Combination therapy inhibits development and progression of mammary tumours in immunocompetent mice

Abstract

We have determined the effect of combining the chemotherapy agent doxorubicin and the anti-resorptive drug zoledronic acid on the early stages of spontaneous mammary tumour development using the immunocompetent PyMT mouse model that closely mimics human breast cancer development. 6-week-old PyMT mice were treated weekly for 6 weeks with PBS, 2 mg/kg doxorubicin, 100 μg/kg zoledronic acid or doxorubicin followed 24 h later by zoledronic acid (n = 15/group). Untreated, 6-week-old animals were used for comparison of tumour development. Tumour volume, apoptosis and angiogenesis were analysed on H&E, caspase 3, CD31 and CD34 stained histological sections. Proliferation was measured by BrdU incorporation and Ki67 staining and tumour macrophage infiltration assessed by F4/80 immunohistochemistry. Animals treated with doxorubicin followed by zoledronic acid did not develop palpable mammary tumours, whereas in all other treatment groups tumours progressed to late stage adenocarcinomas. Tumours from the combination treatment group were of comparable size to those in 6-week-old untreated animals, remaining pre-malignant with well-differentiated acinar arrangements and with tumour volume only reaching on average 26% of that in the PBS control group. Tumour cell apoptosis and proliferation was significantly reduced compared to control, single agent or untreated 6-week-old mice. Significantly fewer circulating tumour cells were present in animals following sequential treatment compared to all other groups. Combination treatment with doxorubicin followed by zoledronic acid inhibits development and progression of spontaneously occurring mammary tumours.

Oestrogen receptor positive breast cancer metastasis to bone: inhibition by targeting the bone microenvironment in vivo

“…ZOL is shown to inhibit migration and invasion of ER-ve breast cancer cells but has comparatively modest inhibitory effects on ER?ve cells in vitro [36][37][38]. In agreement with this, we found no effects of ZOL on migration or invasion of MCF7 or T47D cells in vitro (data not shown).…”

Zoledronic acid enhances antitumor efficacy of liposomal doxorubicin

“…Ottewell et al reported that the inhibition of tumor growth was observed by sequential injection with DXR and ZOL in a mouse model of breast and mammary tumor (31,32). They concluded that sequential treatment with DXR followed by ZOL elicited substantial antitumor effects in vivo, but ZOL followed by DXR did not (31).…”

Neoadjuvant Chemotherapy with or without Zoledronic Acid in Early Breast Cancer—A Randomized Biomarker Pilot Study

“…It is possible that day 5 is too late, and any early antitumor effects of ZOL may have been missed and, in addition, the time of peak increase in apoptosis may be variable between patients. In the preclinical studies reporting increased levels of tumor cell apoptosis following the addition of ZOL to chemotherapy, tumors were always collected 24 hours after the last of 6 weekly injections of ZOL (4,6,7). Following a 4 mg intravenous dose of ZOL administered over 15 minutes, there is a sharp increase in concentration with a peak plasma concentration after the end of infusion of approximately 1 mmol/L (23) followed by a rapid decline in plasma concentration with prolonged (terminal elimination half-life approximately 7 days) but very low-drug plasma concentrations thereafter.…”

“…The antitumor effects included increased tumor cell apoptosis, reduced tumor proliferation, and inhibition of tumor vascularization (4). The same treatment schedule has also been shown to prevent the development and progression of spontaneous mammary tumors in the immunocompetent PyMT mouse model, again in the absence of bone disease (7).…”