Drug-induced tolerant persisters in tumor: mechanism, vulnerability and perspective implication for clinical treatment

Abstract

Cancer remains a significant global health burden due to its high morbidity and mortality. Oncogene-targeted therapy and immunotherapy have markedly improved the 5-year survival rate in the patients with advanced or metastatic tumors compared to outcomes in the era of chemotherapy/radiation. Nevertheless, the majority of patients remain incurable. Initial therapies eliminate the bulk of tumor cells, yet residual populations termed drug-tolerant persister cells (DTPs) survive, regenerate tumor and even drive distant metastases. Notably, DTPs frequently render tumor cross-resistance, a detrimental phenomenon observed in the patients with suboptimal responses to subsequent therapies. Analogous to species evolution, DTPs emerge as adaptative products at the cellular level, instigated by integrated intracellular stress responses to therapeutic pressures. These cells exhibit profound heterogeneity and adaptability shaped by the intricate feedforward loops among tumor cells, surrounding microenvironments and host ecology, which vary across tumor types and therapeutic regimens. In this review, we revisit the concept of DTPs, with a focus on their generation process upon targeted therapy or immunotherapy. We dissect the critical phenotypes and molecule mechanisms underlying DTPs to therapy from multiple aspects, including intracellular events, intercellular crosstalk and the distant ecologic pre-metastatic niches. We further spotlight therapeutic strategies to target DTP vulnerabilities, including synthetic lethality approaches, adaptive dosing regimens informed by mathematical modeling, and immune-mediated eradication. Additionally, we highlight synergistic interventions such as lifestyle modifications (e.g., exercise, stress reduction) to suppress pro-tumorigenic inflammation. By integrating mechanistic insights with translational perspectives, this work bridges the gap between DTP biology and clinical strategies, aiming for optimal efficacy and preventing relapse.

Keywords: Drug-tolerant persisters; Immunoregulation; Immunotherapy; Targeted therapy.

Fig. 1

Three non-mutually exclusive models for DTP emergence in MRD tumors. A In the pre-existing selection mechanism, drug pressure screens pre-existing tolerant cells with inherited or stable epigenetic resistance traits, similar to a Darwinian selection process. These clones survive treatment, emphasizing deterministic selection of pre-existing tolerant cells in TN tumors. B In the drug induction mechanism, DTPs originate from de novo evolution of tumor sensitive cells triggered by drugs, through epigenetic modifications such as histone methylation/acetylation/glycosylation and DNA methylation, similar to Lamarckian induction. Highly heterogeneous DTPs exhibit transient drug tolerance, manifested as the recovery drug sensitivity after drug withdrawal. Ultimately, DTPs may acquire permanent drug resistance via genetic mutations during a continuous treatment, or revert to tumor sensitive cells capable of drug sensitivity following discontinuation therapy. C In the dynamic fluctuation-dependent model, DTP is derived from rare pre-DTP cells with transient high tolerant gene expression with random fluctuations within the tumor. These cells were selectively retained and epigenetically stabilized after treatment. Notably, DTPs display distinct phenotypic traits, including non/slow proliferation, cell cycle arrest, EMT phenotype, CSC property, reversible drug resistance and evolvability. Image made with BioRender.com

Fig. 2

Illustrates Various Molecular Mechanisms Facilitating the Formation and Survival of DTPs under Targeted Therapy and Immunotherapy. A Genomic Abnormality (top left): Drug-induced epigenetic plasticity and DNA instability contribute to alterations in chromatin status within DTPs, thereby promoting the generation of and subsequent tumor recurrence. In detail, epigenetic plasticity includes histone modifications, DNA methylation and RNA epigenetics, while DNA instability includes polymerase, LINE- 1 and APOBEC3. B Transcriptional Regulation (top right): DTPs upregulate various TFs and TCs, as well as initiate chromatin remodeling via SWI/SNF complexes, triggering unique transcriptome shift and leading to a phenotypic transition to DTP. C Metabolic Remodeling (bottom right): To endure harsh environments created by drug toxicity conditions, DTPs rely on metabolic reprogramming, particularly enhanced mitochondrial oxidative respiration, intracellular antioxidant pathways and ACh metabolism. The core components of mitochondrial oxidative respiration are FAM and OXPHOS, which generate substantial energy reserves essential for sustaining DTP viability. DTPs overexpress and activate NRF2, ALDH and GPX4, which endow them with robust antioxidant stress resistance to safeguard against oxidative stress. D Signaling Pathway Activation (bottom left): Drugs initiate the activation of survival signaling pathways (PI3 K/AKT/mTOR, RTK/RAS, ER stress) as well as developmental signaling pathways (FGF, Notch, WNT/β-catenin) within DTPs, ultimately enhancing their survival. Image made with BioRender.com

Fig. 3

Multiple Cross-linking Mechanisms among Tumor Cells or/and the Surrounding Environment Sustain the Formation and Persistence of DTPs under Targeted Therapy and Immunotherapy. A Inter-crosstalk among Tumor Cells: a) In DTPs, cytochrome c is released via caspase-independent MOMP to activate HRI kinase, which in turn promotes ATF translation and enhances ISR. Tolerant tumor cell-derived exosomes, such as microRNAs and proteins, facilitate DTPs to avoid various types of death. b) In contrast, treatment-induced death-sensitive cells release debris or clusters containing various splicosomal proteins to alter mRNA splicing of cell cycle-related proteins or activate PI3 K/AKT/mTOR pathway. Dying sensitive cells release PGE2 and arachidonic acid in a caspase- 3-dependent manner, which activate WNT-β-catenin within DTPs and ultimately stimulate resistance. B Inter-crosstalk between Tumor Cell and Environment: (i) Tumor infiltering immune cells: c) The over-expressed PD-L1, PD-L2, and CD70 on tumor cells can inhibit recognition by immune cells and impedes immune elimination of tumor cells. d) Treatment-induced CD8 + T cells can produce IFN-γ, which can enhance cross-resistance of DTPs. Treatment also promotes regulatory T cell elimination, M1 conversion of macrophage and MHC class I and II antigen presentation of dendritic cells. A unique EOMES + CD8 + T cell has been identified. (ii) Extracellular matrix: e) Stromal cells secrete pro-survival HGF, which recruits neutrophils and activates HGF receptor MET, thereby providing a favorable situation to DTP formation. The extensive collagen and fibronectin constitute the ECM with high stiffness, which can reduce the penetration of drug into tumor cells and promotes DTP production. Tumor cells adhere to collagen and interact with integrin-β1 to drive drug resistance. f) Cluster 0 CAFs, PLA2G2 CAFs, FGFR4 CAFs and OIT3 endothelial cells play a crucial role in mediating tumor DTPs survival. Cluster 0 CAFs can secrete growth factors (IL- 6, TNFSF9, FGF7) and immune-modulatory factors (CCL11, CXCL1, CXCL12). Image made with BioRender.com

Fig. 4

Ameliorative Management Strategies for DTP Tumors. A, B The focused approach is prevention/reversal of DTP status and induction of DTP death. On the one hand, we can prevent or reverse the DTP state through strategies such as regulating the transcriptional process, blocking the DTP survival pathway, and inhibiting the DTP apoptotic escape. On the other hand, methods to induce DTP death include increased intracellular stress, cell cycle and DNA damage-related death, and metabolism-related cell death. C Based on scientific, mathematical, and computer science-based mathematical models, the optimal drug regimen for the individual patient can be determined, including the dose, time, route, and frequency of administration, as well as the time and interval of withdrawal. D Immune surveillance or attack of DTP also plays an important role in the management of DTP tumors. These include TKI-induced immune cell recruitment, STING checkpoint, PD- 1/PD-L1 inhibitor, anti-fibrosis/ECM strategy, adaptive TCR or CAR-T, and personalized cancer vaccines and healthy lifestyle. Image made with BioRender.com