Saposins (sap) A and C activate the degradation of galactosylceramide in living cells

AbstractIn loading tests using galactosylceramide which had been labelled with tritium in the ceramide moiety, living skin fibroblast lines derived from the original prosaposin-deficient patients had a markedly reduced capacity to degrade galactosylceramide. The hydrolysis of galactosylceramide could be partially restored in these cells, up to about half the normal rate, by adding pure saposin A, pure saposin C, or a mixture of these saposins to the culture medium. By contrast, saposins B and D had little effect on galactosylceramide hydrolysis in the prosaposin-deficient cells. Cells from β-galactocerebrosidase-deficient (Krabbe) patients had a relatively high residual galactosylceramide degradation, which was similar to the rate observed for prosaposin-deficient cells in the presence of saposin A or C. An SV40-transformed fibroblast line from the original saposin C-deficient patient, where saposin A is not affected, showed normal degradation of galactosylceramide. The findings support the hypothesis, which was deduced originally from in vitro experiments, that saposins A and C are the in vivo activators of galactosylceramide degradation. Although the results with saposin C-deficient fibroblasts suggest that the presence of only saposin A allows galactosylceramide breakdown to proceed at a normal rate in fibroblasts, it remains to be determined whether saposins A and C can substitute for each other with respect to their effects on galactosylceramide metabolism in the whole organism

Natural ceramide is unable to escape the lysosome, in contrast to a fluorescent analogue.

Since the generation upon cell stimulation of the second messenger ceramide has been reported to occur in an endosomal/lysosomal compartment, we investigated whether ceramide formed in the lysosomes can escape this compartment. The metabolic fate of radiolabelled ceramide produced by intralysosomal hydrolysis of LDL-associated [ceramide-3H]sphingomyelin or [stearoyl-1-(14)C]sulfatide was examined in fibroblasts from control individuals and a patient with inborn lysosomal ceramidase deficiency (Farber disease). The behavior of this radioactive ceramide was compared to that of a fluorescent (lissamine-rhodaminyl) ceramide analogue deriving from sulfatide degradation. While in Farber cells the natural, radiolabelled ceramide remained completely undegraded and accumulated in the lysosomes, the fluorescent derivative was rapidly converted to sphingomyelin. These findings strongly suggest that, in contrast to fluorescent derivatives, endogenous long-chain ceramide is unable to exit from lysosomes, therefore making the lysosomal ceramide unlikely to be a biomodulatory molecule

Cetuximab pharmacokinetic/pharmacodynamics relationships in advanced head and neck carcinoma patients

International audienceAims Cetuximab associated with cisplatin and 5-fluorouracil is used to treat patients with inoperable or metastatic head and neck squamous cell carcinomas (HNSCC) up until disease progression or unacceptable toxicities. To date, no biomarkers of efficacy are available to select patients who will benefit from treatment. Methods An ancillary pharmacokinetics (PK) exploration was performed in the context of a prospective study investigating circulating-tumour cells vs progression-free survival (PFS). Cetuximab plasma concentrations were analysed according to a population PK model. Individual exposure parameters were confronted with soluble epidermal growth factor receptor (sEGFR) concentrations, tumour response and PFS. Results PK data (28 patients, 203 observations) were best described by a two-compartment model with linear elimination. Performance status (PS) significantly correlated to both cetuximab clearance and central volume of distribution with both parameters increasing by 33.3% (95% CI 1-65.6) for each 1-point increase of PS compared to PS = 0. Univariate analysis showed that patients with higher trough cetuximab concentrations at Day 7 (C-min,C-D7) had better tumour response (P = 0.03) and longer PFS (P = 0.035). However, multivariate analysis revealed that only PS and tumour size at baseline remained significantly associated with PFS. Levels of sEGFR increased during cetuximab treatment but were not associated with PFS in the multivariate analysis. Conclusions Our study prospectively indicates that PS is likely a confounding factor in the relationship between cetuximab PK and PFS, patients with a poor PS having lower cetuximab plasma exposure and lower PFS

Recherche translationnelle : médecine personnalisée, médecine de précision, thérapies ciblées : marketing ou science ?

La médecine personnalisée repose sur : 1) des méthodes cliniques et paracliniques (y compris des biomarqueurs) pour un diagnostic plus discriminant et plus précis des maladies ; 2) des thérapies ciblées ou le choix du meilleur traitement parmi ceux possibles pour chaque patient ; 3) des méthodes d’ajustement de posologie pour maximiser le rapport bénéfice/risque des médicaments choisis ; 4) des biomarqueurs d’efficacité, de toxicité, d’arrêt de traitement, de rechute, etc. Malheureusement, c’est encore trop souvent un concept théorique faute de méthodes diagnostiques et de traitements adaptés, en particulier des médicaments correspondant à chaque sous-type pathologique et donc pour chaque patient. La médecine stratifiée en est une composante, utilisant des biomarqueurs et des tests diagnostiques compagnons pour cibler les patients susceptibles de présenter la meilleure balance bénéfice-risque pour un principe actif donné. Le concept de thérapie ciblée, surtout utilisé en oncologie, repose sur l’existence d’une cible moléculaire définie, impliquée ou non dans le processus pathologique, et/ou sur l’existence d’un biomarqueur permettant d’identifier la population cible, qui devrait être logiquement restreinte par rapport à la population atteinte de la pathologie considérée. Thérapies ciblées et biomarqueurs représentent des enjeux importants pour l’industrie pharmaceutique, en termes d’accès au marché, de retour sur investissement et d’image auprès des prescripteurs. En même temps, ils ne représentent probablement que la première génération de produits issus de la combinaison de la recherche clinique et de la recherche physiopathologique et moléculaire, c’est-à-dire de la recherche translationnelle

Translational Research: Precision Medicine, Personalized Medicine, Targeted Therapies: Marketing or Science?

Personalized medicine is based on: 1) improved clinical or non-clinical methods (including biomarkers) for a more discriminating and precise diagnosis of diseases; 2) targeted therapies of the choice or the best drug for each patient among those available; 3) dose adjustment methods to optimize the benefit-risk ratio of the drugs chosen; 4) biomarkers of efficacy, toxicity, treatment discontinuation, relapse, etc. Unfortunately, it is still too often a theoretical concept because of the lack of convenient diagnostic methods or treatments, particularly of drugs corresponding to each subtype of pathology, hence to each patient. Stratified medicine is a component of personalized medicine employing biomarkers and companion diagnostics to target the patients likely to present the best benefit-risk balance for a given active compound. The concept of targeted therapy, mostly used in cancer treatment, relies on the existence of a defined molecular target, involved or not in the pathological process, and/or on the existence of a biomarker able to identify the target population, which should logically be small as compared to the population presenting the disease considered. Targeted therapies and biomarkers represent important stakes for the pharmaceutical industry, in terms of market access, of return on investment and of image among the prescribers. At the same time, they probably represent only the first generation of products resulting from the combination of clinical, pathophysiological and molecular research, i.e. of translational research