Assessment of multiparametric MRI in a human glioma model to monitor cytotoxic and anti-angiogenic drug effects.

Early imaging or blood biomarkers of tumor response is needed to customize anti-tumor therapy on an individual basis. This study evaluates the sensitivity and relevance of five potential MRI biomarkers. Sixty nude rats were implanted with human glioma cells (U-87 MG) and randomized into three groups: one group received an anti-angiogenic treatment (Sorafenib), a second a cytotoxic drug [1,3-bis(2-chloroethyl)-1-nitrosourea, BCNU (Carmustine)] and a third no treatment. The tumor volume, apparent diffusion coefficient (ADC) of water, blood volume fraction (BVf), microvessel diameter (vessel size index, VSI) and vessel wall integrity (contrast enhancement, CE) were monitored before and during treatment. Sorafenib reduced tumor CE as early as 1 day after treatment onset. By 4 days after treatment onset, tumor BVf was reduced and tumor VSI was increased. By 14 days after treatment onset, ADC was increased and the tumor growth rate was reduced. With BCNU, ADC was increased and the tumor growth rate was reduced 14 days after treatment onset. Thus, the estimated MRI parameters were sensitive to treatment at different times after treatment onset and in a treatment-dependent manner. This study suggests that multiparametric MR monitoring could allow the assessment of new anti-tumor drugs and the optimization of combined therapies.

Noninvasive assessment of E2F-1-mediated transcriptional regulation in vivo.

Targeted therapies directed against individual cancer-specific molecular alterations offer the development of disease-specific and individualized treatment strategies. Activation of the transcription factor E2F-1 via alteration of the p16-cyclinD-Rb pathway is one of the key molecular events in the development of gliomas. E2F-1 binds to and activates the E2F-1 promoter in an autoregulatory manner. The human E2F-1 promoter has been shown to be selectively activated in tumor cells with a defect in the pRb pathway. Paradoxically, E2F-1 also carries tumor suppressor function. Our investigations focused on analyzing the dynamics of the activity of the E2F-1 responsive element under basal conditions and certain stimuli such as chemotherapy using molecular imaging technology. We constructed a retrovirus bearing the Cis-E2F-TA-LITG reporter system to noninvasively assess E2F-1-dependent transcriptional regulation in culture and in vivo. We show that our reporter system is sensitive to monitor various changes in cellular E2F-1 levels and its transcriptional control of our reporter system to follow the state of the Rb/E2F pathway and the DNA damage-induced up-regulation of E2F-1 activity in vivo. Exposure to 1,3-bis(2-chloroethyl)-1-nitrosourea leads to increased E2F-1 expression levels in a dose- and time-dependent manner, which can be quantified by imaging in vivo, leading to an alteration of cell cycle progression and caspase 3/7 activity. In summary, noninvasive imaging of E2F-1 as a common downstream regulator of cell cycle progression using the Cis-E2F-TA-LUC-IRES-TKGFP reporter system is highly attractive for evaluating the kinetics of cell cycle regulation and the effects of novel cell cycle targeting anticancer agents in vivo.

Granulocyte-colony stimulating factor impedes recovery from damage caused by cytotoxic agents through increased differentiation at the expense of self-renewal.

G-CSF is routinely used to hasten recovery from chemotherapy-induced neutropenia. We have recently shown that G-CSF, when combined with stem cell-damaging cytotoxic agents, results in enhanced stem cell damage and loss of marrow reserve. To investigate the mechanisms of stem cell damage caused by G-CSF, we gave C57BL/6 (B6) mice repeated doses of cyclophosphamide ([CY] 84 mg/kg) or carmustine ([BCNU] 13.2 mg/kg) and G-CSF (250 microg/kg/day) for either four days or eight days. Two different regimens of G-CSF were chosen to study the influence of increased proliferation on hematopoiesis which was measured at the end of the first, third and sixth 14-day cycle of each cytotoxic agent and 7 and 20 weeks after completion of all cycles. A spectrum of hematopoietic indices was measured including WBC, bone marrow cellularity, granulocyte/macrophage-colony-forming cells (GM-CFC), colony-forming cells with high proliferative-potential (HPP-CFC), cobblestone area-forming cells ([CAFC]-day 7 and CAFC-day 28), and long-term marrow repopulating ability in vivo. Despite the absence of differences in peripheral blood cell counts or bone marrow cellularity 14 days after each dose, progenitor cell levels (HPP-CFC, GM-CFC, and CAFC-7) were increased up to 2.5-fold with cytotoxic agent and G-CSF administration compared with cytotoxic agent administration alone. Mice given G-CSF for eight days had the greatest number of progenitors suggesting a dose-response relationship for G-CSF administration. G-CSF resulted in a decrease in hematopoietic stem cell (CAFC-28) content when measured two weeks after each cycle of saline, CY, and BCNU. Twenty weeks after six cycles of BCNU, the reduction in stem cell levels persisted and was further decreased when G-CSF was added to BCNU for four or eight days. Data from this study suggest that the most likely explanation for the damaging effects of G-CSF is that G-CSF directly or indirectly induces stem cells to differentiate into more committed hematopoietic cells resulting in a loss of marrow reserve. This effect is enhanced in animals with an already compromised hematopoietic stem cell compartment as seen with repeated doses of BCNU.