Fernando Giuliani

Comparison of antitumor effects of daunorubicin covalently linked to poly-l-amino acid carriers

Daunorubicin was covalently linked to poly-L-aspartic and poly-L-lysine of different molecular weights via the methylketone side-chain of the drug by the use of a method that employs the 14-bromo derivative of the antibiotic. During reaction ester and C-N linkages were formed with poly-L-aspartic acid and poly-L-lysine respectively. Whereas a reduction of drug toxicity was observed with both types of conjugate, only the linking to the anionic polymer produced an enhancement of drug activity. In contrast, when drug was covalently attached to poly-L-lysine, cytotoxic activity and in vivo potency and efficacy were markedly reduced. The different therapeutic properties of these conjugates can be explained in terms of the different nature and stability of chemical bonds formed between the drug and the amino groups and carboxyl functions of the polyamino acid carrier.

Comparison of the activity of doxorubicin analogues using colony‐forming assays and human xenografts

The potential use of nude mouse xenografts as a source of human tumor tissue for preclinical assessment of drug activity was examined by a comparison of in vivo and in vitro sensitivity to four anthracycline derivatives of eight xenografts maintained in nude mice and tumor colony‐forming units (CFU) from the xenografts grown in agar. Results obtained in the two systems with doxorubicin (Dx) and a new, closely related derivative (epi‐doxorubicin, epi‐Dx) correlated well. In vivo tumor growth delay and maximum in vitro tumor CFU kill for these two drugs showed a significant correlation (r = 0.64, P <.01). Separation of tumors into “sensitive” and “insensitive” tumor populations on the basis of maximum in vitro CFU kill also predicted the in vivo response to these two drugs in 88% of cases. Similar analyses performed on in vitro and in vivo results with two other new anthracyclines (4′‐deoxy‐doxorubicin, deoxy‐Dx and 4′‐O‐methyl‐doxorubicin, O‐Me‐Dx) showed a significant negative correlation between in vivo and in vitro results; the in vitro system failed to predict in vivo activity of these two drugs. No significant differences in in vitro activity against normal, granulocyte/macrophage progenitors (CFU‐GM) or against various tumor CFUs were detected. Thus, the selectivity (activity against normal tissue compared with that against tumor) of the four drugs appeared equal. These data suggest that in vitro screening of drugs using tumor CFUs from nude mouse xenografts may predict the in vivo activity of drugs for which pharmacologic data are available, but illustrate the difficulties in attempting to predict the in vivo activity of new drugs for which no such data are available.

Comparative effects of doxorubicin and 4′-epi-doxorubicin on nucleic acid metabolism and cytotoxicity in a human tumor cell line

SummaryThe effects of 4′-epi-doxorubicin (4′E-Dx) and doxorubicin (Dx) on cell survival were investigated after treatments for 1 or 24 h. It was found that after short-term exposure, 4′E-Dx causes a higher level of killing than Dx, whereas a similar cytotoxic response is detectable after 24 h. Under the same experimental conditions (treatment for 1 or 24 h) at equimolar concentrations, the two anthracyclines were equally inhibitory to DNA or RNA synthesis. Both the degree and the rate of induction of DNA strand breakage over a 1-h drug exposure were higher for 4′E-Dx than for Dx. These data were related to results of experiments carried out to investigate the rates of uptake and egress of the anthracyclines. From this study we concluded that no relationship can be established between the cytotoxicity of 4′E-Dx and Dx and their ability to inhibit DNA and RNA synthesis. In addition, the different DNA-damaging action of the two drugs does not appear to be solely dependent on the different rates of cellular uptake.

Biochemical and biological activity of the anthracycline analog, 4-demethyl-6-0-methyl-doxorubicin

SummaryThe chromophore-modified derivative of doxorubicin, 4-demethyl-6-0-methyl-doxorubicin, has been tested for antitumor activity in a range of experimental murine tumor systems. In contrast to the inactive 6-0-methyl derivative of daunorubicin, 4-demethyl-6-0-methyl-doxorubicin provided antitumor effects comparable to that of the parent compound. In addition, detailed DNA-interaction studies showed that the doxorubicin derivative retains the ability to bind DNA by the intercalation mechanism. However, the binding affinity was appreciably reduced following structural modification in the anthraquinone chromophore. On the basis of the proposed models of intercalation, these results could be rationalized in terms of steric influence of the bulky methoxy group. The results of this study are in agreement with the correlation already observed between DNA binding and relative antitumor activity of anthracyclines.

Influence of Tumor Growth Kinetics on Response to Doxorubicin Treatment of C3H Mammary Carcinoma

The influence of tumor growth kinetics on response to doxorubicin treatment of C3H mammary carcinoma was investigated. Gompertzian growth curves were obtained for the tumor mass of each mouse by a computerized best fit program. The response was assessed by evaluating: a) the total clonogenic cell reduction as a fraction of the initial tumor volume or the tumor volume that should result at the end of treatment in a free growth condition, and b) the partial clonogenic cell reduction at each drug administration, assuming a first order cell kill hypothesis. Slowly growing tumors at each dose level showed a significantly poorer response than rapidly growing tumors. Each response index exhibited a linear correlation with the specific instantaneous growth rate at the time of treatment. Data also suggested a dose-response dependence.

In vitro activity of 4′ -iodo-4′ -deoxydoxorubicin on human colo-rectal cancer as measured by a short-term antimetabolic assay

SummaryA short-term antimetabolic assay based upon the inhibition of incorporation of nucleic acid precursors was used to compare the cytotoxicity of a new halogenated anthracycline, 4′-iodo-4′-deoxydoxorubicin (IDX), with that of its parent compound doxorubicin (DX) on human colo-rectal carcinoma specimens. IDX showed a marked dose-dependent effect, with frequencies of activity consistently greater than those of DX at all concentrations. The minimal dose required to induce a significant antimetabolic effect for IDX was 1/10 that for DX.