A cell composition composed of spermatogonial stem cells, Sertoli cells, Leydig cells and optionally peritubular cells, is provided, as is a culture composition, artificial testicular construct, hydrogel composition, and device containing the same. A method for using the device as a physiologically relevant in vitro model of human testicular function to screen compounds for pharmacological or toxicological activity is also provided.

Tumor stem cells can be obtained by culturing a tumor cell population, and exposing the cultured tumor cell population to free radicals. In certain embodiments, the free radical agent can be a nitric oxide (NO) donor. In one embodiment, the free radical agent can be Diethylenetriamine NONOate (DETA NONOate) or agents that constitutively increase cellular nitric oxide, such as phosphodiesterase inhibitors or L-arginine, or agents that increase NO synthase in the population. The methods can further include inducing stem cells present in the population to expand and/or inducing dedifferentiation of tumor cells into tumor stem cells. Additionally, the present invention provides methods of selecting stem cells from a tumor cell population. Another aspect provides methods of screening for anti-tumor stem cell teherapeutic compounds by providing high nitric oxide (HNO) tumor cells, exposing the HNO cells to at least one compound, assessing one or more indicators of HNO cell health and determining toxicity of the compound to HNO tumor cells.

A cell composition composed of spermatogonial stem cells, Sertoli cells, Leydig cells and optionally peritubular cells, is provided, as is a culture composition, artificial testicular construct, hydrogel composition, and device containing the same. A method for using the device as a physiologically relevant in vitro model of human testicular function to screen compounds for pharmacological or toxicological activity is also provided.