Response to combined molecular targeting: defining the role of P-STAT3.

Src family kinase (SFK)-targeting agents are currently undergoing clinical investigation for treatment of solid malignancies. Epidermal growth factor receptor (EGFR)-independent phosphorylation of STAT3 (P-STAT3) has been identified as a mechanism of tumor resistance to agents targeting SFK. Tumor P-STAT3 levels may be an important indicator of EGFR- and SKF-targeted antitumor treatment efficacy.

Egloff AM ，Grandis JR 《-》

Combined blockade of Src kinase and epidermal growth factor receptor with gemcitabine overcomes STAT3-mediated resistance of inhibition of pancreatic tumor growth.

We previously established a mechanistic rationale for Src inhibition as a novel therapeutic target in pancreatic cancer and have identified activated STAT3 as a potential biomarker of resistance to Src inhibition. The purpose of this study was to translate the current understanding of complementary activated tyrosine kinase signaling pathways by targeting Src kinase and epidermal growth factor receptor (EGFR). IC(50) values for dasatinib, a Src kinase inhibitor, erlotinib, an EGFR tyrosine kinase inhibitor and gemcitabine were determined and sensitive and resistant pancreatic cancer cell lines were identified. The in vitro and in vivo effects of these agents on multiple signaling pathways and tumorigenicity in pancreatic cancer were investigated. The combination of dasatinib, erlotinib, and gemcitabine resulted in cooperative inhibition of cell migration and invasion of both sensitive and resistant pancreatic cancer cells as well as cooperative inhibition of multiple signaling pathways including FAK, AKT, ERK, JNK, MAPK, and STAT3 at concentrations that were ineffective as individual agents or as double combinations of agents. The triple combination of agents was also most effective at inhibiting the growth of xenografts of both sensitive and resistant pancreatic cancer cells in vivo without increasing toxicity. Furthermore, combined inhibition of Src and EGFR with gemcitabine inhibited constitutively activated STAT3 in vitro and in vivo. These results provide evidence that combined targeted biological therapy in addition to cytotoxic chemotherapy can overcome treatment resistance. Such treatment strategies may be used to tailor therapy based on identified biomarkers of resistance to targeted monotherapy.

Nagaraj NS ，Washington MK ，Merchant NB 《-》

Combined Src/EGFR Inhibition Targets STAT3 Signaling and Induces Stromal Remodeling to Improve Survival in Pancreatic Cancer.

Lack of durable response to cytotoxic chemotherapy is a major contributor to the dismal outcomes seen in pancreatic ductal adenocarcinoma (PDAC). Extensive tumor desmoplasia and poor vascular supply are two predominant characteristics which hinder the delivery of chemotherapeutic drugs into PDAC tumors and mediate resistance to therapy. Previously, we have shown that STAT3 is a key biomarker of therapeutic resistance to gemcitabine treatment in PDAC, which can be overcome by combined inhibition of the Src and EGFR pathways. Although it is well-established that concurrent EGFR and Src inhibition exert these antineoplastic properties through direct inhibition of mitogenic pathways in tumor cells, the influence of this combined therapy on stromal constituents in PDAC tumors remains unknown. In this study, we demonstrate in both orthotopic tumor xenograft and Ptf1acre/+;LSL-KrasG12D/+;Tgfbr2flox/flox (PKT) mouse models that concurrent EGFR and Src inhibition abrogates STAT3 activation, increases microvessel density, and prevents tissue fibrosis in vivo. Furthermore, the stromal changes induced by parallel EGFR and Src pathway inhibition resulted in improved overall survival in PKT mice when combined with gemcitabine. As a phase I clinical trial utilizing concurrent EGFR and Src inhibition with gemcitabine has recently concluded, these data provide timely translational insight into the novel mechanism of action of this regimen and expand our understanding into the phenomenon of stromal-mediated therapeutic resistance. IMPLICATIONS: These findings demonstrate that Src/EGFR inhibition targets STAT3, remodels the tumor stroma, and results in enhanced delivery of gemcitabine to improve overall survival in a mouse model of PDAC.

Dosch AR ，Dai X ，Reyzer ML ，Mehra S ，Srinivasan S ，Willobee BA ，Kwon D ，Kashikar N ，Caprioli R ，Merchant NB ，Nagathihalli NS ... -  《-》

Continuous inhibition of epidermal growth factor receptor phosphorylation by erlotinib enhances antitumor activity of chemotherapy in erlotinib-resistant tumor xenografts.

Iwai T ，Moriya Y ，Shirane M ，Fujimoto-Ouchi K ，Mori K ... -  《-》

Phase I/II study of the Src inhibitor dasatinib in combination with erlotinib in advanced non-small-cell lung cancer.

Haura EB ，Tanvetyanon T ，Chiappori A ，Williams C ，Simon G ，Antonia S ，Gray J ，Litschauer S ，Tetteh L ，Neuger A ，Song L ，Rawal B ，Schell MJ ，Bepler G ... -  《-》