BACKGROUND: The MAP2K1 K57T mutation is known to be a potential mechanism of primary and secondary resistance to EGFR inhibitors in metastatic colorectal cancer (CRC) and has also been reported to promote resistance to BRAF and MEK inhibitors. It is important to overcome therapeutic resistance to EGFR inhibitors to improve the treatment outcomes of metastatic CRC. METHODS: We established patient-derived tumor cells (PDCs) from metastatic lesions that newly appeared during treatment with a BRAF inhibitor (LGX-818) plus an EGFR inhibitor (cetuximab) in a patient with BRAF-mutant CRC. To investigate therapeutic options to overcome acquired resistance due to MAP2K1 mutation in BRAF-mutant CRC, we performed cell viability assays using the PDCs. RESULTS: We tested whether the PDCs were resistant to an EGFR inhibitor (cetuximab) and a BRAF inhibitor (sorafenib) as these cells were established at the time of resistance to the EGFR plus BRAF inhibitors. Moreover, the anti-tumor effect of AZD6244 (MEK inhibitor) was evaluated because PDCs harbored a MAP2K1 mutation at the time of resistance to the EGFR plus BRAF inhibitors. MTT proliferation assays showed that monotherapy with cetuximab, sorafenib, or AZD6244 did not suppress cell viability. We next tested viability of the PDCs to combination treatment with cetuximab plus AZD6244 and sorafenib plus AZD6244. Proliferation of PDCs was significantly inhibited by sorafenib and AZD6244, but not by cetuximab plus AZD6244. Investigation of the combined effect of sorafenib and AZD6244 using the calculated combination index (CI) showed synergistic effects of sorafenib and AZD6244 in combination therapy applied to PDCs with the MAP2K1 K57T mutation. CONCLUSION: Our results suggest that combination treatment with BRAF and MEK inhibitors might be a novel treatment strategy for MAP2K1 K57T-mutant CRC. This finding will be helpful to guide treatment of patients with CRC that is resistant to EGFR inhibitors.

Somatic mutations of LKB1 tumour suppressor gene have been detected in human cancers including non-small cell lung cancer (NSCLC). The relationship between LKB1 mutations and clinicopathological characteristics and other common oncogene mutations in NSCLC is inadequately described. In this study we evaluated tumour specimens from 310 patients with NSCLC including those with adenocarcinoma, adenosquamous carcinoma, and squamous cell carcinoma histologies. Tumours were obtained from patients of US (n=143) and Korean (n=167) origin and screened for LKB1, KRAS, BRAF, and EGFR mutations using RT-PCR-based SURVEYOR-WAVE method followed by Sanger sequencing. We detected mutations in the LKB1 gene in 34 tumours (11%). LKB1 mutation frequency was higher in NSCLC tumours of US origin (17%) compared with 5% in NSCLCs of Korean origin (P=0.001). They tended to occur more commonly in adenocarcinomas (13%) than in squamous cell carcinomas (5%) (P=0.066). LKB1 mutations associated with smoking history (P=0.007) and KRAS mutations (P=0.042) were almost mutually exclusive with EGFR mutations (P=0.002). The outcome of stages I and II NSCLC patients treated with surgery alone did not significantly differ based on LKB1 mutation status. Our study provides clinical and molecular characteristics of NSCLC, which harbour LKB1 mutations.

Recent advances have raised hope that transplantation of adherent somatic cells could provide dramatic new therapies for various diseases. However, current methods for transplanting adherent somatic cells are not efficient enough for therapeutic applications. Here, we report the development of a novel method to generate quasi-natural cell blocks for high-efficiency transplantation of adherent somatic cells. The blocks were created by providing a unique environment in which cultured cells generated their own extracellular matrix. Initially, stromal cells isolated from mice were expanded in vitro in liquid cell culture medium followed by transferring the cells into a hydrogel shell. After incubation for 1 day with mechanical agitation, the encapsulated cell mass was perforated with a thin needle and then incubated for an additional 6 days to form a quasi-natural cell block. Allograft transplantation of the cell block into C57BL/6 mice resulted in perfect adaptation of the allograft and complete integration into the tissue of the recipient. This method could be widely applied for repairing damaged cells or tissues, stem cell transplantation, ex vivo gene therapy, or plastic surgery.