CONTRIBUTION OF PRECLINICAL STUDIES TO EVALUATION OF

OSTEOPOROSIS THERAPY

Gideon A Rodan MD PhDMerck Research Laboratories

Bone Biology and Osteoporosis Research

PRECLINICAL INFORMATION

Hypothesis: Preclinical studies can reduce the burden of proof required of clinical trials, by providing information on

• Safety (general and bone)

• Efficacy

• Mechanism (pharmacological activity and adverse events)

Historical Perspective and Current Osteoporosis Guidelines

• Pre 1994: Increased BMD in 2 year PBO-controlled trials plus preclinical evidence for bone safety/quality

• Reasons for change:– No fracture reduction during third year with

etidronate treatment, hence three year studies

– No fracture reduction during fluoride treatment, in spite of increased BMD, hence fracture endpoint

ETIDRONATE PRECLINICAL STUDIES

• Spontaneous fractures in dogs (Flora et al)

• Impaired fracture healing in dogs (Nunnemaker et al)

• Narrow efficacy/safety window (MRL study)

Control Bisphosphonate

Microradiograph

Growth CartilageEpiphysis

Diaphysis

Metaphysis

Schenk Assay

OsteoidMineralized Bone

Growth Cartilage

Epiphysis

Metaphysis2 ° Spongiosa

Diaphysis

Metaphysis1° Spongiosa

Schenk Assay Control

Growth Cartilage

Epiphysis

Diaphysis

Metaphysis2 ° Spongiosa

Metaphysis1° Spongiosa

OsteoidMineralized Bone

Schenk Assay Alendronate

Growth Cartilage

Epiphysis

Diaphysis

Metaphysis2 ° Spongiosa

Metaphysis1° Spongiosa

OsteoidMineralized Bone

Schenk Assay Etidronate

2525

2020

1515

1010

55

00

00 0.010.01 0.10.1 11 1010 100100

2020

1010

00

Eff

icac

yE

ffic

acy

Cn

Cn -

BV

/TV

(%

)-B

V/T

V (

%)

Dose mg P/kg/day S.C.Dose mg P/kg/day S.C.

Sa

fetyS

afety

OV

/BV

(%)

OV

/BV

(%)

Bone Volume (Bone Volume (CnCn--BV/TV)BV/TV)

Osteoid Osteoid Volume Volume(OV/BV)(OV/BV)

1515

55

0.0011

Dose Response for Inhibition ofResorption and of Mineralization by

Alendronate in Schenk Assay

3535

3030

2525

2020

1515

1010

55

00

00 0.010.01 0.10.1 11 1010 100100

6060

5050

4040

3030

2020

1010

00

Eff

icac

yE

ffic

acy

Cn

Cn -

BV

/TV

(%

)-B

V/T

V (

%)

Dose mg P/kg/day S.C.Dose mg P/kg/day S.C.

Sa

fetyS

afety

OV

/TV

(%)

OV

/TV

(%)

Bone Volume (Bone Volume (CnCn--BV/TV)BV/TV)

Osteoid Osteoid Volume Volume(OV/BV)(OV/BV)

Dose Response for Inhibition ofResorption and Mineralization by

Etidronate in Schenk Assay

FLUORIDE PRECLINICAL STUDIES

• Bone strength increase is not commensurate with bone mass increases (Mosekilde et al. CTI 1987, 40:318-322)

• Abnormal mineralization by x-ray scattering (Fratzl et al JBMR 1994, 9:1541-1549)

• MRL study (Lafage et al, JCI 1995, 95:2127-2133)

Correlation of Vertebral Bone Mass and Bone Strength In Alendronate Treated Animals

30

27.5

25

22.5

20

17.5

15

12.5

10

7.5

50.9 0.95 1.0 1.05 1.1 1.15 1.2 1.25 1.3 1.35

Bone Mineral Density L2-L4 (g/cm2)

Ult

imat

e S

tren

gth

(MP

a)

Non-OVXOVX+VEH

OVX+ALN 0.05 mg/kg IV

OVX+ALN 0.25 mg/kg IV

r=0.9p(x2)=0.0034

JCI, 92, 2577 (1993) Baboons 2 Years

350

250

200

150

100

5030

Ash Weight (mg)U

ltim

ate

Loa

d (N

)

Non-OVXOVX+VEH

OVX+ALN 1.8 mg/kg SC

OVX+ALN 18 mg/kg SC

CTI, 53, 283(1993) Rats 1 Year

300

35 40 45 50 55 60 65 70

Similar Findings in Normal Minipigs (1 Yr), Rats ( 2 Yrs), and Dogs (3 Yrs) Oral Dosing.

Comparison of Alendronate and NaF Effects on Bone Strength vs. Bone Mass

1600

1400

1200

1000

800

600

400

20020 25 30 35 40 45 50

Bone Volume/Tissue Volume %

Fai

lure

Loa

d (N

)

Alendronate

1600

1400

1200

1000

800

600

400

20020 25 30 35 40 45 50

Bone Volume/Tissue Volume %

Sodium Fluoride

JCI, 95, 2127 (1995)

Bone Strength decreases with increased NaF content

1150

JCI, 95, 2127, (1995)

1050

950

850

750

1.6 1.8 2.0 2.2

Bone Fluoride Content (mg/g bone ash)

L4

Cor

e U

ltim

ate

Stre

ngth

(M

Pa)

N.B. In clinical trials NaF increased BMD w/o reducing fractures

PRECLINICAL MODELS FOR BONE SAFETY

CONCLUSIONS• Bone measurements (histology and strength) in

animal models at multiples (5x?) of the therapeutic dose detected deleterious effects of etidronate and fluoride, and could be sensitive enough to evaluate the bone safety of prospective OP therapies.

Recommendation• Use bones from long term toxicology studies to

evaluate bone safety (histology and strength).

PRECLINICAL MODELS FOR EFFICACY

• Estrogen-deficiency bone loss (cancellous>cortical) occurs in most mammals including humans, rodents, primates and other species (in sheep, dogs, rabbits, apparently seasonal).

• Agents that increase BMD and bone strength in preclinical models reduced fracture risk in humans: bisphosphonates, estrogens, SERMs, PTH. However, quantitative relationships would have to be determined in clinical trials.

Recommended Principles for Preclinical Efficacy Studies

• Use adult animals - to eliminate confounding effect of growth.

• Use any species documented to lose an easily quantifiable amount of bone following oophorectomy, cancellous or cortical.

• Use several parameters and accepted methodology (DXA, histomorphometry, QCT, mechanical testing, biochemical markers), look for internal consistency.

• Use multiple doses (2-3).

Recommended Principles for Preclinical Efficacy Studies (Cont.)

• For prevention registration document the prevention of bone loss.

• For treatment registration document the restoration of lost bone (treatment of osteopenia).

• Follow bone retention after cessation of therapy.

Mechanism StudiesProvide important insights for defining the necessary safety and efficacy

studies.

Safety:• For agents binding to the mineral, effects on mineralization and

mineral structure (BPs, F).• For bone forming agents, woven vs. lamellar bone, tumors, ectopic

ossification…

Efficacy:• At the tissue level all resorption inhibitors act similarly (suppression

of bone turnover).• No known mechanistic difference between cancellous and cortical

bone resorption.

INHIBITORS OF RESORPTION vs. FORMATION STIMULATORS • Inhibitors of bone resorption retain existing

normal bone and bone structure and can produce a positive bone balance. Unless they alter bone/mineral structure (e.g. etidronate) they should be totally safe for bone.

• Formation stimulators engender production of new bone (e.g. fluoride), which could be “woven” , normal structure should be confirmed by histology.

SUMMARY AND CONCLUSIONS• Preclinical studies

– Can validate the “bone safety” of osteoporosis therapeutic agents and potentially predict if increases in bone mass will be associated with increases in bone strength.

– Can test the efficacy of prospective therapeutic agents in animal models of estrogen-deficiency bone loss, and potentially other types of bone loss.

– Could, accordingly, help the design of clinical trials.

SUMMARY AND CONCLUSIONS

Topics in current preclinical guidelines which can be revisited:

• Multiple species (cortical remodeling) for efficacy studies.

• Duration of efficacy studies vs. use of long-term toxicology animals for bone safety.

• Different criteria for different resorption inhibitors.