Regorafenib is an oral multi-kinase inhibitor used as salvage therapy for metastatic colorectal cancer (mCRC). We tested whether serum cytokine levels are associated with clinical outcome in the mCRC patients receiving regorafenib. Serum samples were collected before treatment start, day 21, and progressive disease, and eleven angiogenic and inflammatory cytokine serum levels were examined. Fifty-four patients of a total of 62 enrolled patients were eligible for the analyses. The chemokine ligand 5 (CCL5) levels ≤ cut-off value (59959 pg/ml) at baseline was associated with relative tumor shrinkage (P = 0.021), better progression-free survival (PFS) (P = 0.036) and overall survival (OS) (P = 0.019). Vascular endothelial growth factor A (VEGF-A) levels showing a decrease on day 21 were significantly associated with a better PFS (P = 0.021). CCL5 levels ≤ cut-off was associated with any grade hand-foot skin reaction (HFSR) (P = 0.025) and thrombocytopenia (P = 0.013). Low chemokine ligand 2 levels at baseline were associated with grade 2 ≤ HFSR. High angiopoietin-2 and basic fibroblast growth factor (bFGF) levels at baseline were associated with grade 3 ≤ total bilirubin increase and transaminases increase, respectively. Low bFGF levels at baseline were associated with grade 3 ≤ hypertension. No correlation with severe events was observed. Baseline serum CCL5 levels and decrease of the serum VEGF-A levels may serve as potential predictive markers for survival or treatment-specific toxicities in mCRC patients receiving regorafenib.

Tumors consist of heterogeneous cell populations that contain cancer cell subpopulations with anticancer drug‐resistant properties called “persister” cells. While this early‐phase drug tolerance is known to be related to the stem cell‐like characteristic of persister cells, how the stem cell‐related pathways contribute to drug resistance has remained elusive. Here, we conducted a single‐cell analysis based on the stem cell lineage‐related and gastric cell lineage‐related gene expression in patient‐derived gastric cancer cell models. The analyses revealed that 5‐fluorouracil (5‐FU) induces a dynamic change in the cell heterogeneity. In particular, cells highly expressing stem cell‐related genes were enriched in the residual cancer cells after 5‐FU treatment. Subsequent functional screening identified aldehyde dehydrogenase 1A3 (ALDH1A3) as a specific marker and potential therapeutic target of persister cells. ALDH1A3 was selectively overexpressed among the ALDH isozymes after treatment with 5‐FU or SN38, a DNA topoisomerase I inhibitor. Attenuation of ALDH1A3 expression by RNA interference significantly suppressed cell proliferation, reduced the number of persister cells after anticancer drug treatment and interfered with tumor growth in a mouse xenograft model. Mechanistically, ALDH1A3 depletion affected gene expression of the mammalian target of rapamycin (mTOR) cell survival pathway, which coincided with a decrease in the activating phosphorylation of S6 kinase. Temsirolimus, an mTOR inhibitor, reduced the number of 5FU‐tolerant persister cells. High ALDH1A3 expression correlated with worse prognosis of gastric cancer patients. These observations indicate that the ALDH1A3‐mTOR axis could be a novel therapeutic target to eradicate drug‐tolerant gastric cancer cells.

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Background Tumours consist of heterogeneous cancer cells and are likely to contain drug-tolerant cell subpopulations, causing early relapse. However, treatment strategies to eliminate these cells have not been established. Methods We established gastric cancer patient-derived cells (PDCs) to examine the contribution of CD44 splicing variant 9 (CD44v9)-positive cells in gastric cancer drug tolerance. We performed gene expression signature-based in silico screening using JFCR_LinCAGE, our anticancer compound gene expression database and subsequent validation in BALB/c-nu/nu mouse xenograft to identify agents targeting the drug-tolerant cancer cells. Results CD44v9-positive cancer cells were enriched among residual cancer cells after treatment with SN-38, an active metabolic of irinotecan. CD44v9 protein was responsible for this drug resistance. We identified epidermal growth factor receptor (EGFR) inhibitors as agents that can target CD44v9-positive cell populations in gastric cancer PDCs. CD44v9 promoted cell proliferation, and EGFR inhibition attenuated CD44v9 protein expression through downregulation of the AKT and the ERK signalling pathways, leading to preferential suppression of CD44v9-positive cells. Importantly, EGFR inhibitors significantly reduced the number of residual cancer cells after cytotoxic anticancer drug treatment and enhanced the antitumor effect of irinotecan in vivo. Conclusions EGFR inhibitors could be potential agents to eradicate cytotoxic anticancer drug-tolerant gastric cancer cell populations.

The vascular endothelial growth factor (VEGF)/VEGF receptor (VEGFR) axis is an essential regulator of angiogenesis and important therapeutic target in cancer. Ramucirumab is an anti-VEGFR2 monoclonal antibody used for the treatment of several cancers. Increased circulating VEGF-A levels after ramucirumab administration are associated with a worse prognosis, suggesting that excess VEGF-A induced by ramucirumab negatively affects treatment efficacy and that neutralizing VEGF-A may improve treatment outcomes. Here, we evaluated the effect of combination treatment with an anti-VEGFR2 antibody and anti-VEGF-A antibody on gastric tumor progression and normal tissues using a preclinical BALB/c-nu/nu mouse xenograft model. After anti-VEGFR2 antibody treatment in mice, a significant increase in plasma VEGF-A levels was observed, mirroring the clinical response. The elevated VEGF-A was host-derived. Anti-VEGF-A antibody co-administration enhanced the anti-tumor effect of the anti-VEGFR2-antibody without exacerbating the toxicity. Mechanistically, the combination treatment induced intra-tumor molecular changes closely related to angiogenesis inhibition and abolished the gene expression changes specifically induced by anti-VEGFR2 antibody treatment alone. We particularly identified the dual treatment-selective downregulation of ZEB1 expression, which was critical for gastric cancer cell proliferation. These data indicate that the dual blockade of VEGF-A and VEGFR2 is a rational strategy to ensure the anti-tumor effect of angiogenesis-targeting therapy.