No responders yet
The results from the 400mg cohort were disappointing, in our view, because they do not appear to signal any improvement over the 300mg cohort. We were encouraged by the 300mg data because one patient was very close to achieving a PR, so it appeared that the dose was on the cusp of activity. The 400mg dose did not improve on this profile, and moreover, that near-responder from the 300mg cohort remains on drug and has not yet quite reached PR status.
Is poor PK the explanation?
The company also presented pharmacokinetic (PK) data on the 400mg cohort, which may provide insight as to why it is not well differentiated from the 300mg dose. Serum levels of the drug were not well differentiated from 300mg and were in fact trending lower than 300mg at six hours post administration. Moreover, steady-state concentration of the drug at day 8 were lower for the 400mg cohort (vs 300mg), but this was not the case for the 500mg cohort, which is encouraging as it suggests that the drug has not reached saturating concentrations at these doses.
More cohorts might be needed
The last cohort in the study protocol is the 500mg cohort. The cohort is currently over-enrolling, and Sunesis has stated that it intends to release the initial response data (similar to those presented here) for the cohort in Q220. We believe the company would face no hurdles in adding additional higher dosing cohorts, which it may consider as we have still not seen definitive responses.
Valuation: Lowered to $188.7m or $1.56/diluted share
We have lowered our valuation to $188.7m or $1.56 per diluted share from $238.7m or $1.94 per diluted share, as we have reduced the probability of success for vecabrutinib to 15% from 20%. We expect to further update our assumptions with the release of data from the 500mg cohort.
