Background Multidrug efflux transporter P-glycoprotein (P-gp) is usually highly expressed on membrane EHT 1864 of tumor cells and is implicated in resistance to tumor chemotherapy. used in combination with EHT 1864 10μM HZ08 compared with 10μM verapamil. Moreover HZ08 could significantly enhance the sensitivity of vincristine with a similar effect like verapamil in both KB-WT and KB-VCR tumor xenograft models. Conclusions The novel structure HZ08 could be a potent P-gp inhibitor. Introduction The successful chemotherapy of solid and hematological tumors has been affected by intrinsic or acquired drug resistance named as multi-drug resistance (MDR). Multidrug resistant tumors are found to be cross-resistant to a broad but well-defined spectrum of structurally and functionally unrelated cytotoxic drugs such as anthracyclines epipodophyllotoxines vinca alkaloids colchicin and taxanes.[1 2 In most cases the cross resistance profile has been shown to be accompanied by a decrease in drug accumulation of the resistant cells which is due to active efflux of these drugs by the multidrug transporter P-glycoprotein (P-gp).[3 4 P-gp is a type of ATPase and an energy-dependent trans-membrane drug efflux pumpconsisted of 1480 amino acids. It is an important member of the ATP-binding cassette (ABC) transporters.[5 6 Several studies have demonstrated the possibility of EHT 1864 using P-gp inhibitors to reverse the P-gp mediated efflux MDR in an attempt to improve the efficiency of chemotherapeutic agents as well as the pharmacokinetic and pharmacodynamic profiles of a number of challenging molecules especially potent cancer curing compounds. This concept offers new opportunities to overcome drug-drug interactions exhibited by a combination of P-gp substrates/inhibitors resulting in a processed drug absorption distribution metabolism and improved pharmacokinetics. Therefore inhibiting the function of P-gp is usually thought to be one of the most useful method to reverse the acquired MDR. In general the activity of P-gp can be inhibited KLHL12 antibody either by blocking drug binding site competitively or by interfering ATP hydrolysis.[8 9 Most of the inhibitors such as verapamil (VER) inhibit P-gp function by blocking drug binding sites. The mechanism for this kind of inhibitors is similar as P-gp handling its substrates if these compounds are only EHT 1864 mediated through binding sites. Moreover a significantly higher dosage is usually needed to serve as a good P-gp inhibitor for these drugs which can lead to unexpected side effects.[10 11 On the other hand compounds inhibiting ATP hydrolysis may serve as better inhibitors since ATP binding and hydrolysis has been found to be EHT 1864 essential for P-gp function where one molecule of drug is usually effluxed at the expense of two molecules of ATP. These drugs are unlikely to be transported by P-gp and a lower dose is required to accomplish favorable P-gp inhibition especially when used locally at gut lumen and cancer. HZ08 (Fig. 1) was designed and synthesized based on tetraisohydroquinoline as a new P-gp inhibitor and novel MDR modulator in order to reverse cancerous multidrug resistance.[13-15] Tetraisohydroquinoline and its derivatives have been demonstrated to have P-gp inhibition ability.[16 17 Investigations have indicated important structural features of molecules that modulate the function of ABCB1 namely two planar aromatic domains and a basic nitrogen atom within an extended aliphatic chain a bulky aromatic ring system with a heteroatom in the third position toward the anthranilamide nucleus at the opposite end of the tetrahydroquinoline group hydrophobicity and nitrogen or hydrogen bond acceptor groups.[18-21] Meanwhile tetraisohydroquinoline and its derivatives have been shown to be potent inhibitors of ATPase which was important in the ABC transporters caused MDR.[22 23 Therefore HZ08 may show high activity as P-gp inhibitor since it is an ideal tetraisohydroquinoline derivative with an extended aliphatic chain that well coincide the important structural features of molecules that modulate the function of P-gp. Fig 1 The chemical structures of HZ08. Previous studies have reported the reversal effect of HZ08 on some multidrug resistant cell lines and speculated its mechanism probably related to cycle arrest apoptosis sensitization or inhibits P-gp as its substrate. However HZ08 were seldom investigated in animal models and the other possible mechanisms remain unclear.[24-26] In present studies MDCK-MDR1 monolayer transportation model was used to evaluate the P-gp inhibit effect of HZ08 P-gp ATPase assay.