Data from: Lorcaserin-induced rat mammary mutants quantified by CarcSeq

Lorcaserin, a drug for weight management, is a selective agonist of the
serotonin (5-hydroxytryptamine) 2C receptor. Although lorcaserin is a
non-genotoxic rat carcinogen, FDA approval was granted in part based on
dose extrapolation considerations. A post-marketing study, CAMELLIA-TIMI,
designed to detect potential cardiovascular effects of lorcaserin therapy
detected excess cancer risk in the lorcaserin treatment arm. Consequently,
a study of lorcaserin-treated rats was conducted to elucidate the
mechanism of lorcaserin-induced carcinogenesis and facilitate detection of
other carcinogens operating through the same mechanism in the future.
Another study goal was to characterize CarcSeq utility in detecting the
neoplasia-related effects of a non-genotoxic carcinogen. CarcSeq is an
error-corrected next-generation sequencing method for quantitation of
panels of hotspot cancer driver mutations (CDMs) and can detect mutations
with mutant fractions (MFs) ≥10-4. Female Sprague Dawley rats were treated
by gavage daily with 0, 30, or 100 mg/kg lorcaserin, replicating the tumor
bioassay doses but with shorter duration treatments of 12 or 24 weeks.
Lorcaserin and N-nitroso-lorcaserin were quantified in dosing solutions,
terminal plasma and terminal liver samples using ultra high-performance
liquid chromatography-electrospray tandem mass spectrometry.
N-nitroso-lorcaserin was not detected. Mammary DNAs (n = 6/group) were
used to synthesize PCR products from genes containing known hotspot CDMs
(Apc, Braf, Egfr, Hras, Kras, Nfe2l2, Pik3ca, Setbp1, Stk11, and Tp53) and
variant MFs were quantified by CarcSeq. Considering MFs in all targets, no
significant effects of lorcaserin treatment were observed. However,
significant induction of Pik3ca H1047R mutation was observed after 12 and
24 weeks of treatment (ANOVA, P<0.05), with greater numbers of
mutants and mutants with higher MFs observed in 24-week samples compared
to 12-week samples. Given that Pik3ca H1047R mutation can be detected in
normal tissues, is the most prevalent mutation in human breast cancer, and
occurs in several other cancers, these results suggest lorcaserin-induced
carcinogenesis involves promoting the outgrowth of spontaneously-occurring
Pik3ca H1047R mutant clones. The underlying mechanism(s) of promotion are
under investigation. This study provides the first demonstration that
CarcSeq can identify the carcinogenic impact of a non-genotoxic
carcinogen, doing so within a shorter timeframe than is needed to measure
a tumor response.