Introduction: Prostate cancer is one of the most prevalent malignancies among men worldwide and represents a major cause of cancer related morbidity and mortality. Despite advances in screening and therapeutic approaches, resistance to standard treatments, including androgen‑deprivation therapy, remains a major clinical challenge in prostate cancer. As a result, identifying novel compounds that can suppress proliferation or modulate key molecular regulators of the cell cycle is of considerable interest. Papaverine is an isoquinoline alkaloid derived from the opium poppy, widely known for its long‑standing clinical use as a smooth‑muscle relaxant and vasodilator. In recent years, it has gained attention for its potential anticancer effects, including its influence on mitochondrial function, cellular energy metabolism, and the modulation of signaling pathways involved in cell cycle regulation. However, the specific effects of papaverine on prostate cancer cells have not yet been clearly elucidated. Tamoxifen, a selective estrogen receptor modulator widely used in breast cancer therapy, has also demonstrated off target antiproliferative effects in various tumor models.

Aims: The present study aimed to evaluate the effects of papaverine and tamoxifen on the viability and molecular regulatory profile of DU145 prostate cancer cells line. Specifically, the study investigated the cytotoxic potential of these compounds on different concentrations and incubation times, and their ability to alter the expression of CDK4 gene, a key mediator of G1 to S phase progression, along with two microRNAs, miR-146a and miR-22, known to influence cell cycle control and tumorigenic pathways. By integrating cellular and molecular findings, the study sought to clarify whether these compounds could serve as potential modulators of prostate cancer cell growth.

Materials and Methods: DU145 human prostate cancer cell line were cultured under standard conditions and treated with different concentrations of papaverine and tamoxifen. Cell viability was assessed for 24, 48, and 72 hours using the MTT assay (3 [4,5 dimethylimidazole-2-yl] 2,5 diphenyl tetrazolium bromide). Dose–response curves were generated to calculate IC50 values for each compound at the specified time points. To investigate molecular changes, total RNA was extracted from the treated and the control cells, and the expression levels of CDK4 gene, miR-146a, and miR-22 were quantified using Real Time PCR with appropriate internal controls. Relative expression changes were determined using the 2-ΔΔCt method. The data were analyzed using SPSS software. Results were presented as Mean ± SD, and significance level of p ≤ 0.05 was considered statistically significant.

Results: Treatment of DU145 prostate cancer cell line with various concentrations of papaverine and tamoxifen resulted in a significant reduction in cell viability in a concentration and time dependent manner, as measured by the MTT assay for 24, 48, and 72 hours. IC50 values were successfully determined for both compounds across the different time points.

Molecular analysis using Real Time PCR showed that treatment with either papaverine or tamoxifen led to a marked downregulation of CDK4 expression compared with untreated controls. In contrast, both compounds induced a significant up‑regulation of miR‑146a and miR‑22 levels.

Discussion: The observed decrease in viability suggests that papaverine and tamoxifen exert notable antiproliferative effects on DU145 prostate cancer cells. The downregulation of CDK4 gene provides a mechanistic link to cell cycle arrest, as CDK4 is a central regulator of G1‑to‑S phase progression. Such suppression is in line with reduced cellular proliferation and supports the therapeutic potential of these compounds.

The increased expression of miR‑146a and miR‑22 further highlights the involvement of tumor suppressive microRNAs in mediating these effects. Both miRNAs have been implicated in regulating pathways associated with proliferation, apoptosis, and oncogenic signaling. Their upregulation may contribute to the inhibition of cell growth through negative modulation of critical oncogenic targets.

These results align with prior evidence demonstrating tamoxifen’s antiproliferative effects but also importantly emphasize that the molecular and cellular impacts of papaverine in prostate cancer remain poorly understood. The current findings provide initial insight into papaverine’s interaction with cell cycle regulatory genes and microRNAs, suggesting a potential role in prostate cancer growth inhibition. Considering the adverse effect profile associated with tamoxifen, papaverine may therefore represent a more favorable candidate for further investigation, particularly as a potential alternative with a potentially safer therapeutic window.