The decreased influence of overall treatment time on the response of human breast tumor xenografts following prolongation of the potential doubling time (Tpot)

Jann N Sarkaria, John F. Fowler, Mary J. Lindstrom, V. Craig Jordan, R. Timothy Mulcahy

Research output: Contribution to journalArticle

17 Citations (Scopus)

Abstract

Purpose: Repopulation during fractionated radiotherapy has been postulated to result in a significant loss in local control in rapidly proliferating tumors. Clinical data suggest that accelerated fractionation schedules can overcome the influence of repopulation by limiting the overall treatment time. Unfortunately, accelerated therapy frequently leads to increased acute reactions, which may become dose limiting. An alternative to accelerated fractionation would be to decrease the rate of repopulation during therapy. To test the potential efficacy of this alternative, we examined the effect of reducing tumor proliferation rate on the response of MCF-7 human breast carcinoma xenografts treated with a short vs. a long course of fractionated therapy. To reduce the proliferation rate, we deprived nude mice transplanted with MCF-7 xenografts of the growth-stimulating hormone estradiol (E2). We have previously reported that E2 deprivation increases the potential doubling time (Tpot) for MCF-7 xenografts from a mean of 2.6 days to 5.3 days (p < 0.001). Methods and Materials: E2-stimulated and E2-deprived MCF-7 breast carcinoma xenografts were clamped hypoxically and irradiated with four fractions of 5 Gy each, using either a short (3-day) or long (9-day) treatment course. E2 stimulation was restored in all animals at the completion of irradiation. Radiation response was determined by regrowth time and regrowth delay of the irradiated tumors as compared to unirradiated controls. Results: Prolongation of therapy in rapidly proliferating, E2-stimulated tumors (Tpot ≈ 2.6 days) resulted in a significant decrease in regrowth time in two identical experiments. With results pooled for analysis, the regrowth times for the short and long treatments were 62 and 32 days, respectively (combined p < 0.001). The shorter regrowth times suggest that there was less overall tumor damage with the longer fractionated radiotherapy course. No significant difference in regrowth time was observed in the more slowly proliferating, E2-deprived tumors (Tpot ≈ 5.3 days) treated with either the short or long regimen. Median regrowth times were 48 and 54.5 days for the short and long treatments, respectively (combined p = 0.14). Similar changes were observed in regrowth delay. Conclusions: Reduction in the rate of cell proliferation, induced by E2 deprivation in MCF-7 human breast xenografts during fractionated radiotherapy, resulted in a significantly decreased dependence on overall treatment time in comparison to the more rapidly proliferating E2-stimulated tumors. This model suggests that pharmacologically induced reduction in the rate of tumor cell proliferation during a course of fractionated radiotherapy may be a viable alternative to accelerated fractionation for the treatment of rapidly proliferating tumors.

Original languageEnglish (US)
Pages (from-to)833-840
Number of pages8
JournalInternational Journal of Radiation Oncology, Biology, Physics
Volume31
Issue number4
DOIs
StatePublished - Feb 15 1995
Externally publishedYes

Fingerprint

prolongation
Heterografts
breast
tumors
Breast Neoplasms
radiation therapy
Neoplasms
therapy
fractionation
Radiotherapy
deprivation
Therapeutics
cancer
pituitary hormones
Cell Proliferation
schedules
stimulation
mice
animals
Nude Mice

Keywords

  • Fractionated irradiation
  • Mammary tumor xenograft
  • Overall treatment time
  • Potential doubling time
  • Repopulation
  • Tumor proliferation

ASJC Scopus subject areas

  • Cancer Research
  • Oncology
  • Radiology Nuclear Medicine and imaging
  • Radiation

Cite this

The decreased influence of overall treatment time on the response of human breast tumor xenografts following prolongation of the potential doubling time (Tpot). / Sarkaria, Jann N; Fowler, John F.; Lindstrom, Mary J.; Jordan, V. Craig; Mulcahy, R. Timothy.

In: International Journal of Radiation Oncology, Biology, Physics, Vol. 31, No. 4, 15.02.1995, p. 833-840.

Research output: Contribution to journalArticle

@article{4c61e4c44edc4ca0892bdf3555d13e15,
title = "The decreased influence of overall treatment time on the response of human breast tumor xenografts following prolongation of the potential doubling time (Tpot)",
abstract = "Purpose: Repopulation during fractionated radiotherapy has been postulated to result in a significant loss in local control in rapidly proliferating tumors. Clinical data suggest that accelerated fractionation schedules can overcome the influence of repopulation by limiting the overall treatment time. Unfortunately, accelerated therapy frequently leads to increased acute reactions, which may become dose limiting. An alternative to accelerated fractionation would be to decrease the rate of repopulation during therapy. To test the potential efficacy of this alternative, we examined the effect of reducing tumor proliferation rate on the response of MCF-7 human breast carcinoma xenografts treated with a short vs. a long course of fractionated therapy. To reduce the proliferation rate, we deprived nude mice transplanted with MCF-7 xenografts of the growth-stimulating hormone estradiol (E2). We have previously reported that E2 deprivation increases the potential doubling time (Tpot) for MCF-7 xenografts from a mean of 2.6 days to 5.3 days (p < 0.001). Methods and Materials: E2-stimulated and E2-deprived MCF-7 breast carcinoma xenografts were clamped hypoxically and irradiated with four fractions of 5 Gy each, using either a short (3-day) or long (9-day) treatment course. E2 stimulation was restored in all animals at the completion of irradiation. Radiation response was determined by regrowth time and regrowth delay of the irradiated tumors as compared to unirradiated controls. Results: Prolongation of therapy in rapidly proliferating, E2-stimulated tumors (Tpot ≈ 2.6 days) resulted in a significant decrease in regrowth time in two identical experiments. With results pooled for analysis, the regrowth times for the short and long treatments were 62 and 32 days, respectively (combined p < 0.001). The shorter regrowth times suggest that there was less overall tumor damage with the longer fractionated radiotherapy course. No significant difference in regrowth time was observed in the more slowly proliferating, E2-deprived tumors (Tpot ≈ 5.3 days) treated with either the short or long regimen. Median regrowth times were 48 and 54.5 days for the short and long treatments, respectively (combined p = 0.14). Similar changes were observed in regrowth delay. Conclusions: Reduction in the rate of cell proliferation, induced by E2 deprivation in MCF-7 human breast xenografts during fractionated radiotherapy, resulted in a significantly decreased dependence on overall treatment time in comparison to the more rapidly proliferating E2-stimulated tumors. This model suggests that pharmacologically induced reduction in the rate of tumor cell proliferation during a course of fractionated radiotherapy may be a viable alternative to accelerated fractionation for the treatment of rapidly proliferating tumors.",
keywords = "Fractionated irradiation, Mammary tumor xenograft, Overall treatment time, Potential doubling time, Repopulation, Tumor proliferation",
author = "Sarkaria, {Jann N} and Fowler, {John F.} and Lindstrom, {Mary J.} and Jordan, {V. Craig} and Mulcahy, {R. Timothy}",
year = "1995",
month = "2",
day = "15",
doi = "10.1016/0360-3016(94)00540-0",
language = "English (US)",
volume = "31",
pages = "833--840",
journal = "International Journal of Radiation Oncology Biology Physics",
issn = "0360-3016",
publisher = "Elsevier Inc.",
number = "4",

}

TY - JOUR

T1 - The decreased influence of overall treatment time on the response of human breast tumor xenografts following prolongation of the potential doubling time (Tpot)

AU - Sarkaria, Jann N

AU - Fowler, John F.

AU - Lindstrom, Mary J.

AU - Jordan, V. Craig

AU - Mulcahy, R. Timothy

PY - 1995/2/15

Y1 - 1995/2/15

N2 - Purpose: Repopulation during fractionated radiotherapy has been postulated to result in a significant loss in local control in rapidly proliferating tumors. Clinical data suggest that accelerated fractionation schedules can overcome the influence of repopulation by limiting the overall treatment time. Unfortunately, accelerated therapy frequently leads to increased acute reactions, which may become dose limiting. An alternative to accelerated fractionation would be to decrease the rate of repopulation during therapy. To test the potential efficacy of this alternative, we examined the effect of reducing tumor proliferation rate on the response of MCF-7 human breast carcinoma xenografts treated with a short vs. a long course of fractionated therapy. To reduce the proliferation rate, we deprived nude mice transplanted with MCF-7 xenografts of the growth-stimulating hormone estradiol (E2). We have previously reported that E2 deprivation increases the potential doubling time (Tpot) for MCF-7 xenografts from a mean of 2.6 days to 5.3 days (p < 0.001). Methods and Materials: E2-stimulated and E2-deprived MCF-7 breast carcinoma xenografts were clamped hypoxically and irradiated with four fractions of 5 Gy each, using either a short (3-day) or long (9-day) treatment course. E2 stimulation was restored in all animals at the completion of irradiation. Radiation response was determined by regrowth time and regrowth delay of the irradiated tumors as compared to unirradiated controls. Results: Prolongation of therapy in rapidly proliferating, E2-stimulated tumors (Tpot ≈ 2.6 days) resulted in a significant decrease in regrowth time in two identical experiments. With results pooled for analysis, the regrowth times for the short and long treatments were 62 and 32 days, respectively (combined p < 0.001). The shorter regrowth times suggest that there was less overall tumor damage with the longer fractionated radiotherapy course. No significant difference in regrowth time was observed in the more slowly proliferating, E2-deprived tumors (Tpot ≈ 5.3 days) treated with either the short or long regimen. Median regrowth times were 48 and 54.5 days for the short and long treatments, respectively (combined p = 0.14). Similar changes were observed in regrowth delay. Conclusions: Reduction in the rate of cell proliferation, induced by E2 deprivation in MCF-7 human breast xenografts during fractionated radiotherapy, resulted in a significantly decreased dependence on overall treatment time in comparison to the more rapidly proliferating E2-stimulated tumors. This model suggests that pharmacologically induced reduction in the rate of tumor cell proliferation during a course of fractionated radiotherapy may be a viable alternative to accelerated fractionation for the treatment of rapidly proliferating tumors.

AB - Purpose: Repopulation during fractionated radiotherapy has been postulated to result in a significant loss in local control in rapidly proliferating tumors. Clinical data suggest that accelerated fractionation schedules can overcome the influence of repopulation by limiting the overall treatment time. Unfortunately, accelerated therapy frequently leads to increased acute reactions, which may become dose limiting. An alternative to accelerated fractionation would be to decrease the rate of repopulation during therapy. To test the potential efficacy of this alternative, we examined the effect of reducing tumor proliferation rate on the response of MCF-7 human breast carcinoma xenografts treated with a short vs. a long course of fractionated therapy. To reduce the proliferation rate, we deprived nude mice transplanted with MCF-7 xenografts of the growth-stimulating hormone estradiol (E2). We have previously reported that E2 deprivation increases the potential doubling time (Tpot) for MCF-7 xenografts from a mean of 2.6 days to 5.3 days (p < 0.001). Methods and Materials: E2-stimulated and E2-deprived MCF-7 breast carcinoma xenografts were clamped hypoxically and irradiated with four fractions of 5 Gy each, using either a short (3-day) or long (9-day) treatment course. E2 stimulation was restored in all animals at the completion of irradiation. Radiation response was determined by regrowth time and regrowth delay of the irradiated tumors as compared to unirradiated controls. Results: Prolongation of therapy in rapidly proliferating, E2-stimulated tumors (Tpot ≈ 2.6 days) resulted in a significant decrease in regrowth time in two identical experiments. With results pooled for analysis, the regrowth times for the short and long treatments were 62 and 32 days, respectively (combined p < 0.001). The shorter regrowth times suggest that there was less overall tumor damage with the longer fractionated radiotherapy course. No significant difference in regrowth time was observed in the more slowly proliferating, E2-deprived tumors (Tpot ≈ 5.3 days) treated with either the short or long regimen. Median regrowth times were 48 and 54.5 days for the short and long treatments, respectively (combined p = 0.14). Similar changes were observed in regrowth delay. Conclusions: Reduction in the rate of cell proliferation, induced by E2 deprivation in MCF-7 human breast xenografts during fractionated radiotherapy, resulted in a significantly decreased dependence on overall treatment time in comparison to the more rapidly proliferating E2-stimulated tumors. This model suggests that pharmacologically induced reduction in the rate of tumor cell proliferation during a course of fractionated radiotherapy may be a viable alternative to accelerated fractionation for the treatment of rapidly proliferating tumors.

KW - Fractionated irradiation

KW - Mammary tumor xenograft

KW - Overall treatment time

KW - Potential doubling time

KW - Repopulation

KW - Tumor proliferation

UR - http://www.scopus.com/inward/record.url?scp=0028920514&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0028920514&partnerID=8YFLogxK

U2 - 10.1016/0360-3016(94)00540-0

DO - 10.1016/0360-3016(94)00540-0

M3 - Article

C2 - 7860396

AN - SCOPUS:0028920514

VL - 31

SP - 833

EP - 840

JO - International Journal of Radiation Oncology Biology Physics

JF - International Journal of Radiation Oncology Biology Physics

SN - 0360-3016

IS - 4

ER -