Lauren DellaLibera

Background: Stage IV rectal adenocarcinoma is biologically distinct from colon cancer, requiring neoadjuvant chemoradiation therapy (nCRT) prior to surgical resection due to the constrained pelvic anatomy. While nCRT reduces tumor burden, it fundamentally leads to remodeling the tumor microenvironment (TME), induces treatment-related fibrosis that is radiographically indistinguishable from residual tumor on MRI and endoscopy.^1,2 Patients who appear to achieve a clinical complete response (cCR) may still harbor drug-tolerant “Persister” cell subpopulations that contribute to early recurrence of the disease4. Standard Tumor-Node-Metastasis (TNM) staging fails to capture this molecular heterogeneity, creating an urgent need for biologic markers of this residual disease. MicroRNAs (miRNAs) — small, ~22-nucleotide noncoding RNAs that modulate mRNA stability and translation — are powerful candidates, as a single miRNA can dysregulate entire signaling networks. miR-27a has been identified as upregulated in colorectal cancer (CRC) under chemotherapeutic stress, yet its role as a molecular mediator of TME-driven resistance in stage IV rectal adenocarcinoma has not been comprehensively summarized.

Objective: This narrative literature review examines the molecular mechanisms by which miR-27a mediates therapy resistance in stage IV rectal adenocarcinoma and evaluates its translational potential as a prognostic biomarker and therapeutic target.

Search Methods: A literature search was conducted in PubMed/MEDLINE (2016–2025) using the following terms and keywords: “miR-27a,” “microRNA colorectal cancer,” “rectal adenocarcinoma therapy resistance,” “epithelial-mesenchymal transition,” and “neoadjuvant chemoradiation rectal cancer.”

Results: Five peer-reviewed primary research articles were selected based on relevance to miR-27a biology, TME heterogeneity, or clinical translation. Li et al. used single-cell RNA sequencing (scRNA-seq) to identify a stem-like subpopulation (ELFN1-AS1⁺) in CRC tissue linked to metastasis and poor survival; high-risk TMEs were enriched for mitochondrial and metabolic stress pathway genes and showed suppression of AIF1L, establishing the biochemical context for miR-27a dysregulation in the CRC progression.³ Barisciano et al. demonstrated that elevated miR-27a directly suppressed PGC-1α — the master regulator of mitochondrial biogenesis — impairing oxidative phosphorylation (OXPHOS) and driving aerobic glycolysis (Warburg Effect). miR-27a knockdown restored basal respiration, ATP-linked oxygen consumption rate (OCR), and maximal respiratory capacity (p<0.001), while overexpression produced the inverse effect across three CRC cell lines.⁴ Detailed analysis confirmed that miR-27a silenced AMP-activated protein kinase (AMPK), releasing the brake on mTOR signaling; phosphorylated AMPK was inversely correlated with phosphorylated mTOR and phosphorylated P70S6K. Furthermore, manipulation of miR-27a expression bidirectionally shifted IC50 values for 5-FU and oxaliplatin.⁴ You et al. identified that long noncoding RNA (lncRNA) Linc00284 functions as a competing endogenous RNA (ceRNA) sponge for miR-27a; its loss in aggressive TMEs frees miR-27a, which de-represses c-Met and promotes oncogenic invasion.⁵ Gasiule et al. conducted a 9-month in vitro evolution demonstrating that prolonged chemotherapy exposure selects for miR-23b cluster upregulation, driving epithelial-mesenchymal transition (EMT) toward a drug-tolerant mesenchymal phenotype; disruption of miR-23b mediated by CRISPR/Cas9 gene editing restored chemosensitivity.⁶ Clinically, Liu et al. found that circulating exosomal miR-27a achieved an area under the receiver operating characteristic curve (AUC) of 0.808 for CRC diagnosis — outperforming carcinoembryonic antigen (CEA) (AUC 0.709) — and independently predicted shorter overall survival and lymph node metastasis on multivariate analysis; plasma levels of miR-23b declined significantly post-resection, confirming the tumor as the primary source.⁷

Conclusion: These studies collectively establish miR-27a as a central molecular mediator of CRC therapy resistance through three coordinated mechanisms: PGC-1α-mediated metabolic reprogramming (Warburg Effect), AMPK/mTOR axis dysregulation sustaining growth under chemotherapeutic stress, and miRNA-driven EMT producing invasive Persister phenotypes. The diagnostic and prognostic performance of circulating exosomal miR-27a demonstrates that this intracellular biology is detectable non-invasively, capturing disease aggressiveness beyond imaging or CEA. For stage IV rectal adenocarcinoma specifically, integrating a post-nCRT exosomal miR-27a liquid biopsy could enable molecular stratification of Watch-and-Wait versus operative candidates — directly addressing the current reliance on unreliable post-treatment imaging. Future prospective studies should validate plasma miR-27a thresholds against pathologic complete response in resected specimens and evaluate anti-miR-23b477 oligonucleotide strategies as chemo-sensitization agents prior to surgical resection.

Works Cited

1. Habr-Gama A, Fernandez L, São Julião G, Vailati B, Perez R. Alternative treatment to surgery for rectal cancer. Ann Laparosc Endosc Surg. 2018;3(5). doi:10.21037/ales.2018.05.05.
2. Yuval JB, Garcia-Aguilar J. Watch-and-wait management for rectal cancer after clinical complete response to neoadjuvant therapy. Adv Surg. 2021;55:89-107. doi:10.1016/j.yasu.2021.05.007.
3. Li G, Wang D, Chen G. Single-cell RNA sequencing defines prognostic subtypes and identifies AIF1L as a therapeutic target in colorectal cancer. BMC Cancer. 2025;25(1):1885. doi:10.1186/s12885-025-15241-2.
4. Barisciano G, Colangelo T, Rosato V, et al. miR-27a is a master regulator of metabolic reprogramming and chemoresistance in colorectal cancer. Br J Cancer. 2020;122(9):1354-1366. doi:10.1038/s41416-020-0773-2.
5. You J, Xue S, Ruan H, et al. Oncogenic long intervening noncoding RNA Linc00284 promotes c-Met expression by sponging miR-27a in colorectal cancer. Oncogene. 2021;40(24):4151-4166. doi:10.1038/s41388-021-01839-w.
6. Gasiulė S, Dreize N, Kaupinis A, et al. Molecular Insights into miRNA-Driven Resistance to 5-Fluorouracil and Oxaliplatin Chemotherapy: miR-23b Modulates the Epithelial-Mesenchymal Transition of Colorectal Cancer Cells. J Clin Med. 2019;8(12):2115. doi:10.3390/jcm8122115.
7. Liu X, Pan B, Sun L, et al. Circulating exosomal miR-27a and miR-130a act as novel diagnostic and prognostic biomarkers of colorectal cancer. Cancer Epidemiol Biomarkers Prev. 2018;27(7):746-754. doi:10.1158/1055-9965.EPI-18-0067.