Synthesis and Antitumor Evaluation of 2,5-Disubstituted- Indazolo[4,3-<i>g</i><i>h</i>]isoquinolin-6(2<i>H</i>)-ones (9-Aza-anthrapyrazoles)

The synthesis and antitumor evaluation of 2,5-disubstituted-indazolo[4,3-<i>gh</i>]isoquinolin-6(2<i>H</i>)-ones (9-aza-APs) are described. The key intermediates in the synthesis are benz[<i>g</i>]isoquinoline-5,10-diones which are substituted at positions 6 and 9 with groups of different nucleofugacity for S<sub>N</sub>Ar displacements. The initial displacement of fluoride by a substituted hydrazine leads to the pyrazole analogues. Substitution of the remaining leaving group by an amine or BOC-protected amines leads to the 9-aza-APs <b>12</b>. These analogues were converted into their maleate or hydrochloride salts <b>13</b>. In two cases, namely, <b>13x</b> and <b>13z</b>, sidearm buildup was also employed in the synthetic pathway. In vitro evaluation of 9-aza-APs against the human colon tumor cell line LoVo uncovered for most of the compounds a cytotoxic potency lower than that of DuP-941 or mitoxantrone and comparable to that of doxorubicin. Only analogues <b>13c</b>, <b>13n</b>, and <b>13ff</b> were as cytotoxic as DuP-941. Interestingly, while DuP-941 was highly cross-resistant in the LoVo cell line resistant to doxorubicin (LoVo/Dx), the 9-aza-APs carrying a distal lipophilic tertiary amine moiety in both chains were capable of overcoming the MDR resistance induced in this cell line. The 9-aza-APs show outstanding in vivo antitumor activity against both systemic P388 murine leukemia and MX-1 human mammary carcinoma transplanted in nude mice. At their optimal dosages, congeners <b>13a−c</b>, <b>13f</b>, <b>13n</b>, <b>13q</b>, <b>13x</b>, and <b>13dd</b> were highly effective against P388 leukemia with T/C% of 200−381, while the T/C% value of DuP-941 was 147. In the MX-1 tumor model, 24 compounds elicited percentages of tumor weight inhibitions (TWI) ranging from 50% to 99%. Congeners <b>13d</b>, <b>13k</b>, <b>13l</b>, <b>13x</b>, <b>13z</b>, and <b>13ee</b> emerged as the most effective ones, with TWI% 96, simliar to that of DuP-941 (TWI% = 95). On the basis of their efficacy profile in additional experimental tumors and lack of cardiotoxicity in preclinical models, two congeners have surfaced as potential clinical candidates.