RNAi mediated gene silencing of ITPA using a targeted nanocarrier: Apoptosis induction in SKBR3 cancer cells. 
A pure nucleotide pool is required for high-fidelity DNA replication and prevention of carcinogenesis in living cells.  Human inosine triphosphatase (ITPase), encoded by the ITPA gene, plays a critical role in maintaining the purity of the cellular nucleotide pool by excluding nucleotides that enhance mutagenesis.  ITPase is a nucleoside triphosphate pyrophosphatase that hydrolyzes the non-canonical nucleotides inosine triphosphate (ITP) and xanthine triphosphate (XTP).  The monophosphate products of ITPase reactions are subsequently excluded from the nucleotide pool and the improper substitution of ITP and XTP into DNA and RNA is prevented.  Previous studies show that deficiency in ITPA can suppress cellular growth and enhance DNA instability.  In this study, we evaluated the influence of effective ITPA down-regulation on the induction of apoptosis in a human cancer cell line using folate-single wall nanotubes (SWNT) as a targeted nanocarrier.  We assessed whether SWNT enhances IPTA-siRNA transfection efficiency in cancer cells using folate as a homing device.  Since folate receptor is considerably overexpressed in cancer cells, conjugation of SWNTs to folate could enhance their cancer-specific penetrance.  We found that nanocarrier mediated ITPA-siRNA transfection into SKBR3 cells caused significant reduction of ITPA mRNA expression level and complete down-regulation of the ITPase protein product.  The silencing of ITPA led to promotion of apoptosis in SWNT-treated SKBR3 cancer cells.