Thrombospondin-1 (TSP-1) is a matricellular glycoprotein overexpressed in a wide range of cancers and a poor prognosis marker. Among its receptors, CD47 is mainly implicated in tumor angiogenesis and immune evasion. While most efforts focused up to now on disrupting CD47 binding to its macrophage counter-receptor SIRPα (“don’t eat me signal”), the TSP-1/CD47 axis is emerging as promising target for treating solid tumors. We have developed TAX2, a 12 aa cyclic peptide acting as an orthosteric antagonist for TSP-1/CD47 interaction.

The binding properties of TAX2 peptide to TSP-1 from various species were characterized in vitro while the anti-cancer activity and biodistribution of TAX2 were evaluated in tumor-bearing mice. The stability of TAX2 was tested in plasma and whole blood from different species before pharmacokinetic (PK) profiling following a single intravenous (IV) administration. The potential impact of TAX2 on CD47/SIRPα interaction was investigated using molecular modeling and a cell-based reporting assay. Potential off-target interactions were assessed across a panel of 44 targets, while potential unintended immunogenicity of TAX2 was evaluated in cytokine release assays. Toxicology studies were conducted in rats and dogs to characterize the toxicity profile of TAX2 after IV injection. Last, PK data obtained in rodents and dogs were used for prediction of Human PK parameters using allometric scaling.

In silico and in vitro studies showed that TAX2 binds selectively to human, rat, mouse and dog TSP-1, and disrupts the TSP-1/CD47 interaction without affecting CD47’s interaction with SIRPα. The pharmacologically active dose (PAD) of TAX2 in mice was determined at 30 mg/kg based on efficacy studies in several cancer models. In a highly aggressive ovarian cancer model, TAX2 demonstrated its efficacy by improving mouse survival, while offering clinically relevant combination potential with PARP inhibitors. TAX2 PK profile determined in rodents and dogs showed rapid plasma clearance over 1 to 4 hours, while exposure increases proportionally with the dose. Biodistribution studies revealed preferential accumulation in tumors and TSP-1-expressing tissues. TAX2 peptide showed no significant off-target interaction or functional effect across a panel of 44 human targets and did not induce uncontrolled cytokine release in human whole blood, supporting a favorable safety profile. Toxicology studies indicated that TAX2 was well tolerated with NOAEL (No Observable Adverse Effect Level) values of 400 mg/kg in rats and 100 mg/kg dogs. According to PK predictions, the PAD in humans ranges between 9 and 33 mg/kg.

TAX2 peptide, a first-in-class TSP-1/CD47 antagonist, is being developed as an injectable product for the treatment of cancers. These non-clinical data support this concept and TAX2 is now expected to enter in Phase 1/2a clinical trial in advanced solid tumors.