Glioblastoma

= Glioblastoma: The Unknown Killer =

__THE PATIENT__
Jonathan Doebler is one of the approximately 35,000 people who have been diagnosed with glioblastoma multiforme in the past year. He is a physically fit, 50-year-old, Caucasian male who coaches college football. Mr. Doebler enjoys traveling with his wife and twin 13-year-old daughters, hiking, and of course watching Friday night football with his friends. However, over the past months both Jonathan’s family and his friends had noticed significant alterations in his mood, to the point where Jonathan no longer seemed like himself. He frequently mentioned having headaches and experiencing dizziness, and when he finally experienced what his family thought was a minor seizure in the middle of football practice Jonathan mentioned the changes to his doctor. After the examination of a CT scan Jonathan’s doctor confirmed his diagnosis of a primary brain tumor. After further tests involving the extraction of tumor tissue and its examination under a microscope it was determined that Jonathan was suffering from glioblastoma, characterized by necrosis (dead cells become incorporated in the construction of the tumor) and the increase of blood vessels surrounding the tumor. Gliomas, the most common type of brain cancer, originate in the glial tissue and form in the astrocytes of the brain. Glioblastoma (GBM) is the most common type of glioma, and is currently the most common and deadliest invasive primary brain tumor found in human beings.

Jonathan’s tumor has proliferated quickly due to the high traffic of blood flow in the brain, constantly supporting the proliferation of the cells. Brain tumors are classified on a scale of I to IV, grade I tumors being the least malignant with the longest prognosis, and grade IV being the most aggressive and malignant. Jonathan’s cancer is classified as a grade IV astrocytoma, indicating that it has progressed to form new blood vessels on its own to maintain its rapid growth. Upon hearing that he had the most aggressive grade of cancer, Jonathan was naturally concerned for his future and where this tumor would lead. Unlike many other cancers like melanoma and breast cancer, when brain tumors metastasize they typically spread only to other regions of the brain or spinal cord, metastasizing along the cerebrospinal fluid pathways. Because the proliferating cells creating the tumor arrest before complete differentiation, the cells comprising the cancerous tissue have the plasticity to develop into various types of cells.

__THE TUMOR__
The variation in types of cells that make up glioblastoma is exactly what makes it so difficult to treat with chemotherapy—some cells may respond well to a certain type of chemotherapy while others may be resistant and continue to proliferate. Another difficulty researchers have yet to overcome is finding a drug specific enough to attack the tumor without significant damage to normal cells that is also small enough and/or non-polar enough to pass the blood-brain barrier. Although some drugs have been effective in treating the tumor, no “cure” has yet been found. To treat his cancer Jonathan will undergo brain surgery to remove as much of the cancerous cell mass as possible followed by aggressive chemotherapy and concurrent radiotherapy in an attempt to eradicate the cancerous cells left behind. Glioblastoma cells have the camouflaging effect of looking incredibly similar to normal brain tissue, making it difficult to differentiate healthy cells from cancerous. Like many other tumors, glioblastomas are also cushioned by a “zone of migrating, infiltrating tumor cells that invade surrounding tissues,” rendering it impossible to remove all cancerous cells through surgical removal. These obstacles limit the effectiveness of surgery, leaving more cancerous cells to the complicated process of chemotherapy and radiation. Because of the difficulty in treating these tumors, Jonathan’s prognosis is only about 14 months, with a five-year survival likelihood of 10 percent. Although glioblastoma is more common in adults, children tend to show a longer prognosis, with a five-year survival of 25 percent. Having two children of his own Jonathan has also expressed concern for the risk his cancer may pose to his family.

__THE RISKS__
Although he has no known relatives who have suffered from primary brain tumors, he is understandably concerned for any heritability that could impact his children or suggest susceptibility to a similar disease. Luckily for the Doebler family, there does not seem to be a familial link to Jonathan’s cancer. In rare cases glioblastoma can run in families, however in these incidences the tumors typically first occur in childhood. Hereditary brain tumors are typically associated with Turcot’s syndrome, Li-Fraumeni syndrome, and neurofibromatosis, inherited conditions that promote the formation of polyps and include a high risk of brain tumor formation. Researchers are also exploring various potential environmental factors that could influence brain tumor formation; however, exposure to ionizing radiation is currently the only known, non-genetic risk factor for glioblastoma. This most commonly impacts children treated with ionizing radiation as therapy for leukemia, which can then yield tumor growth in the brain. As Jonathan was neither exposed to ionizing radiation nor does his family show any history of the high-risk diseases, the cause of his cancer is currently unknown.

__THE FUTURE __
Jonathan’s diagnosis has come as a debilitating shock to his family, who now likely have less than two years to spend with him. Now a part of the community of those with brain cancer, Jonathan has contacted other patients suffering from gliomas; through this contact he has learned that he represents the average glioblastoma patient. The cancer primarily affects males, is diagnosed most often in old age, and is most common in Caucasians and Asians. Because so little is currently known about the cause of glioblastoma and most of the drugs currently being used as treatment have not been improved in about 30 years, many clinical trials are being run in an attempt to improve the prognosis of glioblastoma patients. In an effort to help promote brain tumor research and hopefully find better drugs and cures for the future, Jonathan has decided to contribute what he can, and volunteer to participate in clinical trials.

**__ The Next Steps __**
The next step for Jonathan Doebler is his search for treatment. Unfortunately, no contemporary treatments are curative, however they have been shown to extend the life expectancy of patients significantly. The typical standard of care for a glioblastoma patient is generally the same for most patients under the age of 70: resection followed by radiation therapy and chemotherapy. In patients over the age of 70 more emphasis is placed on radiation due to the increased potential health risks involved in surgery, however Mr. Doebler, at age 50, will receive the average standard of care.

__SURGERY __ The surgical aspect of GBM treatment is widely accepted as the most critical (and highly perilous) aspect of treatment. The malignant tumor cells invade healthy, surrounding, essential brain cells, rendering complete removal of the cancerous cells impossible without removing vital brain matter. Another basic concern regarding resection is the location of the tumor. Jonathan’s tumor is located in the frontal lobe of the left hemisphere of his brain, dangerously close to Broca’s area, which is responsible for speech production. This proximity makes surgical removal of the tumor even more hazardous, as the removal of this tissue will likely cause drastic changes in his quality of life, including the potential for perioperative motor deficits and language deficits. Therefore, Jonathan will undergo an awake craniotomy, coupled with an intraoperative MRI and functional brain mapping. During this procedure Jonathan will be kept alert as the health care professionals constantly interact with him to ensure coherency and avoid the loss of essential brain matter. Using a grid electrode, Jonathan’s surgeon will electrically stimulate various areas of his brain, recording the location of essential brain structures to avoid throughout the surgery. Jonathan’s neurosurgeon will strive for gross total resection, attempting to remove as much of the tumor as possible. Because of the critical surrounding tissue, this removal will be a difficult feat, raising the question: how much of Jonathan’s tumor needs to be removed in order to improve his prognosis? Recent retrospective studies of glioblastoma patients have shown that for surgery to yield prolonged life, at least 70% of the tumor must be removed. These studies show that more tumor mass removal generally equates to a longer life expectancy, increasing from about 6 months without surgical removal to 12-14 months following a successful resection.

__CHEMOTHERAPY __ After his surgery Jonathan will receive concurrent treatments of chemotherapy and radiation. The most commonly administered drug for chemotherapeutic treatment of is temozolomide, which Jonathan’s doctor has prescribed. This recently discovered drug disrupts cancer cell proliferation by methylating One of the most common complexities in treating brain tumors is getting chemotherapeutic drugs across the blood-brain barrier. Jonathan’s glioblastoma, a high-grade glioma, has begun to physically damage his blood-brain barrier, weakening and sometimes destroying the previously tight, highly selective junctions. Temozolomide is one of the few drugs that crosses the blood-brain barrier fairly well and achieves high concentration in the cerebrospinal fluid, making the drug ideal to treat a wide range of tumors. In aggressive gliomas like Jonathans, the drug passes through the already damaged blood-brain barrier more quickly, potentially allowing it to be more effective; however, the research regarding glioblastoma’s degradation of the blood-brain barrier remains experimental and has yet to become fully conclusive. DNA,damaging DNA to the extent that DNA repair proteins no longer determine that repair is more efficient than death. Tumor cells, sensing this extensive DNAdamage, trigger apoptosis (programmed cell death), preventing the growth of the malignant cells. The effectiveness of temozolomide directly correlates to the presence of // MGMT //, a gene that yields a protein responsible for repairing this DNA damage. Epigenetic silencing of the // MGMT // gene reduces DNA repair activity, leaving the cells more susceptible to cytotoxicity and apoptosis as a result of temozolomide. Jonathan will take temozolomide daily, and will continue to doso after his radiation therapy if deemednecessary by his doctor. Frequent checkups will be necessary to monitor Jonathan’s progress with temozolomide, as some of the many side effects include convulsions, muscle weakness or paralysis on one side of the body, and amnesia. By watching for these warning signs his oncologist will be able to monitor any excessively detrimental effects the drug may have.

__RADIATION __ Adjuvant radiation therapy has been cited as the best method of improving prognosis after surgical resection. The standard of care dictates 6 weeks of external beam radiation 5 times a week in conjunction with chemotherapy. Immediately following his surgery Jonathan will receive external beam radiotherapy 5 days per week for 6 weeks, receiving 200cGy per day for a total of 6000cGy. His doctor will closely regiment this administration, potentially reducing his dose as total dosages exceeding 5400cGy have shown no survival benefit. Radiation therapy not only improves survival, but has also proven beneficial in controlling seizures. Because Jonathan’s seizure alerted his family to his condition and his seizures have continued, he will begin radiation therapy as soon as possible following his resection. The standard of care overall (resection followed by radiation and chemotherapy) is highly effective in prolonging life if given correctly. For example, radiation coupled with chemotherapy yields a life expectancy 1.2x that of radiation alone. For this reason, and due to the extent of increased life expectancy in patients who undergo resection, the vast majority of doctors prescribe the standard of care for patients who are not of an advanced age.

__FOLLOW UP __ After performing an MRI, Jonathan’s doctors proceeded with his surgery. Following a fairly successful resection removing about 80% of his tumor, Jonathan began his radiation therapy and concomitant temozolomide treatment. He remains optimistic, as he has been responding well to therapy thus far. After a study of Jonathan’s tissue, his doctors discovered that his tumor contains //MGMT// with a methylated promoter, which prevents the //MGMT// gene from actively repairing the DNA that temozolomide seeks to damage. Because of this genetic advantage the concurrent radiotherapy/chemotherapy came highly recommended for Jonathan, and he has greatly benefited from his treatment, however he still wishes to participate in clinical trials. Jonathan has thoroughly researched trials for which he is eligible to participate, and has decided to apply for a study testing anti-EGFR drugs (specifically ABT-414) which have recently become increasingly promising. Three months after finishing his radiotherapy Jonathan will be eligible to participate in this study, as he has not received any EGFR targeted agents that would prevent him from doing so. A central assessment confirmed the presence of EGFR amplification in his tumor cells making him an ideal participant, as he is over the age of 18 and otherwise a standard glioblastoma patient. This study intends to examine the efficacy and safety of ABT-414 alone or with temozolomide versus temozolomide or lomustine (another known chemotherapy known to target brain tumors) alone. As treatment Jonathan will receive lomustine, temozolomide, ABT-414, or ABT-414 and temozolomide. His progress will be closely monitored for improvement or relapse, and will hopefully benefit glioblastoma research and the prognosis of those diagnosed in the future.

**__Molecular Basis__**
 Jonathan Doebler has seen the variety of clinical trials available to treat glioblastoma, but he now seeks to have them explained. In order to understand what drugs and other therapies are attempting to target, he must first understand the molecular basis of his cancer.

__PTEN __  Glioblastoma has various molecular “markers,” one of the most common being a mutation in the PTEN signaling pathway. PTEN is a tumor suppressor gene that, when fully functional, suppresses PI3K, a kinase that phosphorylates Akt, signaling a transduction cascade that yields cell proliferation. When PTEN is mutated, the PI3K pathway goes unchecked, leaving Akt constitutively active, permitting cells to proliferate without restraint, contributing to the growth of a tumor. Although Akt has proven difficult to target, a downstream kinase (mTOR/FRAP kinase) has been targeted by an immunosuppressant drug, rapamycin. Researchers hope that by deactivating a component of this pathway, rapamycin will make up for the loss of PTEN by impairing Akt's sustained proliferative cell signaling.

 __TP53 __  Aiding (or, more accurately, failing to prevent) this sustained proliferative cell signaling is, most commonly in glioblastoma along with many other cancers, a mutation of the TP53 gene. TP53 is another tumor suppressor gene responsible for preventing entry into the cell cycle if it senses damaged DNA. A loss of function mutation in TP53 prevents these checkpoints, allowing damaged, cancerous DNA to proceed through the cell cycle and to reproduce and drastically worsening prognosis.

 __Δ ____EGFR AND ABT-414 __  Although mutated tumor suppressor genes are critical for tumor growth, recent studies have brought new mutations to light that seek to explain how the cells sustain their proliferative signaling. The clinical study for which Jonathan has applied tests a drug (ABT-414) that targets ΔEGFR, a growth factor receptor with a deletion mutation. The deletion in ΔEGFR incurs the loss of exons 2-7, creating a mutation in the receptor’s binding site. Although the mutant receptor is rendered unable to bind to any known ligand, it exhibits, “low –level constitutive signaling that is augmented by reduced internalization and downregulation.” <span style="font-family: 'Times New Roman',serif; font-size: 10pt; line-height: 1.5;"> Interestingly, the pathway most commonly constitutively activated by this aberrant receptor is the PI3K/Akt pathway, making ΔEGFR a dangerous mutation to have in conjunction with PTEN mutation, as the mutated PTEN fails to prevent this sustained proliferation <span style="font-family: 'Times New Roman',serif; font-size: 10pt; line-height: 1.5;">. ΔEGFR is almost exclusively found in glioblastomas <span style="font-family: 'Times New Roman',serif; font-size: 10pt; line-height: 1.5;"> and not only results in sustained proliferative cell signaling, but also causes the hyperphosphorylation of Rb <span style="font-family: 'Times New Roman',serif; font-size: 10pt; line-height: 1.5;">. This hyperphosphorylation prevents Rb from suppressing tumor growth, another mechanism that leads to unchecked cell proliferation. Jonathan’s treatment, ABT-414, is a monoclonal antibody drug conjugate whose light chains specifically target the abnormal exon 1/exon 8 junction sequence characteristic of ΔEGFR, yielding more specificity for the drug and thus sparing normal cells <span style="font-family: 'Times New Roman',serif; font-size: 10pt; line-height: 1.5;">. As a combination drug, ABT-414 combines a chemotherapy drug with this antibody, in theory delivering a cytotoxic chemical to cells with ΔEGFR only.

<span style="font-family: 'Times New Roman',serif; font-size: 10pt; line-height: 1.5;"> Monoclonal antibodies are synthetically made molecules that are designed to imitate naturally made antibodies made by the body as an immune system response to foreign invaders. The specificity is designed to target the undesirable cells, preventing normal cells from being damaged as a result of the treatment. The “light chain” of a monoclonal antibody is the small polypeptide subunit that creates this specificity, and can be engineered to target desired receptors/cells.

<span style="font-family: 'Times New Roman',serif; font-size: 10pt; line-height: 1.5;"> __<span style="font-family: Arial,Helvetica,sans-serif; font-size: 14.3000001907349px; line-height: 1.5;">TERT __ <span style="font-family: 'Times New Roman',serif; font-size: 10pt; line-height: 1.5;"> Another important mechanism playing a role in Jonathan’s tumor maintenance is a mutation that enables replicative immortality. A single point mutation in the promoter of Jonathan's TERT (telomerase reverse transcriptase) gene causes his cells to overexpress telomerase, a protein that adds telomeres to the ends of chromosomes to avoid replication error. The severity of GBM tumors is so positively correlated to this mutation of the TERT promoter that TERT mutation is now being used in the classification and prognostication of malignant gliomas.

<span style="font-family: 'Times New Roman',serif; font-size: 10pt; line-height: 1.5;"> __<span style="font-family: Arial,Helvetica,sans-serif; font-size: 14.3000001907349px; line-height: 1.5;">CHROMOSOME 10q __ <span style="font-family: 'Times New Roman',serif; font-size: 10pt; line-height: 1.5;"> While mutations in TP53, EGFR, and telomerase transcriptase genes are fairly common in most cancers, recent research into primary glioblastomas like Jonathans has pointed to a new culprit: chromosome 10q. 60-80% of all primary glioblastomas experience loss of heterozygosity at this position, and it is not uncommon in primary glioblastomas to see the entirety of chromosome 10 deleted. Because 10q aberrations are so common in primary glioblastomas and are frequently associated with the progression of a tumor from low grade astrocytoma to aggressive glioblastoma, it is likely chromosome 10 is the location of one or more significant tumor suppressor genes that, when mutated or lost, contribute to tumor pathogenesis. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 14.3000001907349px; line-height: 1.5;"> <span style="font-family: 'Times New Roman',serif; font-size: 10pt; line-height: 1.5;"> __<span style="font-family: Arial,Helvetica,sans-serif; font-size: 14.3000001907349px; line-height: 1.5;">MGMT __ <span style="font-family: 'Times New Roman',serif; font-size: 10pt; line-height: 1.5;"><span style="font-family: 'Times New Roman',Times,serif;">Although many molecular aberrations have been discovered in conjunction with glioblastoma, one of the few whose mutation and effect is relatively well known is the methylation of the MGMT gene, or the O-6-methylguanine-DNA methyltransferase. This gene <span style="font-family: 'Times New Roman',serif; font-size: 10pt; line-height: 1.5;">is most often considered with regard to temozolomide, the drug Jonathan and almost every other glioblastoma patient has been prescribed. Temozolomide functions by alkylating the DNA (specifically by methylating guanine), creating damage that yields double strand breaks when the cell attempts to repair it. Because double strand breaks are so damaging, the cell will then hopefully induce apoptosis. //MGMT// is a gene located on chromosome 10q, that encodes a DNA repair protein that removes the alkyl groups from the exact position of guanine that temozolomide targets--the O6 position. The methylation of his //MGMT// promoters and the subsequent loss of MGMT expression serve as both a blessing and a curse for Jonathan. Because MGMT is a DNA-repair protein, its silencing often results in the failure to repair mutated tumor suppressor genes, promoting the cancer. This can potentially help explain why the loss of chromosome 10 is so highly correlated with tumor growth, as it results in the loss of MGMT. However, expression of MGMT decreases the effectiveness of temozolomide because it fixes the DNA damage that the drug causes, evading apoptosis. Jonathan's lack of MGMT expression may therefore be a significant contributor to his cancer, but it also prevents his chemotherapy from being rendered ineffective.

<span style="font-family: 'Times New Roman',serif; font-size: 10pt; line-height: 1.5;"> Now with a better understanding of the mechanisms of his cancer, Jonathan has approached his cancer with a stronger will to take charge of his treatment. He keeps an open dialogue with his doctor, investigating any potential new therapies that may prove effective for him, and staying aware of the studies and research occurring on glioblastoma patients. Although his prognosis is poor, Jonathan has taken charge of his life in a positive and forward-thinking manner.

**__ Follow up __**
Jonathan Doebler has now taken all of the standard medical routes to combat his cancer, but is unwilling to passively accept his terrifyingly poor prognosis. Therefore, with his new knowledge of how his cancer is proliferating, Jonathan has decided to take control of his cancer, exploring supplemental medications to help combat his tumor. For any glioblastoma patient, a willingness to take control and challenge one's oncologist is essential to an improved prognosis, as the medical system uniformly prescribes every patient the same standard of care regardless of their individual needs. This standard of care has already proven ineffective through its life expectancy of less than 16 months. Although a daunting diagnosis, glioblastoma is a disease best to be contended with by a patient with an optimistic outlook, a strong sense of will, and a sense of creativity willing to wade through and take on a challenging frontier of varying but promising therapies.