MGMT-inhibitor in combination with TGF-βRI inhibitor or CDK 4/6 inhibitor increases temozolomide sensitivity in temozolomide-resistant glioblastoma cells

BACKGROUND

Glioblastoma (GB) remains an incurable and deadly brain malignancy that often proves resistant to upfront treatment with temozolomide. Nevertheless, temozolomide remains the most commonly prescribed FDA-approved chemotherapy for GB. The DNA repair protein methylguanine-DNA methyl transferase (MGMT) confers resistance to temozolomide. Unsurprisingly temozolomide-resistant tumors tend to possess elevated MGMT protein levels or lack inhibitory MGMT promotor methylation. In this study, cultured human temozolomide resistance GB (43RG) cells were introduced to the MGMT inhibitor O⁶-benzylguanine combined with temozolomide and either LY2835219 (CDK 4/6 inhibitor) or LY2157299 (TGF-βRI inhibitor) seeking to overcome GB treatment resistance.

METHODS

Treatment effects were assessed using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay, western blot, cell viability, and cell cycle progression.

RESULTS

Our in vitro study demonstrated that sequential treatment of O⁶-Benzylguanine with either LY2385219 or LY2157299-enhanced temozolomide enhanced sensitivity in MGMT+ 43RG cells. Importantly, normal human neurons and astrocytes remained impervious to the drug therapies under these conditions. Furthermore, LY2835219 has additional anti-proliferative effects on cell cycling, including induction of an RB-associated G (1) arrest via suppression of cyclin D-CDK4/6-Rb pathway. LY2157299 enhances anti-tumor effect by disrupting TGF-β-dependent HIF-1α signaling and by activating both Smad and PI3K-AKT pathways towards transcription of S/G2 checkpoints.

CONCLUSION

This study establishes the groundwork for the development of a combinatorial pharmacologic approach by using either LY2385219 or LY2157299 inhibitor plus O⁶-Benzylguanine to augment temozolomide response in temozolomide-resistant GB cells.

15-deoxy-Delta12,14-prostaglandin J2 impairs phosphatidylcholine synthesis and induces nuclear accumulation of thiol-modified cytidylyltransferase

Synthesis of phosphatidylcholine, the major phospholipid of animal cell membranes, requires the key enzyme cytidylyltransferase (CCTalpha). Cysteine sulfhydryls within CCTalpha are needed for full catalytic activity. Here we show that prostaglandin 15-deoxy-Delta12,14-PGJ2 (15d-PGJ2) inactivates CCTalpha by inducing generation of reactive oxidant species and the appearance of a cross-linked CCTalpha dimer in cells. N-Acetyl-l-cysteine reduced oxidative stress, prevented CCTalpha cross-linking, and restored CCT function in 15d-PGJ2-treated cells. 15d-PGJ2 modified critical cysteine residues within CCTalpha as determined by mutagenesis studies and by incorporation of biotin-15d-PGJ2 into CCTalpha. These effects of 15d-PGJ2 were associated with CCTalpha accumulation within the nucleus. The data indicate that bioactive prostanoids significantly impair membrane phospholipid production by promoting cysteine cross-bridging within CCTalpha.

Chronic Pseudomonas aeruginosa infection reduces surfactant levels by inhibiting its biosynthesis

Chronic Pseudomonas aeruginosa infection, as occurs in cystic fibrosis, is associated with decreased surfactant phospholipid levels. To investigate mechanisms, we measured synthesis of dipalmitoylphosphatidylcholine (DPPC), the major surfactant phospholipid. Mice received an agarose bead slurry alone, or were infected with beads containing a clinical mucoid isolate of P. aeruginosa. Bacterial infection after 3 days resulted in a approximately 50% reduction in surfactant DPPC content versus control. These changes in surfactant were associated with co-ordinate reductions in mRNAs and immunoreactive levels for CTP: phosphocholine cytidylyltransferase (CCTalpha), the rate-regulatory enzyme required for DPPC synthesis. P. aeruginosa infection of murine lung epithelia decreased CCTalpha gene transcription without altering mRNA stability and by a mechanism other than release of a soluble extracellular inhibitor. Promoter deletional analysis revealed that P. aeruginosa activates a negative response element from -1019 to -799 bp of the CCTalpha proximal 5'-flanking region. Exposure of cells to a P. aeruginosa mutant strain producing alginate reduced CCTalpha promoter activity, whereas these effects were not observed in strains defective in alginate synthesis. Murine type II cells isolated from P. aeruginosa-infected CCTalpha promoter-beta-galactosidase transgenic mice exhibited significantly reduced CCT and beta-galactosidase enzyme activities versus control. Thus, a mucoid P. aeruginosa strain reduces mRNA synthesis of a key biosynthetic enzyme thereby decreasing levels of surfactant.

Proapoptotic effects of P. aeruginosa involve inhibition of surfactant phosphatidylcholine synthesis

Pseudomonas aeruginosa causes sepsis-induced acute lung injury, a disorder associated with deficiency of surfactant phosphatidylcholine (PtdCho). P. aeruginosa (PA103) utilizes a type III secretion system (TTSS) to induce programmed cell death. Herein, we observed that PA103 reduced alveolar PtdCho levels, resulting in impaired lung biophysical activity, an effect partly attributed to caspase-dependent cleavage of the key PtdCho biosynthetic enzyme, CTP:phosphocholine cytidylyltransferase-alpha (CCTalpha). Expression of recombinant CCTalpha variants harboring point mutations at putative caspase cleavage sites in murine lung epithelia resulted in partial proteolytic resistance of CCTalpha to PA103. Further, caspase-directed CCTalpha degradation, decreased PtdCho levels, and cell death in murine lung epithelia were lessened after exposure of cells to bacterial strains lacking the TTSS gene product, exotoxin U (ExoU), but not ExoT. These observations suggest that during the proapoptotic program driven by P. aeruginosa, deleterious effects on phospholipid metabolism are mediated by a TTSS in concert with caspase activation, resulting in proteolysis of a key surfactant biosynthetic enzyme.

Tarlov cysts: a study of 10 cases with review of the literature

OBJECT

Tarlov or perineurial cysts are lesions of the nerve root most often found in the sacral region. Although there is agreement that asymptomatic Tarlov cysts should be followed, it is still debated whether patients with symptomatic Tarlov cysts should be treated surgically. The authors assessed the outcome and efficacy of cyst wall resection in 10 patients with symptomatic Tarlov cysts. The medical literature is reviewed, theories of origin are evaluated, and suggestions as to their cause and pathogenesis are offered.

METHODS

Ten consecutive patients harboring symptomatic Tarlov cysts were treated by the senior author between 1989 and 1999. All patients were assessed for neurological deficits and pain by neurological examination and visual analog scale, respectively. Computerized tomography myelography was performed in all patients to diagnose delayed filling of the cysts. A sacral laminectomy with resection of the sacral cyst or cysts was performed in all patients. Resected material from eight of 10 patients was submitted for histopathological evaluation. Seven (70%) of 10 patients obtained complete or substantial resolution of their symptoms, with an average follow up of 31.7 months. All of these patients had Tarlov cysts larger than 1.5 cm in diameter, producing radicular pain or bladder and bowel dysfunction. Three (30%) of 10 patients experienced no significant improvement. All three patients harbored Tarlov cysts smaller than 1.5 cm in diameter, producing nonradicular pain. Histopathological examination was performed on specimens from eight of 10 patients, which demonstrated nerve fibers in 75% of cases, ganglion cells in 25% of cases, and evidence of old hemorrhage in half.

CONCLUSIONS

Large cysts (> 1.5 cm) and the presence of associated radicular symptoms strongly correlate with excellent outcome. Tarlov cysts may result from increased hydrostatic pressure and trauma.

Intraoperative computed tomography for complex craniocervical operations and spinal tumor resections

OBJECTIVE

To improve intraoperative observation of unexposed anatomic features and to verify surgical correction, a mobile computed tomographic (CT) scanner has been introduced into the operating room. To date, intraoperative CT scanning has been used predominantly for intracranial procedures. We report on the expanded use of intraoperative CT scanning for spinal surgery, because CT scanning provides excellent observation of osseous pathological features. We report on our first 17 cases, which involved complex craniocervical operations and spinal tumor resections.

METHODS

The Tomoscan M CT scanner (Philips Medical Systems, Eindhoven, The Netherlands) is mobile and consists of a translatable gantry, a translatable table, and an operator's workstation. In the operating room, the patient is placed on the CT table and prepared in the usual manner. The aperture of the gantry is covered with sterile plastic drapes. The gantry is docked to the table for intraoperative CT scanning as needed for navigation and verification during surgery. Each series of scans requires approximately 15 to 20 minutes.

RESULTS

Our initial experience with neurosurgical spinal cases demonstrated that the use of intraoperative CT scanning changed the course of surgery in 6 of 17 cases. CT scanning was beneficial in facilitating adequate ventral clival and craniocervical decompressions, promoting more complete tumor resections, and verifying correct graft and instrument placement before surgical closing. Other settings in which we have found the mobile CT scanner useful include the neurointerventional suite and the intensive care unit; it is also useful for radiotherapy planning.

CONCLUSION

On the basis of findings for our first 17 spinal surgery cases, we conclude that intraoperative CT scanning of the spine is both feasible and beneficial for select complex spinal procedures from the craniocervical junction to the sacrum.

Lateral exit-zone stenosis and lumbar radiculopathy

OBJECT

Hypertrophy of the superior facet of the inferior vertebra, resulting in a compression of the nerve root at the lateral foraminal exit, is a recognized cause of radicular symptoms, particularly in patients in whom previous lumbar spine surgery has failed. The lesion-specific presenting symptoms, imaging findings, and surgical treatment of this lesion, however, have received little attention. The authors prospectively studied a series of eight consecutive patients, in whom a diagnosis of lumbar stenosis at the lateral foraminal exit had been made, to elucidate the common presenting signs and symptoms of this disorder, as well as to evaluate the success of the operative treatment.

METHODS

The eight patients were selected from a group of 250 consecutive patients who presented to a tertiary-care hospital and in whom a diagnosis of long-standing lumbar radiculopathy had been made. In all cases the diagnosis was confirmed by imaging studies and by intraoperative findings. The authors performed decompressive procedures on the nerve root via a medial facet-sparing approach.

CONCLUSIONS

The authors conclude that this lesion presents with characteristic physical findings and on imaging studies that distinguish it from other causes of radiculopathy, and they propose a lesion-specific, facet-sparing surgical technique that has yielded excellent results.

Spondyloptotic fracture of the cervical spine in a pregnant, anemic Jehovah's Witness: technical and ethical considerations. Case report

The authors present the case of a 15-year-old Jehovah's Witness with a hematocrit level of 19% who was 4 months pregnant and had a two-level spondyloptotic cervical spine fracture. The patient was transferred to Georgetown University Medical Center with C-5 quadriplegia 3 weeks after having been injured in an automobile collision. The neurosurgical issues in this case included addressing a rare cervical spine injury, assessing and treating a vertebral artery injury, and performing surgery on a pregnant minor with severe anemia who held strong Jehovah's Witness beliefs. An ethics consultation was convened to determine the validity of a pregnant minor's refusal to undergo transfusion on the grounds of her religious beliefs. This case illustrates the potential benefits of thorough technical and ethical evaluations and reveals how they may contribute to the delivery of care in complex neurosurgical cases. To the authors' knowledge, this is the first two-level spondyloptotic cervical spine fracture dislocation to be reported in the literature. The added complexities of the case, given that the patient was an anemic, adolescent, pregnant Jehovah's Witness who refused blood transfusion, also appear to be unprecedented.

Neuropathology of the brainstem and spinal cord in end stage rheumatoid arthritis: implications for treatment

OBJECTIVE

To study the detailed histopathological changes in the brainstem and spinal cord in nine patients with severe end stage rheumatoid arthritis, all with clinical myelopathy and craniocervical compression.

METHODS

At necropsy the sites of bony pathology were related exactly to cord segments and histological changes, and correlated with clinical and radiological findings.

RESULTS

Cranial nerve and brainstem pathology was rare. In addition to the obvious craniocervical compression, there were widespread subaxial changes in the spinal cord. Pathology was localised primarily to the dorsal white matter and there was no evidence of vasculitis or ischaemic changes.

CONCLUSIONS

Myelopathy in rheumatoid arthritis is probably caused by the effects of compression, stretch, and movement, not ischaemia. The additional subaxial compression may be an important component in the clinical picture, and may explain why craniocervical decompression alone may not alleviate neurological signs.

Spinal cord oedema due to venous stasis

Venous hypertension and stagnant hypoxia in the human spinal cord are poorly understood. We report a case in which a partial Brown-Séquard syndrome resulted from obstruction of venous drainage on one side of the spinal cord. Neurological deterioration and eventual recovery paralleled the formation and clearance of oedema. The clinical and MRI findings support the contention that spinal cord injury arising as a result of obstruction to venous outflow occurs primarily in the white matter, spreading secondarily to the grey matter, and observations that obstruction of venous flow in the high cervical spinal cord results in changes in the lower cervical cord.