Biotech Values

[poorgradstudent]

HepC / NS5A paper:

>3. They then did some SAR analysis which enabled them to find a much more potent compound to which the above resistant cell lines were also resistant.

4. They then analyzed where the HCV had mutated so as to become resistant to both these compounds, and this analysis together with the structure of the two compounds revealed that NS5A was their mutual target.
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From my reading, you're accurate with #3 but out of sequence. They found one parent compound (BMS 858), and then used it as a basis for additional chemical modifications to improve bioavailability and symmetry (reasoned from a referenced publication). This compound following structural refinement became BMS-790052. It is actually the final form of the compound, and the one that they used to make resistant lines.

For #4, they found mutations that conferred resistance to BMS-790052 (judged as allowing growth at 20x normal EC50), and then observed that for most of those resistant phenotypes, the new EC50 was still below the plasma levels of the drug in vivo. Also, in many cases, they observed that the discovered mutations reduced the fitness of the virus to the point where they don't really proliferate in vivo with those mutations anyways.

It's also my understanding from reading the paper that they figured out rather early that NS5a was the target. The surprise was as you suggest: NS5A doesn't really have a catalytic activity and is therefore not a classic target for "inhibition", but that it appears the inhibitor that they've designed and characterized interrupts dimer formation by NS5A that is crucial to its role in RNA replication. In that sense, they used the NS5A point mutations that conferred resistance to BMS-790052 as a means to map where the inhibitor was binding (ie. figure out its mode of action) rather than using them as clues to reformulate the compound into a more potent form.