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Patient-derived organoids are being considered as models that can help guide personalized therapy through in vitro anti-cancer drug response evaluation. However, attempts to quantify in vitro drug responses in organoids and compare them with responses in matched patients remain inadequate. In this study, we investigated whether drug responses of organoids correlate with clinical responses of matched patients and disease progression of patients. Organoids were established from 54 patients with colorectal cancer who (except for one patient) did not receive any form of therapy before, and tumor organoids were assessed through whole-exome sequencing. For comparisons of in vitro drug responses in matched patients, we developed an "organoid score" based on the variable anti-cancer treatment responses observed in organoids. Very interestingly, a higher organoid score was significantly correlated with a lower tumor regression rate after the standard-of-care treatment in matched patients. Additionally, we confirmed that patients with a higher organoid score (≥ 2.5) had poorer progression-free survival compared with those with a lower organoid score (< 2.5). Furthermore, to assess potential drug repurposing using an FDA-approved drug library, ten tumor organoids derived from patients with disease progression were applied to a simulation platform. Taken together, organoids and organoid scores can facilitate the prediction of anti-cancer therapy efficacy, and they can be used as a simulation model to determine the next therapeutic options through drug screening. Organoids will be an attractive platform to enable the implementation of personalized therapy for colorectal cancer patients.

Tumor heterogeneity is one of the ongoing huddles in the field of colon cancer therapy. It is evident that there are countless clones which exhibit different phenotypes and therefore, single cell analysis is inevitable. Cancer stem cells (CSCs) are rare cell population within tumor which is known to function in cancer metastasis and recurrence. Although there have been trials to prove intra-tumoral heterogeneity using single cell sequencing, that of CSCs has not been clearly elucidated. Here, we articulate the presence of heterogeneous subclones within CD133 positive cancer stem cells through single cell sequencing. As a proof of principle, we performed phenotype-based high-throughput laser isolation and single cell sequencing (PHLI-seq) of CD133 positive cells in a frozen tumor tissue obtained from a patient with colorectal cancer. The result proved that CD133 positive cells were shown to be heterogeneous both in copy number and mutational profiles. Single cancer stem cell specific mutations such as RNF144A, PAK2, PARP4, ADAM21, HYDIN, KRT38 and CELSR1 could be also detected in liver metastatic tumor of the same patient. Collectively, these data suggest that single cell analysis used to spot subclones with genetic variation within rare population, will lead to new strategies to tackle colon cancer metastasis.

PIK3CA is a frequently mutated gene in cancer, including about ~15 to 20% of colorectal cancers (CRC). PIK3CA mutations lead to activation of the PI3K/AKT/mTOR signaling pathway, which plays pivotal roles in tumorigenesis. Here, we investigated the mechanism of resistance of PIK3CA-mutant CRC cell lines to gedatolisib, a dual PI3K/mTOR inhibitor. Out of a panel of 29 CRC cell lines, we identified 7 harboring one or more PIK3CA mutations; of these, 5 and 2 were found to be sensitive and resistant to gedatolisib, respectively. Both of the gedatolisib-resistant cell lines expressed high levels of active glycogen synthase kinase 3-beta (GSK3β) and harbored the same frameshift mutation (c.465_466insC; H155fs*) in TCF7, which encodes a positive transcriptional regulator of the WNT/β-catenin signaling pathway. Inhibition of GSK3β activity in gedatolisib-resistant cells by siRNA-mediated knockdown or treatment with a GSK3β-specific inhibitor effectively reduced the activity of molecules downstream of mTOR and also decreased signaling through the WNT/β-catenin pathway. Notably, GSK3β inhibition rendered the resistant cell lines sensitive to gedatolisib cytotoxicity, both in vitro and in a mouse xenograft model. Taken together, these data demonstrate that aberrant regulation of WNT/β-catenin signaling and active GSK3β induced by the TCF7 frameshift mutation cause resistance to the dual PI3K/mTOR inhibitor gedatolisib. Cotreatment with GSK3β inhibitors may be a strategy to overcome the resistance of PIK3CA- and TCF7-mutant CRC to PI3K/mTOR-targeted therapies.

Whole-genome sequencing (WGS) of human tumors and normal cells exposed to various carcinogens has revealed distinct mutational patterns that provide deep insights into the DNA damage and repair processes. Although ionizing radiation (IR) is conventionally known as a strong carcinogen, its genome-wide mutational impacts have not been comprehensively investigated at the single-nucleotide level. Here, we explored the mutational landscape of normal single-cells after exposure to the various levels of IR. On average, 1 Gy of IR exposure generated ∼16 mutational events with a spectrum consisting of predominantly small nucleotide deletions and a few characteristic structural variations. In ∼30% of the post-irradiated cells, complex genomic rearrangements, such aschromoplexy, chromothripsis, and breakage-fusion-bridge cycles, were resulted, indicating the stochastic and chaotic nature of DNA repair in the presence of the massive number of concurrent DNA double-strand breaks. These mutational signatures were confirmed in the genomes of 22 IR-induced secondary malignancies. With high-resolution genomic snapshots of irradiated cells, our findings provide deep insights into how IR-induced DNA damage and subsequent repair processes operate in mammalian cells.

The emergence of RAS/RAF mutant clone is the main feature of EGFR inhibitor resistance in KRAS wild-type colon cancer. However, its molecular mechanism is thought to be multifactorial, mainly due to cellular heterogeneity. In order to better understand the resistance mechanism in a single clone level, we successfully isolated nine cells with cetuximab-resistant (CR) clonality from in vitro system. All CR cells harbored either KRAS or BRAF mutations. Characteristically, these cells showed a higher EMT (Epithelial to mesenchymal transition) signature, showing increased EMT markers such as SNAI2. Moreover, the expression level of CXCL1/5, a secreted protein, was significantly higher in CR cells compared to the parental cells. In these CR cells, CXCL1/5 expression was coordinately regulated by SNAI2/NFKB and transactivated EGFR through CXCR/MMPI/EGF axis via autocrine singling. We also observed that combined cetuximab/MEK inhibitor not only showed growth inhibition but also reduced the secreted amounts of CXCL1/5. We further found that serum CXCL1/5 level was positively correlated with the presence of RAS/RAF mutation in colon cancer patients during cetuximab therapy, suggesting its role as a biomarker. These data indicated that the application of serum CXCL1/5 could be a potential serologic biomarker for predicting resistance to EGFR therapy in colorectal cancer.

PIK3CA is a frequently mutated gene in cancer, including about ~15 to 20% of colorectal cancers (CRC). PIK3CA mutations lead to activation of the PI3K/AKT/mTOR signaling pathway, which plays pivotal roles in tumorigenesis. Here, we investigated the mechanism of resistance of PIK3CA‐mutant CRC cell lines to gedatolisib, a dual PI3K/mTOR inhibitor. Out of a panel of 29 CRC cell lines, we identified 7 harboring one or more PIK3CA mutations; of these, 5 and 2 were found to be sensitive and resistant to gedatolisib, respectively. Both of the gedatolisib‐resistant cell lines expressed high levels of active glycogen synthase kinase 3‐beta (GSK3β) and harbored the same frameshift mutation (c.465_466insC; H155fs*) in TCF7, which encodes a positive transcriptional regulator of the WNT/β‐catenin signaling pathway. Inhibition of GSK3β activity in gedatolisib‐resistant cells by siRNA‐mediated knockdown or treatment with a GSK3β‐specific inhibitor effectively reduced the activity of molecules downstream of mTOR and also decreased signaling through the WNT/β‐catenin pathway. Notably, GSK3β inhibition rendered the resistant cell lines sensitive to gedatolisib cytotoxicity, both in vitro and in a mouse xenograft model. Taken together, these data demonstrate that aberrant regulation of WNT/β‐catenin signaling and active GSK3β induced by the TCF7 frameshift mutation cause resistance to the dual PI3K/mTOR inhibitor gedatolisib. Cotreatment with GSK3β inhibitors may be a strategy to overcome the resistance of PIK3CA‐ and TCF7‐mutant CRC to PI3K/mTOR‐targeted therapies., What's new? Mutations in the PI3K/mTOR and WNT/β‐catenin pathways are common in colorectal cancer. Here, in colorectal cancer cells, the authors show that the frameshift mutation H155fs* in transcription factor TCF7 serves a critical role in mediating resistance to the PI3K/mTOR dual inhibitor gedatolisib. TCF7 H155fs* maintained mTOR signaling by inducing the active form of glycogen synthase kinase 3‐beta (GSK3β) and aberrant WNT/β‐catenin signaling. The latter conferred resistance to gedatolisib. Co‐treatment with a GSK3β inhibitor increased sensitivity to gedatolisib, a combination that synergistically inhibited colorectal tumor growth in mice. The findings shed light on gedatolisib resistance mechanisms and potential resistance biomarkers.

As the conventional histopathologic examination of thymic carcinoma (TC) is nonspecific, immunohistochemical studies along with correlative radiographic investigations are needed for its correct diagnosis. TC commonly occurs in the late 5th to early 6th decades of life but is extremely rare in childhood. It may be incidentally detected from chest radiographs taken as routine or for other reasons. However, most patients present with symptoms such as chest pain, cough, shortness of breath, dysphagia and hoarseness, which are directly attributable to the mediastinal mass. Although TC frequently invades the neighboring organs, pleura and pericardium and metastasizes to the lymph nodes, liver and lung at the time of the first diagnosis, initial or late metastasis to the bone has been seldom reported in adults. Indeed, the English literature revealed no earlier report on initial bony metastasis in a child to date. We report a case of TC in a 12-year-old boy who initially presented with scapular osteolysis masquerading as a primary bone tumor to emphasize the usefulness of combined imaging for staging and histologic studies, particularly for such an unexpected case.

Organoids are known to best in vitro model system which mostly mimic genetic, phenotypic feature of its origin. And it is expected and suitable to variable disease modeling and study. For cancer modeling using organoids as co-clinical model, our group derived organoids from 40 colorectal tumor including lymph node, terminal ileum metastatic tumor and ascites. Whole exome sequencing of matched tumor organoids and tissues was performed and their somatic mutation concordance was analyzed. As a results, Organoids reflect their genetic statues of the original tumor tissue and their phenotypic features are maintained. In order to prove the appliance of these organoids as a co-clinical model, clinical drugs on colorectal cancer such as 5-Fluorouracil, oxaliplatin, SN38 and cetuximab were tested. The drug results reflected the actual clinical outcome of the corresponding patients. To find the precise drug treatment option for conventional chemo-refractory patients, we performed 134 anti-cancer drug library screening. Organoids with specific mutations were sensitive to drugs which target these corresponding mutations. For instance, organoid with RNF43 mutation was sensitive to porcupine inhibitor which suppresses auto- and paracrine WNT- driven growth. In conclusion, we suggest that patient derived organoids can be applied in cancer treatment as a co-clinical model, due to their highly correlated genetic information and drug sensitivity with those of the patients themselves. Citation Format: Young-Won Cho, Hwang-Phill Kim, Dong Wook Min, Yoojoo Lim, Sang-Hyun Song, Sae-Won Han, Tae-You Kim. Application of patients derived organoids as co-clinical model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 36.