1. Structure/Function Analysis of
Complement C3 and the Early
Development of Modified C3
Proteins as a Possible
Therapeutic
David C. Fritzinger, Ph.D.

2. Complement System
• Part of the Innate Immune System
• Ancient
• Predates Adaptive Immune System
• Present in all vertebrates, some invertebrates
• Complete system present in bony fish, more primitive
organisms have more primitive complement system
• Recognizes non-self surfaces
• Targets for phagocytosis
• Activation of complement can result in cell lysis
• Provides a link between the innate and adaptive immune
systems
• Consists of more than 30 proteins
• Cell surface and solution phase

3. Complement Pathways

4. Regulation of Alternative Pathway:
Fluid Phase Proteins
• Factor H
• Binds to C3b and prevents binding of factor B
• Serves as cofactor for the cleavage of C3b by factor I
• Factor I
• Cleaves C3b when bound to fH
• Cleavage products cannot form convertase

5. Change in structure between C3
and C3b
C3 C3b

6. Complement and Disease
• Complement is part of the host defense against disease
organisms.
• Under certain circumstances, inappropriate activation of
complement can cause, or be a contributing factor in certain
diseases
• Ischemia/Reperfusion injuries
- Stroke
- Myocardial infarction
• Rheumatoid Arthritis
• Myasthenia gravis
• Others

7. Naja kaouthia

8. Similarity of CVF to C3 from Different Species

9. Comparison of the structures of C3 and
Cobra Venom Factor (CVF)

10. Crystal Structures of C3b, C3c and CVF
C3b C3cCVF
Cub Domain Cub Domain

11. Alternative Pathway C3 Convertases
Formation
C3b + Factor B
CVF + Factor B
Factor D
Factor D
Mg++
Mg++
C3bBb + Ba
CVFBb + Ba
Function
C3 + H2O
C3bBb or CVFBb
C3b + C3a

12. Properties of C3b,Bb and CVF,Bb
C3b,Bb CVF,Bb
T1/2 at 37 o
C 1.5 min. 7 hr.
Inactivation by Factors H and I Susceptible Resistant
C5 Convertase Activity - +
Site of Action Cell Surface Fluid phase

13. Implications of the stability of the CVF-
containing Convertase
• Because of the convertase stability and resistance to
regulators of complement activity:
• CVF is able to exhaustively activate complement in vitro
and in vivo
• This property has therapeutic implications, in that
complement-mediated diseases could be treated by
depleting complement.

14. In vivo complement depletion by CVF
Rat Human

15. Two parts to talk
• Preparation of a Humanized CVF (Substitution of CVF
sequences into human C3)
• Characterization of a number of hybrid proteins
• Preclinical testing of one Humanized CVF
• Toxicity testing
• Possible therapeutic in disease models

16. Humanization” of CVF
• CVF/cobra C3 substitutions demonstrated that the
C-terminus of CVF β-chain (C3 α-chain) is important
for C3 function and for functional differences between
C3 and CVF
• Prepared series of hybrid proteins in which portions of
the C-terminus of the α-chain of human C3 replaced
with homologous CVF sequences.

17. Human C3/CVF hybrids
Human C3

18. Complement Depletion

19. Factor B Cleavage

20. C3 Conversion

21. Measuring convertase decay by SPR!
HC3-1550-4
HC3-1550 1491 RFYHPEKEDGKLNKLCRDELCRCAEENCFIQKSDDKVTLEERLDKACEPGVDYVYKTRLVRIEEQDGNDI 1560
|||||||||||||||||||||||||||||||||||||||||||||||| |||||||||||||||||||||
HC3-1550-4 1491 RFYHPEKEDGKLNKLCRDELCRCAEENCFIQKSDDKVTLEERLDKACETGVDYVYKTRLVRIEEQDGNDI 1560
||||| | | | |.| .|||| |.| ... . ...|||||.|||||||.|.||||||||||
HC3-1496 1491 RFYHPDKGTGLLNKICIGNVCRCAGETCSSLNHQERIDVPLQIEKACETNVDYVYKTKLLRIEEQDGNDI 1560
(31.2 hr.)
(2.4 hr)
(4.3 min)
(3.9 hr)

22. Ionic Interactions between C3b or
CVF and factor B:
HC3-1550-4
HC3-1550 1491 RFYHPEKEDGKLNKLCRDELCRCAEENCFIQKSDDKVTLEERLDKACEPGVDYVYKTRLVRIEEQDGNDI 1560
|||||||||||||||||||||||||||||||||||||||||||||||| |||||||||||||||||||||
HC3-1550-4 1491 RFYHPEKEDGKLNKLCRDELCRCAEENCFIQKSDDKVTLEERLDKACETGVDYVYKTRLVRIEEQDGNDI 1560
||||| | | | |.| .|||| |.| ... . ...|||||.|||||||.|.||||||||||
HC3-1496 1491 RFYHPDKGTGLLNKICIGNVCRCAGETCSSLNHQERIDVPLQIEKACETNVDYVYKTKLLRIEEQDGNDI 1560
CVF,B (HC3-1550-4) C3b,Bb (HC3-1550)

23. Conclusions
• Substitution of small portions of human C3 with
homologous CVF sequences at the C-terminus of the C3
alpha-chain results in human C3 derivatives exhibiting
CVF-like functions
• Comparing activities of different hybrids allows one to
predict the functions of sequences in C3/CVF
• In several cases, predictions are supported by X-ray crystal
structure and activity results

24. Preclinical testing of HC3-1496
• InCode Biopharmaceutics, Inc.
• Received Venture Capital funding from Avalon
Ventures.
• Funding preclinical studies on HC3-1496
- Toxicity testing
- Efficacy in animal disease models

25. CVF replacements in hCVF
(HC3-1496)

26. CVF is not very toxic
• When injected in animals, it depletes complement, but is
only somewhat toxic in large amounts
• However, CVF activates C5
• C5 activation results in C5a anaphylatoxin production
• C5a rapidly inactivated by Carboxypeptidase N
- Product is C5a-desArg (Missing C-terminal arginine)
- C5a-desArg is still active in recruiting Neutraphils, which can cause
lung damage

27. Does hCVF (HC3-1496) activate C5?
1) in vitro C5 activation 2) C5a ELISA
C5 α-chain
C5 α’-chain
C5 β-chain
Factor H

28. In vivo Complement Depletion by
hCVF
In Rats In Primates

29. Pharmacokinetic study of hCVF in mice

30. Is hCVF toxic?
In vivo Complement Depletion by
hCVF: C3a and C5a production
C3a Production C5a Production

31. In vivo Complement Depletion by
hCVF: Physiological Affects
Heart Rate Blood Pressure

32. In vivo Complement Depletion by
HC3-1496: Physiological Affects
Mean Airway Pressure

33. hCVF in Animal Disease Models:
Myocardial Ischemia/Reperfusion
Ejection Volume
*

34. hCVF in Animal Disease Models:
Myocardial Ischemia/Reperfusion
C3b deposition
PBS hCVF CVF
Control hCVF CVF

35. hCVF in animal disease models:
Paroxysmal Nocturnal Hemoglobinuria
(PNH) Disease Model
• PNH is a rare disease
• Clonal stem cell disorder-caused by PIG-A mutation
• Affected cells generate little or no glycosylphosphatidylinositol
(GPI)
• Are unable to bind certain regulators of complement activation
- DAF (CD55)
- CD59: interrupts formation of MAC
• Affected cells more prone to be lysed by complement
• Only current treatment is Eculizumab (Alexion s Soliris)
• Humanized anti-C5 antibody
• Prevents MAC formation

36. hCVF in animal disease models:
Paroxysmal Nocturnal Hemoglobinuria
(PNH) Disease Model
• Experiment performed in vitro
• Human serum samples treated with either hCVF, CVF, or
PBS
• Serum samples tested for remaining complement activity
• Samples blinded and sent to Mike Pangburn’s lab at
University of Texas Health Center in Tyler, TX
• Used FACS to measure amount of CD59 on cell surface
of erythrocytes from PNH patients
• Cells treated with serum samples and recombinant factor
H fragment which causes lysis of cells.

37. PNH Data

38. hCVF in animal disease models:
Paroxysmal Nocturnal Hemoglobinuria
(PNH) Disease Model
% PNH cells lysed
Serum
treatment
% Complement
depleted Patient 1 Patient 2 Patient 3 Patient 4 Average
Untreated
Serum 0 84 87 95 91 89.3
hCVF 73 3 3 4 9 4.8
hCVF 100 0 11 7 0 4.5
CVF 100 0 0 0 0 0.0
No Serum NA 0 0 0 1 0.3

39. hCVF in animal disease models: Collagen
induced Arthritis (CIA)
• Mice immunized with chicken CII collagen.
• Two weeks later, a booster immunization was
given.
• Two groups
1) Untreated control.
PBS injection.
2) Experimental
500 µg/kg HC3-1496 administered 6 days after booster
immunization.
250 µg/kg HC3-1496 administered 5 days/week.
• Arthritis monitored by measuring diameter of hind
paws, fore paws and ankles. Data on graph
represents sum of measurements.

40. hCVF in animal disease models: Collagen
induced Arthritis (CIA)

41. hCVF is less immunogenic
than CVF
Mice injected with CVF Mice injected with hCVF

42. Other disease models
• AMD (Age-related Macular Degeneration)
• Myasthenia gravis
• Immunomodulation during recombinant Factor
VIII treatment of hemophilia
• Increasing effectiveness of mAb cancer
treatment: ADCC (Antibody-dependent cell
mediated toxicity)
• Ventilator Induced Lung Injury

43. Conclusions
• Injection of hCVF into both monkeys and mice show the protein
is essentially non-toxic
• hCVF shown to be effective therapeutic in several disease
models
• hCVF has potential as a therapeutic in complement-mediated
diseases
• Like CVF, hCVF (HC3-1496) is capable of rapidly
depleting complement, both in vitro and in vivo.
• Unlike CVF, hCVF does not activate C5
• Lessens chance of neutrophil activation and resulting tissue
damage
• hCVF also appears to be less immunogenis than CVF

44. Future work
• Two main areas of work.
• Improve stability of proteins in vivo.
- It is most likely that hCVF is degraded by factors H and I
- Need to reduce binding of factor H to hybrid protein.
- Crystal structure of C3b:fH complex.
- Have identified several residues in C3b important for factor H binding and
prepared clones to produce several of these proteins.
• Reduce immunigenicity of proteins
- CVF substitution in HC3-1496 is only 167 amino acids: ~10% of protein.
- Of these 167 amino acids, about 40% are identical to human C3.
Therefore, we believe that immunogenicity should not be a problem.
Moreover, we have shown results that suggest that hCVF has minimal
immunogenicity in mice.
- Have shown that changing one or several amino acids can have large effect
on protein activity.
- It should be possible to design a hybrid protein with activity approximately
equal to HC3-1496 that only contains a few substitutions.

45. University of Texas HSC
Michael Pangburn
Viviana Ferreira
Charles River Laboratories
Stephen Wilson
Harvard University
Greg Stahl
Utrecht University
Piet Gros
Bert Janssen
Incode Biopharmaceutics, Inc.
William St. John
Paul Finnegan
University of Hawaii Cancer Center
Carl-Wilhelm Vogel
Brian Hew
Mike Thorne
June Lee
Katina Wong
Acknowledgements