1. Roland B. Scott Memorial Symposium Pharmacologic Treatment of Sickle Cell Disease
Kwaku Ohene-Frempong, MD
Professor of Pediatrics, University of Pennsylvania
Director Emeritus, Sickle Cell Center
The Children’s Hospital of Philadelphia
It is my pleasure to speak with you this afternoon about oxyhemoglobin desaturation and vasculopathy in children with sickle cell disease.

2. Disclosure Nothing to disclose
Kwaku Ohene-Frempong, MD
Professor of Pediatrics, University of Pennsylvania
Director Emeritus, Sickle Cell Center
The Children’s Hospital of Philadelphia
It is my pleasure to speak with you this afternoon about oxyhemoglobin desaturation and vasculopathy in children with sickle cell disease.

3. Sickle Cell Disease: Pharmacologic Treatment
Sickle cells - first observation Walter Noel’s blood smear - Dec 31, 1904
Some of the major complications of sickle cell disease (SCD) such as acute chest syndrome, stroke and pain episodes are attributed to vasoocclusive tissue damage. Cerebral vasculopathy is a major risk factor for stroke. The primary pathophysiologic mechanisms for lung disease are unknown. Pulmonary vasculopathy may be a risk factor for acute chest syndrome pulmonary hypertension. Both are leading causes of morbidity and mortality in adults with sickle cell disease.

5. Pathophysiology of SCD
Sickle Cell Disease: Pharmacologic Treatment
Pathophysiology of SCD
In a red blood cell containing mostly Hb S…
- O2
…Hb S molecules polymerize into long fibers; mishapen, dehydrated and adherent sickle cells.
When deoxygenated
…single Hb S molecules in free in solution;
allows red cell to be soft, round, and deformable
When oxygenated…
- O2
+ O2
+ O2
Some of the major complications of sickle cell disease (SCD) such as acute chest syndrome, stroke and pain episodes are attributed to vasoocclusive tissue damage. Cerebral vasculopathy is a major risk factor for stroke. The primary pathophysiologic mechanisms for lung disease are unknown. Pulmonary vasculopathy may be a risk factor for acute chest syndrome pulmonary hypertension. Both are leading causes of morbidity and mortality in adults with sickle cell disease.

6. Pathophysiology of SCD
Sickle Cell Disease: Pharmacologic Treatment
Pathophysiology of SCD
1. Molecular pathology
2. Biochemical pathology
Cellular pathology
Vascular pathology
Clinical pathology
Some of the major complications of sickle cell disease (SCD) such as acute chest syndrome, stroke and pain episodes are attributed to vasoocclusive tissue damage. Cerebral vasculopathy is a major risk factor for stroke. The primary pathophysiologic mechanisms for lung disease are unknown. Pulmonary vasculopathy may be a risk factor for acute chest syndrome pulmonary hypertension. Both are leading causes of morbidity and mortality in adults with sickle cell disease.

7. Sickle Cell Disease: Pharmacologic Treatment
Pathophysiology of SCD Consequences of Hb S polymerization and RBC sickling
Red cell injury
Hemolysis
RBC dehydration and dense cell formation
Adhesion of RBC to venule endothelium
Formation of heterocellular aggregates (WBC, ISC)
Vasooclusion
Local hypoxia, increased Hb S polymer formation
Propagation of vasooclusion in adjacent vasculature
Dysregulation of vasomotor tone by vasodilator mediators (NO)
Some of the major complications of sickle cell disease (SCD) such as acute chest syndrome, stroke and pain episodes are attributed to vasoocclusive tissue damage. Cerebral vasculopathy is a major risk factor for stroke. The primary pathophysiologic mechanisms for lung disease are unknown. Pulmonary vasculopathy may be a risk factor for acute chest syndrome pulmonary hypertension. Both are leading causes of morbidity and mortality in adults with sickle cell disease.

8. Molecular pathology of SCD
Sickle Cell Disease: Pharmacologic Treatment
Molecular pathology of SCD
It all started in the genes!
Some of the major complications of sickle cell disease (SCD) such as acute chest syndrome, stroke and pain episodes are attributed to vasoocclusive tissue damage. Cerebral vasculopathy is a major risk factor for stroke. The primary pathophysiologic mechanisms for lung disease are unknown. Pulmonary vasculopathy may be a risk factor for acute chest syndrome pulmonary hypertension. Both are leading causes of morbidity and mortality in adults with sickle cell disease.

9. Molecular pathology of SCD Regular Hemoglobin Genes and Products
Sickle Cell Disease: Pharmacologic Treatment
Molecular pathology of SCD Regular Hemoglobin Genes and Products
Gower 1: z2 e2
Gower 2: a2 e2
Portland: x2 g2
F: a2 g2
A2: a2 d2
A: a2 b2
< 2%
< 3%
96%
Hemoglobins by age > 1 yr
Some of the major complications of sickle cell disease (SCD) such as acute chest syndrome, stroke and pain episodes are attributed to vasoocclusive tissue damage. Cerebral vasculopathy is a major risk factor for stroke. The primary pathophysiologic mechanisms for lung disease are unknown. Pulmonary vasculopathy may be a risk factor for acute chest syndrome pulmonary hypertension. Both are leading causes of morbidity and mortality in adults with sickle cell disease.

10. Molecular pathology of SCD Hemoglobin Genes and Products in SCD-SS
Sickle Cell Disease: Pharmacologic Treatment
Molecular pathology of SCD Hemoglobin Genes and Products in SCD-SS
Gower 1: z2 e2
Gower 2: a2 e2
Portland: x2 g2
F: a2 g2
A2: a2 d2
S: a2 bs2
2-20% 3%
80-95%
Hemoglobins in SS by age > 1 yr
Some of the major complications of sickle cell disease (SCD) such as acute chest syndrome, stroke and pain episodes are attributed to vasoocclusive tissue damage. Cerebral vasculopathy is a major risk factor for stroke. The primary pathophysiologic mechanisms for lung disease are unknown. Pulmonary vasculopathy may be a risk factor for acute chest syndrome pulmonary hypertension. Both are leading causes of morbidity and mortality in adults with sickle cell disease.

11. Molecular pathology of SCD The sickle mutation
Sickle Cell Disease: Pharmacologic Treatment
Molecular pathology of SCD The sickle mutation
The s Mutation
6th Codon of -Globin Gene
GAG
Glutamic acid
GTG
Valine
Some of the major complications of sickle cell disease (SCD) such as acute chest syndrome, stroke and pain episodes are attributed to vasoocclusive tissue damage. Cerebral vasculopathy is a major risk factor for stroke. The primary pathophysiologic mechanisms for lung disease are unknown. Pulmonary vasculopathy may be a risk factor for acute chest syndrome pulmonary hypertension. Both are leading causes of morbidity and mortality in adults with sickle cell disease.
The same mutation found in all
s genes around the world

12. Molecular pathology of SCD Normal versus sickle beta globin
Sickle Cell Disease: Pharmacologic Treatment
Molecular pathology of SCD Normal versus sickle beta globin 1 2 3 4 5 6 7 8 9 10
146 A
Normal
val
glu
Some of the major complications of sickle cell disease (SCD) such as acute chest syndrome, stroke and pain episodes are attributed to vasoocclusive tissue damage. Cerebral vasculopathy is a major risk factor for stroke. The primary pathophysiologic mechanisms for lung disease are unknown. Pulmonary vasculopathy may be a risk factor for acute chest syndrome pulmonary hypertension. Both are leading causes of morbidity and mortality in adults with sickle cell disease. S 1 2 3 4 5 6 7 8 9 10
146
Sickle

13. RBC containing mostly normal Hb
oxygenated
deoxygenated
- O2
+ O2
RBC containing mostly Hb S
oxygenated
deoxygenated
- O2
+ O2
+ O2

14. Clinical Pathology of SCD
Sickle Cell Disease: Pharmacologic Treatment
Clinical Pathology of SCD
1. Anemia
2. Vasoocclusion
3. Chronic organ damage
Some of the major complications of sickle cell disease (SCD) such as acute chest syndrome, stroke and pain episodes are attributed to vasoocclusive tissue damage. Cerebral vasculopathy is a major risk factor for stroke. The primary pathophysiologic mechanisms for lung disease are unknown. Pulmonary vasculopathy may be a risk factor for acute chest syndrome pulmonary hypertension. Both are leading causes of morbidity and mortality in adults with sickle cell disease.

15. Clinical Pathology of SCD
Sickle Cell Disease: Pharmacologic Treatment
Clinical Pathology of SCD
1. Anemia
Chronic intravascular hemolytic anemia
Acute episodes of severe anemia
Transient red cell aplasia (parvovirus B19)
Acute splenic sequestration
Acute hemolysis (“hyperhemolysis”)
Some of the major complications of sickle cell disease (SCD) such as acute chest syndrome, stroke and pain episodes are attributed to vasoocclusive tissue damage. Cerebral vasculopathy is a major risk factor for stroke. The primary pathophysiologic mechanisms for lung disease are unknown. Pulmonary vasculopathy may be a risk factor for acute chest syndrome pulmonary hypertension. Both are leading causes of morbidity and mortality in adults with sickle cell disease.

16. Clinical Pathology of SCD
Sickle Cell Disease: Pharmacologic Treatment
Clinical Pathology of SCD
Vasoocclusive complications
Microvascular occlusion
clinically silent
Macrovascular occlusion
acute ischemic/infarctive damage
pain episodes
stroke
priapism
acute chest syndrome
renal papillary necrosis
splenic infarction
Some of the major complications of sickle cell disease (SCD) such as acute chest syndrome, stroke and pain episodes are attributed to vasoocclusive tissue damage. Cerebral vasculopathy is a major risk factor for stroke. The primary pathophysiologic mechanisms for lung disease are unknown. Pulmonary vasculopathy may be a risk factor for acute chest syndrome pulmonary hypertension. Both are leading causes of morbidity and mortality in adults with sickle cell disease.

17. Clinical Pathology of SCD
Sickle Cell Disease: Pharmacologic Treatment
Clinical Pathology of SCD
3. Chronic organ damage
Splenic dysfunction
high risk of bacterial infection
Progressive dysfunction of:
lungs - oxyhemoglobin desaturation, pulmonary hypertension
kidneys - proteinuria, renal failure
gallbladder - gallstones
eyes - proliferative retinopathy
joints - osteonecrosis, arthritis
heart - CHF
Some of the major complications of sickle cell disease (SCD) such as acute chest syndrome, stroke and pain episodes are attributed to vasoocclusive tissue damage. Cerebral vasculopathy is a major risk factor for stroke. The primary pathophysiologic mechanisms for lung disease are unknown. Pulmonary vasculopathy may be a risk factor for acute chest syndrome pulmonary hypertension. Both are leading causes of morbidity and mortality in adults with sickle cell disease.

18. Pharmacological therapy in SCD Potential targets
Sickle Cell Disease: Pharmacologic Treatment
Pharmacological therapy in SCD Potential targets
Intracellular Hb composition
Intracellular Hb concentration
RBC Transit time
circulatory factors
local tissue factors
systemic factors
O2 extraction from oxy-Hb S
Vascularity/ vascular pathology
Nitric oxide bioavailability
Multi-genetic and environmental factors
Some of the major complications of sickle cell disease (SCD) such as acute chest syndrome, stroke and pain episodes are attributed to vasoocclusive tissue damage. Cerebral vasculopathy is a major risk factor for stroke. The primary pathophysiologic mechanisms for lung disease are unknown. Pulmonary vasculopathy may be a risk factor for acute chest syndrome pulmonary hypertension. Both are leading causes of morbidity and mortality in adults with sickle cell disease.

19. Pharmacotherapy of SCD
Some of the major complications of sickle cell disease (SCD) such as acute chest syndrome, stroke and pain episodes are attributed to vasoocclusive tissue damage. Cerebral vasculopathy is a major risk factor for stroke. The primary pathophysiologic mechanisms for lung disease are unknown. Pulmonary vasculopathy may be a risk factor for acute chest syndrome pulmonary hypertension. Both are leading causes of morbidity and mortality in adults with sickle cell disease.

20. Pathophysiology of SCD Vasoocclusion (1)
Sickle Cell Disease: Pharmacologic Treatment
Pathophysiology of SCD Vasoocclusion (1)
A. Prolongation of the RBC microvascular transit time caused by:
Enhanced red cell adhesion to endothelium and heterocellular aggregate formation
Abnormal cation homeostasis with cell dehydration, dense-cell formation, and
irreversibly sickled cell formation
Abnormal vasomotor tone favoring vasoconstriction (via NO, endothelin-1, and eicosanoid dysregulation)
Some of the major complications of sickle cell disease (SCD) such as acute chest syndrome, stroke and pain episodes are attributed to vasoocclusive tissue damage. Cerebral vasculopathy is a major risk factor for stroke. The primary pathophysiologic mechanisms for lung disease are unknown. Pulmonary vasculopathy may be a risk factor for acute chest syndrome pulmonary hypertension. Both are leading causes of morbidity and mortality in adults with sickle cell disease.

21. Pathophysiology of SCD Vasoocclusion (2)
Sickle Cell Disease: Pharmacologic Treatment
Pathophysiology of SCD Vasoocclusion (2)
B. Reduction in delay time to HbS polymer formation caused by:
Red-cell deoxygenation
Increase in intracellular HbS concentration
Low concentrations of protective Hb types (eg, HbF, HbA2)
Fall in pH
C. Miscellaneous potential modulators
Free-radical release and reperfusion injury
Coagulation activation with proadhesive thrombin formation
Some of the major complications of sickle cell disease (SCD) such as acute chest syndrome, stroke and pain episodes are attributed to vasoocclusive tissue damage. Cerebral vasculopathy is a major risk factor for stroke. The primary pathophysiologic mechanisms for lung disease are unknown. Pulmonary vasculopathy may be a risk factor for acute chest syndrome pulmonary hypertension. Both are leading causes of morbidity and mortality in adults with sickle cell disease.

22. Pharmacotherapy of SCD Hb F Induction
Sickle Cell Disease: Pharmacologic Treatment
Pharmacotherapy of SCD Hb F Induction
Agent
Mode of action
Human trials
Hydroxyurea
Stress erythropoiesis; selection of F-cells
Phase 3, successful
Short chain fatty acids
Histone deacetylase inhibitor; reactivation of -gene expression
Promising in small studies; high doses required; variable responses
Decytabine
Cytosine analog; DNA methyltransferase inhibitor
Promising in small pilots
Some of the major complications of sickle cell disease (SCD) such as acute chest syndrome, stroke and pain episodes are attributed to vasoocclusive tissue damage. Cerebral vasculopathy is a major risk factor for stroke. The primary pathophysiologic mechanisms for lung disease are unknown. Pulmonary vasculopathy may be a risk factor for acute chest syndrome pulmonary hypertension. Both are leading causes of morbidity and mortality in adults with sickle cell disease.

23. Pharmacotherapy of SCD Anti-adhesion agents
Sickle Cell Disease: Pharmacologic Treatment
Pharmacotherapy of SCD Anti-adhesion agents
Agent
Mode of action
Human trials
RheothRx
Improve micro-vascular blood flow
Phase 3, reduced duration of pain episode, analgesic use
Some of the major complications of sickle cell disease (SCD) such as acute chest syndrome, stroke and pain episodes are attributed to vasoocclusive tissue damage. Cerebral vasculopathy is a major risk factor for stroke. The primary pathophysiologic mechanisms for lung disease are unknown. Pulmonary vasculopathy may be a risk factor for acute chest syndrome pulmonary hypertension. Both are leading causes of morbidity and mortality in adults with sickle cell disease.

24. Pharmacotherapy of SCD Nitric oxide donors/regulators
Sickle Cell Disease: Pharmacologic Treatment
Pharmacotherapy of SCD Nitric oxide donors/regulators
Agent
Mode of action
Human trials
NO
Improve micro-vascular blood flow
Shortens duration of pain
Arginine
NO synthase substrate
Reduce PA systolic pressure
Sildenafil
Phosphodiesterase-5 inhibitor
May help in pulmonary hypertension and priapism
Some of the major complications of sickle cell disease (SCD) such as acute chest syndrome, stroke and pain episodes are attributed to vasoocclusive tissue damage. Cerebral vasculopathy is a major risk factor for stroke. The primary pathophysiologic mechanisms for lung disease are unknown. Pulmonary vasculopathy may be a risk factor for acute chest syndrome pulmonary hypertension. Both are leading causes of morbidity and mortality in adults with sickle cell disease.

25. Hydroxyurea Therapy in Sickle Cell Disease Kwaku Ohene-Frempong, M.D.
The Children’s Hospital of Philadelphia

26. Effect of Hb F on Polymerization of Deoxy-Hb S
A. 100% Hb S
Hb S
B. 75% Hb S / 25% Hb F
F/S Hybrid
Hb F

27. Hydroxyurea Therapy in Sickle Cell Disease
Effect of Hb F on SCD
1. In vitro gelation studies have shown that Hb F
is effective inhibitor of gelation.
2. Patients with high Hb F levels (> 20%) documented
to have mild clinical course.
3. Patients with S-HPFH produce 25-35% Hb F in every
RBC beyond infancy, and are clinically asymptomatic.

28. Hydroxyurea Therapy in Sickle Cell Disease
Effect of Hb F on SCD

29. Hydroxyurea Therapy in Sickle Cell Disease
Beneficial RBC Effects of HU Treatment in SCD-SS
Increase in F-cell numbers and Hb F concentration per F cell
Inhibition of cation depletion and dense-cell formation
Reduction in stress reticulocytes and hemolytic rate
Increased deformability with improved rheology
Inhibition of sickle red cell-endothelium adhesion
Inhibition of sickle erythrocyte adhesion to extracellular
matrix components, including fibronectin,thrombospondin, and laminin

30. Hydroxyurea Therapy in Sickle Cell Disease
Beneficial non-RBC Effects of HU Treatment in SCD-SS
Quantitative reduction in leucocyte count
Qualitative changes in leucocytes, including reduction in leucocyte-free-radical production and activation marker L-selectin
Reduction in soluble VCAM-1 concentrations (indicative of decreased endothelial activation)
In-vivo NO release

31. Hydroxyurea Therapy in Sickle Cell Disease
Multicenter Study of Hydroxyurea
in Sickle Cell Anemia
(MSH Study)
EFFECT OF HYDROXYUREA
ON THE FREQUENCY OF PAINFUL CRISES
IN SICKLE CELL ANEMIA
Charache, et al.. NEJM, 1995

32. Multicenter Study of Hydroxyurea in SCA (MSH)
Effect of Hydroxyurea Therapy
on SCD Complications
Placebo HU p value
Pain, episodes/yr < 0.001
Pain hospitalization < 0.001
No. with acute chest < 0.001
No. transfused

33. Steinberg, et al: JAMA 2003: 280; 1645

34. Hydroxyurea Therapy in Sickle Cell Disease
Effect of HU and Hb F on Mortality
Steinberg, et al: JAMA 2003: 280; 1645

35. Hydroxyurea Therapy in Sickle Cell Disease
Questions
So why is every adult with SCD-SS
NOT on hydroxyurea?
What to do about the children?

36. Hydroxyurea Therapy in Sickle Cell Disease
Effects of Hydroxyurea on SCD

37. Hydroxyurea Therapy in Sickle Cell Disease
Effects of Hydroxyurea on SCD
Zimmerman, et al. 2004

38. Hydroxyurea Therapy in Sickle Cell Disease
Effects of Hydroxyurea on SCD
Zimmerman, et al. 2004

39. Hydroxyurea Therapy in Sickle Cell Disease
Effects of Hydroxyurea on SCD
Hankins, et al. 2005

40. Hydroxyurea Therapy in Sickle Cell Disease
Effects of Hydroxyurea on SCD
Hankins, et al. 2005

41. Hydroxyurea Therapy in Sickle Cell Disease
Effects of Hydroxyurea on SCD
Hankins, et al. 2005

42. Hydroxyurea Therapy in Sickle Cell Disease
Effects of Hydroxyurea on SCD
Hankins, et al. 2005

43. Hydroxyurea Therapy in Sickle Cell Disease
What are the treatment goals?
Hematologic
Hb F (> 20%)
Hb concentration ( g/dL)
2. Clinical
pain episodes
acute chest episodes
3. Therapeutic dose
dose adjustments to maintain goals
4. Period of observation

44. Hydroxyurea Therapy in Sickle Cell Disease
Effects of Hydroxyurea on SCD
Zimmerman, et al. 2004

45. Consensus Development Conference on Hydroxyurea Treatment for
NIH
Consensus Development Conference on
Hydroxyurea Treatment
for
Sickle Cell Disease
February 25-27, 2008

46. Hydroxyurea Therapy in Sickle Cell Disease
Short- and Long-Term Side Effects

47. Hydroxyurea Therapy in Sickle Cell Disease
Barriers to Treatment
1. Patient Level
• Fears - cancer, birth defects, infertility, uncertainty of
other potential long-term risks
• Concern - non-FDA-approved status for children means
HU an experimental drug
• Lack of knowledge about HU as a therapeutic option
• Lack of perception that HU is currently the only therapy
that directly modifies disease process
• Lack of adherence to treatment regimen
• Need for frequent monitoring of hydroxyurea response

48. Hydroxyurea Therapy in Sickle Cell Disease
Barriers to Treatment
2. Parent / Family / Caregiver Level
• Fears - cancer, birth defects, infertility, uncertainty of
other potential long-term risks
• Concern - non-FDA-approved status for children means
HU an experimental drug
• Lack of knowledge about HU as a therapeutic option
• Lack of perception that HU is currently the only therapy
that directly modifies disease process
• Difficulty in communication between patients and caregivers regarding the use of HU and other therapeutic options

49. Hydroxyurea Therapy in Sickle Cell Disease
Barriers to Treatment
3. Provider Level
• Lack of knowledge about HU as a therapeutic option
Concerns - cancer, birth defects, infertility, uncertainty of other potential long-term risks
Provider bias and negative attitudes toward SCD patients and their treatment
• Lack of clarity in HU treatment regimens and undertreatment in adults
• Limited number of physicians with expertise in use of HU for SCD
• Failure to engage patients/caregivers in treatment decision making in a developmentally appropriate manner
Lack of perception that hydroxyurea is currently the only therapy that directly modifies the disease process

50. Hydroxyurea Therapy in Sickle Cell Disease
Barriers to Treatment
4. Systems Level (a)
Financing (lack of insurance, type of insurance, underinsurance,
scope of coverage, copays, reimbursement, payment structures)
• Geographic isolation
• Lack of coordination between academic centers and community-based
clinicians
• Limited access to comprehensive care centers and comprehensive
care models
• Problems in transitioning from pediatric to adult care

51. Hydroxyurea Therapy in Sickle Cell Disease
Barriers to Treatment
4. Systems Level (b)
• Limited access (e.g., geographic distribution, recruitment, and retention
of clinicians competent in provision of comprehensive care to SCD patients)
Inadequate Government, industry, and philanthropic support for the
care of patients who have sickle cell disease
• Development and promotion of hydroxyurea are hindered by lack of
commercial interest in the development and promotion of hydroxyurea
• Lack of visibility and empowerment of SCD advocacy groups
• Cultural and language barriers to the provision of appropriate care
• Inadequate information technology systems to support the long-term

52. Hydroxyurea Therapy in Sickle Cell Disease
Final Question
So why are we not using hydroxyurea for many more patients with
sickle cell disease?