PGP and neoplasm: Recently, Hung et al. demonstrated that YC-1 is able to modulate the transport function of Pgp and thus to chemosensitize hypoxic tumor cells via the nitric oxide (NO)- cyclic GMP (cGMP)- cGMP-dependent protein kinase (PKG)- extracellular signal-regulated kinase signaling pathway through noncompetitive inhibition [42].