Strategies to improve the Standard of Care for Glioblastoma Multiforme
Here we are at the third episode of Ben Williams’ guide translation project on treatment options for Glioblastoma Multiforme. This is chapter 2 of the guide that talks about how to fight chemoresistance, how to optimize the chemotherapy program, what is the ideal number of Temodar cycles and concludes with the perspective of combining the Standard of Care with additional treatments. As I have said several times, this information that is sometimes complex to read is nevertheless valuable and my suggestion is to use it to discuss it with the medical team that is following you, where you can also present references to supporting scientific works. Enjoy the reading!
There are several ways that cancer cells use to avoid being killed by cytotoxic chemotherapy. We have already mentioned that the damage inflicted by chemotherapy is quickly repaired before actually killing the cell (due to the activity of the MGMT repair enzyme). A second source of resistance is that the chemotherapy agent is extruded from the cancer before the next cell division (chemotherapy typically affects only those cells that are dividing). A third way is that the chemotherapy agent does not penetrate the blood-brain barrier. While it is generally believed that Temodar effectively crosses the blood-brain barrier, empirical studies on its concentration within the tumor tissue have shown that its penetration is incomplete.
One of the main sources of chemo resistance for many types of cancer comes from the glycoprotein transport systems (technically called ABC transporters) that extrude the chemotherapy agent before it has a chance to kill the cell. This is important because chemotherapy is only effective when cells are dividing and only a fraction of the cell population is dividing at any given time. The longer the chemotherapy stays in the cell, the more likely it is to be present at the time of cell division. If the extrusion of the chemotherapy drug could be inhibited, the chemotherapy should in principle become more effective. Calcium channel blockers, which include drugs commonly used for hypertension such as verapamil, have therefore been studied for this purpose (11).
Unfortunately, these agents have powerful effects on the cardiovascular system, so dosages high enough to produce clinical benefits are usually not usable. However, a recent study (12) reported substantial clinical benefit for breast cancer patients with a relatively low dose (240 mg / day). A previous randomized trial with advanced lung cancer (13) also demonstrated a significant benefit of verapamil, using a dose of 480 mg / day, both in terms of tumor regression rate and survival time.
The combination of verapamil with tamoxifen (which in turn blocks the extrusion with a slightly different mechanism) may possibly increase the clinical benefit (14). In laboratory studies, it has been shown that the calcium channel blockers nicardipine and nimodipine (15, 16) also increase the efficacy of chemotherapy and can have direct effects on tumor growth itself. Quinine derivatives such as quinidine and chloroquine also inhibit the extrusion mechanism. Among the most potent inhibitors of the extrusion mechanism is a common drug used in the treatment of alcoholism, the Antibuse, also known as disulfiram (17,18). Yet another class of drugs that keep chemotherapy inside the cell for longer periods of time are proton pump inhibitors used for acid reflux (for example, Prilosec) (19).
One approach to blocking the glycoprotein pump without using toxic doses of the single agent is to combine several agents together, using lower doses of each single agent, as the combination of different agents has been shown to be synergic in laboratory studies (20).
The most promising clinical results to combat chemo-resistance came from the addition of chloroquine, an old anti-malaria drug, to the traditional chemotherapy agent BCNU. See Chapter 5, Chloroquine section for further details.
The disruption of the blood brain barrier (BBB) is also potentially very important and has been extensively studied. The issue is complicated by the fact that the tumor tissue already has a substantially disrupted BBB (this mechanism underlies the use of contrast agents to identify the tumor). However, this disruption is incomplete, and any chemotherapy agent that does not cross the intact BBB will not come into contact with all the cancer cells. Various ways to stop BBB have been investigated, but none have generally been successful, mainly due to their systemic side effects. Recently, however, common erectile dysfunction drugs (Viagra, Levitra, Cialis) have been found to disrupt BBB in laboratory animals. In a rat brain tumor model, adding Viagra or Levitra to a common chemotherapy agent, Adriamycin, showed a significant increase in survival (26).
Optimization of the chemotherapy program
The standard program for using Temodar at full dose is to be administered on days 1-5 for each 28-day cycle. The large EORTC-NCIC Phase 3 study (2005) also added daily Temodar during radiation at a lower dose, followed by the standard five-day schedule after completion of the radiation. But there has never been a compelling reason why this standard program should be preferred over various alternatives.
In addition to the standard program, three other programs have been studied: (1) a daily low dose “metronomic” program; (2) an alternating weekly program; (3) a “dose-intensive” schedule in which Temodar is used on days 1-21 of each 28-day cycle. Although it is possible to compare the results of these different studies in different clinical trials, only a few studies have compared the different programs within the same clinical trial.
In a randomized single-center study with newly diagnosed patients, the alternating weekly schedule of 150 mg / m2 on days 1-7 and 15-21 was compared to the metronomic schedule of 50 mg / m2 per day (29). Patients who completed 6 cycles of adjuvant Temodar were switched to 13-cis retinoic acid (also known as Accutane) maintenance therapy. One-year survival rates were 80% versus 69% and two-year survival rates 35% versus 28%, both in favor of the alternate week program. However, no differences were statistically significant.
Median survival times for the alternating week and the metronomic patterns were 17.1 versus 15.1 months for the standard approach.
A second very large randomized study compared the standard 5-day with a heavy dose schedule (75-100 mg / m2 on days 1-21). The logic of the dose-intensive program was that it would have better counteracted the MGMT enzyme (30). Median PFS (progression-free survival) provided better results for the intense dose arm (6.7 months versus 5.5 months from the time of study randomization), while median overall survival favored the standard program (16.6 versus 14.9 months from randomization). Although neither of the two differences was considered statistically significant, the intense dosing program had substantially greater toxicity and therefore should not be recommended.
In a more recent retrospective study (313), 40 patients undergoing the standard 5-day program with temozolomide and 30 patients undergoing a metronomic program (75 mg / m2) were included in the final analysis. The metronomic program led to statistically significant increases in both progression-free survival and overall survival, and in both univariate and multivariate analysis. More importantly, this study found that the benefit of the metronomic program occurs mainly for those patients with EGFR overexpression (EGFR protein expression in more than 30% of cancer cells) or EGFR gene amplification. The median overall survival for EGFR overexpressing patients treated with metronomic temozolomide was 34 months, compared with 12 months with the standard schedule.
The researchers also analyzed tumor tissue samples from patients who had undergone repeated resection at the time of relapse. Interestingly, they found that samples of EGFR-overexpressing tumors treated with metronomic temozolomide had significantly fewer cells positive for NF-kB / p65 (a promoter of cell proliferation and survival) than tumors from untreated patients. No such changes were observed between primary and recurrent EGFR-overexpressing tumors in patients treated with the standard program. Recurrent amplified EGFR tumors treated with the metronomic scheme showed fewer amplified EGFR cells and weaker EGFR staining at the time of relapse than the primary tumor. No such differences were observed in EGFR-amplified tumors treated with the standard program. The authors conclude that this metronomic program alters the survival of EGFR-expressing GBM cells more effectively than the standard program. Hopefully these results will lead to future clinical trials. An important note that emerged during the review of this study is that there is no explanation why some patients were selected for the higher dose metronomic program rather than the standard program and it is possible that these patients were more basic. healthy and that the selection bias contributed to the different result.
The lowest dose of Temodar in metronomic chemotherapy reported to date has been presented to patients with newly diagnosed glioblastoma (44). After completion of standard radiation treatment, continuous daily doses of temozolomide approximately 1/10 of the full dose normally used were used in combination with Vioxx (also known as rofecoxib, a COX-2 inhibitor which was later replaced by celecoxib in studies of this group). Median progression-free survival was 8 months and overall survival for 13 patients was 16 months, with minimal toxicity. A second retrospective study (45) from the same medical group compared the very low dose schedule (20 mg / m2) with a more typical metronomic dosage (50 mg / square meter), although only 17 patients and six patients were included in the the first and second group. Patients who received only radiotherapy were also included.
Although physicians are likely to resist any alternative to the standard temozolomide program for newly diagnosed patients outside of clinical trials, a medium dose metronomic program is worthy of consideration for patients with unmethylated MGMT status, and particularly those patients with unmethylated MGMT status and amplified EGFR. For patients ineligible to receive the standard high-dose temozolomide schedule, a very low-dose TMZ metronomic schedule may provide some benefit, perhaps through selective toxicity to immunosuppressive cells and in combination with COX-2 inhibition as described in the above mentioned studies.
How many cycles of TMZ?
An important question is how long the use of TMZ should be continued. The Stupp clinical trial continued for only six cycles after radiotherapy, but many patients continued the protocol for longer periods of time.
In what is perhaps the only prospective randomized study comparing different number of cycles of adjuvant temozolomide, 20 patients with newly diagnosed glioblastoma were assigned to six cycles and another 20 patients were assigned to 12 cycles (355). Median progression-free survival outcomes were 12.8 months in the 6-month group and 16.8 months in the 12-month group, a statistically significant cutoff (p = 0.069). Median overall survival was 15.4 versus 23.8 months and achieved statistical significance despite the low number of patients included in the study (p = 0.044). A serious limitation of this study is that no information was collected on the MGMT status of the patients, and therefore it is possible that the percentage of patients with methylated MGMT promoter tumors was not the same in the two arms.
A retrospective study conducted in Canada (51) compared patients who received the six standard temozolomide courses with those who had more than six courses (up to 12). Patients who received six cycles had a median survival of 16.5 months, while those who received more than six cycles had a median survival of 24.6 months.
The latest attempts to define the optimal duration of monthly temozolomide (TMZ) therapy were published as an abstract for the 2015 SNO Annual Meeting. In the first of these studies (reference 325, abstract ATCT-08), a large team of researchers retrospectively analyzed data from four large randomized trials with the aim of comparing 6 cycles of monthly TMZ with> 6 cycles. Only patients who had completed 6 cycles of TMZ and had no progress within 28 days of completion of cycle 6 were included. Important prognostic factors such as age, performance status, extent of resection and MGMT status were incorporated into the analysis. For these patients, treatment with more than 6 cycles of TMZ was associated with significantly improved progression-free survival [HR = 0.77, p = 0.03] regardless of the prognostic factors examined and was particularly beneficial for those with methylated MGMT status. Surprisingly, overall survival was not significantly different between the two groups (p = 0.99).
In the second abstract (reference 326, ATPS-38 abstract), a Japanese group attempted to clarify whether more than 12 cycles of TMZ were useful in terms of increased survival. Patients in this study were divided into four groups: a) 12 cycles, b) 24 cycles, c) more than 24 cycles until relapse, and d) over 12 cycles (this group includes groups b) and c)). 12, 14, 12 and 40 patients were included in each of these groups. There was no significant difference in progression-free survival between groups a) and b), implying a lack of benefit of 24 versus 12 cycles. Importantly, patients who were able to continue TMZ treatment for at least 12 cycles (all patients in this study) had a median progression-free survival of 4.3 years and a median overall survival of 6. 3 years. This study failed to show an advantage of continuing TMZ cycles beyond 12 months.
Combination of standard treatment with additional agents
Few oncologists believe that single agent treatments are likely to be curative. The problem is to find the optimal combinations, based on toxicity and differences in the mechanisms of action. Before the introduction of temozolomide, the PCV combination of procarbazine, CCNU and vincristine had been the most widely used combined treatment for glioblastomas, but its use has never been shown to produce a better result than treatment with BCNU as a single agent. However, there is now a great deal of research studying the effects of combining temozolomide with other therapies, most of which support the view that such combinations improve treatment outcome, sometimes substantially. A variety of add-on therapies will be discussed in the following chapters.
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(313) Cominelli, Manuela et al. “EGFR Amplified and Overexpressing Glioblastomas and Association with Better Response to Adjuvant Metronomic Temozolomide.” Journal of the National Cancer Institute 107.5 (2015): djv041.
(325) Blumenthal, Deborah T et al. “ATCT-08THE IMPACT OF EXTENDED ADJUVANT TEMOZOLOMIDE IN NEWLY-DIAGNOSED GLIOBLASTOMA: A SECONDARY ANALYSIS OF EORTC AND NRG ONCOLOGY/RTOG.” Neuro-Oncology 17. suppl 5 (2015): v2-v2.
(326) Ikuta, Soko et al. “ATPS-38ASSESSMENT OF OPTIMIZED THERAPEUTIC TERM WITH TEMOZOLOMIDE FOR NEWLY DIAGNOSED GLIOBLASTOMA.” Neuro-Oncology 17.suppl 5 (2015): v26-v26.
(355) Bhandari, Menal. “Comparative Study of Adjuvant Temozolomide six Cycles Versus Extended 12 Cycles in Newly Diagnosed Glioblastoma Multiforme.” Journal Of Clinical And Diagnostic Research, 2017, doi:10.7860/jcdr/2017/27611.9945.
Well, I hope you enjoyed the reading, I have been as faithful as possible. A new chapter very soon!