Kuhnert Frank, Tam Betty Y Y, Sennino Barbara, Gray John T, Yuan Jenny, Jocson Angeline, Nayak Nihar R, Mulligan Richard C, McDonald Donald M, Kuo Calvin J
Division of Hematology, Stanford University School of Medicine, Stanford, CA 94305, USA.
Proc Natl Acad Sci U S A. 2008 Jul 22;105(29):10185-90. doi: 10.1073/pnas.0803194105. Epub 2008 Jul 16.
The simultaneous targeting of both endothelial cells and pericytes via inhibition of VEGF receptor (VEGFR) and PDGFbeta receptor (PDGFRbeta) signaling, respectively, has been proposed to enhance the efficacy of antiangiogenic tumor therapy. Clinical and preclinical modeling of combined VEGFR and PDGFRbeta signaling inhibition, however, has used small molecule kinase inhibitors with inherently broad substrate specificities, precluding detailed examination of this hypothesis. Here, adenoviral expression of a soluble VEGFR2/Flk1 ectodomain (Ad Flk1-Fc) in combination with a soluble ectodomain of PDGFRbeta (Ad sPDGFRbeta) allowed highly selective inhibition of these pathways. The activity of Ad sPDGFRbeta was validated in vitro against PDGF-BB and in vivo with near-complete blockade of pericyte recruitment in the angiogenic corpus luteum, resulting in prominent hemorrhage, thus demonstrating an essential function for PDGF signaling during ovarian angiogenesis. Combination therapy with Ad PDGFRbeta and submaximal doses of Ad Flk1-Fc produced modest additive antitumor effects; however, no additivity was observed with maximal VEGF inhibition in numerous s.c. models. Notably, VEGF inhibition via Ad Flk1-Fc was sufficient to strongly suppress tumor endothelial and pericyte content as well as intratumoral PDGF-B mRNA, obscuring additive Ad sPDGFRbeta effects on pericytes or tumor volume. These studies using highly specific soluble receptors suggest that additivity between VEGFR and PDGFRbeta inhibition depends on the strength of VEGF blockade and appears minimal under conditions of maximal VEGF antagonism.
通过分别抑制血管内皮生长因子受体（VEGFR）和血小板衍生生长因子β受体（PDGFRβ）信号通路同时靶向内皮细胞和周细胞，已被提出可增强抗血管生成肿瘤治疗的疗效。然而，VEGFR和PDGFRβ信号联合抑制的临床和临床前模型使用的是具有固有广泛底物特异性的小分子激酶抑制剂，这使得无法对这一假设进行详细研究。在这里，可溶性VEGFR2/Flk1胞外域（Ad Flk1-Fc）与PDGFRβ可溶性胞外域（Ad sPDGFRβ）的腺病毒表达允许对这些通路进行高度选择性抑制。Ad sPDGFRβ的活性在体外针对血小板衍生生长因子BB（PDGF-BB）得到验证，在体内对血管生成的黄体中周细胞募集几乎完全阻断，导致明显出血，从而证明了血小板衍生生长因子信号在卵巢血管生成中的重要作用。Ad PDGFRβ与亚最大剂量的Ad Flk1-Fc联合治疗产生了适度的相加抗肿瘤作用；然而，在众多皮下模型中，最大程度抑制VEGF时未观察到相加作用。值得注意的是，通过Ad Flk1-Fc抑制VEGF足以强烈抑制肿瘤内皮细胞和周细胞含量以及肿瘤内PDGF-B mRNA，掩盖了Ad sPDGFRβ对周细胞或肿瘤体积的相加作用。这些使用高度特异性可溶性受体的研究表明，VEGFR和PDGFRβ抑制之间的相加作用取决于VEGF阻断的强度，并且在最大程度VEGF拮抗的条件下似乎最小。
