Preclinical toxicology (subacute and acute) and efficacy of a new squalenoyl gemcitabine anticancer nanomedicine.

This study investigates 1) the anticancer efficacy of a new squalenoyl prodrug of gemcitabine (SQgem) in nanoassembly form compared with gemcitabine at equitoxic doses and 2) the subacute and acute preclinical toxicity of these compounds. The toxicity studies revealed that SQgem nanoassemblies, like gemcitabine, were toxic, and they led to dose-dependent mortality after daily i.v. injections for 1 week, irrespective of the route of administration. However, a 4- to 5-day spaced dosing schedule (injections on day 0, 4, 8, and 13) was proved to be safer in terms of weight loss and hematological and other toxicity. Using this spaced dosing schedule, SQgem nanoassemblies exhibited impressive anticancer activity in mice bearing L1210 leukemia because this treatment led to 75% long-term survivors. In contrast, at equitoxic doses, neither free gemcitabine nor cytarabine led to longterm survivors and all the mice of these groups died of the disease. Further toxicity studies performed at lethal doses by blood and serum analysis and organ weight determinations revealed that the hematological toxicity was the dose-limiting toxicity in both SQgem nanoassemblies and gemcitabine, whereas probable gastrointestinal toxicity was also associated with free gemcitabine. The SQgem nanoassemblies did not display hepatotoxicity, which is one of the clinically encountered toxicities of gemcitabine. To summarize, these preclinical studies demonstrated that the toxicological profile of new squalenoyl gemcitabine nanomedicine was not distinct from that of the parent gemcitabine, whereas it was much more potent than gemcitabine at equitoxic doses and cytarabine at clinically relevant doses. These data support the candidature of SQgem for clinical trials.

A new nanomedicine of gemcitabine displays enhanced anticancer activity in sensitive and resistant leukemia types.

Gemcitabine is an anticancer nucleoside analogue active against various solid tumors. However, it possesses important drawbacks like a poor biological half-life and the induction of resistance. With the objective of overcoming the above drawbacks, we designed a new nanomedicine of gemcitabine and studied its anticancer efficacy against leukemia at preclinic. Gemcitabine has been covalently coupled with 1,1',2-tris-nor-squalenic acid to obtain the new anticancer nanomedicine 4-(N)-Tris-nor-squalenoyl-gemcitabine (SQdFdC NA). The SQdFdC NA exhibited, in comparison to gemcitabine, 3.26- and 3.22-folds higher cytotoxicity respectively, in murine resistant leukemia L1210 10K cells and in human leukemia resistant cell line CEM/ARAC8C. Following intravenous treatment of murine aggressive metastatic leukemia L1210 wt bearing mice, the SQdFdC NA caused significant increase in survival time compared to gemcitabine and also led to long-term survivals, which was not the case after gemcitabine treatment. This was attributed to significantly higher deposition of SQdFdC NA in spleen and liver (P<0.05), the major metastatic organs. In comparison to gemcitabine, SQdFdC NA displayed greater ability to induce S-phase arrest of the cancer cells followed by increased apoptotic induction. Interestingly, like gemcitabine, SQdFdC NA didn't induce appreciable differences in blood parameters even at doses higher than those used for anticancer evaluation. The preclinical data obtained in vitro and in vivo with SQdFdC NA demonstrate that this nanomedicine represents a new therapeutic system for the effective treatment of leukemia.

Mapping of the catalytic groove preferences of factor Xa reveals an inadequate selectivity for its macromolecule substrates.

Factor Xa (FXa) hydrolyzes two peptide bonds in prothrombin having (Glu/Asp)-Gly-Arg-(Thr/Ile) for P(3)-P(2)-P(1)-P(1)' residues, but the exact preferences of its catalytic groove remain largely unknown. To investigate the specificity of FXa, we synthesized full sets of fluorescence-quenched substrates carrying all natural amino acids (except Cys) in P(3), P(2), P(1)', P(2)', and P(3)' and determined the k(cat)/K(m) values of cleavage. Contrary to expectation, glycine was not the "best" P(2) residue; peptide with phenylalanine was cleaved slightly faster. In fact, FXa had surprisingly limited preferences, barely more pronounced than trypsin; in P(2), the ratio of the k(cat)/K(m) values for the most favorable side chain over the least was 289 (12 with trypsin), but in P(1)', this ratio was only 30 (versus 80 with trypsin). This unexpected selectivity undoubtedly distinguished FXa from thrombin, which exhibited ratios higher than 19,000 in P(2) and P(1)'. Thus, with respect to the catalytic groove, FXa resembles a low efficiency trypsin rather than the highly selective thrombin. The rates of cleavage of the peptidyl substrates were virtually identical whether or not FXa was in complex with factor Va, suggesting that the cofactor did not exert a direct allosteric control on the catalytic groove. We conclude that the remarkable efficacy of FXa within prothrombinase originates from exosite interaction(s) with factor Va and/or prothrombin rather than from the selectivity of its catalytic groove.