1. RESULTS AND CONCLUSIONS
•GMX-1778 & APO-866 caused toxicity on MK precursors in vitro
• This manifested as reduction in ATP levels and reduced colony
formation
• There was a species difference in sensitivity human and
monkey > mouse (less sensitive) (data not shown)
• NAMPTi toxicity on MK cells in vitro was mitigated by NA co-
treatment
•In 5-14 day rat toxicity studies, NAMPTi caused hypocellularity in
hematopoietic tissues, with accompanying decreases in circulating
reticulocyte, RBC and lymphocyte counts. However, there was no
significant reduction in circulating platelet counts
•Toxicity on MK is on-target; tracks with potency.
• Less potent NAMPTi had reduced toxicity on MK precursors
in vitro and did not cause bone marrow hypocellularity in rats
•MK cells may be susceptible to NAMPTi toxicity because of high
metabolic activity during the differentiation process
•Clinical safety considerations:
• The viability of NA to rescue NAMPTi-mediated
thrombocytopenia has not been demonstrated
• Co-treatment with NA may mitigate NAMPTi-mediated
thrombocytopenia to potentially improve the risk-benefit
profile
• Bone marrow toxicity is clinically monitorable and expected
to be reversible
• Patient compliance to NA co-treatment regimen is an
important consideration
Effects of Nicotinamide Phosphoribosyltransferase inhibitors on platelet development.
J. Singh1
, T. Zabka1
, H. Uppal1
, D. Diaz1
, J. Tarrant1
, E. Clarke2
, G. DosSantos2
, T. Lin1
, B. McCray1
, N. La1
, T. Nguyen1
, P. Dhawan1
, E. Doudement1
, A. Kauss1
, D. Dambach1
, D. Misner 1
1
Safety Assessment, Genentech, South San Francisco, CA. 2
ReachBio, Seattle, WA.
MATERIALS & METHODS
MK viability:
•MK precursor cell viability was measured by ATP (cell-titer glo), and
differentiation was measured by colony formation in MK-CFC assays.
MK cells were treated with NAMPTi in the presence or absence of NA
Rat Toxicity studies:
•Rats (5 males per group) were dosed daily for 5-14 days with GMX-
1778 or APO-866, followed by terminal clinical pathology and
anatomic pathology evaluation
•GMX-1778 was dosed by oral gavage at doses of at doses of 0
(vehicle control), 10, 30, or 100 mg/kg/day QD or BID
•APO-866 was dosed by intra-peritoneal injection at 0 (vehicle control)
and 60 mg/kg/day BID
INTRODUCTION
•Nicotinamide Adenine Dinucleotide (NAD) is a cofactor for glycolysis
which is 50-100x increased in tumor cells
•Nicotinamide Phospho Ribosyl Transferase (NAMPT) is the rate
limiting enzyme in a salvage pathway of NAD generation
•NAMPT is upregulated in tumors
•Therapeutic rationale: NAMPT inhibition > ↓ NAD production > ↓
glycolysis > ↓ tumor growth
•NAD can be replenished by treatment with the precursor, nicotinic
acid (NA)
• Two structurally diverse NAMPT inhibitors (NAMPTi), GMX-1778
and APO-866, failed to demonstrate clinical efficacy due to dose-
limiting thrombocytopenia (Holen, 2008; Hovstadius, 2005)
• GMX-1778 and APO-866 were tested for toxicity on
megakaryocytes (MK) in vitro. Toxicity was measured
biochemically (cellular ATP levels) and functionally (colony forming
capacity, or MK-CFC assay)
• Short-term (5-14) day rat toxicity studies were conducted to
recapitulate clinical thromobocytopenia
1. (A) and (B): GMX-1778 and APO-866 reduce colony forming capability of human
MK cells; NA mitigates NAMPTi toxicity on MK cells.
GMX-1778 APO-866
ACKNOWLEDGEMENTS: J. Hsu, T. O’Brien, D. Sampath, B. Liederer, M. Zak.
REFERENCES
•Holen K. et al (2008). PK, toxicities of FK866, NAD biosynthesis Inhibitor. Invest New
Drugs 26:45–51
•Hovstadius P. et al (2005). Ph. I Study of CHS828 in Patients with Solid Tumor
Malignancy. Clin. Cancer Res. 8: 2843–50
2. NAMPTi reduce cellular ATP during the 14-day human MK differentiation.
GMX-1778
APO-866
IC50 on A2780 cells (nM) 0.9 1.0
NAMPTi tested
GMX-1778 (nM)
NAMPTi GMX-1778 APO866
NA co-treatment (µM) IC50 nM NA co-treatment (µM) IC50 nM
0 2.4 0 1.9
0.01 3.3 0.01 2.4
0.1 41 0.1 66
1 >100 1 >100
4. NAMPTi-related bone marrow hypocellularity in rats associated with decreased
circulating reticulocyte, RBC, and lymphocyte counts; platelet counts were not reduced.
Bone marrow from control rat Bone marrow from NAMPTi-treated rat
NA (1 µM)
mitigated
NAMPTi-related
ATP reduction
in MKs (data not
shown)
1. (A)
1. (B)
Day 3 Day 6
Day 9
Day 14