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Vascular-targeting antiangiogenic therapy (VTAT) of cancer can be advantageous over conventional tumor cell targeted cancer therapy if an appropriate target is found. Our hypothesis is that endoglin (ENG; CD105) is an excellent target in VTAT. ENG is selectively expressed on vascular and lymphatic endothelium in tumors. This allows us to target both tumor-associated vasculature and lymphatic vessels to suppress tumor growth and metastasis. ENG is essential for angiogenesis/vascular development and a co-receptor of TGF-β. Our studies of selected anti-ENG monoclonal antibodies (mAbs) in several animal models and in vitro studies support our hypothesis. These mAbs and/or their immunoconjugates (immunotoxins and radioimmunoconjugates) induced regression of preformed tumors as well as inhibited formation of new tumors. In addition, they suppressed metastasis. Several mechanisms were involved in the suppressive activity of the naked (unconjugated) anti-ENG mAbs. These include direct growth suppression of proliferating endothelial cells, induction of apoptosis, ADCC (antibody-dependent cell-mediated cytotoxicity) and induction of T cell immunity. To facilitate clinical application, we generated a human/mouse chimeric anti-ENG mAb termed c-SN6j and performed studies of pharmacokinetics, toxicology and immunogenicity of c-SN6j in nonhuman primates. No significant toxicity was detected by several criteria and minimal immune response to the murine part of c-SN6j was detected after multiple i.v. injections. The results support our hypothesis that cSN6j can be safely administered in cancer patients. This hypothesis is supported by the ongoing phase 1 clinical trial of c-SN6j (also known as TRC105) in patients with advanced or metastatic solid cancer in collaboration with Tracon Pharma and several oncologists (NCT00582985).

Anti-metastatic activity of an antitumor agent is exceedingly important because metastasis is the primary cause of death for most solid cancer patients. In this report, we show that 3 anti-endoglin (ENG) monoclonal antibodies (mAbs) SN6a, SN6j and SN6k which define individually distinct epitopes of ENG of tumor vasculature are capable of suppressing tumor metastases in the multiple metastasis models. The metastasis models were generated by i.v., s.c. (into flank) or mammary gland fat pad injection of 4T1 murine mammary carcinoma cells and splenic injection of two types of colon26 murine colorectal carcinoma cells. Individual mAbs were injected i.v. via the tail vein of mice. SN6a and SN6j effectively suppressed the formation of metastatic colonies of 4T1 in the lung in all of the three 4T1 metastatic models. In addition, these mAbs were effective for suppressing the primary tumors of 4T1 in the skin and mammary fat pad. These mAbs effectively suppressed microvessel density and angiogenesis in tumors as measured by the Matrigel plug assay in mice. No significant side effects of the administered mAbs were detected. Furthermore, SN6a and SN6j extended survival of the tumor-bearing mice. SN6j, SN6k and their immunoconjugates with deglycosylated ricin A-chain were all effective for suppressing hepatic metastasis of colon26. The findings in the present study are clinically relevant in view of the ongoing clinical trial of a humanized (chimerized) form of SN6j.

Summary. Macrophage inflammatory protein-1 alpha (MIP-1a) is a chemokine primarily associated with bone absorption. We examined whether MIP-1a was produced by purified fresh tumour cells isolated from bone marrow samples from 31 multiple myeloma (MM) patients. High levels of MIP-1a were found in supernatants of myeloma cell cultures. Immunohistochemical staining showed MIP-1a in the cytoplasm of myeloma cells. MIP-1a mRNA expression was detected in 18 of 31 patients. Bone lesions were seen in 16 of the 18 MIP-1a-positive patients but only in six of the 13 MIP-1a-negative patients (P ¼ 0AE0097, v 2 -test). The data indicate that MIP-1a is produced by myeloma cells and possibly plays a role in the pathogenesis of bone lesions in MM patients.

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