BACKGROUND: Multidrug resistance (MDR) limits successful cancer chemotherapy. P-glycoprotein (P-gp), BCRP and MRP1 are the key triggers of MDR. Unfortunately, no MDR modulator was approved by FDA to date. Here, we will investigate the effect of BI-2865, a pan-KRAS inhibitor, on reversing MDR induced by P-gp, BCRP and MRP1 in vitro and in vivo, and its reversal mechanisms will be explored.
METHODS: The cytotoxicity of BI-2865 and its MDR removal effect in vitro were tested by MTT assays, and the corresponding reversal function in vivo was assessed through the P-gp mediated KBv200 xenografts in mice. BI-2865 induced alterations of drug discharge and reservation in cells were estimated by experiments of Flow cytometry with fluorescent doxorubicin, and the chemo-drug accumulation in xenografts\' tumor were analyzed through LC-MS. Mechanisms of BI-2865 inhibiting P-gp substrate\'s efflux were analyzed through the vanadate-sensitive ATPase assay, [125I]-IAAP-photolabeling assay and computer molecular docking. The effects of BI-2865 on P-gp expression and KRAS-downstream signaling were detected via Western blotting, Flow cytometry and/or qRT-PCR. Subcellular localization of P-gp was visualized by Immunofluorescence.
RESULTS: We found BI-2865 notably fortified response of P-gp-driven MDR cancer cells to the administration of chemo-drugs including paclitaxel, vincristine and doxorubicin, while such an effect was not observed in their parental sensitive cells and BCRP or MRP1-driven MDR cells. Importantly, the mice vivo combination study has verified that BI-2865 effectively improved the anti-tumor action of paclitaxel without toxic injury. In mechanism, BI-2865 prompted doxorubicin accumulating in carcinoma cells by directly blocking the efflux function of P-gp, which more specifically, was achieved by BI-2865 competitively binding to the drug-binding sites of P-gp. What\'s more, at the effective MDR reversal concentrations, BI-2865 neither varied the expression and location of P-gp nor reduced its downstream AKT or ERK1/2 signaling activity.
CONCLUSIONS: This study uncovered a new application of BI-2865 as a MDR modulator, which might be used to effectively, safely and specifically improve chemotherapeutic efficacy in the clinical P-gp mediated MDR refractory cancers.

UNASSIGNED: One Kirsten Ras (KRAS) G12C mutated non-small cell lung cancer (NSCLC) patient had improved poor performance status and obtained mixed response with the first-line KRAS-targeted treatment of sotorasib. After disease progression, partial response was achieved with chemotherapy plus immunotherapy. KRAS G12C mutated immunoenvironment in NSCLC may favor the immunotherapy.
UNASSIGNED: KRAS is one of the most commonly mutated genes, which used to be untargetable. The phase II CodeBreak 100 trial revealed 6.8-month median progress-free survival (PFS) and 12.5-month overall survival (OS) in previously treated KRAS G12C-mutant NSCLC patients treated with KRAS inhibitor, sotorasib. The specimens of the brain, lymph node (LN), and blood from the patient were analyzed by next-generation sequencing. Hematoxylin and eosin staining and immunohistochemistry were performed for pathological characterization. Computed tomography (CT) and magnetic resonance imaging (MRI) scan were used for treatment response evaluation. The patient was diagnosed in a bad Eastern Cooperative Oncology Group performance status (ECOG-PS) with metastatic KRAS G12C-mutated lung adenocarcinoma who had achieved mixed response to sotorasib as the first-line treatment. Although 5-month PFS of the treatment with sotorasib was not surprising, the patient achieved significantly improved ECOG-PS score from 4 to 1. Subsequently, partial response (PR) was achieved with the treatment of pemetrexed plus pembrolizumab. This case highlights superior efficacy of first-line treatment with sotorasib for the advance untreated KRAS G12C-mutant patients. The high efficacy of the treatment with chemotherapy plus immunotherapy revealed that immunoenvironment of KRAS G12C-mutated patient may favor the immunotherapy.

KRASG12C inhibitors (adagrasib and sotorasib) have shown clinical promise in targeting KRASG12C-mutated lung cancers; however, most patients eventually develop resistance. In lung patients with adenocarcinoma with KRASG12C and STK11/LKB1 co-mutations, we find an enrichment of the squamous cell carcinoma gene signature in pre-treatment biopsies correlates with a poor response to adagrasib. Studies of Lkb1-deficient KRASG12C and KrasG12D lung cancer mouse models and organoids treated with KRAS inhibitors reveal tumors invoke a lineage plasticity program, adeno-to-squamous transition (AST), that enables resistance to KRAS inhibition. Transcriptomic and epigenomic analyses reveal ΔNp63 drives AST and modulates response to KRAS inhibition. We identify an intermediate high-plastic cell state marked by expression of an AST plasticity signature and Krt6a. Notably, expression of the AST plasticity signature and KRT6A at baseline correlates with poor adagrasib responses. These data indicate the role of AST in KRAS inhibitor resistance and provide predictive biomarkers for KRAS-targeted therapies in lung cancer.

Kirsten rats sarcoma viral oncogene (KRAS), the first discovered human oncogene, has long been recognized as \"undruggable\". KRAS mutations frequently occur in multiple human cancers including non-small cell lung cancer(NSCLC), colorectal cancer(CRC) and pancreatic ductal adenocarcinoma(PDAC), functioning as a \"molecule switch\" determining the activation of various oncogenic signaling pathways. Except for its intrinsic pro-tumorigenic role, KRAS alteration also exhibits an unique immune signature characterized by elevated PD-L1 level and high tumor mutational burden(TMB). KRAS mutation shape an immune suppressive microenvironment by impeding effective T cells infiltration and recruiting suppressive immune cells including myeloid-derived suppressor cells(MDSCs), regulatory T cells(Tregs), cancer associated fibroblasts(CAFs). In immune checkpoint inhibitor(ICI) era, NSCLC patients with mutated KRAS tend to be more responsive to ICI than patients with intact KRAS. The hallmark for KRAS mutation is the existence of multiple kinds of co-mutations. Different types of co-alterations have distinct tumor microenvironment(TME) signatures and responses to ICI. TP53 co-mutation possess a \"hot\" TME and achieve higher response to immunotherapy while other loss of function mutation correlated with a \"colder\" TME and a poor outcome to ICI-based therapy. The groundbreaking discovery of KRAS G12C inhibitors significantly improved outcomes for this KRAS subtype even though efficacy was limited to NSCLC patients. KRAS G12C inhibitors also restore the suppressive TME, creating an opportunity for combinations with ICI. However, an inevitable challenge to KRAS inhibitors is drug resistance. Promising combination strategies such as combination with SHP2 is an approach deserve further exploration because of their immune modulatory effect.