Analysis of O6-methylguanine-DNA methyltransferase mRNA in fine needle biopsies from human melanoma metastases by reverse transcription and polymerase chain reaction

Overcoming Resistance to Temozolomide in Glioblastoma: A Scoping Review of Preclinical and Clinical Data

Glioblastoma (GB) is the most common and most aggressive primary brain tumor in adults, with an overall survival almost 14.6 months. Optimal resection followed by combined temozolomide chemotherapy and radiotherapy, also known as Stupp protocol, remains the standard of treatment; nevertheless, resistance to temozolomide, which can be obtained throughout many molecular pathways, is still an unsurpassed obstacle. Several factors influence the efficacy of temozolomide, including the involvement of other DNA repair systems, aberrant signaling pathways, autophagy, epigenetic modifications, microRNAs, and extracellular vesicle production. The blood-brain barrier, which serves as both a physical and biochemical obstacle, the tumor microenvironment's pro-cancerogenic and immunosuppressive nature, and tumor-specific characteristics such as volume and antigen expression, are the subject of ongoing investigation. In this review, preclinical and clinical data about temozolomide resistance acquisition and possible ways to overcome chemoresistance, or to treat gliomas without restoration of chemosensitinity, are evaluated and presented. The objective is to offer a thorough examination of the clinically significant molecular mechanisms and their intricate interrelationships, with the aim of enhancing understanding to combat resistance to TMZ more effectively.

Synergistic effect of cryptotanshinone and temozolomide treatment against human glioblastoma cells

Glioblastoma multiforme (GBM) is a complex disease to treat owing to its profound chemoresistance. Therefore, we evaluated the combined effect and therapeutic efficacy of temozolomide (TMZ), a potent alkylating agent and the current gold standard therapy for GBM, and cryptotanshinone (CTS), which inhibits glioma cell proliferation in GBM cells. Using LN229 and U87-MG human GBM cells in a short-term stimulation in vitro model, the cytotoxic and anti-proliferative effects of single and combined treatment with 4 μM CTS and 200 μM TMZ were investigated. Furthermore, cell viability, DNA damage, apoptosis rate, and signal transducer and activator of transcription 3 (STAT3) protein were measured using cytotoxic assay, comet assay, flow cytometry, and western blotting analysis, respectively. The two drugs' synergistic interaction was validated using the synergy score. We found that the anti-proliferative effects of combination therapy using the two drugs were greater than that of each agent used alone (CTS or TMZ). Western blot analysis indicated that treatment of GBM cells with CTS combined with TMZ more significantly decreased the expression of MGMT and STAT3, than that with TMZ alone. Combined treatment with CTS and TMZ might be an effective option to overcome the chemoresistance of GBM cells in a long-term treatment strategy.

Acquired temozolomide resistance in MGMTlow gliomas is associated with regulation of homologous recombination repair by ROCK2

It was reported that MGMT^low gliomas may still be resistant to TMZ, while the mechanisms remain poorly understood. In this study, we demonstrated that rho-associated kinase 2 (ROCK2), a cytoskeleton regulator, was highly expressed in MGMT^low recurrent gliomas, and its expression strongly correlated with poor overall survival (OS) time in a subset of MGMT^low recurrent gliomas patients with TMZ therapy. And we also found that overactive ROCK2 enhanced homologous recombination repair (HR) in TMZ-resistant (TMZ-R) glioma cell lines with low MGMT expression. Silencing ROCK2 impaired HR repair, and induced double-strand break (DSB) and eradicated TMZ-R glioma cells in culture. Notably, in MGMT^low TMZ-R models, as a key factor of HR, ataxia telangiectasia-mutated (ATM) expression was upregulated directly by hyper-activation of ROCK2 to improve HR efficiency. ROCK2 enhanced the binding of transcription factor zinc finger E-box binding homeobox 1 (ZEB1) to ATM promoter for increasing ATM expression. Moreover, ROCK2 transformed ZEB1 into a gene activator via Yes-associated protein 1 (YAP1). These results provide evidence for the use of ROCK inhibitors in the clinical therapy for MGMT^low TMZ-resistant glioma. Our study also offered novel insights for improving therapeutic management of MGMT^low gliomas.

Analysis of O(6)-methylguanine-DNA methyltransferase in melanoma tumours in patients treated with dacarbazine-based chemotherapy

In a retrospective study we analysed the levels of the DNA repair protein O(6)-methylguanine-DNA methyltransferase (MGMT) in melanoma metastases in patients receiving dacarbazine (DTIC) either as a single drug or as part of combination chemotherapy regimens, and related the expression levels to the clinical response to treatment. Biopsies of subcutaneous and lymph node metastases obtained before chemotherapy in 65 patients with disseminated malignant melanoma were examined for MGMT protein levels by immunohistochemistry using a monoclonal anti-human MGMT antibody. All patients received chemotherapy with DTIC, given either as a single drug or in combination with vindesine and in some cases cisplatin. DTIC as single agent was given to 44 patients, while 21 received combination chemotherapy. Objective responses to chemotherapy were seen in 12 patients, while 53 patients failed to respond to treatment. The expression of MGMT was determined according to the proportion of antibody-stained tumour cells, using a cut-off level of 50%. In 12 of the patients more than one metastasis was analysed, and in seven of these cases the MGMT expression differed between tumours in the same individual. Among the responders a larger proportion (six out of 12, 50%) had tumours containing less than 50% MGMT-positive tumour cells than among the non-responders (12 out of 53, 23%). These data are consistent with the hypothesis that MGMT contributes to resistance to DTIC-based treatment, although the difference between responders and non-responders with respect to the proportion of MGMT-positive tumour cells was not statistically significant (P = 0.077).

Systemic therapy of malignant melanoma

The present status of medical treatment of malignant melanoma is briefly reviewed, both with regard to adjuvant therapy for individuals with high-risk melanoma and a high probability of harbouring subclinical micrometastases, as well as to therapy for established disseminated (macrometastatic) disease. At present, disseminated, macrometastatic melanoma is incurable in the majority of cases. Single agent chemotherapy has modest effects and results in disease remission in a minority of patients, usually of short duration, Combination chemotherapy, or the combination of chemotherapeutic drugs and cytokines, results in increased response rates and occasionally remissions of prolonged duration. So far, no regimen has demonstrated improved survival compared to single agent therapy in disseminated melanoma. New insights into the mechanisms of resistance to chemotherapeutic drugs may lead to development of predictive tests that can identify individuals with tumors sensitive to a specific agent, as well as to the development of strategies to circumvent drug resistance. It has recently been shown that adjuvant therapy of high-risk melanoma with large doses of interferon-alpha 2b significantly prolongs relapse-free and overall survival, at the price of considerable toxicity. Ongoing studies aim to define the optimum dose and duration of adjuvant interferon therapy. Recent advances in molecular biology and immunology may lead to the development of new treatment modalities, such as improved vaccines and other biologic therapies, which may benefit patients with malignant melanoma.