Treatment of Hypoparathyroidism With PTH

In this protocol, we will investigate the mechanisms by which PTH(1-84) treatment improves
bone quality in patients with hypoparathyroidism. Detailed imaging, cellular and biochemical
studies will be performed on subjects with hypoparathyroidism who are also participating in
the NPS Pharmaceutical Company's study known as "CL1-11 REPLACE study." The parent NPS
trial, being conducted under NPS's IND #76,514, is a multi-site, randomized, double-blind,
placebo-controlled trial of PTH(1-84) in hypoparathyroidism. In the NPS protocol,
hypoparathyroid subjects are assigned to either placebo, 50, 75 or 100 mcg of PTH(1-84) a
day, in a dose-titration design, for a 26 week period. The primary efficacy endpoint is a
50% reduction in calcium and calcitriol supplementation. The Columbia site is one of the
investigative sites for the NPS protocol. A letter from NPS accompanying this document
certifies that Dr. Bilezikian is a subinvestigator in the NPS project.

The protocol described in this proposal is different from the NPS study. It is being
conducted under IND #70,449 to Dr. Bilezikian. It will pursue a number of additional studies
that are not being sponsored by NPS or covered by their IND. Under IND #70,449 assigned to
Dr. Bilezikian, we will investigate the effects of PTH(1-84) administration in
hypoparathyroidism on bone quality in hypoparathyroidism. In addition to the biochemical
hallmarks of hypoparathyroidism, it has been found that the microarchitectural structure of
the bone and the entire bone remodeling system are markedly abnormal in this disease. The
studies outlined in this add-on protocol are designed to elucidate the specific ways in
which PTH(1-84) replacement restores to normal bone microstructure and bone metabolism in
hypoparathyroidism. These mechanistic studies are beyond the scope of the parent NPS study,
which is designed to assess only the safety and efficacy of PTH(1-84) in hypoparathyroidism.
These special studies are being conducted only by Dr. Bilezikian's group at Columbia. In the
summary which is provided here, we present the three major studies that will be conducted.

PROTOCOL #1: THE EFFECT OF PTH(1-84) ADMINISTRATION ON SKELETAL MICROSTRUCTURE AS DETERMINED
BY HIGH RESOLUTION IMAGING OF THE SKELETON.[(PERIPHERAL QUANTITATIVE COMPUTED TOMOGRAPHY
(HR-PQCT)).

Protocol. For all subjects enrolled at the Columbia site, we will perform HR-pQCT. Baseline
measurement will be obtained twice at Visit 4 of the NPS protocol (2 weeks prior to
randomization) and at Visit 16 of the NPS protocol (the final injection day). The reason for
the duplicate measurements at each time point is to minimize any variance, thus improving
the accuracy further of the data to be obtained.

Anticipated Results. Based upon our preliminary data, we expect that the abnormalities that
we have observed at baseline in subjects with hypoparathyroidism will be improved by
administration of PTH(1-84). The improvement in skeletal microstructure will be associated
with greater bone strength as determined by finite element analysis and by individual
assignment of strength to the specific orientation of trabecular plates and rods in the
forearm and the tibia. In addition, the remarkable abnormalities in cortical structure will
be a specific focus of attention, particularly in view of the fact that in a disease
characterized by excessive secretion of PTH (primary hyperparathyroidism), cortical thinning
is observed. Thus, with this add-on protocol, we will be able to test the hypothesis that
PTH regulates the spatial distribution between cortical and trabecular bone. This
anticipated result will add great value to the protocol and give us insights that would not
otherwise be possible to make.

PROTOCOL #2: THE EFFECT OF PTH(1-84) ADMINISTRATION ON OSTEOBLAST CELLS AS DETERMINED BY
MEASUREMENT OF CIRCULATING OSTEOGENIC PRECURSORS

Protocol. For all subjects enrolled in the NPS protocol at the Columbia site, we will
perform measurements of peripheral circulating osteoblast cells. The assay will be performed
at Visit 5 (randomization) of the NPS Protocol, then again at 4, 8, 12, and 24 weeks after
administration of PTH(1-84).

Anticipated Results. Based upon our preliminary observations, we expect that PTH(1-84) will
stimulate the recruitment, in the circulation, of cells with an osteoblastic phenotype. We
expect that PTH(1-84) will also stimulate the maturation of cells as defined by ligand
markers that can date the chronological age of these cells. The ability to demonstrate a
specific osteoblastic effect on circulating cells will be correlated with changes in
structural parameters to be obtained in these patients using HR-pQCT.

PROTOCOL #3: THE EFFECT OF PTH(1-84) ADMINISTRATION ON SCLEROSTIN, A KEY MEDIATOR OF PTH'S
OSTEOANABOLIC ACTIONS.

Protocol. We will measure sclerostin levels at Visit 5 (randomization) of the NPS Protocol,
then again at 4, 8, 12, and 24 weeks post-randomization. This will be the first time ever
that sclerostin levels will be measured in hypoparathyroid subjects being replaced with
PTH(1-84).

Anticipated Results. We expect that the administration of PTH(1-84) in subjects with
hypoparathyroidism will be associated with acute reductions in sclerostin. By virtue of the
experimental design of the study, we will be able to test further the kinetics of change,
namely whether the anticipated acute fall in sclerostin levels will be sustained over time.
The results can be related to the cellular actions of PTH to recruit and to activate the
osteogenic cells that will be conducted in Protocol #2 as well as to the osteoanabolic
effects we expect to demonstrate in Protocol #1. .

GENERAL STUDY FEATURES RELATED TO ALL PROTOCOLS

Enrollment and Eligibility Criteria. The enrollment criteria follow the protocol being
sponsored by the NPS IND. They can be provided as an Appendix if requested. Study subjects
who are enrolled in the NPS study will automatically be eligible for the protocols described
above and will constitute the study population for these additional studies. We expect to
enroll 16 patients for each of the remaining three years of the grant period.

Safety Measures. The safety measures to be conducted are identical to the NPS protocol
sponsored under its IND #76,514. They can be provided as an Appendix if requested. They have
been sent to the office of Dr. Mary Parks.

Overall Summary and Significance. These add-on protocols will be done uniquely at the
Columbia site under the sponsorship of IND #70449 assigned to Dr. Bilezikian. They hold the
promise of defining, in ways not possible by the standard protocol being sponsored by NPS,
the mechanisms by which PTH(1-84) is therapeutic in subjects with hypoparathyroidism.