http://genomed.dlearn.kmu.edu.tw

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du.tw
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Survival curve radiation dose cell survival
fraction
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Reproductive Integrity
Cell survival ?? cell death
For differentiated cells that do not proliferate
e.g., nerve, muscle ? lose of specific
function (death)
For proliferating cells e.g., hematopoietic
stem cells, culture cells ? lose for
sustained proliferation (death) ? lose of
reproductive integrity (reproductive
death)
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Definition of survival for radiobiology
Retain reproductive integrity
Proliferate indefinitely to produce colony (a
large clone colony clonogenic)
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The in vitro survival curve
Cell culture
Established cell lines
Tissue ? trypsin? cell culture in vitro
Dose-survival curve
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PE plating efficiency
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Serial dilution
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The shape of the survival curve
Width of shoulder Dq or n semi-threshold dose
log
Linear quadratic function
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Multi-target model
Initial slope ? single-event killing
D1
final slope ? multiple-event killing
D0
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D1 D0 the dose required to reduce the
fraction of surviving cells to 37 of it
previous value.
D0 (straight at high dose) the average dose
required to deliver one inactivating event
(one hit) per cell. the dose required to reduce
survival from 0.1 to 0.037 or 0.01
to 0.0037. D0 (37 survival)
dose required to reduce survival to e-1 (0.37)
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Dq (quasithreshold dose) Width of shoulder
semi-threshold dose (almost the threshold dose)
n extrapolation number
Logen Dq/D0
D0/0.37(e-1) Dq/n
D0/e-1 Dq/n
n e-1xDq/D0 ln n -Dq/D0
Threshold dose the dose below which there is no
effect.
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Linear quadratic model
Two components to cell killing by radiation
One that is proportional to dose One that is
proportional to square of dose
(dual-radiation action two separate breaks)
S e-aD-bD2
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S e-aD-bD2
S the fraction of surviving a dose D a,b
constant
When aD bD2 ? D a/b
Linear quandratic contribution equally to cell
killing at same dose
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The mechanism of cell killing
Target DNA (nucleus), nuclear membrane
Chromosome, specifically the DNA, as the primary
target for radiation-induced lethality.
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Apoptotic and mitotic death AD
(falling off)
http//www-micro.msb.le.ac.uk/3035/kalmakoff/bacul
o/baculohostinteract.html
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http//www.niaaa.nih.gov/publications/arh25-3/imag
e01.gif
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http//www.copewithcytokines.de/cope.cgi?000638
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http//www.ucihs.uci.edu/anatomy/histo/corenotes/c
elldeath2004.pdf
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The detection of this DNA ladder is still
currently used to distinguish at the molecular
level apoptosis from necrosis.

• Apoptosis Dsb in linker DNA between nucleosome?
  185bp ladder in Gel
• nercosis? smear in Gel

Fig.3-9
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Radiation-induced apoptosis is highly cell type
dependent.

• Hemopoietic cells lymphoid cells
• ? prone to rapid radiation-induced apoptosis.
• Most tumors
• ? mitotic cell death apoptosis.
• or mitotic cell death only.

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Apoptotic and mitotic death MD

• The most common form of cell death from radiation
  is mitotic death (MD).
• ? Cell die in attempting to divide because of
  damaged chromosomes.

Review
Cell death by mitotic catastrophe a molecular definition
http//www.nature.com/cgi-taf/DynaPage.taf?file/o
nc/journal/v23/n16/abs/1207528a.htmldynoptionsdo
i1097246946
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• Asymmetric exchange-type chromosome aberrations
  (i.e., dicentrics and rings )
• Loss reproductive integrity
• Unable to proliferate
• death

Asymmetric exchange-type chromosome aberrations
represent the principle mechanism for
radiation-induced mitotic death in mammalian
cells.
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No apoptosis
Cell surviving cell without visible aberration
? correlation
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Exchange type aberrations require two chromosome
breaks.
The probability of an interaction between the two
breaks is related to D (low dose) or D2 (high
dose).
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Chromosome aberrations in human lymphocytes
Ch 2
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Survival curves for various mammalian cells in
culture
First in vitro survival curve
All mammalian cells, normal malignant, exhibit
similar x-ray survival curve (initial shoulder
but size vary)
The Do of X-ray survival curves for most culture
cells range from 1 to 2 Gy (100-200 rad or cGy).
(page 41)
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radiosensitivity
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Survival-curve shape and mechanism of cell death
Most cells fall between apopototic mitotic death
mitotic death
Note! Shoulder
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• Mitotic death results (principally) from
  exchange-type chromosomal aberration.
• log-linear plot with broad shoulder
• Characterized by subsequently dose-rate effect
  (page 74).

• Apoptotic death result unknow mechanism.
• straight line on log-linear plot.
• Characterized by expotential function of dose.
• little or no dose-rate effect.

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S e-aD-bD2 Linear quadratic model
apoptotic death
mitotic death
S e-(aMaA)D-bMD2
aA cell killing from apoptotic death (vary
linear) aM cell killing from mitotic death
(vary linear) bM cell killing from mitotic
death (vary square)
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Oncogenes and radioresistance
Transfection of activated oncogenes to culture
cells ? Increase radioresistance
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Genetic control of radiosensitivity
ATM (AT-mutated) gene
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Intrinsic Radiosensitivity and predictive assay
Courtenary assay
Semisolid agar gel with growth factor
Nonclonogenic assay
Cell growth in multi-wells plate, e.g.
MTT assay or chapter 15
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The effective survival curve for a multifraction
regimen
multifraction regimen are most often used in
clinical radiotherapy
What is multifraction regimen?
Dilute dose to fraction at time intervals
sublethal damage time for repair ? Shoulder
The effective survival curve
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For human, effective D0 (37 survival) 300cGy
3Gy
D10 (the dose required to kill 90 10
survival) one decade of cell killing 2.3 X D0

• Natural log 10
• 2.3
• equal Slope

Ps equal Slope Logen Dq/D0 (F3.3 page 37)
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The Do of effecitive survival curve (slope) has a
value close to 300cGy for cells of human
origin. This is an avarage value and can differ
significantly for different tumors.
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Calculations of tumor cell kill
109
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The radiosensitivity of mammalian cells compared
with microorganisms
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