Plm-102, a Next Generation FLT3 Inhibitor, Shows Potent Anti-Leukemic Activity on Resistance to Gilteritinib in FLT3 Mutated Acute Myeloid Leukemia

Introduction: Mutations in the FMS-like tyrosine kinase 3 (FLT3) gene occur in approximately 25 ~ 30% of all acute myeloid leukemia (AML) cases, with FLT3-ITD mutations having a poor prognosis. In 2022, the FDA granted approval to Gilteritinib, a 2nd generation FLT3 inhibitor, for the treatment of relapsed or refractory AML. Although Gilteritinib has demonstrated efficacy in R/R AML patients, its response duration is limited due to the development of secondary resistance. Herein, we report a next-generation drug candidate, PLM-102, which has shown promising pre-clinical results to overcome the current unmet needs of Gilteritinib resistance, including FLT3-ITD-TKD and Ras mutations in FLT3-mutated AML.

Aims: The main objective of this study is to investigate the effect of PLM-102 in in-vitro and in-vivo acquired Gilteritinib-resistant models and to elucidate the underlying signaling pathways.

Methods: To establish Gilteritinib-resistant cell lines, we exposed the AML cells to FLT3 ligand at 10 ng/ml and Gilteritinib at concentrations ranging from 10 nM to 100 nM for four months. Subsequently, for the following four months, we treated the cells with Gilteritinib alone at 100 nM, omitting FLT3 ligand from the treatment. Whole Exome Sequencing (WES) and mRNA sequencing were performed on primary FLT3 mutated AML cells and Gilteritinib resistance FLT3 mutated AML cells. Subsequently, cell viability assays were carried out on both parent FLT3-mutated AML cells and Gilteritinib-resistant FLT3-mutated AML cells. To assess the activities of PLM-102 at the on-target and off-target resistant mechanisms, immunoblot studies were conducted. An in vivo study was performed using a Gilteritinib-resistant MOLM-14 AML xenograft mouse model.

Results: We conducted Whole Exome Sequencing on the Gilteritinib-resistant MOLM-13 and MOLM-14 cell lines. The analysis revealed the presence of KRAS^G13D and FLT3-ITD-C828G mutations in the Gilteritinib-resistant MOLM-13 cell line, and NRAS^G13D and FLT3-ITD-G697R mutations in the Gilteritinib-resistant MOLM-14 cell line.

In the evaluation of the efficacies of Gilteritinib and PLM-102 in Gilteritinib-resistant MOLM-14 cell lines. The GI₅₀ values for Gilteritinib and PLM-102 were determined to be 427 nM and 6.17 nM, respectively.

In the studies with a xenograft model with Gilteritinib-resistant MOLM-14 cells (20 mg/kg, p.o.), the Tumor Growth Inhibition (TGI, %) values were determined as 71.9% vs 17.1% for PLM-102 vs Gilteritinib, respectively. These results demonstrated the superior in-vivo efficacies of PLM-102 in Gilteritinib-resistant cells.

mRNA sequencing was performed on both MOLM-14 cells and Gilteritinib-resistance MOLM-14 cells, resulting in an upregulation of the cytokine-mediated signaling pathway, including chemokines, in the Gilteritinib-resistant MOLM-14 cells. Additionally, we conducted mRNA sequencing on Gilteritinib-resistant MOLM-14 cells treated with and without PLM-102 at a concentration of 10 nM. Interestingly, in the group treated with PLM-102 at 10 nM, we observed a notable decrease in the cytokine-mediated signaling pathway, including chemokines. These findings provide valuable insights into the potential mechanism by which PLM-102 exerts its anti-leukemic effect in Gilteritinib-resistant cells by modulating the cytokine-mediated signaling pathway.

In Gilteritinib-resistant MOLM-14 cells harboring the NRAS^G13D mutation, we confirmed hyperactivation of the MEK-ERK signaling pathway. The significantly improved effects in the combination of PLM-102 and Trametinib, a MEK inhibitor, were observed through cell viability assays and a xenograft model, further supporting their potential as a synergistic therapeutic approach.

Currently, the GLP toxicological studies of PLM-102 has successfully completed, and the Investigational New Drug (IND) for human clinical studies will be submitted near future.

Conclusions: Our results have confirmed that RAS-MEK-ERK signaling pathway and cytokine signaling pathway were activated by Gilteritinib resistance. Notably, PLM-102 exhibits exceptional anti-leukemic activity in Gilteritinib-resistant cell lines through the unique mechanism of inhibiting the RAS-MEK-ERK-cytokine signaling pathway. These results highlight the potential of PLM-102 as a third-generation inhibitor with favorable efficacies in patients with resistance to current FLT3 inhibitors.