John Ridgway

Inhibition of Dll4 signalling inhibits tumour growth by deregulating angiogenesis.

Haploinsufficiency of Dll4, a vascular-specific Notch ligand, has shown that it is essential for embryonic vascular development and arteriogenesis. Mechanistically, it is unclear how the Dll4-mediated Notch pathway contributes to complex vascular processes that demand meticulous coordination of multiple signalling pathways. Here we show that Dll4-mediated Notch signalling has a unique role in regulating endothelial cell proliferation and differentiation. Neutralizing Dll4 with a Dll4-selective antibody rendered endothelial cells hyperproliferative, and caused defective cell fate specification or differentiation both in vitro and in vivo. In addition, blocking Dll4 inhibited tumour growth in several tumour models. Remarkably, antibodies against Dll4 and antibodies against vascular endothelial growth factor (VEGF) had paradoxically distinct effects on tumour vasculature. Our data also indicate that Dll4-mediated Notch signalling is crucial during active vascularization, but less important for normal vessel maintenance. Furthermore, unlike blocking Notch signalling globally, neutralizing Dll4 had no discernable impact on intestinal goblet cell differentiation, supporting the idea that Dll4-mediated Notch signalling is largely restricted to the vascular compartment. Therefore, targeting Dll4 might represent a broadly efficacious and well-tolerated approach for the treatment of solid tumours.

Therapeutic antibody targeting of individual Notch receptors.

The four receptors of the Notch family are widely expressed transmembrane proteins that function as key conduits through which mammalian cells communicate to regulate cell fate and growth. Ligand binding triggers a conformational change in the receptor negative regulatory region (NRR) that enables ADAM protease cleavage at a juxtamembrane site that otherwise lies buried within the quiescent NRR. Subsequent intramembrane proteolysis catalysed by the γ-secretase complex liberates the intracellular domain (ICD) to initiate the downstream Notch transcriptional program. Aberrant signalling through each receptor has been linked to numerous diseases, particularly cancer, making the Notch pathway a compelling target for new drugs. Although γ-secretase inhibitors (GSIs) have progressed into the clinic, GSIs fail to distinguish individual Notch receptors, inhibit other signalling pathways and cause intestinal toxicity, attributed to dual inhibition of Notch1 and 2 (ref. 11). To elucidate the discrete functions of Notch1 and Notch2 and develop clinically relevant inhibitors that reduce intestinal toxicity, we used phage display technology to generate highly specialized antibodies that specifically antagonize each receptor paralogue and yet cross-react with the human and mouse sequences, enabling the discrimination of Notch1 versus Notch2 function in human patients and rodent models. Our co-crystal structure shows that the inhibitory mechanism relies on stabilizing NRR quiescence. Selective blocking of Notch1 inhibits tumour growth in pre-clinical models through two mechanisms: inhibition of cancer cell growth and deregulation of angiogenesis. Whereas inhibition of Notch1 plus Notch2 causes severe intestinal toxicity, inhibition of either receptor alone reduces or avoids this effect, demonstrating a clear advantage over pan-Notch inhibitors. Our studies emphasize the value of paralogue-specific antagonists in dissecting the contributions of distinct Notch receptors to differentiation and disease and reveal the therapeutic promise in targeting Notch1 and Notch2 independently.

Chronic DLL4 blockade induces vascular neoplasms

Arising from: J. Ridgway et al. 444, 1083–1087 (2006)10.1038/nature05313Delta-like 4 (DLL4)-mediated Notch signalling has emerged as an attractive target for cancer therapy. However, the potential side effects of blocking this pathway remain uncertain. Here we show that chronic DLL4 blockade causes pathological activation of endothelial cells, disrupts normal organ homeostasis and induces vascular tumours, raising important safety concerns.

ALK1 signaling regulates early postnatal lymphatic vessel development

In vertebrates, endothelial cells form 2 hierarchical tubular networks, the blood vessels and the lymphatic vessels. Despite the difference in their structure and function and genetic programs that dictate their morphogenesis, common signaling pathways have been recognized that regulate both vascular systems. ALK1 is a member of the transforming growth factor-beta type I family of receptors, and compelling genetic evidence suggests its essential role in regulating blood vascular development. Here we report that ALK1 signaling is intimately involved in lymphatic development. Lymphatic endothelial cells express key components of the ALK1 pathway and respond robustly to ALK1 ligand stimulation in vitro. Blockade of ALK1 signaling results in defective lymphatic development in multiple organs of neonatal mice. We find that ALK1 signaling regulates the differentiation of lymphatic endothelial cells to influence the lymphatic vascular development and remodeling. Furthermore, simultaneous inhibition of ALK1 pathway increases apoptosis in lymphatic vessels caused by blockade of VEGFR3 signaling. Thus, our study reveals a novel aspect of ALK1 signaling in regulating lymphatic development and suggests that targeting ALK1 pathway might provide additional control of lymphangiogenesis in human diseases.

Human FcERI-IgG and humanized anti-IgE monoclonal antibody MaE11 block passive sensitization of human and rhesus monkey lung☆

IgE antibodies are thought to play an important role in the induction of allergic inflammation of the bronchi. In this study we assessed the capacity of two inhibitors, FcERI-IgG, an immunoadhesin made up of the alpha chain of the high-affinity IgE receptor joined to a truncated IgG heavy chain, and MaE11, a humanized murine anti-human IgE antibody, to prevent allergen sensitization. Lung parenchyma strips from rhesus monkeys and human beings were passively sensitized for 20 hours with serum from a ragweed-sensitive patient in the presence of 0, 1-, 5-, or 10-fold concentrations of the inhibitors relative to IgE. The parenchymal strips were then suspended in a superfusion apparatus for measurement of isometric tone and collection of superfusate for histamine analysis in response to challenge with antigen E (AgE). Nonsensitized tissues did not react to AgE challenge, whereas AgE challenge of passively sensitized tissues resulted in a time-dependent parenchymal contraction and histamine release. Both FcERI-IgG and MaE11 completely abolished the AgE-induced contraction and histamine release in a dose-dependent manner. In addition, passively sensitized lung tissues failed to respond to direct challenge with either FcERI-IgG or MaE11. The results of this study suggest that FcERI-IgG and MaE11 may have important immunotherapeutic benefit for the amelioration of IgE-mediated diseases.

Balancing efficacy and safety of an anti-DLL4 antibody through pharmacokinetic modulation

Purpose: Although agents targeting Delta-like ligand 4 (DLL4) have shown great promise for angiogenesis-based cancer therapy, findings in recent studies have raised serious safety concerns. To further evaluate the potential for therapeutic targeting of the DLL4 pathway, we pursued a novel strategy to reduce toxicities related to DLL4 inhibition by modulating the pharmacokinetic (PK) properties of an anti-DLL4 antibody. Experimental Design: The F(ab′)2 fragment of anti-DLL4 antibody (anti-DLL4 F(ab′)2) was generated and assessed in efficacy and toxicity studies. Results: Anti-DLL4 F(ab′)2 enables greater control over the extent and duration of DLL4 inhibition, such that intermittent dosing of anti-DLL4 F(ab′)2 can maintain significant antitumor activity while markedly mitigating known toxicities associated with continuous pathway inhibition. Conclusions: PK modulation has potentially broad implications for development of antibody-based therapeutics. Our safety studies with anti-DLL4 F(ab′)2 also provide new evidence reinforcing the notion that the DLL4 pathway is extremely sensitive to pharmacologic perturbation, further underscoring the importance of exercising caution to safely harness this potent pathway in humans. Clin Cancer Res; 22(6); 1469–79. ©2015 AACR.