HO-1 Limits the Efficacy of Vemurafenib/PLX4032 in BRAFV600E Mutated Melanoma Cells Adapted to Physiological Normoxia or Hypoxia

Abstract

Induction of heme oxygenase 1 (HO-1) favors immune-escape in BRAFV600 melanoma cells treated with Vemurafenib/PLX4032 under standard cell culture conditions. However, the oxygen tension under standard culture conditions (~18 kPa O2) is significantly higher than the physiological oxygen levels encountered in vivo. In addition, cancer cells in vivo are often modified by hypoxia. In this study, MeOV-1 primary melanoma cells bearing the BRAFV600E mutation, were adapted to either 5 kPa O2 (physiological normoxia) or 1 kPa O2 (hypoxia) and then exposed to 10 μM PLX4032. PLX4032 abolished ERK phosphorylation, reduced Bach1 expression and increased HO-1 levels independent of pericellular O2 tension. Moreover, cell viability was significantly reduced further in cells exposed to PLX4032 plus Tin mesoporphyrin IX, a HO-1 inhibitor. Notably, our findings provide the first evidence that HO-1 inhibition in combination with PLX4032 under physiological oxygen tension and hypoxia restores and increases the expression of the NK ligands ULBP3 and B7H6 compared to cells exposed to PLX4032 alone. Interestingly, although silencing NRF2 prevented PLX4032 induction of HO-1, other NRF2 targeted genes were unaffected, highlighting a pivotal role of HO-1 in melanoma resistance and immune escape. The present findings may enhance translation and highlight the potential of the HO-1 inhibitors in the therapy of BRAFV600 melanomas.

Role of heme oxygenase-1 in tumor immune escape

“…We have recently demonstrated that, in BRAF V600mutated melanoma cells treated with vemurafenib (PLX4032), HO-1 overexpression reduces natural killer (NK) recognition impairing the expression of NK ligands (B7-H6 and ULBP3), both under standard culture conditions (Furfaro et al 2020) and under physiological oxygen tension or hypoxia (Furfaro et al 2022). Moreover, the induction of HO-1 in cervical cancer cells reduces the expression of specific markers of NK activation (NKG2D, NKp30, and NKp46) and the production of IFNγ and Interestingly, a potent immune-suppressive response is observed in regulatory CD8 + T cells that specifically recognized HO-1 and that crucially contribute to the suppression of T-mediated antitumoral response (Andersen et al 2009).…”

“…https://doi.org/10.1530/REM-23-00062023:1 e230006TNFα in a co-culture model(Gomez-Lomeli et al 2014).In both experimental systems, the downregulation or the enzymatic inhibition of HO-1 in cancer cells restores the NK antitumor activity restoring the expression of NK ligands on cancer cells(Furfaro et al 2020(Furfaro et al , 2022 or NK-activating receptors (Gomez-Lomeli et al 2014). In line with these results, HO-1 overexpression in acute myeloid leukemia (AML) cells has been shown to decrease NK cytotoxicity activity by inhibiting CD48-2B4 axis both in vitro and in vivo and is associated with a poor prognosis in term of overall survival, refractory, and relapse (Zhang et al 2022).…”

PLX4032 resistance of patient-derived melanoma cells: crucial role of oxidative metabolism

“…One of the reasons of this gap is the limited availability of in vitro models able to reproduce a reliable condition of therapy resistance occurring in vivo. In this regard, it is crucial to carefully evaluate i) the choice of cancer cell line, ii) the strategy of drug administration and iii) the criteria of selecting drug-resistant cancer cells (16).…”