Telomerase Activity in Melanoma: Impact on Cancer Cell Proliferation Kinetics, Tumor Progression, and Clinical Therapeutic Strategies—A Scoping Review

1. Introduction

Melanoma remains a significant global health challenge, with incidence rates steadily rising worldwide [1]. Recent epidemiology data indicate that melanoma accounts for approximately 1.5% of all newly diagnosed cancer, with age-adjusted incidence rates increasing from 15.1 per 100,000 in 1999 to 23.0 per 100,000 in 2021 [1]. As of 2025, melanoma represents one of the most prevalent cancers, with over 816,580 individuals living with a melanoma diagnosis in the United States alone [2]. A defining molecular characteristic of melanoma is the aberrant activation of telomerase, with 69-82% of cutaneous melanoma exhibiting detectable telomerase activity [3,4]. This activation is predominantly mediated by telomerase reverse transcriptase (TERT) promoter mutations [5,6] which occur at frequencies ranging from 50% to 82% in melanoma cases, representing the most common noncoding mutation in this malignancy [7,8].

Telomerase activation represents a critical mechanism enabling replicative immortality in melanoma cells, directly facilitating sustained cancer cell proliferation and tumor progression [9,10]. The enzyme complex maintains telomere length at chromosomal ends, thereby bypassing cellular senescence and apoptosis pathways that normally limit cell division [3,4,11]. The most prevalent TERT promoter mutations (C228T and C250T, located at 124 and 146 pb from the ATG start site) generate de novo binding sites for ETS (Erythroblast Transformation Specific) transcription factors, resulting in 2- to 4-fold increases in TERT mRNA expression and telomerase activity [6,7,8]. This heightened telomerase activity correlates strongly with cancer cell proliferation rates, telomere length maintenance, and population doubling capacity [12,13,14,15]. Importantly, telomerase activity levels in melanocytic lesions demonstrate progressive elevation from benign nevi to primary melanomas and metastatic disease [4], suggesting a direct relationship with disease progression. Furthermore, telomerase activation has been implicated in therapeutic resistance to BRAF and MEK inhibitors [16], contributing to treatment failure and poor clinical outcomes [17].

Despite the well-established prevalence of telomerase activation in melanoma, several critical knowledge gaps persist regarding the relationship between telomerase activity levels and cancer cell population doubling time in melanoma [18,19]. Additionally, although telomerase inhibitors have demonstrated preclinical efficacy, their clinical translation has been limited by delayed cytotoxic effects and therapeutic resistance mechanisms that remain poorly understood [18,19,20]. Currently no scoping review has systematically mapped the evidence linking telomerase activity to melanoma cell proliferation kinetics and doubling time. More literature about immunity and telomerase will be included in the results section.

This scoping review aims to identify key studies by comprehensively synthesizing current knowledge and highlighting existing gaps. In doing so, the review will provide a foundation for future research directions and inform the development of telomerase-based strategies. The research team is notable for its international representation, comprising experts in oncology, basic science, nursing, and pharmacy. This work will serve as a valuable reference for clinicians and researchers in the future. Drawing from the example of arsenic, when it was first submitted for publication, few believed that such an apparently irrelevant emerging drug would one day become the cornerstone of leukemia treatment. Time will tell whether telomerase can become a useful target for refractory cases of melanoma once current well-known treatments have been exhausted.

2. Materials and Methods

A comprehensive search was conducted across four major electronic databases: Scopus, ScienceDirect, MEDLINE/PubMed, and CINHAL (Cumulated Index to Nursing and Allied Health Literature). It utilized a combination of keywords, including “telomerase”, “melanoma”, “cancer”, “cell proliferation” and “doubling time”. We used the preferred reporting items for systematic reviews and meta-analyses (PRISMA) methodology.

2.1. Inclusion Criteria and Exclusion Criteria

Inclusion criteria are: quantitative, qualitative, or mixed methods research on telomerase activity in melanoma and its role cancer cell proliferation and doubling time, published in English between 2020 to 2025. Exclusion criteria are: unrelated to telomerase or not meeting inclusion criteria. Two authors (O.A. and P.T.) independently reviewed eligible study of title and abstract screening, followed by full-text assessment. Any discrepancies or disagreements were resolved through discussion and re-examination of the articles. A third researcher (D.A.) was available to arbitrate if consensus could not be reached.

2.2. Quality Assessment and Data Analysis (Figure 1 and Table S1-S3)

While a formal quality assessment (e.g., MMAT or ROBIS) is typically reserved for systematic reviews, this scoping review evaluated sources credibility based on study design rigor and peer-review status. Data were synthesized using a thematic analysis approach, grouping findings into three core categories: (1) TERT prompter mutations and proliferation markers, (2) therapeutic targeting of telomerase, and (3) clinical prognostic correlations. These approaches allowed for identifying critical knowledge gaps regarding specific cell proliferation doubling times.

Figure 1. Flow diagram for Prisma: preferred reporting items for systematic review and meta-analysis.

Figure 1. Flow diagram for Prisma: preferred reporting items for systematic review and meta-analysis.

3. Results

3.1. TERT Promoter Mutations as Drivers of Proliferation

From Table 1, TERTp (TERT promoter) is important for diagnosis and prognosis and may serve as a therapeutic target through telomerase inhibition, or TERT-directed immunotherapies [28]. It supports a two-step model of telomere-driven carcinogenesis: TERT promoter mutations extend proliferative lifespan (first hit), while TPP1 promoter variants enhance telomerase activity and telomere lengthening (second hit). Both show UV mutation signatures, underscoring sunlight’s role in melanoma progression[25]. Sanford concludes that dual promoter mutations in TERT and TPP1 remove “telomeric guardrails,” driving immortalization and tumor growth, while offering novel targets for telomerase- or ETS-based therapies [25].

Chun-On et al. identified somatic promoter variants in the TPP1 gene (shelterin complex) [31], present in 5–6% of cutaneous melanomas and frequently co-occurring with TERT promoter mutations [31]. These variants alter ETS transcription factor binding sites, increasing TPP1 expression. TPP1 promoter mutations thus represent a critical “second hit” cooperating with TERT activation to sustain telomere maintenance and drive melanoma progression. The findings highlight the importance of non-coding regulatory mutations and suggest new therapeutic targets[31]. Table S1 shows summary of molecular mechanism and mutation frequencies.

In summary across multiple studies, TERT promoter mutations are a hallmark of cutaneous melanoma, representing high-frequency (70–80%) noncoding driver mutations, functional upregulation of telomerase, cooperation with MAPK signaling, and outcomes such as telomere stabilization, senescence bypass, and tumor persistence [7,8,16] (Figure 2). These alterations act as a molecular signature of UV-induced carcinogenesis, offering diagnostic and prognostic value in tumor biology and therapeutic resistance.

3.2. diagnostic Algorithms and Telomere Maintenance Mechanism (TMM)

Telomerase is essential for telomere maintenance in stem cells and most cancers, but measuring its activity has been difficult [32]. EXTEND (EXpression-based Telomerase ENzymatic activity Detection) is a computational method that estimates activity from a 13-gene signature including TERT and TERC[15]. Validated across cancer cell lines, patient tumors, and non-neoplastic tissues, EXTEND outperformed TERT expression alone in predicting telomerase activity[15]. Applied to over 9,000 tumors, it showed that telomerase activity varies by cancer type and correlates with stage, molecular subtype, oncogenic pathways, and prognosis[15].

Telomeres protect chromosome ends and regulate cell lifespan, but in cancer telomere maintenance mechanisms (TMMs) become dysregulated, enabling unlimited division[32]. Two main pathways exist: telomerase-dependent (TEL) and alternative lengthening of telomeres (ALT) [33]. Hakobyan et al. analyzed RNA sequencing from 33 TCGA cancer types, categorizing tumors into five TMM phenotypes [24]. Normal tissues showed low activity, while cancers had higher TEL and ALT, with ALT varying more widely[24]. Clinically, MSI-H tumors exhibited higher TMM activity, particularly in TEL and ALT branches. Survival analyses linked ALT high/TEL high and ALT high/TEL low phenotypes to poorer outcomes, suggesting TMM activity drives tumor aggressiveness[24].

3.3. Therapeutic Targeting of Telomerase in Melanoma

Zhang et al. (2018) investigated 6-thio-2’-deoxyguanosine (6-thio-dG), a telomerase-directed nucleoside, as a treatment for therapy-resistant melanoma [26]. In pre-clinical models, 6-thio-dG selectively impaired telomerase-positive cancer cells while sparing normal skin cells[26]. In BRAF-mutated melanoma lines, it showed strong anti-proliferative effects, inducing telomere dysfunction, apoptosis, and senescence. In vivo, 6-thio-dG reduced tumor growth in xenografts without toxicity. Molecular analyses revealed suppression of telomere maintenance, cell cycle, DNA damage response, and resistance markers such as AXL (AXL Receptor Tyrosine Kinase). Its efficacy depended on telomerase activity, as TERT depletion reduced sensitivity [26].

Patient biopsies showed enrichment of telomere pathways in tumors progressing on targeted or immune therapies, implicating telomere reactivation in resistance [26]. The telomerase-directed agent 6-thio-dG impaired growth of resistant melanoma cells and down-regulated proteins such as AXL, BRD4 (Bromodomain Containing 4), and ATM, (Ataxia-Telangiectasia Mutated) highlighting its potential to overcome therapy resistance[26]. In BRAF-mutated melanoma, most patients carried TERT promoter mutations, with shorter progression-free survival than wild-type cases[16]. Resistant cell lines exhibited high TERT expression, driving MAPK reactivation independent of telomere lengthening[16]. Inhibiting TERT with 6-thio-dG reduced proliferation and, when combined with vemurafenib, suppressed resistant growth by up to 90%, in 3D models [16]. Therefore, TERT serves as both a biomarker and therapeutic target, and combining MAPK inhibitors with TERT-directed agents may improve outcomes. Telomerase inhibition remains attractive given its cancer specificity and minimal effects on normal cells [18].

Telomerase-targeted approaches include antisense oligonucleotides (e.g., imetelstat) that block telomerase RNA, inducing telomere shortening and apoptosis, and small-molecule inhibitors such as BIBR1532 or G-quadruplex stabilizers (telomestatin, BRACO-19, RHPS4) that disrupt telomerase binding[34]. Immunotherapies (hTERT vaccines, adoptive T-cell therapies) and gene therapy using telomerase promoters to drive cytotoxic proteins or oncolytic viruses (OBP-301) show promise, though immune tolerance and variability remain challenges [35]. Based on recent studies on immunity in melanoma, there is a relationship between immunity and telomerase [43], it will lead to more telomerase-based cancer vaccine development. One such trial is combination therapy with ipilimumab in metastatic melanoma patients [44].

Additional strategies include alternative splicing modulation to shift hTERT toward inactive isoforms, natural products (curcumin, resveratrol, EGCG) and off-target drugs (aspirin, rapamycin) with telomerase-inhibiting activity, and shelterin complex targeting (TRF1/TRF2 disruption) to induce telomere dysfunction[36]. CRISPR/Cas9 can edit hTERT or engineer immune cells, while ALT-positive tumors may respond to ATR inhibitors, G4 ligands, or ALT-specific oncolytic viruses [22].

Combination therapies enhance efficacy by pairing telomerase inhibition with chemotherapy, CRISPR, or dual-target molecules, while personalized therapy tailors treatment using biomarkers such as telomere length, ALT status, and tumor mutations[18]. The TICCA framework (Transient, Immediate, Complete, Combinatory Attack) integrates short-term inhibition, rapid telomere disruption, multi-pronged strategies, and combination regimens to overcome resistance[18].

Since 2010, multiple agents have entered clinical trials, including hTERT vaccines (GV1001, UV1, GX301, INVAC-1), telomerase inhibitors (imetelstat, KML-001), oncolytic viruses (OBP-301, KH901), and nucleoside analogues (6-thio-dG) [36]. Notably, 6-thio-dG induces telomere dysfunction, suppresses resistance markers, and enhances checkpoint blockade efficacy, while imetelstat has improved survival in NSCLC patients, supporting telomerase inhibition as a viable cancer therapy[29].

Clinically, C250T mutation was linked to poor prognosis, with shorter progression-free survival (5 months) and overall survival (36 months) compared to C228T (23 and 106 months) and wild-type tumors (55 and 223 months). High TERT mRNA also predicted worse outcomes, but C250T remained the strongest biomarker [17]. Telomerase, particularly hTERT, contributes to chemo-resistance by maintaining telomeres and enhancing DNA repair[17]. Vault complexes and ABC transporters further support drug resistance, often regulated alongside hTERT by STAT5. Cancer stem cells, with high telomerase and ABC activity, are especially resistant, but telomerase inhibition (e.g., Imetelstat, BIBR1532, G-quadruplex stabilizers) can sensitize tumors to therapy [20]. Imetelstat is a first-in-class telomerase inhibitor, a lipid-conjugated oligonucleotide that targets the RNA template of telomerase (hTERC), thereby blocking telomere elongation.

In summary, telomerase activity drives resistance via telomere maintenance, mitochondrial protection, CSC survival, and transporter modulation, making it a critical therapeutic target[20].

4. Discussion

Telomerase has become central in cancer research, linking tumor biology with therapeutic innovation. Frequent TERT promoter mutations in melanoma, glioblastoma, and other cancers are among the most common noncoding mutations, providing a genetic mechanism for telomerase reactivation [6]. Once viewed only as a telomere-maintaining enzyme, telomerase is now recognized as a driver of immortality and regulator of pathways such as Wnt/β-catenin and NF-κB [9,36]. It is increasingly considered a prognostic marker, though predictive value varies by tumor type [29]. While Hakobyan links high activity to poor outcomes, Mishra argues telomerase does not always predict prognosis [24,37].

In melanoma, TERT promoter mutations occur in 70–80% of cases, strongly increasing telomerase activity and stabilizing short telomeres [6,7]. The model includes GABPα/β recruitment to ETS motifs and MAPK amplification, especially in BRAF V600E melanoma [38,39]. Yet Heidenreich notes promoter mutations alone do not guarantee activity, as transcription factor dynamics, structural variants, and chromatin context also play roles[40]. In bladder cancer, TERT activation can occur via THOR hypermethylation without mutations [41], while breast and colorectal cancers often rely on gene amplification [37].

Understanding these pathways is vital for targeted therapies, as telomerase is a near-universal hallmark of advanced malignancy [42]. Resistance to BRAF and MEK inhibitors in melanoma is increasingly linked to TERT overexpression and promoter mutations, with patients showing shorter progression-free survival compared to wild-type [16]. Preclinical studies demonstrate that 6-thio-dG reduces growth in resistant models [16,26], supporting combined telomerase-targeted and MAPK inhibitor therapy. Future research should examine mutation-specific effects, as Blanco García (2023) showed C250T variants predict worse survival than C228T or wild-type, underscoring the need for variant-level biomarker analysis in guiding treatment strategies[17].

This scoping review highlights a critical paradox in melanoma research while telomerase activation via TERT promoter mutations is a well-established driver of immortality, precise quantitative data linking enzymatic activity levels directly to population doubling time remains scarce. most studies rely on surrogate markers of proliferations, such as ki-67 index or tumor volume growth, rather than calculating specific doubling times.

The scarcity of direct doubling time correlations suggests that telomerase activity may function as a “permissive “factor rather than a direct accelerator of cell cycle speed. A noted by Hakobyan, the co-activation of ALT and telomerase pathways complicates this relationship [24]. Tumors may maintain high proliferative protentional without necessarily exhibiting a linear reduction in doubling time, possibly due to metabolic constraints or microenvironmental factors.

The findings regarding 6-thio-dG and TERT -directed immunotherapies underscore the potential of targeting this pathway. However, the resistance mechanisms described by Delyon, particularly MAPK pathway reactivation, suggest that telomerase inhibitors (e.g., imetelstat) will likely require combination with BRAF/MEK inhibitors to be clinically effective[16]. The “TICCA” framework proposed by ALI and Walter represents a logical evolution of this strategy, moving from monotherapy to combinatorial attacks[18].

Limitations of This Study

The review included only studies published between 2020 and 2025 in English, potentially excluding relevant foundational work and non-English publications that could provide valuable historical context on telomerase biology in melanoma. The heterogeneity of included study designs ranging from narrative reviews to preclinical experimental studies and retrospective cohort analyses limited formal quality assessment using standardized instruments such as MMAT or ROBIS, making direct comparisons challenging. While included studies demonstrated telomerase activity role in telomere dependent proliferation and therapy resistance, precise quantitively correlations between telomerase enzymatic activity levels and measured cell populations doubling times were sparse and inconsistently reported. Clinical outcomes data and patients level survival l analyses were limited, restricting conclusion about direct therapeutic relevance. The review didn’t systematically examine tissue specific variations across melanoma subtypes (cutaneous, acral, mucosal), which may influence applicability to diverse populations

Future research should focus on:

Prospective clinical trial directly measuring telomerase enzymatic activity alongside quantified cell population doubling times are essential to establish correlations between telomerase expression, telomere dynamics, and proliferation kinetics in vivo, research should examine mutation specific effects of TERT promoter variants (C250T versus C228T) in influencing telomerase activity and cellular phenotypes, as variant level biomarkers may better predict therapeutic response, investigations should characterized extratelomeric functions of telomerase including roles in mitochondrial metabolism, NF -kB signaling, and drug efflux transporters to identify synergistic opportunities for combined inhibition strategies, comparative efficacy studies should evaluating emerging telomerase directed strategies including 6-thio-dG,imetelstat,G-quadruplex stabilizers, and the TICCA framework within controlled clinical settings, research should clarify the interplay between telomerase dependant and ALT pathways in determining progression and resistance, future studies should explore biomarker driven approaches integrating telomere length, TERT mutation analysis, and immune checkpoint expression to guide personalized intervention strategies.

5. Conclusions

Telomerase is increasingly recognized as a central driver of melanoma progression through both telomere-dependent and independent mechanisms. By maintaining telomere length, it enables unlimited proliferation and genomic stability, while its non-canonical roles influence signaling pathways, metabolism, and resistance to apoptosis. Frequent TERT promoter mutations, particularly C250T, highlight its prognostic significance and link telomerase activity to poor patient outcomes. Moreover, telomerase overexpression contributes to resistance against BRAF and MEK inhibitors, underscoring its role in treatment failure. Emerging therapies such as 6-thio-dG demonstrate the potential to disrupt telomere function and overcome resistance, especially when combined with MAPK inhibitors. The review identifies a significant gap in the literature regarding direct quantification of doubling times. Future studies should prioritize calculating specific kinetics parameters alongside enzymatic activity to move beyond static biomarkers toward dynamic model of tumor growth.