“Paradoxical” findings of tumor vascularity and oxygenation in recurrent glioblastomas refractory to bevacizumab

Abstract

Anti-angiogenic therapy induces the apparent normalization of vascular structure, decreases microvessel density (MVD), and improves tumor oxygenation in glioblastomas (GBMs). Six initial and recurrent tumor pairs after bevacizumab (Bev) treatment were compared with GBMs from nine patients resected under neoadjuvant Bev treatment with regard to histological characteristics; MVD; MIB-1 index; and expression of vascular endothelial growth factor (VEGF) and its receptors, hypoxia markers (hypoxia-inducible factor 1 alpha, carbonic anhydrase 9), and nestin as a marker of glioma stem-like cells. In recurrent tumors post-Bev treatment, while the MVD remained low compared with the paired initial tumors (pre-Bev tumors), the expression of hypoxic markers were increased and were even higher in expression compared with the paired pre-Bev tumors in three of the six cases. MIB-1 indices were similar among the initial GBMs, neoadjuvant group, and recurrent tumors post-Bev treatment. The nestin-positive cell ratio of the post-Bev recurrent tumors was as high as that of the pre-Bev tumors. The expression of VEGF and VEGFR1 was increased in the post-Bev recurrent tumors in three and four cases, respectively, compared with the paired pre-Bev tumors. In the majority of Bev-refractory GBMs, tumor hypoxia was present with a paradoxical decrease in MVD. These findings suggest that re-activation of tumor angiogenesis is not initially involved in the acquisition of resistance to Bev.

Persistent restoration to the immunosupportive tumor microenvironment in glioblastoma by bevacizumab

“…Hypoxia‐inducible factor‐1α was also able to activate the expression of PD‐L1 by binding of HIF to a specific hypoxic response element in the promoter of PD‐L1 in cancer cells . We have previously reported that Bev improves tumor oxygenation in glioblastomas, and that tumor hypoxia is regained in the post‐Bev refractory tumors, to a similar or even higher level compared with the paired pre‐Bev initial tumors . In the present study, however, immunosuppressive cells and molecules in the tumors of refractory Bev group were still suppressed compared with the naïve Bev group despite recovery of hypoxia.…”

“…42,43 We have previously reported that Bev improves tumor oxygenation in glioblastomas, 4 and that tumor hypoxia is regained in the post-Bev refractory tumors, to a similar or even higher level compared with the paired pre-Bev initial tumors. 5 In the present study, however, immunosuppressive cells and molecules in the tumors of refractory Bev group were still suppressed compared with the naïve Bev group despite recovery of hypoxia. The expression of immune checkpoint molecules and immunosuppressive cells were strongly associated with VEGF-A.…”

“…The present study used 47 glioblastoma tissues from 31 patients obtained at 3 different settings: 15 tumors resected following Bev therapy (under the Bev efficacy, defined as the "effective Bev group"), 20 tumors of initial glioblastoma (defined as the "naïve Bev group"), and 12 post-Bev recurrent tumors (defined as the "refractory Bev group") ( Table S1). The 15 tumors resected following Bev therapy (cases [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] were the tumors resected after 1-3 times of the preoperative Bev administration at a dose of 10 mg/kg for a safer surgical resection or as a consequence of the clinical course, and included 3 tumors enrolled in the phase II study of neoadjuvant Bev (UMIN000025579). Tumor resection was carried out 21-36 days after the last Bev treatment.…”

“…We have previously reported, using tumor specimens resected following Bev therapy (under the Bev efficacy), that Bev induces the normalization of vascular structure, reduction of microvessel density, and improves tumor oxygenation . In addition, by comparing tumors resected before treatment (initial tumor), following Bev therapy (under the Bev efficacy), and at the time of recurrence, tumor hypoxia was regained while the microvessel density was still paradoxically lowered in recurrent tumors after Bev therapy, suggesting that the re‐activation of tumor angiogenesis might not be involved in the first stage of refractoriness to Bev …”

“…4 In addition, by comparing tumors resected before treatment (initial tumor), following Bev therapy (under the Bev efficacy), and at the time of recurrence, tumor hypoxia was regained while the microvessel density was still paradoxically lowered in recurrent tumors after Bev therapy, suggesting that the re-activation of tumor angiogenesis might not be involved in the first stage of refractoriness to Bev. 5 Bevacizumab is known to enhance the effects of immunotherapy, because VEGF-A suppresses antitumor immunity by inhibiting the maturation of DCs and stimulating the proliferation of Tregs. 6,7 Indeed, the combination of atezolizumab, the anti-PD-L1 antibody, and Bev induced a strong and synergistic antitumor effect on tumors with high levels of VEGF-A, by the induction of CTLs.…”