Blockade of neutral sphingomyelinase 2 exerts antitumor effect on metastatic castration resistant prostate cancer cells and promotes tumor regression when combined with Enzalutamide.

Prostate cancer (PCa) is the second leading cause of cancer-related deaths among American men. The development of metastatic castration resistant PCa (mCRPC) is the current clinical challenge. Antiandrogens such as Enzalutamide (ENZ) are commonly used for CRPC treatment. However, patients with androgen receptor (AR)-negative tumors do not respond to ENZ, while AR-positive tumors frequently develop resistance, limiting the long-term efficacy of this therapy. This study investigates the efficacy of neutral sphingomyelinase 2 (n-SMase2) inhibition by DPTIP, both alone and in combination with ENZ, as a therapeutic strategy for mCRPC. In vitro assays were conducted to determine the half-maximal inhibitory concentration (IC₅₀) of DPTIP and ENZ in mCRPC cells. The effect of these treatments on cell proliferation, migration, and colony formation was assessed. The antitumor effect of DPTIP was also evaluated in a preclinical PCa mouse model. Elevated n-SMase2 expression was observed in PCa patients compared to normal subjects at both mRNA and protein levels. In CWR-R1ca and PC-3 cells, DPTIP had IC₅₀ values of 10.31 and 14.57 µM, while ENZ had IC₅₀ values of 33.7 and 81 µM, respectively. Combined treatment significantly suppressed cell proliferation, colony formation, and migration of mCRPC cells. Mechanistically, the ERK1/2 activity and the expression of nSMase2 and NF-kB p65 were inhibited by DPTIP. The in vivo combination of DPTIP and ENZ reduced tumor size and weight more effectively than either drug alone, without significant changes in body weight. This study highlights the therapeutic potential of targeting n-SMase2 for mCRPC. Inhibition of n-SMase2 using DPTIP, both as a standalone treatment and in combination with ENZ, effectively suppressed the growth and migration of mCRPC cells. These findings suggest a promising novel approach to treating mCRPC and warrant further investigation in clinical settings.