Modulators of ATP-binding cassette transporters

1. A kit for use in measuring the activity of CFTR in a biological sample in vitro or in vivo, comprising:

(i) a compound of formula (I):

or a pharmaceutically acceptable salt thereof,

wherein:

Each R 1 is an optionally substituted C 1-6 aliphatic, an optionally substituted aryl, an optionally substituted heteroaryl, an optionally substituted C 3-10 cycloaliphatic, an optionally substituted 3 to 10 membered heterocycloaliphatic, carboxy, amido, amino, halo, or hydroxy, provided that at least one R 1 is an optionally substituted cycloaliphatic, an optionally substituted heterocycloaliphatic, an optionally substituted aryl, or an optionally substituted heteroaryl attached to the 5- or 6- position of the pyridyl ring;

Each R 2 is hydrogen, an optionally substituted C 1-6 aliphatic, an optionally substituted C 3-6 cycloaliphatic, an optionally substituted phenyl, or an optionally substituted heteroaryl;

Each R 3 and R′ 3 together with the carbon atom to which they are attached form an optionally substituted C 3-7 cycloaliphatic or an optionally substituted heterocycloaliphatic;

Each R 4 is an optionally substituted aryl or an optionally substituted heteroaryl; and

Each n is 1,2,3 or 4; and

(ii) instructions for:

a) contacting the compound with the biological sample; and

b) measuring activity of said CFTR.

2. The kit according to claim 1 , further comprising instructions for

a) contacting an additional compound with the biological sample;

b) measuring the activity of said CFTR in the presence of said additional compound, and

c) comparing the activity of the CFTR in the presence of the additional compound with the activity of the CFTR in the presence of a compound of formula (I).

3. The kit according to claim 1 wherein the compound of formula (I) is selected from

4. The kit of claim 1 , 2 or 3 , wherein the CFTR is ΔF508 CFTR.

5. The kit of claim 1 , 2 or 3 , wherein the CFTR is G551D CFTR.