: a systematic review of papers published between 1990 and 2013

A systematic review was performed to evaluate how the maximum recommended starting dose (MRSD) was determined in first-in-human (FIH) studies with monoclonal antibodies (mAbs). Factors associated with the choice of each MRSD determination method were also identified. PubMed was searched for FIH studies with mAbs published in English between January 1, 1990 and December 31, 2013, and the following information was extracted: MRSD determination method, publication year, therapeutic area, antibody type, safety factor, safety assessment results after the first dose, and number of dose escalation steps. Seventy-nine FIH studies with mAbs were identified, 49 of which clearly reported the MRSD determination method. The no observed adverse effects level (NOAEL)-based approach was the most frequently used method, whereas the model-based approach was the least commonly used method (34.7% vs 16.3%). The minimal anticipated biological effect level (MABEL)- or minimum effective dose (MED)-based approach was used more frequently in 2011–2013 than in 1990–2007 (31.6% vs 6.3%, P=0.036), reflecting a slow, but steady acceptance of the European Medicines Agency’s guidance on mitigating risks for FIH clinical trials (2007). The median safety factor was much lower for the MABEL- or MED-based approach than for the other MRSD determination methods (10 vs 32.2–53). The number of dose escalation steps was not significantly different among the different MRSD determination methods. The MABEL-based approach appears to be safer and as efficient as the other MRSD determination methods for achieving the objectives of FIH studies with mAbs faster.

Antidrug Antibody Formation in Oncology: Clinical Relevance and Challenges

: In oncology, an increasing number of targeted anticancer agents and immunotherapies are of biological origin. These biological drugs may trigger immune responses that lead to the formation of antidrug antibodies (ADAs). ADAs are directed against immunogenic parts of the drug and may affect efficacy and safety. In other medical fields, such as rheumatology and hematology, the relevance of ADA formation is well established. However, the relevance of ADAs in oncology is just starting to be recognized, and literature on this topic is scarce. In an attempt to fill this gap in the literature, we provide an up-to-date status of ADA formation in oncology. In this focused review, data on ADAs was extracted from 81 clinical trials with biological anticancer agents. We found that most biological anticancer drugs in these trials are immunogenic and induce ADAs (63%). However, it is difficult to establish the clinical relevance of these ADAs. In order to determine this relevance, the possible effects of ADAs on pharmacokinetics, efficacy, and safety parameters need to be investigated. Our data show that this was done in fewer than 50% of the trials. In addition, we describe the incidence and consequences of ADAs for registered agents. We highlight the challenges in ADA detection and argue for the importance of validating, standardizing, and describing well the used assays. Finally, we discuss prevention strategies such as immunosuppression and regimen adaptations. We encourage the launch of clinical trials that explore these strategies in oncology.

IMPLICATIONS FOR PRACTICE

Because of the increasing use of biologicals in oncology, many patients are at risk of developing antidrug antibodies (ADAs) during therapy. Although clinical consequences are uncertain, ADAs may affect pharmacokinetics, patient safety, and treatment efficacy. ADA detection and reporting is currently highly inconsistent, which makes it difficult to evaluate the clinical consequences. Standardized reporting of ADA investigations in the context of the aforementioned parameters is critical to understanding the relevance of ADA formation for each drug. Furthermore, the development of trials that specifically aim to investigate clinical prevention strategies in oncology is needed.

Arsenite-mediated promotion of anchorage-independent growth of HaCaT cells through placental growth factor

Various cancers including skin cancer are increasing in 45 million people exposed to arsenic above the World Health Organization's guideline value of 10 μg l(-1). However, there is limited information on key molecules regulating arsenic-mediated carcinogenesis. Our fieldwork in Bangladesh demonstrated that levels of placental growth factor (PlGF) in urine samples from residents of cancer-prone areas with arsenic-polluted drinking water were higher than those in urine samples from residents of an area that was not polluted with arsenic. Our experimental study in human nontumorigenic HaCaT skin keratinocytes showed that arsenite promoted anchorage-independent growth with increased expression and secretion of PlGF, a ligand of vascular endothelial growth factor receptor1 (VEGFR1), and increased VEGFR1/mitogen-activated protein kinase/ERK kinase (MEK)/extracellular signal-regulated kinase (ERK) activities. The arsenite-mediated promotion of anchorage-independent growth was strongly inhibited by PlGF depletion with decreased activities of the PlGF/VEGFR1/MEK/ERK pathway. Moreover, arsenite proteasome-dependently degrades metal-regulatory transcription factor-1 (MTF-1) protein, resulting in a decreased amount of MTF-1 protein binding to the PlGF promoter. MTF-1 negatively controlled PlGF transcription in HaCaT cells, resulting in increased PlGF transcription. These results suggest that arsenite-mediated MTF-1 degradation enhances the activity of PlGF/VEGFR1/MEK/ERK signaling, resulting in promotion of the malignant transformation of keratinocytes. Thus, this study proposed a molecular mechanism for arsenite-mediated development of skin cancer.

Phase 1 dose-escalation study of the antiplacental growth factor monoclonal antibody RO5323441 combined with bevacizumab in patients with recurrent glioblastoma

BACKGROUND

We conducted a phase 1 dose-escalation study of RO5323441, a novel antiplacental growth factor (PlGF) monoclonal antibody, to establish the recommended dose for use with bevacizumab and to investigate the pharmacokinetics, pharmacodynamics, safety/tolerability, and preliminary clinical efficacy of the combination.

METHODS

Twenty-two participants with histologically confirmed glioblastoma in first relapse were treated every 2 weeks with RO5323441 (625 mg, 1250 mg, or 2500 mg) plus bevacizumab (10 mg/kg). A standard 3 + 3 dose-escalation trial design was used.

RESULTS

RO5323441 combined with bevacizumab was generally well tolerated, and the maximum tolerated dose was not reached. Two participants experienced dose-limiting toxicities (grade 3 meningitis associated with spinal fluid leak [1250 mg] and grade 3 cerebral infarction [2500 mg]). Common adverse events included hypertension (14 participants, 64%), headache (12 participants, 55%), dysphonia (11 participants, 50%) and fatigue (6 participants, 27%).The pharmacokinetics of RO5323441 were linear, over-the-dose range, and bevacizumab exposure was unaffected by RO5323441 coadministration. Modulation of plasmatic angiogenic proteins, with increases in VEGFA and decreases in FLT4, was observed. Dynamic contrast-enhanced/diffusion-weighted MRI revealed large decreases in vascular parameters that were maintained through the dosing period. Combination therapy achieved an overall response rate of 22.7%, including one complete response, and median progression-free and overall survival of 3.5 and 8.5 months, respectively.

CONCLUSION

The toxicity profile of RO5323441 plus bevacizumab was acceptable and manageable. The observed clinical activity of the combination does not appear to improve on that obtained with single-agent bevacizumab in patients with recurrent glioblastoma.

Inhibition of stromal PlGF suppresses the growth of prostate cancer xenografts

The growth and vascularization of prostate cancer is dependent on interactions between cancer cells and supporting stromal cells. The primary stromal cell type found in prostate tumors is the carcinoma-associated fibroblast, which produces placental growth factor (PlGF). PlGF is a member of the vascular endothelial growth factor (VEGF) family of angiogenic molecules and PlGF mRNA levels increase after androgen deprivation therapy in prostate cancer. In this study, we show that PlGF has a direct dose-dependent proliferative effect on human PC-3 prostate cancer cells in vitro and fibroblast-derived PlGF increases PC-3 proliferation in co-culture. In xenograft tumor models, intratumoral administration of murine PlGF siRNA reduced stromal-derived PlGF expression, reduced tumor burden and decreased the number of Ki-67 positive proliferating cells associated with reduced vascular density. These data show that targeting stromal PlGF expression may represent a therapeutic target for the treatment of prostate cancer.

Placental growth factor supports neuroendocrine tumor growth and predicts disease prognosis in patients

Placental growth factor (PlGF), a VEGF-homolog implicated in tumor angiogenesis and adaptation to antiangiogenic therapy, is emerging as candidate target in malignancies. Here, we addressed the expression, function, and prognostic value of PlGF in neuroendocrine tumors (NETs). PlGF was determined in NET patients' sera collected retrospectively (n=88) and prospectively (n=87) using Roche-Elecsys and correlated with clinicopathological data. Tumoral PlGF was evaluated by immunohistochemistry, effects of PlGF on proliferation and migration in vitro were assessed using different NET cell lines and effects on tumor growth in vivo in orthotopic xenografts. Circulating and tumoral PlGF was elevated in patients with pancreatic NETs (pNETs) compared with control sera and respective healthy tissue. De novo PlGF expression occurred primarily in the tumor stroma, suggesting paracrine stimulatory circuits. Indeed, PlGF enhanced NET proliferation and migration in vitro and, conversely, neutralizing antibodies to PlGF reduced tumor growth in vivo. Elevated circulating PlGF levels in NET patients correlated with advanced tumor grading and were associated with reduced tumor-related survival in pNETs. Subsequent determinations confirmed and extended our observation of elevated PlGF levels in a prospective cohort of grade 1 and grade 2 pNETs (n=30) and intestinal NETs (n=57). In low-grade pNETs, normal circulating PlGF levels were associated with better survival. In intestinal NETs, circulating PlGF above median emerged as an independent prognostic factor for shorter time-to-progression in multivariate analyses. These data assign to PlGF a novel function in the pathobiology of NETs and propose PlGF as a prognostic parameter and therapeutic target.

Targeting placental growth factor/neuropilin 1 pathway inhibits growth and spread of medulloblastoma

Medulloblastoma is the most common pediatric malignant brain tumor. Although current therapies improve survival, these regimens are highly toxic and are associated with significant morbidity. Here, we report that placental growth factor (PlGF) is expressed in the majority of medulloblastomas, independent of their subtype. Moreover, high expression of PlGF receptor neuropilin 1 (Nrp1) correlates with poor overall survival in patients. We demonstrate that PlGF and Nrp1 are required for the growth and spread of medulloblastoma: PlGF/Nrp1 blockade results in direct antitumor effects in vivo, resulting in medulloblastoma regression, decreased metastasis, and increased mouse survival. We reveal that PlGF is produced in the cerebellar stroma via tumor-derived Sonic hedgehog (Shh) and show that PlGF acts through Nrp1-and not vascular endothelial growth factor receptor 1-to promote tumor cell survival. This critical tumor-stroma interaction-mediated by Shh, PlGF, and Nrp1 across medulloblastoma subtypes-supports the development of therapies targeting PlGF/Nrp1 pathway.

Increased expression of placental growth factor in high-grade endometrial carcinoma

Placental growth factor (PlGF), a homolog of vascular endothelial growth factor (VEGF), exerts pleiotropic functions in cancer by affecting tumor cells as well as endothelial and inflammatory cells. Moreover, PlGF expression correlates with tumor stage, recurrence, metastasis and patient outcome in different types of cancer. Recently, administration of anti-PlGF therapy reduced tumor growth and metastasis in preclinical tumor models. In the present study, we evaluated the diagnostic and prognostic value of systemic and local expression of PlGF in primary endometrial carcinomas. PlGF levels in tumor lysates (n=128) and serum (n=88) of patients with primary endometrial cancer were determined using ELISA. PlGF mRNA expression in endometrial carcinoma tissues was quantified by quantitative qRT-PCR. Results were compared to endometrial cancer stage and grade. Systemic PlGF levels were not altered in patients with endometrial cancer (FIGO stage I-II-III) as compared to healthy controls. Only in FIGO stage IV patients, serum PlGF levels were slightly increased. Local PlGF mRNA and protein expression in endometrial tumors progressively increased with tumor grade. In endometrioid carcinomas, PlGF mRNA expression was significantly increased in endometrioid grade 3 tumors as compared to normal endometrial tissue. PlGF protein expression was significantly increased in endometrioid grade 2 and 3 carcinomas and in serous carcinomas as compared to normal endometrial tissue. Our study showed that systemic/serum PlGF levels cannot be used as a diagnostic or prognostic marker in endometrial cancer. However, the increased local expression of PlGF, primarily in high-grade carcinomas, underscores the possibility for preclinical assessment of anti-PlGF therapy in endometrial cancer.

Overcoming resistance to antiangiogenic therapies

The concept of targeting new blood vessel formation, or angiogenesis, in tumors is an important advancement in cancer therapy, resulting, in part, from the development of such biologic agents as bevacizumab, a monoclonal antibody directed against vascular endothelial growth factor (VEGF)-A. The rationale for antiangiogenic therapy is based on the hypothesis that if tumors are limited in their capacity to obtain a new blood supply, so too is their capacity for growth and metastasis. Additional evidence suggests that pruning and/or "normalization" of irregular tumor vasculature and reduction of hypoxia may facilitate greater access of cytotoxic chemotherapy (CT) to the tumor. Indeed, for metastatic colorectal cancer, bevacizumab in combination with established CT regimens has efficacy superior to that of CT alone. Despite ~2-month longer progression-free and overall survival times than with CT alone, patients still progress, possibly because of alternative angiogenic "escape" pathways that emerge independent of VEGF-A, or are driven by hypoxic stress on the tumor. Other VEGF family members may contribute to resistance, and many factors that contribute to the regulation of tumor angiogenesis function as part of a complex network, existing in different concentrations and spatiotemporal gradients and producing a wide range of biologic responses. Integrating these concepts into the design and evaluation of new antiangiogenic therapies may help overcome resistance mechanisms and allow for greater efficacy over longer treatment periods.

The discovery of placenta growth factor and its biological activity

Angiogenesis is a complex biological phenomenon crucial for a correct embryonic development and for post-natal growth. In adult life, it is a tightly regulated process confined to the uterus and ovary during the different phases of the menstrual cycle and to the heart and skeletal muscles after prolonged and sustained physical exercise. Conversly, angiogenesis is one of the major pathological changes associated with several complex diseases like cancer, atherosclerosis, arthritis, diabetic retinopathy and age-related macular degeneration. Among the several molecular players involved in angiogenesis, some members of VEGF family, VEGF-A, VEGF-B and placenta growth factor (PlGF), and the related receptors VEGF receptor 1 (VEGFR-1, also known as Flt-1) and VEGF receptor 2 (VEGFR-2, also known as Flk-1 in mice and KDR in human) have a decisive role. In this review, we describe the discovery and molecular characteristics of PlGF, and discuss the biological role of this growth factor in physiological and pathological conditions.

Inhibition of placenta growth factor with TB-403: a novel antiangiogenic cancer therapy

INTRODUCTION

There is clinical evidence that therapies targeting the vascular endothelial growth factor pathway are effective in delaying cancer progression. However, tumors may be either intrinsically resistant or evolve resistance to such therapies. Hence, there is a need for new therapies targeting angiogenesis.

AREAS COVERED

The data are obtained by searching in the PubMed database. The search terms used included antiangiogenic therapy, TB-403 (RO5323441), placenta growth factor (PlGF) and VEGFR-1 (Flt-1). We review preclinical data concerning the function and inhibition of PlGF and summarize data on expression of PlGF in cancer patients. Data from early-phase clinical trials of TB-403 (RO5323441), a monoclonal antibody inhibiting PlGF, are discussed. Future development strategies, therapeutic potentials and limitations of TB-403 are further evaluated.

EXPERT OPINION

There are some conflicting data on the function of PlGF and the importance of its role in primary tumor growth. Data from some preclinical models of PlGF inhibition and early-phase clinical trials with TB-403 are, however, promising, although the true potential of the drug is yet to be determined. Further clinical development should be preceded by molecular studies in the context of well-designed preclinical models and/or small translational studies. Future challenges involve identifying predictive biomarkers.

A phase I, dose-escalation study of TB-403, a monoclonal antibody directed against PlGF, in patients with advanced solid tumours

Background:

TB-403 (RO 5323441), a humanised monoclonal antibody, is a novel antiangiogenesis agent directed against placental growth factor. The safety, pharmacokinetics (PK), and antitumour activity of TB-403 were assessed in a phase I, dose-escalation study in patients with advanced solid tumours.

Methods:

Patients in sequential dose groups received either weekly doses of 1.25, 5.0, or 10 mg kg⁻¹ or doses of 20 or 30 mg kg⁻¹ every third week.

Results:

Twenty-three patients were enrolled and received TB-403. The most common adverse events (AEs) were fatigue, constipation, pyrexia, dyspnoea, and nausea. One serious AE, a lung embolus in a patient with non-small cell lung cancer treated with 10 mg kg⁻¹ weekly, was deemed possibly related to TB-403. No dose-limiting toxicities were observed, and a maximum-tolerated dose was not reached. The PK parameters were dose linear and the terminal half-life values ranged from 9 to 14 days. Six patients exhibited stable disease for at least 8 weeks. Two patients, (oesophageal squamous cell carcinoma and pancreatic adenocarcinoma) both treated with 5 mg kg⁻¹ weekly, remained stable for 12 months.

Conclusion:

TB-403 treatment in this patient population is well tolerated, with a safety profile distinct from that of vascular endothelial growth factor-axis inhibitors.

Prognostic impact of placenta growth factor and vascular endothelial growth factor A in patients with breast cancer

Placenta growth factor (PlGF) and vascular endothelial growth factor A (VEGF-A) are angiogenic growth factors interacting competitively with the same receptors. VEGF-A is essential in both normal and pathologic conditions, but the functions of PlGF seem to be restricted to pathologic conditions such as ischemic heart disease, arthritis and tumor growth. Angiogenesis is a complex process with several growth factors involved. Because PlGF modulates VEGF-A responses, we investigated their mutual relationship and impact on breast cancer prognosis. Quantitative PlGF and VEGF-A levels were measured in 229 tumor tissue specimen from primarily operated patients with unilateral breast cancer. Non-malignant breast tissue was also dissected near the tumor and quantitative measurements were available for 211 patients. PlGF and VEGF-A protein levels in homogenized tissue lysates were analyzed using the Luminex system. We found significantly higher median levels of PlGF and VEGF-A in tumor tissue compared to non-malignant tissue (PlGF: 69.8 vs. 31.4 pg/mg, p < 0.001 and VEGF-A: 1148.2 vs. 163.5 pg/mg, p < 0.001). PlGF and VEGF-A were correlated in both malignant tissue (r = 0.41, p < 0.001) and in non-malignant tissue (r = 0.69, p < 0.001). The proportion of node positive patients was higher with high PlGF expression (61.4%) than with low PlGF expression (45.6%) in tumor tissue, p = 0.024. High levels of PlGF and VEGF-A in tumor tissue were associated with significant shorter recurrence-free survival (RFS) in both univariate analysis (PlGF: p = 0.023; VEGF-A: p = 0.047) and in multivariate analysis (PlGF: p = 0.026; VEGF-A: p = 0.036). Neither PlGF nor VEGF-A expression in non-malignant tissue were predictors for RFS. In conclusion, our results support the mutual relationship between PlGF and VEGF-A and encourage further investigations as prognostic markers in breast cancer patients.