MitoQ Prevents Human Breast Cancer Recurrence and Lung Metastasis in Mice

Abstract

In oncology, the occurrence of distant metastases often marks the transition from curative to palliative care. Such outcome is highly predictable for breast cancer patients, even if tumors are detected early, and there is no specific treatment to prevent metastasis. Previous observations indicated that cancer cell mitochondria are bioenergetic sensors of the tumor microenvironment that produce superoxide to promote evasion. Here, we tested whether mitochondria-targeted antioxidant MitoQ is capable to prevent metastasis in the MDA-MB-231 model of triple-negative human breast cancer in mice and in the MMTV-PyMT model of spontaneously metastatic mouse breast cancer. At clinically relevant doses, we report that MitoQ not only prevented metastatic take and dissemination, but also local recurrence after surgery. We further provide in vitro evidence that MitoQ does not interfere with conventional chemotherapies used to treat breast cancer patients. Since MitoQ already successfully passed Phase I safety clinical trials, our preclinical data collectively provide a strong incentive to test this drug for the prevention of cancer dissemination and relapse in clinical trials with breast cancer patients.

Keywords: MitoQ; breast cancer; cancer relapse; metastasis; metastasis prevention; mitochondria; mitochondria-targeted antioxidant; mitochondrial superoxide; translational research.

Figure 1

MitoQ biodistribution in mouse tissues. Female BALB/c mice received increasing doses of MitoQ per os, and tissues were collected 4 h later for analysis using LC/MS/MS. (a) MitoQ molality in function of the administered dose of MitoQ in mouse lungs (n = 3–4), (b) as in a, but in mouse heart (n = 5). (c) As in a, but in mouse liver (n = 3–6). (d) As in a, but in mouse kidneys (n = 3–5). All data are shown as means ± SEM.

Figure 2

MitoQ inhibits the metastatic take of triple-negative human MDA-MB-231 breast cancer in mice. (a) Experimental protocol for tumor take assays where breast cancer cells were pretreated ± 1 µM MitoQ for 6 h before tail vein injection of 10⁶ viable cells in female NMRI nude mice. (b) Metastatic take of MDA-MB-231 human breast cancer cells in the lungs of mice using the protocol depicted in a. Left pictures are representative of lungs insufflated with Indian ink, where metastases appear as white dots quantified in the right graph (vehicle group n = 18; MitoQ group n = 11). Bar = 0.5 cm. All data are shown as means ± SEM. * p < 0.05 compared to vehicle, by Mann-Whitney test (b).

Figure 3

MitoQ prevents primary tumor recurrence and the metastatic dissemination of orthotopic triple-negative human MDA-MB-231 breast cancer in mice. (a) Experimental protocol for spontaneous MDA-MB-231 metastasis after orthotopic injection in the mammary fat pad of female NMRI nude mice. (b) On the left, primary tumor growth in mice using the protocol depicted in a (n = 10 per group until the day of surgery; n = 7 in the vehicle-treated group and n = 8 in the MitoQ-treated group after surgery). The blue arrow indicates the day of primary tumor resection. On the right, primary tumor doubling times from 100 to 200 mm³ before surgery (n = 10 per group). (c) Kaplan-Meier graph showing recurrence-free mouse survival after surgery. Data are expressed as percentage of mice per treatment group (n = 7 for vehicle and n = 8 for MitoQ). (d) At the end of the protocol shown in a, mouse lungs were removed, sliced, stained for cytokeratin 19 (CK19), counterstained with hematoxylin, and analyzed for the presence of metastases. Representative pictures are on the left at two different magnifications (bars = 16 mm for the two pictures on the top and 1 mm for the two pictures on the bottom), and metastasis quantification is on the right. All data are shown as means ± SEM. *** p < 0.001, ns: p > 0.05 compared to vehicle; by 2-way ANOVA (b left), Student t test (b right), Log-Rank (Mantel-Cox) test (c), or Mann-Whitney test (d).

Figure 4

In vitro, MitoQ does not interfere with conventional chemotherapies used to treat breast cancer. (a) Counting of MDA-MB-231 cancer cells treated with increasing doses of chemotherapy ± MitoQ. Treatments were: 48 h with doxorubicin ± 100 nM MitoQ (n = 3), 24 h with epirubicin ± 100 nM MitoQ (n = 3), 48 h with 5-fluorouracil (5-FU) ± 100 nM MitoQ (n = 3), 48 h with cisplatin ± 100 nM MitoQ (n = 3), 72 h with gemcitabine ± 100 nM MitoQ (n = 3), and 48 h with paclitaxel ± 100 nM MitoQ (n = 3). (b) As in a, but using SkBr3 cancer cells (n = 3–4). All data are shown as means ± SEM. All p values are > 0.05; by 2-way ANOVA with Tukey’s post-hoc test (a,b).

Figure 5

MitoQ prevents lung metastasis in spontaneous metastatic breast cancer in mice. (a) Experimental protocol for female MMTV-PyMT mouse treatment. (b) Total weight of primary breast tumors collected on the day of sacrifice of MMTV-PyMT mice treated as depicted in a (n = 11–17). (c) Lung metastases in MMTV-PyMT mice treated as depicted in a. Left pictures are representative of lungs insufflated with Indian ink, where metastases appear as white dots quantified in the right graph (n = 20–23). Bar = 0.5 cm. All data are shown as means ± SEM. * p < 0.05, ns: p > 0.05 compared to vehicle; by Mann-Whitney test (b,c).