Comparison of new nitrosoureas esters with modified steroidal nucleus for cytogenetic and antineoplastic activity

Nitrosourea is decomposed under physiological conditions to react with biological macromolecules by two mechanisms: alkylation (with proteins and nucleic acids) and carbamoylation (with proteins but not nucleic acids). It has been suggested that the alkylating action is responsible for the therapeutic effects of nitrosoureas, and that the carbamoylation activity leads to toxicity effects. In order to reduce systemic toxicity and improve specificity and distribution for cancer therapy, 2-haloethyl nitrosourea has been esterified with modified steroids, which are used as biological platforms for transporting the alkylating agent to the tumor site in a specific manner. The cytogenetic and antineoplastic effect were studied of seven newly synthesized esters of N,N-bis(2-chloroethyl)alanyl carboxyl derivatives with a modified steroidal nucleus (compounds 1-7). As a very sensitive indicator of genotoxicity the Sister Chromatid Exchange (SCE) assay was used and as a valuable marker of cytostatic activity the cell Proliferation Rate Index (PRI) in cultures of normal human lymphocytes was used. The order of magnitude of the cytogenetic activity on a molar basis (15, 30, 120 microM) of the compounds was 7>>6>3>5>2>4>1. The most active compound 7 has an enlarged (seven carbon atoms) A ring modified with a lactam group (-NHCO-) with the nitrosourea moiety esterified at position 17 In the group of seven substances a correlation was observed between the magnitude of SCE response and the depression in PRI (r=-O, 65, p<0.001). According to the criterion of activity of National Cancer Institute (NCI), the order of antineoplastic activity of compounds on lymphoid L1210 leukemia is 7>6>2>5>4>3>1 and on lympocytic P388 leukemia cells is 7>2>6>5>4>3>1. The present results are in agreement with previous suggestions that the effectiveness in cytogenetic activity may well be correlated with antitumor effects [T/C: 248% for the compound 7 in 250 mg/kg b.w.; T/C: mean survival time of drug-treated animals (T) (excluding long term survivals) vs. corn-oil-treated controls (C)].