Bevacizumab (Avastin)

by Stephen Western
Astrocytoma Options.com

Bevacizumab (trade name Avastin, manufactured by Genentech, a subsidiary of Roche) is a monoclonal antibody against human VEGF-A (vascular endothelial growth factor A), which is administered intravenously. In May of 2009, the FDA granted accelerated approval to bevacizumab for use in recurrent glioblastoma, based on two phase II trials (discussed below) in which the drug led to increased response rates, progression-free survival, and other clinical benefits such as decreased cerebral edema and decreased requirement for corticosteroids.

Interpretation of response to anti-VEGF agents based on conventional MRI imaging is complicated. Such agents may have immediate impacts on blood-brain barrier permeability leading to rapid reduction in contrast enhancement as seen on MRI, making the true influence on tumour growth rates difficult to detect. Though some preclinical studies with mice show that the drug is likely slowing tumour growth during short-term usage, recently completed phase III clinical trials have not shown an increased overall survival benefit to adding bevacizumab to first-line radiochemotherapy [1].

Angiogenesis, or the growth of new blood vessels to supply the tumour, is influenced by various growth factors, the most important of which is vascular endothelial growth factor (VEGF). Use of bevacizumab and other drugs targeting VEGF or VEGF receptors may indeed have short-term benefits, such as a decrease in cerebral edema (a significant danger in itself), or a short-term tumour shrinkage or stabilization. Tumours treated with such drugs however, have a tendency to shift to a migratory, invasive, "mesenchymal" phenotype, which is clearly shown in animal studies. In these studies, animal survival may nevertheless be prolonged due to the initial efficacy of the drug, prior to the development of resistance and the activation of alternative angiogenic pathways. This pattern is seen also in humans, where the benefits of VEGF blockade tend to be short-lived.

Preclinical Studies

In one study [2], mice were implanted intracranially with U87 glioblastoma cells, and treated with bevacizumab. After four weeks of treatment there was a predictable reduction in tumour blood vessel density. However, after seven weeks of treatment, the tumour had adapted to the anti-VEGF therapy by increasing production of an alternative angiogenic growth factor, basic fibroblast growth factor (bFGF). By this point the tumour vessel density had surprisingly increased to a higher level than the control mice. Also, tumour cell proliferation as measured by Ki-67 staining was roughly twice the level in the controls, and there was a dramatic increase in two hypoxia markers (HIF-2a and CA9). The bevacizumab treatment also led to increased perivascular invasion and the appearance of satellite tumours. The increase in invasive potential and the appearance of renewed angiogenesis was related to the increased expression of multiple invasion-related genes (MMP2, MMP9, MMP12) and alternative angiogenic genes (angiopoietins and fibroblast growth factors). The authors conclude that "the long-term success of antiangiogenic agents in the clinic will depend on our ability to control tumor migration".

In a similar study [3], glioblastoma spheroid cultures were implanted into rat brains, which were then treated with bevacizumab. While the treatment modestly slowed tumour doubling time and proliferation (the latter by 11%), there was a large (68%) increase in the number of tumour cells invading normal brain tissue. The treatment also led to reduced vessel permeability and reduced blood flow. Subsequent to the decrease in blood flow and oxygenation there was an increase in glycolysis, with evidence of increased lactate and hypoxia inducible factor 1a (HIF1a), and a decrease in the number of mitochondria per cell. Similar to the previous study, other angiogenic molecules, such as angiopoietins, were increased.

An earlier study hypothesized that the satellite tumours which appeared after anti-VEGF treatment co-opted existing blood vessels as an alternative to new angiogenesis [4]. This is likely an additional way that tumours adapt to anti-angiogenic therapy.

While these animal studies clearly show that treatment with bevacizumab or similar drugs can lead to increased invasion and alternative angiogenic pathways, the human evidence is controversial. Some studies conclude that the rate of disseminated tumour progression following bevacizumab is similar to what is found in general for recurrent glioblastoma [5]. Other studies show a higher-than-expected rate of recurrence distant from the original site [6].

Human trials

In the two phase II trials which led to the 2009 FDA approval of bevacizumab for recurrent glioblastoma, percentage of patients progression-free at six months (PFS6) and median progression-free survival (mPFS) were elevated in comparison to historical controls.

In the BRAIN trial (AVF3708g), 85 recurrent glioblastoma patients received bevacizumab alone. Their median age was 54 years. 81% entered the trial at first relapse and the remainder joined at second relapse. PFS6 was 46.4% for patients receiving bevacizumab at first relapse, and 27.8% for patients who received the drug at second relapse. Median PFS was 4.4 months (first relapse) and 3.1 months (second relapse). Median survival from the start of the trial was 9.1 and 9.2 months. The drug was well tolerated and there was a trend to decreasing need for corticosteroids [8].

In the NCI trial (NCI 06-C-0064E), 48 recurrent glioblastoma patients (median age 53, median number of prior chemotherapies, 2) received bevacizumab alone. PFS6 was 29%, median PFS was 3.7 months and median survival from the start of the trial was 7.1 months. There was a reduction of cerebral edema in 50% of patients [9].

To compare these results with the standard of care drug temozolomide, a trial of TMZ (5 in 28 day schedule) for 112 glioblastoma patients at first relapse led to a PFS6 of 19% (eligible histology group), a median PFS of 2.9 months. Patient in this trial had a median age of 52 years and 65% had received prior nitrosourea chemotherapy [10].

Recent Phase III trials: AVAglio and RTOG 0825

The positive results of phase II trials of bevacizumab for recurrent glioblastoma led to two phase III trials of the drug in conjunction with standard radiotherapy and temozolomide in newly diagnosed glioblastoma. The results of both these trials were reported at the June 2013 meeting of the American Society of Clinical Oncology (ASCO).

In the RTOG 0825 trial, 637 patients were randomized to receive either bevacizumab (BEV) or placebo in conjunction with radiation therapy and temozolomide. The median progression-free survival was increased for those receiving BEV to 10.7 months versus 7.3 months in the placebo group. Overall survival was similar in both groups (15.7 months with BEV, 16.1 months for placebo). In a press release dated June 2013, principal investigator Mark Gilbert stated "While we found a difference in progression-free survival in the bevacizumab arm, there was an overall increase in symptom burden and decline in neurocognitive function and some measures of quality of life comparing the patients receiving bevacizumab with those on placebo" [11]. The investigators concluded that the addition of bevacizumab to first-line treatment in newly diagnosed glioblastoma is unwarranted.

The AVAglio trial had similar outcomes to RTOG 0825 [1]. In this trial 921 newly diagnosed glioblastoma patients were randomized into two groups similar to the RTOG 0825 trial. Patients receiving bevacizumab had an improved progression-free survival of 10.6 months versus 6.2 months in the placebo group. As in RTOG 0825, overall survival was not improved (median 16.8 months versus 16.7 months).

Who is most likely to benefit

In the phase II NCI trial described above [9], older patients had an increased progression-free survival with bevacizumab compared with younger patients, a reversal of the typical pattern in which younger patients fare better. The same pattern has been demonstrated in a small trial of bevacizumab for recurrent anaplastic astrocytomas [13]. Further, a retrospective study of 140 recurrent anaplastic glioma patients showed that those who received bevacizumab had significantly shorter survival than those who received a different drug at recurrence [14]. An abstract included in the 2014 annual SNO meeting called Clinical Outcome of Bevacizumab-Treated Patients with Recurrent Malignant Gliomas (abstract AI-22) looked at survival outcomes of 25 patients treated with BEV. Overall survival from treatment was better for primary GBM patients than for secondary GBM patients, another reversal of the typical pattern. In conclusion, older primary GBM patients may gain more benefit from bevacizumab than younger patients, or those with secondary GBM having evolved from lower grade astrocytomas.

Delayed versus early use of bevacizumab may be preferable

A large retrospective study [17] published online in Neuro-Oncology (March 2014) suggests that delaying the use of bevacizumab until later recurrences (second, third, or more) may be preferable to the earlier use of the drug. 468 primary glioblastoma patients treated with bevacizumab (BV) at UCLA and Kaiser Permanente Los Angeles between 2005 and 2012 were studied. 80 received BV up-front along with chemoradiation, 264 received BV at first recurrence, 88 at second recurrence and 36 at third or higher recurrence. Statistical analysis showed that there was no significant difference in progression-free survival or overall survival after BV treatment, according to the number of recurrence at the time of BV treatment. In other words, after BV treatment, patients in the different categories lived a similar amount of time, regardless of whether they received BV treatment at first, second, third or higher recurrence. This suggests that delaying BV until other options have been exhausted may lead to better overall survival.

Similarly, there was no significant difference in survival after failure of BV, when comparing those who received or didn't receive further chemotherapy following BV failure. This indicates that recurrent tumours previously treated with BV are resistant to further therapies. Also, the simultaneous use of BV with another chemotherapy (usually irinotecan or lomustine) modestly increased median PFS, but did not significantly improve overall survival in this study. The conclusion of this study is that the use of bevacizumab can be delayed without a reduction of efficacy, with the exception of high-risk patients (eg patients over age 60) who are at increased risk of being unable to receive treatment at future recurrences. Whether or not delayed rather than early use of BV leads to increased overall survival still requires testing in a prospective clinical trials.

Drug combinations

Bevacizumab is often combined with irinotecan for recurrent glioma patients, though the benefit of this addition has not been definitively proven. Various preclinical studies have tested other drugs in combination with bevacizumab, showing benefit for example, with experimental PI3K/mTOR inhibitors. One study showed that the transcription factor STAT3 is increased following bevacizumab compared to pre-treatment tumour samples [15]. The combination of the VEGF receptor inhibitor cediranib with an experimental STAT3 inhibitor led to decreased tumour volume in mice.

Bevacizumab plus chloroquine

One of the effects of anti-angiogenic therapy is a decrease in blood flow to the tumour and consequently, a lowering of oxygen levels in the tumour (hypoxia). One of the responses to hypoxic conditions and the stress that induces is the survival mechanism known as autophagy, in which intracellular materials are digested inside the cell. By blocking autophagy with chloroquine, hypoxic conditions become less tolerable and the cell may die rather survive. The combination of anti-angiogenic drugs (such as bevacizumab) with chloroquine may therefore be highly effective. An abstract presented at the 2011 SNO meeting showed this to be the case in glioblastoma xenografts. The study was later published in Cancer Research [18].

"Human glioblastoma xenografts exhibited persistent growth inhibition when treated with autophagy inhibitor chloroquine plus antiangiogenic bevacizumab; chloroquine prevented the evasive hypoxia-associated growth seen with bevacizumab alone and reversed the more than 2-fold increased expression of autophagy mediator BNIP3 seen in xenografts growing during bevacizumab monotherapy. These findings suggest that hypoxia-mediated autophagy promotes tumor cell survival after antiangiogenic therapy, a novel adaptive response to antiangiogenic therapy that can be pharmacologically disrupted to allow antiangiogenic therapy to fulfill its therapeutic promise."

Figure 6A. The combination of bevacizumab plus chloroquine is far more effective than either drug alone in subcutaneous GBM xenografts in mice.

Bevacizumab plus DCA in vivo

A study [16] published in 2013 tested the effects of bevacizumab, DCA, or both drugs combined in athymic nude mice implanted with subcutaneous U87 and U118 glioblastoma tumours. First, the effects of bevacizumab alone were studied. Application of the drug led to increased expression of the two hypoxia markers, hypoxia-inducible factor 1 alpha (HIF-1a) and carbonic anhydrase IX (CA9). Downstream HIF transcriptional targets involved in glycolysis, including glucose transporters GLUT1 and GLUT3 and pyruvate dehydrogenase kinases 1 and 3 (PDK1 and PDK3), were strongly increased. In contrast, genes involved in mitochondrial oxidative metabolism were repressed, including pyruvate dehydrogenases and members of all five OXPHOS complexes. These results show that in this model, bevacizumab leads to lower oxygen levels (hypoxia) and a compensation for this by increasing glucose flux and glycolysis at the expense of oxidative mitochondrial metabolism. In the mice, tumours became completely resistant to bevacizumab by about 40 days after implantation.

Next, the researchers tested DCA and the combination of DCA and bevacizumab in the same mouse models. While DCA alone led to relatively minor changes in tumour growth rate, the combination therapy strongly decreased tumour volume compared to untreated controls. In the U87 model this effect was significant before day 15, and in the U118 model, tumour growth was nearly completely stopped by the combination therapy, with only a very minor increase in tumour volume at day 105. When the tumours were analyzed for molecular markers, combination treated tumours had significantly less staining for Ki-67, a marker of proliferation, compared to untreated and bevacizumab-only treated tumours, suggesting a cytostatic mechanism for the combination therapy. As DCA is an available drug with modest side-effects, its use in combination with bevacizumab (Avastin) should be seriously considered by patients and researchers.

For more information on DCA, see the discussions on the Repurposed Drugs and Targeting Tumour Metabolism pages.

Conclusion

While bevacizumab has shown clinical benefit for recurrent glioblastoma, with a prolongation of progression-free survival and a decrease in cerebral edema, tumours adapt to this treatment with an increased migratory, mesenchymal phenotype, assisted by an influx of tumour-associated macrophages and other bone-marrow derived cells. For bevacizumab to significantly increase survival for glioblastoma patients, this adaptive response must be anticipated and blocked with drugs which inhibit invasion and the influx of migration- and angiogenesis-promoting immune cells such as macrophages and neutrophils (with drugs such as plerixafor). Only then will the true potential of this drug be realized.

References

1. Roche announces final phase III study results of Avastin plus radiotherapy and chemotherapy in people with an aggressive form of brain cancer. Media Release. June 2013.
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2. Mediators of glioblastoma resistance and invasion during antivascular endothelial growth factor therapy. Lucio-Eterovic et al. 2009.
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3. Anti-VEGF treatment reduces blood supply and increases tumor cell invasion in glioblastoma. Keunen et al. 2011.
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4. Anti-VEGF antibody treatment of glioblastoma prolongs survival but results in increased vascular cooption. Rubenstein et al. 2000.
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5. Disseminated progression of glioblastoma after treatment with bevacizumab. Bloch et al. 2013.
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6. Concurrent bevacizumab and temozolomide alter the patterns of failure in radiation treatment of glioblastoma multiforme. Shields et al. 2013.
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7. Targeting Src family kinases inhibits bevacizumab-induced glioma cell invasion. Huveldt et al. 2013.
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8. Bevacizumab alone and in combination with irinotecan in recurrent glioblastoma. Friedman et al. 2009.
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9. A phase II trial of single-agent bevacizumab followed by bevacizumab plus irinotecan at tumor progression in recurrent glioblastoma. Kreisl et al. 2009.
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10. A phase II study of temozolomide vs. procarbazine in patients with glioblastoma multiforme at first relapse. Yung et al. 2000.
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11. Addition of bevacizumab to initial treatment for brain tumors does not extend patients' lives. Press release. June 2, 2013.
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12. Survival benefit from bevacizumab in newly diagnosed glioblastoma (GBM) according to transcriptional subclasses. Huse et al. ASCO Annual Meeting 2013.
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13. Salvage chemotherapy with bevacizumab for recurrent alkylator-refractory anaplastic astrocytoma. Chamberlain et al. 2009.
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14. Survival outcomes of patients with recurrent anaplastic glioma treated with bevacizumab. Hamza et al. Annual Meeting of the Society for Neuro-Oncology 2013.
    READ SOURCE DOCUMENT (see abstract 051)


15. Modulating antiangiogenic resistance by inhibiting the signal transducer and activator of transcription 3 pathway in glioblastoma. de Groot et al. 2012.
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16. Dichloroacetate reverses the hypoxic adaptation to bevacizumab and enhances its antitumor effects in mouse xenografts. Kumar et al. 2013.
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17. Deferred use of bevacizumab for recurrent glioblastoma is not associated with diminished efficacy. Piccioni et al. 2014.
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18. Hypoxia-Induced Autophagy Promotes Tumor Cell Survival and Adaptation to Antiangiogenic Treatment in Glioblastoma. Hu et al. 2012.
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This page was created on 12/27/2013 and last updated on 04/19/2020