Maspin Expression in Prostate Tumor Cells Averts Stemness and Stratifies Drug Sensitivity

Abstract

Future curative cancer chemotherapies have to overcome tumor cell heterogeneity and plasticity. To test the hypothesis that the tumor suppressor maspin may reduce microenvironment-dependent prostate tumor cell plasticity and thereby modulate drug sensitivity, we established a new schematic combination of 2D, 3D and suspension cultures to enrich prostate cancer cell subpopulations with distinct differentiation potentials. We report here that, depending on the level of maspin expression, tumor cells in suspension and 3D collagen I manifest the phenotypes of stem-like and dormant tumor cell populations, respectively. In suspension, the surviving maspin-expressing tumor cells lost the self-renewal capacity, underwent senescence, lost the ability to dedifferentiate in vitro and failed to generate tumors in vivo. Maspin-nonexpressing tumor cells that survived the suspension culture in compact tumorspheres, displayed a higher level of stem cell marker expression, maintained the self-renewal capacity, formed tumorspheres in 3D matrices in vitro and were tumorigenic in vivo. The drug sensitivities of the distinct cell subpopulations depend on the drug target and the differentiation state of the cells. In 2D, Docetaxel, MS275 and Salinomycin were all cytotoxic. In suspension, while MS275 and Salinomycin were toxic, Docetaxel showed no effect. Interestingly, cells adapted to 3D collagen I were only responsive to Salinomycin. Maspin expression correlated with higher sensitivity to MS275 in both 2D and suspension, and to Salinomycin in 2D and 3D collagen I. Our data suggest that maspin reduces prostate tumor cell plasticity, and enhances tumor sensitivity to Salinomycin which may hold promise in overcoming tumor cell heterogeneity and plasticity.

The Opportunity of Precision Medicine for Breast Cancer With Context‐Sensitive Tumor Suppressor Maspin

“…Conversely, under suspension conditions designed to evaluate cell stemness, the high maspin expressing MCF10‐A and NC1 cells yielded irregularly shaped cell aggregates whereas the maspin knock down clones grew into compact circumferential tumorspheres indicative of a stem‐like phenotype. These data are consistent with the observation that maspin re‐expression in prostate tumor cells DU145 rendered epithelial acini formation in an in vivo xenograft model for tumor bone metastasis [Cher et al, ] and in an organotypic 3D collagen I model system [Bernardo et al, , ]. Moreover, these results are in agreement with a previous report [Bernardo et al, ] that maspin re‐expression in prostate tumor cells averts stemness.…”

An Essential Role of Maspin in Embryogenesis and Tumor Suppression

“…mammary gland, in pregnant mice (35, 36). Earlier, we showed that maspin is expressed in prostate epithelial cells, Pten +/+ , but not in Pten −/− (16). As shown in Fig.…”

“…Total RNA was extracted from snap frozen mouse tissues and the pair of Pten +/+ and Pten −/− prostate epithelial cell lines (16) using the RNeasy Mini Kit (Qiagen Valencia, CA). One microgram of each RNA sample was reverse-transcribed using the iScript cDNA Synthesis kit (Bio-Rad, Irvine, CA).…”

“…Functional evidence demonstrates multifaceted tumor suppressive effects of maspin in limiting cancer stem cell self-renewal and plasticity, blocking cancer invasion and metastasis, and modulating cancer cell drug response (10, 16–20). While the biological evidence of the maspin effect in tumor progression was predominantly derived from in vivo studies using orthotropic (1, 17) and subcutaneous xenograft models (16), mouse maspin, which is 89% homologous with human maspin at the amino acid level (21), has also been shown to suppress mammary gland tumor progression in the WAP-TAg/WAP- Maspin bi-transgenic model (22) and IKKα-stimulated prostate tumor metastasis in the TRAMP mouse model (23). In addition, maspin protein delivered via non-viral liposome was shown to suppress the progression of polyoma middle T antigen-driven mammary tumor development (24).…”

The secretion and biological function of tumor suppressor maspin as an exosome cargo protein

“…Consistently, maspin has been shown to restrict tumor cell stemness [5] by preserving the epigenetic program for differentiation [6], and to inhibit tumor invasion and metastasis, at least in part, by blocking tumor-induced extracellular matrix remodeling [7]. Further, accumulated evidence showed that maspin expression in epithelial cells plays a critical role in suppressing stromal activities.…”