The literature resviearchw was conducted using the MEDLINE and LIVIVO databases. By employing the search terms “bitter melon” and “breast cancer”, researchers we were able to identify a total of 19 relevant original research articles published between 1994 and 2023.

In 1994, Rybak et al. were the first to identify breast cancer cell lines as one of the most sensitive cancer cell lines in relation to the Momordica Anti-HIV Protein 30 kDa (MAP30) and Gelonium Anti-HIV Protein 31 kDa (GAP31) bitter melon-isolated proteins treatment ^[1][16]. Huang et al. measured the anticancer capacities of MAP30 and GAP31 by proliferation of MDA-MB-231 breast cancer cells and concluded that their endopeptidase digestion generates fragments with a potent anticancer activity, whereas their antitumor effects do not rely on the ribosome inactivation activity ^[2][17]. Accordingly, Lee-Huang et al. examined the efficacy of MAP30 and GAP31 on MDA-MB-231 cells and reported reduced in vitro cancer cell proliferation and Human Epidermal growth factor Receptor 2 (HER2) gene expression, alongside significantly higher survival rates in treated human breast cancer bearing Severe Combined ImmunoDeficiency (SCID) xenograft mouse models ^[3][18].

Bai et al. isolated the triterpenoid 3β, 7β, 25-trihydroxycucurbita-5,23(E)-dien-19-al (TCD) from wild bitter melon and showed that TCD inhibited the proliferation of MDA-MB-231 and MCF-7 breast cancer cells, as well as provoked breast cancer cell apoptosis. More precisely, the aforementioned triterpenoid repressed Akt-Nuclear Factor kappa B (NF-κB) signaling, activated both the p38 mitogen-activated protein kinase and p53, generated ROS, downregulated histone deacetylase protein expression, as well as promoted cytoprotective autophagy ^[4][19]. In 2013, Weng et al. noted that the triterpene 3β,7β-dihydroxy-25-methoxycucurbita-5,23-diene-19-al (DMC) could effectively induce apoptosis in MCF-7 and MDA-MB-231 cells by activating the Peroxisome Proliferator-Activated Receptor (PPAR) γ. On the one hand, DMC inhibited mammalian Target Of Rapamycin (mTOR)-p70S6K signaling via Akt repression and 5′ AMP-activated Protein Kinase (AMPK) upregulation and blocked the expression of cyclin D1, Cyclin Dependent Kinase 6 (CDK6), B-cell lymphoma 2 (Bcl-2), X-linked Inhibitor of Apoptosis Protein (XIAP), cyclooxygenase-2, NF-κB, and estrogen receptor α. On the other hand, DMC successfully induced Growth Arrest- and DNA Damage-Inducible gene 153 (GADD153) and Glucose-Regulated Protein 78 (GRP78) expression, alongside a cytoprotective autophagy ^[5][20]. Some years later, the same study group proposed the triterpenoid 5β,19-epoxy-19-methoxycucurbita-6,23-dien-3β,25-diol as a potent PPARγ activator in MCF-7 breast cancer cells, which diminished the expression of histone deacetylase 1, increased the phosphorylation of p53, generated ROS, and promoted G1 cell cycle arrest through cyclin D1 and CDK6 downregulation ^[6][21].

In 2019, Lepionka et al. fed Sprague-Dawley rats experimental diets supplemented with Momordica charantia extract and outlined that, even though this diet modification boosted cis-9, trans-11 conjugated linoleic acid levels, the breast cancer incidence did not drop in rats treated with 7,12-dimethylbenz[a]anthracene. Furthermore, a profound impact on serum fatty acids content was noted, while co-existing cancerous process contributed to the reduction in saturated fatty acids, monounsaturated fatty acids, polyunsaturated fatty acids, and 8-iso prostaglandin F2α, in serum ^[7][22]. Two years later, Białek et al. evaluated the effect of bitter gourd extract on the lipidomic profile of cardiac tissue in female Sprague-Dawley rats with breast cancer. This dietary supplementation resulted in the diminution of cholesterol levels via the downregulation of the endogenous conversion of squalene to cholesterol in the heart tissue. Furthermore, the cardiac incorporation of conjugated fatty acids was evidently less in the cancerous process, whereas malondialdehyde levels experienced only slight changes ^[8][23].

Cao et al. investigated the effects of the bitter melon-extracted ribosome inactivating protein alpha-momorcharin on the inhibition of human breast cancer by purifying it by the means of column chromatography and, consecutively, injecting it into a xenograft nude mouse model induced by MDA-MB-231 and MCF-7 breast cancer cells. Alpha-momorcharin was found to efficiently inhibit in vivo tumor growth, increase caspase-3 activities, as well as lead to cell cycle arrest at the G0/G1 or G2/M phases ^[9][24]. Similarly, Deng et al. explored the anticancer activity of alpha-momorcharin in EMT-6 and MDA-MB-231 transplanted tumor mouse models and demonstrated that polyethylene glycolylation increased its plasma half-life in vivo. Interestingly, modification of alpha-momorcharin with polyethylene glycol correlated with an enhanced anticancer effectiveness, alongside a more moderate toxic profile ^[10][25]. Besides, Fang et al. purified the 14-kDa ribonuclease MC2 in the seeds of Momordica charantia, which exhibited not only cytostatic, but also cytotoxic effects on MCF-7 breast cancer cells via karyorrhexis, chromatin condensation, DNA fragmentation, caspase-7/-8/-9 activation, B-Cell Lymphoma 2 (BCL-2) Antagonist/Killer (BAK), and cleaved PARP production, as well as p38, c-Jun N-terminal Kinase (JNK), Extracellular signal-Regulated Kinase (ERK), and Akt differential activation ^[11][26].

Ehigie et al. treated MDA-MB-436 breast cancer cells with different fractions derived from the aqueous extract of the leaves of bitter melon, which downregulated mitochondrial membrane potential and intracellular ATP levels, but enhanced ROS levels. These cytotoxic effects of bitter melon were mediated by loss of mitochondrial function via loss of respiration, leading to cell death, rather than by the classical release of cytochrome c or caspase-3 activated apoptosis ^[12][27]. Moreover, Grossmann et al. focused their research on the effects of eleostearic acid, a component of bitter melon seed oil, on MDA-MB-231 and MDA-ERα7 human breast cancer cells. Eleostearic acid hindered cancer cell proliferation, induced apoptosis, caused mitochondrial membrane potential loss, provoked apoptosis-inducing factor and endonuclease G nuclear translocation, as well as arrested the cancer cell cycle. Nevertheless, lipid peroxidation was shown to significantly determine the inhibitory actions of eleostearic acid ^[13][28]. Muhammad et al. observed that bitter gourd extract application to breast cancer cells led to the induction of autophagosome-bound Long Chain 3 (LC3)-B, the accumulation of p62/SQSTM1 (p62) protein, an enhanced phospho-AMPK expression, as well as the downregulation of the mTOR/Akt signaling pathway. In vivo, the aforementioned extract inhibited tumor growth by upregulating p62 accumulation and provoking autophagy and apoptosis in syngeneic and xenograft mouse models ^[14][29]. After treating MCF-7 and MDA-MB-231 breast cancer cells with Momordica charantia extract, Ray et al. also described a significant reduction in cancer cell proliferation, accompanied by an amplified PARP cleavage and caspase activation. Survivin and claspin expression levels remained low, MCF-7 cells accumulated during the G2/M cell cycle phase, p53, p21, and pChk1/2, were upregulated, whereas cyclins B1 and D1 expression was hindered ^[15][30]. Nagasawa et al. monitored the effects of bitter gourd extract on spontaneous breast cancer development in SHN virgin mice, which significantly inhibited in vivo tumor growth with negligible side effects ^[16][31].

Feng et al. proved that even 4T1 triple-negative breast cancer cells might successfully internalize bitter gourd-derived vesicle extracts, which inhibited cancer cell proliferation and migration, while it also stimulated ROS production and disrupted mitochondrial function. Of note, bitter melon-derived vesicle extracts also dramatically diminished breast cancer growth in female BALB/c mice with negligible side effects ^[17][32]. Similarly, Shim et al. applied bitter melon extract to triple-negative breast cancer cell lines and measured low esterified cholesterol, Acetyl-CoA Acetyltransferase 1 (ACAT-1), sterol regulatory element-binding proteins-1 and -2, fatty acid synthase, and low-density lipoprotein receptor expression levels. Remarkably, this extract also inhibited both tumor growth and ACAT-1 expression in triple-negative breast cancer xenograft mouse models ^[18][33].

Last, but not least, Kilcar et al. tested the effects of the bitter gourd extract on the uptake of Technetium-99m-labeled paclitaxel against MCF-7 and MDA-MB-231 breast cancer cells and highlighted a significant estrogen receptor-dependent interaction ^[19][34]. Altogether, these results indicate that bitter melon and its bioactive components may successfully inhibit breast cancer development and progression both in vitro and in vivo.