Krayem Mohammad, Sabbah Malak, Najem Ahmad, Wouters An, Lardon Filip, Simon Stephane, Sales François, Journe Fabrice, Awada Ahmad, Ghanem Ghanem E, Van Gestel Dirk
Laboratory of Oncology and Experimental Surgery, Institut Jules Bordet, Université Libre de Bruxelles, Rue Héger-Bordet 1, 1000 Brussels, Belgium.
Department of Radiation Oncology, Institut Jules Bordet, Université libre de Bruxelles, 1000 Brussels, Belgium.
Cancers (Basel). 2019 Aug 1;11(8):1093. doi: 10.3390/cancers11081093.
Radiotherapy (RT) in patients with melanoma historically showed suboptimal results, because the disease is often radioresistant due to various mechanisms such as scavenging free radicals by thiols, pigmentary machinery, or enhanced DNA repair. However, radiotherapy has been utilized as adjuvant therapy after the complete excision of primary melanoma and lymph nodes to reduce the rate of nodal recurrences in high-risk patients. The resistance of melanoma cells to radiotherapy may also be in relation with the constitutive activation of the MAPK pathway and/or with the inactivation of p53 observed in about 90% of melanomas. In this study, we aimed to assess the potential benefit of adding RT to BRAF-mutated melanoma cells under a combined p53 reactivation and MAPK inhibition in vitro and in a preclinical animal model. We found that the combination of BRAF inhibition (vemurafenib, which completely shuts down the MAPK pathway), together with p53 reactivation (PRIMA-1) significantly enhanced the radiosensitivity of BRAF-mutant melanoma cells. This was accompanied by an increase in both p53 expression and activity. Of note, we found that radiation alone markedly promoted both ERK and AKT phosphorylation, thus contributing to radioresistance. The combination of vemurafenib and PRIMA-1 caused the inactivation of both MAPK kinase and PI3K/AKT pathways. Furthermore, when combined with radiotherapy, it was able to significantly enhance melanoma cell radiosensitivity. Interestingly, in nude mice bearing melanoma xenografts, the latter triple combination had not only a synergistic effect on tumor growth inhibition, but also a potent control on tumor regrowth in all animals after finishing the triple combination therapy. RT alone had only a weak effect. In conclusion, we provide a basis for a strategy that may overcome the radioresistance of BRAF-mutated melanoma cells to radiotherapy. Whether this will translate into a rational to use radiotherapy in the curative setting in BRAF-mutated melanoma patients deserves consideration.
黑色素瘤患者的放疗（RT）在历史上显示出不理想的结果，因为该疾病由于各种机制往往具有放射抗性，如通过硫醇清除自由基、色素生成机制或增强的DNA修复。然而，放疗已被用作原发性黑色素瘤和淋巴结完全切除后的辅助治疗，以降低高危患者的淋巴结复发率。黑色素瘤细胞对放疗的抗性也可能与MAPK途径的组成性激活和/或在约90%的黑色素瘤中观察到的p53失活有关。在本研究中，我们旨在评估在体外和临床前动物模型中，在联合p53再激活和MAPK抑制的情况下，对BRAF突变的黑色素瘤细胞添加放疗的潜在益处。我们发现，BRAF抑制（维罗非尼，可完全关闭MAPK途径）与p53再激活（PRIMA-1）的联合显著增强了BRAF突变黑色素瘤细胞的放射敏感性。这伴随着p53表达和活性的增加。值得注意的是，我们发现单独放疗显著促进了ERK和AKT磷酸化，从而导致放射抗性。维罗非尼和PRIMA-1的联合导致MAPK激酶和PI3K/AKT途径失活。此外，当与放疗联合时，它能够显著增强黑色素瘤细胞的放射敏感性。有趣的是，在携带黑色素瘤异种移植的裸鼠中，后一种三联组合不仅对肿瘤生长抑制具有协同作用，而且在完成三联组合治疗后对所有动物的肿瘤再生长具有有效控制。单独放疗只有微弱的效果。总之，我们为一种可能克服BRAF突变黑色素瘤细胞对放疗抗性的策略提供了依据。这是否会转化为在BRAF突变黑色素瘤患者的治愈性治疗中使用放疗的合理依据值得考虑。
