积累的研究表明，羟基磷灰石纳米颗粒（HANPs）显示出选择性的抗肿瘤效应，使它们成为治疗骨肉瘤（OS）的良好候选物。然而，HANPs具有不同长宽比的调节肿瘤免疫微环境（TIM）的能力几乎没有被报道过。为了探索这个问题，我们通过湿化学方法制备了三种长宽比从1.86到6.25的HANPs。在OS UMR106细胞或巨噬细胞与纳米颗粒接触24或72小时后，肿瘤细胞表现出免疫原性细胞死亡（ICD），表现为钙粘蛋白（CRT）、三磷酸腺苷（ATP）和高迁移率族群盒子1（HMGB1）的增加，并且巨噬细胞通过释放促炎细胞因子而被活化。接下来，在HANPs存在的情况下，肿瘤细胞和巨噬细胞之间产生有益的相互作用，以提高抗肿瘤免疫的活化。在OS携带的同源性大鼠模型中，HANPs抑制了OS的生长，与CRT和HMGB1的表达以及肿瘤组织中巨噬细胞极化呈正相关。此外，HANPs促进CD8+T细胞渗入肿瘤并促进全身性树突状细胞成熟。特别是，具有最高长宽比的HANPs表现出最强的免疫调节和抗肿瘤功能。本研究表明HANPs在控制OS治疗的TIM方面具有潜力成为一种安全有效的无药物纳米材料。研究的意义声明：新兴研究表明羟基磷灰石纳米颗粒（HANPs）抑制肿瘤细胞增殖和肿瘤生长。然而，其底层的抗肿瘤机制仍然不清楚，并且纯HANPs调节肿瘤免疫微环境（TIM）的能力几乎没有被报道过。在这里，我们证明不同长宽比的HANPs有可能延缓骨肉瘤（OS）的生长并调节TIM，通过促进CD8+T细胞和F4/80+巨噬细胞的侵袭，并在肿瘤中诱导免疫原性细胞死亡（ICD）。这项工作揭示了HANPs抗击OS的新的分子机制，并暗示HANPs可能成为一种新型的ICD诱导剂用于OS治疗。版权所有 © 2023 Elsevier Ltd.

Accumulating studies demonstrated that hydroxyapatite nanoparticles (HANPs) showed a selective anti-tumor effect, making them a good candidate for osteosarcoma (OS) treatment. However, the capacity of HANPs with different aspect ratios to regulate tumor immune microenvironment (TIM) was scarcely reported before. To explore it, the three HANPs with aspect ratios from 1.86 to 6.25 were prepared by wet chemical method. After a 24 or 72 h-exposure of OS UMR106 cells or macrophages to the nanoparticles, the tumor cells exhibited immunogenic cell death (ICD) indicated by the increased production of calreticulin (CRT), adenosine triphosphate (ATP) and high mobility group box 1 (HMGB1), and macrophages were activated with the release of pro-inflammatory cytokines. Next, the beneficial crosstalk between tumor cells and macrophages generated in the presence of HANPs for improved anti-tumor immunity activation. In the OS-bearing cognate rat model, HANPs inhibited OS growth, which was positively correlated with CRT and HMGB1 expression, and macrophage polarization in the tumor tissues. Additionally, HANPs promoted CD8+ T cell infiltration into the tumor and systemic dendritic cell maturation. Particularly, HANPs bearing the highest aspect ratio exhibited the strongest immunomodulatory and anti-tumor function. This study suggested the potential of HANPs to be a safe and effective drug-free nanomaterial to control the TIM for OS therapy. STATEMENT OF SIGNIFICANCE: : Emerging studies demonstrated that hydroxyapatite nanoparticles (HANPs) inhibited tumor cell proliferation and tumor growth. However, the underlying anti-tumor mechanism still remains unclear, and the capacity of HANPs without any other additive to regulate tumor immune microenvironment (TIM) was scarcely reported before. Herein, we demonstrated that HANPs, in an aspect ratio-dependent manner, showed the potential to delay the growth of osteosarcoma (OS) and to regulate TIM by promoting the invasion of CD8+ T cells and F4/80+ macrophages, and inducing immunogenic cell death (ICD) in tumors. This work revealed the new molecular mechanism for HANPs against OS, and suggested HANPs might be a novel ICD inducer for OS treatment.Copyright © 2023. Published by Elsevier Ltd.