The evolution of S100B inhibitors for the treatment of malignant melanoma.

Malignant melanoma continues to be an extremely fatal cancer due to a lack of viable treatment options for patients. The calcium-binding protein S100B has long been used as a clinical biomarker, aiding in malignant melanoma staging and patient prognosis. However, the discovery of p53 as a S100B target and the consequent impact on cell apoptosis redirected research efforts towards the development of inhibitors of this S100B-p53 interaction.

Target binding to S100B reduces dynamic properties and increases Ca(2+)-binding affinity for wild type and EF-hand mutant proteins.

Mutations in the second EF-hand (D61N, D63N, D65N, and E72A) of S100B were used to study its Ca(2+) binding and dynamic properties in the absence and presence of a bound target, TRTK-12. With (D63N)S100B as an exception ((D63N)K(D)=50±9 μM), Ca(2+) binding to EF2-hand mutants were reduced by more than 8-fold in the absence of TRTK-12 ((D61N)K(D)=412±67 μM, (D65N)K(D)=968±171 μM, and (E72A)K(D)=471±133 μM), when compared to wild-type protein ((WT)K(D)=56±9 μM). For the TRTK-12 complexes, the Ca(2+)-binding affinity to wild type ((WT+TRTK)K(D)=12±10 μM) and the EF2 mutants was increased by 5- to 14-fold versus in the absence of target ((D61N+TRTK)K(D)=29±1.

In vitro screening and structural characterization of inhibitors of the S100B-p53 interaction.

S100B is highly over-expressed in many cancers, including malignant melanoma. In such cancers, S100B binds wild-type p53 in a calcium-dependent manner, sequestering it, and promoting its degradation, resulting in the loss of p53-dependent tumor suppression activities. Therefore, S100B inhibitors may be able to restore wild-type p53 levels in certain cancers and provide a useful therapeutic strategy.

Phenothiazines inhibit S100A4 function by inducing protein oligomerization.

S100A4, a member of the S100 family of Ca(2+)-binding proteins, regulates carcinoma cell motility via interactions with myosin-IIA. Numerous studies indicate that S100A4 is not simply a marker for metastatic disease, but rather has a direct role in metastatic progression. These observations suggest that S100A4 is an excellent target for therapeutic intervention.

The effects of CapZ peptide (TRTK-12) binding to S100B-Ca2+ as examined by NMR and X-ray crystallography.

Structure-based drug design is underway to inhibit the S100B-p53 interaction as a strategy for treating malignant melanoma. X-ray crystallography was used here to characterize an interaction between Ca(2)(+)-S100B and TRTK-12, a target that binds to the p53-binding site on S100B. The structures of Ca(2+)-S100B (1.

Small molecules bound to unique sites in the target protein binding cleft of calcium-bound S100B as characterized by nuclear magnetic resonance and X-ray crystallography.

Structural studies are part of a rational drug design program aimed at inhibiting the S100B-p53 interaction and restoring wild-type p53 function in malignant melanoma. To this end, structures of three compounds (SBi132, SBi1279, and SBi523) bound to Ca(2+)-S100B were determined by X-ray crystallography at 2.10 A (R(free) = 0.

Divalent metal ion complexes of S100B in the absence and presence of pentamidine.

As part of an effort to inhibit S100B, structures of pentamidine (Pnt) bound to Ca(2+)-loaded and Zn(2+),Ca(2+)-loaded S100B were determined by X-ray crystallography at 2.15 A (R(free)=0.266) and 1.