Effects of alkylating antineoplastics alone or in combination with 3‐aminobenzamide on genotoxicity, antitumor activity, and NAD levels in human lymphocytes in vitro and on ehrlich ascites tumor cells in vivo

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Abstract
Enhanced cytogenetic damage by the homo‐aza‐steroidal ester of p‐bis (2‐chloroethyl)‐aminophenylacetic acid (ASE) was observed when human lymphocytes in vitro or Ehrlich ascites tumor (EAT) cells in vivo were exposed to nontoxic concentrations of 3‐aminobenzamide (3‐AB). 3‐AB at these concentrations was found to enhance synergistically the cytogenetic damage induced in vivo by cyclophosphamide (CP), a metabolically activated chemotherapeutic, or chlorambucil (CBC) in EAT cells. One hour before i.p. injection of 5‐bromodeoxyuridine (BrdUrd) adsorbed to activated charcoal, EAT‐bearing mice treated i.p. with ASE or CP showed a dose‐dependent increase in sister chromatid exchange (SCE) rates and cell division delays. The treatment of human lymphocytes in vitro with ASE led to the depletion of cellular NAD, and addition of 3‐AB, a potent inhibitor of poly(ADP‐ribose)polymerase [P(ADPR)polymerase], to ASE‐treated human lymphocytes prevented the drop of NAD, which remained at approximately control levels. Also, the in vivo treatment of EAT cells with CBC, ASE, or CP led to the depletion of NAD, whereas addition of 3‐AB to CBC‐, ASE‐, or CP‐treated cells prevented the drop of NAD, which remained at nearly control levels. 3‐AB in conjunction with CBC, ASE, or CP increased the survival time of the EAT‐bearing mice and markedly reduced the ascitic volume. Thus cytogenetic damage induced by ASE plus 3‐AB in vitro and by CBC, ASE, or CP plus 3‐AB in vivo correlates well with (1) the prevention of NAD depletion in the presence of 3‐AB in cells treated with the same alkylating agents in vitro or in vivo and (2) the in vivo antitumor effect by ASE, CBC, or CP in combination with 3‐AB.

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