To better understand how Dendritic Cell (DC) subsets are differentiating, we investigated two essential arms of DC differentiation and how they interact to mediate this process. The transcription factors Interferon Regulatory Factor 4 and 8 (IRF4 and IRF8) are critical for DC differentiation, but have varying roles depending on the stimuli. While IRF8 is required for FLT3-L induced plasmacytoid DC differentiation, and IRF4 is required for GM-CSF induced conventional DC differentiation, it is not well characterized how these two molecules are differentially regulated. We found that Protein Kinase C βII (PKCβII) is activated by both FLT3-L and GM-CSF, and that it is required for DC differentiation when either of these stimuli is used to generate DCs from progenitor cells. Since PKCβII and these IRFs are contributing to DC differentiation we hypothesized they were interacting. We discovered that PKCβII upregulates IRF8 when activated by FLT3-L or phorbol ester (PMA, a known activator of PKCβII), and IRF8 upregulation is lost with the addition of a PKCβII inhibitor. Likewise, IRF4 upregulation is induced by PKCβII in cells treated with GM-CSF or PMA, and lost in the presence of a PKCβII inhibitor. We have also found that in IRF8 knockout DCs there are higer levels of PKCβII, suggesting a feedback mechanism by which these IRFs can be autoregulated. Thus, PKCβII regulating these IRFs may be the key to understanding and manipulating DC differentiation.

KRAS is one of the most frequently mutated oncogenes. Clinical studies with recently developed covalent KRASG12C inhibitors have shown promising anticancer activity in patients with KRASG12C tumors (substitution of glycine to cysteine at amino acid 12). Not all KRASG12C patients respond to single-agent treatment or, despite initial responses, develop drug resistance. Here, we investigate therapeutic options to overcome resistance to KRASG12C inhibitor therapy in non-small cell lung cancer (NSCLC). Cancer cell lines and in vivo tumor xenograft models representing high fibroblast growth factor receptor-1 expression (FGFR1hi) and KRASG12C tumors were treated with FGFR or KRASG12C inhibitors. The impact of single-agent versus combination treatment was measured in cell signaling, functional, and in vivo tumor growth assays. Analysis of a genome-wide genetic screen and corresponding mutation and expression data from DepMap identified a subset of NSCLC cells that harbor high FGFR1 expression (FGFR1hi) and KRASG12C mutations. FGFR1hi cancer cells exhibited mesenchymal-like features including high levels of vimentin and low levels of E-cadherin. To assess the functional role of high FGFR1 expression in KRASG12C-mutant cancer cells, pemigatinib, a potent and selective inhibitor of FGFR1-3, was tested alone or in combination with KRASG12C inhibitors. The combination of pemigatinib and KRASG12C inhibitors was synergistic in mesenchymal-like lung cancer cells with high FGFR1 expression, whereas no synergy was observed in cells with low FGFR1 expression. Furthermore, inhibition of FGFR1 activity was essential as a FGFR2-3 specific inhibitor demonstrated only modest activity in combination with KRASG12C inhibitors. Notably, treatment of FGFR1hi KRASG12C LU99 cells with covalent KRASG12C inhibitors resulted in an increase in FRS2 phosphorylation, a marker of FGFR pathway activation, which was suppressed by pemigatinib. To determine whether increased FGFR1 activity may be an acquired resistance mechanism, KRASG12C-mutant Mia-Paca-2 clones resistant to KRASG12C inhibitors were generated. Subsequent protein analysis identified high levels of FGFR1 expression in a subset of resistant clones. In vivo studies with mesenchymal KRASG12C-mutant xenografts confirmed increased antitumor efficacy and inhibition of pERK with the combination of KRASG12C inhibitors and pemigatinib, compared with single-agent treatment. In contrast, in vivo combination activity was not observed in NSCLC tumors possessing an epithelial-like phenotype. We demonstrate that NSCLC with a mesenchymal-like phenotype and harboring high FGFR1 expression and KRASG12C mutations may uniquely benefit from combination treatment with current KRASG12C-covalent inhibitors and blockade of FGFR1-mediated activity. Our results support pemigatinib as a promising agent for combination therapy with KRAS inhibitors. Citation Format: Margaret Favata, Michael Weber, Angela Abdollahi, Valerie Dostalik Roman, Matt Farren, Aidan Gilmartin, Sunkyu Kim, Susan Wee, Jonathan Rios-Doria. Pemigatinib, an FGFR inhibitor, overcomes resistance to KRASG12C inhibitors in mesenchymal-like NSCLC tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 430.