Nurix Therapeutics’ NX-1607 is the first oral small molecule inhibitor of CBL-B to enter clinical trials. CBL-B negatively regulates immune activation in T, B, and NK cells; while immune checkpoint inhibitors are often effective, they have limitations, including lack of efficacy in certain cancers, patient variability, and resistance. NX-1607 enhances T cell activation by gluing CBL-B in an inactive conformation and, driven by preclincial data, NX-1607 is currently in a Ph. I trial. This article details its discovery story and initial clincial results, presented at the ACS Spring 2024 meeting.

Kymera’s KT-413 is a CRBN-based dual-mechanism degrader that degrades both IRAK4 and the transcription factors IKZF1/3, acting as an IMiD, with promising clinical activity for the treatment of ABC-like subtype of DLBCL. This fascinating case study demonstrates how a dual-mechanism degrader of IKZF1/3 and IRAK4 can be designed to maximize NF-κB inhibition while simultaneously upregulating the Type I interferon response. This approach restores the apoptotic response and enables oncogene-mediated cell death, resulting in a robust antiproliferative and pro-apoptotic effect in MYD88 mutants.

AbbVie’s ABBV-467 is a highly potent, selective MCL-1 (myeloid cell leukemia-1) inhibitor which entered the clinic in 2022 in a Ph. I trial in patients with advanced hematologic cancers. MCL-1 has had a rough time in the clinic with multiple trials being halted or terminated due to cardiac toxicity, which is suspected to be an on-target effect. AbbVie’s approach with ABBV-467 was to target a highly potent/short half-life compound which could induce rapid apoptosis and tumor regressions in a short exposure period before the onset of any adverse events. Is this the end for MCL-1?

STX-478 is a wild-type-sparing, oral, CNS-penetrant, novel allosteric inhibitor of mutant phosphatidylinositol-3 kinase α (PI3Kα), targeting a cryptic pocket near the ATP-binding site. PI3Kα plays a central role in many cancers, and has been recently highlighted in coverage of 2021 Molecule of the Year nominee and PI3Kα degrader inavolisib. Currently approved PI3Kα modulators are limited by their off-target activities on WT PI3Kα and other kinases, leading to significant side effects including hyperglycemia and rash.

Arvinas’ ARV-393 is an orally bioavailable PROTAC that degrades BCL6 via CRBN-mediated ubiquitination and proteasomal degradation intended for the treatment of NHL. At the AACR San Diego 2024 meeting, Arvinas disclosed the structure and discovery story of this molecule, which exhibits first-in-class potential. This article covers the key SAR observations that led to the invention of this orally bioavailable PROTAC®, its performance in a triple-hit, high-grade BCL and R-CHOP-resistant cell line, and why sustaining BCL6 knockdown beyond 24 hours was critical for the success of this program.