Background: KRAS is the most frequently mutated RAS/RAF family member (mutated in 15% of cancers), followed by BRAF (5%) and NRAS (3%). Several BRAF and MEK inhibitors (MEKi) are approved for BRAF V600E cancers, and the G12C inhibitor sotorasib is approved for KRAS G12C non-small cell lung cancer (NSCLC). However, there is still a need for agents targeting other RAS/RAF mutations (mt), including KRAS G12 V which is mutated in ∼7%, ∼9% and ∼19% of NSCLC, colorectal and pancreatic cancers, respectively. VS-6766 is a unique RAF/MEK clamp that potently inhibits MEK kinase activity and induces a dominant negative RAF-MEK complex preventing phosphorylation of MEK by ARAF, BRAF and CRAF. This unique mechanism allows VS-6766 to block MEK signaling without the compensatory re-activation of MEK that appears to limit the efficacy of MEKi. Material and Methods: In vitro assays were performed to evaluate the anti-proliferative activity of VS-6766 in human tumor cell lines with MAPK pathway alterations and in RAS-less mouse embryonic fibroblasts (MEFs) stably transfected with various KRAS variants. The anti-tumor activity of VS-6766 was assessed in genetically engineered mouse models (GEMM) of KRAS G12 V/Trp53 KO and KRAS G12C/Trp53 KO NSCLC. Results: VS-6766 showed strong anti-proliferative potency across tumor cell lines carrying KRAS, BRAF, CRAF, NRAS or NF1 alterations. Among KRAS mt cell lines, the anti-proliferative potency of VS-6766 differed by KRAS variant, with greatest potency observed with G12 V > G12C > G12D, which is consistent with G12 V signaling through CRAF/MEK/ERK and G12D signaling more through PI3 K/AKT/mTOR. Similarly, in MEFs stably transfected with different KRAS variants, VS-6766 showed best potency with KRAS G12 V and G12C, and least potency with G12D and KRAS wildtype. Accordingly, in the KRAS G12 V NSCLC GEMM model, previously shown to be CRAF-dependent, VS-6766 monotherapy induced stronger tumor regression than in a corresponding G12C NSCLC GEMM model. Strikingly, the combination of VS-6766 with FAK inhibition conferred tumor regressions in 87% (27/31) and 71% (36/51) of all tumors in the KRAS G12 V and KRAS G12C NSCLC models, respectively. Clinically, objective responses to VS-6766 monotherapy occurred mainly in patients with KRAS G12 V with 4 out of the 7 responders bearing KRAS G12 V (Guo, 2020). In KRAS mt NSCLC patients treated with VS-6766 in combination with the FAK inhibitor defactinib, a G12 V preference was also observed with confirmed responses in 2/2 patients with KRAS G12 V and tumor reduction in 4/6 patients with KRAS G12C (Krebs, 2021). Conclusions: These data support the ongoing registration-directed study evaluating VS-6766 ± defactinib for patients with KRAS G12 V NSCLC (NCT04620330), as well as the clinical combinations of VS-6766 with the KRAS G12C inhibitors sotorasib (NCT05074810) or adagrasib (NCT05375994) for KRAS G12C NSCLC. No conflict of interest.

KRAS is mutated in 25% of non-small cell lung cancer (NSCLC) adenocarcinoma, with KRAS G12C and G12V mutations occurring in ∼13% and ∼7% of patients, respectively. Whereas G12C inhibitors (G12Ci) sotorasib (AMG 510) and adagrasib (MRTX849) have demonstrated promising antitumor activity in patients with KRAS G12C mutant (mt) NSCLC, KRAS G12V mt NSCLC remains an unmet need. VS-6766 is a unique dual RAF/MEK inhibitor which has shown single agent activity against KRAS G12V mt NSCLC (Guo Lancet Oncology 2020).

Abstract This abstract was withdrawn by the authors.

Abstract This abstract was withdrawn by the authors.

MM-302 is a HER2-targeted antibody–liposomal doxorubicin conjugate designed to target doxorubicin to HER2-expressing tumor cells. MM-302 showed an acceptable safety profile and promising activity in a Phase I study in HER2-positive metastatic breast cancer (NCT01304797), and it is now being evaluated in a Phase II trial in the same setting (NCT02213744). The goal of this work is to determine the correlation between single-cell HER2 expression and liposome uptake on MM-302 patient biopsies as well as on preclinical tumor models. Frozen biopsies were collected 3 days post infusion of MM-302 (8-50 mg/m2; alone or in combination with trastuzumab, with or without cyclophosphamide), and stained for PEG (surrogate for MM-302), HER2 and cytokeratin, side-by-side with two cell standard arrays: A PEG array, obtained by cell incubation with increasing amounts of MM-302, and a HER2 array, containing a panel of cell lines at various HER2 levels. The HER2 expression and liposome uptake in individual tumor cells of the human samples was quantified based on the PEG and HER2 fluorescent intensities of the standards. MM-302 cellular delivery was investigated in vivo in IHC 0, 1 + , 2+ and 3+ tumor models. Uptake of MM-302 into HER2-expressing cells was detected in ∼80% of patient biopsies. Interestingly, HER2 expression within individual samples was found to be heterogeneous, ranging from ∼1 X 105 to over 1 X 106 HER2 receptors per cell. Evaluation of cellular HER2 expression and MM-302 uptake within the same sample revealed that the magnitude of MM-302 tumor cell uptake was comparable across the range of HER2 expression from ∼1 X 105 to over 1 X 106 HER2 receptors per cell. These findings were in line with preclinical in vivo studies showing HER2-mediated delivery of MM-302 to IHC 1 + , 2 + , and 3+ tumors but not to IHC 0 tumors. Our data suggest that MM-302 effectively targets tumor cells expressing various levels of HER2 in patients' tumors. Hence, in addition to treating HER2-positive patients, MM-302 may be a promising agent for treating patients with intermediate HER2 expression (HER2 IHC 1 + /2 + , FISH-negative).