Short-term early exposure to lapatinib confers lifelong protection from mammary tumor development in MMTV-erbB-2 transgenic mice

Metformin reduces basal subpopulation and attenuates mammary epithelial cell stemness in FVB/N mice

Metformin shows promise in breast cancer prevention, but its underlying mechanisms remain unclear. This study investigated the impact of metformin on the repopulation dynamics of mammary epithelial cells (MECs) and the signaling pathways in non-tumorigenic FVB/N mice. This study aimed to enhance our understanding of the role of metformin in reducing the susceptibility of MECs in premalignant tissues to oncogenic factors. In this study, female mice were administered 200 mg/kg/day of metformin via intraperitoneal (i.p.) injection from 8 to 18 weeks of age. After this treatment period, morphogenesis, flow cytometry, analyses of MEC stemness, and RNA sequencing were performed. The study findings indicated that metformin treatment in adult mice reduced mammary gland proliferation, as demonstrated by decreased Ki67+ cells and lateral bud formation. Additionally, metformin significantly reduced both basal and mammary repopulating unit subpopulations, indicating an impact on mammary epithelial cell repopulation. Mammosphere, colony-forming cell, and 3D culture assays revealed that metformin adversely affected mammary epithelial cell stemness. Furthermore, metformin downregulated signaling in key pathways including AMPK/mTOR, MAPK/Erk, PI3K/Akt, and ER, which contribute to its inhibitory effects on mammary proliferation and stemness. Transcriptome analysis with RNA sequencing indicated that metformin induced significant downregulation of genes involved in multiple critical pathways. KEGG-based pathway analysis indicated that genes in PI3K/Akt, focal adhesion, ECM-receptor, small cell lung cancer and immune-modulation pathways were among the top groups of differentially regulated genes. In summary, our research demonstrates that metformin inhibits MEC proliferation and stemness, accompanied by the downregulation of intrinsic signaling. These insights suggest that the regulatory effects of metformin on premalignant mammary tissues could potentially delay or prevent the onset of breast cancer, offering a promising avenue for developing new preventive strategies.

Metformin-induced downregulation of c-Met is a determinant of sensitivity in MDA-MB-468 breast cancer cells

Metformin, the widely used anti-diabetic drug, is emerging as a promising anti-cancer agent. However, response variation among different tumors remains a significant challenge. Hence, identification of the factors that determine metformin sensitivity is of greatest significance for its clinical implementation. In this study, we showed that MDA-MB-468 cells were most sensitive among the five breast cancer cell lines tested. We found that metformin-induced inhibition of MDA-MB-468 cells was correlated with downregulation of c-Met at both protein and mRNA levels. To understand the functional significance of c-Met downregulation in metformin-mediated tumor inhibition, we established control and c-Met overexpressing sublines of MDA-MB-468 cells (468/C and 468/Met) using lentiviral expression system. We demonstrated that overexpression of c-Met significantly attenuated metformin induced inhibition of MDA-MB-468 cells. Metformin-induced inhibition of ALDH1+ cells, which are enriched with cancer stem cells, was also abrogated in 468/Met cells as compared to 468/C cells. Signal transduction analysis of the paired cell lines indicated that c-Met-induced activation of STAT3 and AKT1, and upregulation of Gab1 are related to c-Met-modulated metformin responsiveness. These findings highlight c-Met as a potential key regulator of metformin-mediated inhibition of proliferation and stemness of breast cancer cells, indicating that c-Met overexpression may be a critical factor contributing to metformin resistance. The data also suggest that combination of metformin with c-Met inhibitors could be a useful strategy to improve metformin-mediated anti-cancer efficacies in breast cancer treatment.

Development of a stable and high loaded liposomal formulation of lapatinib with enhanced therapeutic effects for breast cancer in combination with Caelyx®: In vitro and in vivo evaluations

Lapatinib, a dual tyrosine kinase inhibitor, has poor water solubility, which results in poor and incomplete absorption from the gastrointestinal tract. To overcome this obstacle, we designed a stable and high-loaded liposomal formulation encapsulating lapatinib and examined its therapeutic efficacy in vitro and in vivo on TUBO and 4T1 cell lines. We also assessed the impact of liposomal lapatinib on the extent of the tumor and spleen-infiltrating lymphocytes and the autophagy and apoptosis gene expression within the tumor site. Our results showed that liposomal lapatinib inhibits cell proliferation and significantly induces autophagy and apoptosis compared to control groups. Moreover, when it used in combination with liposomal doxorubicin, it extended the time to end from 22.4 ± 3.5 in the control group to 40 days in the TUBO cell line and from 29.2 ± 1.7 to 38.6 ± 2.2 days in 4T1 triple-negative breast cancer cell line, which reveals its promising effects on the survival of tumor-bearing mice. Our results indicated the need for further evaluations to understand liposomal lapatinib's potential effects on autophagy, apoptosis, and particularly on immune system cells.

Tyrosine Kinase Inhibitors Are Promising Therapeutic Tools for Cats with HER2-Positive Mammary Carcinoma

Feline mammary carcinoma (FMC) is a common neoplasia in cat, being HER2-positive the most prevalent subtype. In woman’s breast cancer, tyrosine kinase inhibitors (TKi) are used as a therapeutic option, by blocking the phosphorylation of the HER2 tyrosine kinase domain. Moreover, clinical trials demonstrated that TKi produce synergistic antiproliferative effects in combination with mTOR inhibitors, overcoming resistance to therapy. Thus, to uncover new chemotherapeutic strategies for cats, the antiproliferative effects of two TKi (lapatinib and neratinib), and their combination with a mTOR inhibitor (rapamycin), were evaluated in FMC cell lines (CAT-M, FMCp and FMCm) and compared with a human breast cancer cell line (SkBR-3). Results revealed that both TKi induced antiproliferative effects in all feline cell lines, by blocking the phosphorylation of EGFR members and its downstream effectors. Furthermore, combined treatments with rapamycin presented synergetic antiproliferative effects. Additionally, the DNA sequence of the her2 TK domain (exons 18 to 20) was determined in 40 FMC tissue samples, and despite several mutations were found none of them were described as inducing resistance to therapy. Altogether, our results demonstrated that TKi and combined protocols may be useful in the treatment of cats with mammary carcinomas, and that TKi-resistant FMC are rare.

Lapatinib‑induced inhibition of ovarian function is counteracted by the STAT3 pathway both in vivo and in vitro

The present study was designed to ascertain whether lapatinib, a tyrosine kinase inhibitor of epidermal growth factor receptor (EGFR), affects ovarian reserve and fertility potential in a mouse model. Female C57BL/6 mice were treated with either vehicle or lapatinib (100 or 200 mg/kg/day orally) for 4 weeks, after which body weight, vaginal smears, follicle numbers, serum anti‑Müllerian hormone (AMH) levels and mating outcomes were analyzed to assess the ovarian reserve and reproductive function. Slices from the ovaries of 4‑week‑old mice were cultured with lapatinib (0, 5 or 10 µM) for 24 and 48 h, and protein expression levels were assessed to validate the changes in signaling pathways. The results indicated that mice treated with 200 mg/kg lapatinib showed a slight decrease in body weight compared to those treated with vehicle or 100 mg/kg lapatinib. There was no statistical difference in estrous cyclicity among the three groups. No significant difference was observed in follicle numbers, AMH levels, histological morphologies of the ovaries or mating outcomes in the three groups of mice. Western blotting and immunohistochemical staining of the EGF receptor and its main downstream signaling pathways showed decreased phosphorylation of EGFR and mitogen‑activated protein kinase (MAPK)3/1 and increased phosphorylation of signal transducers and activators of transcription (STAT)3 in the lapatinib‑treated groups compared to the control group. Our study suggests that lapatinib has little effect on ovarian reserve and reproductive function in a mouse model. This lack of effect of lapatinib on ovarian function may be due to the activation of the STAT3 signaling pathway that counteracts the inhibitory effects of lapatinib on EGF receptors.

In Utero Exposure to Bisphenol a Promotes Mammary Tumor Risk in MMTV-Erbb2 Transgenic Mice Through the Induction of ER-erbB2 Crosstalk

Bisphenol A (BPA) is the most common environmental endocrine disrupting chemical. Studies suggest a link between perinatal BPA exposure and increased breast cancer risk, but the underlying mechanisms remain unclear. This study aims to investigate the effects of in utero BPA exposure on mammary tumorigenesis in MMTV-erbB2 transgenic mice. Pregnant mice were subcutaneously injected with BPA (0, 50, 500 ng/kg and 250 µg/kg BW) daily between gestational days 11–19. Female offspring were examined for mammary tumorigenesis, puberty onset, mammary morphogenesis, and signaling in ER and erbB2 pathways. In utero exposure to low dose BPA (500 ng/kg) induced mammary tumorigenesis, earlier puberty onset, increased terminal end buds, and prolonged estrus phase, which was accompanied by proliferative mammary morphogenesis. CD24/49f-based FACS analysis showed that in utero exposure to 500 ng/kg BPA induced expansion of luminal and basal/myoepithelial cell subpopulations at PND 35. Molecular analysis of mammary tissues at PND 70 showed that in utero exposure to low doses of BPA induced upregulation of ERα, p-ERα, cyclin D1, and c-myc, concurrent activation of erbB2, EGFR, erbB-3, Erk1/2, and Akt, and upregulation of growth factors/ligands. Our results demonstrate that in utero exposure to low dose BPA promotes mammary tumorigenesis in MMTV-erbB2 mice through induction of ER-erbB2 crosstalk and mammary epithelial reprogramming, which advance our understanding of the mechanism associated with in utero exposure to BPA-induced breast cancer risk. The studies also support using MMTV-erbB2 mouse model for relevant studies.

Caloric restriction inhibits mammary tumorigenesis in MMTV-ErbB2 transgenic mice through the suppression of ER and ErbB2 pathways and inhibition of epithelial cell stemness in premalignant mammary tissues

Caloric intake influences the onset of many diseases, including cancer. In particular, caloric restriction (CR) has been reported to suppress mammary tumorigenesis in various models. However, the underlying cancer preventive mechanisms have not been fully explored. To this end, we aimed to characterize the anticancer mechanisms of CR using MMTV-ErbB2 transgenic mice, a well-established spontaneous ErbB2-overexpressing mammary tumor model, by focusing on cellular and molecular changes in premalignant tissues. In MMTV-ErbB2 mice with 30% CR beginning at 8 weeks of age, mammary tumor development was dramatically inhibited, as exhibited by reduced tumor incidence and increased tumor latency. Morphogenic mammary gland analyses in 15- and 20-week-old mice indicated that CR significantly decreased mammary epithelial cell (MEC) density and proliferative index. To understand the underlying mechanisms, we analyzed the effects of CR on mammary stem/progenitor cells. Results from fluorescence-activated cell sorting analyses showed that CR modified mammary tissue hierarchy dynamics, as evidenced by decreased luminal cells (CD24highCD49flow), putative mammary reconstituting unit subpopulation (CD24highCD49fhigh) and luminal progenitor cells (CD61highCD49fhigh). Mammosphere and colony-forming cell assays demonstrated that CR significantly inhibited mammary stem cell self-renewal and progenitor cell numbers. Molecular analyses indicated that CR concurrently inhibited estrogen receptor (ER) and ErbB2 signaling. These molecular changes were accompanied by decreased mRNA levels of ER-targeted genes and epidermal growth factor receptor/ErbB2 family members and ligands, suggesting ER-ErbB2 signaling cross-talk. Collectively, our data demonstrate that CR significantly impacts ER and ErbB2 signaling, which induces profound changes in MEC reprogramming, and mammary stem/progenitor cell inhibition is a critical mechanism of CR-mediated breast cancer prevention.

Anti-tumour effect of lapatinib in canine transitional cell carcinoma cell lines

Transitional cell carcinoma (TCC) accounts for >90% of canine malignant tumours occurring in urinary bladder, and the prognosis is poor. Our previous study, using RNA sequencing, showed that human epidermal growth factor 2 (HER2) was the most activated upstream regulator related to carcinogenesis in canine TCC. The aim of this study was to examine the anti-tumour effect of lapatinib, a tyrosine kinase inhibitor of HER2, on canine TCC cell lines in vitro and in vivo. Five canine TCC cell lines (TCCUB, Love, Sora, LCTCC, and MCTCC) were used. Western blotting showed that HER2 protein expression was observed in all of the canine TCC cell lines. Lapatinib inhibited phosphorylation of HER2 and cell growth in a dose-dependent manner. Cell cycle analyses using flow cytometry showed that lapatinib significantly increased the sub-G₁ and G₀ /G₁ phase fractions and significantly decreased the S and G₂ /M phase fractions in the cell lines (Sora and TCCUB). For the in vivo experiments, the canine TCC cells (Sora) were subcutaneously injected into nude mice. Six days after inoculation, lapatinib (100 mg/kg) or vehicle was administered daily via intraperitoneal administration for 14 days. Tumour volume was significantly smaller in the lapatinib group compared with the vehicle control group. Histologically, lapatinib significantly increased necrotic areas in the tumour tissues. These findings suggest that lapatinib exerts anti-tumour effects on canine TCC cells by inhibiting HER2 signalling and inducing cell cycle arrest.

FGFR inhibitor, AZD4547, impedes the stemness of mammary epithelial cells in the premalignant tissues of MMTV-ErbB2 transgenic mice

The fibroblast growth factor receptor (FGFR) family of receptor tyrosine kinases (RTKs) regulates signaling pathways involved in cell proliferation and differentiation. Currently, the anti-tumor properties of FGFR inhibitors are being tested in preclinical and clinical studies. Nevertheless, reports on FGFR inhibitor-mediated breast cancer prevention are sparse. In this study, we investigated the anti-cancer benefits of AZD4547, an FGFR1-3 inhibitor, in ErbB2-overexpressing breast cancer models. AZD4547 (1-5 µM) demonstrated potent anti-proliferative effects, inhibition of stemness, and suppression of FGFR/RTK signaling in ErbB2-overexpressing human breast cancer cells. To study the in vivo effects of AZD4547 on mammary development, mammary epithelial cell (MEC) populations, and oncogenic signaling, MMTV-ErbB2 transgenic mice were administered AZD4547 (2-6 mg/kg/day) for 10 weeks during the 'risk window' for mammary tumor development. AZD4547 significantly inhibited ductal branching and MEC proliferation in vivo, which corroborated the in vitro anti-proliferative properties. AZD4547 also depleted CD24/CD49f-sorted MEC populations, as well as the CD61^highCD49f^high tumor-initiating cell-enriched population. Importantly, AZD4547 impaired stem cell-like characteristics in primary MECs and spontaneous tumor cells. Moreover, AZD4547 downregulated RTK, mTOR, and Wnt/β-catenin signaling pathways in premalignant mammary tissues. Collectively, our data provide critical preclinical evidence for AZD4547 as a potential breast cancer preventative and therapeutic agent.