The synthesis and antitumor evaluation of 2, 5-disubstituted-indazolo[4,3-gh]isoquinolin-6(2H)-ones (9-aza-APs) are described. The key intermediates in the synthesis are benz[g]
isoquinoline-5,10-diones which are substituted at positions 6 and 9 with groups of different nucleofugacity for SNAr 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 12. These analogues were converted into their
maleate or hydrochloride
salts 13. In two cases, namely, 13x and 13z, 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 13c, 13n, and 13ff 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 13a-c, 13f, 13n, 13q, 13x, and 13dd 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 13d, 13k, 13l, 13x, 13z, and 13ee 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.