Influence of soluble or matrix-bound isoforms of vascular endothelial growth factor-A on tumor response to vascular-targeted strategies

Abstract

Antiangiogenic therapy based on blocking the actions of vascular endothelial growth factor‐A (VEGF) can lead to “normalization” of blood vessels in both animal and human tumors. Differential expression of VEGF isoforms affects tumor vascular maturity, which could influence the normalization process and response to subsequent treatment. Fibrosarcoma cells expressing only VEGF120 or VEGF188 isoforms were implanted either subcutaneously (s.c.) or in dorsal skin‐fold “window” chambers in SCID mice. VEGF120 was associated with vascular fragility and hemorrhage. Tumor‐bearing mice were treated with repeat doses of SU5416, an indolinone receptor tyrosine kinase inhibitor with activity against VEGFR‐2 and proven preclinical ability to induce tumor vascular normalization. SU5416 reduced vascularization in s.c. implants of both VEGF120 and VEGF188 tumors. However, in the window chamber, SU5416 treatment increased red cell velocity in VEGF120 (representing vascular normalization) but not VEGF188 tumors. SU5416 treatment had no effect on growth or necrosis levels in either tumor type but tended to counteract the increase in interstitial fluid pressure seen with growth of VEGF120 tumors. SU5416 pretreatment resulted in the normally fragile blood vessels in VEGF120‐expressing tumors becoming resistant to the vascular damaging effects of the tubulin‐binding vascular disrupting agent (VDA), combretastatin A4 3‐O‐phosphate (CA4P). Thus, vascular normalization induced by antiangiogenic treatment can reduce the efficacy of subsequent VDA treatment. Expression of VEGF120 made tumors particularly susceptible to vascular normalization by SU5416, which in turn made them resistant to CA4P. Therefore, VEGF isoform expression may be useful for predicting response to both antiangiogenic and vascular‐disrupting therapy.

Differential Expression of VEGFA Isoforms Regulates Metastasis and Response to Anti-VEGFA Therapy in Sarcoma

“…Our previous studies in mice have shown that expression of short isoforms of VEGFA (120/164) lead to changes in the primary tumor microenvironment known to associate with metastasis including reduced pericyte coverage and increased interstitial fluid pressure (12,13); important factors influencing cell survival during metastasis (15,29). In addition, our studies in vitro have shown that VEGF188-expressing tumor cells have increased levels of apoptosis and decreased proliferation compared with VEGF120-expressing cells (24).…”

“…Staining for CD31 in FFPE sections and manual counts of vascular density were performed as described previously (13). CD34 and a-smooth muscle actin (aSMA) immunofluorescence staining of FFPE sections was used to establish the percent of vessels associated with perivascular cells.…”

“…However, little is known about underlying mechanisms. Preclinical studies have shown that tumor cell expression of VEGF120 (mouse equivalent of human VEGF121) influences vascular development during embryonic development, and also response to therapy in tumors in vivo (10)(11)(12)(13). In tumors, VEGF120 expression promotes the formation of leaky vasculature, with low pericyte coverage and high interstitial fluid pressure (13); characteristics that are linked to increased metastasis, the key factor regulating patient survival (14,15).…”

Tumour Cells Expressing Single VEGF Isoforms Display Distinct Growth, Survival and Migration Characteristics

“…These cells produced tumours in vivo that displayed distinct vascular patterns, similar to those seen in corresponding transgenic animals during development. Furthermore, the tumours displayed differences in response to treatment with vascular targeting agents highlighting the importance of VEGF isoform expression in treatment outcome [14], [17]. When grown in vitro , the fibrosarcoma cells exhibited major differences in growth rates, with VEGF164 and VEGF120 expressing cells (fs164 and fs120 respectively) proliferating significantly faster than VEGF188 (fs188) and wild type control cells (fswt) [14] suggesting that VEGF isoform expression also controls tumour cell growth characteristics.…”

Patient-Derived Xenograft Models for Endometrial Cancer Research

“…However, a surgical procedure is required to access the tissue/organ of interest for microscopy, having therefore the consequence that immediately after image acquisition the animal must be sacrificed. Intravital microscopy has been reported to be used in studies involving a metastatic process [46,47] and the response of tumour blood vessels to vascular targeted therapy [48,49]. …”