Impact of Studies Predating Rituximab

1. Achieving better cytotoxic potential of NK cells for
immune potency & mAb therapy such as Rituxan.
Colin M Perrott
Engineering of newer anti-CD20 mAbs attempts to increase their ADCC
effectiveness substantially, often at the cost of CDC efficiency.
Serum can augment NK cell cytotoxicity beyond that of media.
We propose this cytotoxic stimulation arises from serum DHEAS via
PKC-βII activation and relies on continued enzymatic transformation
of cholesterol.
1

2. Abstract
We review the broad functions by which Rituxan eliminates B-cells and note that newer mAb’s are
engineered to increase the binding affinity required for cell lysis by ADCC, loss in CDC
performance notwithstanding. A simple process model that we described recently underscores
this logic. It demonstrates also that the final process efficiency achieved via the mAb is
necessarily a multiple of the baseline cytotoxity of critical effector cells such NK cells. It is
important therefore to understand the spectrum of natural factors that stimulate and also inhibit NK
cell cytotoxicity as the processes of aging and also illness ensue.
Recently we concluded that enhanced Rituxan induced B-cell lysis in serum likely arises from
heightened NK cell cytotoxicity compared to that achieved in vitro with standard laboratory media.
We surmised that the androgenic steroid ester DHEAS could be the key stimulant factor. Here, we
describe some available research data which shows DHEAS is a powerful stimulator of NK cell
cytotoxicity and acts in conjunction with known agents such as IL-2. Furthermore, this effect is
opposite the inhibitory role of glucocorticoids. Additionally, DHEAS is known to act beneficially on
the NF-kB cellular pathway but via a different mechanism from that of glucocorticoid binding.
Given that DHEAS is the most abundant steroid in human serum and declines sharply with
advancing age, it is important to determine options for managing this hormone beneficially in the
normal course of healthy living - and also as a precursor to mAb therapy such as with Rituxan.
Since there are known antagonists to its function, these should be explored in an attempt to
achieve a comprehensive model of the impost of age on immune potency.
April 2009 Cytotoxic potential in mAb therapy : 2
Colin M Perrott

3. IgG1 is not a stick insect !
Despite the Pictures we see at times.
Domains are closely paired – except for CH2 domains near the hinge region.
Antigen Binding
HINGE
Complement Activation
Effector Cell Binding
Sources: Center for BioMolecular Modeling;http://www.rpc.msoe.edu/cbm2/IgG.html Sharkey & Goldenberg CA Cancer J Clin (2006)
April 2009 Cytotoxic potential in mAb therapy : 3
Colin M Perrott

4. INDICATIONS AND USAGE
Rituxan® (rituximab) is indicated for single agent treatment of patients with:
• Relapsed or refractory, low-grade or follicular, CD20-positive, B-cell NHL
• Non-progressing (including stable disease), low-grade, CD20-positive B-cell NHL after first-line CVP
http://www.rituxan.com/lymphoma/hcp/MOA/index.m
ADCC (antibody-dependent cell-mediated cytotoxicity):
Natural killer cells, T cells, and macrophages recognize and
kill antibody-labeled target cells, leading to cell lysis
April 2009 Cytotoxic potential in mAb therapy : 4
Colin M Perrott

5. INDICATIONS AND USAGE
Rituxan® (rituximab) is indicated for combination treatments of:
• Previously untreated follicular, CD20-positive, B-cell NHL in combination with CVP chemotherapy
• Previously untreated diffuse large B-cell, CD20-positive NHL in combination with CHOP or other
anthracycline-based chemotherapy regimens http://www.rituxan.com/lymphoma/hcp/MOA/index.m
CDC (complement-dependent cytotoxicity):
Binding of the antibody recruits complement proteins,
which punch holes in the cell membrane, flooding the
cell and leading to cell lysis
Apoptosis:
Binding of the antibody signals the cell
to self-destruct resulting in cell lysis.
Apoptosis is regarded as relatively
ineffective in actual therapy.
April 2009 Cytotoxic potential in mAb therapy : 5
Colin M Perrott

6. CDC and ADCC
One process acts on CH2 and the other on CH3
Are they mutually exclusive – given that domains CH2 are not closely paired ?
Two regions of the CH2 domain are critical for FcγR’s and complement C1q binding.
Mutations made in the CH2 domain can increase both ADCC and CDC
Mutations at the interface CH2 / CH3 can increase the half-life of IgG1
Residue material bound into the hinge region has significant effect on performance
Simplistic signal analysis:
∇ The CH3 and variable domains communicate via the molecular backbone near the hinge
∇ The detailed electrochemical processes reflect the entire molecular structure of the region
∇ Changes occurring or created at CH2 may influence CH3 signaling and vice-versa
Source: Invivogen: http://www.invivogen.com/family.php?ID=164
April 2009 Cytotoxic potential in mAb therapy : 6
Colin M Perrott

7. New anti CD20 monoclonal antibodies for B-cell non-Hodgkin lymphoma
GA-101
Glycol-engineered Fc portion and a modified elbow hinge. 50-fold higher
binding affinity to the FcRIIIa resulting in a 10 to 100-fold increase in ADCC in
vitro. Apoptosis inducer. Reduced CDC effectiveness.
AME-133v
Binds with an increased affinity to FcRIIIa (CD16): 10-fold increase found in
cytotoxicity relative to rituximab in vitro. Phase 1/2 study ongoing for patients
with relapsed/refractory follicular lymphoma
rhuMAb v114
30-fold greater binding to the low-affinity variant of FcRIII than to
rituximab: 2 to 10 times improved ADCC relative to rituximab in vitro.
Ofatumumab (HuMaxCD20)
Humanized antibody that binds to a different CD20 epitope than rituximab:
Phase 1/2 trials demonstrated activity in patients with follicular lymphoma and
CLL.
IMMU-106 (hA20)
Humanized antibody: Phase 1/2 studies showed a 53% ORR in patients with
recurrent B- cell NHL, including 6 patients that achieved CR.
Source; Bello and Sotomayor (2007) Hematology, 233-242
ADCC, antibody-dependent cell-mediated cytotoxicity; CLL, chronic lymphocytic leukemia;
ORR, overall response rate; CR, complete response
April 2009 Cytotoxic potential in mAb therapy : 7
Colin M Perrott

8. There are new mAbs in the pipeline.
Notice :
There is an interaction between expected ADCC and CDC performances.
Designs attempt huge proportional changes to the binding affinity FcγR.
Why ?
The philosophy seeks uniform effectiveness across a broad range of
CD20 expression levels from CLL upward.
-- But --
Success relies on plentiful stimulated effector cells in vivo.
April 2009 Cytotoxic potential in mAb therapy : 8
Colin M Perrott

9. Rituxan lysis of B-cells is parameter sensitive
Constituents of serum are very important to the total outcome of therapy
MODEL OF RITUXAN LYSIS
1
0.9
0.8
Cell Lysis Probability
0.7
0.6
0.5
0.4
0.3
ADCC in media
0.2
CDC by serum
Lysis in Serum
0.1
Idealized Process
0
0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85
ABS CD20 expression (millions)
WM B-cell CD20 expression is in the range ~ 0.3 to 0.6 million/cell
April 2009 Cytotoxic potential in mAb therapy : 9
Colin M Perrott

10. There is quite a lot we can
understand just from the math
The results show that CDC and
ADCC do not exclude each other.
They are alternatives for cell lysis
10

11. Predicted gain from improved NK cell Cytotoxicity
A significant gain occurs from media to serum, but
♣ very big steps are still required from there !
MODEL: CDC + variable ADCC Cytotoxicity
1
0.9
Cell Lysis Probability
0.8 ADCC in media
Lysis in Serum
2x Cytotoxicity
0.7
4x Cytotoxicity
16x Cytotoxicity
0.6
0.5
0.4
0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85
ABS CD20 expression (millions)
WM B-cell CD20 expression is in the range ~ 0.3 to 0.6 million/cell
April 2009 Cytotoxic potential in mAb therapy : 11
Colin M Perrott

12. Near enough does not fill the gap!
Survivor cells may range up to 30% in human serum.
They will attempt to proliferate
- cell populations always attempt to exploit available resources
- the population declines if resources cannot be used
- higher initial cell populations show more dramatic response
OPPORTUNISTIC GROWTH
1
Bi-level Systems
1
0.8
POPULATIONNêK
POPULATION NêK
0.8
0.6
0.6
0.4 0.4
0.2
0.2
0 20 40 60 80 100
PERIOD T 60 80 100 120 140 160
PERIOD T
April 2009 Cytotoxic potential in mAb therapy : 12
Colin M Perrott

13. Predicted gain from improved NK cell Cytotoxicity
What matters is the number of cells surviving….
….and the NK cell cytotoxicity in patients’ serum
MODEL: CDC + variable ADCC Cytotoxicity
0.6
Cell Survival Probability
0.5
ADCC in media
0.4
Lysis in Serum
2x Cytotoxicity
0.3 4x Cytotoxicity
16x Cytotoxicity
0.2
0.1
0
0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85
ABS CD20 expression (millions)
WM B-cell CD20 expression is in the range ~ 0.3 to 0.6 million/cell
April 2009 Cytotoxic potential in mAb therapy : 13
Colin M Perrott

14. What might the cytotoxic enhancement involve?
Proposition from in vitro studies:
ADCC and CDC operate in a complementary fashion.
We concluded:
Serum augments the cytotoxity of effector cells ( stimulated NK cells)
substantially in comparison to the level achieved by IL-2 based media.
Model Features:
The enhancement has constant magnitude for all CD20 expression.
There is a simple up-scaling of the cytotoxic efficiency of the effector cells
as a result of the introduction of human serum.
Model Outcomes:
Complement is essential to cell lysis at all CD20 expression levels
CDC is the prime mechanism at CD20 higher than ~ 650K/cell
ADCC provides the baseline performance and is environmentally sensitive
Critical Point:
Process enhancement by serum is probably due to NK cell cytotoxicity
being heightened by a component of the serum… most likely DHEAS
April 2009 Cytotoxic potential in mAb therapy : 14
Colin M Perrott

15. The active factor must be plentiful in serum of healthy people
It must stimulate NK cells
Be an agonistic with IL-2
A logical contender is serum DHEAS
Source: Kiechl, S. et al. Arterioscler Thromb Vasc Biol 2000;20:1094-1100
April 2009 Cytotoxic potential in mAb therapy : 15
Colin M Perrott

16. THE CHOLESTEROL ENGINE
CHOLESTEROL TNF, IL-1β
ACTH IL-1β, TGF-β SULFOTRANSFERASE,
Sult2A1
TNF
DHEA DHEAS
IL-6
DEHYDROEPIANDOSTERONE DHEA SULFATE
IL-6
IL-6 SULFATASE
TNF
PROMOTER
SUPPRESSOR
ALDOSTERONE CORTISOL
THE ENGINE RESPONDS TO HORMONES, AGE & CYTOKINES
DHEAS IS AN ABUNDANT PRO-HORMONE IN THE SERUM OF HUMANS
AND PRIMATES. RODENT MODELS CAN BE MISLEADING.
ACTH = Corticotrophin, a hormone secreted by the anterior pituitary gland
All steps in the reaction pathways are dependent on specific enzyme activity.
April 2009 Cytotoxic potential in mAb therapy : 16
Colin M Perrott

17. AN OVERVIEW OF LITERATURE;
Komaki et al recorded serum DHEAS increase during fasting by non-obese
individuals from ~5.5 to ~8.0 μmol/L. This had associated x1.75 increase in
spontaneous natural killer (NK) cell cytotoxicity without change in the dominant
cytokines (IL-1β, IL-2, IL-6, TNF-α, IFN-γ), in GM-CSF, sIL-2R or corticotrophin.
The cytotoxic function (NKCC) of NK cells is regulated by:
An autocrine mechanism related to cytokines [e.g. IL-2, IFN-γ, and IFN-β], or
Protein kinase C (PKC)-dependent mobilization of proteolytic granules.
Solerte et al report dose dependent enhancement of NKCC by DHEAS that
correlates positively with locally generated insulin-like growth factor IGF-1. This
and other data favor mechanistic action by PKC (specifically PKC-βII isoform)
activation. This agrees with other studies of DHEAS effect on the NF-κB pathway.
The IGF-1 might also regulate pro-inflammatory cytokine responses contrary to the
immunosuppressive action of glucocorticoids.
Specificity to the PKC-βII isoform is important. It determines functional outcomes
and requires precision in attempts at mediation or interpretation of dynamic
effects. In other cell types, PKC-βII and VEGF expression increase concurrently.
April 2009 Cytotoxic potential in mAb therapy : 17
Colin M Perrott

18. DHEAS and IL-2 stimulate NK cell cytotoxicity
S. B. Solerte et al, Dehydroepiandrosterone Sulfate Enhances Natural Killer Cell Cytotoxicity in Humans Via
Locally Generated Immunoreactive Insulin-Like Growth Factor I, J Clin Endocrinol Metab 84: 3260–3267, 1999
Variations in NKCC, expressed as the percent increase in cytotoxicity, after incubation with DHEAS (from 10-8-10-5 mol/L·mL);
a) DHEAS plus SST (10-6 mol/L·Ml); b) DHEAS plus IL-2 (100 IU/mL), and; c) IL-2 plus SST.
Data (mean ± SD) are related to healthy young (open bars) and healthy elderly (closed bars) subjects.
Asterisks denote statistical significance between groups * P<0.05 and ** P<0.01
Patient age had limited effect on NK cell responses.
NK cell action generates Immunoreactive Insulin-Like
Growth Factor IGF-I. This was suppressed by
somatostatin-14 (SST). SST inhibits intracellular
signaling via cAMP, acts against growth hormone and
many other hormones. It comes from hypothalamic and
CNS neurons, pancreatic cells and cells in the GI
epithelium.
April 2009 Cytotoxic potential in mAb therapy : 18
Colin M Perrott

19. DHEAS and IL-2 stimulate NK cell cytotoxicity
Variations in NKCC, expressed as lytic response (LU) after incubation with DHEAS (from 10-8-10-5 mol/L·mL; a), DHEAS plus
SST (10-6 mol/L·mL; b), and DHEAS plus IL-2 (100 IU/mL; c). Data (mean ± SD) are related to healthy young (open circles) and
healthy elderly (closed circles) subjects. Asterisks denote statistical significance between groups at P < 0.05 (*) and P < 0.01 (**).
Solerte, S. B. et al. J Clin Endocrinol Metab 1999;84:3260-3267
NK cells from older patients showed about half the NKCC
responsiveness of those from younger patients: x1.50
increase in NKCC for the young and x1.25 increase for
the older at the first dosage level for DHEAS.
Our Rituxan lysis model required ADCC efficiency
increase by x1.43 from 47.2 ±13.8% to 67.6 ± 8.5%.
SST suppressed the benefits of both DHEAS and IL-6.
April 2009 Cytotoxic potential in mAb therapy : 19
Colin M Perrott

20. Conclusions
Our model is consistent with current objectives in mAb development.
It underscores the importance of spontaneous cellular cytotoxicity.
The data is consistent with NK cell cytotoxicity stimulation by DHEAS
in the absence of cytokine or other chemical / hormonal assistance.
Age-related or illness induced decline of DHEAS level potentially sets
the baseline for
☻ innate immune resilience, and
☻ response to Rituxan or like mAb therapy.
SUPPLEMENTARY INFORMATION FOLLOWS
20

21. Complement lysis mechanisms
CDC & CDCC
CDCC
CDC
After Catron et al, (2004) doi:10.1182/blood-2004-03-1110
April 2009 Cytotoxic potential in mAb therapy : 21
Colin M Perrott

22. Possible interactions of complement, serum and effector cells
♣ ADCC, ♣ CDCC and ♠ S-ADCC (with DHEAS assist)
ADCC
S-ADCC ?
DHEAS
CDCC
Modified From Zhou, X. et al. Oncologist 2008;13:954-966
April 2009 Cytotoxic potential in mAb therapy : 22
Colin M Perrott

23. A ROLE FOR PENDANT SPECIES ON THE IgG ?
Complement activation occurs at CH2, close to the hinge region.
This region is between the reactive ends, CH3 in Fc and CDR’s on Fab.
Electrochemical changes might influence flexibility and receptor affinity.
Fa
Fa b
b
Fa
b
b
Fa
Fc
Fc
Fab
ab
F
Fc
April 2009 Cytotoxic potential in mAb therapy : 23
Colin M Perrott

24. April 2009 Cytotoxic potential in mAb therapy : 24
Colin M Perrott

25. THE CHOLERSTEROL ENGINE IN SOME MORE DETAIL
April 2009 Cytotoxic potential in mAb therapy : 25
Colin M Perrott

26. AN INTERESTING STUDY;
DHEAS CORRELATES WITH NK-CELL CYTOTOXICITY IN SERA FROM PATIENTS DURING
FASTING ( BMI~20 ). NO CHANGES WERE DETECTED IN IL-2 OR OTHER CYTOKINES.
G Komaki et al, American Journal of Clinical Nutrition (1997) 66: 147-152
Alterations in lymphocyte subsets and pituitary-adrenal gland-related hormones during fasting
We investigated changes in the immunoendocrine system during fasting. Ten hospitalized patients aged 14-46 y with
psychosomatic disorders fasted for 7 or 10 d. Blood samples were collected before and on days 3 and 7 of the 7-d
fasts. When fasting continued to 10 d, an additional sample was taken on day 10. We measured blood cellularity (white
blood cells and total lymphocytes), the total number and percentage of lymphocyte subsets (CD2, CD3, CD4, CD8, and
CD19), natural killer (NK) cell activity, cytokines (interleukin 1 beta, interleukin 2, interleukin 6, granulocyte-macrophage
colony stimulating factor, tumor necrosis factor alpha, and interferon gamma), and soluble interleukin 2 receptors.
Corticotropin, cortisol, and dehydroepiandrosterone sulfate (DHEAS) concentrations were also determined. Although
the total number of lymphocytes decreased during fasting, NK cell activity increased significantly. Plasma cortisol and
DHEAS concentrations also increased significantly whereas changes in corticotropin concentrations were not
significant. The total number and percentage of CD4 cells decreased significantly during fasting but no other
lymphocyte subsets changed significantly. The percentage of CD4 cells was negatively correlated with cortisol
concentrations during fasting. No detectable changes occurred in cytokines or soluble interleukin 2 receptors during the
study. All measured immunoendocrine values that changed during fasting returned to pre-fasting values during the re-
feeding period. These findings indicate that fasting affects immune variables such as T cell subsets and NK cell activity
at least in part through changes in adrenal gland-related hormones.
Serum DHEAS increase from ~5.5 to ~8 μmol/L was associated with increased
NK cell cytotoxicity from ~16 CU to ~28 CU, being a ratio of x 1.75.
April 2009 Cytotoxic potential in mAb therapy : 26
Colin M Perrott

27. A MORE EXACTING STUDY;
S. B. Solerte et al, Dehydroepiandrosterone Sulfate Enhances Natural Killer Cell Cytotoxicity in Humans Via
Locally Generated Immunoreactive Insulin-Like Growth Factor I, J Clin Endocrinol Metab 84: 3260–3267, 1999
Experimental and clinical investigations suggest the hypothesis that dehydroepiandrosterone sulfate (DHEAS) can
positively influence natural killer (NK) immunity via locally produced insulin-like growth factor I (IGF-I) from NK cells. In
the present study, the NK cell cytotoxicity (NKCC) and IGF-I levels in the supernatant of NK cells were studied at
baseline and after exposure to various molar concentrations of DHEAS (from 1025-1028 mol/LzmL/7.75 3 106 NK cells)
in healthy subjects of young and old age. DHEAS-induced NKCC was also determined after DHEAS coincubation with
somatostatin-14 (1026 mol/LzmL/7.75 3 106 NK cells) and with interleukin-2 (IL-2; 100 IU/mLz7.75 3 106 NK cells). NK
cells were previously isolated by Ficoll-Hypaque density gradient and then by immunomagnetic procedure; the purity
obtained was 97 6 1%. NKCC was determined against K562 tumoral targets. We observed that the increase in NKCC
after DHEAS exposure was dose dependent and was correlated with the amount of IGF-I released in the supernatant of
cultured NK cells. NKCC and IGF-I generation from NK cells were more elevated in healthy elder subjects than in
healthy young subjects. The coincubation of DHEAS with somatostatin-14 (SST) significantly suppressed NKCC and
IGF-I release from NK in both groups, whereas higher NKCC was found after DHEAS plus IL-2 exposure than after
incubation with DHEAS alone. Taken together, this study suggests a role for NK-generated IGF-I in the modulation of
NKCC by DHEAS in humans. Although DHEAS may contribute to the IL-2-mediated NKCC, its activity on NK cytolytic
function can be dependent on a autocrine mechanism (IGF-I-mediated), probably independent of cytokine activation.
The higher NKCC response to DHEAS found in old subjects than in younger might counterbalance the age-dependent
decline in circulating DHEAS, thus contributing to maintain the pattern of NK immunity during aging.
Note: NK cells were separated from patient’s PMBC, suspended in a standard medium and then tested for cytotoxicity
with the medium alone and also with additions of laboratory supplied DEAS, IL-2, and SST. Patient BMI was ~22
across the cohort.
April 2009 Cytotoxic potential in mAb therapy : 27
Colin M Perrott