Raquel Luque

Temozolomide (TMZ), an oral alkylating prodrug which delivers a methyl group to purine bases of DNA (O6-guanine; N7-guanine and N3-adenine), is frequently used together with radiotherapy as part of the first-line treatment of high-grade gliomas. The main advantages are its high oral bioavailability (almost 100% although the concentration found in the cerebrospinal fluid was approximately 20% of the plasma concentration of TMZ), its lipophilic properties, and small size that confer the ability to cross the blood-brain barrier. Furthermore, this agent has demonstrated activity not only in brain tumors but also in a variety of solid tumors. However, conventional therapy using surgery, radiation, and TMZ in glioblastoma results in a median patient survival of 14.6 months. Treatment failure has been associated with tumor drug resistance. This phenomenon has been linked to the expression of O6-methylguanine-DNA methyltransferase, but the mismatch repair system and the presence of cancer stem-like cells in tumors have also been related to TMZ resistance. The understanding of these mechanisms is essential for the development of new therapeutic strategies in the clinical use of TMZ, including the use of nanomaterial delivery systems and the association with other chemotherapy agents. The aim of this review is to summarize the resistance mechanisms of TMZ and the current advances to improve its clinical use.

BACKGROUND: Standard treatment for glioblastoma is radiation with concomitant and adjuvant temozolomide for 6 cycles, although the optimal number of cycles of adjuvant temozolomide has long been a subject of debate. We performed a phase II randomized trial investigating whether extending adjuvant temozolomide for more than 6 cycles improved outcome. METHODS: Glioblastoma patients treated at 20 Spanish hospitals who had not progressed after 6 cycles of adjuvant temozolomide were centrally randomized to stop (control arm) or continue (experimental arm) temozolomide up to a total of 12 cycles at the same doses they were receiving in cycle 6. Patients were stratified by MGMT methylation and measurable disease. The primary endpoint was differences in 6-month progression-free survival (PFS). Secondary endpoints were PFS, overall survival (OS), and safety (Clinicaltrials.gov NCT02209948). RESULTS: From August 2014 to November 2018, 166 patients were screened, 7 of whom were ineligible. Seventy-nine patients were included in the stop arm and 80 in the experimental arm. All patients were included in the analyses of outcomes and of safety. There were no differences in 6-month PFS (control 55.7%; experimental 61.3%), PFS, or OS between arms. MGMT methylation and absence of measurable disease were independent factors of better outcome. Patients in the experimental arm had more lymphopenia (P < 0.001), thrombocytopenia (P < 0.001), and nausea and vomiting (P = 0.001). CONCLUSIONS: Continuing temozolomide after 6 adjuvant cycles is associated with greater toxicity but confers no additional benefit in 6-month PFS. KEY POINTS: 1. Extending adjuvant temozolomide to 12 cycles did not improve 6-month PFS.2. Extending adjuvant temozolomide did not improve PFS or OS in any patient subset.3. Extending adjuvant temozolomide was linked to increased toxicities.

Circulating biomarkers in blood may provide an interesting alternative to risky tissue biopsies in the diagnosis and follow-up of glioblastoma patients. We have assessed MGMT methylation status in blood and tissue samples from unresected glioblastoma patients who had been included in the randomized GENOM-009 trial. Paired blood and tissue samples were assessed by methylation-specific PCR (MSP) and pyrosequencing (PYR). After establishing the minimum PYR cut-off that could yield a significant difference in overall survival, we assessed the sensitivity, specificity, positive predictive value and negative predictive value (NPV) of the analyses. Methylation could be detected in cfDNA by both MSP and PYR but with low concordance with results in tissue. Sensitivity was low for both methods (31% and 38%, respectively), while specificity was higher for MSP in blood than for PYR in plasma (96% vs 76%) and NPV was similar (56 vs 57%). Concordance of results in tissue by MSP and PYR was 84.3% (P < 0.001) and correlated with outcome. We conclude that detection of cfDNA in the blood of glioblastoma patients can be an alternative when tumor tissue is not available but methods for the detection of cfDNA in blood must improve before it can replace analysis in tumor tissue.

BACKGROUND: Based on the TROPIC study results, cabazitaxel was approved for the management of metastatic castration-resistant prostate cancer (mCRPC) progressing on or after docetaxel. METHODS: This multi-centre program provided early access to cabazitaxel to patients with mCRPC before its commercialization. Safety data from 153 Spanish patients receiving cabazitaxel 25 mg/m(2) i.v. Q3W, plus oral prednisone/prednisolone 10 mg daily, are reported. RESULTS: Median age of patients was 70 years (26.8% ≥ 75 years), 94.1 and 26.8% had bone and visceral metastasis, respectively. Most had an Eastern Cooperative Oncology Group ≤ 1 (88.9%) and had received a median of 8.0 cycles of last docetaxel treatment. The median of cabazitaxel cycles and cumulative dose were 6.0 (Interquartile range [IQR]: 4.0; 8.0) and 148.9 (IQR: 98.2; 201.4) mg/m(2), respectively. Adverse events (AEs) possibly related to cabazitaxel occurred in 143 (93.5%) patients. The most frequent grade ≥ 3 AEs were neutropenia (n = 25, 16.3%) and asthenia (n = 17, 11.1%). Febrile neutropenia and grade ≥ 3 diarrhea occurred in 5.2% of the patients each. There were five (3.3%) possibly treatment-related deaths, mainly infection-related. G-CSFs were used in 114 (74.5%) patients, generally as prophylaxis (n = 107; 69.9%). Grade ≥ 3 peripheral neuropathy and nail disorders were uncommon. CONCLUSIONS: Cabazitaxel administration, in a real-world setting, is tolerated by Spanish patients with mCRPC, and the AEs are manageable.