RESEARCH POSTER PRESENTATION DESIGN © 2015

www.PosterPresentations.com

2 0 0 0

3 0 0 0

4 0 0 0

5 0 0 0

Ge

o M

ea

n p

CR

EB

P la c e b o D o s e d

0 0 2 2 4 0 2 2 4

D a y 1

0

D a y 1

H o u r s P o s t D o s e

D a y 4 D a y 4

Schedule of PD Assessments

Adenosine Receptor Mediated pCREB Signaling

Relationship Between Mean AB928 Plasma Levels and PD Endpoints

AB928 PK Profile Supports Once Daily Dosing at Steady State

AB928 (150 mg qd) Provides Maximal Inhibition of A2aR-Mediated pCREB Increases

on CD8+ T cells at Steady State

PK/PD Correlation in AB928 Dosed Subjects Measured by pCREB Inhibition of 5 mM NECA

Effects on CD8+ T cells

INTRODUCTION

METHODS

RESULTS

• AB928 has demonstrated an excellent oral PK profile in

human subjects, consistent with once-daily dosing.

• Dose levels of AB928 have been identified that provide

maximal adenosine receptor coverage in the blood. At

these dose levels, AB928 has been shown to be safe and

well-tolerated and no effects have been noted on

physiological parameters generally associated with

adenosine inhibition.

• Assessing pCREB levels on whole blood CD8+ T cells

following ex vivo stimulation with 5 µM NECA provides an

excellent measure of the PD effects of AB928 in dosed

subjects. Consistent with previously generated in vitro

data, AB928 plasma levels ≥ 1 µM are associated with ≥

90% adenosine receptor inhibition.

• The clear PK/PD correlation obtained for AB928 in the

ongoing Phase 1 study in healthy volunteers will be used

to guide dose selection for future combination studies in

oncology, several of which are expected to be initiated

later this year.

We also wish to thank PRA Health Sciences in the Netherlands for assistancewith flow cytometry: Sijranke Post, Richard Draaijer, Tom Huizinga, PatrickVeerman , Frank Beltman, Riejanne Bax-Seigers and Janet Stegehuis.

CONCLUSIONS

Seitz L, Ashok D, Leleti M, Powers J, Rosen B, Miles D, Sharif E, Jin L, Park A, Young S, Soriano F, Rieger A, Karakunnel J, Walters MJ

Arcus Biosciences, Inc. 3928 Point Eden Way, Hayward, CA 94545, USA

Clinical Pharmacokinetic-Pharmacodynamic Relationship for AB928, a Dual Antagonist of the A2aR and A2bR Adenosine Receptors

In many tumors, extracellular adenosine contributes to an

immunosuppressed tumor micro-environment (TME) via

activation of the A2a receptor (A2aR), expressed on lymphocytes,

and the A2b receptor (A2bR), expressed on myeloid cells. Relative

to other tissues like the brain, adenosine concentrations in the

TME are much higher. Also unlike the brain, tumors contain high

levels of albumin, to which many small molecule drugs bind non-

specifically. AB928 is a novel and selective dual A2aR/A2bR

antagonist designed to potently block the immunosuppressive

effects of adenosine in the TME.

An ongoing placebo-controlled (3:1) study of AB928 is being

conducted in healthy volunteers to study the safety, tolerability,

pharmacokinetics (PK) and pharmacodynamics (PD) of the drug.

This poster describes the preliminary PK and PD (receptor

coverage in blood T cells) data from the healthy volunteer study.

This information is being used to help guide dose selection in

several combination studies in oncology that will be initiated

later this year.

Phase 1 Healthy Volunteer Study: This Phase 1 healthy

volunteer study has single ascending dose (SAD) and multiple

ascending dose (MAD) arms. In the SAD arm, we are

evaluating single doses of 10, 25, 75, and 150 mg, and two

doses of 100 mg, 12 hours apart. In the MAD arm, we are

evaluating single daily doses of 10, 25, 75, 150 and 200 mg

administered for 4 consecutive days. As of the data cut-off

date (DCO) of 3/30/18, all doses up to 150 mg in the SAD and

MAD arms have been completed. The study is ongoing and

remains blinded; no trends have been observed on

physiological parameters potentially sensitive to adenosine

inhibition and there have been no safety events preventing

escalation to higher cohorts.

NECA-Induced pCREB Increases in Peripheral Immune Cells Are Blocked by AB928

Bioanalytical / PK analysis: Plasma samples were prepared bya protein precipitation extract procedure. The analyte, AB928,and internal standard, D6-AB928, were extracted from plasmawith acetonitrile/methanol (90/10, v/v). Concentrations ofAB928 in the extracts were determined by LC-MS/MS.Descriptive pharmacokinetic parameters were obtained by astandard non-compartmental analysis from the plasmaconcentration-time curves using Phoenix WinNonlin v6.3 orhigher (Certara, Princeton, NJ).

Multi-color Phospho-flow Cytometry: Monoclonal antibodiesto cell type specific markers including fluorochrome labelledanti-pCREB (Cyclic AMP Response Element Binding Protein)antibody were used to identify inhibition of CREBphosphorylation in placebo and dosed subjects.

Clinical Study Design

Predose No NECA

Predose No NECA

Predose + NECA

Predose + NECA

+ AB928 + NECA

+ AB928 + NECA

NECA induced a significant increase in pCREB (grey vs. redhistograms) in peripheral blood immune cells. This increase, inresponse to 5 mM NECA, is still inhibited at trough plasma levelsfollowing 4 once daily doses with 150 mg AB928 (bluehistograms). Prior to dosing, NECA-induced pCREB elevationswere observed in CD8+ T cells in all subjects evaluated to date.The ability to capture the effects of NECA on CD14+ cells wasimpeded by the smaller assay window; however, when thepCREB signal was observed on monocytes, AB928 was able toinhibit it as shown here.

3769

Rationale for NECA Concentration Selection: Previous

experiments conducted in vitro indicate that NECA is at least

20 times more potent than adenosine at inducing CREB

phosphorylation in human blood; thus, our PD analysis is

focused on the 5 µM NECA stimulation under physiologically

relevant conditions. 5 mM NECA provided maximal induction

of pCREB. We believe this provides receptor inhibition data

comparable to what we might expect from ≥ 100 µM intra-

tumoral adenosine. AB928 displays ~100% penetration of

mouse tumors (plasma: tumor AUC ratio ~1) (see Walters et al,

Abstract No. 3518 at this meeting).

2 0 0 0 4 0 0 0 6 0 0 0 8 0 0 0

0

5 0

1 0 0

P la s m a L e v e l A B 9 2 8 (n M )

% I

nh

ibit

ion

re

lati

ve

to

Pre

do

se

(5

mM

NE

CA

)

Variability range of

placebo subjects

pCREB in Human Whole Blood: The inhibition of A2aR-mediated

effects by AB928 was determined in blood samples from the

Phase 1 study by the decreased phosphorylation of CREB

following stimulation ex vivo with the adenosine receptor agonist

NECA (5'-N-ethylcarboxamidoadenosine). At each PD time point,

levels of pCREB were assessed by flow cytometry both in the

absence and following ex vivo stimulation with 1, 5 and 10 µM

NECA. In order to capture the antagonism of AB928 on both the

A2aR and A2bR receptors, we assessed levels of pCREB on blood

CD8+ T cells and CD14+ monocytes.