Metformin, a widely used anti-diabetic drug, has garnered attention for its potential in cancer management, particularly in breast and colorectal cancer. It is established that metformin reduces mitochondrial respiration, but its specific molecular targets within mitochondria vary. Proposed mechanisms include inhibiting mitochondrial respiratory chain Complex I and/or Complex IV, and mitochondrial glycerophosphate dehydrogenase, among others. These actions lead to cellular energy deficits, redox state changes, and several molecular changes that reduce hyperglycemia in type 2 diabetic patients. Clinical evidence supports metformin’s role in cancer prevention in type 2 diabetes mellitus patients. Moreover, in these patients with breast and colorectal cancer, metformin consumption leads to an improvement in survival outcomes and prognosis. The synergistic effects of metformin with chemotherapy and immunotherapy highlights its potential as an adjunctive therapy for breast and colorectal cancer. However, nuanced findings underscore the need for further research and stratification by molecular subtype, particularly for breast cancer. This comprehensive review integrates metformin-related findings from epidemiological, clinical, and preclinical studies in breast and colorectal cancer. Here, we discuss current research addressed to define metformin’s bioavailability and efficacy, exploring novel metformin-based compounds and drug delivery systems, including derivatives targeting mitochondria, combination therapies, and novel nanoformulations, showing enhanced anticancer effects.

Trastuzumab-emtansine (T-DM1) is an antibody-drug conjugate (ADC) approved for the treatment of HER2 (human epidermal growth factor receptor 2)-positive breast cancer. T-DM1 consists of trastuzumab covalently linked to the cytotoxic maytansinoid DM1 via a non-cleavable linker. Despite its efficacy, primary or acquired resistance frequently develops, particularly in advanced stages of the disease. Second generation ADCs targeting HER2 are meant to supersede T-DM1 by using a cleavable linker and a more potent payload with a different mechanism of action. To determine the effect of one of these novel ADCs, SYD985, on tumors resistant to T-DM1, we developed several patient-derived models of resistance to T-DM1. Characterization of these models showed that previously described mechanisms—HER2 downmodulation, impairment of lysosomal function and upregulation of drug efflux pumps—account for the resistances observed, arguing that mechanisms of resistance to T-DM1 are limited, and most of them have already been described. Importantly, SYD985 was effective in these models, showing that the resistance to first generation ADCs can be overcome with an improved design.

Antibody–drug conjugates (ADC) are antineoplastic agents recently introduced into the antitumor arsenal. T-DM1, a trastuzumab-based ADC that relies on lysosomal processing to release the payload, is approved for HER2-positive breast cancer. Next-generation ADCs targeting HER2, such as [vic-]trastuzumab duocarmazine (SYD985), bear linkers cleavable by lysosomal proteases and membrane-permeable drugs, mediating a bystander effect by which neighboring antigen-negative cells are eliminated. Many antitumor therapies, like DNA-damaging agents or CDK4/6 inhibitors, can induce senescence, a cellular state characterized by stable cell-cycle arrest. Another hallmark of cellular senescence is the enlargement of the lysosomal compartment. Given the relevance of the lysosome to the mechanism of action of ADCs, we hypothesized that therapies that induce senescence would potentiate the efficacy of HER2-targeting ADCs. Treatment with the DNA-damaging agent doxorubicin and CDK4/6 inhibitor induced lysosomal enlargement and senescence in several breast cancer cell lines. While senescence-inducing drugs did not increase the cytotoxic effect of ADCs on target cells, the bystander effect was enhanced when HER2-negative cells were cocultured with HER2-low cells. Knockdown experiments demonstrated the importance of cathepsin B in the enhanced bystander effect, suggesting that cathepsin B mediates linker cleavage. In breast cancer patient-derived xenografts, a combination treatment of CDK4/6 inhibitor and SYD985 showed improved antitumor effects over either treatment alone. These data support the strategy of combining next-generation ADCs targeting HER2 with senescence-inducing therapies for tumors with heterogenous and low HER2 expression. Significance: Combining ADCs against HER2-positive breast cancers with therapies that induce cellular senescence may improve their therapeutic efficacy by facilitating a bystander effect against antigen-negative tumor cells.

Background: Early-stage invasive ductal carcinoma displays high survival rates due to early detection and treatments. However, there is still a chance of relapse of 3–15% after treatment. The aim of this study was to uncover the distinctive transcriptomic characteristics and monitoring prognosis potential of peritumoral tissue in early-stage cases. Methods: RNA was isolated from tumoral, peritumoral, and non-tumoral breast tissue from surgical resection of 10 luminal early-stage invasive ductal carcinoma patients. Transcriptome expression profiling for differentially expressed genes (DEGs) identification was carried out through microarray analysis. Gene Ontology and KEGG pathways enrichment analysis were explored for functional characterization of identified DEGs. Protein-Protein Interactions (PPI) networks analysis was performed to identify hub nodes of peritumoral tissue alterations and correlated with Overall Survival and Relapse Free Survival. Results: DEGs closely related with cell migration, extracellular matrix organization, and cell cycle were upregulated in peritumoral tissue compared to non-tumoral. Analyzing PPI networks, we observed that the proximity to tumor leads to the alteration of gene modules involved in cell proliferation and differentiation signaling pathways. In fact, in the peritumoral area were identified the top ten upregulated hub nodes including CDK1, ESR1, NOP58, PCNA, EZH2, PPP1CA, BUB1, TGFBR1, CXCR4, and CCND1. A signature performed by four of these hub nodes (CDK1, PCNA, EZH2, and BUB1) was associated with relapse events in untreated luminal breast cancer patients. Conclusions: In conclusion, our study characterizes in depth breast peritumoral tissue providing clues on the changes that tumor signaling could cause in patients with early-stage breast cancer. We propose that the use of a four gene signature could help to predict local relapse. Overall, our results highlight the value of peritumoral tissue as a potential source of new biomarkers for early detection of relapse and improvement in invasive ductal carcinoma patient’s prognosis.

Metformin, a widely used anti-diabetic drug, has garnered attention for its potential in cancer management, particularly in breast and colorectal cancer. It is established that metformin reduces mitochondrial respiration, but its specific molecular targets within mitochondria vary. Proposed mechanisms include inhibiting mitochondrial respiratory chain Complex I and/or Complex IV, and mitochondrial glycerophosphate dehydrogenase, among others. These actions lead to cellular energy deficits, redox state changes, and several molecular changes that reduce hyperglycemia in type 2 diabetic patients. Clinical evidence supports metformin’s role in cancer prevention in type 2 diabetes mellitus patients. Moreover, in these patients with breast and colorectal cancer, metformin consumption leads to an improvement of survival outcomes and prognosis. The synergistic effects of metformin with chemotherapy and immunotherapy highlights its potential as an adjunctive therapy for breast and colorectal cancer. However, nuanced findings underscore the need for further research and stratification by molecular subtype, particularly for breast cancer. This comprehensive review integrates metformin-related findings from epidemiological, clinical, and preclinical studies in breast and colorectal cancer. Here, we discuss current research addressed to define metformin's bioavailability and efficacy, exploring novel metformin-based compounds and drug delivery systems, including derivatives targeting mitochondria, combination therapies, and novel nanoformulations, showing enhanced anticancer effects.

Background: Obesity, characterized by the secretion of several pro-inflammatory cytokines and hormones, significantly increases the risk of developing breast cancer and is associated with poorer outcomes. Mitochondrial and antioxidant status are crucial in both tumor progression and treatment response. Methods: This study investigates the impact of an ELIT cocktail (17β-estradiol, leptin, IL-6, and TNFα), which simulates the obesity-related inflammation condition in postmenopausal women, using a 3D culture model. We examined the effects of ELIT exposure on mammosphere formation, oxidative stress and mitochondrial markers, and treatment sensitivity in luminal (T47D, MCF7) and triple-negative (MDA-MB-231) breast cancer cell lines. After that, 3D-derived cells were re-cultured under adherent conditions focusing on the mechanisms leading to dissemination and drug sensitivity. Results: Our results indicated that ELIT condition significantly increased mammosphere formation in luminal breast cancer cell lines (from 3.26% to 6.38% in T47D cell line and 0.68% to 2.32% in MCF7 cell line) but not in the triple-negative MDA-MB-231 cell line. Further analyses revealed a significant decrease in mitochondrial and antioxidant-related markers, particularly in the T47D cell line, where higher levels of ESR2, three-fold increased by ELIT exposure, may play a critical role. Importantly, 3D-derived T47D cells exposed to ELIT showed reduced sensitivity to tamoxifen and paclitaxel, avoiding a 34.2% and 75.1% reduction in viability, respectively. Finally, through in silico studies, we identified specific biomarkers, including TOMM20, NFE2L2, CAT, and ESR2, correlated with poor prognosis in luminal breast cancer. Conclusions: Taken together, our findings suggest that antioxidant and mitochondrial markers are key factors that reduce treatment sensitivity in obesity-related luminal breast cancer. The identified biomarkers may serve as valuable tools for the prognosis and development of more effective therapies in these patients.