Effects of the novel cyclosporine derivative PSC833 on glucose metabolism in rat primary cultures of neuronal and glial cells Fatima Cruz, Armin Wolf* Novartis Pharma AG, Experimental Toxicology, CH-4002 Basel, Switzerland Received 19 September 2000; accepted 2 February 2001 Abstract Cyclosporine A (CsA) and the cyclosporine D congener PSC833 are known to cause transient CNS symptoms at high dosages in animal and man. Since impaired glucose metabolism plays a fundamental role in many heriditary and drug-induced neurological disorders, it was the purpose of the present study to evaluate whether this mechanism of pathogenesis might apply to PSC833 and CsA, using neural cells from rats. PSC833 and CsA were investigated in primary cultures of rat neuronal and glial cells at the concentration of 0.1, 1, 10, and 20 M for 24 and 48 hr. Lactate dehydrogenase was determined as a marker of cytotoxicity. Cell proliferation was determined in astrocytes. Cellular glucose metabolism was investigated by 13 C-NMR using [1- 13 C]glucose as a substrate. Glucose and lactate concentrations in the cell culture supernatants were determined spectrophotometrically. PSC833 at 10 M was not cytotoxic in neuronal or glial cells nor did it inhibit proliferation in astrocytes 24 hr after incubation. Under the same conditions, the determination of [1- 13 C]glucose and [3- 13 C]lactate revealed significantly increased glucose consumption and lactate production in both cell types, as well as decreased levels of Krebs cycle intermediates. In the cell culture medium of both cell types after treatment with 10 M PSC833, the rates of glucose consumption and lactate formation increased in comparision to controls, between 60 – 83% and 54 –78%, respectively. PSC833 (10 M) and CsA (20 M) resulted in nearly similar increased glucose consumption and lactate production. The major PSC833 metabolite in rats, M9, which was devoid of CNS effects, did not cause significant changes in glucose metabolism. The present data suggest that PSC833-impaired tricarboxylic acid cycle activity, resulting in decreased Krebs cycle metabolites, can cause energy depletion and acidosis, which might contribute to the transient neurological symptoms of PSC833 and CsA. © 2001 Elsevier Science Inc. All rights reserved. Keywords: PSC833; Cyclosporine A; Neurotoxicity; Neuronal primary culture; Astrocyte primary culture; NMR; Glucose metabolism 1. Introduction PSC833 [(3’-keto-Bmt1)-(Val2)-cyclosporine] represents a novel class of multidrug resistance modifier successfully used to reverse MDR of anticancer drugs by Pgp-170 kDa protein, preventing the efflux of anticancer drugs out of cancer cells. The compound is remarkably free of side effects, and although being a member of the cyclosporine family, it is devoid of immunosuppressive activity. Concerning its in vitro pharma- cological activities to reverse MDR, PSC833 is about 3–10 times more potent than CsA, which is itself about one order of magnitude more potent than other known chemosensitizers, including verapamil, quinidine, or amiodarone, which have already entered clincial trials in MDR reversal [1,2]. PSC833 has been formulated for oral and intravenous co-administration with anticancer drugs. Preliminary clincial results obtained so far in Phase I/II trials suggest very promising results of PSC833 co-therapy during acute leukemia [3]. Neurotoxicity is a well-known adverse side effect of CsA seen in clinical as well as preclinical studies [4 – 6]. Among cyclosporines, the cyclosporine D (CsD) derivatives can induce CNS effects after oral treatment in rats, in the form of reversible impairment of locomotion and excitatory be- havior at concentrations less than 100 mg/kg/day. In order to demonstrate similar CNS effects with CsA in rats, doses greater than 100 mg/kg/day are necessary [7]. Chemically, PSC833 is a CsD derivative. A single intravenous bolus injection of PSC833 at a dose level of 30 mg/kg caused transient neurological symptoms, such as ataxia, impaired * Corresponding author. Tel.: +41-61-324-1735; fax: +41-61-324- 1027. E-mail address: armin.wolf@pharma.novartis.com (A. Wolf). Abbreviations: CsA, cyclosporine A; DMEM, Dulbecco’s modified Eagle’s medium; FBS, fetal bovine serum; LDH, L-lactate dehydrogenase (EC 1.1.1.27); MDR, multidrug resistance, PC, pyruvate carboxylase (EC 1.2.4.1); PDH, pyruvate dehydrogenase complex (EC 1.2.4.1, 1.8.1.4. 2.3.1.12, 3.1.3.43); and TCA, tricarboxylic acid. Biochemical Pharmacology 62 (2001) 129 –139 0006-2952/01/$ – see front matter © 2001 Elsevier Science Inc. All rights reserved. PII: S0006-2952(01)00642-6