There is a desperate need for novel and efficacious chemotherapeutic strategies for human brain cancers. There are abundant molecular alterations along the p53 and MDM2 pathways in human glioma, which play critical roles in drug resistance. The present study was designed to evaluate the in vitro and in vivo antitumor activity of a novel brain-penetrating small molecule MDM2 degrader, termed SP-141. In a panel of nine human glioblastoma and medulloblastoma cell lines, SP-141, as a single agent, potently killed the brain tumor-derived cell lines with IC₅₀ values ranging from 35.8 to 688.8 nM. Treatment with SP-141 resulted in diminished MDM2 and increased p53 and p21^cip1 levels, G2/M cell cycle arrest, and marked apoptosis. In intracranial xenograft models of U87MG glioblastoma (wt p53) and DAOY medulloblastoma (mutant p53) expressing luciferase, treatment with SP-141 caused a significant 4- to 9-fold decrease in tumor growth in the absence of discernible toxicity. Further, combination treatment with a low dose of SP-141 (IC₂₀) and temozolomide, a standard anti-glioma drug, led to synergistic cell killing (1.3- to 31-fold) in glioma cell lines, suggesting a novel means for overcoming temozolomide resistance. Considering that SP-141 can be taken up by the brain without the need for any special delivery, our results suggest that SP-141 should be further explored for the treatment of tumors of the central nervous system, regardless of the p53 status of the tumor.

Background: Neuroblastoma is an aggressive pediatric solid tumor with an overall survival rate of 98%) of pathologically-diagnosed neuroblastomas have wild-type p53 with intact functional activity. However, the mouse double minute 2 (MDM2) homolog, an E3 ubiquitin ligase, is overexpressed in neuroblastoma and leads to inhibition of p53. MDM2 also exerts p53-independent oncogenic functions. Thus, MDM2 seems to be an attractive target for the reactivation of p53 and attenuation of oncogenic activity in neuroblastoma. Methods: In this study, we evaluated the anticancer activities and underlying mechanisms of action of SP141, a first-in-class MDM2 inhibitor, in neuroblastoma cell lines with different p53 backgrounds. The findings were confirmed in mouse xenograft models of neuroblastoma. Results: We demonstrate that SP141 reduces neuroblastoma cell viability, induces apoptosis, arrests cells at the G2/M phase, and prevents cell migration, independent of p53. In addition, in neuroblastoma xenograft models, SP141 inhibited MDM2 expression and suppressed tumor growth without any host toxicity at the effective dose. Conclusions: MDM2 inhibition by SP141 results in the inhibition of neuroblastoma growth and metastasis, regardless of the p53 status of the cells and tumors. These findings provide proof-of-concept that SP141 represents a novel treatment option for both p53 wild-type and p53 null neuroblastoma.

The human concentrative nucleoside transporter 1 (hCNT1) a product of the SLC28A1 gene is one of the three concentrative nucleoside transporters, with a substrate specificity for physiological pyrimidine nucleosides. It has recently been implicated in tumor suppression. We have unraveled a splice variant RNA transcript that is overexpressed in some tumor tissues and some cancer cells. This study established that observation. We examined several clones of hCNT1 generated from RT-PCR of total RNA from human kidney tissue purchased from Ambion. The resulting cDNA clones were then sequenced, and a variant that retained intron 4, and skipped some exons fully or partly, specifically exons 5 and 13 were completely missed and only part of exon 6 was spliced. Tissue expression analysis by PCR indicated a similar distribution of expression of RNA of the splice variant hCNT1-IR as that of the dominant variant hCNT1, particularly in the small intestine, kidney and liver. Further, analysis of various tumor samples with PCR primers designed from this novel hCNT1 splice variant (hCNT1-IR) revealed interestingly that it is overexpressed in some cancer tissues relative to normal tissues, particularly kidney, liver and pancreatic cancers. We have identified a novel intron retaining and exon skipping splice variant of the hCNT1 nucleoside transporter, and designated it hCNT1-IR, which has a similar tissue expression distribution as the normal hCNT1 variant, but unlike the normal transcript, hCNT1-IR is overexpressed in some cancers and may serve as a potential cancer biomarker.