On June 19, 2016, Epizyme Inc (NASDAQ:EPZM) presented a study update from its ongoing phase II trial in its lead oncology candidate, Tazemetostat.
The Science
Tazemetostat is an oral administration oncology candidate that is part of a family of drugs called small molecule EZH2 inhibitors. The science behind this one seems a little counterintuitive at first glance, but stick with us. EZH2 is involved in cell reproduction and proliferation. At its core, it helps cells to divide. It’s also a transcription suppressor in many cases, however. This means it turns off the genes associated with transcription, which is the core process that underlies cell reproduction.
All this sounds good, right? Well, not exactly. It doesn’t act directly on cancer cells, so the benefit associated with what might otherwise be a suppressing of cancer cell reproduction doesn’t come from EZH2 expression. Instead, an overexpression of EZH2 leads to a suppressing of the genes that would normally, in turn, suppress cancer cell reproduction. This suppression leads to what is essentially uninhibited reproduction of solid tumor cells. This is where Tazemetostat comes in. The drug inhibits EZH2, which in turn, stops it from having the suppressive impact on the genes that are normally responsible for tumor cell suppression. This leaves the latter free to suppress tumor cells (and in turn, inhibit proliferation). Or at least, that’s the theory.
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The Data
So far there has been relatively little data to support this hypothesis – that is, directly related to Tazemetostat as opposed to the EZH2 inhibition concept – aside from a bit of preclinical study and a safety and proof of concept phase I. The concept itself, however, is pretty well supported by outside investigation, so the Epizyme trials are far from a complete stab in the dark. The latest data detailed study enrollment, safety and a look at clinical activity in the patient populations that have surpassed what is called their futility hurdle. Futility hurdle here just relates to some predetermined impact criteria. In this instance, this criterion is defined by seeing at least one objective response in the first ten patients enrolled, across two diffuse large B-cell lymphoma (DLBCL) arms.
So essentially, we’re looking for a confirmation of the meeting of this futility hurdle (we’ve already had some indication it’s been met) and, beyond that, a suggestion that there is some clinical impact on the progression of the DLBCL solid tumors in patients.
How did the data perform against these expectations? Well, across four separate patient groups, Tazemetostat showed a response in each group. Of 47 patients studied, the drug translated to a partial response in nine, a complete response in four and a stabilization (just meaning the cancer didn’t progress) in thirteen. This is a decent outcome, but not perfect for Epizyme. Yes, a complete and a partial response in any number of patients is good. but the company would have been hoping for a slightly higher response rate. That said, the data warrants a continuation, and from a hurdle perspective, we can consider this one cleared – barely, but cleared.
