Anti-tumor efficacy of a potent and selective non-covalent KRASG12D inhibitor

Abstract

The ability to effectively target mutated KRAS has remained elusive despite decades of research. The recent identification of KRAS G12C inhibitors has provided an effective treatment option for patients harboring this particular mutation and has also provided insight toward targeting other KRAS mutants, including KRAS G12D . MRTX1133 was identified via a structure-based drug design (SBDD) strategy as a potent, selective, and non-covalent KRAS G12D inhibitor directed at the switch II binding pocket. MRTX1133 demonstrated a high-affinity interaction with KRAS G12D with KD or IC50 values each determined at ~0.2 pM or <2 nM using SPR direct binding or HTRF competition assays, respectively. MRTX1133 also demonstrated ~700-fold selectivity for KRAS G12D vs KRAS WT binding utilizing SPR. Interestingly, MRTX1133 demonstrated potent inhibition of active KRAS G12D using an HTRF effector interaction assay with a IC50 value of 9 nM. Insight toward the structural basis of binding of MRTX1133 to both the inactive GDP-bound and active GMPPCP-bound conformations of KRAS G12D is also provided by co-crystal structures. MRTX1133 demonstrated potent inhibition of ERK1/2 phosphorylation and cell viability in KRAS G12D -mutant cell lines with median IC50 values of ~5 nM. Consistent with binding affinity determination in cell-free systems, MRTX1133 demonstrated >1000-fold selectivity for inhibition of ERK1/2 phosphorylation in KRAS G12Dmutant cell lines compared with KRAS WT cell lines. Dose-dependent inhibition of KRASmediated signal transduction was also observed in multiple KRAS G12D -mutant tumor models in vivo. MRTX1133 demonstrated marked tumor regression (>30%) in a subset of KRAS G12Dmutant cell line-and patient-derived xenograft (PDX) models, including 8 out of 11 (73%) pancreatic ductal adenocarcinoma (PDAC) models evaluated. Pharmacological studies and CRISPR-based screens demonstrated co-targeting KRAS G12D in concert with putative feedback or bypass pathways including EGFR and PI3Kα led to enhanced anti-tumor activity relative to targeting each individual protein. Together, these data indicate the feasibility of utilizing SBDD approaches to selectively target alternative KRAS mutant variants with non-covalent, highaffinity small molecules targeting either the active or inactive state of KRAS. In addition, these data illustrate the therapeutic susceptibility and broad dependence of KRAS G12D mutationpositive tumors, including PDAC, on KRAS for tumor cell growth and survival. SignificanceThe development of clinically active KRAS G12C -selective inhibitors represents a milestone achievement for the treatment of cancer; however, the discovery of additional KRAS-mutant selective inhibitors has remained elusive. MRTX1133 is a potent KRAS G12D -selective small molecule inhibitor, is active in vitro and in vivo, induces regression in multiple xenograft tumor models and demonstrates increased anti-tumor activity in rationally designed combinations. These data confirm KRAS G12D functions as an oncogenic driver, including in pancreat...

Translational alterations in pancreatic cancer: a central role for the integrated stress response

“…Thus, a large panel of inhibitors targeting either MEK/ERK or PI3K/AKT/mTOR (see examples in Figure 2 ) has been developed, but showed limited efficacy in human subjects, in part due to toxicities (reviewed in 54 ). A glimmer of hope is now coming from KRAS G12C inhibitors [such as AMG510 (sotorasib) and MRTX849 (adagrasib)], and from a newly identified KRAS G12D inhibitor which could be administered to >30% of PDA patients ( 55 ).…”

KRAS inhibitors: going noncovalent

“…This is not unexpected since lung cancers treated with KRAS G12C inhibitors are also capable of rapidly developing resistance. Therefore, combination therapies are likely to be more effective and the current study by Hallin et al already proposes several potent combinations [8]. In contrast to PDAC, KRAS mutations are usually not considered an initial driving event in CRC, instead being responsible for the progression of adenomas to malignant carcinomas.…”

“…A more recent study has now evaluated the mechanism of action and antitumor activity of MRTX1133 [ 8 ]. First, the authors performed a series of assays to validate the binding efficacy of the drug to KRAS G12D when compared with wild‐type KRAS.…”

“…The authors also tested the cellular activity of MRTX1133 in cell lines carrying the G12D mutation in KRAS [ 8 ]. MRTX1133 inhibited downstream signaling pathways in a concentration‐dependent manner with an IC50 of < 3 n m .…”

Glimmers of hope for targeting oncogenic KRAS-G12D

“…Recently, Nature Medicine published a study led by Mirati's James G. Christensen showing encouraging preclinical data for the small molecule compound MRTX1133 as a KRAS-G12D inhibitor in treating KRAS-G12D mutant cancers, particularly PDAC (Fig. 1) [15].…”