Biomarkers predicting tumor response and evasion to anti-angiogenic therapy

Autophagy as a mechanism for anti-angiogenic therapy resistance

Autophagy is a lysosomal-dependent degradation process that is highly conserved and maintains cellular homeostasis by sequestering cytosolic material for degradation either non-specifically by non-selective autophagy, or targeting specific proteins aggregates by selective autophagy. Autophagy serves as a protective mechanism defending the cell from stressors and also plays an important role in enabling tumor cells to overcome harsh conditions arising in their microenvironment during growth as well as oxidative and non-oxidative injuries secondary to therapeutic stressors. Recently, autophagy has been implicated to cause tumor resistance to anti-angiogenic therapy, joining an existing literature implicating autophagy in cancer resistance to conventional DNA damaging chemotherapy and ionizing radiation. In this review, we discuss the role of angiogenesis in malignancy, mechanisms of resistance to anti-angiogenic therapy in general, the role of autophagy in driving malignancy, and the current literature in autophagy-mediated anti-angiogenic therapy resistance. Finally, we provide future insight into the current challenges of using autophagy inhibitors in the clinic and provides tips for future studies to focus on to effectively target autophagy in overcoming resistance to anti-angiogenic therapy.

Circulating Biomarkers for Tumor Angiogenesis: Where Are We?

BACKGROUND

In recent years, several anti-angiogenic drugs have been developed and their addition to standard treatment has been associated with clinical benefits. However, the response to anti-angiogenic therapy is characterized by considerable variability. In this context, the development of dynamic non-invasive biomarkers would be helpful to elucidate the emergence of anti-angiogenic resistance as well as to correctly address the treatment.

OBJECTIVES

The purpose of this review is to describe current reports on circulating diagnostic and prognostic biomarkers related to angiogenesis. We further discuss how this non-invasive strategy could improve the monitoring of tumor treatment and help clinical strategy.

RESULTS

We discuss the latest evidence in the literature regarding circulating anti-angiogenic markers. Besides growth factor proteins, different circulating miRNAs could exert a pro- or anti-angiogenic activity so as to represent suitable candidates for a non-invasive strategy. Recent reports indicate that tumor-derived exosomes, which are small membrane vesicles abundant in biological fluids, also have an impact on vascular remodeling.

CONCLUSION

Numerous circulating biomarkers related to angiogenesis have been recently identified. Their use will allow identifying patients who are more likely to benefit from a specific anti-angiogenic treatment, as well as detecting those who will develop resistance and/or adverse effects. Nonetheless, further studies are required to elucidate the role of these biomarkers in clinical settings.

Imaging Response of Antiangiogenic and Immune-Oncology Drugs in Metastatic Renal Cell Carcinoma (mRCC): Current Status and Future Challenges

This report aims to review criteria which have been proposed for treatment evaluation in mRCC under anti-angiogenic and immune-oncologic therapies and discuss future challenges for imagers. RECIST criteria seem to only partially reflect the clinical benefit derived from anti-angiogenic drugs in mRCC. New methods of analysis propose to better evaluate response to these drugs, including a new threshold for size criteria (-10%), attenuation (Choi and modified Choi criteria), functional imaging techniques (perfusion CT, ultrasound or MRI), and new PET radiotracers. Imaging of progression is one of the main future challenges facing imagers. It is progression and not response that will trigger changes in therapy, therefore it is tumour progression that should be identified by imaging techniques to guide the oncologist on the most appropriate time to change therapy. Yet little is known on dynamics of tumour progression, and much data still needs to be accrued to understand it. Finally, as immunotherapies develop, flare or pseudo-progression phenomena are observed. Studies need to be performed to determine whether imaging can distinguish between patients undergoing pseudo-progression for which therapy should be continued, or true progression for which the treatment must be changed.

Total and not bevacizumab-bound vascular endothelial growth factor as potential predictive factors to bevacizumab-based chemotherapy in colorectal cancer

AIM: To identify suitable biomarkers of response to bevacizumab (BV) - it remains an open question. The measurement of serum vascular endothelial growth factor (VEGF) has been proposed as a predictive factor for this drug, even if literature data are contradictory.

METHODS: We prospectively evaluated the role of BV, total and not BV-bound VEGF and angiopoietin-2 (Ang-2) serum levels as potential predictive factors of response for BV in combination with an oxaliplatin-based chemotherapy. BV, Ang-2, total and not BV-bound VEGF levels were measured at baseline, before 2^nd and 5^th cycle of oxaliplatin-based chemotherapy in 20 consecutive metastatic colorectal cancer patients.

RESULTS: Results were correlated to response to treatment. Variability in BV levels have been found, with decreased level in less responding patients. In particular, the concentration of BV increased of 3.96 ± 0.69 folds in serum of responsive patients after 3 more cycles of therapy compared to those with stable or progressive disease with a 0.72 ± 0.25 and 2.10 ± 0.13 fold increase, respectively. The determination of free and total VEGF demonstrated that the ratio between the two values, evaluated immediately before the 2^nd and the 5^th cycle of therapy, decreased from 26.65% ± 1.33% to 15.50% ± 3.47% in responsive patients and from 53.41% ± 4.75 to 34.95% ± 2.88% in those with stable disease. Conversely, in those with progression of disease, the ratio showed the opposite behavior coming up from 25.99% ± 5.23% to 51.71% ± 5.28%. The Ang-2 levels did not show any relationship.

CONCLUSION: Our data show that the ratio of not BV-bound VEGF to total VEGF serum and BV plasma concentrations for predicting the response to BV plus oxaliplatin-based chemotherapy could be a promising biomarker of response to BV.

Adaptation to antiangiogenic therapy in neurological tumors

Because tumors require a vascular supply for their survival and growth, angiogenesis is considered an important therapeutic target in most human cancers including cancer of the central nervous system. Antiangiogenic therapy has focused on inhibitors of the vascular endothelial growth factor (VEGF) signaling pathway. VEGF pathway-targeted drugs have shown therapeutic efficacy in several CNS tumors and have been tried most frequently in glioblastoma. These therapies, however, have been less effective than anticipated as some patients do not respond to therapy and some receive only modest benefit. Underlying this suboptimal response are multiple mechanisms of drug resistance involving changes in both tumor cells and their microenvironment. In this review, we discuss the multiple proposed mechanisms by which neurological tumors evolve to become resistant to antiangiogenic therapies. A better understanding of these mechanisms, their context, and their interplay will likely facilitate improvements in pharmacological strategies for the targeted treatment of neurological tumors.

Correlation of baseline biomarkers with clinical outcomes and response to fulvestrant with vandetanib or placebo in patients with bone predominant metastatic breast cancer: An OCOG ZAMBONEY sub-study

Background

Bone metastases are common in women with breast cancer and often result in skeletal related events (SREs). As the angiogenic factor vascular endothelial growth factor (VEGF) regulates osteoclast activity and is associated with more extensive bone metastases and SRE risk in metastatic breast cancer, we hypothesized that blockade of VEGF signaling could be a therapeutic strategy for inhibiting bone metastases progression and possibly prolonging overall (OS) or progression-free survival (PFS). The Zamboney trial was a randomized placebo-controlled study designed to assess whether patients with bone predominant metastatic breast cancer benefited from addition of the VEGF receptor (VEGFR) targeting agent, vandetanib, to endocrine therapy with fulvestrant. As a companion study, evaluation of biomarkers and their potential association with response to vandetanib or SRE risk was performed.

Methods

Baseline overnight fasted serum from enrolled patients was analyzed for levels of various putative biomarkers including; VEGF-A, soluble (s)VEGFR2, sVEGFR3, transforming growth factor (TGF)-β1 and activinA by ELISA. Spearman correlation coefficients and Wilcoxon rank sum tests were used to investigate potential relationships between biomarker values and baseline clinical parameters. Prognostic and predictive ability of each marker was investigated using Cox proportional hazards regression with adjustments for treatment and baseline strata of serum CTx (<400 versus ≥400 ng/L).

Results

Of 129 enrolled patients, serum was available for analysis in 101; 51 in vandetanib and 50 in placebo arm. Mean age amongst consenting patients was 59.8 years. Clinical characteristics were not significantly different between patients with or without serum biomarker data and serum markers were similar for patients by treatment arm. Baseline sVEGFR2 was prognostic for OS (HR=0.77, 95% CI=0.61–0.96, p=0.020), and although a modest association was observed, it was not significant for PFS (HR=0.90, 95% CI=0.80–1.01, p=0.085) nor time to first SRE (HR=0.82, 95% CI=0.66–1.02, p=0.079). When interaction terms were evaluated, sVEGFR2 was not found to be predictive of response to vandetanib, although a modest association remained with respect to PFS (interaction p=0.085). No other marker showed any significant prognostic or predictive ability with any measured outcome.

Conclusions

In this clinical trial, sVEGFR2 appeared prognostic for OS, hence validation of sVEGFR2 should be conducted. Moreover, the role of sVEGFR2 in breast cancer bone metastasis progression should be elucidated.

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Baseline VEGF, sVEGFR3, TGF-β or activinA were not associated with clinical outcomes in patients treated with fulvestrant in conjunction with vandetanib or placebo.

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Baseline sVEGFR2 was modestly associated with clinical outcomes including PFS, OS and time to first skeletal event.

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Increased baseline sVEGFR2 was associated with improved clinical outcomes in this study sample.

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These findings support the need for future studies of the role of sVEGFR2 in bone metastasis progression.

Mechanisms of evasive resistance to anti-VEGF therapy in glioblastoma

Angiogenesis inhibitors targeting the VEGF signaling pathway have been US FDA approved for various cancers including glioblastoma (GBM), one of the most lethal and angiogenic tumors. This has led to the routine use of the anti-VEGF antibody bevacizumab in recurrent GBM, conveying substantial improvements in radiographic response, progression-free survival and quality of life. Despite these encouraging beneficial effects, patients inevitably develop resistance and frequently fail to demonstrate significantly better overall survival. Unlike chemotherapies, to which tumors exhibit resistance due to genetic mutation of drug targets, emerging evidence suggests that tumors bypass antiangiogenic therapy while VEGF signaling remains inhibited through a variety of mechanisms that are just beginning to be recognized. Because of the indirect nature of resistance to VEGF inhibitors there is promise that strategies combining angiogenesis inhibitors with drugs targeting such evasive resistance pathways will lead to more durable antiangiogenic efficacy and improved patient outcomes. Further identifying and understanding of evasive resistance mechanisms and their clinical importance in GBM relapse is therefore a timely and critical issue.

Quantitative insight in utilizing circulating angiogenic factors as biomarkers for antiangiogenic therapy: systems pharmacology approach

Circulating angiogenic factors (CAF) like vascular endothelial growth factor (VEGF), placental growth factor (PlGF), and sVEGFR2 have potential as biomarkers for antiangiogenic therapy. The interpretation of changes in CAF is complicated by the dynamic nature of the tumor and host cells emanating CAF in response to VEGF pathway inhibition. We developed a systems pharmacology model of anti-VEGF agents to investigate CAF modulation by tumor and host cells, and the relationship between overall CAF changes in response to sunitinib and antitumor efficacy. This model distinguishes between the tumor cells' contributions from tumor-independent response to therapy and total plasma CAF correlating with antitumor activity. Altered VEGF is more likely to serve as a useful biomarker reflecting tumor responses in cancer patients whose pretreatment VEGF is higher than baseline VEGF in healthy subjects. Our findings provide a mechanistic insight into tumor modulation of angiogenic molecules, and may explain the inconsistent results found in previous biomarker studies.

Predictive markers of efficacy for an angiopoietin-2 targeting therapeutic in xenograft models

The clinical efficacy of anti-angiogenic therapies has been difficult to predict, and biomarkers that can predict responsiveness are sorely needed in this era of personalized medicine. CVX-060 is an angiopoietin-2 (Ang2) targeting therapeutic, consisting of two peptides that bind Ang2 with high affinity and specificity, covalently fused to a scaffold antibody. In order to optimize the use of this compound in the clinic the construction of a predictive model is described, based on the efficacy of CVX-060 in 13 cell line and 2 patient-derived xenograft models. Pretreatment size tumors from each of the models were profiled for the levels of 27 protein markers of angiogenesis, SNP haplotype in 5 angiogenesis genes, and somatic mutation status for 11 genes implicated in tumor growth and/or vascularization. CVX-060 efficacy was determined as tumor growth inhibition (TGI%) at termination of each study. A predictive statistical model was constructed based on the correlation of these efficacy data with the marker profiles, and the model was subsequently tested by prospective analysis in 11 additional models. The results reveal a range of CVX-060 efficacy in xenograft models of diverse tissue types (0-64% TGI, median = 27%) and define a subset of 3 proteins (Ang1, EGF, Emmprin), the levels of which may be predictive of TGI by Ang2 blockade. The direction of the associations is such that better efficacy correlates with high levels of target and low levels of compensatory/antagonizing molecules. This effort has revealed a set of candidate predictive markers for CVX-060 efficacy that will be further evaluated in ongoing clinical trials.

Serial measurements of serum PDGF-AA, PDGF-BB, FGF2, and VEGF in multiresistant ovarian cancer patients treated with bevacizumab

INTRODUCTION

Anti-VEGF treatment has proven effective in recurrent ovarian cancer. However, the identification of the patients most likely to respond is still pending. It is well known that the angiogenesis is regulated by several other pro-angiogenic proteins, e.g. the platelet - derived growth factor (PDGF) system and the fibroblast growth factor (FGF) system. These other signaling pathways may remain active or become upregulated during anti-VEGF treatment.The aim of the present study was to investigate if potential changes of PDGF-BB, PDGF-AA, and FGF2 before and during bevacizumab treatment had predictive value for early progression or survival. Furthermore, we wanted to investigate the importance of serum VEGF in the same cohort.

METHODS

This study included 106 patients with chemotherapy-resistant epithelial ovarian cancer who were treated with single agent bevacizumab as part of a biomarker protocol. Patients were evaluated for response by the Response Evaluation Criteria In Solid Tumors (RECIST) and/ or Gynecologic Cancer Intergroup (GCIG) CA125 criteria. Serum samples were collected at baseline and prior to each treatment. FGF2, PDGF-BB, PDGF-AA were quantified simultaneously using the Luminex system, and VEGF-A was measured by ELISA. Eighty-eight baseline samples were avaliable for FGF2, PDGF-BB, PDGF-AA analysis, and 93 baseline samples for VEGF.

RESULTS

High baseline serum VEGF was related to poor overall survival. Furthermore, high serum PDGF-BB and FGF2 was of prognostic significance. None of the markers showed predictive value, neither at baseline level nor during the treatment.

Evaluation of changes in the tumor microenvironment after sorafenib therapy by sequential histology and 18F-fluoromisonidazole hypoxia imaging in renal cell carcinoma

The mechanistic dissociation of ‘tumor starvation’ versus ‘vascular normalization’ following anti-angiogenic therapy is a subject of intense controversy in the field of experimental research. In addition, accurately evaluating changes of the tumor microenvironment after anti-angiogenic therapy is important for optimizing treatment strategy. Sorafenib has considerable anti-angiogenic effects that lead to tumor starvation and induce tumor hypoxia in the highly vascularized renal cell carcinoma (RCC) xenografts. ¹⁸F-fluoromisonidazole (¹⁸F-FMISO) is a proven hypoxia imaging probe. Thus, to clarify early changes in the tumor microenvironment following anti-angiogenic therapy and whether ¹⁸F-FMISO imaging can detect those changes, we evaluated early changes in the tumor microenvironment after sorafenib treatment in an RCC xenograft by sequential histological analysis and ¹⁸F-FMISO autoradiography (ARG). A human RCC xenograft (A498) was established in nude mice, for histological studies and ARG, and further assigned to the control and sorafenib-treated groups (80 mg/kg, per os). Mice were sacrificed on Days 1, 2, 3 and 7 in the histological study, and on Days 3 and 7 in ARG after sorafenib treatment. Tumor volume was measured every day. ¹⁸F-FMISO and pimonidazole were injected intravenously 4 and 2 h before sacrifice, respectively. Tumor sections were stained with hematoxylin and eosin and immunohistochemically with pimonidazole and CD31. Intratumoral ¹⁸F-FMISO distribution was quantified in ARG. Tumor volume did not significantly change on Day 7 after sorafenib treatment. In the histological study, hypoxic fraction significantly increased on Day 2, mean vessel density significantly decreased on Day 1 and necrosis area significantly increased on Day 2 after sorafenib treatment. Intratumoral ¹⁸F-FMISO distribution significantly increased on Days 3 (10.2-fold, p<0.01) and 7 (4.1-fold, p<0.01) after sorafenib treatment. The sequential histological evaluation of the tumor microenvironment clarified tumor starvation in A498 xenografts treated with sorafenib. ¹⁸F-FMISO hypoxia imaging confirmed the tumor starvation. ¹⁸F-FMISO PET may contribute to determine an optimum treatment protocol after anti-angiogenic therapy.