CONTRIBUTION OF PRECLINICAL STUDIES TO EVALUATION OF OSTEOPOROSIS

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					CONTRIBUTION OF PRECLINICAL
 STUDIES TO EVALUATION OF
   OSTEOPOROSIS THERAPY
       Gideon A Rodan MD PhD
       Merck 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)
                   Schenk Assay

       Epiphysis
Growth Cartilage
    Metaphysis
      Diaphysis




                                               Microradiograph




                    Control   Bisphosphonate
            Schenk Assay Control

      Epiphysis

Growth Cartilage
    Metaphysis
  1° Spongiosa

     Metaphysis
  2 ° Spongiosa




      Diaphysis
                             Osteoid
                             Mineralized Bone
        Schenk Assay Alendronate

      Epiphysis

Growth Cartilage
     Metaphysis
   1° Spongiosa

     Metaphysis
  2 ° Spongiosa



      Diaphysis
                           Osteoid
                           Mineralized Bone
         Schenk Assay Etidronate

      Epiphysis

Growth Cartilage

     Metaphysis
   1° Spongiosa

     Metaphysis
  2 ° Spongiosa

      Diaphysis
                            Osteoid
                            Mineralized Bone
 Dose Response for Inhibition of
Resorption and of Mineralization by
  Alendronate in Schenk Assay
                  25                                         20
                                     Cn-
                       Bone Volume ( Cn-
                       BV/TV)
                  20
                       Osteoid Volume                        15
                       (OV/BV)
   Cn-BV/TV (%)




                  15




                                                                  OV/BV (%)
                                                                  OV/BV (%)
     Efficacy




                                                             10




                                                                   Safety
                                                                   Safety
                  10
                                                             5
                  5


                  0                                          0



                       0    0.001    0.01   0.1   1   10   100
                              1
                            Dose mg P/kg/day S.C.
Dose Response for Inhibition of
Resorption and Mineralization by
 Etidronate in Schenk Assay
               35                                                60
                        Bone Volume ( Cn-
               30                                                50
                        BV/TV)
               25       Osteoid Volume                           40
Cn-BV/TV (%)




                        (OV/BV)




                                                                      OV/TV (%)
                                                                      OV/TV (%)
               20
  Efficacy




                                                                       Safety
                                                                       Safety
                                                                 30
               15
                                                                 20
               10
                                                                 10
               5

               0                                                 0



                    0             0.01      0.1   1   10   100
                           Dose mg P/kg/day S.C.
   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
                                       Non-OVX                                                                      Non-OVX
                                       OVX+VEH                                                                      OVX+VEH
                                       OVX+ALN 0.05 mg/kg IV                                                        OVX+ALN 1.8 mg/kg SC
                            30         OVX+ALN 0.25 mg/kg IV                                              350       OVX+ALN 18 mg/kg SC

                           27.5
                                                                                                          300
                            25
 Ultimate Strength (MPa)




                           22.5




                                                                                      Ultimate Load (N)
                                                                                                          250
                            20
                           17.5                                                                           200
                            15
                                                                                                          150
                           12.5
                            10
                                                               r=0.9                                      100
                            7.5                                p(x2)=0.0034
                             5                                                                            50
                                  0.9 0.95 1.0 1.05 1.1 1.15 1.2 1.25 1.3 1.35                                  30 35   40 45   50 55    60 65 70
                                       Bone Mineral Density L2-L4 (g/cm2)                                                Ash Weight (mg)

 JCI, 92, 2577 (1993)                           Baboons 2 Years                     CTI, 53, 283(1993)                     Rats 1 Year
                                        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
                                      Alendronate                                   Sodium Fluoride
                   1600                                            1600
                   1400                                            1400
Failure Load (N)




                   1200                                            1200
                   1000                                            1000
                    800                                             800
                    600                                             600
                    400                                             400

                    200                                             200
                          20   25    30    35       40   45   50          20   25    30    35    40    45    50
                               Bone Volume/Tissue Volume %                     Bone Volume/Tissue Volume %

    JCI, 95, 2127 (1995)
       Bone Strength decreases with
          increased NaF content
        L4 Core Ultimate Strength (MPa)
                                          1150
                                          1050

                                           950

                                           850

                                           750


                                                 1.6            1.8          2.0               2.2
                                                       Bone Fluoride Content (mg/g bone ash)
                JCI, 95, 2127, (1995)


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 Studies
Provide 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.