Structure-Activity Relationships of Small Phosphopeptides, Inhibitors of Grb2 SH2 Domain, and Their Prodrugs

Article abstract of DOI:10.1021/jm031005k

To develop potential antitumor agents directed toward HER2/ErbB2 overexpression in cancer, we have designed inhibitors of the recognition between the phosphotyrosine of the receptor and the SH2 domain of the adaptor protein Grb2. In the first part of the paper, we report the synthesis of mimetics of the constrained (α-Me)phosphotyrosine residue such as (α-Me)-4-phosphonomethylphenylalanine (-CH₂PO₃H ₂), (α-Me) 4-phosphonodifluoromethylphenylalanine (-CF ₂PO₃H₂), and (α -Me)-4-phosphonophenylalanine (-PO₃H₂). The incorporation of these residues in the mAZ-pTyr-Xaa-Asn-NH₂ series provided compounds with very high affinity for the Grb2 SH2 domain, in the 10 ^-8-10^-9 range of K_d values. These compounds behave as potent antagonists of the Grb2-Shc interaction. Our results highlight the importance of the doubly negative charge borne by the pY + 1 amino acid in accordance with the interactions observed in the complex crystallized between mAZ-pTyr-(αMe)pTyr-Asn-NH₂ and the Grb2 SH2 domain. mAZ-pTyr-(αMe)pTyr-Asn-NH₂ was derivatized as the S-acetyl thioester (SATE) of the phosphotyrosine residues, and its surrogates provided prodrugs with very potent antiproliferative activity on cells overexpressing HER2/ErbB2, with ED₅₀ values amounting to 0.1 μM. Finally a new prodrug is put forth under the form of a monobenzyl ester of phosphate group that is as active as and much easier to synthesize than SATE prodrugs. These compounds show promising activity for further testing on in vivo models.