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DIABETES/METABOLISM RESEARCH AND REVIEWS
RESEARCH ARTICLE
Diabetes Metab Res Rev 2009; 25: 558–565.
Published online 22 July 2009 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/dmrr.999
Effects of therapy in type 1 and type 2 diabetes
mellitus with a peptide derived from islet
neogenesis associated protein (INGAP)
Kathleen M. Dungan1 *
John B. Buse2
Robert E. Ratner3
1
Division of Endocrinology, Diabetes,
and Metabolism, The Ohio State
University School of Medicine,
Columbus, OH, USA
2
Division of Endocrinology, University
of North Carolina School of Medicine,
Chapel Hill, NC, USA
3
MedStar Research Institute,
Hyattsville, MD, USA
*Correspondence to:
Kathleen M. Dungan, 4th Floor
McCampbell Hall, 1581 Dodd Drive,
Columbus, OH 43210, USA. E-mail:
[email protected]
Abstract
Background Islet neogenesis associated protein (INGAP) has beta cell
regenerating effects in experimental models.
Methods Subjects with T1DM (N = 63) and T2DM (N = 126) received
300 or 600 mg/day of INGAP peptide in a 90 day, randomized, double-blind,
placebo-controlled trial.
Results In T1DM, on-treatment Arginine-stimulated C-peptide (AUC0 – 30 )
significantly increased from baseline in the 600 mg group (p = 0.0058 versus
placebo); no significant changes were seen in the 300 mg group. In T2DM,
stimulated C-peptide was significantly better preserved in the 600 mg group
compared to placebo at day 120, 30 days after washout (p = 0.031 versus
placebo), but did not reach statistical significance during treatment or in the
300 mg group. In T2DM, A1C decreased significantly more in the 600 mg
group compared to placebo at day 90 (−0.94% versus −0.47%, respectively,
p = 0.009) and day 120, 30 days after washout (−0.73% versus −0.24%,
respectively, p = 0.013). This was accompanied by significant reductions in
mean glucose. No difference from placebo was detected in the 300 mg group
or in T1DM. Injection site reactions were the most common adverse event,
occurring in 8 (36%) of placebo, 19 (90%) of 300 mg, and 15 (75%) of
600 mg groups (T1DM) and 14 (33%) of placebo, 27 (64%) of 300 mg, and
29 (69%) of 600 mg groups (T2DM).
Conclusions INGAP peptide increases C-peptide secretion in T1DM and
improves glycaemic control in T2DM. Longer-term exposure, more frequent
dosing, better tolerated formulations or combination with other therapies
may be necessary to achieve optimal clinical response. Copyright © 2009
John Wiley & Sons, Ltd.
Keywords
INGAP; islet neogenesis; type 1 diabetes; type 2 diabetes
Background
Received: 24 February 2009
Revised: 20 May 2009
Accepted: 16 June 2009
Copyright © 2009 John Wiley & Sons, Ltd.
Type 1 diabetes (T1DM) is marked by autoimmune-mediated islet cell
destruction, and despite advances in therapy, complications continue to
haunt patients and providers. Likewise, beta cell mass is already reduced
by 50% at the time of diagnosis of type 2 diabetes (T2DM) and continues
to decline throughout the course of T2DM [1]. The decline in beta cell
function in T2DM drives the progressive deterioration in glycaemic control
Effects of INGAP Peptide in Type 1 and Type 2 Diabetes
and requirement for insulin [2]. Of obvious clinical
interest is the potential to reverse the destruction of
islet cells and promote islet cell regeneration in both
T1DM and T2DM. Some evidence suggests that mature
pancreatic ductal and acinar cells harbour inherent
flexibility that allows transdifferentiation into islets, and
that islet regeneration occurs throughout life in those
with and without diabetes [3,4]. To date, no therapy
has demonstrated direct evidence of inducing islet cell
neogenesis in humans.
Recently, efforts to discover therapeutic targets for
enhancing islet cell neogenesis have led to the discovery
of the 16 kDa islet neogenesis associated protein (INGAP),
which has an active 15 amino acid segment termed
INGAP peptide [5,6]. INGAP belongs to a subfamily
(Reg III) of Reg proteins, many of which have been
found to have pancreatic regenerative activity [7].
INGAP has regenerative activity in human islet-derived
and ductal cell lines [5,7]. Administration of INGAP
peptide to non-diabetic and diabetic animal models is
associated with increased islet cell number and beta
cell mass [8,9], reversal of hyperglycemia [9–11], and
differentiation of ductal cells into neuroendocrine cells
[12]. Therefore, INGAP may have important beta cell
regenerating potential in humans.
Phase I studies with INGAP peptide in humans showed
good tolerability at doses tested (up to 120 mg per day),
but there was no clear effect on basal or stimulated Cpeptide levels (data on file, Proctor & Gamble, Cincinnatti,
OH). Subsequent dose-rising studies showed tolerability
up to 800 mg subcutaneously. We performed proof of
concept studies to determine the effects of INGAP peptide
on glycaemic control and insulin secretory capacity in
patients with long-standing T1DM or insulin-dependent
T2DM.
Materials and methods
The SPIRIT 1 (T1DM) and SPIRIT 2 (T2DM) trials were
randomized double-blinded studies separately conducted
at 10 and 17 US sites respectively (see Supporting
Information for the SPIRIT 1 and SPIRIT 2 investigator
names). The studies were approved by institutional
review boards at each site. Written informed consent
was obtained from all patients. For SPIRIT 1, patients
aged 18–65 with T1DM diagnosed at or before age 20,
C-peptide ≤0.3 ng/mL, and haemoglobin A1c (A1C) less
than 10% were included. Inclusion criteria for SPIRIT
2 included age 35–70, T2DM diagnosed after age 30,
duration at least 5 years with at least a 2-year insulinfree period, insulin requirement of at least 20 units per
day, and A1C 6.5–10%. Exclusion criteria for SPIRIT
1 included body mass index (BMI) >38 kg/m2 ; for
SPIRIT 2, subjects with positive islet cell (ICA 512) or
glutamic acid decarboxylase (GAD 65) antibodies, or BMI
>40 kg/m2 were excluded. For both studies, patients
with unstable retinopathy or cardiac disease, history of
pancreatitis or elevated pancreatic enzymes, liver or renal
Copyright © 2009 John Wiley & Sons, Ltd.
559
dysfunction, pregnancy, unstable glycaemic control, and
previous treatment with glucagon-like peptide-1 receptor
agonists were excluded.
Patients were randomized to placebo, 300 or 600 mg
INGAP peptide delivered subcutaneously in equivalent
volumes daily from days 1 to 90. Patients were
followed for an additional 30-day washout period and
assessments were repeated at 120 days. INGAP peptide
dose selection was based on consideration of animal and
human pharmacokinetic data and associated metabolic
and/or histologic responses observed in animal studies
(data on file, Proctor & Gamble, Cincinnatti, OH). The
treatment duration was limited to 3 months because
animal toxicology testing had been limited to 3 months of
exposure.
Patients were required to return all used and unused
drug supplies at each visit in order to determine
compliance. During the 1-week run-in period and
throughout the study, patients performed self-monitored
blood glucose (SMBG) measurements before meals and
at bedtime. Insulin dosage was adjusted as needed
throughout the study.
Arginine-stimulated C-peptide was performed following an 8-h overnight fast on day 1, day 56 (T1DM), or day
90 (T2DM), and 30 days after treatment discontinuation
on day 120. Patients delayed diabetes medications the
morning of the test until after completion. Blood samples
for C-peptide were drawn 5 min before the arginine (5
gm) bolus, and at 2.5, 5, 7.5, 10, 15, 20, and 30 min after
the bolus. For the T2DM, blood glucose was adjusted to
450 mg/dL before testing.
Fasting C-peptide (days 1, 28, 56, 90, 120), proinsulin
(days 1, 28, 56, 90, 120), islet cell 512 (ICA512) and GAD
65 antibodies (days 1, 90, 120) were assessed periodically
in SPIRIT 1. Anti-INGAP Peptide IgG antibodies were
examined with an enzyme linked immunosorbent assay
(ELISA) in both studies. Haematology and serum
chemistries were measured periodically for safety.
The efficacy endpoints of primary interest were prespecified as the change in arginine-stimulated C-peptide
and A1C from baseline. Other endpoints included change
in fasting blood glucose (FBG) and mean daily insulin
dose as well as safety and tolerability measures. As prespecified, efficacy results were analysed for patients who
were at least 75% compliant and reported as mean +/−
standard deviation (SD) unless noted otherwise. Safety
analyses were performed in all randomized patients. The
arginine-stimulated C-peptide results were expressed as
an area under the curve (AUC) from 0 to 30 min following
arginine administration. Differences in efficacy endpoints
were determined using analysis of variance (ANOVA).
Statistical significance was established at p values <0.05.
Sample sizes of 20 patients per group (T1DM) and 40
per group (T2DM) were calculated to provide a nominal
80% power to detect a difference of 0.15 and 1.5 ng/mL,
respectively in change in stimulated C-peptide, assuming
a SD of 0.15 ng/mL (T1DM) and 2.5 ng/mL (T2DM).
Forty patients per group (T2DM) also gave a nominal
Diabetes Metab Res Rev 2009; 25: 558–565.
DOI: 10.1002/dmrr
K. M. Dungan et al.
560
80% power to detect a difference of 0.7% in change in
A1C, assuming a SD of 0.8%.
Efficacy
Patients who met entry criteria and were at least
75% compliant (T1DM, N = 51; T2DM, N = 106) were
analysed separately for efficacy (Table 2).
Results
In the T1DM cohort, 63 patients were enrolled, 22 in the
placebo, 21 in the 300 mg, and 20 in the 600 mg groups.
For T2DM, 126 patients were enrolled, 42 in each group.
The treatment groups were well-balanced for baseline
characteristics in both studies (Table 1).
T1DM
The change in stimulated C-peptide from baseline to day
56 was significantly greater than placebo in the 600 mg
group (1.15 ng/mL versus −0.877 ng/mL, p = 0.0058).
Stimulated C-peptide for both treatment groups increased
compared to placebo at day 120, 30 days following
Table 1. Patient characteristics
Type 1 diabetes
Sex
Male
Female
Age
Race
Caucasian
Hispanic
Asian Indian
Weight (kg)
Daily insulin (Units)
Fasting glucose (mg/dL)
HbA1c (%)
Randomized to treatment
Completed
Discontinued
Reason for discontinuation
Adverse event
Voluntary withdrawal
Withdrawal before dose
Type 2 diabetes
Sex
Male
Female
Age
Race
American Indian
Asian Indian
Black
Caucasian
Hispanic
Weight (kg)
Daily insulin (Units)
Fasting glucose (mg/dL)
HbA1c (%)
Randomized to treatment
Completed
Discontinued
Reason for discontinuation
Adverse event
Voluntary withdrawal
Withdrawal before dose
Placebo
300 mg
600 mg
Overall
N = 22
N = 21
N = 20
N = 63
12 (55%)
10 (45%)
39.4 + / − 2.08
9 (43%)
12 (57%)
39.7 + / − 2.04
10 (50%)
10 (50%)
39.8 + / − 2.04
31 (49%)
32 (51%)
39.6 + / − 1.17
21 (95%)
1 (5%)
0 (0%)
83.0 + / − 3.49
49.9 + / − 3.89
181 + / − 12.6
7.30 + / − 0.25
18 (86%)
3 (14%)
0 (%)
77.9 + / − 2.97
49.3 + / − 3.88
169 + / − 13.9
7.44 + / − 0.26
18 (90%)
1 (5%)
1 (5%)
72.4 + / − 5.08
46.0 + / − 5.41
163 + / − 16.5
7.28 + / − 0.16
57 (90%)
5 (8%)
1 (2%)
77.9 + / − 2.28
48.5 + / − 2.49
171 + / − 8.20
7.34 + / − 0.13
22 (100%)
0 (0%)
15 (71%)
6 (29%)
14 (70%)
6 (30%)
51 (81%)
12 (19%)
0 (0%)
0 (0%)
0 (0%)
2 (10%)
4 (19%)
0 (0%)
5 (25%)
0 (0%)
1 (5%)
7 (11%)
4 (6%)
1 (2%)
N = 42
N = 42
N = 42
N = 126
30 (71%)
12 (29%)
57.9 + / − 1.21
25 (60%)
17 (40%)
58.2 + / − 1.10
30 (71%)
12 (29%)
56.4 + / − 1.14
85 (67%)
41 (33%)
57.5 + / − 0.66
1 (2%)
0 (0%)
5 (12%)
32 (76%)
4 (10%)
98.1 + / − 2.53
77.4 + / − 8.64
183 + / − 12.1
7.86 + / − 0.14
0 (0%)
1 (2%)
2 (5%)
29 (69%)
10 (24%)
96.3 + / − 2.27
74.0 + / − 6.45
162 + / − 10.2
7.78 + / − 0.14
0 (0%)
2 (5%)
8 (19%)
26 (62%)
6 (14%)
97.5 + / − 2.56
75.0 + / − 7.85
166 + / − 7.06
8.10 + / − 0.16
1 (1%)
3 (2%)
15 (12%)
87 (69%)
20 (16%)
97.3 + / − 1.41
75.5 + / − 4.40
170 + / − 5.79
7.91 + / − 0.086
36 (86%)
6 (14%)
35 (83%)
7 (17%)
33 (79%)
9 (21%)
85 (83%)
12 (9.5%)
1 (2%)
3 (7%)
2 (5%)
6 (14%)
0 (0%)
1 (2%)
4 (10%)
4 (10%)
1 (2%)
11 (8.7%)
7 (5.6%)
4 (3.1%)
Continuous variables are presented as mean +/− standard error. Dichotomous variables are shown as number of patients plus (percentage).
Copyright © 2009 John Wiley & Sons, Ltd.
Diabetes Metab Res Rev 2009; 25: 558–565.
DOI: 10.1002/dmrr
561
Effects of INGAP Peptide in Type 1 and Type 2 Diabetes
Table 2. Efficacy oparameters (per-protocol population)
Change from baseline
Measure
Placebo
300 mg INGAP
600 mg INGAP
45.4
− 0.48
0.8
138
12
14
169
− 2.99
− 24.17
6.24
− 0.877
− 0.446
7.298
− 0.225
− 0.116
0.188
0.0448
0.0030
13.8
− 1.40
− 1.55
38.2
− 0.1
− 1.6
144
− 15
4
164
− 12.73
7.22
6.14
− 1.86
0.834
7.21
− 0.140
0.0733
0.146
0.0820
0.0867b
15.7
4.80
1.30
45.1
− 1.0
1.0
132
− 1.0
7
147
− 0.75
− 21.02
4.27
1.15a
1.31
7.20
− 0.407
− 0.1571
0.165
− 0.0032
0.0339
12.9
− 0.900
− 2.85
71.1
2.03
2.79
140
0.58
− 5.22
161
11.3
6.09
173
− 4.47
− 5.60e
7.80
− 0.220
− 0.280
3.25
− 0.213
0.665
25.5
1.30a
0.200
60.0
0.00
0.00
147
− 14.4a
− 12.2c
165
22.1
− 6.80
181
7.43d
− 5.27b
8.05
− 0.935a
− 0.728b
3.35
− 0.870
0.303
24.7
− 7.90
− 4.75
Type 1 diabetes
Daily insulin use
(units)
Daily mean glucose
(mg/dL)
Fasting serum glucose
(mg/dL)
Arginine-stimulated C-peptide (AUC)
(ng/mL)
Hb A1c
(%)
Fasting C-peptide
(ng/mL)
Proinsulin
(pmol/L)
Baseline
On-treatment
Washout
Baseline
On-treatment
Washout
Baseline
On-treatment
Washout
Baseline
On-treatment
Washout
Baseline
On-treatment
Washout
Baseline
On-treatment
Washout
Baseline
On-treatment
Washout
Type 2 diabetes
Daily insulin use
(units)
Mean SMBG
(mg/dL)
Fasting serum glucose
(mg/dL)
Arginine-stimulated C-peptide (AUC)
(ng/mL)
Hb A1c
(%)
Fasting C-peptide
(ng/mL)
Proinsulin
(pmol/L)
Baseline
On-treatment
Washout
Baseline
On-treatment
Washout
Baseline
On-treatment
Washout
Baseline
On-treatment
Washout
Baseline
On-treatment
Washout
Baseline
On-treatment
Washout
Baseline
On-treatment
Washout
55.3
− 1.84
− 1.69
140
− 1.43
6.64
153
− 23.9
− 3.11
172
− 14.3
− 24.3
7.86
− 0.467
− 0.243
3.27
− 0.785
0.090
25.9
− 2.25
− 5.80
On-treatment assessments that are commensurate with stimulated C-peptide levels are shown. a p < 0.01, b p < 0.05, c p = 0.064, d p = 0.063,
e p = 0.055 versus placebo.
discontinuation (day 120) but did not attain statistical
significance. There was also a greater increase in fasting
C-peptide between the 300 mg group and placebo after
washout (p = 0.0169) and between the 600 mg group
and placebo at 28 days (p = 0.0033) but not at other
time points (data not shown). Percent change in daily
insulin dose and measures of glycaemic control between
each treatment group and placebo were not significantly
different.
ICA512 antibodies did not change statistically, but five
patients in the 300 mg group had >50% increase in
GAD65 antibody titers, compared to no notable change in
the 600 mg or placebo groups.
Copyright © 2009 John Wiley & Sons, Ltd.
T2DM
There was no significant on-treatment difference in
stimulated C-peptide for either group. There was a
significant difference in stimulated C-peptide in the
600 mg group compared to placebo at day 120, 30 days
after treatment discontinuation (p = 0.0314), but not in
the 300 mg group (p = 0.055).
A1C decreased significantly more with 600 mg than
with placebo at 90 days (−0.47% versus −0.94% in
placebo versus 600 mg group, p = 0.0091) and day
120, 30 days following discontinuation (−0.24% versus
−0.73% in placebo versus treatment group, p = 0.013).
This was associated with a significant reduction in
Diabetes Metab Res Rev 2009; 25: 558–565.
DOI: 10.1002/dmrr
K. M. Dungan et al.
562
mean SMBG at day 90 (−1.4 mg/dL versus −14.4 mg/dL
in placebo versus 600 mg, p = 0.0098) but not after
washout (6.6 mg/dL versus −12.2 mg/dL in placebo
versus 600 mg, p = 0.064). There was no significant
difference in A1C or SMBG between the 300 mg group
and placebo. There was no significant change in daily
insulin dose or FBG.
Safety and tolerability
In T1DM, two patients in the 300 mg group (9.5%) and
five patients in the 600 mg group (23%) withdrew due
to adverse events (AE). 5/7 withdrew due to injection
site reactions, two patients in the 300 mg (one with
nodule, both with pain, and one with stinging) and five
patients in the 600 mg (each due to infusion site reaction,
nodule, pain, and swelling) groups. Two patients (both
in the 600 mg groups) withdrew due to serious AE;
one patient withdrew due to hyperglycemia, and one
patient withdrew due to hypoglycemia. Both events were
assessed as doubtfully related to study drug. All seven
patients recovered from the AEs. The remaining dropouts were unrelated to AEs (voluntary events). The most
common AEs were injection site reactions, none of which
were serious, occurring in 8 (36%) of placebo, 19 (90%)
of the 300 mg, and 15 (75%) of the 600 mg groups
(Table 3). Hypoglycemia was not increased with INGAP
peptide.
In T2DM, 22 patients withdrew overall, including 6
(14%) receiving placebo, 7 (17%) receiving 300 mg, and
9 (21%) receiving 600 mg. Withdrawal due to (AEs)
occurred in 1 (2%) patient in the placebo, 6 (14%)
patients in the 300 mg, and 4 (10%) patients in the
600 mg group. Eight of the 11 patients withdrew due
to injection site reactions, one patient due to urticaria
(placebo group), one due to nausea (300 mg group), and
one patient due to exacerbation of back pain (600 mg
group). Skin reactions leading to withdrawal included
no patients in the placebo group, five patients receiving
300 mg (reported once each was bruising, discomfort,
erythema, induration, pain, pruritus, and stinging, and
while burning was reported twice), and three patients
receiving 600 mg (each reporting pruritus). None of the
withdrawals were due to severe AE. The remaining dropouts were unrelated to AEs (voluntary). Two patients
in the 600 mg group experienced serious AEs, both of
which were assessed as doubtfully related to study drug.
The first patient experienced angina and required stent
placement. The second patient developed cellulitis during
the washout period. Both patients completed the study.
The most common AEs were injection site reactions,
occurring in 14 (33%) of placebo, 27 (64%) of the
300 mg, and 29 (69%) of the 600 mg groups (Table 3).
Hypoglycemia occurred in one subject (2%) of the placebo
group, compared to four (10%) of each treatment group.
Five T1DM patients receiving INGAP peptide and
eight T2DM patients receiving INGAP peptide or
placebo developed less than 2-fold elevation in lactate
dehydrogenase. In the T2DM cohort, 18 patients from
all three treatment groups developed less than 3-fold
elevation in creatinine kinase (CK). These abnormalities
possibly reflect unintentional intramuscular injection as
there was no evidence to suggest myocardial damage. In
the T1DM cohort, nine patients (five receiving 300 mg,
three receiving 600 mg, and one receiving placebo) had
less than 2-fold elevations in amylase or lipase. In all cases,
the abnormalities normalized by day 120, 30 days after
discontinuation, and there were no cases of pancreatitis.
Elevated eosinophil counts occurred in 14 cases with
T1DM and 25 cases with T2DM among patients receiving
INGAP peptide, and resolved in all by day 120. There
Table 3. Adverse events (all patients)∗
Type 1 diabetes
Type 2 diabetes
Placebo
(N = 22)
300 mg
(N = 21)
600 mg
(N = 20)
Placebo
(N = 42)
300 mg
(N = 42)
600 mg
(N = 42)
n (%)
n (%)
n (%)
n (%)
n (%)
n (%)
18 (82%)
1 (5%)
0 (0%)
0 (0%)
19 (90%)
0 (0%)
2 (10%)
0 (0%)
19 (95%)
1 (5%)
5 (25%)
0 (0%)
30 (71%)
0 (0%)
1 (2%)
0 (0%)
38 (90%)
0 (0%)
6 (14%)
0 (0%)
36 (86%)
2 (5%)
4 (10%)
0 (0%)
AE classiÞcation by organ system
n (%)
n (%)
n (%)
n (%)
n (%)
n (%)
Arthralgia
Diarrhoea
Injection and infusion site reactions
Headache
Hypoglycemia
Upper respiratory infection
Urinary tract infection
Gastroenteritis
Nausea/vomiting
2 (9%)
1 (5%)
8 (36%)
3 (14%)
3 (14%)
9 (41%)
0 (0%)
2 (9%)
0 (0%)
0 (0%)
19 (90%)
0 (0%)
2 (10%)
2 (10%)
3 (14%)
1 (5%)
1 (5%)
3 (15%)
15 (75%)
1 (5%)
2 (10%)
3 (15%)
0 (0%)
2 (10%)
4 (10%)
14 (33%)
4 (10%)
1 (2%)
4 (10%)
1 (2%)
27 (64%)
3 (7%)
4 (10%)
6 (14%)
1 (2%)
29 (69%)
5 (12%)
4 (10%)
5 (12%)
5 (12%)
2 (5%)
2 (5%)
Number of patients
Any adverse events (AEs)
Serious AEs
Withdrew from study due to AEs
Died
N, number of patients within specified treatment group; n, number of patients who reported adverse events within specified treatment group; %,
percent of patients who reported adverse events within specified treatment group; ∗ , AEs with an overall frequency ≥5% are shown.
Copyright © 2009 John Wiley & Sons, Ltd.
Diabetes Metab Res Rev 2009; 25: 558–565.
DOI: 10.1002/dmrr
Effects of INGAP Peptide in Type 1 and Type 2 Diabetes
were no systemic allergic reactions and there were no
other significant laboratory abnormalities.
In patients with T1DM, antibodies to INGAP peptide
were moderate (1 : 200–1 : 800) or high (>1:800) in 10
(48%) of the 300 mg group and 8 (40%) of the 600 mg
group by day 90. In patients with T2DM, antibodies to
INGAP peptide were moderate (1 : 200–1 : 800 at one or
more time points) or strong (>1:800 at one or more
time points) in 1 patient receiving placebo, 26 receiving
300 mg, and 15 patients receiving 600 mg INGAP peptide.
Discussion
In patients with T1DM, autoimmune destruction of beta
cells leads to absolute insulin deficiency. In the case
of T2DM, insulin resistance plays a major role in the
pathophysiology, but the primary reason for deterioration
in glycaemia is progressive beta cell failure [2]. Evidence
is growing to support that islet regeneration continues
throughout life in non-diabetic and diabetic people [3]. No
treatment has been demonstrated to reverse the decline in
beta cell secretory capacity in humans with T1 or T2DM.
These proof of concept studies are the first to report
the results of an agent developed specifically to induce
regeneration in subjects with T1 and T2DM.
In T1DM, a significant increase in arginine stimulated
C-peptide was seen during therapy with 600 mg of INGAP
peptide, though much of this effect was lost by 30 days
after treatment. A limitation is that no stimulated Cpeptide was performed on day 90. This suggests an
augmentation in endogenous insulin secretion that did
not persist following cessation of therapy, possibly due
to persistent autoimmune destruction of new beta cells.
As these were proof of concept studies, a per-protocol
analysis only was performed. It is acknowledged that the
drop-out rate in the T1DM study in particular raises the
possibility that an intention-to-treat analysis would have
shown no statistical effect at all. It is unclear whether the
lack of persistent effect in the 300 mg group could also be
explained by the increase in GAD antibody titers, which
occurred predominantly in this group.
Assessment of clinical outcomes that result from
therapeutic preservation or restoration of islet tissue
will ultimately require large studies with long-term
follow-up. However, in patients with T1DM, return of
endogenous insulin secretion reflects reversal of the
primary hormone deficiency state and is expected to
correlate with clinical benefits. An American Diabetes
Association-sponsored workshop recommended, and the
Food and Drug Administration (FDA) has recently
accepted, measures of C-peptide as the primary efficacy
outcome for therapies that are intended to preserve
or restore insulin secretion [13,14]. The glucagon
stimulation test has been advocated as a validated
means of standardizing C-peptide assessment, with the
major drawback being nausea [15]. However, since the
workshop, and after the implementation of this study,
Copyright © 2009 John Wiley & Sons, Ltd.
563
the mixed meal tolerance test (MMTT) was recently
reported to be more sensitive and reproducible than the
glucagon stimulation test [16]. Previous data support the
reproducibility, sensitivity, tolerability, and ease of use
of arginine-stimulated C-peptide for measuring beta cell
function compared to an MMTT [17]. Arginine-stimulated
C-peptide correlates with islet cell mass and insulin
independence in animal models and in islet cell transplant
patients [18,19]. The major advantages of the argininestimulated C-peptide are that it takes less time than the
MMTT and is not subject to variability in gastrointestinal
absorption. However, compared to glucagon stimulation
and MMTT, the arginine stimulation test has been less
well-studied overall.
A dose response is suggested during treatment in
patients with T2DM, in which stimulated C-peptide was
better maintained in the 600 mg group compared to
placebo, but only after study drug discontinuation (day
120). The reason for the difference in results with patients
having T1DM is unclear. One explanation is the difficulty
in assessing beta cell function in the setting of improving
glycaemic control among patients with insulin resistance
[3]. Furthermore, the high variability in C-peptide in the
T2DM cohort reduces the ability of the study to detect a
change in stimulated C-peptide.
In T2DM, mean SMBG and A1C were significantly
lower in the 600 mg group compared to placebo at
day 90 and A1C was also significantly lower following
discontinuation (day 120). The improvement in SMBG
was not sustained after washout. Additional studies
are necessary to determine whether longer exposure
to INGAP peptide is beneficial. Since C-peptide was
marginally affected, increased insulin secretion, measured
with the current technique, does not entirely explain the
improvement in glycaemic control observed in T2DM.
In vitro data have demonstrated that INGAP peptide
enhances glucose-dependent insulin secretion in rat islet
cultures, suggesting that INGAP peptide may enhance
beta cell function acutely in the absence of neogenesis
[20,21].
The results from this study differ from that of patients
with T1DM in which only a trend in improved glycaemic
control was seen. This may be a result of fundamental
differences in pathophysiology between T1DM and T2DM,
or differences in statistical power between the two trials
to assess outcomes: the T1 trial with greater power
for C-peptide and the T2 trial for HbA1c. Assessments
of glycaemic control are dependent upon a variety of
factors, including insulin dosage, diet, and activity levels,
factors which may be more easily influenced in patients
with T2DM. Patients with T2DM have greater beta
cell reserve and presumably more islet progenitor cells
and may therefore manifest improvements in glycaemic
control more readily in response to INGAP therapy than
patients with T1DM. The antibody response to INGAP
in both studies raise the possibility of antibodies to
the peptide; the assay employed, however, does not
determine whether there was neutralizing activity and
thus further studies are needed.
Diabetes Metab Res Rev 2009; 25: 558–565.
DOI: 10.1002/dmrr
K. M. Dungan et al.
564
One last difference between the two groups was a nearly
3-fold greater drop-out rate in T1DM than in T2DM, all
largely due to injection site reactions. Differences in body
habitus may play a role in tolerability. The injection site
reactions were likely a result of pH, as all patients received
the same volume.
There is a rationale for combination therapy with
immunomodulatory agents (to reduce ongoing autoimmune losses in the case of T1DM) or other agents thought
to have beta cell protective or proliferative effects (as
in the case of either T1 or T2DM). Future study should
address whether controlling active islet autoimmunity
will improve the result of INGAP peptide therapy in
T1DM. Immunomodulators have shown efficacy in reducing decline of C-peptide secretion in subjects with recently
diagnosed T1DM [22,23]. INGAP peptide when combined with lisofylline, an IL-12 signal inhibitor, induced
remission of diabetes and histologic evidence of islet
regeneration in non-obese diabetic (NOD) mice with
established T1DM, while INGAP peptide therapy alone
showed limited activity [11]. It is also possible that efficacy of INGAP peptide could be augmented by one of
several agents related to endogenous signals implicated
in the regulation of islet regeneration [23,24], such as
incretins [25,26], or agents that exhibit beta cell antiapoptotic properties, such as thiazolidinediones [5].
In conclusion, daily short-term administration of INGAP
peptide in patients with T1DM resulted in evidence
of increased endogenous insulin secretion in the perprotocol analysis, whereas in patients with T2DM,
improvements in glycaemic control were observed. In
this treat-to-glycaemic target setting, INGAP therapy did
not result in statistically significant reductions in insulin
use. Injection site reactions were the most common
adverse effects. In addition to combination therapies
discussed above, further study is indicated to determine
whether INGAP peptide might be observed with the
following: (1) longer courses of therapy, (2) addressing
the short half-life of the peptide by dividing the daily
dose among two or more spaced injections to prolong
target tissue exposure, (3) treatment during favourable
conditions such as normalized glycaemia and early in
the course of disease, and finally, (4) better tolerated
formulations. These proof of concept study results suggest
that continued development of INGAP peptide in patients
with T1DM and T2DM is warranted.
Supporting information
Supporting information may be found in the online
version of this article.
Acknowledgements
This study was supported by Proctor & Gamble, Inc, (Cincinnatti,
OH). Post-trial analysis was supported by Exsulin Corporation,
Burnsville, MN. Additional support was provided through
Copyright © 2009 John Wiley & Sons, Ltd.
National Institutes of Health grant # RR-000046 and the John
and Mary Cleghorn Foundation. J.B. and R.R. were investigators
in the study and their institutions received compensation through
contracts with Proctor & Gamble, Inc. for this work but no direct
payments were made to either author. K.D. has no relevant
conflicts.
Conflict of interest
None declared.
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