Abstract Ovarian cancers are highly lethal tumors which account for approximately four percent of all women's cancers and are the fifth leading cause of cancer-related death among women. At diagnosis, the majority of patients have metastatic disease and the long-term survival remains low. Certain ovarian cancers are highly lethal tumors due to the emergence of therapy-resistant ovarian cancer cells. Protein kinase C-iota (PKC-ι) has been shown to aid in the ability of cancer cells to resist drug-induced apoptosis. Recently, it has been reported that PKC-ι, which is located in chromosome 3 at 3q26.2, is the most common genomic amplicon as identified by comparative genomic hybridization [Proc Natl Acad Sci U S A 102:12519-12524(2005)]. Additionally, an increase in PKC-ι DNA copy number was associated with decreased progression-free survival of ovarian cancer patients. Moreover, only PKC-ι gene amplification is highly correlated with protein overexpression, tumor size, lymph node metastasis and clinical stage out of four genes studied on the 3q26 amplification [Genes Chromosomes Cancer 47:127-136(2008)]. The focus of this research was to determine the regulation of p53 by pan-atypical PKC inhibitor, 2-acetyl-1,3-cyclopentanedione (ACPD) [Diabetes. 63:2690-2701 (2014)] and the novel PKC-ι inhibitor, ICA-1, (1H-imidazole-4-carboxamide, 5-amino-1-[2,3-dihydroxy-4-[(phosphonooxy) methyl]cyclopentyl]-,[1R-(1α, 2β, 3 β, 4 α) [The Inter. J. Biochem. & Cell Biol. 43:784-794(2011)]. In contrast to ACPD which inhibits both PKC-ι and PKC-zeta (PKC-z), ICA-1 specifically inhibits the activity of PKC-ι. The effects of ACPD and ICA-1 on HEY (serous surface epithelial tumor cells) and T80 (non-malignant ovarian cells) proliferation was quantified by Trypan blue exclusion assay. Results showed that incubation of HEY ovarian cancer cells with ICA-1 (1 μm) decreased proliferation by 12% compared to controls at 72 hours post-treatment. In contrast, ACPD (2 μM) inhibited proliferation by 81% compared to controls at 24 hours post-treatment. Incubation of T80 cells with ICA-1 resulted in increased proliferation, which is the opposite effect seen in the malignant cells. Through Western blot analysis, we found that HEY cells treated with 2μM ICA had lower levels of phosphorylated p53 compared to the control while T80 cells treated with 2μM ICA-1 had higher levels of phosphorylated p53 compared to the control. This pattern was also seen with phosphorylated PKC-ι. We propose that the mechanism involves inverse regulation of p53 by atypical PKC inhibitor ICA-1 in the normal ovarian cancer cells versus the malignant cells. Normally, MDM2 negatively regulates and degrades p53, but this phenomenon is reversed in the non-malignant cells after treatment with ICA-1. These results suggest that PKC-ι is involved in the regulation of p53. Citation Format: Minjel Shah, Christopher Apostolatos, Hercules Apostolatos, Mildred Acevedo-Duncan. Inverse regulation of p53 by atypical PKC inhibitors in ovarian cancer cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1037. doi:10.1158/1538-7445.AM2015-1037