Silymarin, a plant-derived flavonoid from the plant Silybum marianum, is considered the most potential drug to treat almost all kind of liver diseases, particularly alcoholic liver disease, acute and chronic viral hepatitis and toxins-mediated liver dysfunctions. The main component of the silymarin complex is silybin, synonymous with silibinin, sometimes incorrectly called silybinin, which is a mixture of two diastereomers A and B in approximately 1:1 proportion. The drug possess hepatoprotective and antioxidant activity. The hepatoprotective effect is due to stimulation of synthesis of structural and functional proteins and phospholipids, as well as acceleration of the regeneration of hepatocytes. Antioxidant effect is determined by interaction of bioflavones with free radicals in the liver and its detoxication. In such manner the process of peroxidation of the lipids is interrupted and further liver destruction is prevented. Side effect is a mild laxative effect has occasionally been observed.

HM-30181 is a highly selective and potent inhibitor of Multi-drug resistance 1 (MDR1, ABCB1), also known as P-glycoprotein (P-gp). Co-administration of HM30181 greatly increased oral bioavailability of tubulin-stabilizing chemotherapeutic agent paclitaxel. Oraxol is an oral dosage form of paclitaxel administered orally with the HM30181A molecule. Oraxol offers patients with paclitaxel-responsive tumors the possibility of oral therapy without the requirement for premedication to prevent infusion-related hypersensitivity-type reactions. Current clinical data suggests the promising potential of a better clinical response and tolerability profile, which can likely to be attributed to the better pharmacokinetic profile achieved. Oraxol is presently in a Phase 3 trial in metastatic breast cancer and poised to enter into a combination study for treatment of advanced gastric cancer with ramucirumab through a clinical trial collaboration with Eli Lilly and Company.

HM-30181 is a highly selective and potent inhibitor of Multi-drug resistance 1 (MDR1, ABCB1), also known as P-glycoprotein (P-gp). Co-administration of HM30181 greatly increased oral bioavailability of tubulin-stabilizing chemotherapeutic agent paclitaxel. Oraxol is an oral dosage form of paclitaxel administered orally with the HM30181A molecule. Oraxol offers patients with paclitaxel-responsive tumors the possibility of oral therapy without the requirement for premedication to prevent infusion-related hypersensitivity-type reactions. Current clinical data suggests the promising potential of a better clinical response and tolerability profile, which can likely to be attributed to the better pharmacokinetic profile achieved. Oraxol is presently in a Phase 3 trial in metastatic breast cancer and poised to enter into a combination study for treatment of advanced gastric cancer with ramucirumab through a clinical trial collaboration with Eli Lilly and Company.

Dofequidar (MS-209), a quinolone-derived sphingomyelin synthase inhibitor that blocks P-glycoprotein and multidrug resistance-associated protein-1, is under development by Schering for the potential treatment of multidrug resistant tumors. MS-209 had been in phase III clinical trials for the treatment of breast cancer and non-small lung cancer. But this research was discontinued in 2004. Detected adverse events are: nausea, vomiting, leukopenia, neutropenia, anorexia, constipation.

HM-30181 is a highly selective and potent inhibitor of Multi-drug resistance 1 (MDR1, ABCB1), also known as P-glycoprotein (P-gp). Co-administration of HM30181 greatly increased oral bioavailability of tubulin-stabilizing chemotherapeutic agent paclitaxel. Oraxol is an oral dosage form of paclitaxel administered orally with the HM30181A molecule. Oraxol offers patients with paclitaxel-responsive tumors the possibility of oral therapy without the requirement for premedication to prevent infusion-related hypersensitivity-type reactions. Current clinical data suggests the promising potential of a better clinical response and tolerability profile, which can likely to be attributed to the better pharmacokinetic profile achieved. Oraxol is presently in a Phase 3 trial in metastatic breast cancer and poised to enter into a combination study for treatment of advanced gastric cancer with ramucirumab through a clinical trial collaboration with Eli Lilly and Company.

Combretastatin A4 is a vascular disrupting agent (VDA) that targets tumor vasculature to inhibit angiogenesis. Combretastatin A4 is a tubulin-binding agent that binds at or near the colchicine binding site of β-tubulin and inhibits tubulin assembly. This tubulin-binding agent was originally isolated from an African shrub, Combretum caffrum. Combretastatin A4 is cytotoxic to umbilical-vein endothelial cells (HUVECs) and to a range of cells derived from primary tumors and these cytotoxicity profiles have been used to assess several novel analogs of the drug for future development. Combretastatin A4 has antitumor activity by inhibiting AKT function. The inhibited AKT activation causes decreased cell proliferation, cell cycle arrest, and reduced in vitro migration/invasiveness and in vivo metastatic ability. Several studies in mice have shown that a single administration of combretastatin A4 (100 mg/kg) does not significantly affect primary tumor growth. However, repeated administration (12.5 – 25.0mg/kg twice daily) for periods of 10 – 20 days resulted in approximately 50% retardation of growth of ectopic Lewis lung carcinoma and substantial growth delay of T138 spontaneous murine breast tumors. In clinical studies, Combretastatin A4 has been well tolerated in patients at doses up to 56 mg/m2, following a protocol of five daily 10-minute intravenous infusions every 21 days. The disodium combretastatin A4 phosphate prodrug is currently undergoing clinical trials in the UK and USA.

Tariquidar, a non-competitive, specific P-glycoprotein (Pgp) inhibitor, is an anthranilamide derivative with multidrug resistance properties. Tariquidar binds to the ATP-binding cassette (ABC) transport protein Pgp, thereby inhibiting transmembrane transport of anticancer drugs resulting in their increased intracellular concentrations augmenting cytotoxicity of an anticancer drug. Tariquidar was discovered by Xenova Group and was developed for the treatment of multidrug resistance in cancer. In October 2002 the US Food and Drug Administration (FDA) has granted fast track review status to tariquidar for the treatment of multi-drug resistance in first-line treatment of non-small cell lung cancer (NSCLC) patients. Tariquidar is still undergoing research as an adjuvant against multidrug resistance in cancer.

Zosuquidar (LY-335979) is an experimental antineoplastic drug. It is is a potent modulator of P-glycoprotein-mediated multi-drug resistance with Ki of 60 nM. Zosuqidar was initially characterized by Syntex Corporation, which was acquired by Roche in 1990. Roche licensed the drug to Eli Lilly in 1997. It was granted orphan drug status by the FDA in 2006 for AML. Zosuquidar Trihydrochloride had been in phase III clinical trials by Kanisa Pharmaceuticals for the treatment of acute myeloid leukaemia. However, this research has been discontinued.

Elacridar is an oral bioenhancer that targets multiple drug resistance in tumors. Elacridar is a strong and relatively specific inhibitor of P-gp and BCRP, two main efflux transporters. Development of elacridar is assumed to have been discontinued.

Dexniguldipine (B8509-035, (-)-(R)-niguldipine) is a new dihydropyridine derivative, that exerts selective antiproliferative activity in a variety of tumor models and, in addition, has a high potency in overcoming multidrug resistance. Dexniguldipine is ( - )-(R)-enantiomer of niguldipine, of which the ( )-(S)-enantiomer shows pronounced cardiovascular hypotensive activity due to its high affinity for the voltage-dependent Ca2 channel. As compared with the (S)-enantiomer, the (R)-enantiomer has a 40-fold lower affinity for the Ca 2 channel and, accordingly, only minimal hypotensive activity in animal pharmacology models. Dexniguldipine have shown antiproliferative activity in several tumor cell lines, but the concentrations necessary to inhibit growth have varied by several orders of magnitude between cell lines. Initial results of preclinical investigations for the evaluation of the mechanism of its antiproliferative activity demonstrate that dexniguldipine interferes with intracellular signal transduction by affecting phosphoinositol pathways, protein kinase C expression, and intracellular Ca 2 metabolism. In a series of human tumor xenografts in vitro, dexniguldipine demonstrated selective antiproliferative activity against several tumor types, e.g., melanoma and renal-cell carcinoma. Striking results were obtained in a hamster model, in which neuroendocrine lung tumors could be completely eradicated by 20 weeks of oral treatment with 32.5mg/kg dexniguldipine, whereas Clara-cell-type lung tumors were not affected. In in vitro studies, dexniguldipine has been found to bind to P-glycoprotein (P-gp) and to enhance the cytotoxicity of chemotherapeutic agents such as doxorubicin and etoposide in several cell lines The synergistic effect may well be associated with the reversal of multidrug resistance (MDR) related to the activity of P-gp. In the clinical therapy of cancer, resistance to many cytostatic drugs is a major cause of treatment failure. However, the high potency of dexniguldipine (about 10-fold as compared with that of verapamil in vitro) and its low cardiovascular activity provide the opportunity to achieve blood or tumor concentrations that might be high enough to overcome Mdr 1 resistance in patients without producing dose-limiting cardiovascular effects.