Polo-like kinase1 (PLK-1), a member of the polo-like kinase family of serine/threonine protein kinases, plays an essential role in regulating the cell cycle. PLK-1 has a strong relationship with numerous regulatory events progressing during G2/M transition, chromosomal segregation, spindle assembly maturation, and mitotic exit. In addition, PLK-1 also regulates DNA damage response, DNA replication, transcription, translation, chromosomes dynamics, and checkpoint adoption. Elevated levels of PLK-1 have been observed in a plethora of cancers, including neuroblastoma (NB). NB is the most prevalent solid tumor that develops during the early embryonic stage and accounts for 15% of pediatric cancer-related deaths. Current cytotoxic treatment strategies for NB are limiting and failed to prevent relapse and metastasis. In the present study, we hypothesized that inhibition of cell cycle regulator PLK-1 by a small molecule inhibitor HMN-214 will inhibit NB growth. To determine the role of PLK-1 in NB, we analyzed multiple NB patient datasets and observed that PLK-1 expression is inversely correlated with overall patient survival. PLK-1 also strongly correlates with MYCN amplification and overall NB disease progression in our patient dataset analysis. Further, we used six NB cell lines, including MYCN- amplified and -non-amplified cell lines, to evaluate the anti-proliferative effects of HMN-214 in NB. Results showed that HMN-214 significantly and in a dose-dependent manner inhibits NB proliferation and colony formation capacity. Additionally, we found that HMN-214 significantly induces apoptosis and blocks cell cycle progression at the G2-M phase in treatment groups compared to controls. Our molecular analysis further revealed that HMN-214 significantly inhibits the mRNA and protein levels of PLK-1 and CDK1 in contrast to control treatments. Further, we developed a 3D spheroid tumor model for NB to mimic in vivo tumor growth and utilized it to determine the effects of HMN-214 on NB tumor growth. Results showed that HMN-214 significantly and in a dose-dependent manner inhibits NB 3D spheroidal tumor growth by specifically inducing tumor cell death. Overall, our data highlights the role of PLK-1 in the oncogenic progression of NB and showed the efficacy of HMN-214 in inhibiting NB growth. Our future efforts will be directed towards elucidating the role of PLK-1 in NB and developing effective therapeutic strategies incorporating PLK-1 inhibitor.
