In the search for a new class of bone-sparing agents for treating osteopenic disorders, we hypothesized that tartronic acid derivatives, sharing the chemical characteristics both of bisphosphonates and of Gla residues contained in matrix proteins such as osteocalcin, could positively affect bone metabolism. A series of tartronates was therefore tested for their ability to affect bone metabolism. In vitro resorption tests were performed examining pit formation by freshly isolated rat and rabbit osteoclasts plated onto bone slices and exposed to the drugs for 48 h. Tartronates bearing a linear side-chain (DF 1222 and DF 1363A) were the most effective in inhibiting pit excavation in the pM-nM range. Tartronates did not affect osteoclast viability, number, adhesion, or tartrate resistant acid phosphatase activity. Transient cell retraction was observed in osteoclasts plated onto glass and exposed to DF 1222. The maximal effect was seen in cells treated for 4 h at a concentration of 1 pM. DF 1222 accelerated mineralization in cultures of periosteal cells without affecting other osteoblast-like functions. This product was therefore tested in vivo in ovariectomized mice. Bone mass in femur was evaluated, by ash gravimetry, 21 days after ovariectomy. Unfortunately, DF 1222, the most active of tartronates in vitro, was inactive in this test because of its high hydrophilicity and the subsequent too short residence time. On the contrary, its tetrahydropyranyl ether derivative, DF 1363A, endowed with a significantly higher lipophilicity, showed a dose-dependent bone-sparing effect when administered subcutaneously at 10, 30, and 100 mg/kg/die, thus confirming the activity seen in in vitro tests. Because of their feasible parallel effect on both bone resorption and formation, tartronate derivatives may be tested to candidate this class of products for clinical studies. (J Bone Miner Res 1997;12:972-981)

As part of a program aimed at exploring the effect of the introduction of heteroatoms into the anthracene-9,10-dione chromophore, we have synthesized novel 1,4-bis[(aminoalkyl)amino]-benzo[g]phthalazine-5,10-diones (BPDs) 1 which are related to the antitumor agents ametantrone and mitoxantrone. Derivatives 1 were prepared by chromic acid oxidation of acylated benzo[g]phthalazines 5 followed by acid hydrolysis or by silylation-amination of 5,10-dihydroxybenzo[g]phthalazine-1,4-dione (8). The 1-[(aminoalkyl)amino]-4-amino congeners 2 were isolated in low yields as byproducts from the oxidation of 5. Against a panel of human tumor cell lines, the benzo[g]phthalazine-5,10-diones 1 and 2 exhibited cytotoxic activity comparable or even superior to that of mitoxantrone. In compounds 1, structure-activity relationships different than those operative in the carbocyclic series appeared to emerge. DNA-binding studies with the ametantrone-like compound 1c and its single-armed congener 2c indicated that the introduction of a 2,3-diaza subunit into the anthracene-9,10-dione chromophore reduces the affinity of the drug for DNA in comparison with ametantrone. On the other hand, the number of side-chain groups does not affect binding to a great extent. These findings seem to suggest mechanisms of cell death other than those induced by simple interaction of the 1,4-BPDs 1 and 2 with DNA.

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