Permeability of the blood-brain barrier in the rat after local proton irradiation

The Monoterpenoid Perillyl Alcohol: Anticancer Agent and Medium to Overcome Biological Barriers

Perillyl alcohol (POH) is a naturally occurring monoterpenoid related to limonene that is present in the essential oils of various plants. It has diverse applications and can be found in household items, including foods, cosmetics, and cleaning supplies. Over the past three decades, it has also been investigated for its potential anticancer activity. Clinical trials with an oral POH formulation administered to cancer patients failed to realize therapeutic expectations, although an intra-nasal POH formulation yielded encouraging results in malignant glioma patients. Based on its amphipathic nature, POH revealed the ability to overcome biological barriers, primarily the blood–brain barrier (BBB), but also the cytoplasmic membrane and the skin, which appear to be characteristics that critically contribute to POH’s value for drug development and delivery. In this review, we present the physicochemical properties of POH that underlie its ability to overcome the obstacles placed by different types of biological barriers and consequently shape its multifaceted promise for cancer therapy and applications in drug development. We summarized and appraised the great variety of preclinical and clinical studies that investigated the use of POH for intranasal delivery and nose-to-brain drug transport, its intra-arterial delivery for BBB opening, and its permeation-enhancing function in hybrid molecules, where POH is combined with or conjugated to other therapeutic pharmacologic agents, yielding new chemical entities with novel mechanisms of action and applications.

Models for Translational Proton Radiobiology-From Bench to Bedside and Back

The number of proton therapy centers worldwide are increasing steadily, with more than two million cancer patients treated so far. Despite this development, pending questions on proton radiobiology still call for basic and translational preclinical research. Open issues are the on-going discussion on an energy-dependent varying proton RBE (relative biological effectiveness), a better characterization of normal tissue side effects and combination treatments with drugs originally developed for photon therapy. At the same time, novel possibilities arise, such as radioimmunotherapy, and new proton therapy schemata, such as FLASH irradiation and proton mini-beams. The study of those aspects demands for radiobiological models at different stages along the translational chain, allowing the investigation of mechanisms from the molecular level to whole organisms. Focusing on the challenges and specifics of proton research, this review summarizes the different available models, ranging from in vitro systems to animal studies of increasing complexity as well as complementing in silico approaches.

Enhanced brain delivery and therapeutic activity of trastuzumab after blood-brain barrier opening by NEO100 in mouse models of brain-metastatic breast cancer

BACKGROUND

The antitumor efficacy of human epidermal growth factor receptor 2 (HER2)-targeted therapies, such as humanized monoclonal antibody trastuzumab (Herceptin®, Roche), in patients with breast-to-brain cancer metastasis is hindered by the low permeability of the blood-brain barrier (BBB). NEO100 is a high-purity version of the natural monoterpene perillyl alcohol, produced under current good manufacturing practice (cGMP) regulations, that was shown previously to reversibly open the BBB in rodent models. Here we investigated whether NEO100 could enable brain entry of trastuzumab to achieve greater therapeutic activity.

METHODS

An in vitro BBB, consisting of human astrocytes and brain endothelial cells, was used to determine trastuzumab penetration in the presence or absence of NEO100. For in vivo studies, we administered intravenous (IV) trastuzumab or the trastuzumab-drug conjugate ado-trastuzumab emtansine (T-DM1; Kadcyla®, Roche), to mouse models harboring intracranial HER2+ breast cancer, with or without BBB opening via IA NEO100. Brain and tumor tissues were examined for the presence of trastuzumab and infiltration of immune cells. Therapeutic impact was evaluated based on overall survival.

RESULTS

NEO100 greatly increased trastuzumab penetration across an in vitro BBB. In vivo, IA NEO100-mediated BBB opening resulted in brain tumor-selective accumulation of trastuzumab, without detectable presence in normal brain tissue, along with increased presence of immune cell populations. IV delivery of trastuzumab or T-DM1 achieved significantly greater overall survival of tumor-bearing mice when combined with IA NEO100.

CONCLUSION

IA NEO100 facilitates brain tumor entry of trastuzumab and T-DM1 and significantly enhances their therapeutic efficacy, along with increased antibody-dependent immune cell recruitment.

Improving CNS Delivery to Brain Metastases by Blood-Tumor Barrier Disruption

Brain metastases encompass nearly 80% of all intracranial tumors. A late stage diagnosis confers a poor prognosis, with patients typically surviving less than 2 years. Poor survival can be equated to limited effective treatment modalities. One reason for the failure rates is the presence of the blood-brain barrier (BBB) and blood-tumor barrier (BTB) that limit the access of potentially effective chemotherapeutics to metastatic lesions. Strategies to overcome these barriers include new small molecule entities capable of crossing into the brain parenchyma, novel formulations of existing chemotherapies, and disruptive techniques. Here, we review BBB physiology and BTB pathophysiology. Additionally, we review the limitations of routinely practiced therapies and three current methods being explored for BBB/BTB disruption for improved delivery of chemotherapy to brain tumors.

Permeability estimates in histopathology-proved treatment-induced necrosis using perfusion CT: can these add to other perfusion parameters in differentiating from recurrent/progressive tumors?

BACKGROUND AND PURPOSE

Differentiating treatment effects from RPT is a common yet challenging task in a busy neuro-oncologic practice. PS probably represents a different aspect of angiogenesis and vasculature and can provide additional physiologic information about recurrent/progressive enhancing lesions. The purpose of the study was to use PS measured by using PCT to differentiate TIN from RPT in patients with previously irradiated brain tumor who presented with a recurrent/progressive enhancing lesion.

MATERIALS AND METHODS

Seventy-two patients underwent PCT for assessment of a recurrent/progressive enhancing lesion from January 2006 to November 2009. Thirty-eight patients who underwent surgery and histopathologic diagnosis were included in this analysis. Perfusion parameters such as PS, CBV, CBF, and MTT were obtained from the enhancing lesion as well as from the NAWM.

RESULTS

Of 38 patients, 11 were diagnosed with pure TIN and 27 had RPT. Patients with TIN showed significantly lower mean PS values than those with RPT (1.8 ± 0.8 versus 3.6 ± 1.6 mL/100 g/min; P value=.001). The TIN group also showed lower rCBV (1.2 ± 0.3 versus 2.1 ± 0.7; P value<.001), lower rCBF (1.2 ± 0.5 versus 2.6 ± 1.7; P value=.004), and higher rMTT (1.4 ± 0.4 versus 1.0 ± 0.4; P value=.018) compared with the RPT group.

CONCLUSIONS

PCT and particularly PS can be used in patients with previously treated brain tumors to differentiate TIN from RPT. PS estimates can help increase the accuracy of PCT in differentiating these 2 entities.

Perfusion MRI in the evaluation of cerebral blood volume and mean transit time in untreated and recurrent glioblastomas

Perfusion MRI by means of dynamic contrast-enhanced T2-weighted MR imaging allows quantitative analysis of cerebral blood volume (CBV) and mean transit time (MTT) in intra-axial brain tumors. Our aim was to compare recurrent glioblastomas to untreated glioblastomas, determining if there are differences in perfusion parameters between the two groups. Serial MR examinations were performed in 26 patients with glioblastoma histologically demonstrated before surgical resection and in 19 patients with recurrent glioblastoma after surgery and radiotherapy. Tumor recurrence was established using both histological and clinical criteria. Normalized CBV and MTT ratios were considered and compared between the two groups. A statistically significant difference, both in average and maximum normalized CBV ratios between the two groups was found. In particular, average and maximum normalized CBV ratios were greater in untreated than in recurrent glioblastomas. On the contrary, average and maximum normalized MTT ratios were greater in the recurrent glioblastomas, than in untreated tumors. Perfusion MRI by means of dynamic contrast-enhanced T2-weighted MR imaging is a valuable adjunct to conventional MR imaging in assessing different hemodynamic features between untreated and recurrent glioblastomas. In particular, tumor recurrence must be suspected even if the average and maximum normalized CBV ratios are far below those of untreated glioblastomas. In addition, increased average and maximum MTT ratios could be considered typical markers of neoplastic recurrence in irradiated cerebral tissue.

FIRST-PASS PERFUSION COMPUTED TOMOGRAPHY

OBJECTIVE

To differentiate recurrent tumors from radiation effects and necrosis in patients with irradiated brain tumors using perfusion computed tomographic (PCT) imaging.

METHODS

Twenty-two patients with previously treated brain tumors who showed recurrent or progressive enhancing lesions on follow-up magnetic resonance imaging scans and had a histopathological diagnosis underwent first-pass PCT imaging (26 PCT imaging examinations). Another eight patients with treatment-naïve, high-grade tumors (control group) also underwent PCT assessment. Perfusion maps of cerebral blood volume, cerebral blood flow, and mean transit time were generated at an Advantage Windows workstation using the CT perfusion 3.0 software (General Electric Medical Systems, Milwaukee, WI). Normalized ratios (normalized to normal white matter) of these perfusion parameters (normalized cerebral blood volume [nCBV], normalized cerebral blood flow [nCBF], and normalized mean transit time [nMTT]) were used for final analysis.

RESULTS

Fourteen patients were diagnosed with recurrent tumor, and eight patients had radiation necrosis. There was a statistically significant difference between the two groups, with the recurrent tumor group showing higher mean nCBV (2.65 versus 1.10) and nCBF (2.73 versus 1.08) and shorter nMTT (0.71 versus 1.58) compared with the radiation necrosis group. For nCBV, a cutoff point of 1.65 was found to have a sensitivity of 83.3% and a specificity of 100% to diagnose recurrent tumor and radiation necrosis. Similar sensitivity and specificity were 94.4 and 87.5%, respectively, for nCBF with a cutoff point of 1.28 and 94.4 and 75%, respectively, for nMTT with a cutoff point of 1.44 to diagnose recurrent tumor and radiation necrosis.

CONCLUSION

PCT may aid in differentiating recurrent tumors from radiation necrosis on the basis of various perfusion parameters. Recurrent tumors show higher nCBV and nCBF and lower nMTT compared with radiation necrosis.

Blood-brain barrier permeability after gamma whole-body irradiation: an in vivo microdialysis study

The effects of total-body irradiation on the permeability of rat striatal blood-brain barrier (BBB) to [3H]alpha-aminoisobutyric acid (AIBA) and [14C]sucrose were investigated using the microdialysis technique. Seven days, 3 and 6 weeks, and 3, 5, and 8 months after gamma exposure at a dose of 4.5 Gy, no modification of the permeability to both [3H]AIBA and [14C]sucrose was observed. But, in the course of the initial syndrome, we observed a significant but transient increase in the BBB permeability to the two markers between 3 and 17 h after exposure. A secondary transient "opening" of the BBB to [14C]sucrose was noticed about 28 h following irradiation without the corresponding increase in BBB permeability to [3H]AIBA. On the contrary, the transport of [3H]AIBA through the BBB was decreased between 33 and 47 h postradiation. In conclusion, our experiments showed early modifications of BBB permeability after a moderate-dose whole-body exposure. Confirmation of these results with other tracers, in another experimental model or in humans, would have clinical applications for designing appropriate pharmacotherapy in radiotherapy and treatment of accidental overexposure.

Effect of brain irradiation on blood-CSF barrier permeability of chemotherapeutic agents

Effect of irradiation on blood-cerebrospinal fluid (CSF) barrier (BCB) was studied quantitatively by observing the effect of methotrexate (MTX) permeation into the CSF before, during, and after brain irradiation after i.v. injection of MTX. Observation of 15 brain tumor patients indicated that in large brain tumors, the BCB was seriously damaged; in small tumors, the BCB would gradually open. Compared with the findings before irradiation, the increase of permeability of MTX was zero to threefold. It is thus advisable to give chemotherapy only after 20 Gy of irradiation.

The influence of neonatal thymectomy on the development of radiation myelopathy in rats

To investigate the possible contribution of cellular immunity in the development of radiation injury of the central nervous system, Wag/Rij rats were thymectomized at birth and irradiated to the cervical spinal cord at the age of 3 months. At the time of paralysis or at the end of the follow-up period (when rats were 1-year-old) the animals were sacrificed and the mediastinum was examined histologically. In 95% of the neonatally thymectomized animals no thymus was left. These rats showed a firm impairment of the cellular immunity, as they had a 40% reduction of the T-lymphocytes in the spleen, and a 70% reduction of the mixed lymphocyte reaction, compared to age-matched controls. Both single dose and two-fraction irradiation experiments were performed. No modification of the latency time to develop paralysis was observed comparing thymectomized and age-matched controls. The incidence of foreleg paralysis after cervical spine irradiation (single dose or two-fraction) was identically distributed in the follow-up period for both neonatally thymectomized and control Wag/Rij rats. The ED50 value derived in the single dose experiments was 20.3 Gy for the control animals, and 20.9 Gy for thymectomized rats, and in the two fraction experiments 29 Gy for controls and 29.6 Gy for thymectomized rats. None of these differences are significant. It appears that neonatal thymectomy, in spite of its firm suppression of the cellular immunity, has no major influence on the development of radiation myelopathy in rats.

Influence of radiation on the blood-brain barrier and optimum time of chemotherapy

A pilot study of the destructive effects of radiation on the blood-brain barrier (BBB) was made on 14 patients with localized and limited brain tumors by 99MTc-GH imaging from August 1988 to November 1989. Count/pixel data were obtained from the unirradiated, irradiated, and tumor areas before and after radiotherapy of 30-40 Gy. It was observed that, a) the BBB in the unirradiated area outside the radiation portal was not changed, b) the degree of destructive effect on the BBB in the irradiated normal area was directly proportional to the radiation dose. For 30-40 Gy, the count/pixel change enhances to average 24.7% [(147.6-118.4)/118.4], and c) the BBB in the tumor area is partially destroyed on an average of 22.1% [(206.8-169.4)/169.4] by the tumor. The radiotherapy further enhances this effect to an average of 74.7% [(206.8-118.4)/118.4]. Case 3 showed that before radiation, the degree of destructive effect on the BBB in the tumor area was 22% [(167-137)/137] higher than normal brain tissue. After a dose of 30 Gy of irradiation, it increased to 76.7% [(242-137)/137]; 8 months later it decreased to 17% [(160.3-137)/137]. It has been proven that the BBB can recover at least partially. Based on these observations, the authors believe that in the combined treatment of operated brain tumors, radiotherapy should precede chemotherapy so as to enhance the destruction of the BBB, facilitating the incorporation of drugs into the tumor. The dose at which to start chemotherapy is 20-30 Gy.

The late effects of radiation on the blood brain barrier

Rats were irradiated with 60 to 20 Gy in a single dose focussed to a volume of 0.5 cc in the center of the left hemisphere. Breakdown of the BBB was detected by the presence of spikes on EEG after subcutaneous injection of Bicuculline methiodide, and the presence of staining following Evans Blue dye injection. Breakdown of the BBB (mean and standard deviation) occurred in 38/46 of the 60 Gy rats at 98 +/- 16 days, 7/11 of the 50 Gy rats at 128 +/- 25 days, 11/18 of the 40 Gy rats at 162 +/- 3 days, 5/11 of the 30 Gy rats at 178 +/- 5 days and, 7/12 of the 20 Gy rats at 217 +/- 7 days post irradiation. This study suggests that endothelial damage could be the principle mechanism mediating the late radiation syndrome.