Targeting regulated cell death (RCD) with small-molecule compounds in triple-negative breast cancer: a revisited perspective from molecular mechanisms to targeted therapies

Abstract

Triple-negative breast cancer (TNBC) is a subtype of human breast cancer with one of the worst prognoses, with no targeted therapeutic strategies currently available. Regulated cell death (RCD), also known as programmed cell death (PCD), has been widely reported to have numerous links to the progression and therapy of many types of human cancer. Of note, RCD can be divided into numerous different subroutines, including autophagy-dependent cell death, apoptosis, mitotic catastrophe, necroptosis, ferroptosis, pyroptosis and anoikis. More recently, targeting the subroutines of RCD with small-molecule compounds has been emerging as a promising therapeutic strategy, which has rapidly progressed in the treatment of TNBC. Therefore, in this review, we focus on summarizing the molecular mechanisms of the above-mentioned seven major RCD subroutines related to TNBC and the latest progress of small-molecule compounds targeting different RCD subroutines. Moreover, we further discuss the combined strategies of one drug (e.g., narciclasine) or more drugs (e.g., torin-1 combined with chloroquine) to achieve the therapeutic potential on TNBC by regulating RCD subroutines. More importantly, we demonstrate several small-molecule compounds (e.g., ONC201 and NCT03733119) by targeting the subroutines of RCD in TNBC clinical trials. Taken together, these findings will provide a clue on illuminating more actionable low-hanging-fruit druggable targets and candidate small-molecule drugs for potential RCD-related TNBC therapies.

Keywords: Anoikis; Apoptosis; Autophagy-dependent cell death; Combination strategy; Ferroptosis; Mitotic catastrophe; Necroptosis; Pyroptosis; Regulated cell death (RCD); Triple-negative breast cancer (TNBC).

Fig. 1

Core apoptotic signaling pathways in triple negative breast cancer (TNBC). In the extrinsic pathway, the interaction between death receptors and their ligands activates caspase 8, which then activates caspase 3, and eventually lead to apoptosis. Death receptors belong to tumor necrosis factor (TNF) receptors superfamily, which is essential for the transmission of intracellular and extracellular signals. The death receptors include FAS, TNFR1, DR4, and DR5. Death receptors bind to the corresponding proapoptotic ligand like FASL, TNF-α, and TNF-related apoptosis-inducing ligand (TRAIL), to trigger extrinsic apoptosis. In mitochondrial dependent apoptotic pathway, when DNA damage occurs, the pro-apoptotic proteins of the Bcl-2 family (such as Bax and Bak) will be upregulated and activated. Anti-apoptotic proteins (such as Bcl-2 and Bcl-xl) inhibits the action of Bax and Bak. A series of apoptogenic factors will be released into the cytosol, including cytochrome c, apaf-1, and procaspase 9, which forms a complex called apoptosome. This complex can activate caspase 9 followed by the transformation of pro-caspase 3 to caspase 3 and thus trigger apoptosis. When cells receive extracellular stimulation, they transmit the signal to inhibitor of kappa-B kinase (IKK), and inhibitor of IκB is separated from the trimer complex formed with NF-κB. The released NF-κB rapidly enters the nucleus and binds to specific sequences on deoxyribonucleic acid (DNA) to participate in physiological processes such as anti-apoptotic effects. Besides, apoptosis can also be induced by regulating the expression of p53 protein. Abbreviations: Apaf-1: Apoptotic protease activating factor 1; Bcl-2: B-cell lymphoma 2; Bcl-xl: B-cell lymphoma-extra large; DR4/5: Death receptor 4/5; FADD: Fas/fas associated via death domain; IκBα: Nuclear factor kappa-B inhibitor α; NF-κB: Nuclear factor kappa-B; RIP: Receptor-interacting protein; STAT3: Signal transducer and activator of transcription 3; TNF-α: Tumor necrosis factor-α; TNFR1: tumor necrosis factor receptor1; TRADD: TNFRSF1A associated via death domain; TRAF2: TNF receptor-associated factor 2; TRAIL: TNF-related apoptosis-inducing ligand

Fig. 2

Core autophagy-dependent cell death signaling pathways in triple negative breast cancer (TNBC). Autophagy is a complex regulation process involving many upstream signaling pathways. Mammalian target of rapamycin (mTOR) is a negative regulator of autophagy, which is composed of mammalian target of rapamycin complex (mTORC) 1 and mTORC2. Among them, mTORC1 is the main autophagy regulator and phosphatidylinositol 3 kinase complex 1 (PI3KC1)-protein kinase B (Akt)-mTORC1 pathway inhibits the occurrence of autophagy. P53 pathway negatively regulates mTOR pathways to promote autophagy. When mTORC1 is inhibited, it can indirectly activate unc-51-like kinase 1 (ULK1) complex (including ULK1, autophagy associated protein (ATG) 101, ATG13, and focal adhesion kinase interacting protein of 200 kDa (FIP200)). ULK1 complex is closely related to Beclin1, and ULK1 can phosphorylate ATG14, which promotes the binding of Beclin1 to vacuolar protein sorting 34 (VPS34) and ultimately participates in the regulation of autophagy. Forkhead box O (FoxO) had been shown to regulate autophagy by transcriptional dependent mechanism. P62 can bind light chain 3 (LC3)-labeled autophagosomes to substrates, promote the combination of substrates and autophagosomes, and promote the occurrence of autophagy. Additionally, the inhibiting of Ras-Raf-MAPK pathway and NF-κB pathway could also regulate autophagy. Abbreviations: AKT: Protein kinase B; ATG: Autophagy associated protein; ERK: Extracellular signal-regulated kinase; FIP200: Focal adhesion kinase interacting protein of 200 kDa; FoxO: Forkhead box O; LC3: Light chain 3; MEK: Mitogen-activated protein kinase kinase; mTORC1: Mammalian target of rapamycin complex 1; PI3KC1: Phosphatidylinositol 3 kinase complex 1; ULK1: Unc-51-like kinase 1; Vps34: Vacuolar protein sorting 34

Fig. 3

The key mitotic catastrophe, necroptosis and ferroptosis pathways in triple-negative breast cancer (TNBC). a DNA damage inhibits checkpoint kinase 1 (chk1) and cyclin-dependent kinase (CDK) 2 targets and then inhibits the recovery of cell cycle checkpoints, resulting in mitotic catastrophe. The rad3-related protein (ATR)-chk1 signaling pathway is activated in the absence of G2 checkpoints, restores S/G2 and G2/M cell cycle checkpoints and avoids the production of mitotic catastrophe. PI3K-like kinase (PIKK)/mammalian target of rapamycin (mTOR) inhibitors cause the accumulation of single-stranded deoxyribonucleic acid (ssDNA), replication catastrophe and mitotic failure, and ultimately lead to mitotic catastrophe. Polo-like kinase 1 (Plk1)-interacting checkpoint helicase (PICH) depletion can also lead to mitotic catastrophe. Bromodomain and extraterminal protein (BET) inhibitors eventually cause mitotic catastrophe by inhibiting B-cell lymphoma-extra-large (Bcl-xL). The production of the above mitotic catastrophe will eventually cause the death of TNBC cells; b Aquaporin1 (AQP1) can inhibit receptor-interacting protein (RIPK) 1/RIPK3/mixed lineage kinase domain-like (MLKL)-mediated necroptosis by binding to the D324 site of RIPK1. The fas associated via death domain (FADD)/TNFRSF1A associated via death domain (TRADD) complex depends on both RIPK1/caspase-8-mediated apoptosis and RIPK1/RIPK3/MLKL-mediated necroptosis. The production of the above necroptosis will eventually cause the death of TNBC cells; c Zn protoporphyrin IX (Znpp) inhibits the accumulation of unstable iron pools by inhibiting HO-1, reduces reactive oxygen species (ROS) levels and reduces ferroptosis caused by lipid peroxidation. Cystine enters and exits the cell membrane through solute carrier family 7 member 11 (SLC7A11)/solute carrier family 3 member 2 (SLC3A2), converts to cysteine, causes glutathione (GSH) levels to rise, activates Glutathione peroxidase 4 (GPX4) and inhibits ferroptosis caused by lipid peroxidation. The production of the above ferroptosis will eventually cause the death of TNBC cells

Fig. 4

The key pyroptosis and anoikis pathways in triple-negative breast cancer (TNBC). a Maternally expressed gene 3 (MEG3) activates the NLR family, pyrin domain containing 3 (NLRP3)/procaspase-1/apoptosis-associated speck-like protein containing a CRAD (ASC) complex, procaspase-1 is converted to caspase-1, and pyroptosis is induced via gasdermin D (GSDMD). In addition, caspase-11 and caspase-4/5 can also induce pyroptosis via GSDMD. Inhibition of mitochondrial signal transducer and activator of transcription 3 (STAT3) phosphorylation can increase reactive oxygen species (ROS) levels, activate bak and B-cell lymphoma 2 (Bcl-2) targets, activate caspase-9 and caspase-3 in the presence of cytochrome c (Cyt-c), and ultimately promote the cleavage of gasdermin E (GSDME), to transform apoptosis into pyroptosis. In addition, procaspase-8 can also activate caspase-3 to induce pyroptosis via GSDME. The above pyroptosis will eventually cause the death of TNBC cells. b cFLIP inhibits the production of anoikis by inhibiting the conversion of procaspase-8/fas associated via death domain (FADD)/TNFRSF1A associated via death domain (TRADD) complex to caspase-8. After epidermal growth factor receptor (EGFR) is activated, it inhibits the phosphorylation of Tyr705 on STAT3 and resists anoikis. EGFR and SRC/FAK activate the PI3K/Akt pathway, mediate late Bcl-2 interacting mediator of cell death (BIM) degradation, activate myeloid cell leukemia-1 (Mcl-1)/B-cell lymphoma-extra large (Bcl-xL)/Bcl-2, reduce Bax/Bak activity, and inhibit the production of anoikis. SRC/FAK also activates the Ras/Raf/MEK/extracellular signal-regulated kinase (ERK) pathway, relieves the inhibitory effect of proteasome on Mcl-1/Bcl-xL/BCL-2, reduces the activity of Bax/Bak, and inhibits anoikis. In addition, caveolin-1 (cav-1) can also restore the activity of Mcl-1/Bcl-xL/BCL-2 and ultimately inhibit anoikis. After adenosine 5′-monophosphate-activated protein kinase (AMPK) is activated, it can reduce glucose-6-phosphate dehydrogenase (G6PD) and increase phospho-acetyl-CoA carboxylase (p-ACC) and finally activate anoikis. In addition, the overexpression of protein kinase c theta (PRKCQ)/protein kinase C theta (PKCθ), C-X-C motif chemokine receptor 4 (CXCR4), C–C motif chemokine receptor 7 (CCR7) and integrin-β1 will inhibit anoikis. The production of the above anoikis will eventually cause the death of TNBC cells