Tgrx-678 Penetrates Blood-Brain Barrier and Exhibits Preclinical Anti-Tumor Activity in Murine Ph+ CNS Leukemia and ALL Models

Central nervous system leukemia (CNSL) relapse is relatively common among Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL) and chronic myeloid leukemia (CML) lymphoid blast crisis patients. TGRX-678, a novel allosteric inhibitor specifically targeting ABL1 myristoyl pocket (STAMP), was previously reported to exhibit high potency against BCR::ABL1 WT and drug-resistant mutations in various in vitro and in vivo efficacy assays, and is currently being evaluated in a phase II clinical trial (NCT06453902). Herein we report the ability of TGRX-678 to penetrate blood-brain barrier in rats and the anti-tumor effects of TGRX-678 in murine CNS leukemia model and Ph+ ALL subcutaneous mouse model. Sprague Dawley (SD) rats were given single dose of TGRX-678 at 50 mg/kg through oral gavage. Plasma and brain samples were collected at indicated time points post-dose and analyzed by liquid chromatography tandem mass spectrometry (LC-MS/MS) method. The maximum concentration (Cmax) and AUC0-last in brain of TGRX-678 were 1130 ng/g and 16346 hr*ng/g, respectively. The concentration ratio of brain to plasma was 0.44~0.74. For further validation, radio-labeled form [14C]-TGRX-678 was prepared and given single dose at 50 mg/100 µCi/kg to Sprague-Dawley (SD) and male Long-Evans (LE) rats. Liquid scintillation counter and quantitative whole-body autoradiography (QWBA) method were used to determine the radioactivity concentrations of plasma and brain, respectively. The results demonstrated high penetration of TGRX-678 into the brain tissue, with concentrations as high as 0.58~0.69-fold of those seen in the plasma (In male LE rat, 7131 ng Eq./g in plasma and 4885 ng Eq./g in brain at 0.5 hrs post-dose; 11981 ng Eq./g in plasma and 6950 ng Eq./g in brain at 4 hrs post-dose. In female SD rat, 15320 ng Eq./g in plasma and 9800 ng Eq./g in brain at 4 hrs post-dose; in male SD rat, 10656 ng Eq./g in plasma and 6400 ng Eq./g in brain at 4 hrs post-dose). We then tested the anti-tumor effects of TGRX-678 in murine CNS leukemia models. Female NCG mice were injected with 2*105 K562-luciferase cells into the right common carotid artery. TGRX-678 (50mg/kg) was orally administrated once a day for 12 consecutive days. Bioluminescent signals, as the main index to evaluate tumor growth and drug efficacy, were monitored regularly by IVIS Lumina III (Perkin Elmer). TGRX-678 completely inhibited K562 cells proliferation in the brain (TGI=100.1% post 12-day dosing) and the drug was well tolerated. In Ph+ ALL subcutaneous mouse model, NCG mice were inoculated with SUP-B15 cells and orally dosed with TGRX-678 (5, 15, 45 mg/kg) once daily for 21 days. Tumor volumes and body weights were recorded 3 times a week. Tumor regression was observed in all three dose groups (TGI= 119.5%, 124.7%, 125.6% post 21-day dosing, respectively). In conclusion, TGRX-678 can penetrate blood-brain barrier, and potently inhibit Ph+ leukemia cell growth in CNS and subcutaneous mouse model, suggesting TGRX-678's potential therapeutic applications in patients with Ph+ CNS leukemia and ALL.