Modulations of Programmed Cell Death-Ligand 1 and Multidrug-Resistance Protein 5 in Triple-Negative Breast Cancer by Kānuka Leaf Extract
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Dhaliwal, Harmandeep
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Li, Yan
Yoo, Michelle
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Auckland University of Technology
Abstract
Triple negative breast cancer (TNBC) is a clinically aggressive and biologically heterogeneous subtype defined by the absence of ER, PR, and HER2 overexpression. This receptor negative profile limits systemic therapy options to cytotoxic chemotherapy, contributing to high metastatic potential, early relapse, and poor overall prognosis. These challenges underscore the urgent need for alternative therapeutic strategies capable of addressing both tumour intrinsic drivers and the immunological features that enable tumour progression. Natural products with multimodal bioactivity have emerged as promising candidates because they can simultaneously target cancer cell vulnerabilities and modulate the tumour immune microenvironment.
Within this context, the present thesis provides the first comprehensive evaluation of Kunzea ericoides (kānuka) leaf extract as a potential anticancer and chemo sensitising agent in TNBC. This work characterises the extract’s phytochemical composition, defines its tumour intrinsic and immunomodulatory effects, and identifies mechanistic intersections between drug resistance and immune evasion.
Phytochemical profiling using LC-MS revealed that methanolic extraction yields a phenolic-rich preparation predominantly composed of catechin derivatives and quercetin glucuronides. This complex mixture of polyphenols suggests the capacity to engage multiple cellular pathways. Functional assays in TNBC cell lines demonstrated that kānuka extract induces potent cytotoxic and pro apoptotic effects, reducing cell viability and triggering concentration dependent apoptosis. The consistency of these responses across models highlights the extract’s intrinsic anticancer activity.
Beyond direct cytotoxicity, kānuka extract modulated key immunological pathways associated with tumour immune escape. Western blot analyses showed a marked reduction in PD L1 protein expression in MDA MB 231 and BT 549 cells following treatment. Given PD L1’s central role in suppressing T cell activation through PD 1 engagement, this downregulation suggests that kānuka may impair tumour mediated immune suppression. Jurkat-TNBC coculture assays revealed differential modulation of IL 2 secretions, indicating that the extract influences cytokine mediated communication between tumour cells and Jurkat T cells. Together, these findings demonstrate that kānuka exerts both tumour intrinsic and immune modulatory effects with potential to enhance antitumour immunity.
A novel mechanistic insight emerged from the investigation of multidrug resistance protein 5 (MRP5). CRISPR mediated MRP5 knockdown reduced PD L1 expression and significantly increased sensitivity to doxorubicin, revealing a previously uncharacterised link between efflux transporter activity and immune checkpoint regulation. This dual role suggests that chemoresistance and immune evasion may be co regulated in TNBC. Consistent with this model, kānuka extract increased intracellular doxorubicin accumulation and synergistically potentiated doxorubicin induced cytotoxicity. The dose dependent rise in caspase activity further supports a synergistic or additive interaction.
Collectively, the results support a mechanistic framework in which kānuka extract acts through multiple pathways: inducing apoptosis, suppressing immune checkpoint expression, modulating tumour and T cell cytokine interactions, enhancing intracellular drug accumulation, and synergising with doxorubicin. This multifactorial activity profile aligns with the behaviour of polyphenol rich botanical preparations and highlights kānuka’s therapeutic potential in TNBC, particularly in combination regimens aimed at overcoming chemoresistance and improving immune responsiveness.
Future work should isolate active constituents of kānuka leaf extract, dissect the underline molecular pathways with greater resolution, evaluate its pharmacokinetics and toxicity, and validate its efficacy in vivo. These findings establish a strong foundation for continued investigation of Kunzea ericoides as a potential adjunctive or standalone therapeutic candidate for TNBC.