Treatment Strategies Based on Histological Targets against Invasive and Resistant Glioblastoma

Abstract

Glioblastoma (GBM) is the most common and the most malignant primary brain tumor and is characterized by rapid proliferation, invasion into surrounding normal brain tissues, and consequent aberrant vascularization. In these characteristics of GBM, invasive properties are responsible for its recurrence after various therapies. The histomorphological patterns of glioma cell invasion have often been referred to as the "secondary structures of Scherer." The "secondary structures of Scherer" can be classified mainly into four histological types as (i) perineuronal satellitosis, (ii) perivascular satellitosis, (iii) subpial spread, and (iv) invasion along the white matter tracts. In order to develop therapeutic interventions to mitigate glioma cell migration, it is important to understand the biological mechanism underlying the formation of these secondary structures. The main focus of this review is to examine new molecular pathways based on the histopathological evidence of GBM invasion as major prognostic factors for the high recurrence rate for GBMs. The histopathology-based pharmacological and biological targets for treatment strategies may improve the management of invasive and resistant GBMs.

Figure 1

Illustration of “Go or Grow” theory in malignant gliomas. Malignant gliomas often consist of two subpopulations of cells, which mutually interact and mutually change, that are characterized by uncontrolled-proliferation and by abnormal migration. One subpopulation of cells is rapidly proliferating and forming a stationary tumor mass, while the other subpopulation is actively migrating and moves into surrounding brain without cell division. Some of glioma cells in “Go” stage show characteristic morphological patterns of tumor cell migration, referred to as “secondary structures of Scherer.” These “secondary structures of Scherer,” which are also shown in Figure 2, have been classified into histological patterns: (i) perineuronal satellitosis, (ii) perivascular satellitosis, (iii) subpial spread, and (iv) invasion along the white matter tracts.

Figure 2

Specific histomorphological patterns of diffuse invasion, so-called “secondary structures of Scherer” in glioblastoma. As a rule, glioma cells migrate along existing brain structures such as brain parenchyma, blood vessels, white matter tracts, and subpial spaces. The secondary structures of Scherer are referred to four criteria as (a) perineuronal satellitosis (indicated by arrows), (b) perivascular satellitosis (indicated by arrow heads), (c) subpial spread (region above black dots), and (d) invasion along the white matter tracts (indicated by arrow heads). Hematoxylin and eosin staining. Scale bars in (a), (b), and (d) are 50 μm; scale bar in (c), 100 μm.

Figure 3

Representative images showing histomorphological structures of GC. Many histological features are similar to invasive patterns of GBM (secondary structures of Scherer in Figure 2). (a) Diffuse parenchymal infiltration of GC cells without the formation of a circumscribed tumor mass. The secondary structures of Scherer are seen also in GC as follows: (b) perineuronal satellitosis (indicated by arrows), (c) subpial spread (region above black dots), and (d) invasion along the white matter tracts (indicated by arrow heads). Hematoxylin and eosin staining. Scale bar in (a), 375 μm; scale bars in (b) and (d), 50 μm; scale bar in (c), 100 μm.

Figure 4

Representative histomorphological features of “Go or Grow” in GBM. The two subpopulations consist of uncontrolled-proliferating and abnormally migrating cells which interact mutually, which is so-called ‘‘Go or Grow” in gliomas. One subpopulation, rapidly proliferating cells, forms tumor mass being stationary (a, c, e). The other subpopulation, actively migrating cells, moves into surrounding brain without cell division (b, d, f). (a, b) Hematoxylin and eosin staining. (c, d) Immunohistochemistry for Ki-67 antigen, a marker of proliferating cells. The Ki-67 positive cells showing dark brown cell nuclei are detected as proliferating cells. (e, f) Immunohistochemistry for oligodendrocyte transcription factor (OLIG2), which is expressed universally in GBM cell nuclei. Vascular cells in GBM (observed in (e)) and normal glia cells (observed in (f)) are negative for OLIG2. Note that only one Ki-67 positive cell is detected in migrating GBM cells (arrow in (d)), whereas many OLIG2 positive GBM cells are seen in the same area (f). Also note that the sizes of cell nuclei recognized in (f) are smaller than that in (e). This means that migrating GBM cells into surrounding brain have smaller nuclei because they are actively moving. Scale bars, 100 μm.

Figure 5

The human GBM orthotopic xenograft exhibiting invasive and extensive infiltration in NOD-scid mice. The nestin-expressing NSC-like GBM cells are highly invasive, showing diffuse infiltration into the brain including the corpus callosum, hippocampus, and the subependymal regions. (a, b) Photomicrographs of low-power field of human GBM orthotopic xenograft in NOD-scid mouse brain. (c, d) Photomicrographs of high-power field of corpus callosum infiltrated by human GBM. (e, f) Photomicrographs of high-power field of mass lesion of human GBM. (a, c, e) Hematoxylin and eosin staining. (b, d, f) Immunohistochemistry for nestin. Scale bars in (a) and (b), 500 μm; scale bars in (c), (d), (e), and (f), 100 μm.