Purpose: This study is aimed at investigating the in vivo antitumor activity of a novel cellimpermeable glucuronide prodrug, 9-aminocamptothecin glucuronide (9ACG), and elucidating the synergistically antitumor effects of antiangiogenesis therapy by targeting the tumor microenvironment. Experimental Design:We analyzed the antitumor effects of 9ACG alone or combined with antiangiogenic monoclonal antibody DC101on human tumor xenografts by measuring tumor growth and mouse survival in BALB/c nu/nu nude and NOD/SCID mice. The drug delivery, immune response, and angiogenesis status in treated tumors were assessed by high performance liquid chromatography, immunohistochemistry, and immunofluorescence assays. Results: We developed a nontoxic and cell-impermeable glucuronide prodrug, 9ACG, which can only be activated by extracellular h-glucuronidase to become severely toxic. 9ACG possesses potent antitumor activity against human tumor xenografts in BALB/c nu/nu nude mice but not for tumors implanted in NOD/SCID mice deficient in macrophages and neutrophils, suggesting that these cells play an important role in activating 9ACG in the tumor microenvironment. Most importantly, antiangiogenic monoclonal antibody DC101 potentiated single-dose 9ACG antitumor activity and prolonged survival of mice bearing resistant human colon tumor xenografts by providing strong h-glucuronidase activity and prodrug delivery through enhancing inflammatory cell infiltration and normalizing tumor vessels in the tumor microenvironment. We also show that inflammatory cells (neutrophils) were highly infiltrated in advanced human colon cancer tissues compared with normal counterparts. Conclusions: Our study provides in vivo evidence that 9ACG has potential for prodrug monotherapy or in combination with antiangiognesis treatment for tumors with infiltration of macrophage or neutrophil inflammatory cells.

Membrane-tethered proteins (mammalian surface display) are increasingly being used for novel therapeutic and biotechnology applications. Maximizing surface expression of chimeric proteins on mammalian cells is important for these applications. We show that the cytoplasmic domain from the B7-1 antigen, a commonly used element for mammalian surface display, can enhance the intracellular transport and surface display of chimeric proteins in a Sar1 and Rab1 dependent fashion. However, mutational, alanine scanning and deletion analysis demonstrate the absence of linear ER export motifs in the B7 cytoplasmic domain. Rather, efficient intracellular transport correlated with the presence of predicted secondary structure in the cytoplasmic tail. Examination of the cytoplasmic domains of 984 human and 782 mouse type I transmembrane proteins revealed that many previously identified ER export motifs are rarely found in the cytoplasmic tail of type I transmembrane proteins. Our results suggest that efficient intracellular transport of B7 chimeric proteins is associated with the structure rather than to the presence of a linear ER export motif in the cytoplasmic tail, and indicate that short (less than ~ 10-20 amino acids) and unstructured cytoplasmic tails should be avoided to express high levels of chimeric proteins on mammalian cells.

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