Dose schedule modulates the pharmacodynamic response to ANA773, a prodrug of a toll-like receptor (TLR)-7 selective-agonist

2079 The immune response elicited by TLR7 agonism is believed to have potential benefit in the treatment of cancer. ANA773 is an oral prodrug of a selective TLR7 agonist, one of several receptors within the TLR family. Activation of TLR7 by the biologically active metabolite of ANA773 initiates a cascade of immune stimulatory events that includes the secretion of cytokines and chemokines and the activation of the cellular immune response. This immune induction is likely responsible for the tumor growth inhibition observed in mice with the active metabolite of ANA773. To further elucidate the effects of ANA773 on immune activation, a number of pharmacodynamic studies were performed in cynomolgus monkeys to investigate whether different ANA773 dosing schedules affects the type, magnitude, and duration of the immune response.
 Methods: Three different repeat dose schedules were explored, A) alternate day dosing spanning either 14 or 28 days followed by 7 days of recovery (QOD), B) dosing daily for 7 consecutive days followed by 7 days of recovery (7 on 7 off), and C) daily dosing for 3 consecutive days followed by 4 days of recovery (3 on 4 off). The 3 on 4 off dose schedule was repeated over 3 treatment courses. Immune parameters measured included cytokine and chemokine secretion, neopterin production, and cellular responses.
 Results: A) The 14 and 28 day QOD regimens elicited minimal to moderate levels of cytokine, chemokine, neopterin and cellular responses that, for the most part, did not build with repeated doses, producing the most stable level of immune enhancement observed with the various dosing schedules. B)The 7 on 7 off dose schedule elicited cytokine, chemokine, and neopterin responses that built during the first 3-4 days, but then diminished after the fourth dose, prior to the end of the 7-day dosing period. The cellular response was induced subsequent to the cytokine and chemokine response and declined during the non-dosing period.C) The 3 on 4 off schedule also promoted cytokine, chemokine, and neopterin responses that built with 3 repeated doses of ANA773 and declined during the non-dosing period from days 4 to 7. The cytokine and chemokine responses were re-induced with repeated courses of 3 on 4 off dosing, which suggest that a 4-day off-period is sufficient to re-set these responses between courses. The 3 on 4 off schedule elicited T cell, NK cell and B cell activation that was either amplified or sustained with repeated courses, demonstrating that this dosing regimen, along with the 7 on 7 off regimen, strongly promotes the cellular response.
 The results from these repeat dose schedule studies demonstrate that immunostimulatory responses to ANA773 can be effectively modulated in vivo by dose schedule.