A quantitative, surface plasmon resonance-based approach to evaluating DNA binding by the c-Myc oncoprotein and its disruption by small molecule inhibitors.

The use of small molecules to interfere with protein-protein interactions has tremendous therapeutic appeal and is an area of intense interest. Numerous techniques exist to assess these interactions and their disruption. Many, however, require large amounts of protein, do not allow interactions to be followed in real time, are technically demanding or require large capital expenditures and high levels of expertise. Surface plasmon resonance (SPR) represents a convenient alternative to these techniques with virtually none of their disadvantages. We have devised an SPR-based method that allows the heterodimeric association between the c-Myc (Myc) oncoprotein and its obligate partner Max to be quantified in a manner that agrees well with values obtained by other methods. We have adapted it to examine the ability of previously validated small molecules to interfere with Myc-Max heterodimerization and DNA binding. These inhibitors comprised two distinct classes of molecules that inhibit DNA binding by preventing Myc-Max interaction or distorting pre-formed heterodimers and rendering them incapable of DNA binding. Our studies also point out several potential artifacts and pitfalls to be considered when attempting to employ similar SPR-based methods. This technique should be readily adaptable to the study of other protein-protein interactions and their disruption by small molecules.