Preclinical evaluation of proteolytic targeting of LCK as a therapeutic approach in T cell acute lymphoblastic leukemia

T cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy, and there is an unmet need for targeted therapies, especially for patients with relapsed disease. We have recently identified pre-T cell receptor and lymphocyte-specific protein tyrosine kinase (LCK) signaling as a common therapeutic vulnerability in T-ALL. LCK inhibitor dasatinib showed efficacy against T-ALL in preclinical studies and in patients with T-ALL; however, this is transient in most cases. Leveraging the proteolysis targeting chimera (PROTAC) approach, we developed a series of LCK degraders using dasatinib as an LCK ligand and phenyl-glutarimide as a cereblon-directing moiety. Our lead compound SJ11646 exhibited marked efficiency in cereblon-mediated LCK degradation in T-ALL cells. Relative to dasatinib, SJ11646 showed up to three orders of magnitude higher cytotoxicity in LCK-activated T-ALL cell lines and primary leukemia samples in vitro, with drastically prolonged suppression of LCK signaling. In vivo pharmacokinetic and pharmacodynamic profiling indicated a 630% increase in the duration of LCK suppression by SJ11646 over dasatinib in patient-derived xenograft models of T-ALL, which translated into its extended leukemia-free survival over dasatinib in vivo. Last, SJ11646 retained a high binding affinity to 51 human kinases, particularly ABL1, KIT, and DDR1, all of which are known drug targets in other cancers. Together, our dasatinib-based phenyl-glutarimide PROTACs are promising therapeutic agents in T-ALL and valuable tools for developing degradation-based therapeutics for other cancers.

Abstract 423: Induced proximity and proteolytic targeting of LCK as a novel therapeutic approach in T-cell leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive cancer, with a particularly dismal prognosis in patients with relapsed diseases. Our group recently discovered LCK dependency as a therapeutic vulnerability in 33% of T-ALL and LCK inhibitor dasatinib exhibited strong efficacy in vitro and in vivo (Nat Cancer 2, 284, 2021). However, the transient LCK inhibition by dasatinib resulted in only partial responses, and novel agents are needed to suppress LCK signaling in T-ALL in a sustained fashion to achieve long-term efficacy. We synthesized a set of proteolytic targeting chimeras (PROTACs) that bring LCK to cereblon (CRBN) E3 ligase for ubiquitination and degradation. LCK-PROTACs showed extremely high anti-leukemia sensitivity, i.e., up to 1,561.3 fold increase over dasatinib in LCK-activated T-ALL cell line. Complete LCK degradation was induced by most LCK-PROTACs. Based on solubility, permeability, stability, and anti-leukemia effects in vitro, we prioritized SJ001011646 for further evaluations. SJ001011646 induced 50% LCK degradation at the concentration at ~0.001nM, with superior cytotoxic effects in patient-derived primary T-ALL samples compared to dasatinib. In addition, we confirmed the formation of ternary complex of LCK, SJ001011646, and CRBN, using the AlphaLISA assay. In a wash-out experiment, LCK-dependent T-ALL cells were exposed to SJ001011646 or dasatinib for 18 hours and then monitored for viability recovery. Both dasatinib and SJ001011646 led to dramatic growth inhibition within 2 days. While dasatinib-treated cells started to recover 96 hours after drug removal, cells treated with SJ001011646 failed to recover even after 240 hours. To systematically identify therapeutic targets of SJ001011646, we performed proteomic profiling of T-ALL cells before and after drug treatment in vitro. Overall, 126,670 unique peptides were identified and mapped to 10,158 proteins, of which LCK was most significantly reduced by PROTAC. In parallel, kinome-binding profiling confirmed LCK as a primary target of SJ001011646. Finally, we explored pharmacokinetic and pharmacodynamic properties of SJ001011646 in vivo, using patient-derived xenograft models of T-ALL. Given at the same dosage level as a single injection, SJ001011646 showed 367% increase in the duration of LCK suppression compared to dasatinib. Taken together, we described the development and preclinical evaluation of LCK-targeting PROTACs in T-ALL. Inducing proximity to CRBN and therefore degradation, these agents can produce sustained LCK suppression with much improved anti-leukemia efficacy than small molecule inhibitors, and are therefore promising novel therapeutic agents in T-ALL.

Citation Format: Jianzhong Hu, Jamie Jarusiewicz, Jaeki Min, Lei Yang, Divyabharathi Chepyala, Marisa Actis, Guoqing Du, Brandon Smart, Dylan Maxwell, Boer Xie, Satoshi Yoshimura, Junming Peng, David T. Teachey, Zoran Rankovic, Jun J. Yang. Induced proximity and proteolytic targeting of LCK as a novel therapeutic approach in T-cell leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 423.

Phenyl-Glutarimides: Alternative Cereblon Binders for the Design of PROTACs

Targeting cereblon (CRBN) is currently one of the most frequently reported proteolysis-targeting chimera (PROTAC) approaches, owing to favorable drug-like properties of CRBN ligands, immunomodulatory imide drugs (IMiDs). However, IMiDs are known to be inherently unstable, readily undergoing hydrolysis in body fluids. Here we show that IMiDs and IMiD-based PROTACs rapidly hydrolyze in commonly utilized cell media, which significantly affects their cell efficacy. We designed novel CRBN binders, phenyl glutarimide (PG) analogues, and showed that they retained affinity for CRBN with high ligand efficiency (LE >0.48) and displayed improved chemical stability. Our efforts led to the discovery of PG PROTAC 4 c (SJ995973), a uniquely potent degrader of bromodomain and extra-terminal (BET) proteins that inhibited the viability of human acute myeloid leukemia MV4-11 cells at low picomolar concentrations (IC50 =3 pM; BRD4 DC50 =0.87 nM). These findings strongly support the utility of PG derivatives in the design of CRBN-directed PROTACs.

Efficient three-component Strecker reaction of aldehydes/ketones via NHC-amidate palladium(II) complex catalysis

A simple and efficient one-pot, three-component method has been developed for the synthesis of alpha-aminonitriles. This Strecker reaction is applicable for aldehydes and ketones with aliphatic or aromatic amines and trimethylsilyl cyanide in the presence of a palladium Lewis acid catalyst in dichloromethane solvent at room temperature.