A Hypothetical Model Suggesting Some Possible Ways That the Progesterone Receptor May Be Involved in Cancer Proliferation.

Cancer and the fetal-placental semi-allograft share certain characteristics, e.g., rapid proliferation, the capacity to invade normal tissue, and, related to the presence of antigens foreign to the host, the need to evade immune surveillance. Many present-day methods to treat cancer use drugs that can block a key molecule that is important for one or more of these characteristics and thus reduce side effects. The ideal molecule would be one that is essential for both the survival of the fetus and malignant tumor, but not needed for normal cells. There is a potential suitable candidate, the progesterone induced blocking factor (PIBF). The parent 90 kilodalton (kDa) form seems to be required for cell-cycle regulation, required by both the fetal-placental unit and malignant tumors. The parent form may be converted to splice variants that help both the fetus and tumors escape immune surveillance, especially in the fetal and tumor microenvironment. Evidence suggests that membrane progesterone receptors are involved in PIBF production, and indeed there has been anecdotal evidence that progesterone receptor antagonists, e.g., mifepristone, can significantly improve longevity and quality of life, with few side effects.

Discovery of a potential biomarker for immunotherapy of melanoma: PLAC1 as an emerging target.

BACKGROUND: Melanoma has increased in incidence worldwide prompting investigators to search for new biomarkers for targeted immunotherapy of this disease. Placenta specific 1 (PLAC1) is a new member of cancer-testis antigens with widespread expression in many types of cancer. Here, we aimed to study for the first time the expression pattern of PLAC1 in skin cancer samples including cutaneous melanoma, basal cell carcinoma (BCC), squamous cell carcinoma (SCC) in comparison to normal skin and nevus tissues and potential therapeutic effect of anti-PLAC1 antibody in melanoma cancer cell lines in vitro. MATERIALS AND METHODS: Polyclonal and monoclonal antibodies were applied for immunohistochemical profiling of PLAC1 expression using tissue microarray. The cytotoxic action of anti-PLAC1 antibody alone or as an antibody drug conjugate (with anti-neoplastic agent SN38) was investigated in melanoma cell lines. RESULTS: We observed that 100% (39 of 39) of melanoma tissues highly expressed PLAC1 with both cytoplasmic and surface expression pattern. Investigation of PLAC1 expression in BCC (n = 110) samples showed negative results. Cancer cells in SCC samples (n = 66) showed very weak staining. Normal skin tissues and nevus samples including congenital melanocytic nevus failed to express PLAC1. Anti-PLAC1-SN38 exerted a specific pattern of cytotoxicity in a dose- and time-dependent manner in melanoma cells expressing surface PLAC1. CONCLUSIONS: Our findings re-inforce the concept of re-expression of embryonic/placental tissue antigens in cancer and highlight the possibility of melanoma targeted therapy by employing anti-PLAC1 antibodies. The data presented here should lead to the future research on targeted immunotherapy of patients with melanoma.

A High-dose Pharmacokinetic Study of a New IgG4 Monoclonal Antibody Temelimab/GNbAC1 Antagonist of an Endogenous Retroviral Protein pHERV-W Env.

PURPOSE: Temelimab/GNbAC1 is a humanized immunoglobulin G4 monoclonal antibody antagonist of the human endogenous retrovirus W envelope protein, which is associated with multiple sclerosis (MS) pathophysiology and possibly with other autoimmune disorders. Human endogenous retrovirus W envelope protein is expressed in the central nervous system of patients with MS, and sufficient amount of temelimab must reach the target. The safety of very high dosages of temelimab should be tested to support further clinical trials in MS. METHODS: This randomized, placebo-controlled, dose-escalation study evaluated the safety and pharmacokinetic profile of temelimab in 24 healthy volunteers after a single intravenous infusion at doses of 36, 60, 85, and 110 mg/kg administered sequentially. FINDINGS: Temelimab was well tolerated, with no particular adverse drug reactions at any dose. The maximal dose of 110 mg/kg could be administered, and no antidrug antibodies were induced. After administration of 36-110 mg/kg, mean temelimab Cmax increased from 859 to 2450 µg/mL, and AUC values increased from 319,900 to 1,030,000 µg·h/mL. There was an approximate dose-proportional increase in exposure, similar to observations at lower doses. IMPLICATIONS: The favorable data in terms of safety and pharmacokinetic variables support temelimab use at high doses in future MS trials to optimally neutralize the temelimab target in the central nervous system. ClinicalTrials.gov identifier: NCT03574428.

Therapy Aimed to Suppress the Production of the Immunosuppressive Protein Progesterone Induced Blocking Factor (PIBF) May Provide Palliation and/or Increased Longevity for Patients With a Variety of Different Advanced Cancers - A Review.

Progesterone induced blocking factor (PIBF) is a unique protein that is not present in normal cells, but is found predominantly in rapidly growing cells of the fetal placental unit or cancer cells. There is a larger "parent" form that is a nuclear protein involved in cell to cell regulation, allowing tumor cells to proliferate and invade tissues. The parent compound is cleaved into smaller intracytoplasmic isoforms that can suppress cellular immune response, especially, but not limited to natural killer cells. The progesterone receptor antagonist mifepristone can suppress messenger RNA for PIBF, but can also suppress the intracytoplasmic protein. Treating cancer cell lines, intact animals with a variety of spontaneous cancers, and people with various cancers with mifepristone, has been found to inhibit cancer growth, and provide both palliation of symptoms and longevity possibly by suppressing this unique immunomodulatory protein.

PLAC1: biology and potential application in cancer immunotherapy.

The emergence of immunotherapy has revolutionized medical oncology with unprecedented advances in cancer treatment over the past two decades. However, a major obstacle in cancer immunotherapy is identifying appropriate tumor-specific antigens to make targeted therapy achievable with fewer normal cells being impaired. The similarity between placentation and tumor development and growth has inspired many investigators to discover antigens for effective immunotherapy of cancers. Placenta-specific 1 (PLAC1) is one of the recently discovered placental antigens with limited normal tissue expression and fundamental roles in placental function and development. There is a growing body of evidence showing that PLAC1 is frequently activated in a wide variety of cancer types and promotes cancer progression. Based on the restricted expression of PLAC1 in testis, placenta and a wide variety of cancers, we have designated this molecule with new terminology, cancer-testis-placenta (CTP) antigen, a feature that PLAC1 shares with many other cancer testis antigens. Recent reports from our lab provide compelling evidence on the preferential expression of PLAC1 in prostate cancer and its potential utility in prostate cancer immunotherapy. PLAC1 may be regarded as a potential CTP antigen for targeted cancer immunotherapy based on the available data on its promoting function in cancer development and also its expression in cancers of different histological origin. In this review, we will summarize current data on PLAC1 with emphasis on its association with cancer development and immunotherapy.

Placenta-specific1 (PLAC1) is a potential target for antibody-drug conjugate-based prostate cancer immunotherapy.

Our recent findings strongly support the idea of PLAC1 being as a potential immunotherapeutic target in prostate cancer (PCa). Here, we have generated and evaluated an anti-placenta-specific1 (PLAC1)-based antibody drug conjugate (ADC) for targeted immunotherapy of PCa. Prostate cancer cells express considerable levels of PLAC1. The Anti-PLAC1 clone, 2H12C12, showed high reactivity with recombinant PLAC1 and selectivity recognized PLAC1 in prostate cancer cells but not in LS180 cells, the negative control. PLAC1 binding induced rapid internalization of the antibody within a few minutes which reached to about 50% after 15 min and almost completed within an hour. After SN38 conjugation to antibody, a drug-antibody ratio (DAR) of about 5.5 was achieved without apparent negative effect on antibody affinity to cell surface antigen. The ADC retained intrinsic antibody activity and showed enhanced and selective cytotoxicity with an IC50 of 62 nM which was about 15-fold lower compared to free drug. Anti-PLAC1-ADC induced apoptosis in human primary prostate cancer cells and prostate cell lines. No apparent cytotoxic effect was observed in in vivo animal safety experiments. Our newly developed anti-PLAC1-based ADCs might pave the way for a reliable, efficient, and novel immunotherapeutic modality for patients with PCa.

Endometrial factors similarly induced by IFNT2 and IFNTc1 through transcription factor FOXS1.

In ruminants, Interferon tau (IFNT) is the pregnancy recognition protein produced by the mononuclear trophectoderm of the conceptus, and is secreted into the uterine lumen during the peri-attachment period. In our previous study, the high-throughput RNA sequencing (RNA-seq) data obtained from bovine conceptuses during the peri-attachment period identified two IFNT mRNAs, IFNT2 and IFNTc1. However, how each of these IFNT variants regulates endometrial gene expression has not been characterized. Using RNA-seq analysis, we evaluated how IFNT2 and IFNTc1 affected transcript expression in primary bovine endometrial epithelial cells (EECs). IFNT treatment induced 348 differentially expressed genes (DEGs); however, there are few DEGs in IFNT2 or IFNTc1 treated EECs, indicating that IFNT2-induced DEGs were similar to those induced by IFNTc1 treatment. In in silico analysis, we identified four IFNT2- and IFNTc1-induced pathways: 1) type II interferon signaling, 2) proteasome degradation, 3) type III interferon signaling, and 4) DNA damage response. We further demonstrated that IFNT2 and IFNTc1 up-regulated several transcription factors, among which forkhead box S1 (FOXS1) was identified as the most highly expressed gene. Furthermore, the knockdown of FOXS1 in IFNT2- or IFNTc1-treated EECs similarly down-regulated 9 genes including IRF3 and IRF9, and up-regulated 9 genes including STAT1, STAT2, and IRF8. These represent the first demonstration that effects of each IFNT on EECs were studied, and suggest that endometrial response as well as signaling mechanisms were similar between two IFNT variants existed in utero.

N-(4-methoxyphenyl) caffeamide-induced melanogenesis inhibition mechanisms.

BACKGROUND: The derivative of caffeamide exhibits antioxidant and antityrosinase activity. The activity and mechanism of N-(4-methoxyphenyl) caffeamide (K36E) on melanogenesis was investigated. METHODS: B16F0 cells were treated with various concentrations of K36E; the melanin contents and related signal transduction were studied. Western blotting assay was applied to determine the protein expression, and spectrophotometry was performed to identify the tyrosinase activity and melanin content. RESULTS: Our results indicated that K36E reduced α-melanocyte-stimulating hormone (α-MSH)-induced melanin content and tyrosinase activity in B16F0 cells. In addition, K36E inhibited the expression of phospho-cyclic adenosine monophosphate (cAMP)-response element-binding protein, microphthalmia-associated transcription factor (MITF), tyrosinase, and tyrosinase-related protein-1 (TRP-1). K36E activated the phosphorylation of protein kinase B (AKT) and glycogen synthase kinase 3 beta (GSK3ß), leading to the inhibition of MITF transcription activity. K36E attenuated α-MSH induced cAMP pathways, contributing to hypopigmentation. CONCLUSIONS: K36E regulated melanin synthesis through reducing the expression of downstream proteins including p-CREB, p-AKT, p-GSK3ß, tyrosinase, and TRP-1, and activated the transcription factor, MITF. K36E may have the potential to be developed as a skin whitening agent.

Regulation of the MDM2-p53 pathway by the nucleolar protein CSIG in response to nucleolar stress.

Nucleolar proteins play an important role in the regulation of the MDM2-p53 pathway, which coordinates cellular response to stress. However, the mechanism underlying this regulation remains poorly understood. Here, we report that the nucleolar protein CSIG is a novel and crucial regulator of the MDM2-p53 pathway. We demonstrate that CSIG translocates from the nucleolus to the nucleoplasm in response to nucleolar stress. Moreover, knockdown of CSIG attenuates the induction of p53 and abrogates G1 phase arrest in response to nucleolar stress. CSIG interacts directly with the MDM2 RING finger domain and inhibits MDM2 E3 ubiquitin ligase activity, thus resulting in a decrease in MDM2-mediated p53 ubiquitination and degradation. Our results suggest that the CSIG-MDM2-p53 regulatory pathway plays an important role in the cellular response to nucleolar stress.

Placental Growth Factor Promotes Ovarian Cancer Cell Invasion via ZEB2.

BACKGROUND/AIMS: The aggressive manner of ovarian cancer (OVC) cells accounts for the majority of its lethality. Recently, we have shown that placental growth factor (PLGF) promotes metastases of OVC cells through miR-543-regulated MMP7. In the current study, we analyzed the effects of PLGF on another cell invasion associated protein, ZEB2, in OVC cells. METHODS: The PLGF and ZEB2 levels in OVC tissues were compared to the paired adjacent non-tumor ovary tissue. We modified ZEB2 levels in OVC cells, and examined its effects on PLGF mRNA and protein levels by RT-qPCR and by Western blot, respectively. We also modified PLGF levels in OVC cells, and examined its effects on ZEB2 mRNA and protein levels by RT-qPCR and by Western blot, respectively. Then, we examined the cell invasiveness in PLGF-modified OVC cells in a transwell cell invasion assay. Finally, we used specific signal pathway inhibitors to treat PLGF-modified OVC cells and examined the effects on ZEB2 activation. RESULTS: PLGF and ZEB2 levels were both significantly increased in OVC tissues, compared to the paired adjacent non-tumor ovary tissue. The PLGF and ZEB2 levels were strongly correlated. ZEB2 modification did not alter PLGF levels. Overexpression of PLGF in OVC cells significantly increased ZEB2 levels and cell invasiveness, while PLGF depletion in OVC cells significantly decreased ZEB2 levels and cell invasiveness. Application of a specific MAPK-p38 inhibitor, but not application of specific inhibitors for MAPK-p42/p44, PI3k/Akt, or JNK signaling pathways, to PLGF-overexpressing OVC cells substantially abolished the PLGF-induced ZEB2 activation. CONCLUSION: PLGF enhances OVC cell invasion through MAPK-p38-dependent activation of ZEB2.

Aflibercept: A Review in Metastatic Colorectal Cancer.

Aflibercept is a recombinant fusion protein that acts as a soluble decoy receptor for vascular endothelial growth factor (VEGF), a key regulator of angiogenesis. It binds to all isoforms of VEGF-A as well as VEGF-B and placental growth factor, and, thus, prevents them from binding to and activating their cognate receptors. In the USA and EU, intravenously administered aflibercept in combination with an infusion of leucovorin, fluorouracil and irinotecan (FOLFIRI) is approved for the treatment of patients with metastatic colorectal cancer that is resistant to or has progressed after treatment with an oxaliplatin-containing regimen. The efficacy of aflibercept in this indication was assessed in a multinational, pivotal phase 3 trial (VELOUR), in which the approved regimen of aflibercept 4 mg/kg every 2 weeks plus FOLFIRI significantly prolonged median overall survival by 1.44 months compared with FOLFIRI alone (primary endpoint). The addition of aflibercept also significantly prolonged progression-free survival and significantly increased the objective response rate compared with FOLFIRI alone. Addition of aflibercept to FOLFIRI was associated with anti-VEGF-related adverse events and an increased incidence of FOLFIRI-related adverse events, but the tolerability of the combination was generally acceptable in this pre-treated population. The most common grade 3 or 4 adverse events with aflibercept plus FOLFIRI included neutropenia, diarrhoea and hypertension. In conclusion, aflibercept plus FOLFIRI is a useful treatment option for patients with metastatic colorectal cancer previously treated with an oxaliplatin-containing regimen, with or without bevacizumab.

Combined Anti-PLGF and Anti-Endostatin Treatments Inhibit Ocular Hemangiomas.

BACKGROUND/AIMS: The degree of neovascularization determines the aggressiveness of ocular hemangiomas (OH). So far, the anti-angiogenic treatments using either antagonists against vascular endothelial growth factor A (VEGF-A), or endostatin, do not always lead to satisfactory therapeutic outcome. METHODS: We examined the VEGF receptor 1 (VEGFR1) levels in the OH specimen. We compared the effects of anti-PLGF, endostatin, as well as their combined treatments on the growth of OH in a mouse model, using bioluminescence imaging in living animals. We also examined vascularization by CD31 expression. RESULTS: We detected higher VEGFR1 levels in the OH, compared to paired normal tissue. Thus, we hypothesize that as a major ligand for VEGFR1, placental growth factor (PLGF) may also play a role in the neovascularization and tumorigenesis of OH. In an implanted OH model in mice, we found that both anti-PLGF and endostatin significantly decreased OH growth as well as vascularization, while combined treatments had a significantly more pronounced effect. CONCLUSION: Our data suggest that combined anti-PLGF and endostatin may be a more effective therapy for inhibition of ocular vascularization and the tumor growth in OH.

Erythropoietin-mediated expression of placenta growth factor is regulated via activation of hypoxia-inducible factor-1α and post-transcriptionally by miR-214 in sickle cell disease.

Placental growth factor (PlGF) plays an important role in various pathological conditions and diseases such as inflammation, cancer, atherosclerosis and sickle cell disease (SCD). Abnormally high PlGF levels in SCD patients are associated with increased inflammation and pulmonary hypertension (PHT) and reactive airway disease; however, the transcriptional and post-transcriptional mechanisms regulating PlGF expression are not well defined. Herein, we show that treatment of human erythroid cells and colony forming units with erythropoietin (EPO) increased PlGF expression. Our studies showed EPO-mediated activation of HIF-1α led to subsequent binding of HIF-1α to hypoxia response elements (HREs) within the PlGF promoter, as demonstrated by luciferase transcription reporter assays and ChIP analysis of the endogenous gene. Additionally, we showed miR-214 post-transcriptionally regulated the expression of PlGF as demonstrated by luciferase reporter assays using wild-type (wt) and mutant PlGF-3'-UTR constructs. Furthermore, synthesis of miR-214, located in an intron of DNM3 (dynamin 3), was transcriptionally regulated by transcription factors, peroxisome proliferator-activated receptor-α (PPARα) and hypoxia-inducible factor-1α (HIF-1α). These results were corroborated in vivo wherein plasma from SCD patients and lung tissues from sickle mice showed an inverse correlation between PlGF and miR-214 levels. Finally, we observed that miR-214 expression could be induced by fenofibrate, a Food and Drug Administration (FDA) approved PPARα agonist, thus revealing a potential therapeutic approach for reduction in PlGF levels by increasing miR-214 transcription. This strategy has potential clinical implications for several pathological conditions including SCD.

CSIG promotes hepatocellular carcinoma proliferation by activating c-MYC expression.

Cellular senescence-inhibited gene (CSIG) protein significantly prolongs the progression of replicative senescence, but its role in tumorigenesis is unclear. To reveal the role of CSIG in HCC, we determined its expression in HCC tissues and surrounding tissues and its functions in tumor cell proliferation in vitro and in vivo. CSIG protein was overexpressed in 86.4% of the human HCC cancerous tissues as compared with matched surrounding tissues, and its protein expression was greater in HCC cells than the non-transformed hepatic cell line L02. Furthermore, upregulation of CSIG significantly increased the colony formation of SMMC7721 and HepG2 cells, and silencing CSIG could induce cell cycle arrest and cell apoptosis. The tumorigenic ability of CSIG was confirmed in vivo in a mouse xenograft model. Our results showed that CSIG promoted the proliferation of HepG2 and SMMC7721 cells in vivo. Finally, CSIG protein directly interacted with c-MYC protein and increased c-MYC protein levels; the ubiquitination and degradation of c-MYC protein was increased with knockdown of CSIG. CSIG could also increase the expression of c-MYC protein in SMMC7721 cells in vivo, and it was noted that the level of c-MYC protein was also elevated in most human cancerous tissues with high level of CSIG.

Inhibition of placental growth factor in renal cell carcinoma.

BACKGROUND/AIM: Placental growth factor (PlGF) is up-regulated in major malignant diseases or following antiangiogenic therapy, although it is present in low levels under normal physiological conditions. TB403, a monoclonal antibody against PlGF, was investigated in clear cell renal cell carcinoma (ccRCC) xenografts since it has been proposed as a potential target in oncology. MATERIALS AND METHODS: Human ccRCCs were implanted in athymic nude mice to evaluate the efficacy of TB403 and to excise xenograft tumors for molecular experiments. RESULTS: TB403 did not significantly inhibit tumor growth in treatment-naïve or sunitinib-resistant ccRCC xenografts. Gene expression profiling resulted in over-expression of the C1orf38 gene, which induced immunoreactivity in macrophages. Angiogenesis PCR arrays showed that VEGFR-1 was not expressed in ccRCC xenografts. CONCLUSION: PlGF blockade did not have a broad antiangiogenic efficacy; however, it might be effective on-target in VEGFR1-expressing tumors. The inhibition of VEGF pathway may induce the activity of tumor-associated-macrophages for angiogenesis escape.

Inhibition of metastasis of oral squamous cell carcinoma by anti-PLGF treatment.

Neovascularization plays a critical role in cancer metastasis. However, the molecular mechanism regulating the neovascularization in oral squamous cell carcinoma (OSCC) is poorly understood. Placental growth factor (PLGF) has been known to regulate pathological angiogenesis and has been recently shown to regulate matrix metalloproteinases (MMPs) for extracellular matrix degradation during neovascularization. Here we aimed to examine whether PLGF may regulate MMPs in the metastasis of OSCC. We found that PLGF and MMP9 levels strongly correlated in OSCC in the patients, both increased in the OSCC from the patients with metastasis of the primary OSCC. Thus, we used several human OSCC cell lines to examine the relationship between PLGF and MMP9. We found that overexpression of PLGF in OSCC cells increased expression of MMP9, while inhibition of PLGF in OSCC cells decreased expression of MMP9. However, adaptation of MMP9 levels in OSCC cells did not affect the levels of PLGF. These data suggest that PLGF may regulate MMP9 in OSCC cells, but not vice versa. Moreover, inhibition of ERK1/2, but not inhibition of PI3k or JNK pathways, substantially abolished the effect of PLGF on MMP9, suggesting that PLGF may increase expression of MMP9 via ERK/MAPK signaling pathway. Thus, our data demonstrate that PLGF-induced cancer neovascularization may be partially mediated through its effect on MMP9 activation in OSCC.

Psg22 expression in mouse trophoblast giant cells is associated with gene inversion and co-expression of antisense long non-coding RNAs.

Pregnancy-specific glycoproteins (PSGs) are secreted carcinoembryonic antigen (CEA)-related cell adhesion molecules-related members of the immunoglobulin superfamily and are encoded by multigene families in species with haemochorial placentation. PSGs may be the most abundant trophoblast-derived proteins in human maternal blood in late pregnancy and there is evidence that dysregulation of PSG expression is associated with gestational pathology. PSGs are produced by syncytiotrophoblast in the human placenta and by trophoblast giant cells (TGCs) and spongiotrophoblast in rodents, and are implicated in immune regulation, angiogenesis and regulation of platelet function. PSGs are encoded by 17 genes in the mouse and ten genes in the human. While functions appear to be conserved, the typical protein domain organisation differs between species. We analysed the evolution of the mouse Psg genomic locus structure and report inversion of the Psg22 gene within the locus. Psg22 is the most abundant Psg transcript detected in the first half of mouse pregnancy and we identified antisense long non-coding RNA (lncRNA) transcripts adjacent to Psg22 associated with an active local chromatin conformation. This suggests that an epigenetic regulatory mechanism may underpin high Psg22 expression relative to the other Psg gene family members in TGCs.

Placental growth factor in cancer.

INTRODUCTION: Placental growth factor (PLGF) belongs to the VEGF family, which among the three VEGF receptors binds exclusively to VEGFR1, present on various cell types. Isoform PLGF-2 also binds the neuropilin co-receptors. PLGF is dispensable for development and health but has a prominent role in pathology including cancer. This has triggered the question whether PLGF targeting might offer an alternative to current antiangiogenesis therapy, which encounters problems of refractoriness and acquired resistance. AREAS COVERED: This article reviews the available literature on the characteristics of PLGF, its role(s) in cancer and the findings on PLGF inhibition in preclinical models with attention to as yet unresolved questions and summarizes data from initial clinical trials. EXPERT OPINION: Preclinical studies show that inhibition of PLGF, either by genetic inhibition or by pharmacological blockade using distinct independently generated anti-PLGF antibodies, slows down tumor growth and metastasis and even induces regression of pre-existing medulloblastoma, the most frequent brain cancer in children. These promising preclinical findings, together with the acceptable safety profile of anti-PLGF administration in Phase I clinical trials, have attracted attention to PLGF as a potential target for therapy.

The angiogenic asset of soft tissue sarcomas: a new tool to discover new therapeutic targets.

STS (soft tissue sarcomas) are rare malignant tumours deriving from cells of mesenchymal origin and represent only 1% of all malignant neoplasms. It has been extensively demonstrated that angiogenesis has an important role in cancer malignancy. Particularly, a lot of studies demonstrate the importance of angiogenesis in the development of carcinomas, whereas little is known about the role of angiogenesis in sarcomas and especially in STS. This review aims at summarizing the new discoveries about the nature and the importance of angiogenesis in STS and the new possible therapeutic strategies involved. Only a few studies concerning STS focus on tumour neovascularization and proangiogenic factors and look for a correlation with the patients prognosis/survival. These studies demonstrate that intratumoural MVD (microvessels density) may not accurately represent the angiogenic capacity of STS. Nevertheless, this does not exclude the possibility that angiogenesis could be important in STS. The importance of neoangiogenesis in soft tissue tumours is confirmed by the arising number of publications comparing angiogenesis mediators with clinical features of patients with STS. The efficacy of anti-angiogenic therapies in other types of cancer is well documented. The understanding of the involvement of the angiogenic process in STS, together with the necessity to improve the therapy for this often mortal condition, prompted the exploration of anti-tumour compounds targeting this pathway. In conclusion, this review emphasizes the importance to better understand the mechanisms of angiogenesis in STS in order to subsequently design-specific target therapies for this group of poorly responding tumours.

Differential antitumor activity of aflibercept and bevacizumab in patient-derived xenograft models of colorectal cancer.

The recombinant fusion protein aflibercept (ziv-aflibercept in the United States) binds VEGF-A, VEGF-B, and placental growth factor (PlGF). The monoclonal antibody bevacizumab binds VEGF-A. Recent studies hypothesized that dual targeting of VEGF/PlGF is more beneficial than targeting either ligand. We compared activity of aflibercept versus bevacizumab in 48 patient-derived xenograft (PDX) colorectal cancer models. Nude mice engrafted subcutaneously with PDX colorectal cancer tumors received biweekly aflibercept, bevacizumab, or vehicle injections. Differential activity between aflibercept and bevacizumab, determined by mouse (m), human (h), VEGF-A, and PlGF levels in untreated tumors, was measured. Aflibercept induced complete tumor stasis in 31 of 48 models and bevacizumab in 2 of 48. Based on statistical analysis, aflibercept was more active than bevacizumab in 39 of 48 models; in 9 of 39 of these models, bevacizumab was considered inactive. In 9 of 48 remaining models, aflibercept and bevacizumab had similar activity. Tumor levels of hVEGF-A (range 776-56,039 pg/mg total protein) were ∼16- to 1,777-fold greater than mVEGF-A (range 8-159 pg/mg total protein). Tumor levels of mPlGF (range 104-1,837 pg/mg total protein) were higher than hPlGF (range 0-543 pg/mg total protein) in 47 of 48 models. Tumor cells were the major source of VEGF; PlGF was primarily produced by tumor stroma. Because tumor levels of hVEGF-A were far greater than mVEGF-A, bevacizumab's inability to bind mVEGF-A is unlikely to explain higher and more consistent aflibercept activity. Neutralizing PlGF and VEGFR-1 activation may be a factor and should be investigated in future studies. In these colorectal cancer PDX models, aflibercept demonstrated greater antitumor activity than bevacizumab.