RELAZIONE FINALE PROGETTO DI RICERCA VINCITORE PREMIO SIF-TAKEDA
Dott.ssa Federica Finetti
(Università di Siena)
Relazione finale relativa al progetto di ricerca vincitore del premio SIF-Takeda in farmacologia oncologica: "Epidermalgrowthfactor and Prostaglandin E2 in tumorprogression" della Dr.ssa Federica Finetti (Università di Siena)
Background
Chronic inflammation is a critical component of tumor progression. Several inflammatory diseases increase risk of cancer. Moreover, the activation of a pathway that promotes the production of inflammatory cytokines and the recruitment of inflammatory cells is observed in tumors that are not directly related to inflammatory condition (1). We and others have previously reported that exogenous PGE2 contributes to tumor progression either by activating signaling cascades downstream to specific prostaglandin E receptors (EPs) or transactivating signaling pathways downstream to epidermal growth factor receptor (EGFR). In squamous cell carcinoma, we demonstrated that PGE2 promotes tumor cell growth and invasion by activation of EP2 type receptor, cSrc and protein kinase A, which, in turn, transactivates EGFR and its downstream signaling (2). Inhibition of EGFR activation, through monoclonal antibodies (as cetuximab) or small tyrosine kinase inhibitors (i.e. erlotinib and gefitinib), is an important treatment modality in several tumors, where EGFR receptor is highly expressed, constitutively activated or mutated. However, not all patients respond to this therapy. Potential mechanisms for lack of response to EGFR inhibition include constitutive activation of signaling pathways independent from EGFR (3-5). Since the resistance to EGFR inhibition may be circumvented by combination therapy employing EGFR inhibitors together with treatment targeting downstream EGFR signals, the identification of new molecular target is fundamental.
The hypothesis at the basis of this project is that in tumor cells PGE2 and EGFR cooperate to increase tumor malignance. To explore this idea we decide to study prostate cancer, where overexpression of EGFR promotes metastatic progression and correlates with high Gleason score, and where EGFR inhibition has been unsatisfactory for the lack of response to target therapy.
Results I
By using the DU145 cell line, a model of EGFR dependent metastatic castration-resistant prostate cancer, expressing or silenced for mPGES-1, we investigated the involvement of mPGES-1/EGFR signaling cascade on tumor growth and EMT phenotype. We also evaluated the mPGES-1 contribution to tumor cell responsiveness to the EGFR inhibitors.
We investigated whether blocking the EGFR activation, either with the monoclonal antibody, cetuximab, or the tyrosine kinase inhibitor, erlotinib, would affect tumor growth. By comparing prostate cancer cells bearing an intact mPGES-1 functional enzyme (SC) with those in which the mPGES-1 was silenced (KD) we found a marked change in cell phenotype.The presence of mPGES-1 in SC cells resulted in a massive PGE2 output and a marked increase of EGFR expression relative to KD cells. SC showed mesenchymal traits in their gene pattern, in the expression of vimentin and fibronectin and in their invasiveness capability. Further, overexpression of mPGES-1 also correlated with increased in vivo tumor growth. Erlotinib treatment reduced the growth of both SC and KD xenograft tumors, but the tumor mass where significantly smaller when PGE2 was inhibited, suggesting that it could be of advantage to combine EGFR and PGE2 signaling inhibition, in prostate cancer cells.
Results II
In order to confirm the key role of mPGES-1 in tumor progression, we also evaluated the function of high PGE2 output in stemness features of prostate cancer cells. We observed a large increase of the CD44+/CD24- ratio and the decrease of α6-integrin expression in SC compared to KD cells, both markers of prostate cancer stem cells. Importantly, EGFR inhibition did not affect the ratio of CD44+/CD24- or the expression levels of α6-integrin, indicating that PGE2 regulates per se the induction of stem cells.
Moreover, we decided to explore the contribution of mPGES-1 in human prostate cancer progression. In particular, we analyzed tissues from human patients with different Gleason score (> or < 6), PSA and T levels, for mPGES-1 and EGFR expression. We measured expression levels of mPGES-1 and EGFR by immunohistochemical staining. Preliminary results from 15 patients (7 organ confined tumors with Gleason score <6, low PSA levels and T2 stage) and 8 advanced tumors, with Gleason score ≥7, high PSA levels and T3/T4 stage) showed that both markers were simultaneously detected only in advanced prostate cancer samples. Consistently, in these sample, α6-integrin, was mostly undetectable .
Conclusions
In this work we describe, in prostate tumor cancer, the contribution of mPGES-1/PGE2 pathway to oncogenesis. In particular, the work shows that mPGES-1/PGE2 signaling, byaffecting mesenchymal and stem-cell like markers, and EGFR expression, cooperates with the EGFR pathway in promoting an aggressive prostate cancer phenotype, and identifies in the mPGES-1/PGE2/EGFR axis a new pharmacological target for aggressive prostate cancer.
Reference List
(1) Mantovani A. Cancer: Inflamingmetastasis. Nature 2009 1;457(7225):36-7.
(2) Donnini S, Finetti F, Solito R, Terzuoli E, Sacchetti A, Morbidelli L, et al. EP2 prostanoid receptor promotes squamous cell carcinoma growth through epidermal growth factor receptor transactivation and iNOS and ERK1/2 pathways. FASEB J 2007 ;21(10):2418-30.
(3)Loupakis F, Ruzzo A, Cremolini C, Vincenzi B, Salvatore L, Santini D, et al. KRAS codon 61, 146 and BRAF mutations predict resistance to cetuximab plus irinotecan in KRAS codon 12 and 13 wild-type metastatic colorectal cancer. Br J Cancer 2009 18;101(4):715-21.
(4) Loupakis F, Pollina L, Stasi I, Ruzzo A, Scartozzi M, Santini D, et al. PTEN expression and KRAS mutations on primary tumors and metastases in the prediction of benefit from cetuximab plus irinotecan for patients with metastatic colorectal cancer. J ClinOncol 2009 1;27(16):2622-9.
(5) Jimeno A, Messersmith WA, Hirsch FR, Franklin WA, Eckhardt SG. KRAS mutations and sensitivity to epidermal growth factor receptor inhibitors in colorectal cancer: practical application of patient selection. J ClinOncol 2009 1;27(7):1130-6.