Hall 3 - Cell Survival Curves

Question 1

What is plating efficiency?

Answer 1

(Colonies counted / cells seeded) x 100%

Question 2

What is the surviving fraction?

Answer 2

Cells that survive after RT normalized by plating efficiency

(Colonies counted / cells seeded) / (PE/100)

Question 3

What is tumor control probability?

Answer 3

e^-n

n: avg number of surviving cells in tumor

*37% TCP requires reduction to average of 1 surviving cell

Question 4

How many cells in 1 gram of tumor?

Answer 4

10^9

Question 5

What is a log-linear survival curve?

Answer 5

Dose plotted on a linear scale
Surviving fraction on a logarithmic scale

Question 6

At low doses for low LET radiation, the survival curve starts out _____ then _____.

Answer 6

straight, curves downward at higher doses

Question 7

For high LET radiation, survival is ______.

Answer 7

Linear

Question 8

When is the single-hit, single target model applied?

Answer 8

High LET
M phase
Cells without DNA repair

Question 9

What are the two assumptions of the single-hit, multi-target model?

Answer 9

1. Each cell contains n targets, all of which must be inactivated for cell kill
2. Each target can be inactivated by passage of a charged particle (a hit)

*Now mostly replaced by linear-quadratic model

Question 10

For the single-hit, multi-target model, what are D1 and D0? When there is one hit per target, what is the surviving fraction?

Answer 10

D1 = single-event killing (initial slope)
D0 = multiple-event killing (final slope)

Surviving fraction = 0.37 of initial value = 1/e

SF = 1 - [1 - e^(-D/D0)] ^n

D10 = dose to reduce the surviving fraction to 0.10 = 2.3 x D0

Question 11

What is the extrapolation number (n) in the single-hit, multi-target model?

Answer 11

Where D0 intercepts y-axis
Number of targets per cell

Question 12

What is Dq in the single-hit, multi-target model?

Answer 12

Quasithreshold dose
Where D0 intercepts x-axis
Theoretical dose below which radiation produces no effect

Question 13

How is irreparable damage represented in the linear-quadratic model?

Answer 13

alpha x D

Question 14

How is repairable damage represented in the linear-quadratic model?

Answer 14

beta x D^2

Question 15

When are irreparable and repairable killing equal?

Answer 15

When D = alpha/beta

Question 16

What is it called when cells not directly irradiated can be affected by nearby irradiated cells?

Answer 16

Bystander effect

Question 17

In apoptosis, what recruits phagocytes to engulf dying cells?

Answer 17

Phosphatidylserine

*Does not trigger inflammation

Question 18

Apoptosis does/does not correlate strongly with radiosensitivity?

Answer 18

Does

Question 19

What part of the linear-quadratic model represents apoptosis?

Answer 19

Alpha (linear/shoulderless)

*No dose rate effect

Question 20

What caspases are involved in the extrinsic apoptotic pathway?

Answer 20

8 and 10

Bind death ligands (FasL, TNF-alpha, TRAIL) to cell surface receptors

*8 can cleave Bid and activate the intrinsic pathway

Question 21

What is the surviving fraction in the linear quadratic model?

Answer 21

SF = e ^ -(aD + bD^2)

Question 22

What is the adapter protein in the intrinsic apoptotic pathway? What caspase does it affect?

Answer 22

Apaf-1
9

DNA damage&raquo_space; ATM/p53&raquo_space; pro-apoptosis (Bax, Bak, Bid, Bim, Puma, Nova) outbalance anti-apoptosis (Bcl-2, Bcl-xl, Mcl-l)&raquo_space; cytochrome c&raquo_space; complexes with Apaf-1&raquo_space; caspase 9

Question 23

What are the initiator caspases?

Answer 23

2, 8, 9, 10

Question 24

What are the effector caspases?

Answer 24

3, 6, 7

Question 25

What inhibits the effector caspases?

Answer 25

X-linked inhibitor of apoptosis (XIAP)

Question 26

What is DIABLO?

Answer 26

A pro-apoptotic protein that frees caspases to initiate apoptosis

Question 27

What is the alternative pathway to activate apoptosis?

Answer 27

Acid sphingomyelinase (ASMase) Increased after RT >> converts sphingomyelin to ceramide >> activates intracellular caspase cascade in endothelial and tumor cells

Question 28

What do TUNEL, DNA laddering on gel, and annexin V staining assay for?

Answer 28

Apoptosis

Question 29

Does necrosis require ATP?

Answer 29

No, passive process *Inflammatory (cell swells)

Question 30

What is the most common form of cell death from radiation?

Answer 30

Mitotic catastrophe (mitotic cell death) *Multinucleated giant cells possible

Question 31

What does the survival curve look like in mitotic death-dominant cells?

Answer 31

Broad shoulder Linear-quadratic function of dose Dose-rate effect

Question 32

What initiates the formation of autophagosomes?

Answer 32

BECLIN-1

Question 33

What protein does autophagy require? Is it reversible?

Answer 33

ATG protein family Yes Selective if targeted to specific proteins or organelles (nonselective if bulky)

Question 34

What three things can trigger senescence?

Answer 34

1. Telomere shortening 2. Oncogene activation 3. Radiation (DNA damage)

Question 35

What mediates senescence?

Answer 35

p53/Rb activation Cip/Kip or INK4 proteins *Elevated levels of cell cycle inhibitors (p16-INK4a, p21/Cip1)