Enrichment of putative prostate cancer stem cells after androgen deprivation: Upregulation of pluripotency transactivators concurs with resistance to androgen deprivation in LNCaP cell lines

Abstract

Prostate cancer stem cells (PCSC) offer theoretical explanations to many clinical and biological behaviors of the disease in human. In contrast to approaches of using side populations and cell-surface markers to isolate and characterize the putative PCSC, we hypothesize that androgen deprivation leads to functional enrichment of putative PCSC. Human prostate cancer lines LNCaP, LAPC4 and LAPC9 were depleted of androgen in cell cultures and in castrated SCID mice. The resultant androgen deprivation-resistant or castration-resistant populations, in particular in LNCaP and its derivative cell lines, displayed increased expression of pluripotency transactivators and significantly higher tumorigenicity. Individual tumor cell clones were isolated from castration-resistant bulk cultures of LNCaP (CR-LNCaP) and tested for tumorigenicity in male SCID mice under limiting dilution conditions. As few as 200 cells were able to form spheres in vitro, and generate tumors with similar growth kinetics as 10(6) LNCaP or 10(4) CR-LNCaP cells in vivo. These putative PCSC were CD44(+) /CD24(-) and lack the expression of prostate lineage proteins. When transplanted into the prostate of an intact male SCID mouse, these putative PCSC seemed to show limited differentiation into Ck5(+) , Ck8(+) , Ck5(+) /Ck8(+) , and AR(+) cells. On the other hand, stable transduction of LNCaP with retrovirus encoding Sox2 led to androgen-deprivation resistant growth and down-regulation of major prostate lineage gene products in vitro. Concurrence of overexpression of pluripotency transactivators and resistance to androgen deprivation supported the role of putative PCSC in the emergence of prostate cancer resistant to androgen deprivation.