BYL719, which selectively inhibits the alpha isoform of the phosphatidylinositol 3-kinase (PI3K) catalytic subunit (p110a), is currently in clinical trials for the treatment of solid tumors, ...especially luminal breast cancers with PIK3CA mutations and/or HER2 amplification. This study reveals that, even among these sensitive cancers, the initial efficacy of p110α inhibition is mitigated by rapid re-accumulation of the PI3K product PIP3 produced by the p110β isoform. Importantly, the reactivation of PI3K mediated by p110β does not invariably restore AKT phosphorylation, demonstrating the limitations of using phospho-AKT as a surrogate to measure PI3K activation. Consistently, we show that the addition of the p110β inhibitor to BYL719 prevents the PIP3 rebound and induces greater antitumor efficacy in HER2-amplified and PIK3CA mutant cancers.
•p110α inhibition leads to reactivation of PI3K signaling via p110β•Restoration of PI3K is reliably determined by measuring PIP3 levels, not p-AKT•Dual inhibition of p110α and β blocks rebound of PIP3 and induces tumor regressions
Costa et al. show that PI3Kα inhibition only briefly blocks PI3K signaling even in responsive cancer cells due to PI3Kβ activation. Thus, combined PI3Kα and PI3Kβ inhibition provides greater antitumor efficacy. The authors also find PIP3 to be a better marker of active PI3K signaling than phosphorylated AKT.
Fewer than half of children with high-risk neuroblastoma survive. Many of these tumors harbor high-level amplification of MYCN, which correlates with poor disease outcome. Using data from our large ...drug screen we predicted, and subsequently demonstrated, that MYCN-amplified neuroblastomas are sensitive to the BCL-2 inhibitor ABT-199. This sensitivity occurs in part through low anti-apoptotic BCL-xL expression, high pro-apoptotic NOXA expression, and paradoxical, MYCN-driven upregulation of NOXA. Screening for enhancers of ABT-199 sensitivity in MYCN-amplified neuroblastomas, we demonstrate that the Aurora Kinase A inhibitor MLN8237 combines with ABT-199 to induce widespread apoptosis. In diverse models of MYCN-amplified neuroblastoma, including a patient-derived xenograft model, this combination uniformly induced tumor shrinkage, and in multiple instances led to complete tumor regression.
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•Amplified MYCN is synthetic lethal with the BCL-2 inhibitor ABT-199 in neuroblastoma•MYCN upregulates the MCL-1 inhibitor, NOXA•MYCN-amplified neuroblastomas are further sensitized to ABT-199 with MLN8237•ABT-199 with MLN8237 induce tumor regressions in MYCN-amplified neuroblastoma mice
Ham et al. show that MYCN-amplified neuroblastomas are sensitive to treatment with the BCL-2 inhibitor ABT-199 due to MYCN-driven increase of NOXA. Combination treatment with the Aurora Kinase A inhibitor MLN8237 and ABT-199 is synergistic in xenograft models of this tumor type, in part via reducing MCL-1.
The combination of CDK4/6 inhibitors with antiestrogen therapies significantly improves clinical outcomes in ER-positive advanced breast cancer. To identify mechanisms of acquired resistance, we ...analyzed serial biopsies and rapid autopsies from patients treated with the combination of the CDK4/6 inhibitor ribociclib with letrozole. This study revealed that some resistant tumors acquired RB loss, whereas other tumors lost PTEN expression at the time of progression. In breast cancer cells, ablation of
, through increased AKT activation, was sufficient to promote resistance to CDK4/6 inhibition
and
. Mechanistically,
loss resulted in exclusion of p27 from the nucleus, leading to increased activation of both CDK4 and CDK2. Because
loss also causes resistance to PI3Kα inhibitors, currently approved in the post-CDK4/6 setting, these findings provide critical insight into how this single genetic event may cause clinical cross-resistance to multiple targeted therapies in the same patient, with implications for optimal treatment-sequencing strategies. SIGNIFICANCE: Our analysis of serial biopsies uncovered RB and PTEN loss as mechanisms of acquired resistance to CDK4/6 inhibitors, utilized as first-line treatment for ER-positive advanced breast cancer. Importantly, these findings have near-term clinical relevance because
loss also limits the efficacy of PI3Kα inhibitors currently approved in the post-CDK4/6 setting.
.
Macropinocytosis is an actin-dependent but clathrin-independent endocytic process by which cells nonselectively take up large aliquots of extracellular material. Macropinocytosis is used for immune ...surveillance by dendritic cells, as a route of infection by viruses and protozoa, and as a nutrient uptake pathway in tumor cells. In this study, we explore the role of class I phosphoinositide 3-kinases (PI3Ks) during ligand-stimulated macropinocytosis. We find that macropinocytosis in response to receptor tyrosine kinase activation is strikingly dependent on a single class I PI3K isoform, namely PI3Kβ (containing the p110β catalytic subunit encoded by
). Loss of PI3Kβ expression or activity blocks macropinocytosis at early steps, before the formation of circular dorsal ruffles, but also plays a role in later steps, downstream from Rac1 activation. PI3Kβ is also required for the elevated levels of constitutive macropinocytosis found in tumor cells that are defective for the PTEN tumor suppressor. Our data shed new light on PI3K signaling during macropinocytosis, and suggest new therapeutic uses for pharmacological inhibitors of PI3Kβ.
PI3Kβ is required for invadopodia‐mediated matrix degradation by breast cancer cells. Invadopodia maturation requires GPCR activation of PI3Kβ and its coupling to SHIP2 to produce PI(3,4)P2. We now ...test whether selectivity for PI3Kβ is preserved under conditions of mutational increases in PI3K activity. In breast cancer cells where PI3Kβ is inhibited, short‐chain diC8‐PIP3 rescues gelatin degradation in a SHIP2‐dependent manner; rescue by diC8‐PI(3,4)P2 is SHIP2‐independent. Surprisingly, the expression of either activated PI3Kβ or PI3Kα mutants rescued the effects of PI3Kβ inhibition. In both cases, gelatin degradation was SHIP2‐dependent. These data confirm the requirement for PIP3 conversion to PI(3,4)P2 for invadopodia function and suggest that selectivity for distinct PI3K isotypes may be obviated by mutational activation of the PI3K pathway.
GPCR activation of PI3Kβ drives invadopodia‐mediated matrix degradation by breast cancer cells, via PI3Kβ coupling to SHIP2 to produce PI(3,4)P2. Surprisingly, expression of either activated PI3Kβ or PI3Kα rescues the effects of pertussis toxin or TGX221, which inhibit PI3Kβ. In both cases, matrix degradation is SHIP2‐dependent. Thus, selectivity for PI3K isotypes is obviated by mutational activation of PI3K signaling.
PI3Kβ is required for invadopodia-mediated matrix degradation by breast cancer cells. Invadopodia maturation requires GPCR activation of PI3Kβ and its coupling to SHIP2 to produce PI(3,4)P
. We now ...test whether selectivity for PI3Kβ is preserved under conditions of mutational increases in PI3K activity. In breast cancer cells where PI3Kβ is inhibited, short-chain diC8-PIP
rescues gelatin degradation in a SHIP2-dependent manner; rescue by diC8-PI(3,4)P
is SHIP2-independent. Surprisingly, the expression of either activated PI3Kβ or PI3Kα mutants rescued the effects of PI3Kβ inhibition. In both cases, gelatin degradation was SHIP2-dependent. These data confirm the requirement for PIP
conversion to PI(3,4)P
for invadopodia function and suggest that selectivity for distinct PI3K isotypes may be obviated by mutational activation of the PI3K pathway.
The enantiomers of dialkyl 2,3-pentadienedioate undergo interconversion during gas chromatographic separation on chiral stationary phases. In this paper the on-column apparent interconversion kinetic ...and thermodynamic activation data were determined for dimethyl, diethyl, propylbutyl and dibutyl 2,3-pentadienedioate enantiomers by gas chromatographic separation of the racemic mixtures on a capillary column containing a polydimethylsiloxane stationary phase coupled to 2,3-di-O-methyl-6-O-
tertbutyldimethylsilyl-β-cyclodextrin. A deconvolution method was used to determine the individual enantiomer peak areas and retention times that are needed to calculate the interconversion rate constants and the energy barriers. The apparent rate constants and interconversion energy barriers decrease slightly with an increase in the alkyl chain length of the dialkyl 2,3-pentadienedioate esters. The optimum conformation of the dialkyl 2,3-pentadienedioate molecules, their separation selectivity factors and apparent interconversion enthalpy and entropy data changes with the alkyl chain length. The dependence of the apparent interconversion energy barrier
(
Δ
G
a
→
b
app
,
Δ
G
b
→
a
app
)
on temperature was used to determine the apparent activation enthalpy
(
Δ
H
a
→
b
app
,
Δ
H
b
→
a
app
)
and apparent entropy
(
Δ
S
a
→
b
app
,
Δ
S
a
→
b
app
)
(where
a denotes the first and
b second eluted enantiomer). The comparison of the activation enthalpy and entropy
(
Δ
S
a
→
b
app
,
Δ
S
a
→
b
app
)
indicated that the interconversion of dialkyl 2,3-pentadienedioate enantiomers on the HP-5
+
Chiraldex B-DM column series is an entropy driven process at 160
°C. Data obtained for dimethyl 2,3-pentadienedioate enantiomers on the HP-5
+
Chiraldex B-DM column series at 120
°C
(
Δ
G
a
→
b
app
=
123.3
and
Δ
G
b
→
a
app
=
124.4
kJ
mo
l
−
1
)
corresponds (at the 95% confidence interval) with the value of Δ
G
#
=
128
±
1
kJ
mol
−1 found at this temperature by gas chromatography using a two-dimensional stop flow technique on an empty capillary column V. Schurig, F. Keller, S. Reich, M. Fluck, Tetrahedron: Asymmetry 8 (1997) 3475.
Triple negative breast cancer (TNBC) accounts for over 30% of all breast cancer (BC)-related deaths, despite accounting for only 10% to 15% of total BC cases. Targeted therapy development has largely ...stalled in TNBC, underlined by a lack of traditionally druggable addictions like receptor tyrosine kinases (RTKs). Here, through full genome CRISPR/Cas9 screening of TNBC models, we have uncovered the sensitivity of TNBCs to the depletion of the ubiquitin-like modifier activating enzyme 1 (UBA1). Targeting UBA1 with the first-in-class UBA1 inhibitor TAK-243 induced unresolvable endoplasmic reticulum (ER)-stress and activating transcription factor 4 (ATF4)-mediated upregulation of proapoptotic NOXA, leading to cell death. c-MYC expression correlates with TAK-243 sensitivity and cooperates with TAK-243 to induce a stress response and cell death. Importantly, there was an order of magnitude greater sensitivity of TNBC lines to TAK-243 compared to normal tissue-derived cells. In five patient derived xenograft models (PDXs) of TNBC, TAK-243 therapy led to tumor inhibition or frank tumor regression. Moreover, in an intracardiac metastatic model of TNBC, TAK-243 markedly reduced metastatic burden, indicating UBA1 is a potential new target in TNBC expressing high levels of c-MYC.
This study examined the mutagenic, antimutagenic and antioxidant activities of the DMSO extracts from the wheat bran. Wheat bran extracts showed no genotoxicity toward Salmonella typhimurium TA98, ...TA100 and TA102 with or without S9 mix (an external metabolic system). In addition, wheat bran extracts expressed a dose-depend inhibitory effect on the mutagenicity of promutagen aflatoxin B1 (AFB1), an indirect mutagen which requires metabolic activation, and 3-(5-nitro-2-furyl)acrylic acid (5-NFAA), 2-nitrofluorene (2NF) and hydrogen peroxide (H 2 O 2), direct mutagens, in Salmonella typhimurium TA98, TA100 and TA102 strains. Significant total antioxidant capacity of wheat bran extract was found by two standard spectroscopic assays based on ABTS and DPPH reagents. A special attention was focused to the reactive radical scavenging capacity of bran extract as one of its antioxitant activities. Wheat bran extract possessed higher ability to scavenge oxygen- and carbon-centered reactive radicals generated by the thermal decomposition of K 2 S 2 O 8 than BHT (70 and 65% scavenged radicals, respectively) during the electron paramagnetic resonance (EPR)/spintrapping test. The total phenolic content of wheat bran samples expressed in gallic acid equivalent was 2.7 mg/g, total flavonoid content expressed in rutin equivalent was 70.8 μg/g and the most abundant phenolic acids established by GC-MS method were isoferulic (3-hydroxy-4-metoxycinnamic) and ferulic (4-hydroxy-3-metoxycinnamic) acid, sinapic, caffeic, p -coumaric and vanillic acids.
Femoral caput necrosis is an actual therapeutic problem, because it appears mainly in mid-aged people. The necrotic focus is most often localized in the proximal and ventral parts of the femoral bone ...capitulum, which, from the biomechanical point of view is the most loaded part. These cases can be possibly treated by transtrochanteric rotational osteotomy. By means of this operation we rotate the necrotic focus to the less loaded part of the joint in correlation with the acetabulum.
The aim of this paper is to inform about a rarely performed operation after Sugioka: transtrochanteric rotational osteotomy in coincidence with avascular necrosis of the femoral bone caput. We would like to point to the possibility of a joint-saving operation, which enables to postpone implantation of total endoprosthesis to older age.
We analyzed the operational therapy performed at our department in the period 1998-2000, focusing especially on joint-saving operations due to femoral caput necrosis. We turned our attention to transtrochanteric rotational osteotomy after Sugioka. In four casuistics, we describe the results of these operations.
Transtrochanteric rotational osteotomy was performed in 12 patients. The treatment is described in four casuistics. The results after 1-3 years are good. The illness has not progressed in any of patients, pain has regressed, mobility improved and it was not necessary to implant total endoprosthesis.
We consider the transtrochanteric rotational osteootomy, section after Sugioka, as one of the possible treatments in mid-aged patients. Our effort is to perform joint-saving operations in order to postpone the implantation of total endoprosthesis. (Fig. 10, Ref. 13.)
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