Introduction: Prostate cancer is one of the most common cancer in the male population, therefore, due to its frequent occurrence, a number of researches are being carried out that seek to improve, shorten and enable the best quality of treatment for the patient. Tumor progression may be triggered by cancer stem cells (CSCs). During this study, cell metabolism was evaluated using the MTT assay after application of the newly synthesized compound alone or in combination with paclitaxel. Early and late apoptosis was also determined by using Annexin-V and PI staining. Precisely, this destruction of prostate cancer steam cells is considered as promising goal of prostate cancer treatment to improve outcome in patients with advanced stage of disease. Aim: The aim of this paper was to determine the cell viability of prostate cancer cells Du-145 after treatment with the newly synthesized compound (3-Amino-5-oxo-N-naphthyl-5,6,7,8-tetrahydrothieno [2,3-b] quinoline-2-carboxamide) inhibitor of phospholipase C. Materials and methods: Du-145 cells were incubated with either only newly synthesized compound or in combination with paclitaxel. The cells were cultured under specific conditions, and cell viability was determined by the MTT test. Cell death was evaluated after 48 hours using Annexin-V-FITC test and propidium iodide. The data were collected using the BD Accuri C6 cytometer and analyzed using FlowLogic Software. The results: The results obtained after treatment with the newly synthesized compound depended on the concentrations and the time of treatment. After 72 hours, lower concentration of the novosynthetic compound, in the amount of 1 μM showed significant cytotoxicity in comparison to untreated cells. Also, the results showed a significant reduction in surviving cells after using the combination of newly synthesized compound (0,5 μM) and paclitaxel (25 μM) after 48 and 72 hours. 27 Conclusion: It has been found that newly synthesized compound, 3-amino-5-oxo-N-naphthyl-5,6,7,8-tetrahydrothieno [2,3-b] quinoline-2-carboxamide is cytotoxic to prostate cancer cells. Also, it is very important to mention while using the newly synthesized compound, the critical is concentration of the same compound and the time period in which the compound is used.