CELL SURFACE DENSITY OF MICA EXHIBITS FLUCTUATIONS ALONG G1 AND G2/M PHASES OF THE CELL CYCLE BUT IS INDEPENDENT OF THE TP53 STATUS OF THE CELL.

MARÍA VICTORIA REGGE; DANIELA GONZALEZ PIÑERO; ADRIÁN DAVID FRIEDRICH ; MARÍA SOFIA AMARILLA ; MARIANA GANTOV ; BELÉN CANDELA LOZADA MONTANARI; MARÍA NATALIA RUBINSZTAIN; MARÍA CECILIA SANTILLI ; ALDANA TROTTA; CAROLINA INÉS DOMAICA ; MERCEDES BEATRIZ FUERTES; NORBERTO WALTER ZWIRNER

Congreso; Reunion anual de la SAI; 2023

MHC Class I chain-related A (MICA) has emerged as a target for cancerimmunotherapy because it enhances NK-mediated cytolysis through the NK-activatingreceptor NKG2D. The expression of MICA is restricted to tumor cells and has beendescribed to be affected by several drugs and compounds used to treat cancer patients.Most importantly, recently MICA has been validated as target for monoclonal antibody(mAb)-mediated tumor cell elimination. These mAb-mediated treatment alternativestrigger antibody-dependent cell-mediated cytotoxicity (ADCC) and induction of tumorcell death. However, mutations in the tumor suppressor gene TP53, common in over50% of colorectal carcinomas, have been shown to confer resistance to tumor cellapoptosis contributing to malignant progression. Furthermore, since gene expressioncan exhibit fluctuations at different phases of the cell cycle, expression of MICA andsubsequent susceptibility to MICA-targeted, mAb-mediated ADCC might be different inthe G1 vs. G2/M phases of the cell cycle. Thus, the objective of this work was toinvestigate the expression of MICA in the wild type (wt) and p53 -/- HCT116 human colonadenocarcinoma cell line in the G1 and G2/M phases of the cell cycle. Accordingly, wtand p53 -/- HCT116 cell cultures were synchronized for 48 h in serum-depleted mediaand were thereafter cultured in complete media for 24 h. Then, expression of MICA wasassessed in cells in G1 vs G2/M phases, which were identified by flow cytometryaccording to the differential DNA content using 7-AAD. Since efficacy of ADCC dependson target antigen density, we relativized MICA expression at G1 and G2/M to cell areausing the FSC parameter, given that cells in G2/M are larger than cells in G1. Nosignificant differences were observed in the relative expression of MICA between wt andp53 -/- HCT116 in either the G1 or G2/M phases. However, we observed that both celllines exhibited significantly higher amounts of MICA expression in G1 vs G2/M phase(MeanSD: G1 wt : 3.242.48, G2 wt : 1.211.01, p< 0.05; G1 p53-/- : 3.254.04, G2 p53-/- :1.331.17, p< 0.01). These results demonstrate that the expression of MICA fluctuatesthroughout the phases of the cell cycle regardless of the p53 status of the cell.Accordingly, cells in the G1 phase of the cell cycle might be more susceptible to ADCCwith anti-MICA mAb. Furthermore, as wt and p53 -/- HCT116 cells expressed similaramounts of MICA, this indicates that the potential mAb-mediated therapies would beequally effective in tumors with wt or mutated TP53.