Yes sir! Because of the short t 1/2 (half-life), simply

Yes sir! Because of the short t 1/2 (half-life), simply detecting P-21 can be tricky. The lab test may be done too far out from the dose administration and go undetected. But as you state a more frequent, or alternatively, a longer infusion would facilitate the detection. ***It wouldn't take long into phase II to see signs of efficacy.