Transcriptome Analysis Reveals That G Protein-Coupled Receptors Are Potential Diagnostic Markers or Therapeutic Targets in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is associated with poor overall survival and the development of more effective therapies is urgently needed. G Protein-Coupled Receptors (GPCRs) represent the largest family of membrane receptors, with an estimated 800 members in humans, and are attractive therapeutic targets, accounting for approximately 30% of targets of marketed drugs. These receptors are key transducers that bind a vast diversity of ligands (e.g. glycoproteins, peptides, amino acids, nucleotides, nucleosides, ions) allowing the cells to adapt to their environment by regulating a wide variety of physiological processes including the control of blood pressure, heart rate, digestive processes, hormone secretion, cell growth and migration, as well as vision and olfaction. Binding to their ligands leads to conformational rearrangements promoting the engagement and modulation of many distinct downstream signaling effectors that are both G protein-dependent and independent.

Several GPCRs are critical for cell proliferation and survival, and can be aberrantly expressed in cancer cells. For example, the chemokine receptor CXCR4 plays an important role in metastasis and angiogenesis in breast cancer and many other types of tumors. In AML, CXCR4 overexpression has been associated with poor outcome. Moreover, in vivo mouse studies have shown that the use of a small molecule antagonist of CXCR4 increases the mobilization of AML cells into the peripheral blood and improves the apoptotic effects of chemotherapy. This activity has been explored in a phase I/II clinical study showing that the addition of CXCR4 antagonists to chemotherapy in AML might improve the remission rate. The role of GPCRs in mouse leukemogenesis has also been suggested in a transcriptome analysis of two related leukemia clones that differ in their stem cell frequency. In this study, GPCRs were the most differentially expressed class of genes between the two clones.

Currently, an extensive assessment of GPCR expression in human AML is lacking. To address this issue, we studied the expression of GPCRs in a large cohort of AML samples, as well as in normal blood cells, bone marrow cell populations, and cord blood-derived CD34⁺ cells as controls. The 772 GPCRs analyzed in this study consist of all the GPCR members included in the International Union of Basic and Clinical Pharmacology (IUPHAR) database, as well as 370 olfactory, 24 taste and 4 vomeronasal receptors. RNA sequencing data analysis was performed as previously described (Lavallée et al, Blood 2015 Jan 1;125(1):140-3) and revealed that 240 GPCRs are expressed in cells from this AML cohort. Among these receptors, 30 are upregulated and 19 are downregulated in AML samples compared to CD34⁺ normal cells. Upregulated GPCRs are enriched in chemokine (CCR1, CXCR4, CCR2, CX3CR1, CCR7, and CCRL2), adhesion (CD97, EMR1, EMR2, and GPR114) and purine (including P2RY2 and P2RY13) receptor sub-families. The downregulated members include adhesion GPCRs such as LPHN1, GPR125, GPR56, CELSR3, and GPR126, protease-activated receptors (F2R and F2RL1), and the Frizzled family receptors SMO and FZD6. Interestingly, specific deregulation was observed in genetically distinct subgroups of AML, a subset of GPCRs being differentially expressed in normal karyotype AML with NPM1 or FLT3-ITD mutations, and in specimens with Core Binding Factor and MLL rearrangements, thereby representing promising therapeutic targets or diagnostic markers.

In conclusion, our results demonstrate that several GPCR members are deregulated in AML with a clear enrichment in distinct classes, providing the rationale for functional assays using available agonists or antagonists to leukemia-enriched GPCRs. Since these receptors are the targets of several US Federal and Drug Administration approved drugs, our results pave the way to explore selected GPCRs as novel AML therapeutic targets.