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Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the novel coronavirus responsible for the COVID-19 pandemic. The viral protein of SARS-CoV-2, spike protein (SP), mediates entry into host cells, contributing to pathogenesis of COVID-19. Prostate cancer is the most common cancer among men in the United States. Inducible T-cell costimulator ligand (ICOSL) and intercellular cell adhesion molecule 2 (ICAM-2) are expressed in cancer cells and their roles in cancer growth remain controversial. It is unknown if SP can affect the expression of ICAM-2 or ICOSL in prostate cancer. This study investigated the effects of SARS-CoV-2 SP on the expression of ICAM-2 and ICOSL and the time-dependent effect of SP on growth and survival of prostate cancer cells. Methods: The effect of SARS-CoV-2 SP on the survival of a widely-used prostate cancer cell line, LNCaP, was assessed using clonogenic cell survival assay and quick cell proliferation assay. Reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry (IHC) were performed to investigate the expression of ICAM-2 and ICOSL. The survival of an additional prostate cancer cell line, PC-3, was also evaluated by clonogenic survival assay. Results: After 3 days, a significant decrease in the percentage of colonies in LNCaP cells treated with SP was found, which was paralleled by a decrease in optical density (OD) value in LNCaP cells in the presence of SP. A significant decrease in the percentage of colonies treated with SP was also found in PC-3 cells evaluated by clonogenic survival assay. In addition, the mRNA expression of ICAM-2 was lower, whereas the mRNA expression of ICOSL was higher in SP-treated LNCaP cells. This was supported by protein expressions for ICAM-2 and ICOSL evaluated with IHC. Conclusions: In LNCaP cells, SARS-CoV-2 SP downregulates the expression of ICAM-2 but upregulates the expression of ICOSL. SARS-CoV-2 SP inhibits growth of prostate cancer cells in a time-dependent manner. Further studies are needed to fully address the roles of ICAM-2 and ICOSL in the inhibition prostate cancer growth by SARS-CoV-2 SP.