Plasma levels of doxorubicin after IV bolus injection and infusion of the doxorubicin-DNA complex in rabbits and man. Comparison with free doxorubicin.

When injected rapidly IV into rabbits, the plasma levels of free DOX decreased biphasically and the drug was distributed in a volume greater than the body volume. When given as a DNA complex, the area under the concentration versus time curve was increased 10-fold and the distribution volume reduced more than 100-fold. The DOX-DNA complex infused both in rabbits and in human patients reached steady state-concentrations 10 and 20 times higher, respectively, than free DOX infusion, and the distribution volumes were reduced accordingly. These results confirm that the observed lower cardiotoxicity of the DOX-DNA complex arises despite higher plasma concentrations of the drug.

Accumulation and metabolism of new anthracycline derivatives in the heart after IV injection into mice.

In an attempt to establish a relationship between the pharmacokinetics in mouse heart of new anthracycline derivatives and their potential chronic cardiotoxicity and on this way to provide a useful and economical test for screening of new analogs, we followed the accumulation and metabolism of six anthracyclines in the mouse heart after single IV administrations of these drugs at equimolar doses. We found that the six drugs, i.e., daunorubicin (DNR), doxorubicin (DOX), rubidazone (RBZ), detorubicin (DET), N-L-leucyl-DNR (LEU-DNR) and N-L-leucyl-DOX (LEU-DOX), accumulate at various levels in the cardiac tissue and are metabolized to different extents, leading to the appearance in the heart of variable amounts of DNR or DOX. The total exposure of the mouse heart, as evaluated by calculation of the areas under the CXt curves, can be correlated qualitatively with the chronic cardiotoxicity of the six anthracyclines, as recently determined in the rabbit model. We therefore think that our study provides a simple, rapid, and inexpensive predictive test for the screening of new analogs for potential cardiotoxicity. Moreover, it offers the advantage of using the same species for determining the most favorable ratio between therapeutic activity and toxic side-effects.

A covalent linkage between daunorubicin and proteins that is stable in serum and reversible by lysosomal hydrolases, as required for a lysosomotropic drug-carrier conjugate: in vitro and in vivo studies.

Daunorubicin (DNR) has been conjugated to succinylated serum albumin by an amide bond joining the amino group of the drug and a carboxyl side chain of the protein either directly or with the intercalation of a peptide spacer arm varying from one to four amino acids. During in vitro incubation with lysosomal hydrolases, intact DNR could be released extensively only from conjugates prepared with a tri- or tetrapeptide spacer arm. These latter conjugates remained very stable in the presence of serum. When tested in vivo against the intraperitoneal form of L1210 leukemia, the conjugates in which DNR was linked to serum albumin directly or via one amino acid were completely inactive but the conjugate with a dipeptide spacer arm was not more active than free DNR. In parallel with the in vitro studies, the best therapeutic results were obtained with the conjugates formed with tri- and tetrapeptidic spacer arms; they were much more active than DNR, inducing a high percentage of long-term survivors. Thus, use of a tri- or tetrapeptide spacer arm is essential to obtain DNR-protein conjugates that remain stable in serum and from which DNR can be released through the action of lysosomal hydrolases. The in vivo results suggest, moreover, that these conjugates are endocytosed by L1210 cells and that DNR is released intracellularly after digestion by lysosomal enzymes. This conjugation method can be applied to other drugs possessing a free amino group and to various potential carriers, such as antibodies, polypeptide hormones, and glycoproteins, that have amino or carboxyl side chains.

Amino acid and dipeptide derivatives of daunorubicin. 2. Cellular pharmacology and antitumor activity on L1210 leukemic cells in vitro and in vivo.

The accumulation of amino acid and dipeptide derivatives of DNR has been studied in vitro on L1210 cells. Only Leu-DNR reaches accumulation levels close to DNR, while Val-DNR, Ile-DNR, and Leu-Leu-DNR reach intermediate values. Intracellular DNR was found when the L1210 cells were incubated in the presence of DNR, Leu-Leu-DNR, Leu-Ala-DNR, and Leu-DNR. The cytostatic activity of the derivatives in vitro on L1210 cells cannot be correlated with their uptake or conversion into DNR. At equitoxic doses given iv on the iv inoculated form of L1210 leukemia, all the derivatives are less active than DNR. When given iv on the sc inoculated L1210 leukemia, Leu-DNR, Ala-Leu-DNR and Leu-Leu-DNR are much more active than DNR with a striking increase in ILS and reduction of tumor progression. The superiority of those compounds could be due to their greater hydrophobicity and to their hydrolysis in situ by enzymes secreted by tumor cells or present on the tumor cells surface.

Pharmacokinetic, toxicologic, and chemotherapeutic properties of detorubicin in mice: a comparative study with daunorubicin and adriamycin.

We have studied the stability, pharmacology, toxicology, and therapeutic activity in mice of detorubicin, a new semisynthetic derivative of daunorubicin. In vitro, detorubicin remains stable under acidic conditions while it is very quickly hydrolyzed into Adriamycin under neutral pH conditions. In vivo, the hydrolysis of detorubicin into Adriamycin occurs in the bloodstream a few minutes after iv injection. The tissue distribution of detorubicin in mice is, however, very distinct from that observed after administration of Adriamycin and daunorubicin. The therapeutic effect of detorubicin on the sc implanted L1210 leukemia is superior to that of daunorubicin and at least equal to that of Adriamycin. Detorubicin can thus be considered a prodrug of Adriamycin with very distinct pharmacokinetic and perhaps therapeutic properties.