Cell-Permeable PKCβII Peptide Inhibition Reduced Cell Viability in MCF-7 Breast Cancer Cells: Implications for ER+ Breast Cancer Treatment [ID 3627]

INTRODUCTION: Estrogen receptor-positive (ER+)/progesterone receptor-positive (PR+), HER2-negative breast cancer often develops resistance to standard hormonal therapies. Protein kinase C beta II activation (PKCβII) promotes estrogen-driven growth via phosphorylation of estrogen receptors, contributing to therapeutic resistance. We hypothesize that PKCβII inhibition will reduce the viability of ER+ breast cancer, as modeled by MCF-7 cells, and serve as a potential adjunct to current therapies. METHODS: MCF-7 cells were cultured and treated with N-terminous conjugated myristic acid and Transactivation of Transcription (Myr-Tat)-conjugated PKCβII inhibitor (Myr-Tat-PKCβII-; 0.5–20 μM) for 37 minutes; untreated wells served as controls. Cell viability was assessed by light microscopy and spectrophotometric absorbance at 450 nm. Lower absorbance indicated reduced cell viability. Absorbance data were analyzed using the Student t -test. RESULTS: Myr-Tat-PKCβII- reduced MCF-7 cell viability in a concentration-dependent manner. The highest dose (20 μM) significantly decreased viability compared to controls (0.5±0.06 versus 1.03±0.09, P <.05). Lower doses (0.5–5 μM) did not significantly affect cell viability, and showed slightly higher absorbance than controls, suggesting minimal effect on metabolic activity. CONCLUSIONS/IMPLICATIONS: The decrease in absorbance following Myr-Tat-PKCβII- treatment suggests a reduction in metabolic activity and cell survival in MCF-7 cells at 20 μM. These findings support the potential adjunctive use of Myr-Tat-PKCβII- at specific doses. At lower doses, cells may compensate via parallel prosurvival pathways, maintaining viability, whereas higher inhibitory thresholds overcome this compensation. Further studies with optimized dosing and larger sample sizes are needed to strengthen statistical power and provide more insight into the molecular mechanisms underlying PKCβII inhibitor-mediated MCF-7 cell death.