5FU/LV, Irinotecan, Temozolomide and Bevacizumab for MGMT Silenced, Microsatellite Stable Metastatic Colorectal Cancer.

An upfront-intensified treatment combining all the three active cytotoxic agents in mCRC including fluoropyrimidines, oxaliplatin, irinotecan (FOLFOXIRI) plus antiangiogenic blockade with bevacizumab significantly improved progression-free survival (PFS), overall survival (OS) and objective response rate (ORR) compared to standard FOLFIRI and bevacizumab irrespective to RAS/BRAF status, at price of higher rate of specific toxicities. Advantages of an intensified regimen include: 1) exposure to all active available drugs, since more than 10-15% of patients would not receive any second-line therapy due to early performance status deterioration; 2) the chance of achieving a high rate (around 36%) of secondary R0/R1 resection of metastases in patients with liver-limited and initially unresectable liver metastases. Furthermore, results from the phase 3 TRIBE2 study showed that the intensified upfront regimen FOLFOXIRI-bevacizumab followed by the pre-planned reintroduction of the same agents after progressive disease provided a statistically significant and clinically relevant survival benefit when compared with the pre-planned sequential administration of FOLFOX-bevacizumab and FOLFIRI-bevacizumab in unresectable patients with mCRC. Therefore, FOLFOXIRI-bevacizumab regimen is recommended by all major guidelines as one of the possible upfront treatment options for mCRC, and is used in the clinical practice mainly for patients with highly aggressive disease (such as those with right sided and/or RAS or BRAF mutated). Notably, since no biomarkers are available for predicting sensitivity/resistance to single chemotherapeutic drugs, the simultaneous delivery of all active chemotherapeutic agents might overcome resistance to single drugs. MGMT promoter methylation is found in about 40% of colorectal tumors. MGMT deficiency impairs DNA repair following administration of several alkylating agents, including temozolomide. Temozolomide has limited single-agent activity (around 10%) in patients with pretreated MGMT methylated mCRC. Promising activity has been reported for temozolomide in combination with the potentially synergic drug irinotecan (TEMIRI regimen) in clinically and molecularly selected patients. In a recent phase 2 randomized trial, capecitabine in combination with temozolomide (CAPTEM regimen) displayed similar activity and efficacy with respect to standard FOLFIRI as second-line therapy for MGMT methylated RAS mutated mCRC. Heterogeneity of MGMT promoter methylation and residual MGMT protein expression might account for lack of activity of temozolomide in patients with MGMT promoter methylation assessed by means of a qualitative-only assay, i.e. methylation-specific PCR (MSP), which has been used as selection assay for patients' enrollment in published trials. Exploratory analyses have consistently shown the role of quantitative assessment of MGMT promoter methylation by means of digital PCR (methylBEAMing) and MGMT protein expression by immunohistochemistry (IHC) as potential predictive factors in mCRC patients treated with temozolomide. In the randomized phase 2 CAPTEM versus FOLFIRI second-line trial, patients with retained MGMT positivity by IHC had poorer outcomes in terms of PFS, OS and disease control rate (DCR: interaction test with arm: P=0.028). Any residual MGMT protein expression has been associated with lack of response to temozolomide across different trials, further supporting the restriction of temozolomide-based therapies for patients with MGMT IHC negativity coupled with gene methylation (MGMT silencing). Mismatch repair deficiency/microsatellite instability (MSI) has been linked to innate resistance to several alkylating chemotherapeutic agents, including temozolomide, since cytotoxicity of these agents strictly relies on functional mismatch repair. Therefore, patients with MSI-high mCRC are excluded from temozolomide-based therapy. Temozolomide could be regarded as a "targeted" chemotherapy for patients with MSS and MGMT silenced tumors. In this subgroup of patients, an intensified triplet upfront regimen including temozolomide, fluoropyrimidines, irinotecan, associated with bevacizumab, could be a novel combination in molecularly hyperselected mCRC patients. Moving from this rationale the investigators designed this phase 1b trial assessing safety, recommended dose and preliminary activity of 5-fluoruracil, irinotecan, temozolomide and bevacizumab (FLIRT-bevacizumab) as a biomarker-guided initial therapy for patients with MGMT silenced and MSS mCRC. The study will consist in a dose-escalation assessment of the safety of the treatment in subjects with previously untreated MGMT silenced, MSS mCRC. A 3 + 3 design will be used to assess the maximum tolerated dose (MTD) or maximum tested dose of the combination FLIRT-bevacizumab. The MTD will be defined as the dose level at which ≥2/3 or ≥2/6 subjects experience a dose-limiting toxicity (DLT). When the MTD or maximum tested dose has been determined or reached, the RP2D to be tested in a future phase II trial will be one dose level below the MTD or the maximum tested dose if MTD will not be reached. At least 6 patients should be treated at the RD during the dose escalation. The treatment will consist of an induction period of four 28-day cycles of FLIRT- bevacizumab followed by maintenance regimen of 5-FU/LV-bevacizumab administered every 14 days in combination with per os temozolomide according to dose level over days 1-5 every 28 days in patients without progressive disease at the end of the induction period. Patients will undergo tumor assessment at baseline and every 8 ± 1 weeks until confirmed disease progression, unacceptable toxicity, withdrawal of consent, death, whichever occurs first. The treatment will continue until progressive disease, unacceptable toxicities, or consent withdrawal. The phase 1b part of the study has been completed and the RP2D of temozolomide is 150 mg/sqm on days 1-5 every 28 days. The phase 2 part is ongoing.