Lecture 05 + 06 Small Molecules in CF Treatment

Question 1

What goes wrong in the lungs of CF patients?

Answer 1

depleted PCL leading to failure to clear mucous and bacteria leading to infection and inflammation of airways that results in tissue damage and lung function

Question 2

Give examples of current CF treatments and what they are used for

Answer 2

nebulised and oral antibiotics, tobramycin - fight infection
inhaled bronchodilators - open airways
mycolytics, pulmozyme - break down mucous
nebulised hypertonic saline - hydrate ASL which improves clearance
pancreatic enzymes - breakdown food
steroids - decrease inflammation
fat soluble vitamins - help absorb sufficient vitamins
exercise and physiotherapy - clear mucous
high energy supplements - sufficient nutrient absorption

Question 3

What is the problem with current drug treatments for CF patients?

Answer 3

treat the symptoms but not the cause of CF

Question 4

Name two drugs discovered that aim to solve the current problem?

Answer 4

VTX-770 (ivacaftor/kalydeco)

VTX-809 (lumakaftor)

Question 5

Who is VTX-770 aimed to treat?

Answer 5

CF patients with G551D mutation

Question 6

What does the G551D mutation impact in terms of CF patients?

Answer 6

glycine to aspartate mutation
type III classification - regulation and gating defect
1-3% of all CF patients worldwide and 13% in UK

Question 7

How was VTX-770 found?

Answer 7

large scale screen using cell-based fluorescence

what compounds increased the open probability of CFTR and increased immunofluorescence

Question 8

What experimental evidence did they find to support VTX-770?

Answer 8

rat thyroid cells overexpressing wt or G551D CFTR
WT big increase in SCC to FSK due to potentiating cAMP - not seen in CFTR mutant due to decreased open probability at membrane
mutant - expose FSK then VTX-770 gives a big increase in SCC enough to be clinically functional
FSK causes the channels to open and VTX-770 primes the channels so they can open - both compounds required for clinical functionality

Question 9

What was the clinical impact of VTX-770 on patients compared to placebo?

Answer 9

massive positive impact on patients
increased predicted FEV1 compared to placebo
weight better maintained (decreasing weight is a symptom of poorly controlled CF)
decreased chloride in sweat
increased chloride secretion in nose (effect increased with higher dosage)

Question 10

What is VTX-809 aimed to treat?

Answer 10

CF patients with delta-F508 mutation

Question 11

What does the delta-F508 mutation impact in terms of CF patients?

Answer 11

phenylalanine deletion
type II classification - trafficking defect
90% CF patients worldwide
very severe symptoms

Question 12

How was VTX-809 discovered?

Answer 12

large scale screening with immunoblotting assay (Western blotting)
CFTR channel at the membrane is modified with a glycosylation addition increasing its molecular weight
find compounds that increase the shift to the higher molecular weight band

Question 13

What did the in vitro VX-809 studies aim to show?
What technique did they use?
What did the initial study show?

Answer 13

aimed to show that the VX-809 resulted in greater CFTR current and therefore chloride secretion
single channel patch clamp technique
addition of VX-809 showed an increased of CFTR open probability to the average wt level.
VX-809 and 770 was added to the cells to potentiate the effect, further increasing the open probability of the channel

Question 14

What did subsequent in vitro VX-809 studies using cAMP show?

Answer 14

patch clamp technique on human bronchial epithelial cells from homozygous delta-F508 CF patients
added amiloride to block contamination by ENaC
add cAMP to potentiate PKA to increase chloride secretion by CFTR
with no added VX-809 small increase in current
current increases in response to increasing doses of VX-809
add CFTR inhibitor which decreased the currents back to nothing proving the effect was on the CFTR channel only

Question 15

Initial VX-809 monotherapy in CF patients:
How was it set up?
What were the results?

Answer 15

randomised, double-blind, placebo controlled trial in homozygous delta-F508 CF patients
half placebo/half treatment for 28 days
tested the % change in FEV1 and change in chloride found in the sweat

mono therapy showed no pattern of activity and no obvious trend - something about VX-809 therapy not working in CF patients in terms of lung function
small decrease (~6-8mM) of chloride found in the sweat still leaving the CF patients within the clinical threshold

Question 16

What was the impact of VX-809 mono therapy compared to VX-770?

Answer 16

very small improvement seen in patients providing very little benefit

Question 17

Preliminary Orkambi combined therapy study:
What did the study show in terms of chloride in the sweat?
What did the study show in terms of lung function?

Answer 17

sweat [chloride] -
+150mg ivacaftor - small change when combined but an overshoot and worsening seen when taken off the drug
+250mg ivacaftor - larger change (decrease ~12mM) providing small-to-moderate improvement

lung function -
placebo - decreased lung function over time
monotherapy - decreased % in FEV1 over time (may be due to patient groupings)
combined therapy - increased lung function particular with larger does of VX-809 (600mg VX-809 + 250mg ivacaftor)

Question 18

Phase 3 clinical study for Orkambi (VTX-770/809 combined therapy):
How was the study set up?

What did the study show in terms of lung function?

Answer 18

large study with homozygous delta-F508 CF patients over 12 years - given placebo, 600mg 809/250mg 770 or 400mg 809/250mg 770 for 24 weeks. Followed by safety follow up and safety roll-over study (side effects)

Within 2 weeks patients on combined therapy show 3% improvement compared to placebo (slight FEV1 decreased %). So much smaller in terms of effect compared to VX-770 treatment.

Question 19

What may cause patients to to have different responses to the treatment in terms of improvement?

Answer 19

genetic backgrounds - some evidence for non-coding regions on severity of symptoms
compliance - following treatment regime and can’t be controlled

Question 20

Phase 3 clinical study for Orkambi (VTX-770/809 combined therapy):
What was the impact on the number of events CF patients suffered?

What benefit does this provide CF patients?

Answer 20

40% of CF patients on placebo treatment would have some form of CF event (i.e. respiratory infection) whereas on the Orkambi treatment this was reduced to about 30% of patients.
Hospitalisation - around 40-60% decrease when on combined treatment compared to placebo
IV antibiotic treatments - around 50% decrease when on combined treatment compared to placebo

IV antibiotic treatments are only administered when CF patients are very ill. Decreasing the number of events, hospitalisation and IV antibiotic treatments has a big impact on CF patients. Improves patient outcomes and decreases the cost on the healthcare system.

Question 21

What can be summarised about Orkambi treatment in delta-F508 CF patients?

Answer 21

VX-809 can traffic the delta-F508 mutant CFTR channel to the membrane
Alone VX-809 treatment is not sufficient (effective) enough to improve symptoms
The addition of of the VX-770 potentiator treatment enhances the function of the CFTR channel at the membrane helping to relieve symptoms

Question 22

What is the cost of Ivacaftor and Orkambi treatment?

Answer 22

Ivacaftor £189,000/patient/year

Orkambi £104,000/patient/year

Question 23

Despite the higher cost, why is Ivacaftor licensed in the UK and Orkambi not?

What is the ethical problem with this?

Answer 23

Ivacaftor - licensed due to the large impact it has on patients. Patients require less treatments in other areas with reduced hospitalisations and events, decreasing healthcare costs. Cost-benefit analysis shows the expense to benefit the patients and NHS

Orkambi - not as effective on patient outcomes. Most patients still require all the normal CF treatments alongside with only a small decrease in the number of hospitalisations. Not enough benefit to justify the cost.

Ethically - any benefit to the patient should be provided (no matter the cost)

Question 24

What is an alternative drug treatment to lumacaftor being designed?

Answer 24

Tezecafor

Question 25

What alternative therapy is being designed as an alternative to drug treatments?

Answer 25

gene therapy with liposome complexes

Question 26

Why did early gene therapy studies ‘not get far’?

Answer 26

lots of problems

1. cells replaced after so many days with the new cells not keeping the wt gene inserted and the patient requiring continuous treatment
2. researchers used adenoviruses to insert the correct genes which lead to side effects and increased immune response
3. patient outcomes were not improved overall

Question 27

First Non-Viral CFTR gene therapy (2015):
How was it carried out?

What was the problem with this protocol?

Answer 27

140 patients - 62 placebo / 78 gene therapy
placebo - 0.9% nebulised saline
gene therapy - pGM169/GL67A nebulised (liposome)
28 day intervals with 9 doses

No control for the liposome complexes (with scrambled DNA) to see the impact of the liposome complexes on lung function. Ethically can not do this as scrambled DNA could have catastrophic impact on CF patients.
Ethically approved but not scientifically ideal.

Question 28

First Non-Viral CFTR gene therapy (2015):
What were the results in terms of lung function?

What was the impact on looking at the impact on the therapy in individuals?

Answer 28

gene therapy showed no improvement or worsening in terms of lung function (FEV1 change %) whereas placebo patients had a slight decrease in lung function showing that the airways had stabilised

individually shown that more patients improved from the treatment than not compared to the placebo
different subsets of individuals who varied in response to the treatment - some responded well, some didn’t respond at all, some worsened from the treatment

Question 29

First Non-Viral CFTR gene therapy (2015):

What significant benefits did the gene therapy show compared to the placebo?

Answer 29

increased FEV1/FVC
decreased gas trapping (made more like wt)
increased chloride secretion

Question 30

First Non-Viral CFTR gene therapy (2015):

What could explain why some individuals worsened from the gene therapy?

Answer 30

1. DNA taken up by most cells, not 100% effective
2. Compliance with treatment
3. Multi-drug treatments - all CF patients receiving multiple other treatments alongside
4. Is the liposome complexes adversely affecting the patient (i.e. lung function)? need an ethical control
5. heterogenous population - genetic differences (non-coding regions in terms of severity)

Question 31

First Non-Viral CFTR gene therapy (2015):

What is the problem with this gene therapy treatment?

Answer 31

• solves the problem in the lungs but CF patients still suffer and can die from other problems - more than just the lungs are affected by CF, i.e. the gastrointestinal system and liver
• solving the lung function can result in a shift in the problem to other areas