The emerging role of chemokines and chemokine receptors in the biological and clinical behaviour of pituitary neuroendocrine tumours: An exploratory transcriptomic study

The chemokine network in the microenvironment of pituitary neuroendocrine tumours (PitNETs) may modulate tumour biology, aggressiveness, and treatment responses. We aimed to study the role of various chemokines and chemokine receptors in defining PitNET phenotype and clinical outcomes. We included 96 patients (51 females) with available snap-frozen PitNET tissue from surgery between 2014 and 2020. Chemokine and chemokine receptors were studied by RT-qPCR. Fold difference in mRNA expression was calculated using the ΔΔCt method; chemokine and receptor expression levels were normalised to the expression of the control gene TBP, and expressed relative to a reference sample. Ten chemokines and receptors were studied (CCL2, CCL3, CCL4, CXCL8, CX3CL1, CCR2, CCR4, CCR5, CXCR1, CXCR2), and their expression correlated with clinico-pathological and outcome data, as well as other available microenvironment-related data. We found strong positive correlations between all chemokines and chemokine receptors. Higher chemokine and receptor expression levels were seen in patients who had pituitary apoplexy (CCR2, CXCR1), hypopituitarism at diagnosis (CCL2, CCR4), Ki-67 >3% (CCL4, CXCR2), as well as in patients who required re-operation (CCL3, CXCL8, CXCR2), multimodal therapy (CCL2), and had active disease at last-follow-up (CCL2). There was a positive correlation between the number of pituitary surgeries and expression levels of CCL3, CXCL8, CX3CL1, CXCR1, and CXCR2. Compared to nonfunctioning-PitNETs, somatotropinomas had higher expression of CCL2, CCL4, and CCR2, and lower expression of CX3CL1 and CCR4. Expression of CDH1 (encoding E-cadherin) correlated negatively with CCL2, CCL4, CCR2, CCR4, and CXCR2, while the expression of ZEB1 (mesenchymal marker) positively correlated with CCL3, CCL4, and CX3CL1. PitNETs expressing higher levels of CCL4, CX3CL1, CCR4, CCR5, and CXCR1 had more and bigger vessels. Somatotropinomas treated pre-operatively with somatostatin analogues were associated with higher expression of CCL2, CCR4, CXCR1, and CXCR2, while nonfunctioning-PitNETs pre-surgically treated with dopamine agonists were associated with lower expression of CCL3, CCL4, CX3CL1, CCR5, CXCR1, and CXCR2. Our data suggests that chemokines and chemokine receptors may be involved in the modulation of different tumorigenic mechanisms in PitNETs, including tumour proliferation, epithelial-to-mesenchymal transition, and angiogenesis, and may be associated with more aggressive and difficult-to-treat disease.