EpiAxis has completed a pioneering proof of concept (POC) clinical trial known as EPI-PRIMED. In this study, we explored epigenetic removal of aggressive cellular phenotypes via inhibition of LSD1 as a strategy to restore the non-aggressive and non-proliferative cells.
In this POC study, phenelzine sulfate, a monoamine oxidase inhibitor, traditionally used for psychiatric indications, was used as to provide LSD1 inhibition and administered in combination with nanoparticle albumin bound paclitaxel (Abraxane® – nab-paclitaxel). The patient population selected was advanced MBC including triple negative breast cancer (TNBC).
It was hypothesized that treatment with nab-paclitaxel and phenelzine would result in a phenotypic change in the circulating tumor cell (CTC) burden with decreased expression of the aggressive cell surface vimentin (CSV), epidermal growth factor receptor (EGFR), FOXQ1, LSD1, programmed death-ligand 1 (PD-L1) and Snail Family Transcriptional Repressor 1 (SNAI1) biomarkers, together with a corresponding increase in histone methylation markers (H3k9me2 and H3k4me2), reflecting LSD1 inhibition. Secondly, it was hypothesized that removal of these aggressive phenotypes would substantially lower the number of CTCs, as their sensitivity to chemotherapy would have been increased.
The study was designed to have up to 16 participants allocated to 4 dose levels of phenelzine: 45 mg/day, 60 mg/day, 75 mg/day and 90 mg/day in combination with a weekly dose of IV nab-paclitaxel (100 mg/m2). However, the study was terminated after 8 participants had enrolled following an interim analysis of the biomarker data.
That analysis showed early achievement of one of the study’s clinical endpoints, being an Optimal Biological Dose (OBD), which was associated with a meaningful change in the EMT phenotypic index, indicative of mesenchymal reversal, was achieved.
Inhibition of LSD1
LSD1 inhibition in the EPI-PRIMED clinical trial was assessed by nuclear and cytoplasmic immunofluorescence studies, and indicates that both the 45mg and 60mg phenelzine doses provided rapid and significant reductions in both nuclear and cytoplasmic LSD1 through the trial. An implication of these data is that, following initial depletion, long term nuclear LSD1 suppression could be achieved via use of a maintenance dose.
Interestingly, the extent of the observed LSD1 inhibition with the 60 mg phenelzine dose (together with encouraging LSD1 inhibition and biomarker changes) which contributed to the early termination of the study is illustrated below:
Percentage reduction in Nuclear LSD1 Fluorescence (Mean +/- SEM) by visit
Safety, efficacy and bioMarker Data
The data are limited to 8 participants, however, the results are encouraging and include:
>> The combination of phenelzine and nab-paclitaxel was generally well tolerated;
>> The safety profile was consistent with the known side effects of both therapies;
>> The doses of phenelzine used achieved significant reductions in LSD1 inhibition;
>> As the majority of the enrolled participants did not have measurable lesions at baseline, only 2 participants were assessable for RECIST with 1 having stable disease and 1 progressive disease at the end of the study;
>> Post-trial follow-up (as of November 2020) indicates the majority of participants (62.5%, 5/8) remain alive with an encouraging 13 month median PFS estimate;
>> LSD1 inhibition significantly lowered CSC/CTC burden, PD-L1 expressing tumor cell burden and HER2 expressing tumor cell burden; and
>> Nuclear mesenchymal markers for EGFR, FOXQ1, LSD1 and SNAI1 all significantly declined with LSD1 inhibition over time with corresponding increases in H3K4me2 and H3K9me2 expression.
The results of this novel and pioneering clinical study provide biological “proof of concept” for successful epigenetic reprogramming via use of LSD1 inhibition, and provide a strong rationale for clinical development of the EPI-1xx peptide series.