Background: A major problem with the use of current chemotherapy regimens for several cancers, including breast cancer, is development of intrinsic or acquired drug resistance, which results in disease recurrence and metastasis. However, the mechanisms underlying this drug resistance are unknown. To study the molecular mechanisms underlying the invasive and metastatic activities of drug-resistant cancer cells, we generated a doxorubicin-resistant MCF-7 breast cancer cell line (MCF-7/DOX). Methods: We used MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assays, flow cytometry assays, DNA fragmentation assays, Western blot analysis, cell invasion assays, small interfering RNA (siRNA) transfection, reverse transcription-polymerase chain reaction, experimental lung metastasis models, and gelatin and fibrinogen/plasminogen zymography to study the molecular mechanism of metastatic activities in MCF-7/DOX cells. Results: We found that MCF-7/DOX acquired invasive activities. In addition, Western blot analysis showed increased expression of epidermal growth factor receptor (EGFR) and Cox-2 in MCF-7/DOX cells. Inhibition of Cox-2, phosphoinositide 3-kinase (PI3K)/Akt, or mitogen-activated protein kinase (MAPK) pathways effectively inhibited the invasive activities of MCF-7/DOX cells. Gelatin and fibrinogen/plasminogen zymography analysis showed that the enzymatic activities of matrix metalloproteinase-2 (MMP-2), MMP-9, and urokinase-type plasminogen activator were markedly higher in MCF-7/DOX cells than in the MCF-7 cells. In vitro invasion assays and mouse models of lung metastasis demonstrated that MCF-7/DOX cells acquired invasive abilities. Using siRNAs and agonists specific for prostaglandin E (EP) receptors, we found that EP1 and EP3 played important roles in the invasiveness of MCF-7/DOX cells. Conclusions: We found that the invasive activity of MCF-7/DOX cells is mediated by Cox-2, which is induced by the EGFR-activated PI3K/Akt and MAPK pathways. In addition, EP1 and EP3 are important in the Cox-2-induced invasion of MCF-7/DOX cells. Therefore, not only Cox-2 but also EP1 and EP3 could be important targets for chemosensitization and inhibition of metastasis in breast cancers that are resistant to chemotherapy.

Background: A pharmacogenomic platform using patient-derived cells (PDCs) was established to identify the underlying resistance mechanisms and tailored treatment for patients with advanced or refractory lung cancer. Methods: Drug sensitivity screening and multi-omics datasets were acquired from lung cancer PDCs (n = 102). Integrative analysis was performed to explore drug candidates according to genetic variants, gene expression, and clinical profiles. Results: PDCs had genomic characteristics resembled with those of solid lung cancer tissues. PDC molecular subtyping classified patients into four groups: (1) inflammatory, (2) epithelial-to-mesenchymal transition (EMT)-like, (3) stemness, and (4) epithelial growth factor receptor (EGFR)-dominant. EGFR mutations of the EMT-like subtype were associated with a reduced response to EGFR-tyrosine kinase inhibitor therapy. Moreover, although RB1/TP53 mutations were significantly enriched in small-cell lung cancer (SCLC) PDCs, they were also present in non-SCLC PDCs. In contrast to its effect in the cell lines, alpelisib (a PI3K-AKT inhibitor) significantly inhibited both RB1/TP53 expression and SCLC cell growth in our PDC model. Furthermore, cell cycle inhibitors could effectively target SCLC cells. Finally, the upregulation of transforming growth factor-β expression and the YAP/TAZ pathway was observed in osimertinib-resistant PDCs, predisposing them to the EMT-like subtype. Our platform selected XAV939 (a WNT-TNKS-β-catenin inhibitor) for the treatment of osimertinib-resistant PDCs. Using an in vitro model, we further demonstrated that acquisition of osimertinib resistance enhances invasive characteristics and EMT, upregulates the YAP/TAZ-AXL axis, and increases the sensitivity of cancer cells to XAV939. Conclusions: Our PDC models recapitulated the molecular characteristics of lung cancer, and pharmacogenomics analysis provided plausible therapeutic candidates.

DDRI-9: a novel DNA damage response inhibitor that blocks mitotic progression

Modulation of the DNA repair pathway is an emerging target for the development of anticancer drugs. DNA interstrand cross-links (ICLs), one of the most severe forms of DNA damage caused by anticancer drugs such as cisplatin and mitomycin C (MMC), activates the Fanconi anemia (FA)/BRCA DNA repair pathway. Inhibition of the FA/BRCA pathway can enhance the cytotoxic effects of ICL-inducing anticancer drugs and can reduce anticancer drug resistance. To find FA/BRCA pathway inhibitory small molecules, we established a cell-based high-content screening method for quantitating the activation of the FA/BRCA pathway by measuring FANCD2 foci on DNA lesions and then applied our method to chemical screening. Using commercial LOPAC1280 chemical library screening, ouabain was identified as a competent FA/BRCA pathway inhibitory compound. Ouabain, a member of the cardiac glycoside family, binds to and inhibits Na⁺/K⁺-ATPase and has been used to treat heart disease for many years. We observed that ouabain, as well as other cardiac glycoside family members―digitoxin and digoxin―down-regulated FANCD2 and FANCI mRNA levels, reduced monoubiquitination of FANCD2, inhibited FANCD2 foci formation on DNA lesions, and abrogated cell cycle arrest induced by MMC treatment. These inhibitory activities of ouabain required p38 MAPK and were independent of cellular Ca²⁺ ion increase or the drug uptake-inhibition effect of ouabain. Furthermore, we found that ouabain potentiated the cytotoxic effects of MMC in tumor cells. Taken together, we identified an additional effect of ouabain as a FA/BRCA pathway-inhibiting chemosensitization compound. The results of this study suggest that ouabain may serve as a chemosensitizer to ICL-inducing anticancer drugs.

Autophagy is a highly conserved cellular process in which cytoplasmic materials are degraded and recycled as energy sources when nutrient supplies are lacking. Established tumor cells require autophagy for cell growth and tumor promotion. In particular, the survival of pancreatic tumor cells appears to be strongly dependent on autophagy, referred to as autophagy addiction. This dependency of pancreatic tumor cells on autophagy may be a candidate target for pancreatic tumor therapy. EI24 (etoposide-induced gene 2.4 kb; PIG8, p53-induced gene 8) acts as a tumor suppressor, inhibiting cell growth and inducing apoptosis in breast, cervical, and prostate cancer cells. However, recent papers have reported that EI24 is an essential component of the autophagy pathway. This newly discovered role of EI24 as a component of autophagy may act as a tumor promoter, which is contradictory to its known role as a tumor suppressor. We investigated the role of EI24 as a component of autophagy in pancreatic tumor cell proliferation. Here, we demonstrated that knockdown of EI24 using siRNA in pancreatic tumor cells led to impaired autophagy at a late step (increase in LC3-II and accumulation of p62 and autolysosomes). EI24 deficiency in pancreatic tumor cell lines inhibited cell proliferation. We confirmed that loss of EI24 inhibited pancreatic cell proliferation using the CRISPR-Cas9 system. However, loss of EI24 in other cell lines did not affect cell proliferation. Taken together, our results suggest that EI24 acts as a tumor promoter in pancreatic tumor cells, and studying the role of EI24 in reference to its cellular context may lead to a useful therapeutic target.

Although molecular subtypes of small-cell lung cancer (SCLC) have been proposed, their clinical relevance and therapeutic implications are not fully understood. Thus, we aimed to refine molecular subtypes and to uncover therapeutic targets. We classified the subtypes based on gene expression (n = 81) and validated them in our samples (n = 87). Non-SCLC samples were compared with SCLC subtypes to identify the early development stage of SCLC. Single-cell transcriptome analysis was applied to dissect the TME of bulk samples. Finally, to overcome platinum resistance, we performed drug screening of patient-derived cells and cell lines. Four subtypes were identified: the ASCL1+ (SCLC-A) subtype identified as TP53/RB-mutated non-SCLC representing the early development stage of SCLC; the immune activation (SCLC-I) subtype, showing high CD8+/PD-L1+ T-cell infiltration and endothelial-to-mesenchymal transition (EndMT); the NEUROD1 (SCLC-N) subtype, which showed neurotransmission process; and the POU2F3+ (SCLC-P) subtype with epithelial-to-mesenchymal transition (EMT). EndMT was associated with the worst prognosis. While SCLC-A/N exhibited platinum sensitivity, the EndMT signal of SCLC-I conferred platinum resistance. A BET inhibitor suppressed the aggressive angiogenesis phenotype of SCLC-I. We revealed that EndMT development contributed to a poor outcome in SCLC-I. Moreover, heterogenous TME development facilitated platinum resistance. BET inhibitors are novel candidates for overcoming platinum resistance.