Antitumor Activities and Cellular Changes Induced by TrkB Inhibition in Medulloblastoma

Abstract

Neurotrophins are critically involved in regulating normal neural development and plasticity. Brain-derived neurotrophic factor (BDNF), a neurotrophin that acts by binding to the tropomyosin receptor kinase B (TrkB) receptor, has also been implicated in the progression of several types of cancer. However, its role in medulloblastoma (MB), the most common type of malignant brain tumor afflicting children, remains unclear. Here we show that selective TrkB inhibition with the small molecule compound ANA-12 impaired proliferation and viability of human UW228 and D283 MB cells, and slowed the growth of MB tumors xenografted into nude mice. These effects were accompanied by increased apoptosis, reduced extracellular-regulated kinase (ERK) activity, increased expression of signal transducer and activator of transcription 3 (STAT3), and differential modulation of p21 expression dependent on the cell line. In addition, MB cells treated with ANA-12 showed morphological alterations consistent with differentiation, increased levels of the neural differentiation marker β-III Tubulin (TUBB3), and reduced expression of the stemness marker Nestin. These findings are consistent with the possibility that selective TrkB inhibition can display consistent anticancer effects in MB, possibly by modulating intracellular signaling and gene expression related to tumor progression, apoptosis, and differentiation.

Neurotrophin Signaling in Medulloblastoma

“…It is worth noting that differences in results obtained with different cell lines may be related to distinct origins and biological features. For example, D283-MED cells, which produce tumors in mice that respond to TrkB inhibition [111], are representative of Group 3/4 MB and derive from a metastatic site [113]. Studies have begun to uncover molecular differences between MB metastases and primary tumors [114].…”

“…MB cell lines express both BDNF and TrkB [109,110], and TrkB blockade by the selective inhibitor ANA-12 can induce a pronounced inhibition of survival and viability, as well as cell cycle arrest, in cell lines (D283-MED and UW-228) associated with different MB molecular subgroups. In addition, we have recently shown that TrkB inhibition slows the growth of D283-MED MB tumors xenografted into nude mice in vivo, increased apoptosis, reduced ERK activity, increased expression of signal transducer and activator of transcription 3 (STAT3), and resulted in differential modulation of p21 expression [111] ( Figure 2). However, TrkB activation by BDNF may also reduce cell viability under certain experimental conditions, either when given to MB cells alone [109] or combined with a histone deacetylase inhibitor [112].…”

“…A summary of findings from studies investigating neurotrophin signaling in MB is presented in Table 1. Expression and activation by BDNF [93] Inhibition [110,111] Overexpression and NT-3 activation [117] Overexpression [131] Expression [137] Inhibition [136] Main functional effect ↑Cell death (apoptosis [101] or micropinocytosis [106]) ↓Proliferation and ↑differentiation [94] ↓Cell viability [109] BDNF+ HDACi ↓ Cell viability [112] ↓Cell viability, proliferation and survival [110] ↑Apoptosis and differentiation↓ Subcutaneous tumor growth in nude mice [111] ↑Apoptosis and differentiation [125] ↑Proliferation Targeted by miR-9 and miR-125a to inhibit cell proliferation [131] Marker for SHH progenitor/stem cells [137] ↓Migration, proliferation and spinal metastasis [136] Clinical evidence Apoptotic index and neuronal differentiation [95] Unknown Unknown…”

“…In the absence of TrkB antagonist, MB cells continue to grow at high proliferation rates. Treating mice with TrkB antagonist, ANA-12, promotes delay in tumor growth in vivo and cellular changes consistent with growth arrest, apoptosis and differentiation mediated by downregulation of ERK pathway, decreased KI67 and Nestin expression markers and increased expression of p21 and TUBB3 genes (modified from[111]).…”

Genome-wide analysis identifies critical DNA methylations within NTRKs genes in colorectal cancer

“…NTRK2 was shown to serve as an oncogene in multiple cancers (19)(20)(21)(22), and its increased expression was associated with poor outcome (23,24). Based on this, inhibition of NTRK2-encoded TRKB was shown to induce antitumor effects and cellular apoptosis (25,26). Similar to NTRK1, NTRK3 has been demonstrated to be an oncogene in breast cancer and gastric cancer (27,28), but it acts as a tumor suppressor gene in CRC, neuroblastomas, and head and neck squamous cell carcinoma (10,29,30).…”