Second-Generation Peptidomimetic Inhibitors of Protein Farnesyltransferase Demonstrating Improved Cellular Potency and Significant in Vivo Efficacy

Abstract

The synthesis and evaluation of analogues of previously reported farnesyltransferase inhibitors, pyridyl benzyl ether 3 and pyridylbenzylamine 4, are described. Substitution of 3 at the 5-position of the core aryl ring resulted in inhibitors of equal or less potency against the enzyme and decreased efficacy in a cellular assay against Ras processing by the enzyme. Substitution of 4 at the benzyl nitrogen yielded 26, which showed improved efficacy and potency and yet presented a poor pharmacokinetic profile. Further modification afforded 30, which demonstrated a dramatically improved pharmacokinetic profile. Compounds 26 and 29 demonstrated significant in vivo efficacy in nude mice inoculated with MiaPaCa-2, a human pancreatic tumor-derived cell line.

Discovery of a Series of Cyclohexylethylamine-Containing Protein Farnesyltransferase Inhibitors Exhibiting Potent Cellular Activity

“…Although there is no direct evidence that indicates how this type of molecule interacts with the enzyme, these data do not support the idea that the sulfur on the “left” portion of the inhibitors interacts with a metal atom. On the other hand, the difficulty which we and others have experienced finding useful replacements for the methionine portion of the inhibitor does suggest a vital role for the methionine atom. , It should also be considered that the requisite cyclohexylethyl portion of the compounds described in this paper might occupy the farnesylpyrophosphate binding site of FTase, but the kinetic experiments required to explore this issue have not yet been undertaken. It is interesting that compound 30 (IC 50 = 0.14 nM) contains all the structural elements of a transition-state analogue for the alkylation of CAAX with farnesylpyrophosphate.…”

“…Although the exact magnitude of the efficacy of FTase inhibitors has been difficult to reproducibly quantify, these results clearly demonstrate a measurable level of in vivo efficacy against human pancreatic cancer cells. Further in vivo efficacy studies with this type of FTase inhibitor will be reported in due course 26d…”

“…The chemistry essentially followed the reductive amination strategy outlined above on solid phase. The hydroxy acid core ( 3 ) was prepared by the method previously reported,26a replacing phenylboronic acid with o -methylphenylboronic acid. Coupling of the acid to l -methionine methyl or ethyl ester followed by Swern oxidation gave 4 , which was a common intermediate for reductive amination with a wide variety of mono- or disubstituted amines using sodium triacetoxyborohydride in dichloroethane .…”

“…Several posttranslational modifications normally occur before Ras can take part in the signaling cascade, − but the only critical modification is prenylation by protein farnesyltransferase (FTase) of the cysteine of a conserved carboxyl-terminal CA 1 A 2 X motif, which is followed by localization to the inner surface of the cellular membrane. This observation has led several groups to examine inhibitors of FTase as potential anticancer agents. − There is now significant evidence that Ras may not be the only substrate of FTase germane to the issue of oncogenesis, but FTase inhibitors have been demonstrated to slow the growth of Ras-dependent tumors in nude mice. ,, …”

“…It exhibited a potent in vitro IC 50 (0.5 nM inhibition of farnesylation of an H-ras ligand) and slowed the growth of human lung tumor cells in nude mice. − Recently, Augeri et al disclosed that compounds of the general description 2 (either anilines or benzylic amines), in which the cysteinamine portion of FTI-276 was replaced with a pyridyl ring, could dramatically and unexpectedly be improved in their ability to act as FTase inhibitors by including an o -methyl substituent on the flanking phenyl ring of the biphenyl unit (i.e. 2 , R = Me) 26a 1 …”