Abstract 1650: Targeting CD47- SIRPα interaction by novel peptide-based antagonists

Abstract

Background: Cluster of differentiation (CD47) is a trans-membrane glycosylated protein which is upregulated in several cancers. Increased expression of CD47 on tumor cells is associated with immune evasion and cancer progression. CD47 through its interaction with signal regulatory protein alpha (SIRPα), a cell-surface molecule on macrophages inhibits phagocytosis of tumor cells. Disrupting CD47-SIRPα interactions by monoclonal antibodies targeting CD47 and recombinant SIRPα proteins have been used as therapeutic strategies for treating cancer. Our objective was to discover and develop peptide/peptidomimetic based CD47 antagonists for disrupting CD47-SIRPα interactions. Methods: Through rational design based on crystal structure of CD47/SIRPα interacting interface, we designed peptides having potential to disrupt CD47-SIRPα interactions. FACS based cellular binding assay was developed to assess the binding affinity of CD47 antagonists. SIRPα protein labelled with fluorescent dye was incubated with Jurkat T cells expressing high levels of CD47 in the presence/absence of peptides. Binding affinity was measured by decrease in fluorescence. Functional activity of the peptides was evaluated in a FACS-based phagocytosis assays, in which tumor cells were incubated with human/mouse macrophages in the presence/absence of CD47 antagonists. Results: We identified CD47 antagonists demonstrating disruption of CD47-SIRPα interaction in a cellular binding assay. These peptides significantly inhibited phagocytosis of different tumor cells by macrophages. The lead CD47 antagonist displaying good ADME properties including moderate oral bioavailability was evaluated in a B16F10 syngeneic mouse tumor model. The lead CD47 antagonist inhibited primary tumor growth as well tumor metastasis to lungs. Biomarker characterization and efficacy studies in additional tumor models are ongoing. Citation Format: Pottayil G. Sasikumar, Chennakrishnareddy Gundala, Nagaraj M. Gowda, Sudarshan S. Naremaddepalli, Archana Bhumireddy, Rashmi Nair, Wesley Roy Balasubramanian, Anirudha Lakshminarasimhan, Samiulla S. Dodheri, Kiran Aithal, Raghuveer K. Ramachandra, Girish Daginakatte, Murali Ramachandra. Targeting CD47- SIRPα interaction by novel peptide-based antagonists [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1650. doi:10.1158/1538-7445.AM2017-1650

Development of small molecule drugs targeting immune checkpoints

“…Compound #6 demonstrated the best efficacy on recovering macrophage-mediated phagocytosis, with high normalized phagocytosis rates of 66% and 74%, as detected by luciferase assay and fluorescence-activated cell sorting (FACS), respectively. Using the A20 syngeneic lymphoma model, compound #6 exhibited no clinical signs of toxicity and an outstanding TGI value (53%) at an oral dose of 3 mg/kg, suggesting that compound #6 is well-tolerant and has good antitumor efficacy 35 . 1, 2, 4-oxadiazole was inserted into the hydrophobic pocket of CD47, masking the key residues of the CD47/SIRPα interaction (Trp40, Thr107, and Lys6) and forming hydrogen bonds with Thr7 and Thr107 near the core interaction area 66 .…”

Small Molecule Agents Targeting PD-1 Checkpoint Pathway for Cancer Immunotherapy: Mechanisms of Action and Other Considerations for Their Advanced Development

“…It was hypothesized that a substantially reduced native pharmacophore derived from protein–protein interacting interfaces of one of the B7 family protein (such as PD-1) also has the potential to interact with other proteins belonging to IgSF (such as VISTA and TIM3) with structurally similar grooves induced by pockets of sequence similarity ( 71 ). A focused library was designed and synthesized using amino acids in the hotspot region including conserved residues in the hotspot regions to identify selective or spectrum-selective inhibitors targeting one or more non-redundant checkpoint signaling pathways such as PD-L1 and VISTA ( 72 ), PD-L1 and TIM3 ( 73 , 74 ), VISTA ( 75 ), TIM-3 ( 76 ), PD-L1 and T-cell immunoreceptor with immunoglobulin and ITIM domain (TIGIT) ( 77 ), TIGIT ( 78 ), and cluster of differentiation 47 (CD-47) ( 79 ) pathways with desirable physicochemical properties and exposure upon oral administration. It is worth noting that small molecules with dual immune checkpoint inhibition have only been reported from the amino-acids-inspired interface mimic approach.…”