Phase 1 trial evaluating MRG-106, a synthetic inhibitor of microRNA-155, in patients with cutaneous t-cell lymphoma (CTCL).

7564 Background: MRG-106 is an oligonucleotide inhibitor of miR-155, a microRNA with a strong mechanistic link to CTCL, selected based on its activity in mycosis fungoides (MF) cell lines. The objective of this first-in-human study is to evaluate the safety, tolerability, maximum tolerated dose (MTD), pharmacokinetics (PK), and preliminary efficacy of MRG-106 in MF patients. Methods: This Phase 1 trial employs a dose-escalation design to evaluate either intratumoral (IT, 75 mg/dose) or subcutaneous (SC, ≤ 900 mg/dose) administration of MRG-106. Patients were required to have biopsy-proven stage I-III MF and plaque- or tumor-stage lesions. Results: Fifteen patients (12M/3F, median age 59 years) have been dosed over 1-4 weeks. All patients tolerated the IT or SC administrations well with only minor local injection reactions in 8 patients. Thirteen of 15 patients completed dosing as scheduled. There were no clinically significant MRG-106 related adverse events with the exception of one grade 3 pruritus. The MTD has not yet been reached. In the IT cohort, a reduction of ≥50% in the baseline Composite Assessment of Index Lesion Severity (CAILS) score was observed in the MRG-106 treated lesions in all 4 evaluable patients who completed dosing; such responses were maintained to the End of Study visit (Day 28 or 35). Histological examination of pre- and post-treatment biopsies of the MRG-106-injected lesion from most patients revealed a trend in reduction in neoplastic cell density and depth; 1 patient had a complete loss of the neoplastic infiltrate. Gene expression analysis of the pre- and post-treatment biopsies showed reduction of the PI3K/AKT, JAK/STAT, and NFkB survival pathways and increased cell death consistent with the expected MRG-106 mechanism of action. In the SC cohorts, 3/8 patients had a maximal decrease in their modified Severity-Weighted Assessment Tool (mSWAT) of > 39% indicative of a significant response. One patient at the 900 mg SC dose level had a possible flare of their disease after 3 doses that resolved after 3 weeks. Conclusions: Based on favorable clinical safety, efficacy and PK data, additional patients are being accrued. Updated results will be presented as available. Clinical trial information: NCT02580552.