No abstract

Cancer-associated fibroblasts (CAF) are a major component of the colorectal cancer tumor microenvironment. CAFs play an important role in tumor progression and metastasis, partly through TGF-β signaling pathway. We investigated whether the TGF-β family coreceptor endoglin is involved in CAF-mediated invasion and metastasis. CAF-specific endoglin expression was studied in colorectal cancer resection specimens using IHC and related to metastases-free survival. Endoglin-mediated invasion was assessed by transwell invasion, using primary colorectal cancer-derived CAFs. Effects of CAF-specific endoglin expression on tumor cell invasion were investigated in a colorectal cancer zebrafish model, whereas liver metastases were assessed in a mouse model. CAFs specifically at invasive borders of colorectal cancer express endoglin and increased expression intensity correlated with increased disease stage. Endoglin-expressing CAFs were also detected in lymph node and liver metastases, suggesting a role in colorectal cancer metastasis formation. In stage II colorectal cancer, CAF-specific endoglin expression at invasive borders correlated with poor metastasis-free survival. experiments revealed that endoglin is indispensable for bone morphogenetic protein (BMP)-9-induced signaling and CAF survival. Targeting endoglin using the neutralizing antibody TRC105 inhibited CAF invasion In zebrafish, endoglin-expressing fibroblasts enhanced colorectal tumor cell infiltration into the liver and decreased survival. Finally, CAF-specific endoglin targeting with TRC105 decreased metastatic spread of colorectal cancer cells to the mouse liver. Endoglin-expressing CAFs contribute to colorectal cancer progression and metastasis. TRC105 treatment inhibits CAF invasion and tumor metastasis, indicating an additional target beyond the angiogenic endothelium, possibly contributing to beneficial effects reported during clinical evaluations.

Immunotherapy with PD-1/PD-L1-blocking antibodies is clinically effective for several tumor types, but the mechanism is not fully understood. PD-L1 expression on tumor biopsies is generally regarded as an inclusion criterion for this cancer therapy. Here, we describe the PD-L1-blocking therapeutic responses of preclinical tumors in which PD-L1 expression was removed from cancer cells, but not from immune infiltrate. Lack of PD-L1 expression on malignant cells delayed tumor outgrowth in a CD8+ T cell-mediated fashion, showing the importance of this molecule in immune suppression. PD-L1 expression was evident on myeloid-infiltrating cells in the microenvironment of these tumors and targeting stromal PD-L1 with blocking antibody therapy had additional antitumor effect, demonstrating that PD-L1 on both malignant cells and immune cells is involved in the mechanism of immunotherapeutic antibodies. Importantly, comparable results were obtained with PD-1-blocking therapy. These findings have implications for inclusion of cancer patients in PD-1/PD-L1 blockade immunotherapies.

Keywords: endoglin; CD105 TGF-β; BMP9; ALK-1; TRC105; tumor microenvironment

ObjectivePancreatic ductal adenocarcinoma (PDAC) has the characteristics of high-density desmoplastic stroma, a distinctive immunosuppressive microenvironment and is profoundly resistant to all forms of chemotherapy and immunotherapy, leading to a 5-year survival rate of 9%. Our study aims to add novel small molecule therapeutics for the treatment of PDAC.DesignWe have studied whether TAK-981, a novel highly selective and potent small molecule inhibitor of the small ubiquitin like modifier (SUMO) activating enzyme E1 could be used to treat a preclinical syngeneic PDAC mouse model and we have studied the mode of action of TAK-981.ResultsWe found that SUMOylation, a reversible post-translational modification required for cell cycle progression, is increased in PDAC patient samples compared with normal pancreatic tissue. TAK-981 decreased SUMOylation in PDAC cells at the nanomolar range, thereby causing a G2/M cell cycle arrest, mitotic failure and chromosomal segregation defects. TAK-981 efficiently limited tumour burden in the KPC3 syngeneic mouse model without evidence of systemic toxicity. In vivo treatment with TAK-981 enhanced the proportions of activated CD8 T cells and natural killer (NK) cells but transiently decreased B cell numbers in tumour, peripheral blood, spleen and lymph nodes. Single cell RNA sequencing revealed activation of the interferon response on TAK-981 treatment in lymphocytes including T, B and NK cells. TAK-981 treatment of CD8 T cells ex vivo induced activation of STAT1 and interferon target genes.ConclusionOur findings indicate that pharmacological inhibition of the SUMO pathway represents a potential strategy to target PDAC via a dual mechanism: inhibiting cancer cell cycle progression and activating anti-tumour immunity by inducing interferon signalling.