Inr J Radialron Oncology RioI Phvs Vol. I I, pp. 943-950 0360.3016/85 $03.00 + .CKl Pnnted ,n the U.S.A. All rights reserved. Copy&t &‘ 1985 Pergamon Press Ltd.

0 Original Contribution

EFFECTS OF 2-DEOXY-D-GLUCOSE ON GLYCOLYSIS, PROLIFERATION KINETICS AND RADIATION RESPONSE OF HUMAN CANCER CELLS

V. K. JAIN, PH.D.,’ V. K. KALIA, PH.D.,~ R. SHARMA, PH.D.,~

V. MAHARAJAN, PH.D.~ AND M. MENON, M.SC.~

‘Department of Biophysics, National Institute of Mental Health and Neuro Sciences, Bangalore- 029; *Department of Biophysics, All-India Institute of Medical Sciences, New Delhi; 3Cancer Research Institute, Bombay, India

The effects of 2-deoxy-D-glucose (2-DG) on energy metabolism, cell proliferation kinetics, radiation-induced DNA repair, and micronuclei formation in HeLa cells have been studied. Results show that the 2-DG induced modifications of the radiation effects are biphasic: (1) at high 2-DG concentrations (>2.5 mM), DNA repair is inhibited and manifestation of radiation damage is enhanced as observed by an increase in the radiation (X ray) induced micronuclei formation; (2) lower concentrations of 2-DG (~2.5 mM) do not inhibit DNA repair and a decrease in the frequency of micronuclei formation is observed. These data, in correlation with the effects of 2-DG on glycolysis and cell proliferation kinetics, can be explained by the hypothesis that 2-DG induced modifications of radiation effects arise as a result of energy linked differential inhibitions of pathways of repair and fixation of DNA damage. Implications for cancer therapy are discussed.

Radiation response, DNA repair, Micronuclei, 2-deoxy-D-glucose, Cell kinetics, Glycolysis, Cancer therapy.

INTRODUCTION

2-deoxy-D-glucose (2-DG), an antimetabolite of glucose, has been shown to differentially inhibit DNA repair and repair of potentially lethal damage (PLD) in cells in which glycolysis is the main pathway for the supply of metabolic energy.‘,’ 1,12,31 Since malignant tumors have high rates of glycolysis and also contain a substantial number of hypoxic cells, it was suggested”*12 that 2-DG in combination with ionizing radiation could lead to improvement in cancer therapy. Subsequent experiments to test this suggestion in tumor bearing animal models showed that 2-DG could indeed increase the radiation- induced tumor cell loss, tumor regression and survival of mice with Sarcoma-180 tumor.13 Recently, these results have also been confirmed in another tumor mode1.25 Investigations to examine the effects of 2-DG in normal animals under similar experimental conditions revealed that the presence of 2-DG actually reduced the radiation-induced chromosomal damage in normal bone- marrow cells of mice. lo In vitro experiments on normal human peripheral blood leukocytes stimulated by phy- tohaemmatoaglutinin (PHA) also indicated a reduction in the frequency of micronuclei formation in these cells, if 2-DG was present for a few hours after irradiation.16

The differential effects of 2-DG on the radiation response of normal and malignant cells could result from energy linked modifications of repair processes as suggested earlier. “9” However, repair processes, and consequently the expression of radiation damage, could also be influenced by changes in the duration of cell- cycle, since 2-DG has been shown to inhibit cell prolif- eration.2T21,24 The present work was undertaken to ex- amine these aspects more thoroughly in cancer cells of human origin. Therefore, effects of short-term post- irradiation 2-DG treatments were investigated on cellular energy metabolism, cell proliferation kinetics, radiation damage, and its repair at various levels of organization. Some of the results have been reported in a preliminary communication.15

METHODS AND MATERIALS

Growth of cell cultures The strain of HeLa cells used for these experiments

originated from the National Institute of Virology, Pune. Cells in cultures were grown in the minimum essential medium (MEM)* supplemented with 10% calf serum and antibiotics (penicillin: 100 IU/ml; streptomycin:

Supported by: Indian Council of Medical Research, New Delhi.

Reprint requests to: V. K. Jain, Ph.D. Acknowledgments-This work was supported in part by a grant from ICMR, New Delhi. V. K. Kalia received a fellowhip

from CSIR. The Flow-Cytometer was a gift from the Alexander- Von-Humboldt Foundation, West Germany.

Accepted for publication 5 December 1984. * BIOS, Bombay, India.

943

944 Radiation Oncology 0 Biology 0 Physics May 1985. Volume I I, Number 5

100 pg/ml; and kanamycin: 25 pg/ml). Twenty mM hepes buffer? was added to maintain pH at 7.4.

DN24 repair measurements

Stock cultures were grown at 37°C in 150 ml glass culture bottles containing 20 ml of the growth medium. Culture medium was changed every 48 hr.

For experiments on post-irradiation DNA repair and proliferation kinetics, cells were grown on cover slips in Leighton tubes containing 2 ml of the growth medium. Cell density was determined at various time intervals from cell suspensions obtained after trypsinization (0.1% trypsin, 1 min at 37°C) by counting cells in a hemato- cytometer.

Meusurements cf DNA content dispersion and cell-cycle distribution using flow cytometry

Cells were harvested by trypsinization, fixed in 70% ethanol and preserved at 4°C until measurements with the flow cytometer could be made. Methods for DNA specific staining of cells using 4,6-diamidino-2-phenylin- dole (DAPI),$ measurements with the flow cytometer, and calculations of the co-efficient of variation (C.V.), as well as cell-cycle distributions have been described earlier. ‘6.22

Glucose utilization

DNA repair was assayed by a method based on the measurements of unscheduled DNA synthesis using the autoradiographic technique.26 Cells grown on cover slips in Leighton tubes for at least 96 hr were used. Before irradiation, cover slips were incubated at 37°C in fresh medium containing 10 &i/ml of methyl-3-H-thymidine (3H-TdR) obtained from the Bhabha Atomic Research Centre, Bombay (Sp. act. 198 mCi/m mole). After 1 hr, the medium was removed, the cells were washed with tyrode solution, irradiated with y rays (10 Gy), and incubated at 37°C in tyrode containing 1% human serum, 10 &i/ml 3H-TdR, and different concentrations of 2-DG.5 After an interval of 2 hrs, the cover slips were taken out and incubated for 10 min in tyrode solution containing 100 pg/ml of non-radioactive TdR. Subse- quently, the cover slips were washed with 5% cold trichloro-acetic acid followed by tyrode, mounted on slides and fixed in methanol-acetic acid (3: 1). The slides were covered in the dark with pieces of stripping film* for autoradiography. After an exposure for 7 days at 4”C, the slides were developed and stained with Giemsa. To quantitate DNA repair, the number of grains/nucleus were counted under the microscope in at least 200 cells in each group. The S-phase cells could be clearly distin- guished by very dark labelling.

Glucose in the medium was estimated by the Somogyi- Nelson method.28 Measurement o/micronuclei jiequency

Luctate production Lactate was estimated according to the method of

Barker and Summerson.

Irrudiat ion ef cells For experiments on DNA repair, cells attached to

cover slips were irradiated at room temperature in a gamma cell with 60Co-gamma rays at a dose rate of 1 Gy/min (conducted at the Cancer Research Institute, Bombay). Absorbed dose was measured with the help of an energy independent ferrous sulphate dosemeter.

For experiments on micronuclei formation and flow cytometry, cells were irradiated in culture bottles after adding fresh medium (with or without 2-DG), with X rays (200 KV, 20 mA, half-value layer 1 mm Cu) from an X ray therapy machine. The dose rate was 0.45 Gy/min measured with a 0.4 cc ionization chamber. Irradiation was carried out at room temperature in culture bottles at a focal distance of 42.5 cm. The dose distribution in the irradiation field did not vary by more than 5%.

Cells from stock cultures were harvested by trypsini- zation and subcultures were set up in fresh medium (9 ml) in culture bottles at a cell density of about 5 X lo5 cells/ml. After 24 hr of growth, cells were washed and medium containing 2-DG was added. Irradiation with X rays was carried out as described and cells were incubated in the same medium at 37°C from 2-4 hr. 2- DG treatment was terminated by washing the cells with phosphate buffered saline and adding fresh medium. Cells were allowed to grow for at least one cell-cycle before harvesting and processing for observation. Slides were prepared as described earlier16 and micronuclei were identified according to criteria suggested by Coun- tryman and Heddle.’ At least 2000 interphase cells were scanned in each sample for scoring of micronuclei.

RESULTS

Energy metabolism Fig. 1 shows the effects induced by the presence of

various concentrations of 2-DG on glucose utilization and aerobic glycolysis (lactate production) in HeLa cells. Both these processes are inhibited by 2-DG; at equimolar

t Sigma Chemical Company, St. Louis, MO 63 178, U.S.A. $ Serva Feinbiochemica, 6 Heidelberg, Federal Republic of

Germany.

* AR-IO, Eastman Kodak International Sales Company, Inc., New York, U.S.A.

$ Serva Feinbiochemica, 6 Heidelberg, Federal Republic of Germany.

Modification of radiation response by 2-deoxy-D-glucose 0 V. K. JAIN et al. 945

60

60

20

0

o----o GLUCOSE UflLltAllON

o-m LACTATE PRODUCTION

1 I I I I I I1 I I I 0 5 10

CONCENTRATION OF 2-DO (mM)

Fig. 1. Effects of various concentrations of 2433 on the rates of glucose utilization and lactate production by HeLa cells. The points represent average values of 5 experiments.

concentrations of 2-DG and glucose (5 mM), the inhi- bition observed in glucose utilization is 35%, whereas aerobic glycolysis is reduced by 62%. These results are similar to the data obtained earlier on animal tumors.33

The reduction in glycolysis induced by 2-DG in HeLa cells is greater than in the glucose utilization, which indicates that after the transport into the cell, glycolysis may be further inhibited either by 2-DG or some of its metabolic products. It is known that 2-DG is transported inside the cell by the same system as glucose,*,30 and is phosphorylated by hexokinase to 2-DGd-phosphate, which is not further metabolized to any appreciable extent.*’ The enzyme hexose-phosphate isomerase has been shown to be inhibited by 2-DG-6-phosphate.32

Cell cycle

:

G,- phase S - phase (G$+l) - phase

L I I

Cell proliferation kinetics In agreement with previous studies,2,2’,24 the prolifer-

ation rate of cells was found to be severely reduced by the presence of 2-DG. In order to examine the effects on the various phases of the cell-cycle, studies were carried out with the flow cytometer. The distribution of cells in the various phases of the cell-cycle was determined from the flow cytograms. From the measurements of the doubling time of the cell population during the exponential growth phase, the average durations of the various cell-cycle phases were calculated assuming that all the cells were cycling (growth fraction equal to 1). Changes in the rates of cell proliferation and progression through the various phases of the cell-cycle as functions of 2-DG concentrations are depicted in Fig. 2. At low concentrations of 2-DG (4 mM). progression through the Gi- and S-phases is retarded to the greatest extent, but the inhibitory effect becomes saturated at higher concentrations. (G, + M)-phases, on the other hand, show very little change at lower 2-DG concentrations, although progression through these phases is strongly inhibited at concentrations greater than 5 mM. Quali- tatively similar results have been observed in Ehrlich- ascites tumor cells of the mouse.2’.24

DNA repair Fig. 3 shows the effects of 2-DG (10 mM) on the

DNA repair as measured by the unscheduled DNA synthesis technique using autoradiography. The grain counts/nucleus observed in HeLa cells under different experimental conditions have been classified into 3 categories in the histograms shown: (1) cells showing very high grain counts (> 100) (2) cells with intermediate grain counts (2 l- 100) and, (3) cells with very few grains (~20). Fig. 3 indicates that after irradiation with gamma rays, the number of cells in category 2 increased signif- icantly and that such an increase could be prevented by the presence of 10 mM 2-DG in the incubation medium.

I 1

n 0 5 10 0 5 10 0 5 10 0 5 10

CONCENTRATION OF 2-DEOXY-D- GLUCOSE ( mM)

Fig. 2. 2-DG induced reductions in the rate of cell proliferation pLc and rates of cell progress through the various phases of the cell cycle. In the controls (without 24X), the cell-cycle time was 15.2 + 1.7 hr. The cell cycle distributions were determined by flow cytometry. The points show average values of two experiments.

946 Radiation Oncology 0 Biology 0 Physics May 1985. Volume 1 I, Number 5

90 CONTROL CONTROL 10 GY ZOG(lOmM) lOGY+2-OGtlOmM) Oh 2h 2h 2h 2h

GRAINS/NUCLEUS 0.0-20 GRAINS, 21-100 GRAINS, 1. ,100 GRAINS

EFFECT OF 2 DEOXY-D- GLUCOSE ON THE RADIATION INDUCED INCORPORATION OF 3H-THYMlDlNE IN HUMAN CANCER CELLS ( HELA)

Fig. 3. Gamma ray induced DNA repair and its modification by 2-DG in HeLa cells. The incorporation of 3H- TdR was measured after different treatments bv autoradiography. Distributions of grain counts/nucleus in at

_ least 200 cells in each group are shown.

Since cells in category 2 are representative of cells carrying out DNA repair. these data show that DNA repair could be inhibited completely by 2-DG at this concentration. At 5 mM 2-DG, the inhibition in DNA repair was 70%, whereas 2.5 mM 2-DG did not show any significant effect. Inhibition of X-ray induced DNA repair by 2-DG has been observed earlier in respiratory- deficient mutants of yeast.’ and also in UV-irradiated leukocytes in the presence of antimycin A from chronic myeloid leukemia patients.” SThioglucose (5TG). an- other glucose analogue and a strong inhibitor of glycol- ysis, has also been reported to inhibit DNA repair.”

To study the effects of similar treatments on radiation- induced cytogenetic damage, frequencies of micronuclei in HeLa cells were investigated. Fig. 4 shows the effects of 2-DG (5 mM) treatments on the radiation-induced micronuclei formation measured 25 hr after irradiation. The average frequency of cells with micronuclei observed in x-irradiated (2 Gy) cultures was 3.2%. which increased to 4.3 and 5.3% in the presence of 2-DG for 2 and 4 hr. respectively. Thus, the presence of 2-DG significantly increased the micronuclei formation as a result of x-irradiation (p < 0.01. d.f. = 1). In the unirradiated controls, the frequency of cells with micronuclei was 0.5%. and the treatment with 2-DG had no significant effect. The increase in the micronuclei frequency cannot be induced by the effects of 2-DG on cell proliferation kinetics. since a reduction in the rate of cell proliferation (Fig. 2) should lead to a decrease in the frequency of micronuclei. Therefore, the observed increase in mi- cronuclei formation could be the result of the inhibition of DNA repair in the presence of 2-DG.

In contrast to the present results with HeLa cells, it has been reported15,‘” that similar 2-DG treatment (5 mM. 2 hr) led to a decrease in the micronuclei frequency

induced by x-irradiation in PHA-stimulated peripheral human blood leukocytes: Fig. 5 compares the results obtained with the two systems. In human leukocytes, DNA repair is not inhibited by 2-DG under similar experimental conditions; it was suggested that 2-DG could reduce the micronuclei formation in these cells by slowing down the progression of the cell cycle,

A: NO TREATMENT

B: 2-DG (5mM, 2h)

C: X RAYS (2GY)

2 6 - D 2-DG (5mM, 2h) +X RAYS (ZGY)

E. 2- DG (5mM, 4h )+X RAYS (2GY 1

D E

Fig. 4. Effects of 2-DG (5 mM) treatments on X ray induced micronuclei in HeLa cells measured 25 hr after irradiation. Experimental conditions were similar to those in Fig. 3. At least 3,000 cells per group were scanned. The ordinate shows percentage of cells with micronuclei observed after different treatments.

Modification of radiation response by 2-deoxy-D-glucose 0 V. K. JAIN et al. 941

0 X RAYS (2GY 1

0 X RAYS (2GY) + 2-DG(5mM,2h)

0 20 LO 60 60 o 20 60 60 80

POST IRRADIATION TIME ( At/h)

Fig. 5. Effects of 2-DG treatment on the X ray induced micronuclei formation in normal and malignant cells. (A) Human peripheral blood leukocytes (PBL) treated 27 hr after PHA stimulation (data from ref. 16); (B) HeLa cells. 0 - 0: X rays (2 Gy), 0 - 0: X rays (2 Gy) + 2-DG (5 mM, 2 hr).

thereby giving more time for the restitution of chro- mosomal breaks.‘5316 If a similar mechanism operated in the HeLa cells also, one might expect a decrease in the micronuclei formation at lower 2-DG concentrations (~2.5 mM), which do not inhibit DNA repair. To verify this, effects on different concentrations of 2-DG on X ray induced micronuclei formation were studied. The results, presented in Fig. 6, demonstrate that the mi- cronuclei formation is indeed reduced at 2-DG concen- trations lower than 2.5 mM. Interestingly, a minimum value is obtained at a concentration of 1 mM 2-DG.

DISCUSSION

In the present work, the effect of 2-DG on energy metabolism, cell proliferation kinetics, and on two dif- ferent cellular responses to radiation damage (DNA repair and micronuclei formation) have been studied. 2-DG was present only for 2-4 hr immediately after irradiation. Although the radiation dose had to be different for the measurement of these responses (because of practical reasons), the basic experimental design was similar. Therefore, to study possible relationships between energy metabolism, cell proliferation, DNA repair, and radiation response, the results obtained will be discussed in an integrated manner.

Our earlier investigations have shown that the repair of DNA3’ and potentially lethal damage (PLD)’ need continuous flow of metabolic energy in the form of adenosine-u-i-phosphate (ATP). If this energy flow is reduced below a critical threshold value I?,‘, the repair

processes are completely inhibited. The present study shows that 2-DG strongly reduces glycolysis, an impor- tant energy yielding pathway in tumor cells. Since the

1

t

0 X rays(2Gy) o Un irradiated controls 7

‘J-l

Ii w 0 1

~~__-r-____~____-___-____a 0 ‘I’.‘.‘.‘.‘.‘.‘.‘.‘.’

0 2 c 6 6 1C 2-DG CONCENTRATION (ml41

I

Fig. 6. Frequency of cells with micronuclei as a function of 2- DG concentration in x-irradiated HeLa cell cultures. 24x3 treatment was given for 2 hr and the cells were allowed to grow for 50 hr after irradiation.

948 Radiation Oncology 0 Biology 0 Physics May 1985, Volume I I, Number 5

oxygen consumption is not affected much by 2-DG,8,33 inhibition in energy (ATP) supply can be assumed to be proportional to inhibition of glycolysis. In order to examine the relationship between the inhibition of energy flow and other effects induced by 2-DG, we have plotted the average relative values of the cell proliferation rate, DNA repair, and frequencies of micronuclei formation as functions of rate of glycolysis (Fig. 7). It should be pointed out, however, that the rate of cell proliferation, put (Fig. 2) was determined from the mean doubling time, td, of the cell population during the exponential phase of growth. It was assumed that the average duration of the cell-cycle, t,, was equal to td, so that pLc = In 2/b. This is true only when all the cells in the population are cycling (growth fraction equal to 1). Possible changes in the growth fraction due to the presence of 2-DG have not been determined. However, in view of the short duration for which 2-DG was present (2-4 hr) in the experiments under discussion, such effects are expected to be small and will not alter the essential features of relationships depicted in Fig. 7.

reasons for a stronger dependence of repair processes on the rate of glycolysis are not presently clear and need further study. Besides ATP, nicotinamide-di-nucleotide (NAD) could also be necessary for DNA repair. Recently, it has been shown that NAD is required for the synthesis of poly (ADP-ribose), which might be involved in DNA repair.‘4,‘8

Fig. 7 indicates that DNA repair is more strongly dependent upon glycolysis than the rate of cell prolifer- ation. Rate of repair of PLD in irradiated yeast cells was also observed to be inhibited to a greater extent than the cell proliferation rate, by reductions in the rate of ATP-production via the glycolytic pathway.* The

The differences in the energy dependence of DNA repair and cell proliferation, however, may have impor- tant implications for the expression of radiation damage, since the processes of cell proliferation are also intimately associated with the misrepair and fixation of lesions. Fig. 8 shows schematically some of the important events that occur after induced radiation damage in living cells. DNA, which is the carrier of genetic information, forms the most important target. Therefore the radiation- induced cellular damage may be categorized into DNA and non-DNA lesions. Formation of lesions may be followed by a number of physico-chemical and metabolic reactions resulting in reversal, removal or transformation of the lesions. The DNA lesions, for example, may be acted upon by error-free (1) and/or error-prone (2) repair pathways or alternatively, the lesions may be transformed into stable and irrepairable forms (3) leading to the fixation of the cellular damage. The error-free repair (excision repair) pathway restores completely the chromatin structure and the genetic information encoded in the nucleotide sequence of the DNA strands. The error-prone pathways, on the other hand, may induce changes in the genetic information (misrepair), which are compatible with cell survival but lead to altered cell functions (mutations). The cellular radiation response will be determined by the relative contributions of the various pathways, which influence the ultimate fate of the DNA lesions. The misrepaired or unrepaired DNA lesions may give rise to mutations, chromosomal aber- rations, micronuclei and cell death.

1 I ,- MICRONUCLEI I

I

I I

I 1 I ! , I I 0 20 40 60 80 100

RATE OF GLYCOLYSIS 1% OF CONTROL)

Fig. 7. DNA repair, rate of cell proliferation and micronuclei frequency as functions of rate of glycolysis in HeLa cells.

The unscheduled DNA synthesis (UDS) technique used in the present work is supposed to monitor the error-free excision repair pathway. This pathway com- prises the incision and excision steps to remove the lesions from the damaged DNA strand, resynthesis of the removed nucleotide sequence using the undamaged complimentary strand as template and finally rejoining the broken ends to restore the original DNA duplex. The excision repair pathway operates efficiently in the pre-replication phase. The error-prone repair pathways, on the other hand, become manifest during and after DNA replication, involving obscure and complex mech- anisms, which permit the bypass of lesions by the replication fork and subsequent gap filling by steps similar to those responsible for genetic recombination. It has been shown that the pathways for error-prone repair and fixation of DNA lesions are linked with the progression of the cell in the cell-cycle,4v29 whereas the sub-optimal growth conditions facilitate error-free repair and result in an increase of cell surviva1.‘7~20~23

The most common DNA lesions caused by ionizing

Modification of radiation response by 2-deoxy-D-glucose 0 V. K. JAIN ef al.

MUTATION

_--- -TUMOR , AGING, GENETlC DISEASES

;_@dI>@ FIXATION

DNA

IQ-=

CHKOMOSOMAL MICRONUCLEI DEAD DAMAGE ABERRATIONS

t REPAIR

ATP 1 I

ATP

Q-(&J

NON - DNA REPAIRED DNA i

CAWPE ----------------------------------- -1

+GD,G, ___Ic( CELL PROLIFERATION 1 I- POST-l RRADIATION TIME .p+

Fig. 8. A simple model depicting schematically some of the important cellular responses after radiation induced damage.

949

radiations are the strand breaks. DNA strand breaks, if unrepaired, may result in chromosome breaks or frag- ments. After mitotic division, chromosome fragments may give rise to cells with micronuclei and eventually to cell death. A quantitative relationship between the frequencies of chromosomal aberrations and micronuclei has been demonstrated, and the micronuclei formation has been reported to decrease with the repair of chro- mosome breaks in x-irradiated human leukocytes.‘j Re- cently, it has also been shown that the frequency of micronuclei decreases during the repair of potentially lethal damage in x-irradiated Ehrlich ascites tumor cells (Bertche, U., written communication, March 1983). Thus, micronuclei formation is a good index for mea- suring residual DNA damage. The results of the present study show that the 2-DG induced modifications of the micronuclei frequency after irradiation depend upon 2- DG concentration in a biphasic manner (Fig. 6). These results can be explained on the basis of the model shown in Fig. 8, taking into consideration the relationships between error-free DNA repair, cell proliferation, and glycolysis as demonstrated in Fig. 7. The important characteristics of these relationships can be described in 3 regions as follows:

Region Z. If the reduction in the energy supply (glycolysis) is small (low concentrations of 2-M;), the rate of error-free DNA repair (k,) remains unchanged, but the rate of cell proliferation, and hence the rates of misrepair (k2) and fixation (k3) are somewhat reduced. This means a greater number of cells would be able to repair DNA through the error-free pathway (1) resulting in a reduction in the number of cells with micronuclei.

Region ZZ. If the glycolysis is reduced further, the rate of DNA repair (k,) is also reduced, which means that the frequency of cells with micronuclei starts increasing although it still remains below the control values.

Region ZZZ. On decreasing the glycolysis still further (high concentrations of 2-DG), ki decreases more rapidly than k2 and k3 so that in this region k, < (k2 + k3). Consequently, the number of cells able to complete error-free DNA repair reduces drastically, so that the frequency of cells with micronuclei increases above the control value.

Thus, the differential modifications of the radiation effects induced by 2-DC can be understood on the basis of its effects on energy metabolism, since the rate of energy supply via the glycolytic pathway influences the pathways of error-free DNA repair and lesion in different ways (Fig. 7).

fixation

Implications for improving tumor radiotherapy with 2-deoxy-D-glucose

The data and the model presented here support our earlier suggestion’1~12 that 2-DG could be used to opti- mize radiotherapy by differentially enhancing radiation damage to cancer cells and reducing damage to normal cells. However, the present study indicates that to achieve an enhancement of radiation damage in tumors (Region III, Fig. 7), it would be necessary to maintain relatively high concentrations of 2-DG (-5 mM) in the tumor for a few hours after irradiation. If the concentration of 2-DG in the tumor is low, a reduction in the radiation damage in cancer cells may result (Regions I and II).

950 Radiation Oncology 0 Biology 0 Physics May 1985. Volume I I, Number 5

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