molecule towards AMPK. For example, in a study involving a panel
of 70 human kinases, Compound C was found to inhibit several
other kinases including ERK8, MELK1, MNK1, PHK, DYRK, Src,
Lck, and HIPK1 at similar concentrations as AMPK. At 1μM,
Compound C inhibited about 73% of AMPK activity. At this con-
centration, it inhibited 81% of MNK1 activity; 94% of PHKL
activity; 43% of Aurora kinase C activity; 95% of MELK1 activity;
91%, 88%, and 76% of DYRK3, DYRK1A, and DYRK2 activities,
respectively; 74% of HIPK2; 75% of Src; and 80% of Lck enzymatic
activity [23]. It also inhibited kinase activities of the receptor tyro-
sine kinases FGFR1, Yes and Eph-A2 [23]. These authors sug-
gested that since nearly 40μM Compound C is required for
complete inhibition of AMPK activity in vitro, levels that clearly
impact numerous other kinases, the use of this reagent to examine
AMPK functions is not recommended. In another kinase profiling
study of Compound C against 119 kinases, several kinases includ-
ing many receptor tyrosine kinases were inhibited by Compound
C. The efficiency at which Compound C inhibited AMPK at
10, 1, and 0.1μM was found to be 90%, 50%, and 25%, respectively.
However, at 10μM, it inhibited the activities of 64 out of the
119 kinases by greater than 50%. At 1μM, it inhibited the activities
of 34 out of 119 kinases more potently than it inhibited AMPK
[24]. Some of the kinases that Compound C inhibited similarly or
more effectively than AMPK include MARK3, EPHB3, DYRK3,
FGFR1, MLK3, Src, EPH-B4, EPH-B2, MINK1, HIPK2, IRAK4,
Lck, TES1, PRK2, MELK, NUAK1, CK1, CAMKKβ, ABL, PHK,
DYRK1A, CLK2, GCK, ERK8, RIPK2, and VEGFR. At a hun-
dredfold lower concentration (0.1μM), Compound C inhibited
50% activity of PRK2, YES1, Nuak1, VEGFR, DYRK1, PHK, ABL,
ERK8, CLK2, and GCK. Unfortunately, these data are overlooked,
and often Compound C is used as a reference inhibitor of AMPK,
sometimes at concentrations as high as 40μM. Further complicat-
ing the question of selectivity is the finding by Jester et al. [25], that
Compound C also inhibits luciferase, raising concerns about its use
in assays that are coupled to luciferase.5 Use of Compound C in Cancer
Compound C has been widely used in biochemical, cell-based, and
in vivo assays as a “selective” AMPK inhibitor. The compound
found its greatest use in cancer-related studies given that AMPK
functions downstream of a known tumor suppressor gene called
LKB1. In nearly all of these reports, the biochemical and cellular
effects of compound C have been attributed to its inhibitory action
toward AMPK [26–31]. In the study by Yang et al. [31], 10–30μM
Compound C was used in vitro cell proliferation studies to achieve
inhibition of proliferation of human colon cancer cell lines.198 Biplab Dasgupta and William Seibel