Laser Therapy Opens Blood-Brain Barrier
Curator: Larry H. Bernstein, MD, FCAP
Laser Surgery Opens Blood-Brain Barrier to Chemotherapy
http://www.photonics.com/Article.aspx?AID=58445
ST. LOUIS, March 11, 2016 — A laser probe has been used to open the brain’s protective cover, enabling delivery of chemotherapy drugs to patients with glioblastoma — the most common and aggressive form of brain cancer.
In a pilot study conducted by the Washington University School of Medicine in St. Louis, Mo., 14 patients with glioblastoma underwent minimally invasive laser surgery to treat a recurrence of their tumors. Heat from the laser was already known to kill brain tumor cells but, unexpectedly, the researchers found that the technology penetrated the blood-brain barrier.
“The laser treatment kept the blood-brain barrier open for four to six weeks, providing us with a therapeutic window of opportunity to deliver chemotherapy drugs to the patients,” said neurosurgery professor Eric Leuthardt, MD, who also treats patients at Barnes-Jewish Hospital. “This is crucial because most chemotherapy drugs can’t get past the protective barrier, greatly limiting treatment options for patients with brain tumors.
The team is still closely following the patients, though early results indicate they are doing better on average, in terms of survival and clinical outcomes, than what the researchers would expect with other treatment methods.
Glioblastomas are one of the most difficult cancers to treat. Most patients diagnosed with this type of brain tumor survive just 15 months, according to the American Cancer Society.
The research is part of a larger phase II clinical trial that will involve 40 patients. Twenty patients were enrolled in the pilot study, 14 of whom were found to be suitable candidates for the minimally invasive laser surgery, a technology that Leuthardt helped pioneer.
The laser technology was approved by the FDA in 2009 as a surgical tool to treat brain tumors. The Washington team’s research marks the first time the laser has been shown to disrupt the blood-brain barrier, which shields the brain from harmful toxins but inadvertently blocks potentially helpful drugs, such as chemotherapy.
As part of the trial, doxorubicin, a widely used chemotherapy, was delivered intravenously to 13 patients in the weeks following the laser surgery. Preliminary data indicate that 12 patients showed no evidence of tumor progression during the short, 10-week time frame of the study. One patient experienced tumor growth before chemotherapy was delivered; the tumor in another patient progressed after chemotherapy was administered, the researcher reported.
The laser surgery was well-tolerated by the patients in the trial; most went home one to two days afterward, and none experienced severe complications. The surgery was performed while a patient lies in an MRI scanner, providing the neurosurgical team with a real-time look at the tumor. Using an incision of only 3 mm, a neurosurgeon robotically inserted the laser to heat up and kill brain tumor cells at a temperature of about 150 °F.
“The laser kills tumor cells, which we anticipated,” said Leuthardt. “But, surprisingly, while reviewing MRI scans of our patients, we noticed changes near the former tumor site that looked consistent with the breakdown of the blood-brain barrier.”
Leuthardt confirmed and further studied these imaging findings with study co-author Dr. Joshua Shimony, a professor of radiology at Washington University.
The researchers, including co-corresponding author Dr. David Tran, a neuro-oncologist now at the University of Florida, performed follow-up testing, which showed that the degree of permeability through the blood-brain barrier peaked one to two weeks after surgery but that the barrier remained open for up to six weeks.
Other successful attempts to breach the barrier have left it open for only a short time — about 24 hours — not long enough for chemotherapy to be consistently delivered, or have resulted in only modest benefits, the researchers said. The laser technology leaves the barrier open for weeks — long enough for patients to receive multiple treatments with chemotherapy. Further, the laser only opens the barrier near the tumor, leaving the protective cover in place in other areas of the brain. This has the potential to limit the harmful effects of chemotherapy drugs in other areas of the brain, the researchers said.
The findings also suggest that other approaches, such as cancer immunotherapy — which harnesses cells of the immune system to seek out and destroy cancer — could also be useful for patients with glioblastomas.
The researchers are planning another clinical trial that combines the laser technology with chemotherapy and immunotherapy, as well as trials to test targeted cancer drugs that normally can’t breach the blood-brain barrier.
The research was published in Plos One (doi: 10.1371/journal.pone.0148613).
Hyperthermic Laser Ablation of Recurrent Glioblastoma Leads to Temporary Disruption of the Peritumoral Blood Brain Barrier
Feb 24, 2016 http://dx.doi.org:/10.1371/journal.pone.0148613Poor central nervous system penetration of cytotoxic drugs due to the blood brain barrier (BBB) is a major limiting factor in the treatment of brain tumors. Most recurrent glioblastomas (GBM) occur within the peritumoral region. In this study, we describe a hyperthemic method to induce temporary disruption of the peritumoral BBB that can potentially be used to enhance drug delivery.
Methods
Twenty patients with probable recurrent GBM were enrolled in this study. Fourteen patients were evaluable. MRI-guided laser interstitial thermal therapy was applied to achieve both tumor cytoreduction and disruption of the peritumoral BBB. To determine the degree and timing of peritumoral BBB disruption, dynamic contrast-enhancement brain MRI was used to calculate the vascular transfer constant (Ktrans) in the peritumoral region as direct measures of BBB permeability before and after laser ablation. Serum levels of brain-specific enolase, also known as neuron-specific enolase, were also measured and used as an independent quantification of BBB disruption.
Results
In all 14 evaluable patients, Ktrans levels peaked immediately post laser ablation, followed by a gradual decline over the following 4 weeks. Serum BSE concentrations increased shortly after laser ablation and peaked in 1–3 weeks before decreasing to baseline by 6 weeks.
Conclusions
The data from our pilot research support that disruption of the peritumoral BBB was induced by hyperthemia with the peak of high permeability occurring within 1–2 weeks after laser ablation and resolving by 4–6 weeks. This provides a therapeutic window of opportunity during which delivery of BBB-impermeant therapeutic agents may be enhanced.
Trial Registration
ClinicalTrials.gov NCT01851733
Citation: Leuthardt EC, Duan C, Kim MJ, Campian JL, Kim AH, Miller-Thomas MM, et al. (2016) Hyperthermic Laser Ablation of Recurrent Glioblastoma Leads to Temporary Disruption of the Peritumoral Blood Brain Barrier. PLoS ONE 11(2): e0148613. http://dx.doi.org:/10.1371/journal.pone.0148613
Glioblastoma (GBM) is the most common and lethal malignant brain tumor in adults [1]. Despite advanced treatment, median survival is less than 15 months, and fewer than 5% of patients survive past 5 years [2, 3]. Effective treatment options for recurrent GBM remain very limited and much of research and development efforts in recent years have focused on this area of greatly unmet needs. Up to 90% of recurrent tumors develop within the 2–3 cm margin of the primary site and are thought to arise from microscopic glioma cells that infiltrate the peritumoral brain region prior to resection of the primary tumor [4, 5]. Therefore elimination of infiltrative GBM cells in this region likely will improve long-term disease control.
Inadequate CNS delivery of therapeutic drugs due to the blood brain barrier (BBB) has been a major limiting factor in the treatment of brain tumors. The presence of contrast enhancement on standard brain MRI qualitatively reflects a disrupted state of the BBB. For this reason, drug access to the viable contrast enhanced tumor rim is likely significantly higher than to the peritumoral region, which usually does not have contrast enhancement [6, 7]. Evidence supporting this hypothesis came from studies in which drug levels of cytotoxic agents were sampled in tumors and the surrounding brain tissue at the time of surgery or autopsy. Drug concentrations were at the highest in the enhancing portion of tumors, and then rapidly decreased up to 40 fold lower by 2–3 cm distance from the viable tumor edge [8–10]. Overall, these observations suggest that the BBB and its integrity negatively correlate with delivery and potentially therapeutic effects of BBB impermeant drugs.
To circumvent the BBB problem in local drug delivery, recent approaches have focused on bypassing it. A previously described method is the use of Gliadel, a polymer wafer impregnated with the chemotherapeutic agent carmustine (BCNU) and placed intra-operatively in the resection cavity to bypass the BBB. This approach resulted in a statistically significant but modest survival advantage in both newly diagnosed and recurrent GBM [11–13]. The modest benefit of Gliadel could be due to the short duration of drug delivery as nearly 80% of BCNU is released from the wafer over a period of only 5 days [14]. This observation further supports the notion that the BBB is critical to chemotherapy effect. However, Gliadel is not widely utilized as it requires an open craniotomy and can impair wound healing. Another approach of bypassing the BBB is the convection-enhanced delivery system in which a catheter is surgically inserted into the tumor to deliver chemotherapy [15]. This procedure requires prolonged hospitalization to maintain the external catheter to prevent serious complications and as a result has not been used extensively.
The role of hyperthermia in inducing BBB disruption has been previously described in animal models of CNS hyperthermia. In a rodent model of glioma, the global heating of the mouse’s head to 42°C for 30 minutes in a warm water bath significantly increased the brain concentration of a thermosensitive liposome encapsulated with adriamycin chemotherapy [16]. To effect more locoregional hyperthermia, retrograde infusion of a saline solution at 43°C into the left external carotid artery in the Wistar rat reversibly increased BBB permeability to Evans-blue albumin in the left cerebral hemisphere [17]. In another approach, neodymium-doped yttrium aluminum garnet (Nd:YAG) laser-induced thermotherapy to the left forebrain of Fischer rats resulted in loco-regional BBB disruption as evidenced by passage of Evans blue dye, serum proteins (e.g. fibrinogen & IgM), and the chemotherapeutic drug paclitaxel for up to several days after thermotherapy [18]. The effect of hyperthermia on the BBB of human brain has not been examined.
Here we describe an approach to induce sustained, local disruption of the peritumoral BBB using MRI-guided laser interstitial thermal therapy, or LITT. The biologic effects and correlation with MRI findings of LITT have been studied in both animal and human models since the development of LITT over twenty years ago. A well-described zonal distribution of histopathological changes with corresponding characteristic MR imaging findings centered on the light-guide track replace the lesion targeted for thermal therapy. The central treatment zone shows development of coagulative necrosis with complete loss of normal neurons or supporting structures immediately following therapy, corresponding to hyperintense T1-weighted signal intensity relative to normal brain [19–22]. The peripheral zone of the post-treatment lesion is characterized by avid enhancement with intravenous gadolinium contrast agents, which peaks several days following thermal therapy and persists for many weeks after the procedure. Gadolinium contrast enhancement in the brain following LITT is due to leakage of gadolinium contrast into the extravascular space across a disrupted BBB [20–23]. The perilesional zone of hyperintense signal intensity of FLAIR-weighted images develops within 1–3 days of thermal treatment and persists for 15–45 days [22].
We demonstrate that in addition to cytoreductive ablation of the main recurrent tumor, hyperthermic exposure of the peritumoral region resulted in localized, lasting disruption of the BBB as quantified by dynamic contrast-enhanced MRI (DCE-MRI) and serum levels of brain-specific enolase (BSE), thus providing a therapeutic window of opportunity for enhanced delivery of therapeutic agents.
Brain MRI obtained within 48 hours following LITT showed the targeted tumor replaced by a post-treatment lesion corresponding to the volume of treated tissue on intraoperative thermometry maps. The post-treatment lesion lost the original rim of tumor-associated contrast enhancement and instead demonstrated central hyperintense T1-weighted signal compared to the pre-treated tumor and normal brain and a faint, newly developed discontinuous rim of peripheral contrast enhancement extending beyond the original tumor-associated enhancing rim (Fig 2A). These findings are consistent with a loss of viable tumor tissue caused by LITT, thus achieving an effective cytoreduction similar to open surgical resection. Of note, the rim of new peripheral contrast enhancement persisted for at least the next 28 days (Fig 2B–2E). Perilesional edema qualitatively evaluated on FLAIR-weighted images increased from pretreatment imaging at week 2 and persisted at week 4 following LITT (Fig 2F–2I). Perilesional edema decreased on subsequent MRI examinations. These findings qualitatively indicate that peritumoral BBB is disrupted by LITT and that the disruption peaks within approximately 2 weeks after the procedure.
……
Fig 3 demonstrates the Ktrans time curves for our cohort of patients. In all subjects the Ktrans in the ROIs within the enhancing ring around the ablated tumor is highly elevated in the first few days after the procedure and then progressively decreases at approximately the 4-week time point. The bottom right subplot in Fig 3 is an average of the Ktrans time courses from all the subjects with adjacent curves indicating the plus and minus one standard error of the mean curves. This figure demonstrates the peak Ktrans value immediately after the LITT procedure with persistent elevation out to about 4 weeks. Radiographically, persistent contrast enhancement and FLAIR hyperintensity were observed well past 6 weeks and in many cases more than 10 weeks later. Several patients had recurrent tumor by radiographic criteria (increasing size of the edema and enhancing area around the tumor site) and these patients also demonstrated a corresponding increase in the Ktrans value. These recurrences occurred after the 10-week mark and thus were not included in Fig 3. Importantly no difference in the pattern of Ktrans tracing was consistently observed between the 10 patients receiving late doxorubicin treatment and the 4 patients receiving early doxorubicin treatment. In summary, these results indicate that the peritumoral BBB disruption as measured by Ktrans peaked immediately after LITT and persisted above baseline for an additional 4 weeks.
……
To optimize the ELISA assay for BSE, we collected sera from 3 patients with a newly diagnosed low-grade (WHO grade 2) glioma before and after their planned craniotomy and surgical resection, and determined serum concentrations of BSE. WHO grade 2 gliomas were chosen for the optimization because as they are generally non-contrast enhanced tumors on brain MRI, tumor-associated BBB is relatively intact and consequently, serum concentrations of brain-specific factors are predicted to be low pre-operatively and to then rise post-operatively due to the BBB compromise from the surgery. Serum BSE concentrations were low prior to surgery and then, as predicted, consistently increased after open craniotomy and tumor resection, thus indicating that this method had adequate sensitivity in detecting changes in serum levels of BSE due to disruption of the BBB (Fig 4).
Serum concentrations of BSE before and after open craniotomy for surgical debulking in 3 subjects (A, B, and C) with a low-grade glioma, WHO grade II. *p<0.05. http://dx.doi.org:/10.1371/journal.pone.0148613.g004
……
LITT is a minimally invasive neurosurgical technique that achieves effective tumor cytoreduction of brain tumors using a laser to deliver hyperthermic ablation. Here we have demonstrated that an unexpected, potentially useful effect of LITT is its ability to also disrupt the BBB in the peritumoral region that extends outwards 1–2 cm from the viable tumor rim. Importantly, the disruption persists in all 14 evaluable, treated patients for up to 4 weeks after LITT as measured quantitatively by DCE-MRI and up to 6 weeks as measured by serum levels of the brain-specific factor BSE. These observations indicate that after LITT there is a window during which enhanced local delivery of therapeutic agents into the desired location (i.e. peritumoral region) can potentially be achieved.
In all of the patients in this series, the peaks of serum concentrations of BSE showed wider variations and were delayed from several days to 1–2 weeks following the peak of BBB disruption as measured by Ktrans. The wider variations and delay of BSE concentrations lead to relatively low correlation coefficients between the two parameters and could be explained by: 1) the higher data point resolution for the serum values versus DCE-MRI values (weekly versus biweekly, respectively); 2) interval physiologic breakdown of thermally ablated tissue coupled with subsequent diffusion and equilibration between the intracranial and peripheral compartments; and 3) high inter-tumor heterogeneity among patients resulting in a wide variation in the rates at which ablated tissues of different compositions are broken down and released into the circulation. Whether these differences may be in part due to tumor-related factors such as IDH1/2 mutations and MGMT promoter methylation is unclear due to the small number of subjects. More importantly, both methods showed that the peritumoral BBB disruption induced by LITT was temporary, decreasing soon after peaking and being resolved by 4–6 weeks in most patients. In addition, although no significant difference in all the BBB measurement parameters was observed between the early and late doxorubicin treatment arms, the number of evaluable subjects was too small to allow generalization at this time.
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