Cytostatic and Pro-Apoptotic Effects of Justicia spicigera Schltdl. on LNCaP Prostate Cancer Cells: Role of G0/G1 Cell Cycle Arrest and Phytochemical Characterization

<i>Justicia spicigera</i> is a central medicinal plant in Mexican ethnomedicine, yet its therapeutic potential against prostate cancer remains largely unexplored. This study investigated the antiproliferative and pro-apoptotic effects of a 50% hydroalcoholic extract from the leaves and stems of <i>J. spicigera</i> on androgen-sensitive LNCaP prostate cancer cells. Phytochemical profiling via thin layer chromatography (TLC) and LC-MS putatively identified the bioactive flavonoid kaempferitrin within the complex extract. Biological assays, including MTT, trypan blue exclusion, and flow cytometry, revealed that the extract inhibits LNCaP proliferation in a distinct, dose-dependent manner. At a lower concentration (250 µg/mL), the extract exerted a primarily cytostatic effect by inducing significant G₀/G₁ cell cycle arrest without triggering immediate cell death. Conversely, higher concentrations (≥500 µg/mL) were potently cytotoxic, reducing cell viability to below 20% and inducing late apoptosis in approximately 58% of the population within 24 h. These results validate the in vitro biological activity of <i>J. spicigera</i> in a specific prostate cancer model. While the concentrations required for cytotoxicity are relatively high, the observed dose-dependent G₀/G₁ arrest provides a foundational phenotypic profile for this traditional extract, warranting further investigation into its selectivity and potential as a bioactive scaffold.