radiation-induced neoplastic ... - dose-response

RadiationRadiation--Induced Induced NeoplasticNeoplasticTransformation Transformation In Vitro, In Vitro,

HormesisHormesis and Risk Assessmentand Risk AssessmentLes RedpathLes Redpath

Department of Radiation OncologyDepartment of Radiation OncologyUC IrvineUC Irvine

NeoplasticNeoplastic Transformation Transformation In VitroIn Vitro

Clear cancerClear cancer--related endpoint (conversion of related endpoint (conversion of cells from a noncells from a non--tumorigenictumorigenic to a to a tumorigenictumorigenicphenotype)phenotype)Has proven to clearly describe high dose Has proven to clearly describe high dose radiation carcinogenic effects radiation carcinogenic effects in vivoin vivo (dose, (dose, dosedose--rate, LET, chemical promoters, chemical rate, LET, chemical promoters, chemical protectors)protectors)Is proving useful to explore possible Is proving useful to explore possible mechanisms underlying the shape of the dosemechanisms underlying the shape of the dose--response curve at low dosesresponse curve at low doses


Limited in that the complexity of tissue Limited in that the complexity of tissue microenvironment, microenvironment, immunosurveillanceimmunosurveillanceetc. is absentetc. is absentLimited in terms of difficulty in Limited in terms of difficulty in transforming primary cells, particularly transforming primary cells, particularly primary human cellsprimary human cellsLimited number of cell systems Limited number of cell systems amenable to quantitative assay of amenable to quantitative assay of radiation effectsradiation effects


Normal Preneoplastic Neoplastic

Most, if not all, in vitro systems are examining the transformation from some preneoplasticstate to the neoplastic state. Is this relevant?


Most humans are carrying a burden of Most humans are carrying a burden of preneoplasticpreneoplastic cells in their bodiescells in their bodiesGiven that they are part way down the path to Given that they are part way down the path to cancer they could be considered a particularly cancer they could be considered a particularly important targetimportant targetAccording to According to FolkmanFolkman, most tissues harbor , most tissues harbor ““dormantdormant”” tumorigenictumorigenic cells. It is unclear cells. It is unclear whether in vitro studies can mimic any whether in vitro studies can mimic any possible radiation possible radiation ““activationactivation”” of such cellsof such cells


Amenable to the study of low dose effects, Amenable to the study of low dose effects, but requires extensive and laborbut requires extensive and labor--intensive intensive experimentation to achieve even reasonable experimentation to achieve even reasonable statisticsstatisticsTwo experimental systems (C3H10T1/2 and Two experimental systems (C3H10T1/2 and the the HeLaHeLa x skin fibroblast human hybrid cell x skin fibroblast human hybrid cell assay) have demonstrated assay) have demonstrated hormetichormetic responses responses at low doses of low LET radiations and a Jat low doses of low LET radiations and a J--shaped doseshaped dose--response curveresponse curve

HeLa X Skin Fibroblast Hybrid Cells And HeLa X Skin Fibroblast Hybrid Cells And The Study of Tumor Suppressor FunctionThe Study of Tumor Suppressor Function

Tumorigenicity and IAP expression are negatively regulated by a suppressor on chromosome 11

XHeLaT/IAP+

Skin FibroblastNT/IAP-

Hybrid Cell, CGL 1NT/IAP-

Hybrid CellCGL3 & CGL4T/IAP+

Schema Assay of HeLa X Fibroblast Human Schema Assay of HeLa X Fibroblast Human Hybrid Cell Neoplastic Transformation By Hybrid Cell Neoplastic Transformation By

RadiationRadiation

Plate Cells Irradiated(late log/early plateau)

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Dose Dependence of Cs-137 γ Radiation Induced Neoplastic Transformation In Vitro.T

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Dose (cGy) Redpath et al. Radiat. Res. 156; 700-707, 2001

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Dose Dependence of Cs-137 γ Radiation Induced Neoplastic Transformation In Vitro: Low Dose Deviation from Linear Extrapolation from High Doses.

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Redpath et al. Radiat. Res. 156; 700-707, 2001

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DoseDose--response curve for neoplastic transformation response curve for neoplastic transformation of human hybrid cells by 60 of human hybrid cells by 60 kVpkVp XX--raysrays

+/- S.E.

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Dose-response curve for neoplastic transformation of human hybrid cells by 28 kVp X-rays

DoseDose--response curve for response curve for neoplasticneoplastic transformation transformation of human hybrid cells by 28 of human hybrid cells by 28 kVpkVp XX--rays: Two data rays: Two data

sets normalized to the same spontaneous frequencysets normalized to the same spontaneous frequency

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Heyes & Mill, Radiat. Res. 162:120-127, 2004.

Ko et al.,Radiat. Res. 162:646-654, 2004.

NeoplasticNeoplastic Transformation In VitroTransformation In Vitro

In summary, we have routinely observed JIn summary, we have routinely observed J--shaped doseshaped dose--response curves following HDR response curves following HDR treatment and are interested in mechanisms treatment and are interested in mechanisms underlying this shapeunderlying this shapeStudies with the human hybrid cell system Studies with the human hybrid cell system indicate that there may be at least two indicate that there may be at least two phenomena involvedphenomena involvedLow dose hyperLow dose hyper--radiosensitivityradiosensitivity of a of a transformationtransformation--sensitive subpopulation (G2?)sensitive subpopulation (G2?)Induction of DNA repair. Future studies will Induction of DNA repair. Future studies will examine the roles of NHEJ and HR using examine the roles of NHEJ and HR using RNAiRNAi..


We have recently performed doseWe have recently performed dose--rate rate studies using an Istudies using an I--125 irradiator that is 125 irradiator that is allowing us to look at doseallowing us to look at dose--rates <2.0 rates <2.0 mGymGy/min of ca. 30 /min of ca. 30 keVkeV photons with the photons with the aim of comparing the data with that aim of comparing the data with that seen at high doses for high doseseen at high doses for high dose--rates rates of similar energy (28 of similar energy (28 kVpkVp) ) mammography xmammography x--rays (Heyes and Mill, rays (Heyes and Mill, Rad. Res. 162:120, 2004; Ko et al., Rad. Rad. Res. 162:120, 2004; Ko et al., Rad. Res. 162:646, 2004).Res. 162:646, 2004).

Dose Linearity

y = 12.08xR2 = 0.9944

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DoseDose--Response for Induction of Response for Induction of NeoplasticNeoplasticTransformation at Low Dose RatesTransformation at Low Dose Rates

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0.91 mGy/min


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28 kVp, HDRI-125, 1.9 mGy/minI-125, 0.91 mGy/minI-125, 0.47 mGy/minI-125, 0.19 mGy/min

Neoplastic Transformation In Vitro: Relative Risk vs. Dose and Dose-Rate

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28 kVpI-125, 1.9 mGy/minI-125, 0.91 mGy/minI-125, 0.47 mGy/minI-125, 0.19 mGy/min

Neoplastic Transformation In Vitro: Relative Risk vs. Dose and Dose-Rate


Not unexpectedly, the data show that as the Not unexpectedly, the data show that as the dosedose--rate is decreased the effectiveness of rate is decreased the effectiveness of the radiation in inducing the radiation in inducing neoplasticneoplastictransformation decreases.transformation decreases.At doseAt dose--rates of 0.19 and 0.47 rates of 0.19 and 0.47 mGymGy/min no /min no induction of transformation is seen up to a induction of transformation is seen up to a dose of 1000 dose of 1000 mGymGy, and the data suggest that , and the data suggest that there may be a suppression of transformation there may be a suppression of transformation at these doseat these dose--rates, i.e. rates, i.e. certainly docertainly do not not conform to the LNT model.conform to the LNT model.


Now to the $64,000 question! Is there Now to the $64,000 question! Is there any evidence for Jany evidence for J--shaped doseshaped dose--response curves in the animal and human response curves in the animal and human epidemiological data?epidemiological data?The answer is a qualified yes, i.e. there The answer is a qualified yes, i.e. there are trends in this direction but these are trends in this direction but these are not significant.are not significant.

Low Dose Radiation Carcinogenesis In VivoLow Dose Radiation Carcinogenesis In Vivo

Several Several in vivoin vivo studies of the effects of low studies of the effects of low doses of low LET radiation cannot rule out doses of low LET radiation cannot rule out the notion of a threshold dose.the notion of a threshold dose.Ullrich and Ullrich and StorerStorer (1979) indicated (1979) indicated thresholds of 0.22 thresholds of 0.22 GyGy for myeloid for myeloid leukemia, and 0.10 leukemia, and 0.10 GyGy for ovarian, for ovarian, pituitary and pituitary and HarderianHarderian gland tumors, fit gland tumors, fit the data as well as the LNT model. the data as well as the LNT model.

UNSCEAR, 2000 from Little & Muirhead, 1998.

Low Dose Radiation Carcinogenesis In VivoLow Dose Radiation Carcinogenesis In Vivo

Little and Little and MuirheadMuirhead (IJRB 74:47(IJRB 74:47--180, 1998) indicated 180, 1998) indicated that the dosethat the dose--response was curved but with response was curved but with ““absence of absence of evidence of thresholdevidence of threshold””, yet a:, yet a:Fit of a threshold model with a linear dose response Fit of a threshold model with a linear dose response above the threshold resulted in a best estimate of a above the threshold resulted in a best estimate of a threshold of 0.16 threshold of 0.16 SvSv (95% CI 0.05(95% CI 0.05--0.40) with two0.40) with two--sided sided p=0.001 for departure from a threshold of zerop=0.001 for departure from a threshold of zeroFit of a threshold model with a quadratic term above the Fit of a threshold model with a quadratic term above the threshold resulted in a best estimate of a threshold of threshold resulted in a best estimate of a threshold of 0.09 0.09 SvSv (95% CI <0.00(95% CI <0.00--0.29) with two0.29) with two--sided p=0.07 for sided p=0.07 for departure from thresholddeparture from threshold

Lubin et al., Rad. Res. 161:359-368, 2004


It is clear that the degree of It is clear that the degree of suppression and threshold dose is going suppression and threshold dose is going to be target tissueto be target tissue--dependentdependentIt will also be very doseIt will also be very dose--rate dependent rate dependent and there are very little human and there are very little human epidemiological data at low doseepidemiological data at low dose--ratesratesAnimal data at low doseAnimal data at low dose--rate often show rate often show apparent thresholds for low LET apparent thresholds for low LET radiationradiation


Can in vitro experiments provide data that Can in vitro experiments provide data that can give an idea of the relative risk of cancer can give an idea of the relative risk of cancer induction in humans?induction in humans?For a whole lot of reasons alluded to earlier For a whole lot of reasons alluded to earlier one would say no. However, it is interesting one would say no. However, it is interesting that when compares relative risks from that when compares relative risks from epidemiologic data with those from in vitro epidemiologic data with those from in vitro transformation data there is surprising transformation data there is surprising agreement, at least for certain tumors.agreement, at least for certain tumors.

Relative Risk vs. DoseRelative Risk vs. Dose

Comparison of In Vitro and Epidemiologic DataComparison of In Vitro and Epidemiologic Data

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Cs-13760 kVpCo-60Leukemia-mortalityLeukemia-incidenceBreast-incidenceBreast-mortality


What about a comparison of risk estimations (What about a comparison of risk estimations (epiepi vs. vs. in vitro) for low dosein vitro) for low dose--rate radiation?rate radiation?Very little Very little epiepi data for chronic exposures), but there data for chronic exposures), but there is a study from Sweden (is a study from Sweden (LundellLundell et. al., Rad. Res. et. al., Rad. Res. 151:626151:626--632, 1999) for breast cancer as a result of 632, 1999) for breast cancer as a result of low doselow dose--rate (median dose rate to breast of 0.4 rate (median dose rate to breast of 0.4 mGymGy/min) radium plaque treatments for /min) radium plaque treatments for hemangiomashemangiomas..Data from this study is included in a paper on Data from this study is included in a paper on radiationradiation--induced breast cancer by Preston et al., induced breast cancer by Preston et al., Rad. Res. 158:220Rad. Res. 158:220--235, 2002).235, 2002).Both of these papers concluded that the data were Both of these papers concluded that the data were consistent with the LNT model BUT consistent with the LNT model BUT LundellLundell did did indicate that only at doses >1 indicate that only at doses >1 GyGy was there a positive was there a positive association with breast cancer risk.association with breast cancer risk.

Relative Risk vs. DoseRelative Risk vs. DoseBreast cancer following LDR treatment for Breast cancer following LDR treatment for hemangiomahemangioma

G. Stanford

Breast Cancer Incidence Rate vs. DoseBreast Cancer Incidence Rate vs. DoseBreast cancer following LDR treatment for Breast cancer following LDR treatment for hemangiomahemangioma

R. Facius

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Relative Risk vs. Dose for Breast CancerRelative Risk vs. Dose for Breast CancerComparison of HDR and LDR Epidemiologic DataComparison of HDR and LDR Epidemiologic Data

Comparison of Relative Risk for Transformation with Comparison of Relative Risk for Transformation with Breast Cancer Induction at High and Low DoseBreast Cancer Induction at High and Low Dose--RatesRates

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LDR-BCa (Rad. Res. 158:220, 2002) 0.16-0.83 mGy/minHDR-BCa (Rad. Res. 158:220, 2002)

LDR (Cell Transformation Data - 2005) 0.47 mGy/minHDR (Cell Transformation Data - 2001) >3 mGy/min

NeoplasticNeoplastic Transformation Transformation In Vitro, In Vitro, HormesisHormesis and Risk Assessmentand Risk Assessment

In conclusion, In conclusion, neoplasticneoplastic transformation transformation in in vitrovitro has demonstrated strong evidence for has demonstrated strong evidence for hormetichormetic effects of low doses of loweffects of low doses of low--LET LET radiation at both high and low doseradiation at both high and low dose--rates.rates.NeoplasticNeoplastic transformation transformation in vitroin vitro has proven has proven capable of making relative risk estimates of capable of making relative risk estimates of cancer incidence that compare well with those cancer incidence that compare well with those seen epidemiologically for breast cancer and seen epidemiologically for breast cancer and leukemia.leukemia.

Supported by DOE GrantsSupported by DOE Grants

DEDE--FGFG--0707--99ER6287699ER62876DEDE--FGFG--0303--02ER6330902ER63309DEDE--FGFG--0202--0303--ER63548ER63548

AcknowledgementsAcknowledgementsUC IRVINEUC IRVINE LOMA LINDA U.LOMA LINDA U.J. Leslie RedpathJ. Leslie Redpath Greg NelsonGreg NelsonEugene ElmoreEugene Elmore SreveSreve RightnarRightnarXiaoyan LaoXiaoyan LaoRubenaRubena KapadiaKapadia GRAY CANCER INST.GRAY CANCER INST.

Peter JohnstonPeter JohnstonSabee MolloiSabee Molloi Susan ShortSusan ShortTom Taylor Tom Taylor Michael WoodcockMichael WoodcockCatherine ChristieCatherine Christie

UTSWUTSWYiYi--Ching LioChing LioDavid ChenDavid Chen

Dose Distribution

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100 cGy - Measured

100 cGy - Calculated

Breast Cancer Incidence Rate vs. DoseBreast Cancer Incidence Rate vs. DoseBreast cancer following LDR treatment for Breast cancer following LDR treatment for hemangiomahemangioma

R. Facius

Relative Risk vs. DoseRelative Risk vs. DoseBreast cancer following LDR treatment for Breast cancer following LDR treatment for hemangiomahemangioma

R. Facius

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LDR-BCa (Rad. Res. 158:220, 2002)

HDR-BCa (Rad. Res. 158:220, 2002)

Relative Risk vs. Dose for Breast CancerRelative Risk vs. Dose for Breast CancerComparison of HDR and LDR Epidemiologic DataComparison of HDR and LDR Epidemiologic Data

The shape of the dose response curve for The shape of the dose response curve for radiationradiation--induction of cancer by low LET induction of cancer by low LET

radiation radiation –– Two official positionsTwo official positions

BEIR VII Phase 2 report from the U.S. National BEIR VII Phase 2 report from the U.S. National Academy of Sciences supports the LNT model Academy of Sciences supports the LNT model down to zero dose. down to zero dose. The French Academy of Sciences and National The French Academy of Sciences and National Academy of Medicine does not support the Academy of Medicine does not support the LNT model at doses <100 LNT model at doses <100 mSvmSv..The French committee was of the opinion that The French committee was of the opinion that the evidence from laboratory, and some the evidence from laboratory, and some epidemiology studies, was sufficiently strong to epidemiology studies, was sufficiently strong to indicate that the LNT model will likely indicate that the LNT model will likely overestimate risk at doses <100 overestimate risk at doses <100 mSvmSv, and , and almost certainly at doses <10 almost certainly at doses <10 mSvmSv. .

NeoplasticNeoplastic Transformation Transformation In Vitro, In Vitro, HormesisHormesis and Risk Assessmentand Risk Assessment

In conclusion, In conclusion, neoplasticneoplastic transformation transformation in vitroin vitro has been demonstrated to has been demonstrated to describe dosedescribe dose--response curve shapes response curve shapes that are consistent with those seen in that are consistent with those seen in epidemiologic studies of radiationepidemiologic studies of radiation--induced breast cancer and leukemia.induced breast cancer and leukemia.

radiation-induced neoplastic ... - dose-response

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