Targeting the retinoic acid signaling pathway as a modern precision therapy against cancers

Retinoic acid (RA) is a vital metabolite derived from vitamin A. RA plays a prominent role during development, which helps in embryological advancement and cellular differentiation. Mechanistically, RA binds to its definite nuclear receptors including the retinoic acid receptor and retinoid X receptor, thus triggering gene transcription and further consequences in gene regulation. This functional heterodimer activation later results in gene activation/inactivation. Several reports have been published related to the detailed embryonic and developmental role of retinoic acids and as an anti-cancer drug for specific cancers, including acute promyelocytic leukemia, breast cancer, and prostate cancer. Nonetheless, the other side of all-trans retinoic acid (ATRA) has not been explored widely yet. In this review, we focused on the role of the RA pathway and its downstream gene activation in relation to cancer progression. Furthermore, we explored the ways of targeting the retinoic acid pathway by focusing on the dual role of aldehyde dehydrogenase (ALDH) family enzymes. Combination strategies by combining RA targets with ALDH-specific targets make the tumor cells sensitive to the treatment and improve the progression-free survival of the patients. In addition to the genomic effects of ATRA, we also highlighted the role of ATRA in non-canonical mechanisms as an immune checkpoint inhibitor, thus targeting the immune oncological perspective of cancer treatments in the current era. The role of ATRA in activating independent mechanisms is also explained in this review. This review also highlights the current clinical trials of ATRA in combination with other chemotherapeutic drugs and explains the future directional insights related to ATRA usage.

ALDH1A1 promotes PARP inhibitor resistance by enhancing retinoic acid receptor-mediated DNA polymerase θ expression

Poly (ADP-ribose) Polymerase (PARP) inhibitors (PARPi) have been approved for both frontline and recurrent setting in ovarian cancer with homologous recombination (HR) repair deficiency. However, more than 40% of BRCA1/2-mutated ovarian cancer lack the initial response to PARPi treatment, and the majority of those that initially respond eventually develop resistance. Our previous study has demonstrated that increased expression of aldehyde dehydrogenase 1A1 (ALDH1A1) contributes to PARPi resistance in BRCA2-mutated ovarian cancer cells by enhancing microhomology-mediated end joining (MMEJ) but the mechanism remains unknown. Here, we find that ALDH1A1 enhances the expression of DNA polymerase θ (Polθ, encoded by the POLQ gene) in ovarian cancer cells. Furthermore, we demonstrate that the retinoic acid (RA) pathway is involved in the transcription activation of the POLQ gene. The RA receptor (RAR) can bind to the retinoic acid response element (RARE) located in the promoter of the POLQ gene, promoting transcription activation-related histone modification in the presence of RA. Given that ALDH1A1 catalyzes the biosynthesis of RA, we conclude that ALDH1A1 promotes POLQ expression via the activation of the RA signaling pathway. Finally, using a clinically-relevant patient-derived organoid (PDO) model, we find that ALDH1A1 inhibition by the pharmacological inhibitor NCT-505 in combination with the PARP inhibitor olaparib synergistically reduce the cell viability of PDOs carrying BRCA1/2 mutation and positive ALDH1A1 expression. In summary, our study elucidates a new mechanism contributing to PARPi resistance in HR-deficient ovarian cancer and shows the therapeutic potential of combining PARPi and ALDH1A1 inhibition in treating these patients.

Abstract 2428: Cancer stem cells maintain stemness via autocrine activation of the IFN/JAK/STAT signaling pathway

Interferons (IFNs) and Janus Kinase/Signal Transducer and Activator of Transcription (JAK/STAT) signaling are best known for their roles in immunity. However, recent work has suggested that both IFNs and the JAK/STAT pathways are associated with tumor growth and progression, as well as the maintenance of cancer stem cell (CSC) populations. To better understand the regulation of the CSC population maintenance by the IFN/JAK/STAT signaling pathway, we enriched CSCs from a panel of non-small cell lung cancer (NSCLC) cell lines by using spheroid culture and determined the phosphorylation of STAT1. We found that sphere cells exhibit increased level of pSTAT1-Y701 compared to their corresponding bulk cells. We further determined the expression level of a few interferon-stimulated genes (ISGs) and found that sphere cells possess enhanced expression of ISG54 and ISG56 genes, which are normally induced by type I IFN (IFN-I), as well as IFNA and IFNB. These results indicate that the IFN-I/STAT1 signaling is highly activated in CSCs, which produce and secrete increased amount of IFN-I. To directly show the effect of IFN-I on the stemness of NSCLC cells, we treated NSCLC cells with IFNβ, and found that IFNβ can significantly enhance the expression of SOX2, a stem cell-specific transcription factor; Inhibition of the JAK signaling blocked both basal and IFNβ-induced SOX2 expression. In addition, knockdown of STAT1 also reduced SOX2 expression, indicating that STAT1 activation plays an important role in mediating IFN-induced enhancement of stemness. Finally, the ChIP assay demonstrated that STAT1 protein can bind to the promoter region of the SOX2 gene to serve as a transcription factor. In summary, our results indicate that CSCs produce and secrete IFN-I via their enhanced JAK/STAT1 signaling. The secreted IFN-I can bind to the receptor on the CSCs, further activate their JAK/STAT1 signaling, promoting the expression of SOX2 and maintenance of stemness of CSCs via an autocrine manner.

Citation Format: Aidan Li, Xuetao Bai, Na Li, Shurui Cai, Ananya Banerjee, Kousalya Lavudi, Linzhou Wang, Qianyun Ge, Yajing Yang, Qi-En Wang. Cancer stem cells maintain stemness via autocrine activation of the IFN/JAK/STAT signaling pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2428.

ERK inactivation enhances stemness of NSCLC cells via promoting Slug-mediated epithelial-to-mesenchymal transition

Rationale: The mitogen-activated protein kinase pathway (MAPK) is one of the major cancer-driving pathways found in non-small cell lung cancer (NSCLC) patients. ERK inhibitors (ERKi) have been shown to be effective in NSCLC patients with MAPK pathway mutations. However, like other MAPK inhibitors, ERKi rarely confers complete and durable responses. The mechanism of tumor relapse after ERKi treatment is yet defined. Methods: To best study the mechanism of tumor relapse after ERK inhibitor treatment in NSCLC patients, we treated various NSCLC cell lines and patient-derived xenograft (PDX) with ERK inhibitors and evaluated the enrichment of cancer stem cell (CSC) population. We then performed a Next-generation sequencing (NGS) to identify potential pathways that are responsible for the CSC enrichment. Further, the involvement of specific pathways was examined using molecular and cellular methods. Finally, we investigated the therapeutic benefits of ERKi treatment combined with JAK/STAT pathway inhibitor using cellular and xenograft NSCLC models. Results: We found that ERKi treatment expands the CSC population in NSCLC cells through enhanced epithelial-to-mesenchymal transition (EMT)-mediated cancer cell dedifferentiation. Mechanistically, ERK inactivation induces EMT via pSTAT3-mediated upregulation of Slug, in which, upregulation of miR-204 and downregulation of SPDEF, a transcription repressor of Slug, are involved. Finally, the JAK/STAT pathway inhibitor Ruxolitinib blocks the ERK inactivation-induced EMT and CSC expansion, as well as the tumor progression in xenograft models after ERKi treatment. Conclusions: This study revealed a potential tumor relapse mechanism of NSCLC after ERK inhibition through the unintended activation of the EMT program, ascertained the pSTAT-miR-204-SPDEF-Slug axis, and provided a promising combination inhibitor approach to prevent tumor relapse in patients.

2-Dimensional in vitro culture assessment of ovarian cancer cell line using cost effective silver nanoparticles from Macrotyloma uniflorum seed extracts

Our research focused on generating AgNPs using Macrotyloma uniflorum (MU) seed extracts and studied their efficacy in combating tumor growth using the 2-Dimensional method for ovarian cancer cell line-PA-1. Characterization studies including a UV-visible spectrophotometer confirmed the surface plasmon resonance peak of 436 nm. Particle size determination data validated the nanoparticle diameter of 91.8 nm. Synthesized AgNPs possess a negative charge of -28.0 mV, which was confirmed through the zeta potential study. Structural characterization studies including XRD determined the crystal phase of AgNPs at four distant peaks at 2θ (38.17, 44.36, 64.52, and 77.46) and were assigned to 111, 200, 220, and 311 planes of the FCC. FTIR studies have confirmed the presence of O-H, N-H, C=O, ethers, C-Br, and C-I groups in AgNPs respectively. DPPH study has confirmed the presence of free radicles and we observed that at 500 μg/ml concentration, 76.08% of free radicles were formed which shows their efficiency. MTT assay shows the efficacy of MU-AgNPs in reducing the cell viability. At lower concentrations of MU-AgNP, 66% viability was observed and 9% of viability was observed at higher dose. ROS production (21%) was observed using MU-AgNPs with respect to 0.45% in controls, which affirms the capacity to induce DNA damage via apoptosis. Standard drug camptothecin generated 26% of ROS production which confirms higher potential of AgNPs in inducing DNA damage in tumor cells without causing lethality to the healthy cells. Further, the Fluorescence-activated cell sorting (FACS) study using a standard Caspase-3 marker confirms the generation of apoptotic bodies using two different concentrations of MU-AgNPs. At 40 μg, 64% of apoptotic cell death was observed, whereas, using 20 μg, 23% of apoptosis was recorded via fluorescent intensity. Propidium iodide-based Cell cycle study has shown a significant decrease in G0/G1 phase compared to control (88.8%), which further confirmed the apoptotic induction. Matrix metalloproteinases (MMP) studies using JC-1 dye, showed a significant increase in green fluorescence owing to lowered membrane potential, thus ensuring the breakdown of mitochondrial potential compared to untreated and standard drugs. With the obtained results, we are concluding that MU-AgNPs has a tremendous capacity to suppress the ovarian cancer cell proliferation in vitro by inducing DNA damage and apoptosis.

Abstract 1519: ALDH1A1 enhances micro homology-mediated end joining by increasing POLQ expression

Aldehyde dehydrogenase (ALDH) is a superfamily of 19 known enzymes that participated in the metabolism of endogenous and exogenous aldehydes. ALDH1A1 is a major subtype contributing to high ALDH activity out of all ALDH isoforms and plays a critical role in the maintenance of cancer stem cells. Our previous studies have shown that ALDH1A1 is able to reduce the sensitivity of BRCA2-/- ovarian cancer cells to PARP inhibitors by enhancing microhomology-mediated end joining (MMEJ). MMEJ uses 5-25 base pair micro homologous sequences to align the broken strands before joining, and this repair pathway requires DNA polymerase θ (Pol θ, encoded by POLQ). Here we show that ALDH1A1 can increase the expression of Pol θ, at both mRNA and protein levels, in ovarian cancer cell lines. ALDH1A1 is reported to catalyze the production of all-trans retinoic acid (ATRA), which can bind to the retinoic acid receptor (RAR), and promote transcription of the downstream target genes that possess retinoic acid response element (RARE) in their promoter regions. Interestingly we identified several RAREs in the promoter region of the POLQ gene. Thus, we hypothesized that ALDH1A1 promotes Pol θ expression via activation of the RAR signaling pathway. We found that ATRA and RAR agonist (CH55) increased but pan RAR antagonist (AGN193109) treatment decreased the expression of POLQ, indicating that the RAR pathway is involved in the transcription of POLQ. We also demonstrated that RARα can bind to the promoter region of Pol Q, activation of RAR signaling by treatment with ATRA or CH55 increased the enrichment of K27 acetylated histone H3 in this promoter region. Moreover, we showed that mutated ALDH1A1 lacking the enzyme activity was unable to enhance POLQ transcription. These data suggest that ALDH1A1 enhances the Pol Q expression by increasing the production of ATRA which further activates the RAR signaling pathway.

Citation Format: Kousalya Lavudi, Ananya Banerjee, Shurui Cai, Na Li, Xuetao Bai, Wang Qi-En. ALDH1A1 enhances micro homology-mediated end joining by increasing POLQ expression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1519.

Abstract 889: NF-κB-mediated mitophagy contributes to the maintenance of cancer stem cells in ovarian cancer

Tumors contain phenotypically and functionally heterogeneous cancer cells. Among them, a minority of cell subpopulation, termed cancer stem cells (CSCs), which possess the self-renewal capacity and are able to generate the heterogeneous lineage of cancer cells, has been believed to be responsible for the initiation and progression of the tumor. However, it is still unclear how the stemness properties of CSCs are maintained in the tumor. Mitophagy is a process by which damaged mitochondria are cleared via autophagy. The significance of mitophagy in the maintenance of CSC has been investigated in multiple CSC types. Our recent study shows that ovarian CSCs also exhibit enhanced mitophagy, which is mainly attributed to elevated expression of mitophagy receptors BNIP3 and BNIP3L. Downregulation of BNIP3 or BNIP3L significantly diminished mitophagy in ovarian CSCs and compromised their self-renewal capability. Mechanistic investigation further revealed that enhanced NF-κB signaling contributes to the increased expression of BNIP3 and BNIP3L. Inhibition of NF-κB signaling pathway via p65 knockdown or specific inhibitors is able to reduce mitophagy in ovarian CSCs. In summary, our data suggest that selective inhibition of NF-κB is able to deplete CSCs by interfering with mitochondria quality control in these cells and has potential to prevent tumor relapse and metastasis.

Citation Format: Na Li, Tejinder Pal, Shurui Cai, Ananya Banerjee, Xuetao Bai, Kousalya Lavudi, Qi-En Wang. NF-κB-mediated mitophagy contributes to the maintenance of cancer stem cells in ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 889.

A bioinformatic approach of targeting SARS-CoV-2 replication by silencing a conserved alternative reserve of the orf8 gene using host miRNAs

The causative agent of the COVID-19 pandemic, the SARS-CoV-2 virus has yielded multiple relevant mutations, many of which have branched into major variants. The Omicron variant has a huge similarity with the original viral strain (first COVID-19 strain from Wuhan). Among different genes, the highly variable orf8 gene is responsible for crucial host interactions and has undergone multiple mutations and indels. The sequence of the orf8 gene of the Omicron variant is, however, identical with the gene sequence of the wild type. orf8 modulates the host immunity making it easier for the virus to conceal itself and remain undetected. Variants seem to be deleting this gene without affecting the viral replication. While analyzing, we came across the conserved orf7a gene in the viral genome which exhibits a partial sequence homology as well as functional similarity with the SARS-CoV-2 orf8. Hence, we have proposed here in our hypothesis that, orf7a might be an alternative reserve of orf8 present in the virus which was compensating for the lost gene. A computational approach was adopted where we screened various miRNAs targeted against the orf8 gene. These miRNAs were then docked onto the orf8 mRNA sequences. The same set of miRNAs was then used to check for their binding affinity with the orf7a reference mRNA. Results showed that miRNAs targeting the orf8 had favorable shape complementarity and successfully docked with the orf7a gene as well. These findings provide a basis for developing new therapeutic approaches where both orf8 and orf7a can be targeted simultaneously.

A Novel Estrogen Receptor β Agonist Diminishes Ovarian Cancer Stem Cells via Suppressing the Epithelial-to-Mesenchymal Transition

Epithelial ovarian cancer is the most lethal malignancy of the female reproductive tract. A healthy ovary expresses both Estrogen Receptor α (ERα) and β (ERβ). Given that ERα is generally considered to promote cell survival and proliferation, thereby, enhancing tumor growth, while ERβ shows a protective effect against the development and progression of tumors, the activation of ERβ by its agonists could be therapeutically beneficial for ovarian cancer. Here, we demonstrate that the activation of ERβ using a newly developed ERβ agonist, OSU-ERb-12, can impede ovarian cancer cell expansion and tumor growth in an ERα-independent manner. More interestingly, we found that OSU-ERb-12 also reduces the cancer stem cell (CSC) population in ovarian cancer by compromising non-CSC-to-CSC conversion. Mechanistically, we revealed that OSU-ERb-12 decreased the expression of Snail, a master regulator of the epithelial-to-mesenchymal transition (EMT), which is associated with de novo CSC generation. Given that ERα can mediate EMT and facilitate maintenance of the CSC subpopulation and that OSU-ERb-12 can block the transactivity of ERα, we conclude that OSU-ERb-12 reduces the CSC subpopulation by inhibiting EMT in an ERα-dependent manner. Taken together, our data indicate that the ERβ agonist OSU-ERb-12 could be used to hinder tumor progression and limit the CSC subpopulation with the potential to prevent tumor relapse and metastasis in patients with ovarian cancer.

Cytotoxic Potential of Biogenic Zinc Oxide Nanoparticles Synthesized From Swertia chirayita Leaf Extract on Colorectal Cancer Cells

Chemotherapy side effects, medication resistance, and tumor metastasis impede the advancement of cancer treatments, resulting in a poor prognosis for cancer patients. In the last decade, nanoparticles (NPs) have emerged as a promising drug delivery system. Swertia chirayita has long been used as a treatment option to treat a variety of ailments. Zinc oxide nanoparticles (ZnO-NPs) were synthesized from ethanolic and methanolic extract of S. chirayita leaves. ZnO-NPs were characterized using UV-visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron Microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD). Its anti-cancer activities were analyzed using cytotoxicity assays [MTT assay and acridine orange (AO) staining] and quantitative real-time PCR (qRT-PCR) using colorectal cancer (CRC) cells (HCT-116 and Caco-2) and control cells (HEK-293). The ZnO-NPs synthesized from the ethanolic extract of S. chirayita have an average size of 24.67 nm, whereas those from methanolic extract have an average size of 22.95 nm with a spherical shape. MTT assay showed NPs’ cytotoxic potential on cancer cells (HCT-116 and Caco-2) when compared to control cells (HEK-293). The IC₅₀ values of ethanolic and methanolic extract ZnO-NPs for HCT-116, Caco-2, and HEK-293 were 34.356 ± 2.71 and 32.856 ± 2.99 μg/ml, 52.15 ± 8.23 and 63.1 ± 12.09 μg/ml, and 582.84 ± 5.26 and 615.35 ± 4.74 μg/ml, respectively. Acridine orange staining confirmed the ability of ZnO-NPs to induce apoptosis. qRT-PCR analysis revealed significantly enhanced expression of E-cadherin whereas a reduced expression of vimentin and CDK-1. Altogether, these results suggested anti-cancer properties of synthesized ZnO-NPs in CRC.

Abstract 3104: EMT and CSC Enrichment Induced by ERK Inhibition in NSCLC

The activation of Mitogen-activated protein kinase pathway (MAPK/ERK pathway) has been found to play an important role in many cancers including lung cancer, and multiple inhibitors targeting this pathway have been developed. Several ERK inhibitors (ERKi, e.g., Ulixertinib, SCH772984) have been shown to be active against different cancers harboring RAS, BRAF, or MEK mutations, as well as cancers with developed BRAF/MEK inhibitor resistance. Nevertheless, sustained inhibition of ERK can lead to resistance and is likely to cause tumor relapse as well. Studies over the years have shown that a small portion of cells within tumors, which can reproduce themselves and sustain cancer, being called “cancer stem cells (CSCs)”, is the cause of tumor initiation and progression. Many reports have implicated the association of Epithelial-to-Mesenchymal Transition (EMT) program with CSCs and identified EMT-transcription factors (TFs) as CSC regulators. Here, we demonstrated that ERKi treatment induces EMT in non-small cell lung cancer cells (NSCLC), probably by inducing Slug expression. We also found that ERKi treatment can enrich the cancer stem cell (CSC) like population in NSCLC cells, evidenced by increased ALDH+ cells, enhanced in vitro sphere formation capability, and enhanced tumorigenicity in immunodeficient mice. Moreover, in NSCLC cells, we proved ERK knockdown or ERKi treatment can reduce C/EBPα expression, which is believed to be a master epithelial “gatekeeper” whose expression is required to prevent unwarranted mesenchymal transition. Our findings reveal a novel mechanism underlying the tumor relapse after ERKi treatment in NSCLC, and ultimately will help us improve current NSCLC therapeutic methods.

Citation Format: Shurui Cai, Xuetao Bai, Na Li, Ananya Banerjee, Kousalya Lavudi, Tejinder Pal. EMT and CSC Enrichment Induced by ERK Inhibition in NSCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3104.