ZD6474 reverses multidrug resistance by directly inhibiting the function of P-glycoprotein

P-glycoprotein (P-gp) pumps multiple types of drugs out of the cell, using energy generated from ATP, and confers multidrug resistance (MDR) on cancer cells. ZD6474 is an orally active, selective inhibitor of the vascular endothelial growth factor receptor, epidermal growth factor receptor, and rearranged during transfection tyrosine kinases. This study was designed to examine whether ZD6474 reverses P-gp-mediated MDR in cancer cells. Here, we show that clinically achievable levels of ZD6474 reverse P-gp-mediated MDR of the P-gp-overexpressing cell lines derived from breast cancer, MCF-7/adriamycin (ADR), and human oral epidermoid carcinoma, KBV200 to ADR, docetaxel, and vinorelbine. This ability to reverse the P-gp-mediated resistance is comparable to that of another frequently used reversal agent known as verapamil. ZD6474 itself moderately inhibits the proliferation of both MCF-7 and MCF-7/ADR cells with almost equal activity, but its inhibitory effect is not altered by co-incubation with verapamil, suggesting that ZD6474 may not be a substrate of P-gp. In addition, ZD6474 increases the intracellular accumulation of the P-gp substrate, rhodamine-123, and ADR, by enhancing the uptake and/or decreasing the efflux of these compounds in resistant cells. Further studies show that ZD6474 stimulates ATPase activity in a dose-dependent manner, which is required for the proper function of P-gp. In contrast, ZD6474 does not inhibit the expression level of P-gp. Our results suggest that ZD6474 is capable of reversing MDR in cancer cells by directly inhibiting the function of P-gp, a finding that may have clinical implications for ZD6474

Effect of ABCG2/BCRP Expression on Efflux and Uptake of Gefitinib in NSCLC Cell Lines

BCRP/ABCG2 emerged as an important multidrug resistance protein, because it confers resistance to several classes of cancer chemotherapeutic agents and to a number of novel molecularly-targeted therapeutics such as tyrosine kinase inhibitors. Gefitinib is an orally active, selective EGFR tyrosine kinase inhibitor used in the treatment of patients with advanced non small cell lung cancer (NSCLC) carrying activating EGFR mutations. Membrane transporters may affect the distribution and accumulation of gefitinib in tumour cells; in particular a reduced intracellular level of the drug may result from poor uptake, enhanced efflux or increased metabolism

A phase II trial of gefitinib with 5-fluorouracil, leucovorin, and irinotecan in patients with colorectal cancer

Inhibition of epidermal growth factor receptor (EGFR) signalling contributes to the therapy of colorectal cancer. Gefitinib, an oral EGFR tyrosine kinase inhibitor, shows supra-additive growth inhibition with irinotecan and fluoropyrimidines in xenograft models. We designed a study to determine the tolerability and efficacy of gefitinib in combination with irinotecan, infusional 5-fluorouracil (5-FU) and leucovorin (LV), on a 2-week schedule. Among 13 patients with advanced colorectal cancer, 10 required dose reductions of irinotecan and 5-FU because of dehydration, diarrhoea, and neutropenia, seven of whom required hospitalisation, three with neutropenic fever. One patient achieved partial response and seven had disease stabilisation. The combination of this standard chemotherapy regimen with gefitinib is associated with excessive toxicity, suggesting an interaction at a pharmacokinetic or pharmacodynamic level

EGFR-targeting drugs in combination with cytotoxic agents: from bench to bedside, a contrasted reality

The clinical experience recently reported with epidermal growth factor receptor (EGFR)-targeting drugs confirms the synergistic interactions observed between these compounds and conventional cytotoxic agents, which were previously established at the preclinical stage. There are, however, examples of major gaps between the bench and the bedside. Particularly demonstrative is the failure of the tyrosine kinase inhibitors (TKIs) (gefitinib and erlotinib) combined with chemotherapy in pretreated nonsmall cell lung cancer patients. These discrepancies can be due to several factors such as the methodology used to evaluate TKI plus cytotoxic agent combinations in preclinical models and the insufficient consideration given to the importance of the drug sequences for the tested combinations. Recent advances in understanding the biologic basis of acquired resistance to these agents have great potential to improve their clinical effectiveness. The purpose of this review is to critically examine the experimental conditions of the preclinical background for anti-EGFR drug–cytotoxic agent combinations and to attempt to explain the gap between clinical observations and preclinical data

Multicentre phase II studies evaluating imatinib plus hydroxyurea in patients with progressive glioblastoma

Contains fulltext : 79699.pdf (publisher's version ) (Closed access)BACKGROUND: We evaluated the efficacy of imatinib mesylate in addition to hydroxyurea in patients with recurrent glioblastoma (GBM) who were either on or not on enzyme-inducing anti-epileptic drugs (EIAEDs). METHODS: A total of 231 patients with GBM at first recurrence from 21 institutions in 10 countries were enrolled. All patients received 500 mg of hydroxyurea twice a day. Imatinib was administered at 600 mg per day for patients not on EIAEDs and at 500 mg twice a day if on EIAEDs. The primary end point was radiographic response rate and secondary end points were safety, progression-free survival at 6 months (PFS-6), and overall survival (OS). RESULTS: The radiographic response rate after centralised review was 3.4%. Progression-free survival at 6 months and median OS were 10.6% and 26.0 weeks, respectively. Outcome did not appear to differ based on EIAED status. The most common grade 3 or greater adverse events were fatigue (7%), neutropaenia (7%), and thrombocytopaenia (7%). CONCLUSIONS: Imatinib in addition to hydroxyurea was well tolerated among patients with recurrent GBM but did not show clinically meaningful anti-tumour activity

Overcoming ABCG2-mediated drug resistance with imidazo-[1,2-b]-pyridazine-based Pim1 kinase inhibitors

Purpose Multidrug efflux pumps such as ABCG2 confer drug resistance to a number of cancer types, leading to poor prognosis and outcome. To date, the strategy of directly inhibiting multidrug efflux pumps in order to overcome drug resistance in cancer has been unsuccessful. An alternative strategy is to target proteins involved in the regulation of multidrug efflux pump activity or expression. Pim1 kinase has been demonstrated to phosphorylate ABCG2, promote its oligomerisation and contribute to its ability to confer drug resistance. Methods In the present manuscript, imidazo-pyridazine-based inhibitors of Pim1 were examined for their ability to overcome ABCG2-mediated drug resistance. Drug efficacy was measured as a cytotoxic response or an effect on transport by ABCG2. Protein expression patterns were assessed using western immuno-blotting. Results The two Pim1 inhibitors increased the potency of flavopiridol, mitoxantrone, topotecan and doxorubicin, specifically in ABCG2-expressing cells. This effect was associated with an increase in the cellular accumulation of [3H]-mitoxantrone, suggesting direct impairment of the transporter. However, prolonged pre-incubation with the studied inhibitors greatly enhanced the effect on mitoxantrone accumulation. The inhibitors caused a significant time-dependent reduction in the expression of ABCG2 in the resistant cells, an effect that would improve drug efficacy. Conclusion Consequently, it appears that the Pim1 inhibitors display a dual-mode effect on ABCG2-expressing cancer cells. This may provide a powerful new strategy in overcoming drug resistance by targeting proteins that regulate expression of efflux pumps

A single active catalytic site is sufficient to promote transport in P-glycoprotein

P-glycoprotein (Pgp) is an ABC transporter responsible for the ATP-dependent efflux of chemotherapeutic compounds from multidrug resistant cancer cells. Better understanding of the molecular mechanism of Pgp-mediated transport could promote rational drug design to circumvent multidrug resistance. By measuring drug binding affinity and reactivity to a conformation-sensitive antibody we show here that nucleotide binding drives Pgp from a high to a low substrate-affinity state and this switch coincides with the flip from the inward- to the outward-facing conformation. Furthermore, the outward-facing conformation survives ATP hydrolysis: the post-hydrolytic complex is stabilized by vanadate, and the slow recovery from this state requires two functional catalytic sites. The catalytically inactive double Walker A mutant is stabilized in a high substrate affinity inward-open conformation, but mutants with one intact catalytic center preserve their ability to hydrolyze ATP and to promote drug transport, suggesting that the two catalytic sites are randomly recruited for ATP hydrolysis