Integration of PDX models as a preclinical platform for assessment of drug efficacy may allow a higher success-rate in critical end points of clinical benefit.

BACKGROUNDPatients with advanced, metastatic sarcoma have a poor prognosis, and the overall benefit from the few standard-of-care therapeutics available is small. The rarity of this tumor, combined with the wide range of subtypes, leads to difficulties in conducting clinical trials. The authors previously reported the outcome of patients with a variety of common solid tumors who received treatment with drug regimens that were first tested in patient-derived xenografts using a proprietary method (“TumorGrafts”).METHODSTumors resected from 29 patients with sarcoma were implanted into immunodeficient mice to identify drug targets and drugs for clinical use. The results of drug sensitivity testing in the TumorGrafts were used to personalize cancer treatment.RESULTSOf 29 implanted tumors, 22 (76%) successfully engrafted, permitting the identification of treatment regimens for these patients. Although 6 patients died before the completion of TumorGraft testing, a correlation between TumorGraft results and clinical outcome was observed in 13 of 16 (81%) of the remaining individuals. No patients progressed during the TumorGraft-predicted therapy.CONCLUSIONSThe current data support the use of the personalized TumorGraft model as an investigational platform for therapeutic decision-making that can guide treatment for rare tumors such as sarcomas. A randomized phase 3 trial versus physician's choice is warranted.

The TRIM family of genes is largely studied because of their roles in development, differentiation and host cell anti-viral defenses; however, roles in cancer biology are emerging. Loss of heterozygosity of the TRIM3 locus in approximately 20% of human glioblastomas raised the possibility that this NHL containing member of the TRIM gene family might be a mammalian tumor suppressor. Consistent with this, reducing TRIM3 expression increased the incidence of and accelerated the development of PDGF-induced glioma in mice. Furthermore, TRIM3 can bind to the cdk inhibitor p21WAF1/CIP1. Thus, we conclude that TRIM3 is a tumor suppressor mapping to chromosome 11p15.5 and that it can block tumor growth by sequestering p21 and preventing it from facilitating the accumulation of cyclin D1-cdk4.

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Although the molecular changes that characterize gliomas have been studied, the pathogenesis of tumor development remains unclear. p21 contributes to gliomagenesis by stabilizing cyclin D1-cdk4 kinase complexes, suggesting that cyclin D1 and cdk4 may also be required for glial tumor development. In this study, we used a mouse model to attempt to confirm this hypothesis, finding that cyclin D1 and cdk4 played active roles in not only the tumor but also the tumor microenvironment. Loss of cdk4 blocked tumor development, but loss of cyclin D1 did not prevent gliomas from developing. Instead, loss of cyclin D1 impeded progression to higher stages of malignancy. Enforcing expression of cyclin D1 was insufficient to correct the progression defect observed in cyclin D1 deficient animals. In contrast, restoration of cdk4 in the cdk4 deficient animals restored cell proliferation and tumor formation, although at lower tumor grades. Notably, the failure of tumors in the cyclin D1 and cdk4 deficient animals to progress to higher grades was correlated with a failure to fully activate microglia in the tumor microenvironment. Moreover, when PDGF-transformed glial cells were engrafted orthotopically into the mice, the tumors that formed progressed to high grades in wild type mice but not cyclin D1 deficient animals. Together, our findings establish that the cyclinD1-cdk4 axis is not only critical in glial tumor cells, but also in stromal-derived cells in the surrounding tumor microenvironment that are vital to sustain tumor outgrowth.