Thyroid Hormone and P-Glycoprotein in Tumor Cells

Table 1

Selected intra- and extracellular factors that affect activity and/or abundance of P-glycoprotein (P-gp; MDR1).

Factor	P-gp activity	P-gp abundance	Reference
Intracellular pH (pHi)	↓	↓	[20]
Extracellular pH (pHe)	↑	NS	[21]
Hypoxia	↑	↑	[22]
Hypoxia-inducible factor 1- (HIF-1)	NC	↑	[23]
Thyroid hormone/analogues
T4, T3	↑	↑	[6]
Tetrac/nanotetrac	↓	NC	[9]
Osteopontin (OPN)	↓	↓	[24]
Epidermal growth factor (EGF)	↑	NS	[25]
Vascular endothelial growth factor (VEGF)	↓	NC	[26]
Calcium channel blockers	↓	↓	[2]
Ouabain	NS	↑	[27]
Calmodulin antagonists E6, EBB	↓	NS	[28, 29]

T₄: L-thyroxine.
T₃: 3,5,3′-triiodo-L-thyronine.
NC: no change in parameter.
NS: parameter not investigated/recorded.
A variety of additional pharmacologic inhibitors of P-gp are reviewed in [3–5].