Extracts of European mistletoe (Viscum album) are popular as a complementary treatment for patients with many different cancer types. However, whether these extracts actually block bladder cancer progression remains unknown. The influence of different mistletoe extracts on bladder cancer cell growth and proliferation was investigated by exposing RT112, UMUC3, and TCCSup cells to mistletoe from hawthorn (Crataegi), lime trees (Tiliae), willow trees (Salicis), or poplar trees (Populi). The tumor cell growth and proliferation, apoptosis induction, and cell cycle progression were then evaluated. Alterations in integrin α and β subtype expression as well as CD44 standard (CD44s) and CD44 variant (CD44v) expressions were evaluated. Cell cycle-regulating proteins (CDK1 and 2, Cyclin A and B) were also investigated. Blocking and knock-down studies served to correlate protein alterations with cell growth. All extracts significantly down-regulated the growth and proliferation of all bladder cancer cell lines, most strongly in RT112 and UMUC3 cells. Alterations in CD44 expression were not homogeneous but rather depended on the extract and the cell line. Integrin α3 was, likewise, differently modified. Integrin α5 was diminished in RT112 and UMUC3 cells (significantly) and TCCSup (trend) by Populi and Salicis. Populi and Salicis arrested UMUC3 in G0/G1 to a similar extent, whereas apoptosis was induced most efficiently by Salicis. Examination of cell cycle-regulating proteins revealed down-regulation of CDK1 and 2 and Cyclin A by Salicis but down-regulation of CDK2 and Cyclin A by Populi. Blocking and knock-down studies pointed to the influence of integrin α5, CD44, and the Cyclin-CDK axis in regulating bladder cancer growth. Mistletoe extracts do block bladder cancer growth in vitro, with the molecular action differing according to the cell line and the host tree of the mistletoe. Integrating mistletoe into a guideline-based treatment regimen might optimize bladder cancer therapy.
Keywords: bladder cancer; cell cycling; growth; mistletoe; proliferation.