Therapeutic antibody targeting of individual Notch receptors

Abstract

The four receptors of the Notch family are widely expressed transmembrane proteins through which mammalian cells communicate to regulate cell fate and growth. Defects in Notch signalling are linked to many cancers, including acute lymphoblastic leukaemia. Using phage display technology, a multi-department team at Genentech has produced synthetic antibodies that act as potent and specific antagonists of Notch1 and Notch2. Anti-Notch1 shows antitumour activity in pre-clinical mouse models, inhibiting both cancer cell growth and angiogenesis, and is active against human cancer cells in culture. Inhibition of Notch1 and 2 together causes intestinal toxicity, whereas inhibition of each singly largely avoids this effect, a potential therapeutic advantage over 'pan-Notch' inhibitors. The four receptors of the Notch family are transmembrane proteins through which mammalian cells communicate to regulate cell fate and growth. Aberrant signalling through each receptor has been linked to disease, so the Notch pathway is a compelling drug target. But current drugs cannot distinguish between the different Notch proteins. Here, phage display technology has been used to generate highly specialized antibodies, enabling the functions of Notch1 and Notch2 to be discriminated in humans and mice. 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 growth1,2. Ligand binding triggers a conformational change in the receptor negative regulatory region (NRR) that enables ADAM protease cleavage3,4 at a juxtamembrane site that otherwise lies buried within the quiescent NRR5,6. 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 cancer7, making the Notch pathway a compelling target for new drugs. Although γ-secretase inhibitors (GSIs) have progressed into the clinic8, GSIs fail to distinguish individual Notch receptors, inhibit other signalling pathways9 and cause intestinal toxicity10, 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.