Importance of maintenance therapy in C225-induced enhancement of tumor control by fractionated radiation.
OBJECTIVE
C225 strongly enhances tumor radioresponse when given concurrently with radiotherapy. We investigated whether additional therapeutic benefit could be achieved by continuing maintenance treatment with C225 after the completion of fractionated radiotherapy.


METHODS
A431 xenografts were treated with local irradiation or combined with C225 by two different schedules: (1) 6 h before the first dose of irradiation and at 3-day intervals for a total of 3 doses during the 7-day fractionated radiotherapy, or (2) 6 doses of C225 given both during radiotherapy and continuing for 3 additional doses after radiotherapy. Tumor cure was assessed by the radiation dose yielding local tumor control in 50% of animals (TCD50), and time to recurrence was also determined.


RESULTS
Both treatment schedules increased radiocurability as evidenced by reductions in TCD50, but the effect was greater when C225 was given both during and after radiotherapy. C225 reduced the TCD50 of 83.1 (73.2-124.8) Gy by radiation only to 46.2 (39.1-57.5) Gy when given during radiotherapy and to 30.8 (22.2-38.0) Gy when given during and after radiotherapy. Dose modification factors were 1.8 when C225 was given during radiotherapy and 2.7 when given both during and after radiotherapy. C225 was also effective in delaying the onset of tumor recurrences, and was more effective when given as both concurrent and maintenance therapy.


CONCLUSIONS
Data showed that C225 strongly enhanced the curative effect of fractionated radiation, and its effect was greater if administration was extended beyond the end of radiotherapy. This important finding may influence future designs of clinical trials combining anti-EGFR (anti-epidermal growth factor receptor) agents with radiotherapy.
Milas
Luka
L
Department of Experimental Radiation Oncology, The University of Texas M D Anderson Cancer Center, Houston, TX 77030-4009, USA. lmilas@mdanderson.org
Fang
Fu-Min
FM
Mason
Kathy A
KA
Valdecanas
David
D
Hunter
Nancy
N
Koto
Masashi
M
Ang
K Kian
KK
D000818:Animals; D000911:Antibodies, Monoclonal / Q000627:therapeutic use*; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D000068818:Cetuximab; D019583:Dose Fractionation, Radiation; D004334:Drug Administration Schedule; D005260:Female; D051379:Mice; D008819:Mice, Nude; D009364:Neoplasm Recurrence, Local / Q000517:prevention & control; D009369:Neoplasms / Q000188:drug therapy* / Q000532:radiotherapy*; D011836:Radiation Tolerance / Q000187:drug effects* / Q000502:physiology
D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D000068818:Cetuximab