PGP and cancer: Effluxtransports such as P-gp inhibit intracellular accumulation of chemotherapeuticagents while Bcl-2 suppresses apoptosis, thereby increasing the viabilityand survival of cancer cells.317,318 Co-delivery of siRNA–Bcl-2,siRNA–MDR1, and paclitaxel via poly(lactic-co-glycolic acid) nanoparticles is associated with improvement in theantitumor activity of paclitaxel, inhibition of growth and proliferationof cancer cells, and increased accumulation of paclitaxel within cancercells.319 Paclitaxel resistance is graduallybecoming an increasing challenge in anticancer therapeutics.