Arnab Chakravarti

Chemoradiotherapy in Malignant Glioma: Standard of Care and Future Directions

Glioma has been considered resistant to chemotherapy and radiation. Recently, concomitant and adjuvant chemoradiotherapy with temozolomide has become the standard treatment for newly diagnosed glioblastoma. Conversely (neo-)adjuvant PCV (procarbazine, lomustine, vincristine) failed to improve survival in the more chemoresponsive tumor entities of anaplastic oligoastrocytoma and oligodendroglioma. Preclinical investigations suggest synergism or additivity of radiotherapy and temozolomide in glioma cell lines. Although the relative contribution of the concomitant and the adjuvant chemotherapy, respectively, cannot be assessed, the early introduction of chemotherapy and the simultaneous administration with radiotherapy appear to be key for the improvement of outcome. Epigenetic inactivation of the DNA repair enzyme methylguanine methyltransferase (MGMT) seems to be the strongest predictive marker for outcome in patients treated with alkylating agent chemotherapy. Patients whose tumors do not have MGMT promoter methylation are less likely to benefit from the addition of temozolomide chemotherapy and require alternative treatment strategies. The predictive value of MGMT gene promoter methylation is being validated in ongoing trials aiming at overcoming this resistance by a dose-dense continuous temozolomide administration or in combination with MGMT inhibitors. Understanding of molecular mechanisms allows for rational targeting of specific pathways of repair, signaling, and angiogenesis. The addition of tyrosine kinase inhibitors vatalanib (PTK787) and vandetinib (ZD6474), the integrin inhibitor cilengitide, the monoclonal antibodies bevacizumab and cetuximab, the mammalian target of rapamycin inhibitors temsirolimus and everolimus, and the protein kinase C inhibitor enzastaurin, among other agents, are in clinical investigation, building on the established chemoradiotherapy regimen for newly diagnosed glioblastoma.

The Prognostic Significance of Phosphatidylinositol 3-Kinase Pathway Activation in Human Gliomas

PURPOSE The objectives of this study were to examine activation patterns of the phosphatidylinositol 3-kinase (PI3K) pathway in gliomas and to examine the prognostic significance of PI3K pathway activation using snap-frozen clinical specimens. MATERIALS AND METHODS Levels of expression of PI3K pathway members were assessed in 92 prospectively collected gliomas through quantitative Western analysis using total and phospho-specific antibodies for PI3K, Akt, and p70(s6k). Both expression and expression levels of these PI3K pathway members were correlated with histology, markers of apoptosis (cleaved caspase 3), and with clinical outcome (eg, overall survival). RESULTS It was determined that activation of all three PI3K pathway members were significantly more frequent in glioblastoma multiforme than in non-glioblastoma multiforme tumors. Levels of phospho-PI3K, phospho-Akt, and phospho-p70(s6k) were all found to be inversely associated with cleaved caspase 3 levels, suggesting PI3K pathway activation is associated with reduced levels of apoptosis. Perhaps most importantly, activation of PI3K pathway members was found to be significantly associated with reduced survival times when all glioma cases were considered in aggregate. When glioblastoma cases were considered separately, the prognostic value of PI3K activation remained significant, suggesting that PI3K activation may directly be associated with radiation resistance, given that this was the only adjuvant therapy administered to this subset of patients. CONCLUSION Activation of the PI3K pathway is significantly associated with increasing tumor grade, decreased levels of apoptosis, and with adverse clinical outcome in human gliomas. Molecular pathways regulating PI3K activation would appear to be promising targets in the clinical management of glioma patients.

Quantitatively Determined Survivin Expression Levels Are of Prognostic Value in Human Gliomas

PURPOSE Survivin is a novel antiapoptotic gene that has been recently cloned and characterized. Its expression has been found to be of prognostic significance in several tumor types. This is the first study on the prognostic significance of survivin expression in human gliomas. MATERIALS AND METHODS We used quantitative Western blot analysis with densitometry to determine survivin protein expression levels in 92 glioma cases for which frozen tissue was available for analysis. Survivin positivity and expression levels were correlated with histopathologic features of the tumors, apoptosis (as measured by cleaved, or activated, caspase 3 levels), and clinical outcome. RESULTS Survivin expression has clear prognostic value in human gliomas. Patients with detectable survivin expression had significantly shorter overall survival times (P <.0001) compared with those without detectable expression when all glioma patients were considered. Although glioblastoma multiforme (GBM) patients had significantly higher rates of survivin positivity and higher levels of survivin expression (P <.0001) than their non-GBM counterparts, the prognostic value of survivin expression seemed to be independent of histology alone. Survivin-positive GBM patients had significantly shorter overall survival times compared with survivin-negative GBM patients (P <.0001). Likewise, survivin-positive non-GBM patients had shorter survival times compared with survivin-negative non-GBM patients (P =.029). Furthermore, increasing levels of survivin expression significantly correlated with reduced survival times when all glioma patients were considered, and markedly so for GBM patients (P <.0001). Increasing survivin levels significantly correlated with reduced expression of cleaved caspase 3, indicating its association with antiapoptotic activity. CONCLUSION Survivin positivity and protein expression levels, as determined quantitatively, are of significant prognostic value in human gliomas and seem to be associated with reduced apoptotic capacity of these tumors.

Survivin mediates resistance to antiandrogen therapy in prostate cancer.

Resistance to antiandrogen therapy in patients with metastatic prostate cancer poses a major challenge, which, if overcome, may lead to significant advances in the treatment of these patients. Hormone resistance of prostate cancer develops, in part, from upregulation of antiapoptotic genes after androgen deprivation. Given the accumulating evidence that Survivin, a new member of the inhibitor of apoptosis (IAP) family, is associated with both cancer progression and drug resistance, we hypothesized that Survivin plays a potentially important role in hormone therapy resistance, and that targeting of Survivin may enhance sensitivity to antiandrogen therapy in prostate cancer. Patterns of Survivin expression were assessed in three prostate cancer cell lines LNCaP, PC-3, and DU-145 using quantitative Western analysis. All three cell lines were found to strongly express Survivin. In LNCaP cells with intact androgen receptors (ARs), it was observed that androgen stimulation with 5α-dihydrotestosterone (DHT) increased Survivin expression. Conversely, treatment with Flutamide decreased Survivin expression in LNCaP cells. We next studied the functional effect of Survivin on sensitivity to Flutamide. LNCaP cells were infected with replication-deficient adenoviruses encoding either wild-type Survivin pAd-S(WT) or a phosphorylation-defective Survivin Thr34 → Ala dominant-negative mutant pAd-S(T34A), and then treated with Flutamide. Cell viability and apoptosis were assessed in vitro and in vivo. It was determined that Survivin can mediate resistance to such antiandrogen therapies based on our assays. Direct androgen stimulation resulted in pan-cell cycle expression of Survivin, which was found to be mediated by AKT, as it was determined that exogenous insulin-like growth factor-1 (IGF-1), a known activator of AKT signaling, could increase Survivin expression and result in pan-cell cycle expression even in AR-negative prostate cancer cell lines PC-3 and DU-145. Given this alternative mechanism of Survivin expression and our findings that Survivin can mediate resistance to Flutamide treatment, we further investigated whether IGF-1-mediated activation of Survivin via AKT could mediate resistance to antiandrogen therapy. Both in vitro and in vivo, this was found to be the case, supporting a novel mechanism of resistance to antiandrogen therapy. Our study indicates that upregulation of Survivin via IGF-1 signaling confers resistance to Flutamide in prostate cancer cells. Targeted inhibition of Survivin appears to enhance the therapeutic effects of Flutamide in vitro and in vivo, revealing a novel strategy to enhance sensitivity to androgen ablation therapy.

Survivin enhances radiation resistance in primary human glioblastoma cells via caspase-independent mechanisms

The observed radioresistance of human glioblastoma multiforme (GBM) poses a major challenge, which, if overcome, may lead to significant advances in the management of this patient population. There is accumulating evidence from correlative studies that Survivin expression is associated with increased malignant potential of human gliomas. The purpose of this study was to investigate whether Survivin plays a direct role in mediating radiation resistance in primary human glioma cell lines, and, if so, investigating the underlying mechanisms. Our panel of GBM cell lines included two that were relatively radiation resistant (GM20 and GM21) and two that were more radiation sensitive (GM22 and GM23), which demonstrated differential levels of Survivin expression between the two groups. Through the use of adenoviral vectors containing either dominant-negative (pAd-S(T34A)) or wild-type Suvrivin (pAd-S(WT)), we were able to inactivate or overexpress Survivin, respectively. Our findings suggest that Survivin plays a critical role in mediating radiation resistance in primary GBM cells, in part through suppression of apoptotic cell death via a caspase-independent manner. We have identified novel mechanisms by which Survivin may enhance tumor cell survival upon radiation exposure such as regulation of double-strand DNA break repair and tumor cell metabolism, which were most evident in the radiation-resistant cell lines. These differences in Survivin function both in radiation-resistant vs radiation-sensitive cell lines and in the presence vs absence of radiation exposure warrant further investigation and highlight potentially important mechanisms of radiation resistance in these tumors.

Development of a Real-time RT-PCR Assay for Detecting EGFRvIII in Glioblastoma Samples

Purpose: Epidermal growth factor receptor variant III (EGFRvIII) is an oncogenic, constitutively active mutant form of the EGFR that is commonly expressed in glioblastoma and is also detected in a number of epithelial cancers. EGFRvIII presents a unique antigenic target for anti-EGFRvIII vaccines and it has been shown to modulate response to EGFR kinase inhibitor therapy. Thus, detection in clinical samples may be warranted. Existing patents preclude the use of anti-EGFRvIII antibodies for clinical detection. Further, frozen tissue is not routinely available, particularly for patients treated in the community. Thus, detection of EGFRvIII in formalin-fixed paraffin-embedded (FFPE) clinical samples is a major challenge. Experimental Design: We developed a real-time reverse transcription-PCR (RT-PCR) assay for detecting EGFRvIII in FFPE samples and analyzed 59 FFPE glioblastoma clinical samples with paired frozen tissue from the same surgical resection. We assessed EGFRvIII protein expression by immunohistochemistry using two distinct specific anti-EGFRvIII antibodies and examined EGFR gene amplification by fluorescence in situ hybridization. Results: The FFPE RT-PCR assay detected EGFRvIII in 16 of 59 (27%) samples, exclusively in cases with EGFR amplification, consistent with the expected frequency of this alteration. The FFPE RT-PCR assay was more sensitive and specific for detecting EGFRvIII than either of the two antibodies alone, or in combination, with a sensitivity of 93% (95% confidence interval, 0.78-1.00) and a specificity of 98% (95% confidence interval, 0.93-1.00). Conclusion: This assay will facilitate accurate assessment of EGFRvIII in clinical samples and may aid in the development of strategies for stratifying patients for EGFRvIII-directed therapies.

The effect of intravenous erythromycin on solid meal gastric emptying in patients with chronic symptomatic post-vagotomy-antrectomy gastroparesis.

Background: Chronic symptomatic gastroparesis occurs in 3–5% of patients following vagotomy and antrectomy. Erythromycin, a macrolide antibiotic, improves gastric emptying in patients with idiopathic and diabetic gastroparesis. Erythromycins effect on gastric emptying in patients with post‐vagotomy– antrectomy gastroparesis is unknown. The aim of this study was to determine if a single dose of intravenous erythromycin (1 mg/kg or 6 mg/kg) accelerates solid meal gastric emptying in patients with chronic symptomatic post‐vagotomy–antrectomy gastroparesis.

The combination of adenoviral HSV TK gene therapy and radiation is effective in athymic mouse glioblastoma xenografts without increasing toxic side effects

AbstractObject: In mouse models of prostate and breast cancer therapeutic effects are enhanced when adenoviral HSV TK gene therapy is combined with ionizing radiation. In the present study, we adopted this approach for the treatment of human glioblastoma xenografts in an athymic mouse model and assessed treatment results as well as toxic side effects. Methods: About 72 nude mice received intracerebral inoculations of 2 × 105 U87ΔEGFR cells. On day 7 after tumor implantation the study population was randomized into six treatment arms: (1) intratumoral buffer inoculation on day 7, (2) intratumoral adenoviral vector injection (2 × 109 vp) on day 7, (3) single dose radiation (2.1 Gy) on day 9, (4) adenoviral injection + radiation, (5) adenoviral injection + ganciclovir (GCV) (20 ug/g twice daily from day 8 to 17), (6) adenoviral injection + GCV + radiation. On day 21 half of the animals were sacrificed for histological evaluation of the brain tumors, the other half was assessed for survival. Results: This study showed significantly prolonged median survival time of 5 days for the GCV treated groups. The addition of radiation decreased the frequency of neurological symptoms and delayed the onset of deficits without altering the expression of thymidine kinase in the tumor cells. Conclusions: We conclude that adenoviral HSV TK gene therapy in combination with adjuvant radiotherapy does not generate increased toxic side effects in glioblastoma treatment. The prolonged survival time of animals receiving gene therapy and the reduced occurrence of neurological symptoms in irradiated mice constitute promising features of the combined treatment.

Cosegregation of familial intestinal pseudoobstruction and presence of digital arches in a large multigenerational pedigree.

Previous studies have suggested a relationship between the presence of digital arches and the occurrence of early-onset chronic intestinal pseudoobstruction (CIP). We recently had under our care a patient who died of complications from neuropathic familial CIP (FCIP) and who had family members with symptoms and radiographic findings consistent with FCIP. Our aim was to determine if there is a relationship between FCIP and digital arches using members of this patients family tree. Questionnaires, telephone follow-up, and clinical and radiographic evidence were all utilized to determine whether a diagnosis of CIP could be made for the family members of this deceased FCIP patient. Fingerprints were sought for all study subjects. Eight of the 26 study subjects who were fingerprinted had clinically diagnosed FCIP and four of these eight had radiographic confirmation. All eight were positive for one or more arches (sensitivity =100%). Only one of the 18 subjects without a diagnosis of FCIP who were fingerprinted had arches (specificity =94%). The likelihood of linkage between the presence of digital arches and FCIP in our study family was significant by genetic linkage analysis criteria. These results show a significant correlation between FCIP and digital arches (P <0.0001). Whether this relationship is a causal one, ie, the gene responsible for digital arches is also responsible for FCIP, or is the result of linkage between the genes for FCIP and digital arches remains unclear.