Abstract 25P
Background
Our previous work revealed effective treatment of arginine-auxotrophic Glioblastoma multiforme (GBM) cells upon arginine-deprivation by Streptococcus pyogenes arginine deiminase (SpyADI) that can be boosted by combination with cyclin-dependent kinase inhibitors (CDKI). Here, we established a dinaciclib-resistant GBM cell line and examined response to SpyADI as well as high-dose dinaciclib.
Methods
A dinaciclib resistant patient-derived GBM cell line (=HROG63-R) was established upon long-term dinaciclib treatment (20 nM; IC50). The effect of SpyADI/CDKI alone and in combination (colony formation, calcein-AM) was investigated. Flow cytometry was used to assess cell death (Yo-Pro1/PI, calreticulin). Immunostaining was conducted to examine mitochondrial stress, formation of acidic compartments, cellular stress response (GADD45), and resistance mechanisms (ABCB1/ABCC1).
Results
Colony formation and cell viability of HROG63R cells was not impaired by low-dose dinaciclib treatment (20 nM), confirming resistance development. Additionally, HROG63R cells expressed high levels of ABCB1, accompanied by loss of tumor suppressor GADD45, both being inversely expressed in the parental cell line. Using higher dinaciclib doses (50 nM, 100 nM), cell growth was reduced and ABCB1 expression suppressed. By contrast, sensitivity towards SpyADI was preserved via necrosis induction. Immunogenic cell death was not detected at all. Dinaciclib and SpyADI monotherapies resulted in slight mitochondrial membrane hyperpolarization and acidic compartment formation, but these effects were not enhanced in the combinations.
Conclusions
This study highlights the potential of arginine deprivation therapy, even in conditions of resistance development towards targeted therapy. The observed re-sensitization to high-dose dinaciclib via downregulation of the ABC transporters renders combination strategies promising.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
The authors.
Funding
Has not received any funding.
Disclosure
All authors have declared no conflicts of interest.