John N. D. Wurpel

Calcium Channel Blockers Verapamil and Nimodipine Inhibit Kindling in Adult and Immature Rats

Summary: The calcium channel blockers verapamil (VPM) and nimodipine (NMD) were administered to adult or immature (16‐day‐old) rats to determine their effects on amygdala‐kindled seizures. The afterdischarge thresh‐old (ADT) kindling rate and degree of postictal refractoriness were determined for two doses of VPM (0.5 and 5.0 mg/kg in rat pups and 2 and 10 mg/kg in adult rats) or 30 mglkg nimodipine (NMD). Neither VPM nor NMD affected the ADT of the amygdala in adult or immature rats. VPM retarded the rate of kindling in both adult and immature rats in a dose‐dependent manner; the number of stimulations required to progress through seizure stages were increased. NMD 30 mg/kg reduced the kindling rate and AD duration in both adult and immature rats. Neither drug was able to suppress recurrent seizures elicited by repetitive stimulation. These results suggest that verapamil, and possibly NMD may be of clinical utility in treatment of epilepsy, especially complex partial sezures.

Tyrosine Kinase Inhibitors as Reversal Agents for ABC Transporter Mediated Drug Resistance

Tyrosine kinases (TKs) play an important role in pathways that regulate cancer cell proliferation, apoptosis, angiogenesis and metastasis. Aberrant activity of TKs has been implicated in several types of cancers. In recent years, tyrosine kinase inhibitors (TKIs) have been developed to interfere with the activity of deregulated kinases. These TKIs are remarkably effective in the treatment of various human cancers including head and neck, gastric, prostate and breast cancer and several types of leukemia. However, these TKIs are transported out of the cell by ATP-binding cassette (ABC) transporters, resulting in development of a characteristic drug resistance phenotype in cancer patients. Interestingly, some of these TKIs also inhibit the ABC transporter mediated multi drug resistance (MDR) thereby; enhancing the efficacy of conventional chemotherapeutic drugs. This review discusses the clinically relevant TKIs and their interaction with ABC drug transporters in modulating MDR.

Age-dependent differences in the anticonvulsant effects of 2-amino-7-phosphono-heptanoic acid or ketamine infusions into the substantia Nigra of rats

Summary: Infusions of 2‐amino‐7‐phosphonoheptanoic acid (AP7) or ketamine into the substantia nigra pars reticulata (SNPR) of adult rats increase the latency of onset to seizures induced by the convulsant ether flurothyl. Nigral infusions of AP7 or ketamine in concentrations up to 10 times greater than the adult dose are ineffective in 16‐day‐old rats. These results suggest that differences in seizure susceptibility between adult and immature rats may be related to differences in excitatory amino acid neurotransmission in the SN.

PD173074, a selective FGFR inhibitor, reverses MRP7 (ABCC10)-mediated MDR

Multidrug resistance protein 7 (MRP7, ABCC10) is a recently identified member of the ATP-binding cassette (ABC) transporter family, which adequately confers resistance to a diverse group of antineoplastic agents, including taxanes, vinca alkaloids and nucleoside analogs among others. Clinical studies indicate an increased MRP7 expression in non-small cell lung carcinomas (NSCLC) compared to a normal healthy lung tissue. Recent studies revealed increased paclitaxel sensitivity in the Mrp7−/− mouse model compared to their wild-type counterparts. This demonstrates that MRP7 is a key contributor in developing drug resistance. Recently our group reported that PD173074, a specific fibroblast growth factor receptor (FGFR) inhibitor, could significantly reverse P-glycoprotein-mediated MDR. However, whether PD173074 can interact with and inhibit other MRP members is unknown. In the present study, we investigated the ability of PD173074 to reverse MRP7-mediated MDR. We found that PD173074, at non-toxic concentration, could significantly increase the cellular sensitivity to MRP7 substrates. Mechanistic studies indicated that PD173074 (1 μmol/L) significantly increased the intracellular accumulation and in-turn decreased the efflux of paclitaxel by inhibiting the transport activity without altering expression levels of the MRP7 protein, thereby representing a promising therapeutic agent in the clinical treatment of chemoresistant cancer patients.

A-803467, a tetrodotoxin-resistant sodium channel blocker, modulates ABCG2-mediated MDR in vitro and in vivo

ATP-binding cassette subfamily G member 2 (ABCG2) is a member of the ABC transporter superfamily proteins, which has been implicated in the development of multidrug resistance (MDR) in cancer, apart from its physiological role to remove toxic substances out of the cells. The diverse range of substrates of ABCG2 includes many antineoplastic agents such as topotecan, doxorubicin and mitoxantrone. ABCG2 expression has been reported to be significantly increased in some solid tumors and hematologic malignancies, correlated to poor clinical outcomes. In addition, ABCG2 expression is a distinguishing feature of cancer stem cells, whereby this membrane transporter facilitates resistance to the chemotherapeutic drugs. To enhance the chemosensitivity of cancer cells, attention has been focused on MDR modulators. In this study, we investigated the effect of a tetrodotoxin-resistant sodium channel blocker, A-803467 on ABCG2-overexpressing drug selected and transfected cell lines. We found that at non-toxic concentrations, A-803467 could significantly increase the cellular sensitivity to ABCG2 substrates in drug-resistant cells overexpressing either wild-type or mutant ABCG2. Mechanistic studies demonstrated that A-803467 (7.5 μM) significantly increased the intracellular accumulation of [3H]-mitoxantrone by inhibiting the transport activity of ABCG2, without altering its expression levels. In addition, A-803467 stimulated the ATPase activity in membranes overexpressed with ABCG2. In a murine model system, combination treatment of A-803467 (35 mg/kg) and topotecan (3 mg/kg) significantly inhibited the tumor growth in mice xenografted with ABCG2-overexpressing cancer cells. Our findings indicate that a combination of A-803467 and ABCG2 substrates may potentially be a novel therapeutic treatment in ABCG2-positive drug resistant cancers.

ACUTE TEMPORAL DISTRIBUTION OF FATTY ACID ETHYL ESTERS IN PREGNANT LONG-EVANS RATS

Fetal alcohol syndrome is a term used to describe the birth defects associated with maternal ethanol use during pregnancy. Ethanol, a rapidly biotransformed compound, is currently the only biochemical marker used to detect maternal ethanol use during pregnancy. A minor pathway of ethanol biotransformation is the nonoxidative enzymatic reaction which leads to esterification of free fatty acids with the ethyl group of ethanol. This research explored the formation of two fatty acid ethyl esters (FAEEs), palmitic acid ethyl ester (PAEE) and stearic acid ethyl ester (SAEE), in the pregnant rat and its offspring. In this acute study, pregnant (gestational day 9) Long-Evans rats were dosed 5 g/kg with ethanol (25%) p.o., and animals were sacrificed at 15, 30, 60, 120, 240, 480, and 720 min postdose. Tissues removed for PAEE and SAEE analysis included maternal blood, liver, brain, and fetal/ placental tissue. Analysis for the FAEEs was accomplished using a one-step liquid-liquid extraction. The extracts were then...

Modulating the function of ATP-binding cassette subfamily G member 2 (ABCG2) with inhibitor cabozantinib

Graphical abstract Figure. No Caption available. ABSTRACT Cabozantinib (XL184) is a small molecule tyrosine kinase receptor inhibitor, which targets c‐Met and VEGFR2. Cabozantinib has been approved by the Food and Drug Administration to treat advanced medullary thyroid cancer and renal cell carcinoma. In the present study, we evaluated the ability of cabozantinib to modulate the function of the ATP‐binding cassette subfamily G member 2 (ABCG2) by sensitizing cells that are resistant to ABCG2 substrate antineoplastic drugs. We used a drug‐selected resistant cell line H460/MX20 and three ABCG2 stable transfected cell lines ABCG2‐482‐R2, ABCG2‐482‐G2, and ABCG2‐482‐T7, which overexpress ABCG2. Cabozantinib, at non‐toxic concentrations (3 or 5 &mgr;M), sensitized the ABCG2‐overexpressing cells to mitoxantrone, SN‐38, and topotecan. Our results indicate that cabozantinib reverses ABCG2‐mediated multidrug resistance by antagonizing the drug efflux function of the ABCG2 transporter instead of downregulating its expression. The molecular docking analysis indicates that cabozantinib binds to the drug‐binding site of the ABCG2 transporter. Overall, our findings demonstrate that cabozantinib inhibits the ABCG2 transporter function and consequently enhances the effect of the antineoplastic agents that are substrates of ABCG2. Cabozantinib may be a useful agent in anticancer treatment regimens for patients who are resistant to ABCG2 substrate drugs.

Abstract A01: A-803467, a sodium channel blocker, reverses ABCG2-mediated MDR in vitro as well as in vivo

The ATP-binding cassette, subfamily G, isoform 2 protein (ABCG2) is a vital member of the ABC transporter superfamily, which has been involved in multidrug resistance (MDR) in cancer. Its diverse range of substrates includes many antineoplastic agents such as doxorubicin and mitoxantrone. ABCG2 expression has been significantly increased in some solid tumors and hematologic malignancies, which is correlated to poorer clinical outcomes. In addition, ABCG2 expression is a distinguishing feature of cancer stem cells, whereby this membranous transporter imparts resistance to the chemotherapeutic drugs. To enhance the chemosensitivity of cancer cells, attention has been focused on MDR modulators. In this study, we investigated the ability of sodium channel blocker, A-803467 to reverse ABCG2-mediated MDR. We found that A-803467 at non-toxic concentration could significantly increase the cellular sensitivity to ABCG2 substrates in drug-resistant cells overexpressing either wild-type or mutant ABCG2. Mechanistic studies indicated that A-803467 (7.5 μM) significantly increased the intracellular accumulation resulted from inhibition of the efflux of mitoxantrone by inhibiting the transport activity without altering expression level of ABCG2 protein. Furthermore, ATPase analysis indicates that A-803467 stimulates the ATPase activity in membranes overexpressing ABCG2. in-vivo results indicating that tumor volume was significantly decreased by combination of A-803467 with topotecan when compared to the topotecan and A-803467 alone group. Our findings suggest that A-803467 has the potential to be used in combination with ABCG2 chemotherapeutic substrates to augment the response in drug resistant cancers. Citation Format: Nagaraju Anreddy, Priyank Kumar, Atish Patel, Yun-Kai Zhang, Yijun Wang, Rishil Kathawala, John D. Wurpel, Zhe-Sheng Chen. A-803467, a sodium channel blocker, reverses ABCG2-mediated MDR in vitro as well as in vivo. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Drug Sensitivity and Resistance: Improving Cancer Therapy; Jun 18-21, 2014; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(4 Suppl): Abstract nr A01.