definiens: shall mean, with respect to the Leading Compound ( which may include, if applicable, the Development Candidate ) in a given Program, another Collaboration Compound in such Program which ( i ) is not an ester, salt, crystalline polymorph, hydrate or solvate of such Leading Compound, any Backup Compound with respect to such Leading Compound or, in the case of the Pain 2 Program, any other Follow - On Compound, ( ii ) EXECUT ION VERSION -9 - has a Mechanism of Action at the applicable Protein Target Profile that is not substantially the same as the Mechanism of Action at such Protein Target Profile of such Leading Compound ( or of any other Follow - On Compound in such Program in the case of the Pain 2 Program ) and ( iii ) is or is reasonably be expected to be commercially differentiable from such Leading Compound, from any Backup Compound with respect to such Leading Compound and, in the case of the Pain 2 Program, from any other Follow - On Compound ; provided that a Collaboration Compound nominated by [COMPANY] as and determined by the JSC to be a Follow - On Compound with respect to a Leading Compound prior to reaching the Candidate Selection Stage ( A ) shall not continue thereafter to be a Follow - On Compound unless, upon reaching the Candidate Selection Stage, it is determined by the JSC to be or to be expected to be commercially differentiable from such Leading Compound, from any Backup Compound with respect to such Leading Compound and, in the case of the Pain 2 Program, from any other Follow - On Compound and ( 8) that does not continue to be a Follow - On Compound upon reaching the Candidate Selection Stage as provided in clause ( A ) above shall no longer be a Progressed Compound . For clarity, any Lead, Development Candidate or Product Candidate may become a Follow - On Compound ( if othelwise qualifying ) as a result of a substitution hereunder