Meningiomas are the most common primary brain tumor with an incidence rate of 8.33 per
100,000. They originate from the meningeal (dural) coverings of the brain and spinal
cord. Although the majority of meningiomas are benign, these tumors can grow slowly until
they are very large, if left undiscovered, and, in some locations can be severely
disabling and/or life-threatening.
There is a relative paucity of prospective clinical trials that provide an
evidenced-based agreed upon approach to managing meningioma. Furthermore, uniformly
applied guidelines have been difficult to achieve given the typical pattern of slow
growth.
Meningiomas can be organized into two groups. WHO Grade I meningioma are histologically
benign and can be managed by careful observation as recommended in the National
Comprehensive Cancer Network Guidelines. Grade I meningiomas are low grade and have a
7-20% recurrence risk. For most other patients (WHO Grade II and WHO Grade III) there is
an increased risk of recurrence and death. Grade II meningiomas occur in 5-15% of cases
with a 30-40% recurrence risk and Grade III meningiomas occur 1-3% of the time with a
50-80% recurrence risk. For Grade I and Grade II meningiomas, gross total resection is
standard. WHO Grade II and WHO Grade III meningiomas are referred to as high-grade
meningiomas.
Questions remain regarding the selection and timing of treatment, especially in cases of
recurrent meningioma or newly diagnosed high-grade meningioma (WHO Grade II or Grade III
meningioma). For patients undergoing definitive therapy, complete resection (gross total
resection) has been the standard. However, there is a significant subset of patients who
are not successfully managed by surgery alone, or in whom a complete resection is not
possible due to the relationship of the tumor to important anatomy. Complete tumor
resection is not always achievable as many meningiomas arise at or near critical neural
or vascular structures or in sites with limited surgical access When a gross total
resection cannot be accomplished, post-operative radiation therapy is often considered
(e.g., single-session stereotactic radiosurgery, hypofractionated stereotactic radiation
therapy and conventionally fractionated external beam radiation therapy).
The potential for recurrence, whether following subtotal resection or gross-total
resection, is well recognized. As a result, there is increasing evidence from
retrospective review of case histories in support of radiation therapy as primary therapy
for high-grade meningioma (or radiation prior to or following resection surgery). The
relative efficacy of these approaches has not yet been tested in rigorously designed
prospective clinical trials.
The role of chemotherapy in treating meningioma is also unclear; however, there is a need
for additional therapeutic options to treat meningioma cases which cannot be managed by
surgery and/or radiation therapy alone.
One reason for the hesitation to treat primary central nervous system tumours with
chemotherapy is the difficulty of penetrating the blood brain barrier with chemotherapy
agents. Nasal brain delivery of chemotherapy offers a novel, paradigm shifting platform
based on technology to deliver chemotherapy via inhalation to the brain tumor. The
presumed mechanism of nasal brain delivery from preclinical rodent studies is thought to
be via the olfactory and trigeminal nerves. Effective nasal brain delivery has been
demonstrated in humans in other diseases. For example, Reger et al. have reported
effective delivery of intranasal insulin for Alzheimer's disease.
Perillyl alcohol, also called p-metha1,7-diene-6-ol,or 4-isopropenylcyclo-hexenecarbinol,
is a monoterpene, isolated from the essential oils of lavender, peppermint, spearmint,
and several other plants and synthesized by the mevalonate pathway. It has been
previously demonstrated to have anti-cancer properties in preclinical studies in rodent
models for a variety of cancers including mammary, pancreatic, and colon cancer. Although
the exact mechanism of perillyl alcohol induced tumor regression is unknown, perillyl
alcohol has been reported to modulate cellular processes that control cell growth and
differentiation including G1 cell cycle arrest and induction of apoptosis.
Perillyl alcohol has also been shown to inhibit post-translational modification of
proteins involved in signal transduction. It has been postulated that the anti-neoplastic
activity of perillyl alcohol involves a decrease in the levels of isoprenylated Ras and
Ras-related proteins, thereby reducing the physiological functioning of these proteins.
Protein isoprenylation involves the post-translational modification of a protein by the
covalent attachment of a lipophilic farnesyl isoprenoid group to a cysteine residue at or
near the carboxyl terminus. Isoprenoid substrates for prenylprotein transferase enzymes
include farnesyl pyrophosphate plus geranylgeranyl pyrophosphate, two intermediates in
the mevalonate pathway. This action was attributed to the inhibition of farnesyl protein
transferase activity. Farnesylation is the most critical part of the process that leads
to the activation of Ras, and farnesyl transferase inhibitors exert their antitumor
effect in part by inhibiting Ras-mediated signaling. A study revealed that H-Ras and
K-Ras farnesylation were inhibited by perillyl alcohol.
Ras activity is elevated in malignant central nervous system tumors. Strong evidence
demonstrates that Ras protein is highly expressed in meningioma cells, and inhibition of
Ras activity may inhibit the growth of meningiomas. Activated Ras stimulates other
pathways essential for proliferation and progression through the cell cycle and
inhibition of apoptosis in malignant gliomas. Moreover, the formation of malignant
meningioma may require the cooperation of both Ras and Akt signaling. This cooperative
effect has been demonstrated by somatic-cell gene transfer, during which transfer of
either an activated form of K-Ras or Akt alone to neural progenitors was insufficient to
form malignant glioma in vivo, but the combined effect of both pathways could initiate
gliomagenesis. Thus, based on this potential alteration in signal transduction involving
K-Ras in malignant central nervous system tumors, and its ability to induce cell cycle
arrest and apoptosis, perillyl alcohol (NEO100) may be an attractive agent and warrants
further clinical development. Furthermore, intranasal delivery of NEO100 has the
additional, potential benefit of direct drug delivery into the brain and avoiding
systemic toxicity and first pass metabolism.
Intranasal delivery of NEO100 will directly penetrate meningiomas, particularly
skull-based meningiomas which extend along the olfactory groove, tuberculum sella,
spenoid ridge and petroclival region. These represent some of the most challenging
pathologies encountered by neurosurgeons due to the meningioma depth, invasion,
vascularity and relationship to critical cranial nerves and vessels.
Intranasal perillyl alcohol has been tested in a Phase I clinical trial in the US, it has
also been studied in two clinical studies in Brazil in more than 275 patients with
systemic cancers and in malignant glioma. The Brazil studies indicate good tolerance and
no long term central nervous system (CNS) or systemic severe adverse events. Adult
patients with CNS cancers received commercial (Sigma Chemical) perillyl alcohol
(formulated as a 10% solution in ethanol:glycerol) administered intranasally via a
commercial nasal delivery mask four times a day (110 mg/dose or 440 mg/day). Radiographic
regression and a PFS-6 of 50% were reported. A pharmacokinetic study showed that perillic
acid, a metabolite of perillyl alcohol, was detected in the serum of patients 30 minutes
post inhalation after a single dose of 110 mg or 220 mg of perillyl alcohol and lasted
for 3 hours.