Carotenoids, known for their antioxidant properties, have garnered significant attention for their potential antitumour activities. This comprehensive review aims to elucidate the diverse mechanisms by which carotenoids exert antitumour effects, focusing on both well-established and novel findings. We explore their role in inducing apoptosis, inhibiting cell cycle progression and preventing metastasis by affecting oncogenic and tumour suppressor proteins. The review also explores the pro-oxidant function of carotenoids within cancer cells. In fact, although their overall contribution to cellular antioxidant defences is well known and significant, some carotenoids can exhibit pro-oxidant effects under certain conditions and are able to elevate reactive oxygen species (ROS) levels in tumoural cells, triggering mitochondrial pathways that would lead to cell death. The final balance between their antioxidant and pro-oxidant activities depends on several factors, including the specific carotenoid, its concentration and the redox environment of the cell. Clinical trials are discussed, highlighting the conflicting results of carotenoids in cancer treatment and the importance of personalized approaches. Emerging research on rare carotenoids like bacterioruberin showcases their superior antioxidant capacity and selective cytotoxicity against aggressive cancer subtypes, such as triple-negative breast cancer. Future directions include innovative delivery systems, novel combinations and personalized treatments, aiming to enhance the therapeutic potential of carotenoids. This review highlights the promising yet complex landscape of carotenoid-based cancer therapies, calling for continued research and clinical exploration.

Carotenoids are lipophilic pigments naturally occurring in plants and, to a lesser extent, in certain non-photosynthetic organisms. They play a critical role in human health due to their antioxidant and immunomodulatory properties. Key carotenoids such as β-carotene, lycopene, lutein, and zeaxanthin are capable of neutralizing reactive oxygen species, thereby mitigating oxidative stress—a major contributor to the onset and progression of chronic diseases. These compounds also modulate immune responses by influencing lymphocyte proliferation, enhancing natural killer cell activity, and regulating the production of pro- and anti-inflammatory cytokines. Such immunomodulatory effects are associated with a reduced risk of infectious diseases and have shown potential protective roles against inflammatory conditions, cardiovascular and neurodegenerative disorders, and certain types of cancer. Moreover, diets rich in carotenoids are linked to improved immune status, particularly in vulnerable populations such as the elderly and immunocompromised individuals. Despite strong epidemiological evidence, clinical trials involving carotenoid supplementation have produced mixed results, indicating that their effectiveness may depend on the broader dietary context and interactions with other nutrients. In summary, carotenoids are important dietary compounds that contribute to immune regulation and the prevention of various diseases, although further clinical research is needed to determine optimal intake levels and assess their full therapeutic potential.

Bacterioruberin (BR), a C₅₀ carotenoid produced by halophilic archaea, is emerging as a bioactive molecule with potential anticancer relevance, but its activity in solid tumour and multidrug-resistant (MDR) models remains poorly defined. This in vitro study evaluated the cytotoxic, antiproliferative and growth-inhibitory effects of a chemically characterized bacterioruberin-rich carotenoid extract (BRCE) from Haloferax (H.) mediterranei in A549 lung adenocarcinoma, BT-549 triple-negative breast cancer and WM115 melanoma cells, as well as in paired sensitive/multidrug resistant (MDR) lung cancer models. Metabolic activity and proliferation were assessed by thiazolyl blue tetrazolium bromide (MTT) and carboxyfluorescein diacetate succinimidyl ester (CFDA-SE) assays, intracellular reactive oxygen species (ROS) by 2′,7′-dichlorodihydrofluorescein diacetate (H₂DCFDA) staining, and apoptosis-associated morphology by acridine orange/ethidium bromide (AO/EB) staining. Growth inhibition in A549/A549-CDR2 and NCI-H460/NCI-H460/R cells was analysed by sulforhodamine B (SRB) assay, while P-glycoprotein (P-gp) function and expression were examined using Rhodamine 123 (Rh123) accumulation and Western blotting. BRCE reduced metabolic activity and proliferation in a concentration- and time-dependent manner, increased intracellular ROS levels, and induced apoptosis-associated morphological changes in A549 cells. In MDR models, BRCE retained comparable growth-inhibitory activity in sensitive and resistant cells and partially attenuated P-gp-related drug efflux. These findings support further mechanistic investigation of BR in solid tumour and MDR cancer models.

Ultraviolet (UV) radiation is a major environmental stressor that disrupts cellular integrity by inducing oxidative stress, impairing mitochondrial function, and altering immune cell activity, ultimately compromising cellular homeostasis. In this context, carotenoids are widely recognized for their antioxidant and immunomodulatory properties, with C₅₀ carotenoids emerging as a promising subgroup with enhanced biological activity compared with classical C₄₀ carotenoids. Among them, bacterioruberin (BR), a red-pigmented C₅₀ carotenoid mainly produced by haloarchaea, has attracted increasing interest due to its strong antioxidant and cytoprotective potential. Accordingly, this study investigated the mechanisms underlying the protective effects of a bacterioruberin-rich carotenoid extract (BRCE) against UV-induced damage in human peripheral blood mononuclear cells (PBMCs). PBMCs were pre-incubated with BRCE prior to UV exposure and intracellular reactive oxygen species (ROS), mitochondrial membrane potential (Δψm), caspase-3 activation, and the expression of B cell lymphoma 2 (Bcl-2) and granzyme A were evaluated using fluorescence-based assays via confocal microscopy and flow cytometry. BRCE attenuated oxidative stress, preserved mitochondrial membrane potential, reduced caspase-3 activation, and modulated Bcl-2 and granzyme A expression, with more pronounced effects observed at low concentrations. Overall, BRCE exerted a coordinated cytoprotective effect through modulation of oxidative stress, mitochondrial integrity, and apoptosis-related signaling pathways. These findings provide novel insight into the cellular effects associated with the bioactivity of bacterioruberin and support the growing interest in C₅₀ carotenoids as promising photoprotective and immunomodulatory compounds.