Abstract 5: Pre-clinical development of CDK9 inhibitor - LS007 for the treatment of acute myeloid leukemia

Abstract Acute myeloid leukemia (AML) is the most common form of acute leukaemia with an increasing incidence and dismal long-term prognosis with age. The most aggressive subtype, MLL-AML, is characterized by translocations of the mixed-lineage leukaemia gene (MLL) in chromosome band 11q23 and resistance to conventional chemotherapy with a short overall survival of only 9 months. Cyclin-dependent 9 (CDK9) activity is required for MLL-driven oncogenic transcription. Inhibition of CDK9 directly targets the transcriptional machinery required for MLL-fusion proteins (e.g. MLL-AF4, MLL-AF9 and MLL-ENL), thereby leading to apoptosis. We have developed a highly effective drug candidate - LS007 that inhibited CDK9 with a Ki = 4 nM. It suppressed proliferation and induced apoptosis in a range of AML cell lines and patient samples. LS007 was highly efficacious against several AML cell line xenografts and patient-derived xenografts, and well tolerated in mice after oral administration. In a Molm-13 xenograft model, after 21 days of orally daily dosing at 25 mg/kg and 50 mg/kg LS007 inhibited tumor growth (p < 0.001) with T/C = 44 % and 18 %, respectively. Similarly, in a HL-60 xenograft model, LS007 exhibited a significant tumor growth inhibition at 45 mg/kg and 60 mg/kg daily by oral administration with T/C = 40 % and 20 %, respectively. The pharmacokinetic profiles of LS007 was further assessed in the cynomolgus monkeys. After oral doses at the dose of 2, 4 and 8 mg/kg, LS007 was detected in the plasma with the maximum concentration (Cmax) from 55.9 to 279.5 ng/mL and the area under the plasma drug concentration-time graph (AUC) up to 1862.7 h·ng/mL. The mean terminal half-life (T 1/2) was around 3 h. LS007 possessed the favorable pharmacokinetic profiles with oral bioavailability F = 56% in the cynomolgus monkey (at dose 4 mg/kg), suggesting its therapeutic potential as an orally bioavailable anti-AML agent. The GLP- toxicological studies of LS007 in the cynomolgus monkey were completed, and the maximum tolerated doses were identified, which were used to estimate the safe starting dose for the Phase I clinical trials. With its excellent anti-cancer efficacy along with appreciable absorption and safety profiles, LS007 offers a very exciting prospect as a clinical development candidate. The application of Investigational New Drug (IND) has been approved allowing the commencement of clinical trials of LS007 in patients with AML. Citation Format: Wang Hui, Wang Shudong. Pre-clinical development of CDK9 inhibitor - LS007 for the treatment of acute myeloid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5.