Cytochrome P450 proteins are the most important enzymes involved in metabolic activation or detoxification of various drugs used in clinical practice. However, some drug metabolism pathways may be responsible for their increased toxicity. New expression systems of cytochrome P450 proteins in mammalian cells, including human, are designed to explore the influence of metabolism on the cellular and molecular mechanisms of action of potential drugs and those used therapeutically. They can also be used to study the effect of tested compounds on activity and expression of metabolizing enzymes. Human tumor cell lines with overexpression of cytochrome P450 isoenzymes are of particular importance, especially in studies of potential chemotherapeutics. The HepG2 cell line, derived from human liver cancer, is the most commonly used in studies on drug metabolism and toxicity. However, due to the low level of metabolizing enzymes in these cells, the Hep3A4 cell line with overexpression of CYP3A4 isoenzyme was developed. The stable overexpression of cytochrome P450 isoenzymes was also obtained in other human cancer cell lines, including hepatoma HepaRG cells, ovarian cancer IGROV-1 cells, colon cancer Caco-2, and LS180 cells. This review describes currently developed bacterial, yeast, insect and mammalian (including human) cytochrome P450 protein expression systems, in terms of their advantages and disadvantages in the context of their suitability for basic research and use on a commercial scale.