Oxaliplatin, a new widely used anticancer drug, displays frequent, sometimes severe, acute sensory neurotoxicity accompanied by neuromuscular signs that look like the symptoms observed in tetany and myotonia. The whole cell patch-clamp technique was employed to investigate the oxaliplatin effects on the electrophysiological properties of short-term cultured dorsal unpaired median (DUM) neurons isolated from the CNS of the cockroach Periplaneta americana. Within the clinical concentration range, oxaliplatin (40-500 microM), applied intracellularly, decreased the amplitude of the voltage-gated sodium current resulting in a reduction of half the amplitude of the action potential. For comparison, two other platinum derivatives, cisplatin and carboplatin, were found to be ineffective at reducing the sodium current amplitude. In addition, we compared the oxaliplatin action to those of its metabolites dichloro-diaminocyclohexane platinum (dach-Cl(2)-platin) and oxalate. Oxalate (500 microM) was found to be effective, like oxaliplatin, at reducing the inward sodium current amplitude, whereas dach-Cl(2)-platin (500 microM) failed to change the current amplitude. Interestingly, the effect of oxalate or oxaliplatin could be mimicked by using intracellularly applied 10 mM bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid (BAPTA), known as chelator of calcium ions. We concluded that oxaliplatin was capable of altering the voltage-gated sodium channels through a pathway involving calcium ions probably immobilized by its metabolite oxalate. The medical interest of preventing acute neurotoxic side effects of oxaliplatin by infusing Ca(2+) and Mg(2+) is discussed.

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Purpose: Oxaliplatin is active in colorectal cancer. Sensory neurotoxicity is its dose-limiting toxicity. It may come from an effect on neuronal voltage-gated Na channels, via the liberation one its metabolite, oxalate. We decided to use Ca and Mg as oxalate chelators.Experimental Design: A retrospective cohort of 161 patients treated with oxaliplatin ؉ 5-fluorouracil and leucovorin for advanced colorectal cancer, with three regimens of oxaliplatin (85 mg/m 2 /2w, 100/2w, 130/3w) was identified. Ninety-six patients received infusions of Ca gluconate and Mg sulfate (1 g) before and after oxaliplatin (Ca/Mg group) and 65 did not.Results: Only 4% of patients withdrew for neurotoxicity in the Ca/Mg group versus 31% in the control group (P ‫؍‬ 0.000003). The tumor response rate was similar in both groups. The percentage of patients with grade 3 distal paresthesia was lower in Ca/Mg group (7 versus 26%, P ‫؍‬ 0.001). Acute symptoms such as distal and lingual paresthesia were much less frequent and severe (P ‫؍‬ 10 -7 ), and pseudolaryngospasm was never reported in Ca/Mg group. At the end of the treatment, 20% of patients in Ca/Mg group had neuropathy versus 45% (P ‫؍‬ 0.003). Patients with grade 2 and 3 at the end of the treatment in the 85 mg/m 2 oxaliplatin group recovered significantly more rapidly from neuropathy than patients without Ca/Mg. Conclusions: Ca/Mg infusions seem to reduce incidence and intensity of acute oxaliplatin-induced symptoms and might delay cumulative neuropathy, especially in 85 mg/m 2 oxaliplatin dosage.

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To evaluate mechanisms in hemoglobinuric acute renal failure (ARF) rats were infused with hemoglobin under aciduric or alkalinuric conditions. Aciduric rats developed azotemia, distal heme casts, and proximal tubular cell (PTC) necrosis, whereas alkalinuric rats developed no renal damage. Aciduria converted hemoglobin to met-hemoglobin, which precipitated, forming distal casts and inducing ARF. Hematin formation was not observed. The importance of met-hemoglobin production was indicated by its greater toxicity than hemoglobin during aciduria and by its ability to induce ARF even under alkalinuric conditions. A link between obstructing casts and PTC necrosis was identified; tubular obstruction induced by various mechanisms (met-hemoglobin casts; ureteral ligation; ischemic ARF) increased PTC hemoglobin uptake, producing lysosomal overload (giant endolysosomes) and PTC necrosis. This worsened ischemic ARF despite an otherwise subtoxic hemoglobin dose being used that had no discernible acute renal vasoconstrictive effect. Iron chelation (deferoxamine)/hydroxyl radical scavenger (Na benzoate) therapy did not mitigate this exacerbation of ischemic injury, suggesting a nonoxidant mechanism. We conclude that H is nephrotoxic, particularly when intratubular obstruction facilitates PTC heme uptake. Thus aciduria-induced met-hemoglobin cast formation and concomitant ischemic renal injury predispose to its nephrotoxic effect.

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Purpose: Oxaliplatin displays a frequent dose-limiting neurotoxicity due to its interference with neuron voltage-gated sodium channels through one of its metabolites, oxalate, a calcium chelator. Different clinical approaches failed in neurotoxicity prevention, except calcium-magnesium infusions. We characterized oxalate outcome following oxaliplatin administration and its interference with cations and amino acids. We then looked for genetic predictive factors of oxaliplatininduced neurotoxicity.Experimental Design: We first tested patients for cations and oxalate levels and did amino acid chromatograms in urine following oxaliplatin infusion. In the second stage, before treatment with FOLFOX regimen, we prospectively looked for variants in genes coding for the enzymes involved (a) in the oxalate metabolism, especially glyoxylate aminotransferase (AGXT), and (b) in the detoxification glutathione cycle, glutathione S-transferase k, and for genes coding for membrane efflux proteins (ABCC2). Results: In the first 10 patients, urinary excretions of oxalate and cations increased significantly within hours following oxaliplatin infusion, accompanied by increased excretions of four amino acids (glycine, alanine, serine, and taurine) linked to oxalate metabolism. In a further 135 patients, a minor haplotype of AGXT was found significantly predictive of both acute and chronic neurotoxicity. Neither glutathione S-transferase k nor ABCC2 single nucleotide polymorphisms we looked for were linked to neurotoxicity. Conclusion: These data confirm the involvement of oxalate in oxaliplatin neurotoxicity and support the future use of AGXTgenotyping as a pretherapeutic screening test to predict individual susceptibility to neurotoxicity.Oxaliplatin, a platinum-based chemotherapeutic agent with a 1,2-diaminocyclohexane (DACH) carrier ligand, displays a characteristic pattern of neurotoxicity, which is the most frequent dose-limiting toxicity, with an acute onset of distal dysesthesia and/or paresthesia, induced or exacerbated by cold and prolonged muscular contraction after a voluntary contraction. Although these symptoms that occur during or short after infusion are transient and generally mild, when treatment is continued, a persistent sensory peripheral neuropathy can develop, eventually causing superficial and deep sensory loss, sensory ataxia, and functional impairment (1). The mechanism of chronic neurotoxicity evoked by some authors is close to that of cisplatin-being the progressive accumulation of a heavy metal, the DACH platin, in neurons and the implication of the detoxication system of glutathione (2).However, clinical neurophysiologic examinations and nerve biopsy studies have shown that patients displaying sensory symptoms have no signs or very mild signs of axonal degeneration (1). Oxaliplatin has a direct ''pharmacologic'' effect on the excitability of sensory neurons and muscle cells that has not previously been described with other platinum agents (3). Furthermore, the acute symptoms induced by oxaliplati...