59 (PB049) - PIN-A1, a novel Casein Kinase 1α-selective molecular glue degrader, demonstrates strong antitumor activity via activation of the p53 pathway in preclinical models of AML with a favorable safety profile

Abstract

Casein kinase 1α (CK1α) reportedly promotes tumor growth by increasing the negative effects of MDM2 and MDMX on p53. Unlike in many other cancer types, the frequency of TP53 mutations is relatively low (<20%) in acute myeloid leukemia (AML). Therefore, activating the p53 pathway has been considered an attractive strategy to treat the disease with wild-type (WT) TP53. However, promising preclinical activities of p53 activators represented by MDM2 inhibitors have not been fully translated into clinical efficacy, partly due to their on-target hematological toxicities. To develop a drug targeting CK1α, we screened a series of compounds hijacking cereblon (CRBN) E3 ligase and identified a novel CK1α-selective molecular glue degrader (MGD), PIN-A1. Here, we report its robust pharmacological activities in various preclinical models of AML and its superior safety profile to MDM2 inhibitors. First, PIN-A1’s activity against CK1α as a MGD was demonstrated by the formation of ternary complex of PIN-A1-CK1α-CRBN using TR-FRET assay and with the inhibitors of proteasome/neddylation, respectively. Selective degradation of CK1α by PIN-A1 was also confirmed by global proteomics analysis. As predicted, PIN-A1 induced rapid degradation of CK1α protein in human AML MV-4–11 cells with WT TP53, which was followed by increases in the levels of p53 protein and its downstream target genes, ultimately leading to apoptotic cell death. Consistent with these results, screening in a broad panel of liquid cancer cell lines demonstrated preferential sensitivity of AML cells with WT TP53 to the CK1α degrader. When combined with cytarabine or other targeted therapies in AML such as venetoclax (Bcl2i), AMG232 (MDM2i), or gilteritinib (FLT3i), PIN-A1 displayed strong synergistic effects in cell killing. To evaluate its pharmacological activity in vivo, PIN-A1 was tested in a s.c xenograft model of MV-4-11 and a dissemination model of MOLM-14, respectively. Systemic administration of PIN-A1 alone via i.p resulted in robust antitumor activity with >90% CK1α degradation in tumors, which was comparably achieved at a much lower dose in combo treatments. Importantly, animals remained tumor-free (5/8) in the MV-4-11 model or survived longer in the MOLM-14 model even after they were off the combination treatment of PIN-A1 with AMG232. Lastly, while PIN-A1 had minimal effects on the viability and the p53 pathway in human PBMC at efficacious doses for MV-4-11 (Therapeutic index [TI] = >8000) despite >90% CK1α degradation, AMG232 induced the p53 pathway and reduced viability to a similar extent in both cell types (TI = 4). Taken together, these results suggest that a CK1α MGD with its favorable safety profile has a potential to become an effective treatment option for advanced AML. Current activities are focused on more advanced MGD analogs with superior oral systemic exposure. No conflict of interest.