presumably as a result of bad chemical balance of carbonates and carbamates

A set of these compounds showed lower antitumor activity in vitro, and differed from 1 in the glycosylation sample. This result was relating to what it had been previously reported for other glycosylated analogues of 1, which showed a decrease in its antitumor Cilengitide activity and also lacked a couple of deoxysugars. Some exceptions to this rule were compounds that lacking one deoxysugar still included a N mycarose deposit. Since compounds 5 to 8 were generated in a mutant defective in N mycarose biosynthesis, they do not contain this saccharide residue, which matches with their anticipated lower activity. Another pair of compounds combined modifications within the glycosylation pattern and in the 3 side chain, and showed high antitumor activity, being in average compounds 9 and 11 about 5-fold more active than 10. Substances 9 and 11 showed similar antitumor activity in vitro, and were also more potent than 1 for a few tumor cell lines, though in average they were slightly less potent. These two compounds blended two structural features that had been previously found to improve mithramycin pharmacological behavior: a D digitoxose residue Eumycetoma instead of D mycarose at the E position of the trisaccharide chain, and a modified 3 carbon side chain. It has been noted that the oligosaccharide moieties take part in the binding of this family of compounds to DNA, being the sugar E of the trisaccharide sugar chain among the main interaction points. Also, modifications at the 3 side chain have revealed to influence the power of binding to DNA, the capability of inhibiting Sp1 binding to DNA, and the cellular uptake of mithramycins. Since 2-ME2 compounds 9 and 11 are altered specifically at the sugar E and at the 3 side chain, it would be expected showing various properties, as it's the case. Additionally, substance 9 showed a better conduct in vivo than 11 and 1 in hollow fiber assays, both on intraperitoneal and subcutaneous implants. Currently, it's unclear the reason why for this; a better bioavailability and/or differences in DNA specificity, and consequently differences on inhibition of gene transcription mediated by Sp1 and/or other transcription factors, could account for this better behavior. In this sense, compounds 3 and 4, which only vary from 1 at the 3 side chain, also showed a much better activity in vivo in prostate and ovarian tumor xenografs. 6,42 On the other hand, pharmacokinetics of compound 9 doesn't seem the reason for its better behavior in vivo in comparison to the parental compound 1, since similar pharmacokinetics were revealed by studies in mice for both substances. Additionally, though compound 9 is cleared rapidly from the bloodstream, it s efficacious in colon and melanoma xenografs, particularly at higher, more spaced doses, indicating that maximum concentration, not half-life, may be the key for efficacy.