Phase 1 Study of the Safety and Efficacy of MRG-106, a Synthetic Inhibitor of microRNA-155, in CTCL Patients

Introduction & Objectives:

MRG-106 is an oligonucleotide inhibitor of miR-155, a microRNA with a strong mechanistic link to CTCL. The goals of this first-in-human study are to evaluate the safety, tolerability, pharmacokinetics (PK), and preliminary efficacy of MRG-106 in patients with mycosis fungoides (MF).

Methods:

This Ph 1 trial employs a dose-escalation design to evaluate the administration of MRG-106 via subcutaneous (SC) injection, 2-hour intravenous (IV) infusion, or IV rapid bolus injection (≤ 900 mg/dose). An additional cohort received intralesional injections (75 mg/dose) to evaluate tolerability and efficacy with local delivery. Subjects were required to have biopsy-proven MF stage I-III with plaque and/or tumor lesions. Subjects were permitted to remain on concurrent stable CTCL therapy. Subjects received 6 doses (SC/IV) in the first 26 days of the study followed by weekly or bi-weekly doses in patients who continued beyond the first cycle. Safety was monitored by physical exams, clinical laboratory tests, and assessment of adverse events (AEs). Immunophenotyping of peripheral blood was performed to measure the impact of MRG-106 on normal immune cell subsets. The PK properties of MRG-106 were compared between different routes of administration. The effect of MRG-106 on individual skin lesions or total skin disease was assessed by the Composite Assessment of Index Lesion Severity (CAILS) score or the modified Severity Weighted Assessment Tool (mSWAT), respectively.

Biopsies were collected from all subjects treated by intralesional injection and from a subset of subjects in the SC/IV cohorts to assess molecular and cellular responses to MRG-106. Baseline miR-155 expression and changes in gene expression and T cell repertoire (T cell receptor sequencing) in response to MRG-106 treatment were assessed.

Results:

24 subjects (18M/6F, median age 62 yrs) have been in the study for up to 10 months (as of 7/31/2017). 4 subjects received only intralesional doses; 2 subjects were enrolled into both the intralesional and SC cohorts. 18 subjects received only SC injections or IV infusions/bolus injections of MRG-106. 22/26 subjects completed the first treatment cycle per protocol; 2 subjects are on-going. 2 subjects discontinued: one due to progressive disease found shortly after enrollment, and one due to an AE of worsening pruritus (Grade 3), judged as a dose-limiting toxicity at 900 mg SC. The drug was otherwise well-tolerated: of the other 48 drug-related AEs, all were Grade 1 or 2. The MTD has not been reached.

23/24 subjects (95%) showed improvement in either the individually treated lesion (intralesional cohort) or total skin disease (SC/IV cohorts) as measured by maximal change in CAILS or mSWAT.

In the SC/IV-infusion cohorts, 17/18 subjects had an improvement in mSWAT score; 9/18 subjects (50%) reached a PR defined as ≥ 50% reduction in mSWAT score. Of the 9 subjects who received MRG-106 for > 1 cycle, 78% reached a PR, suggesting that longer treatment may provide greater benefit. Improvements in mSWAT scores were observed as early as Study Day 19 (the 1st post-treatment assessment), and for all but one subject, improvements from baseline were maintained through the treatment period.

Based on immunophenotyping of peripheral blood, absolute numbers and proportions of subjects' leukocyte subpopulations were not significantly altered with MRG-106 treatment, with the exception of transient increases in NK and NK T cells observed only at the highest dose. TCR sequencing of pre- and post-treatment biopsies showed that T cell clonality decreased with intralesional injection of MRG-106. miR-155 was elevated in the lesions of most subjects, drug accumulation was observed with all routes of administration, and gene expression changes were associated with inactivation of the STAT, NFκB, and PI3K/AKT pathways.

Conclusions:

These preliminary results suggest that MRG-106 is well-tolerated and has clinical activity as indicated by meaningful reductions in CAILS and mSWAT assessments. Exploratory analyses of lesion biopsies support the clinical activity of MRG-106 with reductions in T cell clonality and gene expression changes consistent with the known mechanism of miR-155. These encouraging data support the continued investigation of MRG-106 in MF patients and expansion of the study to include additional hematological malignancies in which miR-155 is known to be elevated and relevant.