Abstract 4474: An intricate role of p53 and p21 in cellular alterations and drug penetration in spheroids of colorectal cancer cells

Abstract

Abstract The tumor protein p53 and cyclin-dependent kinase inhibitor p21Waf1/Cip1 (p21) are two proteins with an intriguing and a paradoxical role in cancer. Through p53-dependent signals, p21 negatively controls cell cycle progression to protect cells against deleterious effects of DNA damage. Although p53 is a tumor suppressor protein, recent evidence shows that some patients with wild-type (wt) p53 develop aggressive and drug-resistant cancers. Similarly, recent studies also suggest the oncogenic role of p21. In a p53 deficient background, p21 results in the development of a subset of highly proliferative and resistant population of cancer cells. In this study, we examined the role of p53 and p21 in inducing cellular alterations using a panel of colorectal carcinoma cell lines with different p53 and p21 background and spheroid and spheroid-derived cell cultures. First, our data show that despite the presence of proliferating cells, spheroid-derived cultures of HCT116/p53wt cells continue to display an elevated p21 level even after 6 days of culture as a monolayer. These p21-overexpressing proliferating cells show increased resistance to doxorubicin and paclitaxel in comparison to their parental monolayer counterpart. In contrast to HCT116/p53wt cells, DLD-1/p53mut cells did not show elevated p21 levels following reversal from spheroid to monolayer. The increased p21 level in spheroids and spheroid-derived cultures of HCT116/p53wt cells led us to examine the role of p53 and p21 in drug penetration. Spheroids of HCT116/p53wt cells were less permeable to doxorubicin and showed increased expression of intracellular junctional (IJ) proteins (adherens and tight junctions). Knocking-out p21 in HCT116/p53wt cells decreased the level of IJ proteins, resulting in an increased doxorubicin penetration. Re-expression of p21 in p21-knocked-out HCT116/p53wt cells restored IJ protein levels, reducing doxorubicin penetration and the subsequent effect of doxorubicin on spheroids. Interestingly, however, knocking-out p21 in DLD-1/p53mut cells neither altered intracellular junctions nor affected doxorubicin penetration. These data indicate that the effect of p21 on IJ proteins and drug penetration is pertinent only in cells with wt p53. Overall, the data from our study suggest an intricate interplay between wt p53 and p21 in inducing cellular alterations that affect the sensitivity of cells to anti-cancer drugs in spheroids. Citation Format: Viswanath Das, Narendran Annadurai, Marián Hajdúch. An intricate role of p53 and p21 in cellular alterations and drug penetration in spheroids of colorectal cancer cells [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 4474.