From the P2b paper:
"As an exploratory trial, three separate doses were identified to define a range of dosing efficacy : zero (placebo), 20 µg, and 40 µg. The 40 µg dose corresponded approximately to the 25 µg / m² doses that were used in Compassionate Use protocols [ 18 ] . These doses were derived from three sources of extensive prior data collection : pre - clinical in vitro studies with isolated PKC enzymes and their substrates , pre clinical in vivo studies with AD transgenic mice , and compassionate use patients .
These studies and the relevant data are all described in several publications that are referenced in this article . The range of 0 to 40 µg was not arbitrary , but instead was directly derived from empirical experience . In the Phase II A study [ 18 ], Compassionate Use protocols used doses that approximated the 40 µg ( 25 µg / m² ) with frequencies that apparently were too high , thus causing downregulation after 3 consecutive weekly doses . Inference of downregulation was based on direct measurement of PKC epsilon in a patient's blood samples . For this compassionate use patient , it was possible to measure blood PKC epsilon levels [ 18 ] rise in close association with the patient's initial improvement with weekly dosing , followed by a decline in this improvement as the PKC epsilon levels fell , in fact , showing downregulation ( inhibition ) . These and other compassionate use results guided our selection of alternate weekly doses - to avoid this observed downregulation in moderately severe to severe AD patients .
These compassionate use results also suggested that too frequent bryostatin over time would produce downregulation and not the activation of PKC epsilon that our pre - clinical studies indicated was associated with cognitive , synaptogenic , and anti - amyloid benefit . On that basis , therefore , we anticipated that the 40 µg dose might be too high a dose and weekly might be too high a frequency ( e.g. , weekly ) . Given those possibilities , we believed that we should test an intermediate dose of 20 µg , also administered at a lower frequency than that of the compassionate use protocols . A similar sequence of PKC activation followed by prolonged downregulation had been previously demonstrated in a clinical oncology trial [ 20 ] with a dose level and frequency of bryostatin administration comparable to that of our Compassionate Use protocols for AD .
The biochemical data presented in Fig . 1 A , B illustrates in vitro PKC epsilon activation that follows an inverted U - shaped dose - response curve . Such an inverted U - shaped dose - response curve was , in fact , suggested by the improvement signals in the SIB scores that were observed in the present trial ."
