Drug Combo May Prevent Glioblastoma Recurrence

Gamma-secretase inhibitors could play an important role in augmenting the effectiveness of temozolomide chemotherapy for glioblastoma multiforme if the results obtained in recent in vitro, ex vivo, and in vivo experiments are supported in future studies.

Although temozolomide (TMZ) has increased the 2-year survival rate of patients with glioblastoma multiforme (GBM) when it is used in combination with surgical resection and radiotherapy, some cells still escape treatment in most patients and contribute to local tumor recurrence. Gamma-secretase inhibitors (GSIs) are an attractive therapeutic option to bring to the clinic because they have been found in previous studies to stop both glioblastoma cell growth and the formation of glioblastoma neurospheres by blocking the Notch signaling pathway, which is commonly overexpressed in glioblastoma cells, according to Candace A. Gilbert and her colleagues at the University of Massachusetts, Worcester.

Before Ms. Gilbert and her associates tested the combination of TMZ and a GSI in vivo, they tested TMZ alone, a GSI alone, and both together on neurosphere cultures derived from patients’ GBMs. Although GSI treatment alone decreased Notch pathway signaling and reduced neurosphere formation, it could not stop the proliferation of GBM cells and the formation of secondary neurospheres. Although treatment with TMZ alone and combined treatment with TMZ and a GSI yielded similar decreases in initial neurosphere formation, cultures that were treated with the combination recovered to a smaller size, and there were fewer of them than was the case for those that were treated with TMZ alone. When these neurosphere cultures were dissociated to single cells and replated, the cells that underwent combination treatment formed far fewer secondary neurospheres than did those that had been treated with only TMZ. Treatment with both drugs also led to significantly fewer cells in each neurosphere that were capable of self-renewal.

Further in vitro experiments of the combination of drugs showed that a single dose of a GSI could reduce neurosphere recovery and the formation of secondary neurospheres only when the GSI was administered 24 hours after TMZ, in comparison with TMZ alone.

When the tumor cells were treated and then injected subcutaneously into immunocompromised mice, the researchers observed palpable tumor growth in very few mice that received cells treated with TMZ and a GSI (tumor latencies, 43-96 days), compared with tumor growth in all mice that received cells treated with a GSI alone (latencies, 3-16 days) and growth in nearly all mice that received cells treated with TMZ alone (latencies, 25-43 days).

In another group of immunocompromised mice, tumor cells that were injected subcutaneously were allowed to grow to 150 mm3. Ms. Gilbert and her associates found that the xenografts were completely eliminated in half of immunocompromised mice by an intraperitoneal injection of TMZ followed by ingestion of a GSI mixed into their food supply. The mice also survived free of a palpable tumor until they were euthanized at 150 days. The remaining half of the mice that received the combination treatment showed tumor progression at a mean of 26 days.

All tumor masses progressed (doubled in size) in mice that received only TMZ.

“Because Notch activity is associated with GBM stem cell function and survival, and the cells that survive TMZ-only treatment are capable of self-renewal and tumor initiation, it is probable that the cells targeted by TMZ plus GSI treatment possess a cancer stem cell phenotype,” the researchers wrote (Cancer Res. 2010 Aug. 10 [doi:10.1158/0008-5472.CAN-10-1378]).

They suggested that the variability of response to combined treatment in the in vivo studies could have been the result of a TMZ concentration that was not “high enough to induce a cell cycle arrest in all of the cells capable of recovery, which could hinder GSI enhancement,” or a “slight variability” in food consumption.

The need for only a single dose of a GSI to enhance TMZ therapy is beneficial, the researchers noted, because GSIs can cause cytotoxicity in the gastrointestinal tract. They found no change in the weight of the mice during combined treatment.

“These studies suggest a role for TMZ plus GSI therapy to reduce recurrences in patients with low tumor burden after surgical resection of the bulk tumor,” wrote the investigators, who acknowledged that they ultimately need to include radiation in their treatment schedule to see how it contributes to combination therapy with TMZ and GSIs.

In comments on this study, Dr. Alyx B. Porter of the Mayo Clinic in Arizona said that it “certainly provides a springboard for considering future directions in the use of GSIs, and may indeed provide further treatment options for this patient population in whom options are greatly needed.”

Dr. Porter noted that since 2005, the treatment standard for GBM has been concomitant TMZ with radiotherapy followed by adjuvant TMZ. This resulted in a 2-year survival rate of 26.5%, which was higher than any prior treatment regimen had shown. The time to progression on this regimen is about 6 months, she said, which points to the refractory and aggressive nature of this tumor.

Thus far, she added, bevacizumab has been the only agent approved by the Food and Drug Administration for use in the setting of recurrent GBM. Given the dismal prognosis for this patient population, novel agents are needed not only to augment up-front therapy to prevent recurrence but also to provide further treatment options in the recurrent setting. Dr. Porter described the study of Ms. Gilbert and colleagues as “eloquent,” and noted “the remarkable in vitro and in vivo data” suggesting that GSI and TMZ act together to halt neurosphere replication, and the finding that administering a GSI after TMZ may have the maximum impact in affecting neurosphere repopulation. “These data suggest that GSIs may indeed have an impact on glioblastoma recurrence and time to progression.”

Dr. Porter agreed with the authors’ observation that future studies to assess the total impact of the GSI in the GBM population will need to incorporate irradiation in addition to TMZ to reflect a more accurate sense of the full effect and toxicity of the GSI.

The National Institutes of Health and the CVIP Technology Development Fund funded the research. The investigators had no conflicts of interest to disclose.

Gamma-secretase inhibitors could play an important role in augmenting the effectiveness of temozolomide chemotherapy for glioblastoma multiforme if the results obtained in recent in vitro, ex vivo, and in vivo experiments are supported in future studies.

Although temozolomide (TMZ) has increased the 2-year survival rate of patients with glioblastoma multiforme (GBM) when it is used in combination with surgical resection and radiotherapy, some cells still escape treatment in most patients and contribute to local tumor recurrence. Gamma-secretase inhibitors (GSIs) are an attractive therapeutic option to bring to the clinic because they have been found in previous studies to stop both glioblastoma cell growth and the formation of glioblastoma neurospheres by blocking the Notch signaling pathway, which is commonly overexpressed in glioblastoma cells, according to Candace A. Gilbert and her colleagues at the University of Massachusetts, Worcester.

Before Ms. Gilbert and her associates tested the combination of TMZ and a GSI in vivo, they tested TMZ alone, a GSI alone, and both together on neurosphere cultures derived from patients’ GBMs. Although GSI treatment alone decreased Notch pathway signaling and reduced neurosphere formation, it could not stop the proliferation of GBM cells and the formation of secondary neurospheres. Although treatment with TMZ alone and combined treatment with TMZ and a GSI yielded similar decreases in initial neurosphere formation, cultures that were treated with the combination recovered to a smaller size, and there were fewer of them than was the case for those that were treated with TMZ alone. When these neurosphere cultures were dissociated to single cells and replated, the cells that underwent combination treatment formed far fewer secondary neurospheres than did those that had been treated with only TMZ. Treatment with both drugs also led to significantly fewer cells in each neurosphere that were capable of self-renewal.

Further in vitro experiments of the combination of drugs showed that a single dose of a GSI could reduce neurosphere recovery and the formation of secondary neurospheres only when the GSI was administered 24 hours after TMZ, in comparison with TMZ alone.

When the tumor cells were treated and then injected subcutaneously into immunocompromised mice, the researchers observed palpable tumor growth in very few mice that received cells treated with TMZ and a GSI (tumor latencies, 43-96 days), compared with tumor growth in all mice that received cells treated with a GSI alone (latencies, 3-16 days) and growth in nearly all mice that received cells treated with TMZ alone (latencies, 25-43 days).

In another group of immunocompromised mice, tumor cells that were injected subcutaneously were allowed to grow to 150 mm3. Ms. Gilbert and her associates found that the xenografts were completely eliminated in half of immunocompromised mice by an intraperitoneal injection of TMZ followed by ingestion of a GSI mixed into their food supply. The mice also survived free of a palpable tumor until they were euthanized at 150 days. The remaining half of the mice that received the combination treatment showed tumor progression at a mean of 26 days.

All tumor masses progressed (doubled in size) in mice that received only TMZ.

“Because Notch activity is associated with GBM stem cell function and survival, and the cells that survive TMZ-only treatment are capable of self-renewal and tumor initiation, it is probable that the cells targeted by TMZ plus GSI treatment possess a cancer stem cell phenotype,” the researchers wrote (Cancer Res. 2010 Aug. 10 [doi:10.1158/0008-5472.CAN-10-1378]).

They suggested that the variability of response to combined treatment in the in vivo studies could have been the result of a TMZ concentration that was not “high enough to induce a cell cycle arrest in all of the cells capable of recovery, which could hinder GSI enhancement,” or a “slight variability” in food consumption.

The need for only a single dose of a GSI to enhance TMZ therapy is beneficial, the researchers noted, because GSIs can cause cytotoxicity in the gastrointestinal tract. They found no change in the weight of the mice during combined treatment.

“These studies suggest a role for TMZ plus GSI therapy to reduce recurrences in patients with low tumor burden after surgical resection of the bulk tumor,” wrote the investigators, who acknowledged that they ultimately need to include radiation in their treatment schedule to see how it contributes to combination therapy with TMZ and GSIs.

In comments on this study, Dr. Alyx B. Porter of the Mayo Clinic in Arizona said that it “certainly provides a springboard for considering future directions in the use of GSIs, and may indeed provide further treatment options for this patient population in whom options are greatly needed.”

Dr. Porter noted that since 2005, the treatment standard for GBM has been concomitant TMZ with radiotherapy followed by adjuvant TMZ. This resulted in a 2-year survival rate of 26.5%, which was higher than any prior treatment regimen had shown. The time to progression on this regimen is about 6 months, she said, which points to the refractory and aggressive nature of this tumor.

Thus far, she added, bevacizumab has been the only agent approved by the Food and Drug Administration for use in the setting of recurrent GBM. Given the dismal prognosis for this patient population, novel agents are needed not only to augment up-front therapy to prevent recurrence but also to provide further treatment options in the recurrent setting. Dr. Porter described the study of Ms. Gilbert and colleagues as “eloquent,” and noted “the remarkable in vitro and in vivo data” suggesting that GSI and TMZ act together to halt neurosphere replication, and the finding that administering a GSI after TMZ may have the maximum impact in affecting neurosphere repopulation. “These data suggest that GSIs may indeed have an impact on glioblastoma recurrence and time to progression.”

Dr. Porter agreed with the authors’ observation that future studies to assess the total impact of the GSI in the GBM population will need to incorporate irradiation in addition to TMZ to reflect a more accurate sense of the full effect and toxicity of the GSI.

The National Institutes of Health and the CVIP Technology Development Fund funded the research. The investigators had no conflicts of interest to disclose.

Gamma-secretase inhibitors could play an important role in augmenting the effectiveness of temozolomide chemotherapy for glioblastoma multiforme if the results obtained in recent in vitro, ex vivo, and in vivo experiments are supported in future studies.

Although temozolomide (TMZ) has increased the 2-year survival rate of patients with glioblastoma multiforme (GBM) when it is used in combination with surgical resection and radiotherapy, some cells still escape treatment in most patients and contribute to local tumor recurrence. Gamma-secretase inhibitors (GSIs) are an attractive therapeutic option to bring to the clinic because they have been found in previous studies to stop both glioblastoma cell growth and the formation of glioblastoma neurospheres by blocking the Notch signaling pathway, which is commonly overexpressed in glioblastoma cells, according to Candace A. Gilbert and her colleagues at the University of Massachusetts, Worcester.

Before Ms. Gilbert and her associates tested the combination of TMZ and a GSI in vivo, they tested TMZ alone, a GSI alone, and both together on neurosphere cultures derived from patients’ GBMs. Although GSI treatment alone decreased Notch pathway signaling and reduced neurosphere formation, it could not stop the proliferation of GBM cells and the formation of secondary neurospheres. Although treatment with TMZ alone and combined treatment with TMZ and a GSI yielded similar decreases in initial neurosphere formation, cultures that were treated with the combination recovered to a smaller size, and there were fewer of them than was the case for those that were treated with TMZ alone. When these neurosphere cultures were dissociated to single cells and replated, the cells that underwent combination treatment formed far fewer secondary neurospheres than did those that had been treated with only TMZ. Treatment with both drugs also led to significantly fewer cells in each neurosphere that were capable of self-renewal.

Further in vitro experiments of the combination of drugs showed that a single dose of a GSI could reduce neurosphere recovery and the formation of secondary neurospheres only when the GSI was administered 24 hours after TMZ, in comparison with TMZ alone.

When the tumor cells were treated and then injected subcutaneously into immunocompromised mice, the researchers observed palpable tumor growth in very few mice that received cells treated with TMZ and a GSI (tumor latencies, 43-96 days), compared with tumor growth in all mice that received cells treated with a GSI alone (latencies, 3-16 days) and growth in nearly all mice that received cells treated with TMZ alone (latencies, 25-43 days).

In another group of immunocompromised mice, tumor cells that were injected subcutaneously were allowed to grow to 150 mm3. Ms. Gilbert and her associates found that the xenografts were completely eliminated in half of immunocompromised mice by an intraperitoneal injection of TMZ followed by ingestion of a GSI mixed into their food supply. The mice also survived free of a palpable tumor until they were euthanized at 150 days. The remaining half of the mice that received the combination treatment showed tumor progression at a mean of 26 days.

All tumor masses progressed (doubled in size) in mice that received only TMZ.

“Because Notch activity is associated with GBM stem cell function and survival, and the cells that survive TMZ-only treatment are capable of self-renewal and tumor initiation, it is probable that the cells targeted by TMZ plus GSI treatment possess a cancer stem cell phenotype,” the researchers wrote (Cancer Res. 2010 Aug. 10 [doi:10.1158/0008-5472.CAN-10-1378]).

They suggested that the variability of response to combined treatment in the in vivo studies could have been the result of a TMZ concentration that was not “high enough to induce a cell cycle arrest in all of the cells capable of recovery, which could hinder GSI enhancement,” or a “slight variability” in food consumption.

The need for only a single dose of a GSI to enhance TMZ therapy is beneficial, the researchers noted, because GSIs can cause cytotoxicity in the gastrointestinal tract. They found no change in the weight of the mice during combined treatment.

“These studies suggest a role for TMZ plus GSI therapy to reduce recurrences in patients with low tumor burden after surgical resection of the bulk tumor,” wrote the investigators, who acknowledged that they ultimately need to include radiation in their treatment schedule to see how it contributes to combination therapy with TMZ and GSIs.

In comments on this study, Dr. Alyx B. Porter of the Mayo Clinic in Arizona said that it “certainly provides a springboard for considering future directions in the use of GSIs, and may indeed provide further treatment options for this patient population in whom options are greatly needed.”

Dr. Porter noted that since 2005, the treatment standard for GBM has been concomitant TMZ with radiotherapy followed by adjuvant TMZ. This resulted in a 2-year survival rate of 26.5%, which was higher than any prior treatment regimen had shown. The time to progression on this regimen is about 6 months, she said, which points to the refractory and aggressive nature of this tumor.

Thus far, she added, bevacizumab has been the only agent approved by the Food and Drug Administration for use in the setting of recurrent GBM. Given the dismal prognosis for this patient population, novel agents are needed not only to augment up-front therapy to prevent recurrence but also to provide further treatment options in the recurrent setting. Dr. Porter described the study of Ms. Gilbert and colleagues as “eloquent,” and noted “the remarkable in vitro and in vivo data” suggesting that GSI and TMZ act together to halt neurosphere replication, and the finding that administering a GSI after TMZ may have the maximum impact in affecting neurosphere repopulation. “These data suggest that GSIs may indeed have an impact on glioblastoma recurrence and time to progression.”

Dr. Porter agreed with the authors’ observation that future studies to assess the total impact of the GSI in the GBM population will need to incorporate irradiation in addition to TMZ to reflect a more accurate sense of the full effect and toxicity of the GSI.

The National Institutes of Health and the CVIP Technology Development Fund funded the research. The investigators had no conflicts of interest to disclose.