New potential antimalarial agents: therapeutic-index evaluation of pyrroloquinazolinediamine and its prodrugs in a rat model of severe malaria.

Tetra-acetamide pyrroloquinazolinediamine (PQD-A4) and bis-ethylcarbamyl pyrroloquinazolinediamine (PQD-BE) are new derivatives of pyrroloquinazolinediamine (PQD) and are being investigated as potential chemotherapeutic agents for the treatment of malaria. Comparative studies to assess the therapeutic indices of PQD-A4, PQD-BE, and PQD were conducted in Plasmodium berghei-infected rats following daily intragastric dosing for three consecutive days. Artesunate (AS), a standard drug for treatment of severe malaria, was used as a comparator. The minimum doses required to clear malaria parasitemia were 156 micromol/kg of body weight for AS and 2.4 micromol/kg for PQD, PQD-4A, and PQD-BE. The maximum tolerated dose (MTD) of AS was 625 micromol/kg, and its therapeutic index was calculated to be 4. The MTDs of PQD-A4, PQD-BE, and PQD were found to be 190, 77, and 24 micromol/kg, respectively, yielding therapeutic indices of 80, 32, and 10, respectively. Although PQD-A4 and PQD-BE are only half as potent as PQD based on their curative effects, the two new derivatives, PQD-4A and PQD-BE, are 8.0-fold and 3.2-fold safer, respectively, than their parent compound when they are dosed for three consecutive days. Oral PQD-A4 and PQD-BE are 44 to 70 times more potent on an mg basis than intravenous AS. As assessed from the therapeutic index over 3 days, PQD-A4, PQD-BE, and PQD administered orally are 20.0, 8.0, and 2.5 times safer than AS given intravenously. The results indicate that PQD-4A is a promising candidate for antimalarial treatment.