One Kinase, Two Tumor Suppressors: The Molecular Triangle That Decides Whether Cancer Therapy Works

Deep inside every dividing cell, a three-way molecular conversation is quietly determining whether a tumor will grow, spread, and shrug off chemotherapy—or whether it will surrender to treatment. A comprehensive review published in the Journal of Pharmacy & Pharmaceutical Sciences argues that this conversation, between the kinase GSK-3β and the tumor suppressors RKIP and PTEN, may be one of the most consequential—and most misunderstood—signaling networks in modern cancer biology. Drawing on 263 peer-reviewed studies spanning more than three decades, the analysis makes a striking claim: these three molecules do not act as isolated switches, but as a coordinated signaling rheostat whose combined dysregulation reshapes oncogenic networks, drives metastasis, and quietly sabotages both chemotherapy and immunotherapy.

The central character of this molecular triangle is glycogen synthase kinase-3β, a serine/threonine kinase first identified for its role in glycogen metabolism but now recognized as a signaling hub touching nearly every corner of the cell. GSK-3β is unusual among kinases in that it prefers substrates already phosphorylated by other enzymes, such as casein kinase 1, ERK, p38MAPK, and AMPK, allowing it to act as a second-messenger amplifier within pre-activated pathways. Its activity is controlled by a delicate phosphorylation balance: inhibitory phosphorylation at Ser9—carried out by Akt, PKA, p90RSK, and p70S6K—silences the kinase, while phosphorylation at Tyr216, mediated by Fyn and PYK2 or by autophosphorylation, restores full catalytic power. Protein phosphatases PP1 and PP2A can reverse the Ser9 mark, meaning the cell constantly recalibrates GSK-3β output in response to upstream signals.

What makes GSK-3β so vexing for oncologists is its radical context dependency. In tumors driven by aberrant Wnt/β-catenin signaling, active GSK-3β promotes β-catenin degradation and suppresses proliferation—acting as a tumor suppressor. Yet in cancers characterized by chronic NF-κB activation or inflammatory signaling, the very same kinase enhances NF-κB–dependent transcription and supports tumor survival and chemoresistance. The review catalogs this duality across tumor types with unusual precision. In hepatocellular carcinoma, GSK-3β is overexpressed and promotes proliferation, colony formation, and resistance to sorafenib, yet pharmacological inhibition with tideglusib restores RARβ signaling and sensitizes tumors to therapy. In pancreatic ductal adenocarcinoma, GSK-3β enhances NF-κB activity and drives proliferation, but its inhibition paradoxically increases EMT-associated transcription factors such as Snail and Zeb1, potentially promoting invasion. In breast cancer, kinase-dead GSK-3β mutants increased resistance to doxorubicin and tamoxifen and promoted clonogenic growth, while constitutively active GSK-3β was less permissive—one of the clearest demonstrations that GSK-3β is a context-dependent regulator of drug response rather than a simple oncogene.

This signaling plasticity is not random; it is orchestrated by upstream pathway dominance. Loss of PTEN or hyperactivation of Akt leads to inhibitory Ser9 phosphorylation of GSK-3β, altering its downstream targets. Cytoplasmic versus nuclear localization determines whether GSK-3β preferentially regulates oncogenic transcription factors like NF-κB and Snail or cell-cycle regulators like cyclin D1 and c-Myc. The kinase’s role may even evolve during tumor progression, functioning as a tumor suppressor in early stages while promoting invasion, therapy resistance, or metastatic traits later on. The therapeutic implication is profound: successful clinical translation requires stratification based on pathway dominance rather than indiscriminate kinase inhibition.

Alongside GSK-3β, the review examines two tumor suppressors whose loss is consistently linked to aggressive disease. The Raf kinase inhibitor protein (RKIP) is underexpressed in many cancers and acts as a metastasis suppressor by binding to Raf-1 and blocking phosphorylation of MEK, thereby constraining the MAPK/ERK cascade. RKIP also inhibits NF-κB activation by blocking IκB phosphorylation by IKK family kinases, and it regulates tumor cell resistance to both chemotherapy and immunotherapy. In human breast cancer, RKIP must be downregulated for metastasis to develop; patients with reduced RKIP exhibit larger tumors and higher grade, and RKIP mRNA levels are significantly lower in metastatic compared to non-metastatic disease. In gastric cancer, RKIP is lost in approximately 56 percent of primary tumors and absent in roughly 90 percent of lymph node metastases. A meta-analysis of 19 studies encompassing around 3,700 patients confirmed that RKIP loss independently predicts poor overall survival in digestive-tract cancers, with a hazard ratio of 0.55.

PTEN, the phosphatase and tensin homolog, is the central negative regulator of the PI3K/Akt pathway, dephosphorylating PIP3 back to PIP2 and thereby halting mitogenic signaling. PTEN is either mutated, underexpressed, or deleted in a large percentage of human cancers, with prevalence ranging from 50 to 80 percent in endometrial cancer—the highest rate of any solid tumor—to 30 to 40 percent in glioblastoma and 17 to 61 percent in prostate cancer. PTEN loss sustains Akt activation, which in turn phosphorylates GSK-3β at Ser9, altering its substrate specificity and signaling role. The review emphasizes that PTEN and RKIP are frequently co-dysregulated and linked through a dysregulated NF-κB/Snail/YY1 loop: hyperactivation of NF-κB promotes overexpression of YY1 and Snail, which suppress both RKIP and PTEN, reinforcing a feed-forward mechanism that enhances survival signaling, EMT, and resistance to therapy.

The review also highlights how post-translational modifications dynamically regulate this axis. GSK-3β activity is controlled by site-specific phosphorylation at Ser9 and Tyr216, but these marks do not simply switch the kinase on or off—they can alter substrate preference, subcellular localization, and signaling integration. PTEN is subject to extensive C-terminal phosphorylation by CK2 and GSK-3β, which can stabilize the protein while simultaneously reducing its lipid phosphatase activity by promoting a closed conformation—uncoupling PTEN abundance from functional output. RKIP undergoes a phosphorylation-dependent functional switch at Ser153 by PKC, which releases Raf-1 and redirects RKIP to inhibit GRK2, illustrating how the molecule can dynamically alternate between suppressing oncogenic signaling and modulating alternative pathways depending on cellular context.

On the therapeutic front, the review catalogs the most advanced clinical development in this area. LY2090314, an ATP-competitive inhibitor with sub-nanomolar potency against GSK-3β (IC50 approximately 0.9 nM), entered early-phase clinical evaluation in advanced solid tumors and hematologic malignancies but was limited by toxicity and a narrow therapeutic window. Elraglusib (9-ING-41), a maleimide-based ATP-competitive inhibitor with low-micromolar biochemical potency (IC50 approximately 0.7 µM), has progressed into phase I/II trials both as monotherapy and in combination with chemotherapy, with a phase II study in metastatic pancreatic ductal adenocarcinoma reporting objective responses and disease control when combined with gemcitabine and nab-paclitaxel. Tideglusib, an irreversible non-ATP-competitive inhibitor originally developed for neurodegenerative diseases, has shown preclinical promise in sensitizing glioblastoma xenografts to temozolomide and enhancing sorafenib activity in hepatocellular carcinoma models. Early-phase trials of elraglusib have demonstrated a favorable safety profile, with predominantly low-grade and manageable adverse events such as fatigue, gastrointestinal symptoms, and transient visual disturbances.

The review also connects this axis to immunotherapy resistance. GSK-3 inhibitors such as GSK3i and SB415286 downregulate transcription of programmed cell death protein 1 (PD-1) in CD8+ T cells, enhancing cytotoxic function and providing a rationale for combining GSK-3β inhibitors with PD-1/PD-L1 blockade. Conversely, PTEN loss is associated with immune-excluded tumor microenvironments, reduced T-cell infiltration, and resistance to immune checkpoint inhibitors, with low PTEN expression correlating with poor response to immunotherapy in non-small-cell lung cancer and breast cancer cohorts. RKIP downregulation, meanwhile, sustains NF-κB hyperactivation and maintains a tumor-intrinsic resistance state that limits the efficacy of checkpoint blockade. Nitric oxide donors and proteasome inhibitors such as NPI-0052 and bortezomib have been shown to sensitize resistant cancer cells by inhibiting NF-κB and its downstream target Snail, resulting in RKIP induction and reversal of EMT, migration, and invasion.

Perhaps the most sobering insight from the review concerns the challenges of clinical translation. In breast cancer cell models, inhibition of GSK-3β increased resistance to doxorubicin and tamoxifen, yet the same cells became more sensitive to MEK or mTOR blockade—demonstrating that the resistance phenotype is network-dependent rather than GSK-3β-alone dependent. In p53-null colon cancer, by contrast, GSK3B silencing restored chemotherapy sensitivity and drove necroptotic death. In colorectal cancer models harboring PIK3CA and TCF7 mutations, inhibition of GSK3β restored sensitivity to the dual PI3K/mTOR inhibitor gedatolisib by suppressing aberrant WNT/β-catenin signaling. The fundamental challenge in targeting PTEN and RKIP stems from the therapeutic necessity to restore lost function, where neither the lipid phosphatase activity of PTEN nor the protein-scaffolding function of RKIP presents a conventional activation pocket amenable to small-molecule agonism. Only eight FDA-approved compounds have been reported to increase RKIP promoter activity in breast cancer cells, and none is a clinically validated activator. The review concludes that the GSK-3β/RKIP/PTEN axis functions as a dynamic signaling hub whose dysregulation is rarely driven by a single molecule, but rather by disruption of integrated circuitry—and that a systems-level, context-guided approach, incorporating biomarker-driven patient selection, optimized dosing, and combination strategies, will be essential to translate this complex molecular dialogue into practical, patient-centered strategies for better cancer care.

Subject of Research: The cross-talk between GSK-3β, RKIP, and PTEN as potential targets for therapeutic implications in cancer: a comprehensive insight

Article Title: The cross-talk between GSK-3β, RKIP, and PTEN as potential targets for therapeutic implications in cancer: a comprehensive insight

Article References: Mosalam, E. M., Abdallah, M. S., Gardouh, A. R., Hamza, E., Bahaa, M. M., Nazih, M., Al-Dhelaan, R. A., & Kamal, N. (2026). The cross-talk between GSK-3β, RKIP, and PTEN as potential targets for therapeutic implications in cancer: a comprehensive insight. Journal of Pharmacy & Pharmaceutical Sciences, 29, Article 16610. https://doi.org/10.3389/jpps.2026.16610

Image Credits: AI Generated

DOI: 10.3389/jpps.2026.16610

Keywords: cross-talk, between, GSK-3, RKIP, PTEN, potential, targets, therapeutic, implications, cancer, comprehensive, insight