Abstract 3: Metronomic chemotherapy with cyclophosphamide (Cy) and the repositioned drug losartan (Los) for the treatment of M-234p triple negative murine mammary adenocarcinoma

Abstract

Metronomic chemotherapy (MCT) refers to the chronic, equally spaced, delivery of low doses of chemotherapeutic drugs, without extended interruptions. Drug repositioning in oncology refers to the use of drugs formulated for other indications that showed antitumor potential. Los is an antagonist of angiotensin II receptor used to treat hypertension. We aim to study the combined effect of metronomic Cy+Los on M-234p tumor. Female BALB/c mice were orthotopically challenged with M-234p (day 0) and distributed, on day 8, into 4 groups (n=5-6/group) treated as follows, GI: Control, without treatment; GII: Cy 25mg/kg/day in the drinking water; GIII: Los 200mg/kg/day in the drinking water; GIV: Treated as GII+GIII. Mice were weighted, and tumor volume measured 3 times/week. When tumors were exponentially growing, mice were euthanized, tumors excised, and blood samples taken for immunohistochemistry, western blot and flow cytometry. GIV showed tumor growth inhibition compared to GI, GII and GIII and, as a consequence, higher survival (P<0.005). Also, GIV showed 60% (3/5) of complete tumor regressions, without relapses. No weight losses or sings of toxicity were observed. IHC analysis showed a lower N° of Ki67+ cells in GIV (P<0.05). Moreover, a significant increase of apoptosis in GIV vs Control was shown by TUNEL assay (P<0.05). No differences in circulating CD4+, CD8+ and Treg cells were shown by flow cytometry but, a marginally significant increase in Th17 cells in GII and GIV was seen. To share some light on the effect of the therapy on the cancer associated fibroblasts, the protein αSMA was measured by western blot; the expression of this marker was significantly lower in GIV vs GI (P<0.05). To evaluate the anti-metastatic effect of the therapy, mice were inoculated i.v. with 5x105 M-234p cells. On day 3, mice were distributed in the same experimental groups. When the first mouse showed signs of metastatic disease, all of them were euthanized, lungs excised and stained to highlight metastasis. The N° of lung metastasis was significantly lower in GII and GIV. No weight losses or any other sing of toxicity were observed. These results clearly show that metronomic chemotherapy with a combination of Cyclophosphamide and Losartan, administered as an intervention strategy, can inhibit, not only the growth of a triple negative mammary adenocarcinoma, causing permanent regressions, but also its metastasis, while being devoid of toxicity. Those effects would be achieved, at least partially, by inhibition of tumor proliferation, increase of apoptosis and modification of tumor microenvironment through tumor fibroblasts. The characteristics and the efficacy of the therapeutic schedule herein utilized suggest its implementation at the clinical setting in the near future. Citation Format: Julian Guercetti, Leandro E. Mainetti, M.Carolina Grillo, Antonela Del Giúdice, Maria V. Baglioni, Juan M. Cáceres, Ainelén Arboatti, Daniel Francés, Viviana R. Rozados, Maria J. Rico, O.Graciela Scharovsky. Metronomic chemotherapy with cyclophosphamide (Cy) and the repositioned drug losartan (Los) for the treatment of M-234p triple negative murine mammary adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3.

Achievements and challenges in the use of metronomics for the treatment of breast cancer

“…Recently, we found that MCT with CY plus Losartan, an angiotensin II receptor antagonist, is a successful drug combination that, interestingly, caused % 60 of complete regressions in a very aggressive murine model of TNBC [54]. We also shed some light into the mechanisms The main characteristics of the mentioned investigations are summarized in Table 1.…”