Measuring Active Microglia in Progressive Multiple Sclerosis

This is pilot study designed to determine the baseline and longitudinal regional-specific
change in uptake of [11C]PK-11195 in subjects with secondary progressive multiple sclerosis
(SPMS). Eighteen subjects with SPMS will be enrolled in the two-year study. Given low sample
size, a stable treatment regimen is required to control for potential treatment effect. In
addition, subjects must have been on current therapy for at least 6 months to ensure the
measurement is reflective of true disease activity and not treatment effect. Thirteen
age-matched healthy controls (HC) will be enrolled. The role of HC is to establish the
variability or "noise" associated with the instrument (test-retest), which will ensure that
PK uptake measured at any time point in MS is biologically relevant.

This proposal also includes a sub-study to validate a non-invasive quantification methodology
for PK-PET. The most rigorous method, or gold standard, for quantifying PET data is based
upon measuring the arterial input function. Measuring radioactivity within the arterial
circulation requires arterial cannulation. Arterial cannulation is considered safe; however,
is labor-intensive and often discourages subjects from participation. Image-derived input
function (IDIF) is a method to calculate the input function without cannulation of the artery
using the imaging data. Studies in human research volunteers are still required to compare
the results obtained with classical arterial sampling and the IDIF. The current study will
validate IDIF as a substitute for arterial sampling in this context. All healthy controls
will undergo this validation process, which will include arterial and venous sampling. This
validation is also required within subjects. Subjects will be given the option to participate
in this validation stage.

Absolute Quantification of PK-PET (gold standard arterial sampling): Catheters will be placed
in the radial artery for characterizing the plasma input function. This will make it possible
to use a two tissue reversible plasma input (2T4k) model. Blood sampling will be acquired
using both an online continuous blood sampling device as well as manually at discrete times
(5, 10, 15, 20, 30, 40, 50 and 60 minutes post injection). The continuous sampling will be
used to measure the activity concentrations of the whole blood, while the discrete manual
sampling will be used to calculate the plasma concentration, and estimate the fraction of
radioactive metabolites using HPLC. The total blood loss is estimated to be 8-10 tablespoons
(120-150 mL, or about one third of the amount that volunteers donate to the Red Cross when
giving blood). To generate the plasma input functions, the ratio of the plasma data to whole
blood will be calculated for each manual blood sample and fitted through these points to a
model with a one- or two-exponential function. Metabolite correction will be accomplished by
multiplying the plasma curve with a function obtainable from a fit to the measured parent
fraction. Venous blood will be similarly obtained for IDIF metabolic correction and utilized
for validation against classic arterial sampling. The investigators will acquire up to 6
venous samples of 3 mL each with a 2 mL purge prior to each sample, for a total blood loss of
30 mL (one fluid ounce, or about 6.67% of the amount that volunteers donate to the Red Cross
when giving blood).

Dynamic PET acquisition and processing: The data will be acquired in list mode to facilitate
processing at any dynamic framing rate.

Innate immunity is recognized as a major cause of tissue injury in central nervous system
(CNS) disease. In this study the investigators will specifically quantify the innate immune
inflammatory burden in a cohort of secondary progressive multiple sclerosis (SPMS) subjects.
Our hypothesis is that the innate immune response is heightened in SPMS as compared to
healthy controls (HC's) and this activity increases over time and correlates with ongoing
neuronal loss and disability. The investigators will test this hypothesis by using highly
specific molecular imaging techniques, specifically PET, in conjunction with high field MRI.
The investigators will utilize the PET radioligand [11C]1533; PK11195 which binds to the
translocator protein 18 kDa (TSPO) on activated macrophages/microglia. The investigators will
correlate [11C]PK11195 uptake with conventional measures of inflammation and neuronal
integrity on high-resolution MRI.

MS is a chronic inflammatory disease of central nervous system characterized by focal T cell
and macrophage infiltrates associated with demyelination. The primary innate immune cells in
MS consist of infiltrating macrophages/monocytes and resident microglia. Cells of the innate
immune system are effector cells that function to cause CNS injury both through direct
effects on neighboring cells, such as oligodendrocytes, and through generation of soluble
proinflammatory mediators that have distant effects on cells, such as neurons. The innate
immune inflammatory is thus sufficient to explain focal injury and diffuse injury. In the
majority of subjects, MS begins as a relapsing-remitting course but eventually evolves to a
state of progressive decline in disability. Focal inflammatory demyelinating lesions are the
predominant pathological findings in the subjects with relapsing disease whereas diffuse
axonal injury with microglial activation has been found to be the hallmark of progressive
disease.1 Microglial activation itself occurs either as a response to CNS injury for example
as in Wallerian degeneration, or in response to signals from other inflammatory cells
including macrophages and lymphocytes.

Activated microglia and infiltrating macrophages express TSPO (previously referred to as the
peripheral benzodiazepine receptor) which can be detected with radioligand [11C]PK-111952.

Determination of the significance of any [11C]PK-11195 uptake within a cohort of MS subjects
would require a correlation with HC¿s to ensure the observation is a valid measurement of
disease activity.

The MS subjects will also have two baseline [11C]PK-11195 PET scans (separated by 24 to 72
hours, test-retest) to measure disease related intra-individual variability and will have
subsequent scans at 6, 12 and 24 months. Baseline test-retest [11C]PK-11195 PET uptake
between MS subjects and HC's will be compared to ensure minimal disease-related variability
and to ensure our baseline and subsequent longitudinal measurements in MS subjects have met a
level of biological significance. One baseline brain MRI is required for HC and MS subjects.
Subjects will have brain MRI's at 6, 12 and 24 months.

Objective: Aim 1: To quantify level of activity and dynamic change in the innate immune
inflammatory burden over the course of two years in a cohort of SPMS subjects.

Primary objective: Measure the level of baseline and change of whole brain uptake of
[11C]PK-11195 at 6, 12 and 24 months in SPMS subjects.

Objectives:

- To correlate the change in T2-hyperintense lesion volume at 6,12 and 24 months of with
whole brain uptake of [11C]PK-11195 on PET (at the 6,12 and 24 months) in SPMS subjects.

- To correlate the change of conventional MRI measures of neuronal integrity (Gray Matter
Fraction, White Matter Fraction, whole brain volume, T1-hypointense lesion volume) at
6,12 and 24 months with whole brain PET uptake of [11C]PK-11195 (at the 6,12 and 24
months) in SPMS subjects.

- To correlate the change in whole brain PET uptake of [11C]PK-11195 (at the 6,12 and 24
months) and level in disability, as measured by a change in EDSS at 6, 12, and 24 months
in SPMS subjects.

Inclusion Criteria:

- Subjects age 18-80

- Secondary progressive MS subjects either untreated or on consistent treatment for
six-months prior to enrollment

- Norman Controls

Exclusion Criteria:

- Subjects pregnant or woman of child-bearing age not utilizing effective birth control

- Primary progressive MS subjects

- Relapsing remitting MS subjects

- Unstable SPMS subject for which treatment change within the 24 months is likely

Age-Healthy controls will be excluded if have any of the following medical conditions:

- Any central nervous system disorder

- Any systemic auto-immune disorder

- Pregnant or woman of child-bearing age not utilizing effective birth control

Subjects will be withdrawn from the study if treatment is changed during the 24-month study