Inhibition of Akt by the alkylphospholipid perifosine does not enhance the radiosensitivity of human glioma cells
ABSTRACT Akt has been implicated as a molecular determinant of cellular radiosensitivity. Because it is often constitutively activated or overexpressed in malignant gliomas, it has been suggested as a target for brain tumor radiosensitization. To evaluate the role of Akt in glioma radioresponse, we have determined the effects of perifosine, a clinically relevant alkylphospholipid that inhibits Akt activation, on the radiosensitivity of three human glioma cell lines (U87, U251, and LN229). Each of the glioma cell lines expressed clearly detectable levels of phosphorylated Akt indicative of constitutive Akt activity. Exposure to a perifosine concentration that reduced survival by approximately 50% significantly reduced the level of phosphorylated Akt as well as Akt activity. Cell survival analysis using a clonogenic assay, however, revealed that this Akt-inhibiting perifosine treatment did not enhance the radiosensitivity of the glioma cell lines. This evaluation was then extended to an in vivo model using U251 xenografts. Perifosine delivered to mice bearing U251 xenografts substantially reduced tumor phosphorylated Akt levels and inhibited tumor growth rate. However, the combination of perifosine and radiation resulted in a less than additive increase in tumor growth delay. Thus, in vitro and in vivo data indicate that the perifosine-mediated decrease in Akt activity does not enhance the radiosensitivity of three genetically disparate glioma cell lines. These results suggest that, although Akt may influence the radiosensitivity of other tumor types, it does not seem to be a target for glioma cell radiosensitization.
- SourceAvailable from: Wim van Blitterswijk
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- "A discrepancy between in vitro and in vivo radiosensitization was shown in the notoriously radioresistant malignant glioma tumor model. Although De la Pena and coworkers showed clear radiosensitization by perifosine in vitro, subcutaneous gliomas did not show enhanced response to radiation after treatment with perifosine . Becuase only one dose schedule was used, it remains uncertain whether an increased radiation response by perifosine might be obtained at optimal (i.e. "
ABSTRACT: Our improved understanding of the molecular processes that determine cellular sensitivity to ionizing radiation has accelerated the identification of new targets for intervention. Indeed, novel agents have become available for combined clinical use to overcome radioresistance and increase the therapeutic ratio of radiotherapy. Synthetic alkyl-phospholipid analogs (APLs), such as edelfosine, ilmofosine, miltefosine, perifosine and erucylphosphocholine, are a novel class of anti-tumor agents that target cell membranes to induce growth arrest and apoptosis. In addition, APLs strongly enhance the cytotoxic effect of radiation in preclinical models making these compounds attractive candidates as clinical radiosensitizers. In this review, we will discuss mechanisms of action underlying the rationale to combine APLs with radiotherapy and highlight the clinical perspective of this novel combined modality treatment.Anti-cancer agents in medicinal chemistry 03/2014; DOI:10.2174/1871520614666140309224145 · 2.94 Impact Factor
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- "Among four identified AR downstream signaling pathways (activation of Akt and Wnt signaling and higher expressions of bcl-2 and c-myc) in the PCa stem/progenitor cells, we found few available small molecules in clinical trials that could be used to target Wnt and c-myc effectively. For the Akt and bcl-2, we decided to use g-TT and not the currently available Akt inhibitors in our strategy with the following reasons: (i) g-TT could simultaneously target bcl-2 and Akt signaling, (ii) g-TT could overcome the problem of toxicity of the current available PI3K/Akt inhibitors, such as LY294002 (de la Pena et al., 2006; Markman et al., 2010), and (iii) those current available Akt inhibitors, such as LY294002, might result in an unwanted problem of increasing some PCa cells invasion ability (Chang et al., manuscript in preparation ), even though showing better efficacy to reduce PCa sizes (Hutchinson et al., 2004; Dillon et al., 2009). We are aware of the debates about the effect of long-term supplement of a-Vit E to reduce PCa incidence, and even though g-TT and a-Vit E share some similar structure, these two compounds have totally different functions, with g-TT not a-Vit E, effectively inhibiting the growth of PCa stem/progenitor cells. "
ABSTRACT: The androgen deprivation therapy (ADT) to systematically suppress/reduce androgens binding to the androgen receptor (AR) has been the standard therapy for prostate cancer (PCa); yet, most of ADT eventually fails leading to the recurrence of castration resistant PCa. Here, we found that the PCa patients who received ADT had increased PCa stem/progenitor cell population. The addition of the anti-androgen, Casodex(®), or AR-siRNA in various PCa cells led to increased stem/progenitor cells, whereas, in contrast, the addition of functional AR led to decreased stem/progenitor cell population but increased non-stem/progenitor cell population, suggesting that AR functions differentially in PCa stem/progenitor vs. non-stem/progenitor cells. Therefore, the current ADT might result in an undesired expansion of PCa stem/progenitor cell population, which explains why this therapy fails. Using various human PCa cell lines and three different mouse models, we concluded that targeting PCa non-stem/progenitor cells with AR degradation enhancer ASC-J9(®) and targeting PCa stem/progenitor cells with 5-azathioprine and γ-tocotrienol resulted in a significant suppression of the tumors at the castration resistant stage. This suggests that a combinational therapy that simultaneously targets both stem/progenitor and non-stem/progenitor cells will lead to better therapeutic efficacy and may become a new therapy to battle the PCa before and after castration resistant stages.Journal of Molecular Cell Biology 07/2012; 5. DOI:10.1093/jmcb/mjs042 · 8.43 Impact Factor
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ABSTRACT: Objective Perifosine was developed as a membrane-targeted alkylphospholipid that inhibits the PI3K/AKT pathway and has been suggested as a favorable candidate for combined use of radiotherapy. To better define the optimal schedule for this combination, we investigated schedule-dependent cytotoxic effects of perifosine and radiotherapy against prostate carcinoma cell lines in vitro. Methods Human prostate cancer cell line CWR22RV1 and LNCaP were incubated with perifosine (5, 20, 40 μM) and treated with radiation (2, 4, 6, 8 Gy). Three different schedules were used: simultaneous treatment (R + P), perifosine followed by radiotherapy (P → R), and vice versa (R → P). Cell growth inhibition was determined by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay. The effects of drug combinations at the concentration producing 80 % cell growth inhibition were analyzed by the isobologram method (Steel and Peckham). Colony formation assay was also conducted to confirm the result of MTS assay. Western blot analysis was used to explore the molecular mechanism of action for the combination of perifosine and irradiation. Results The R → P schedule showed the most significant cell growth inhibition when compared to other schedules (p < 0.01). This schedule produced an additive effect for CWR22RV1 and a supra-additive effect for LNCaP. The reverse sequence produced a protective effect for CWR22RV1 and an additive/sub-additive effect for LNCaP. R + P schedule showed intermediate effect between R → P and P → R schedules. Western blot analysis showed that phosphorylation of AKT (indicative of anti-apoptosis activity) was inhibited by this combination therapy except for P → R schedule. Conclusion Our new findings suggest that R → P would be the optimal schedule for this combination treatment strategy. The finding is also important as it explains the negative outcomes of several previously reported trials combining radiotherapy and perifosine in the treatment of various tumors. Applications of this schedule-dependent approach might be beneficial for the treatment of prostate cancer and other tumors.06/2013; 2(2). DOI:10.1007/s13566-013-0101-z