Zosuquidar

Zosuquidar (LY335979) is a potent modulator of P-glycoprotein-mediated multidrug resistance with Ki of 60 nM. Zosuquidar binds with high affinity to P-glycoprotein and inhibits P-glycoprotein-mediated multidrug resistance (MDR).

Zosuquidar and an albumin-binding prodrug of zosuquidar reverse multidrug resistance in breast cancer cells of doxorubicin and an albumin-binding prodrug of doxorubicin.[Pubmed:22228402]

Breast Cancer Res Treat. 2012 Jul;134(1):117-29.

The P-glycoprotein (P-gp) is a 170-kDa protein that acts as an energy dependent, transmembrane efflux pump and is encoded by the MDR1 gene. It has been shown to be responsible for multidrug resistance (MDR) in a defined subpopulation of breast cancer patients and thus represents a molecular target for circumventing MDR in this tumor indication. MDR modulators have been developed and demonstrated high selectivity for P-gp with inhibitory activities in the low nanomolar range. Although some objective responses were achieved in clinical trials, combination therapy with these MDR modulators, such as Ca2+ antagonists caused unacceptable toxicity. Targeting P-gp inhibitors to the tumor site is a mean to increase their therapeutic index, and in this context binding of tailor-made prodrugs to circulating albumin is an established technology to reduce the toxicity and enhance the efficacy of anticancer drugs. In this study, we consequently developed an acid-sensitive albumin-binding prodrug of the P-gp inhibitor Zosuquidar (LY335979) in a two-step synthesis using a maleimide hydrazone linker system established in our laboratory that first introduces acetylbenzoic acid at the HO-group of Zosuquidar followed by derivatization with 6-maleimidocaproyl hydrazide to form the acid-sensitive hydrazone bond. The maleimide group enables the prodrug to bind rapidly and selectively to the cysteine-34 position of endogenous albumin after intravenous administration. HPLC analysis demonstrated rapid albumin binding of the Zosuquidar prodrug as well as the quantitative release of the acetylbenzoic ester derivative of Zosuquidar at pH 5.0. Subsequently, its ability to circumvent MDR was tested in two doxorubicin-resistant breast carcinoma cell lines (MCF-7/ADR and MT-3/ADR). The MDR status of these cell lines can be reversed by Zosuquidar which was confirmed in a rhodamine 123 assay using fluorescence microscopy and FACS analysis. Furthermore, Zosuquidar as well its acid-sensitive albumin conjugate re-sensitized cells to doxorubicin as well as to an albumin-binding prodrug of doxorubicin, i.e., the 6-maleimidocaproyl hydrazone derivative of doxorubicin, achieving IC50 values in the same order of magnitude as the parental cell lines. Thus, a novel formulation of Zosuquidar has been developed that could have the potential to improve the toxicity issues and tumor targeting properties of the original compound.

Triggering of Suicidal Erythrocyte Death by Zosuquidar.[Pubmed:26646161]

Cell Physiol Biochem. 2015;37(6):2355-65.

BACKGROUND: The P-glycoprotein inhibitor Zosuquidar (LY335979) is clinically used to augment the effect of cytostatic drugs on suicidal tumor cell death or apoptosis. The present study explored whether the substance is cytotoxic to erythrocytes. Upon injury, erythrocytes may undergo suicidal cell death or eryptosis, which is characterized by cell shrinkage and translocation of cell membrane phosphatidylserine to the erythrocyte surface. Signaling of eryptosis include increase of cytosolic Ca2+-activity ([Ca2+]i), oxidative stress and activation of several kinases, such as p38 kinase and protein kinase C. METHODS: Phosphatidylserine abundance at the erythrocyte surface was quantified from binding of FITC-labelled annexin-V, cell volume from forward scatter, [Ca2+]i from Fluo3-fluorescence, and reactive oxygen species (ROS) from 2',7'-dichlorodihydrofluorescein diacetate (DCFDA) fluorescence. RESULTS: A 48 h treatment of human erythrocytes with Zosuquidar significantly increased the percentage of annexin-V-binding cells (2 and 4 microg/ml), significantly decreased forward scatter (4 microg/ml), significantly increased [Ca2+]i (4 microg/ml), but did not significantly modify ROS. The up-regulation of annexin-V-binding following Zosuquidar (4 microg/ml) treatment was significantly blunted by removal of extracellular Ca2+, by presence of p38 kinase inhibitor SB203580 (2 microM) and by presence of protein kinase C inhibitor calphostin (100 nM). CONCLUSIONS: Exposure of erythrocytes to Zosuquidar triggers suicidal erythrocyte death with erythrocyte shrinkage and erythrocyte membrane scrambling, an effect involving Ca2+ entry and requiring activity of SB203580 and calphostin sensitive kinases.

Zosuquidar, a novel modulator of P-glycoprotein, does not improve the outcome of older patients with newly diagnosed acute myeloid leukemia: a randomized, placebo-controlled trial of the Eastern Cooperative Oncology Group 3999.[Pubmed:20716770]

Blood. 2010 Nov 18;116(20):4077-85.

Zosuquidar, which modulates P-glycoprotein (P-gp) with minimal delay of anthracycline clearance, may reverse P-gp-mediated resistance in acute myeloid leukemia without increased toxicity. A total of 449 adults older than 60 years with acute myeloid leukemia or high-risk myelodysplastic syndrome enrolled in a randomized placebo-controlled double-blind trial (Eastern Cooperative Oncology Group 3999). Overall survival was compared between patients receiving conventional-dose cytarabine and daunorubicin and either Zosuquidar (550 mg; 212 patients) or placebo (221 patients). Median and 2-year overall survival values were 7.2 months and 20% on Zosuquidar and 9.4 months and 23% on placebo, respectively (P = .281). Remission rate was 51.9% on Zosuquidar and 48.9% on placebo. All cause mortality to day 42 was not different (Zosuquidar 22.2% vs placebo 16.3%; P = .158). In vitro modulation of P-gp activity by Zosuquidar and expression of P-gp, multidrug resistance-related protein 1, lung resistance protein, and breast cancer resistance protein, were comparable in the 2 arms. Poor-risk cytogenetics were more common in P-gp(+) patients. P-gp expression and cytogenetics were correlated, though independent prognostic factors. We conclude that Zosuquidar did not improve outcome in older acute myeloid leukemia, in part, because of the presence P-gp independent mechanisms of resistance. This trial is registered at www.clinicaltrials.gov as #NCT00046930.

Analysis of the inhibition potential of zosuquidar derivatives on selected bacterial and fungal ABC transporters.[Pubmed:23356389]

Mol Membr Biol. 2013 Mar;30(2):217-27.

The increasing number of multidrug-resistant pathogenic microorganisms is a serious public health issue. Among the multitude of mechanisms that lead to multidrug resistance, the active extrusion of toxic compounds, mediated by MDR efflux pumps, plays an important role. In our study we analyzed the inhibitory capability of 26 synthesized Zosuquidar derivatives on three ABC-type MDR efflux pumps, namely Saccharomyces cerevisiae Pdr5 as well as Lactococcus lactis LmrA and LmrCD. For Pdr5, five compounds could be identified that inhibited rhodamine 6G transport more efficiently than Zosuquidar. One of these is a compound with a new catechol acetal structure that might represent a new lead compound. Furthermore, the determination of IC(50) values for rhodamine 6G transport of Pdr5 with representative compounds reveals values between 0.3 and 0.9 muM. Thus the identified compounds are among the most potent inhibitors known for Pdr5. For the ABC-type efflux pumps LmrA and LmrCD from L. lactis, seven and three compounds, which inhibit the transport activity more than the lead compound Zosuquidar, were found. Interestingly, transport inhibition for LmrCD was very specific, with a drastic reduction by one compound while its diastereomers showed hardly an effect. Thus, the present study reveals new potent inhibitors for the ABC-type MDR efflux pumps studied with the inhibitors of Pdr5 and LmrCD being of particular interest as these proteins are well known model systems for their homologs in pathogenic fungi and Gram-positive bacteria.