Search

A tumor homing peptide, LyP-1, selectively binds to tumor-associated lymphatic vessels and tumor cells in certain tumors and exhibits an antitumor effect. Here, we show that the protein known as p32 or gC1q receptor is the receptor for LyP-1. Various human tumor cell lines were positive for p32 expression in culture, and the expression was increased in xenograft tumors grown from the positive cell lines. Fluorescence-activated cell sorting analyses with anti-p32 antibodies showed that p32-positive cell lines expressed p32 at the cell surface. These cells bound and internalized LyP-1 peptide in proportion to the cell-surface expression level, which correlated with malignancy rather than total p32 expression in the cells. Like the LyP-1 peptide, p32 antibodies highlighted hypoxic areas in tumors, where they bound to both tumor cells and cells that expressed macrophage/myeloid cell markers and often seemed to be incorporated into the walls of tumor lymphatics. Significant p32 expression was common in human cancers and the p32 levels were often greatly elevated compared with the corresponding normal tissue. These results establish p32, particularly its cell-surface–expressed form, as a new marker of tumor cells and tumor-associated macrophages/myeloid cells in hypoxic/metabolically deprived areas of tumors. Its unique localization in tumors and its relative tumor specificity may make p32 a useful target in tumor diagnosis and therapy. [Cancer Res 2008;68(17):7210–8]

To better elucidate the role of vascular endothelial growth factor (VEGF)165 in soft tissue sarcoma (STS) growth, metastasis, and chemoresistance, we generated stably transfected human STS cell lines with VEGF165 to study the effect of VEGF165 on STS cells in vitro and the effect of culture medium from these cells on human umbilical vascular endothelial cells. Severe combined immunodeficient mice bearing xenografts of transfected cell lines were used to assess the effect of VEGF overexpression and the effect of VEGF receptor (VEGFR) 2 inhibition on STS growth, metastasis, and response to doxorubicin. VEGF165-transfected xenografts formed highly vascular tumors with shorter latency, accelerated growth, enhanced chemoresistance, and increased incidence of pulmonary metastases. Blockade of VEGFR2 signaling using DC101 anti-VEGFR2 monoclonal antibody enhanced doxorubicin chemoresponse; this combined biochemotherapy inhibited tumor growth and decreased pulmonary metastases without overt toxicity. Combined therapy reduced microvessel counts while increasing vessel maturation index. VEGF overexpression did not affect on the sarcoma cells per se; however, conditioned medium from VEGF transfectants caused increased endothelial cell proliferation, migration, and chemoresistance. Addition of DC101 induced endothelial cell sensitivity to doxorubicin and suppressed the activity of matrix metalloproteinases secreted by endothelial cells. We therefore conclude that VEGF is a critical determinant of STS growth and metastasis and that STS chemoresistance, in our model, is a process induced by the interplay between STS cells and tumor-associated endothelial cells. STS growth and metastasis can be interrupted by combined low-dose doxorubicin and anti-VEGFR2, a strategy that attacks STS-associated endothelial cells. In the future, such therapeutic approaches may be useful in treating STS before the development of clinically apparent metastases. (Cancer Res 2006; 66(17): 8770-7)

Genetic and molecular studies suggest that activin receptor-like kinase 1 (ALK1) plays an important role in vascular development, remodeling, and pathologic angiogenesis. Here we investigated the role of ALK1 in angiogenesis in the context of common proangiogenic factors [PAF; VEGF-A and basic fibroblast growth factor (bFGF)]. We observed that PAFs stimulated ALK1-mediated signaling, including Smad1/5/8 phosphorylation, nuclear translocation and Id-1 expression, cell spreading, and tubulogenesis of endothelial cells (EC). An antibody specifically targeting ALK1 (anti-ALK1) markedly inhibited these events. In mice, anti-ALK1 suppressed Matrigel angiogenesis stimulated by PAFs and inhibited xenograft tumor growth by attenuating both blood and lymphatic vessel angiogenesis. In a human melanoma model with acquired resistance to a VEGF receptor kinase inhibitor, anti-ALK1 also delayed tumor growth and disturbed vascular normalization associated with VEGF receptor inhibition. In a human/mouse chimera tumor model, targeting human ALK1 decreased human vessel density and improved antitumor efficacy when combined with bevacizumab (anti-VEGF). Antiangiogenesis and antitumor efficacy were associated with disrupted co-localization of ECs with desmin+ perivascular cells, and reduction of blood flow primarily in large/mature vessels as assessed by contrast-enhanced ultrasonography. Thus, ALK1 may play a role in stabilizing angiogenic vessels and contribute to resistance to anti-VEGF therapies. Given our observation of its expression in the vasculature of many human tumor types and in circulating ECs from patients with advanced cancers, ALK1 blockade may represent an effective therapeutic opportunity complementary to the current antiangiogenic modalities in the clinic. Cancer Res; 71(4); 1362–73. ©2011 AACR.

Integrin α5β1 is overexpressed in tumor-associated stroma and cancer cells, and has been implicated in angiogenesis, tumor survival, and metastasis. Antibody-dependent cellular cytotoxicity (ADCC) by immune effector cells has been shown to contribute to clinical efficacy for several IgG1 monoclonal antibody (mAb) therapeutics. Taking advantage of these two mechanisms, we generated a fully human, fragment crystalizable (Fc)-engineered IgG1 mAb, PF-04605412 (PF-5412), which specifically neutralizes α5 and binds the Fcγ receptors (FcγR) with enhanced affinity. In vitro, PF-5412 potently inhibited α5β1-mediated intracellular signaling, cell adhesion, migration, and endothelial cell (EC) tubulogenesis. PF-5412 induced significantly greater ADCC in α5-expressing tumor cells and ECs compared with a wild-type IgG1 (IgG1/wt) or IgG2 of identical antigen specificity. The degree of ADCC correlated with the abundance of natural killer (NK) cells in the peripheral blood mononuclear cells but was independent of donor FcγRIIIa polymorphism. In animal studies, PF-5412 displayed robust and dose-dependent antitumor efficacy superior to that observed with IgG1/wt, IgG2, or IgG4 of identical antigen specificity. The degree of efficacy correlated with α5 expression, macrophage and NK cell infiltration, and NK activity in the tumor. Depletion of host macrophages abrogated antitumor activity, suggesting a critical contribution of macrophage-mediated antitumor activity of PF-5412. Combination of PF-5412 with sunitinib significantly improved antitumor efficacy compared with either agent alone. The dual mechanism of action and robust antitumor efficacy of PF-5412 support its clinical development for the treatment of a broad spectrum of human malignancies. Cancer Res; 70(24); 10243–54. ©2010 AACR.

Vascular endothelial growth factor (VEGF) and VEGF receptor 2 [fetal liver kinase 1 (Flk-1)/kinase insert domain-containing receptor] have been shown to play a major role in tumor angiogenesis. In this study, we investigated whether anti-Flk-1 monoclonal antibody DC101 could therapeutically inhibit growth and angiogenesis of human soft tissue sarcoma, and we explored its capacity to enhance the tumoricidal effects of doxorubicin. Treatment of well-established leiomyosarcoma SKLMS-1 and rhabdomyosarcoma RD xenografts in severe combined immunodeficient mice with DC101 resulted in significant antitumor activity. In a parallel study, we compared tumor inhibition with continuous low-dose "antiangiogenic" schedule versus once-every-2-weeks high-dose standard schedule of doxorubicin. We found that continuous low-dose treatment inhibited the tumor growth of RD xenografts about 46.5% of that with standard-schedule treatment, but that continuous low-dose treatment did not inhibit the tumor growth of SKLMS-1 xenografts. Notably, combined DC101 and continuous low-dose doxorubicin resulted in more effective growth inhibition of SKLMS-1 and RD xenografts than has been observed with any agent alone in a long-term s.c. tumor xenograft model. The combination therapy was associated with no additional toxicity to the host animal compared with low-dose doxorubicin alone. Histological examination of xenografts showed significantly reduced microvessel counts in the tumors given combined therapy compared with the tumors given either agent alone. These results are consistent with an enhanced inhibition of angiogenesis in vivo by combined DC101 and doxorubicin using Matrigel plug assay. Additionally, DC101 plus doxorubicin directly exerted enhanced inhibitory effects on endothelial cell migration, proliferation, and tube-like formation in vitro. Furthermore, the combination induced an enhanced apoptosis of endothelial cells that was associated with an increase of capase-3 activity. Thus, the inhibition of angiogenesis and induction of endothelial cell apoptosis are likely important mechanisms for the antitumor activity of combined DC101 and doxorubicin. Collectively, our data suggested that anti-VEGF receptor 2 in combination with continuous low-dose doxorubicin may provide a new therapeutic approach for human soft tissue sarcoma in the clinic.

Integrin α5β1 plays an important role in tumor angiogenesis, invasion, and metastasis. Overexpression of α5β1 has been associated with poor prognosis in various types of cancers, and also plays a critical role in the resistance of cancers to radiotherapy and chemotherapy. We have previously reported that PF-04605412 (PF-5412), a fully human Fc-engineered IgG1 mAb against human α5β1, displayed robust and dose-dependent antitumor efficacy in multiple preclinical tumor models. Assessment of PF-5412 mechanism of action (MOA) in standard mouse xenograft models has been limited, however, because this antibody does not cross-react with murine integrin α5. To further our understanding of PF-5412 MOAs, we generated human integrin α5 knock-in mice (ITGA5 KI) in which the entire murine coding sequence of integrin α5 was replaced with the corresponding human coding sequence. Mice that were homozygous for human integrin α5 were viable and no abnormal phenotype or behavior was observed. qPCR and FACS analyses showed that human integrin α5 was expressed in various types of tissues and peripheral blood in ITGA5 KI mice, whereas no mouse integrin α5 was detected. Murine integrin β1 expression in ITGA5 KI mice was comparable to wild type mice. Growth of MC38 murine CRC tumors engineered to express human α5 was inhibited by treatment with PF-5412 in a dose-dependent manner. Tumor regression was observed at high doses of PF-5412 but not at comparable dose levels of α5 antibodies lacking ADCC activity (IgG4). IHC analyses of CD31 positive vessels showed that PF-5412 significantly inhibited blood vessel density and induced greater macrophages infiltration into tumors than non-ADCC-inducing antibodies. Notably, parental MC38 tumors lacking endogenous human α5 expression were also controlled by PF-5412 treatment (60% TGI) in ITGA5 KI mice. PF-5412 efficacy in this model also exceeded that of non-ADCC-inducing antibodies. Immunohistochemistry (IHC) analyses showed that PF-5412 treatment significantly decreased blood vessel density in the parental MC38 tumors. These results demonstrate that PF-5412 benefit does not depend on integrin α5β1 expression by the tumor cell itself, and support the hypothesis that ADCC-mediated killing of tumor endothelium will confer clinical benefit. The results showed here indicate that ITGA5 KI mouse is a relevant model for evaluating anti-human integrin α5 antibody MOA. Citation Format: Lianglin Zhang, Jeffrey L. Stock, Mark W. Elliott, Enhong Chen, Thao Nguyen, Anthony Wong, Craig B. Davis, James G. Christensen. Assessment of mechanisms of action (MOAs) of the Fc-engineered integrin α5β1 targeting antibody PF-04605412 in human integrin α5 knock-in mice. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2336. doi:10.1158/1538-7445.AM2013-2336

Anti-angiogenic therapy targeting the tumor vasculature has demonstrated clinical benefits in certain types of tumors. However, many patients develop resistance and eventually progress on anti-angiogenic therapy. The mechanism of resistance is largely unknown and warrants extensively investigation. We developed a human xenograft tumor model (M24met/R) in mice that has acquired resistance to VEGF receptor tyrosine kinase inhibitors (VEGFR TKI), by chronically treating the parental M24met tumors (M24met/P) with PF-0337210 (20-40 mg/kg, QD, PO) and serially passaging resistant tumor fragments in nude mice. M24met/R tumors were also resistant to axitinib, a selective VEGFR TKI in late stage clinical development. Immunohistochemical (IHC) staining revealed higher degree of hypoxia and lower microvessel density in M24met/R tumors compared to parental tumors. Compared with those in M24met/P, vessels in M24met/R tumors appeared to be larger in diameter and more mature as shown by high incidence of co-localization between endothelial cells and perivascular cells (CD31+Desmin+). Microarray analysis of tumor lysates (human UA133 2.0, mouse 430 2.0 chip) revealed distinct gene expression profiles between M24met/R tumors and size-matched M24met/P tumors. Of note, several angiogenesis-related genes, including human VEGF, bFGF, integrin α5β1, IL-8, PDGF,CSF and murine VEGF, integrin α5β1, ALK1 (activin receptor-like kinase 1), IL-8, c-Met, IL-6 were up-regulated in M24met/R tumors, whereas murine VEGFR1 and 2, PROX1, PDGFR and endogenous angiogenic inhibitor TSP-1 were down-regulated in the resistant tumors. The above observations were verified with ELISA and/or IHC. Next, targeted combination approaches were applied in an attempt to circumvent M24met/R resistance to axitinib. Concurrent administration of axitinib plus either anti-IL-8 monoclonal antibody (mAb), c-Met inhibitor, anti-integrin α5 mAb or anti-ALK1 mAb significantly improved anti-tumor efficacy compared to single agents alone. IHC analyses showed that combinatorial therapy of anti-ALK1 plus axitinib reduced the amount of CD31+Desmin+ vessels compared to axitinib alone, suggesting that targeting ALK1 destroyed VEGFR TKI-resistant vessels. Together, our results suggested that multiple alternative angiogenic factors contributed to the acquired resistance of M24met/R melanoma to VEGFR TKI. Combination treatment using inhibitor of IL-8, c-Met, integrin α5β1 or ALK1 with VEGFR TKI may represent a new strategy to mitigate resistance to VEGFR TKI in the clinic. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3270. doi:10.1158/1538-7445.AM2011-3270

Integrin α5β1 and its ligand fibronectin are significantly and coordinately over-expressed in tumor associated blood vessels and cancer cells. These molecules have been reported to mediate angiogenesis, tumor survival and metastasis. α5β1 has also been implicated as a poor prognostic marker in a number of human tumor types including NSCLC and ovarian carcinoma. Thus, α5β1 is a potential target for cancer therapy. Accumulating evidence suggests an important role of innate immune effector cells in tumor killing via antibody dependent cellular cytotoxicity (ADCC). Taking advantage of both of these mechanisms, we generated an α5 integrin-specific neutralizing monoclonal antibody (mAb, PF-04605412) with high affinity for Fcγ receptors. In vitro, PF-04605412 potently inhibited α5β1-mediated intracellular signaling, cell adhesion, migration, endothelial cell tubulogenesis, and induced apoptosis of endothelial and tumor cells. Compared to a wild type IgG1 of identical antigen specificity (wt IgG1), PF-04605412 induced a significantly greater tumor and endothelial cell cytotoxicity. ADCC activity correlated with the abundance of NK cells within PBMCs of human donors, but was independent of donor FcγRIIIa polymorphism. In in vivo studies using human xenograft, immuno-xenograft and syngeneic tumor models, PF-04605412 (and an anti-murine α5 surrogate mAb) displayed robust and dose-dependent anti-angiogenesis and anti-tumor efficacy including tumor growth delay, regression and metastasis inhibition, all of which were superior to effects observed with an IgG2 or wt IgG1 of identical antigen specificity. Western blotting and immunohistochemistry analysis of tumor samples showed that anti-tumor efficacy was associated with reduction of total and phosphorylated focal adhesion kinase and positively correlated with α5 expression, infiltrating macrophages, markers of effector cell activity, and apoptosis. Furthermore, depletion of host macrophages abrogated anti-tumor efficacy, indicating a critical contribution of ADCC/phagocytosis to the anti-tumor activity of PF-04605412. The PK-PD relationship, efficacy of PF-04605412 in combination with anti-angiogenic and tumor targeting agents will also be reported. The distinct dual mechanism of action and robust anti-tumor efficacy of PF-04605412 supports the clinical development of this agent for the treatment of human cancers. Short Title: Dual functional mAb PF-04605412 Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3811.