Photochemotherapy 💥

Question 1

Difference between Phototherapy vs. Photochemotherapy

Answer 1

Photorherapy = natural chemophores as light absorber
> endogenous chemical absorbs light eg. Bilirubin

Photochemotheraphy = added photosensitiser
> exogenous chemical also required eg. PUVA, PDT

Question 2

Process of Elimianting Bilirubin??

Answer 2

1. Bilirubin gets oxidated (B-Ox in blood) 2. Excreted in urine

Or

1. Bilirubin forms with albumin in blood
2. Exceeted by liver

Question 3

What is PUVA therapy?

Answer 3

Formation of adducts in DNA resulting in inhibition of DNA synthesis = cell death and slower cell growth

Used in treatment of psoriasis, vitiligo and cutaneous lymphoma

Question 4

Whats the problem with (Z,Z) isomer of bilirubin?

Answer 4

Has intramuscular binding (H bonds), making it more lipophilic, and unable to bind with O2

Question 5

Furocoumarin derivative

What is the UVQ absorbence due to?

Answer 5

The pyrone ring

Question 6

8MOP molecule

MOA

Answer 6

1. 8-MOP: purine ring + pyrone ring
   Once taken it can will intracalate with DNA.
2. Once light enters (photon), the furniture ring is excited and reacts forming a bind with Thymine (monofunctional adduct is 4’5’ with pyramidine base.
3. The 2nd photon of light comes in ans excites the carbon on the furan ring.
4. You then get a bifunctionam cross linked adduct (3,4 and 4,5 with pyrimidine base)

Question 7

8-MOP molecule:

Where does the photon have to enter from first to get the bifunctional adduct formation?

Pyrone or purine?

Answer 7

Must FIRST enter via PURINE, then pyrone.

(If entered from pyrone first will only get a bifunctional adduct)

Question 8

Effects of PUVA

Answer 8

1. Phototoxic effect on skin
2. Anitproliferative effect
3. Mutagenic effect
4. Photocarcinogenic activity

Question 9

What is Photodynamic therapy
PDT

Answer 9

Involves administration of a photosensitiser followed by irradiation with visible light

Question 10

Photosensitiser is often a derivative of what?

Answer 10

Porphyrin derivative

Question 11

Mechanism of PDT

Answer 11

Question 12

Photosensitising agents 2

Answer 12

ALA (5-aminolevulinic acid)

And

Verteporfin (Visudyne)

Question 13

Photosensitiser:

How does ALA work

Answer 13

Stimulates synthesis protoporphyrin IX (PpIX) = the immediate precursor to haem and an endogenous photosensitiser

Question 14

Potential uses of PDT

Answer 14

• actinic keratins
• superficial basal cell carcinoma
• superficial squamous cell carcinoma
• Psoriasis, acne
• warts
• hair removal
• brain tumours

Question 15

Radiotherapy has 2 critical cell targets for radiation.

Name them

Answer 15

1. DNA = directly causes double strand breakage
2. Water = causing formation of free radics in the cells Aqueous environment, leading to radical attack on DNA

Question 16

Alpha + beta radiation

Have high or low LET (linear energy transfer)

Answer 16

A and b = HIGH LET

Larger molecules have higher LET, and more likely to come in contact with another molecule.

Question 17

X rays

Have high or low LET?

Answer 17

Low LET

Can pass through the body mostly without contact of biological molecules.

Question 18

Irradiated water

Which molecule is an important mediator which reacts with free radicals to make a damage permanent?

Answer 18

Oxygen

Question 19

What does the
Oxygen Enhancement Ratio (OER)
Compare ?

Answer 19

Compares cell mill with and without oxygen

Question 20

What is the most dangerous molecule?

Answer 20

OH radical