Effect of Retinoic Acid and Lapatinib combined treatment on stem/progenitor cells growth in a triple negative mammary cancer cell line

AGUSTINA TARUSELLI; DAMIAN E. BERARDI; ALEJANDRO J. URTREGER; LAURA B. TODARO

Mar del Plata

Congreso; 61° Reunión Científica de la Sociedad Argentina de Investigación Clínica (SAIC); 2016

Sociedad Argentina de Investigación Clínica (SAIC)

Cancer stem cells (CSC) have been described as resistant to chemotherapy and radiation and they are also considered as the metastasis seed. Recent studies have determined that HER2 receptor would be essential for the maintenance of the stem capacity of CSC, for that reason our objectives are: A) Assess the expression of HER2 receptor both in 4T1 monolayers as well as in its derived CSC population and B) Analyze the modulation of growth potential under the treatment with retinoids (ATRA), Lapatinib (Lp, HER2 inhibitor) and their combination. By Western blot we could determine that HER2 is selectively expressed in the CSC population, mainly in its active form (phosphorylated). The effect of ATRA (1 uM), Lp (1 uM) and their combination on cell growth was evaluated during 96 hours. Lp caused a marked decrease in the proliferative capacity from 72 hours in 4T1 monolayers (evaluated by cell count). The same treatments were applied on CSC enriched mammospheres. The combination of ATRA with Lp strongly decreases the formation of these 3D structures, being them very small and irregular, with evident presence of numerous dead cells (diameter in um: Control 150±8; Lp120±22; ATRA 93±16; ATRA/Lp 72±19). Pretreated mammospheres were disaggregated and seeded at low density in order to determine the clonogenic capacity. While ATRA and Lp reduced this capacity, the combined treatment induced a significantly greater effect than either treatment alone (colony number: C 241±19; Lp 142±14; ATRA 202±6; ATRA/Lp 65±5). In conclusion, we have promoted an important decrease in the CSC population growth of a triple negative breast tumor, through the treatment with Lapatinib, together with retinoid?s mediated cell differentiation. This result could allow a new therapeutic approach for a subset of tumors lacking treatment till nowadays.