hTERT Downregulation Attenuates Resistance to DOX, Impairs FAK-Mediated Adhesion, and Leads to Autophagy Induction in Breast Cancer Cells

Targeting hTERT Promoter G-Quadruplex DNA Structures with Small-Molecule Ligand to Downregulate hTERT Expression for Triple-Negative Breast Cancer Therapy

Human telomerase reverse transcriptase (hTERT) may have noncanonical functions in transcriptional regulation and metabolic reprogramming in cancer cells, but it is a challenging target. We thus developed small-molecule ligands targeting hTERT promoter G-quadruplex DNA structures (hTERT G4) to downregulate hTERT expression. Ligand 5 showed high affinity toward hTERT G4 (Kd = 1.1 μM) and potent activity against triple-negative breast cancer cells (MDA-MB-231, IC50 = 1 μM). In cell-based assays, 5 not only exerts markedly inhibitory activity on classical telomere functions including decreased telomerase activity, shortened telomere length, and cellular senescence but also induces DNA damage, acute cellular senescence, and apoptosis. This study reveals that hTERT G4-targeting ligand may cause mitochondrial dysfunction, disrupt iron metabolism and activate ferroptosis in cancer cells. The in vivo antitumor efficacy of 5 was also evaluated in an MDA-MB-231 xenograft mouse model and approximately 78.7% tumor weight reduction was achieved. No observable toxicity against the major organs was observed.

Comparison of anti-cancer effects of platinum ribavirin and ribavirin via telomerase and Bcl-2 gene expression

Among the common treatments for cancers, chemotherapy is widely used. One of the ways to evaluate the effectiveness of anti-cancer drugs is by checking the expression of tumor markers. Hence, this study aimed to evaluate the anti-cancer effects of the newly synthesized platinum ribavirin (Pt-Rb) compared to ribavirin (Rb) through biomarkers. In this study, cell lines were divided into four groups: groups A and B as healthy negative control group and untreated cancer group respectively. Group C and D were treated with, Rb and Pt-Rb, a novel anti-cancer drug, respectively. After evaluating LC50 for the drugs by MTT test, the expression of telomerase and Bcl-2 (B cell lymphoma-2) genes was evaluated using real-time PCR (RT-qPCR). The results showed a significant decrease in telomerase (0.020 ± 0.007) and Bcl-2(0.120 ± 0.005) gene expression in cancer cells treated with Pt-Rb (group D) compared to telomerase (0.040 ± 0.014) and Bcl-2(0.220 ± 0.014) treated with Rb (group C) and also between group D and telomerase (70.76 ± 0.330) and Bcl-2 (99.52 ± 0.670) in group B. The majority of the groups under investigation showed a significant difference (p < 0.05), suggesting that Pt-Rb had stronger anti-cancer effects than Rb and untreated cancer cells. Additionally, Pt-Rb treatment results demonstrated more increased apoptosis than Rb. Our results demonstrated that Pt-Rb is an effective medication in cancer treatment by lowering anti-apoptotic indicators. Therefore, this chemical has the potential to be an effective anti-cancer therapy, pending further research on animal models and then human volunteers.

Favipiravir, an antiviral drug, in combination with tamoxifen exerts synergistic effect in tamoxifen-resistant breast cancer cells via hTERT inhibition

Tamoxifen (TAM) is one of the most successful treatments for breast cancer; however, TAM resistance continues to be a significant barrier. TAM resistance has been reported to be associated with increased expression of human telomerase reverse transcriptase (hTERT). This enzyme shares structural similarity with RNA-dependent RNA polymerase (RdRp) enzyme of RNA viruses, suggesting that RdRp inhibitors may also inhibit hTERT. Favipiravir (FAV) is an antiviral drug that inhibits RdRp of RNA viruses. Thus, we propose that FAV may also elicit an antitumor effect by suppressing hTERT. This study aimed to investigate the effect of FAV and TAM on TAM-resistant breast cancer (TAMR-1). The cell viabilities were determined. The levels of CDK1/ hTERT, in addition to regulators of hTERT-targeted signaling pathways were measured. Apoptosis, migration, and cell cycle distribution were also determined. Our data revealed that the combination of TAM and FAV suppressed cell proliferation synergistically (CI < 1) and resulted in a significant change in cell migration and apoptosis. Indeed, this was associated with reduced levels of hTERT and CDK1 and shift in the cell cycle distribution. Our findings suggest that the TAM/FAV combination exhibits synergistic effects against TAMR-1 human breast cancer cells by targeting hTERT.

Telomerase and hallmarks of cancer: An intricate interplay governing cancer cell evolution

Transformed cells must acquire specific characteristics to be malignant. Weinberg and Hanahan characterize these characteristics as cancer hallmarks. Though these features are independently driven, substantial signaling crosstalk in transformed cells efficiently promotes these feature acquisitions. Telomerase is an enzyme complex that maintains telomere length. However, its main component, Telomere reverse transcriptase (TERT), has been found to interact with various signaling molecules like cMYC, NF-kB, BRG1 and cooperate in transcription and metabolic reprogramming, acting as a strong proponent of malignant features such as cell death resistance, sustained proliferation, angiogenesis activation, and metastasis, among others. It allows cells to avoid replicative senescence and achieve endless replicative potential. This review summarizes both the canonical and noncanonical functions of TERT and discusses how they promote cancer hallmarks. Understanding the role of Telomerase in promoting cancer hallmarks provides vital insight into the underlying mechanism of cancer genesis and progression and telomerase intervention as a possible therapeutic target for cancer treatment. More investigation into the precise molecular mechanisms of telomerase-mediated impacts on cancer hallmarks will contribute to developing more focused and customized cancer treatment methods.

Regulation and clinical potential of telomerase reverse transcriptase (TERT/hTERT) in breast cancer

Telomerase reverse transcriptase (TERT/hTERT) serves as the pivotal catalytic subunit of telomerase, a crucial enzyme responsible for telomere maintenance and human genome stability. The high activation of hTERT, observed in over 90% of tumors, plays a significant role in tumor initiation and progression. An in-depth exploration of hTERT activation mechanisms in cancer holds promise for advancing our understanding of the disease and developing more effective treatment strategies. In breast cancer, the expression of hTERT is regulated by epigenetic, transcriptional, post-translational modification mechanisms and DNA variation. Besides its canonical function in telomere maintenance, hTERT exerts non-canonical roles that contribute to disease progression through telomerase-independent mechanisms. This comprehensive review summarizes the regulatory mechanisms governing hTERT in breast cancer and elucidates the functional implications of its activation. Given the overexpression of hTERT in most breast cancer cells, the detection of hTERT and its associated molecules are potential for enhancing early screening and prognostic evaluation of breast cancer. Although still in its early stages, therapeutic approaches targeting hTERT and its regulatory molecules show promise as viable strategies for breast cancer treatment. These methods are also discussed in this paper. Video Abstract.

Towards dual function of autophagy in breast cancer: A potent regulator of tumor progression and therapy response

As a devastating disease, breast cancer has been responsible for decrease in life expectancy of females and its morbidity and mortality are high. Breast cancer is the most common tumor in females and its treatment has been based on employment of surgical resection, chemotherapy and radiotherapy. The changes in biological behavior of breast tumor relies on genomic and epigenetic mutations and depletions as well as dysregulation of molecular mechanisms that autophagy is among them. Autophagy function can be oncogenic in increasing tumorigenesis, and when it has pro-death function, it causes reduction in viability of tumor cells. The carcinogenic function of autophagy in breast tumor is an impediment towards effective therapy of patients, as it can cause drug resistance and radio-resistance. The important hallmarks of breast tumor such as glucose metabolism, proliferation, apoptosis and metastasis can be regulated by autophagy. Oncogenic autophagy can inhibit apoptosis, while it promotes stemness of breast tumor. Moreover, autophagy demonstrates interaction with tumor microenvironment components such as macrophages and its level can be regulated by anti-tumor compounds in breast tumor therapy. The reasons of considering autophagy in breast cancer therapy is its pleiotropic function, dual role (pro-survival and pro-death) and crosstalk with important molecular mechanisms such as apoptosis. Moreover, current review provides a pre-clinical and clinical evaluation of autophagy in breast tumor.

Doxorubicin and Cisplatin Modulate miR-21, miR-106, miR-126, miR-155 and miR-199 Levels in MCF7, MDA-MB-231 and SK-BR-3 Cells That Makes Them Potential Elements of the DNA-Damaging Drug Treatment Response Monitoring in Breast Cancer Cells—A Preliminary Study

One of the most innovative medical trends is personalized therapy, based on simple and reproducible methods that detect unique features of cancer cells. One of the good prognostic and diagnostic markers may be the miRNA family. Our work aimed to evaluate changes in selected miRNA levels in various breast cancer cell lines (MCF7, MDA-MB-231, SK-BR-3) treated with doxorubicin or cisplatin. The selection was based on literature data regarding the most commonly altered miRNAs in breast cancer (21-3p, 21-5p, 106a-5p, 126-3p, 126-5p, 155-3p, 155-5p, 199b-3p, 199b-5p, 335-3p, 335-5p). qPCR assessment revealed significant differences in the basal levels of some miRNAs in respective cell lines, with the most striking difference in miR-106a-5p, miR-335-5p and miR-335-3p—all of them were lowest in MCF7, while miR-153p was not detected in SK-BR-3. Additionally, different alterations of selected miRNAs were observed depending on the cell line and the drug. However, regardless of these variables, 21-3p/-5p, 106a, 126-3p, 155-3p and 199b-3p miRNAs were shown to respond either to doxorubicin or to cisplatin treatment. These miRNAs seem to be good candidates for markers of breast cancer cell response to doxorubicin or cisplatin. Especially since some earlier reports suggested their role in affecting pathways and expression of genes associated with the DNA-damage response. However, it must be emphasized that the preliminary study shows effects that may be highly related to the applied drug itself and its concentration. Thus, further examination, including human samples, is required.

The Role of Telomerase in Breast Cancer's Response to Therapy

Currently, breast cancer appears to be the most widespread cancer in the world and the most common cause of cancer deaths. This specific type of cancer affects women in both developed and developing countries. Prevention and early diagnosis are very important factors for good prognosis. A characteristic feature of cancer cells is the ability of unlimited cell division, which makes them immortal. Telomeres, which are shortened with each cell division in normal cells, are rebuilt in cancer cells by the enzyme telomerase, which is expressed in more than 85% of cancers (up to 100% of adenocarcinomas, including breast cancer). Telomerase may have different functions that are related to telomeres or unrelated. It has been shown that high activity of the enzyme in cancer cells is associated with poor cell sensitivity to therapies. Therefore, telomerase has become a potential target for cancer therapies. The low efficacy of therapies has resulted in the search for new combined and more effective therapeutic methods, including the involvement of telomerase inhibitors and telomerase-targeted immunotherapy.

Mechanism of Human Telomerase Reverse Transcriptase (hTERT) Regulation and Clinical Impacts in Leukemia

The proliferative capacity and continuous survival of cells are highly dependent on telomerase expression and the maintenance of telomere length. For this reason, elevated expression of telomerase has been identified in virtually all cancers, including leukemias; however, it should be noted that expression of telomerase is sometimes observed later in malignant development. This time point of activation is highly dependent on the type of leukemia and its causative factors. Many recent studies in this field have contributed to the elucidation of the mechanisms by which the various forms of leukemias increase telomerase activity. These include the dysregulation of telomerase reverse transcriptase (TERT) at various levels which include transcriptional, post-transcriptional, and post-translational stages. The pathways and biological molecules involved in these processes are also being deciphered with the advent of enabling technologies such as next-generation sequencing (NGS), ribonucleic acid sequencing (RNA-Seq), liquid chromatography-mass spectrometry (LCMS/MS), and many others. It has also been established that TERT possess diagnostic value as most adult cells do not express high levels of telomerase. Indeed, studies have shown that prognosis is not favorable in patients who have leukemias expressing high levels of telomerase. Recent research has indicated that targeting of this gene is able to control the survival of malignant cells and therefore offers a potential treatment for TERT-dependent leukemias. Here we review the mechanisms of hTERT regulation and deliberate their association in malignant states of leukemic cells. Further, we also cover the clinical implications of this gene including its use in diagnostic, prognostic, and therapeutic discoveries.