Biology Reference
In-Depth Information
An additional study using non-invasive functional
imaging with 18F-fluorine-L-thymidine (FLT) demon-
strated that PF00477736 could overcome gemcitabine-
induced cell cycle arrest and increase levels of DNA
damage in tumors when the combination treatment
was compared with treatment with gemcitabine alone.
65
Treatment with PF00477736 17 hours post gemcitabine
in nude mice harboring PC-3 human prostate cancer
cells greatly reduced the early FLT flare at 21 hours
(
three months. PK analysis showed exposure to
PF0047736 to increase in a dose proportional manner
from doses of 50 mg to 270 mg. The mean t½ ranged
from 8 to 20 hours. Given these results, future clinical
studies with PF00477736 were planned to identify the
MTD in combination with a higher dose of gemcitabine
(1000 mg/m
2
), and to examine biomarkers including
inhibition of the S/G2 checkpoints in serial tumor biop-
sies at the MTD. However, in late 2010, Pfizer announced
that development of PF0047736 was to be discontinued.
82%), with p-hH3 and flow cytometry measures
used to confirm an increase in the proportion of cells
in mitosis or the G1 phase when compared with gemci-
tabine treatment alone.
111
PF0047736 was tested in a non-randomized, open-
label, uncontrolled, phase I trial in combination with
gemcitabine in patients with advanced solid malignan-
cies. The primary goal was to assess the overall safety,
maximum tolerated dose and PK profile of PF00477736
alone or in combination with gemcitabine.
116
The trial
used a dose expansion protocol in gemcitabine-naive
patients with advanced solid tumors. In contrast to the
trials with XL-844 and AZD7762, two different dose
schedules were investigated with PF00477736. In the first
treatment cycle, PF00477736 was administered alone by
intravenous infusion on days one and eight, prior to
dosing in combination in subsequent cycles. The combi-
nation schedule used was to administer gemcitabine
(750 mg/m
2
) on days 1 and 8, with escalating doses of
PF00477736 administered on days 2 and 9 by either 3-
or 24-hour infusion in 21-day cycles. The treatment cycle
with PF0047736 alone and the first combination cycle
were considered for dose-limiting toxicities. Overall, 36
patients were
IC-83/LY2603618
IC-83/LY2603618 (see
Figure 10.2
) was identified as
the clinical candidate from a lead series of pyrazinyl
ureas that were found to be inhibitors of cell cycle check-
point and repair genes.
117
The compound was originally
identified by Icos, but is now in development by Lily.
Although limited information has been presented
regarding the pre-clinical profile, LY2603618 is currently
in a number of phase I or II clinical trials to investigate
its ability to enhance the effectiveness of chemothera-
peutic drugs, i.e pemetrexed, cisplatin, and gemcitabine.
LY2603618 is the only agent in the group to be investi-
gated in combination with pemetrexed, an antifolate
that acts by inhibiting thymidylate synthase.
118-120
Pemetrexed inhibits cellular de novo thymidine
nucleotide synthesis, and this in turn induces check-
point activation and cell cycle arrest. As pemetrexed is
used to treat advanced or metastatic NSCLC of non-
squamous histology, initial studies sought to show
increased efficacy for the combination of pemetrexed
and LY2603618 versus pemetrexed alone in preclinical
models of NSCLC using the H2122 and H441 cell lines.
In vitro
, exposure of H2122 cells to either 100 nM peme-
trexed or LY2603618 for six days resulted in
treated in the study, 17 received
PF0047736 (50
80 mg) as a 3-hour infusion, and 19 as
a 20-hour infusion (80
e
340 mg). Adverse events were
infrequent for PF00477736 given as a single agent, with
dose-limiting toxicities of increased lipase levels and
neutropenia (65 mg PF0047736 given by 3-hour infu-
sion), and thrombocytopenia and sudden death
(340 mg PF0047736 given by 24-hour infusion) observed
in the first combination cycle. The maximum tolerated
dose was thus determined to be 270 mg PF0047736 given
as a 24-hour infusion in combination with 750 mg/m
2
gemcitabine. In addition to the DLTs, common (
e
90%
>
(IC
50
2nM) or
25% ([IC
50
271nM] inhibition of cell
growth respectively. Levels of pChk1 (Ser296) were
also measured. Compared with vehicle control, treat-
ment with 100 nM pemetrexed for 28 hours resulted in
a 14-fold increase in pChk1 levels. The combination of
pemetrexed for 21 hours, followed by seven hours of
treatment with IC83 reduced this by 46% to 7.6-fold
greater than control. Interestingly, this reduction was
less when LY2603618 and pemetrexed were dosed
concurrently for 28 hours, suggesting that sequential
treatment may be optimal for enhancing the antitumor
effects of pemetrexed. The increase in activity seen
from the combination was attributed to the ability of
LY2603618 to override pemetrexed-induced cell cycle
checkpoint activation.
In vivo
xenografts implanted via the intraperitoneal
route in female athymic nude mice (H2122 and H441
cells) were used to calculate treated versus control
tumor volumes on day 67 of
<
30%
patients) drug-related adverse events (AEs) were found
to be pyrexia, fatigue, neutropenia, nausea, vomiting,
and diarrhea. In addition, 42% of patients experienced
dose delays due to grade three neutropenia, indicating
that the day 1 and day 8 treatment schedule would be
difficult to maintain for an extended period. However,
there were also encouraging signs of clinical activity in
the trial, with four partial responses, two in squamous-
cell carcinomas of the skin, one in non-small-cell lung
cancer, and one in mesothelioma. Nine patients also
exhibited stable disease, with a median duration of about
>
the study following
