Both
bisphosphonates and
radiotherapy are highly effective for the management of bone
metastases. Our in vitro study examined the cytotoxic effects resulting from combinations of
ibandronate and ionising radiations (RX) in various sequences on
breast cancer cells. Single radiation doses were given before, at halftime of, or after acute
ibandronate incubation (48 h). Single or fractionated radiation doses were applied at the end of chronic
ibandronate incubation (5 weeks). Combination of acute
ibandronate exposure and single radiation doses led to synergistic cytotoxic effects in MDA-MB-231 cell line, but only with low
ibandronate concentrations in MCF-7 cell line. In both cell lines, synergy was more marked when
ibandronate followed RX. After long-term
ibandronate exposure, only high single radiation doses induced synergistic effects in MDA-MB-231 cell line. Synergy was only detected with low
ibandronate concentrations in MCF-7 cell line. In both cell lines, fractionated radiation doses exerted similar effects. The combination of
ibandronate with radiation can exert synergistic effects on the inhibition of
breast cancer cells growth, depending on cell line,
drug sequence and dosage. Our data might provide a rationale for associating
bisphosphonates and
radiotherapy for the treatment of bone
metastases from
breast cancer.