Trastuzumab deruxtecan versus trastuzumab emtansine in HER2-positive metastatic breast cancer patients with brain metastases from the randomized DESTINY-Breast03 trial.

BACKGROUND: DESTINY-Breast03 is a randomized, multicenter, open-label, phase III study of trastuzumab deruxtecan (T-DXd) versus trastuzumab emtansine (T-DM1) in patients with human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer (mBC) previously treated with trastuzumab and a taxane. A statistically significant improvement in progression-free survival (PFS) versus T-DM1 was reported in the primary analysis. Here, we report exploratory efficacy data in patients with and without brain metastases (BMs) at baseline. PATIENTS AND METHODS: Patients were randomly assigned 1 : 1 to receive T-DXd 5.4 mg/kg or T-DM1 3.6 mg/kg. Patients with clinically inactive/asymptomatic BMs were eligible. Lesions were measured as per modified RECIST, version 1.1. Outcomes included PFS by blinded independent central review (BICR), objective response rate (ORR), and intracranial ORR as per BICR. RESULTS: As of 21 May 2021, 43/261 patients randomized to T-DXd and 39/263 patients randomized to T-DM1 had BMs at baseline, as per investigator assessment. Among patients with baseline BMs, 20/43 in the T-DXd arm and 19/39 in the T-DM1 arm had not received prior local BM treatment. For patients with BMs, median PFS was 15.0 months [95% confidence interval (CI) 12.5-22.2 months] for T-DXd versus 3.0 months (95% CI 2.8-5.8 months) for T-DM1; hazard ratio (HR) 0.25 (95% CI 0.13-0.45). For patients without BMs, median PFS was not reached (95% CI 22.4 months-not estimable) for T-DXd versus 7.1 months (95% CI 5.6-9.7 months) for T-DM1; HR 0.30 (95% CI 0.22-0.40). Confirmed systemic ORR was 67.4% for T-DXd versus 20.5% for T-DM1 and 82.1% for T-DXd versus 36.6% for T-DM1 for patients with and without BMs, respectively. Intracranial ORR was 65.7% with T-DXd versus 34.3% with T-DM1. CONCLUSIONS: Patients with HER2-positive mBC whose disease progressed after trastuzumab and a taxane achieved a substantial benefit from treatment with T-DXd compared with T-DM1, including those with baseline BMs.

Disturbed spermatogenic signaling in pituitary adenylate cyclase activating polypeptide-deficient mice.

PACAP is a neuropeptide with diverse functions in various organs, including reproductive system. It is present in the testis in high concentrations, and in addition to the stage-specific expression within the seminiferous tubules, PACAP affects spermatogenesis and the functions of Leydig and Sertoli cells. Mice lacking endogenous PACAP show reduced fertility, but the possibility of abnormalities in spermatogenic signaling has not yet been investigated. Therefore, we performed a detailed morphological analysis of spermatozoa, sperm motility and investigated signaling pathways that play a role during spermatogenesis in knockout mice. No significant alterations were found in testicular morphology or motility of sperm in homozygous and heterozygous PACAP-deficient mice in spite of the moderately increased number of severely damaged sperms. However, we found robust changes in mRNA and/or protein expression of several factors that play an important role in spermatogenesis. Protein kinase A expression was markedly reduced, while downstream phospho-ERK and p38 were elevated in knockout animals. Expression of major transcription factors, such as Sox9 and phospho-Sox9, was decreased, while that of Sox10, as a redundant factor, was increased in PACAP-deficient mice. The reduced phospho-Sox9 expression was partly due to increased expression and activity of phosphatase PP2A in knockout mice. Targets of Sox transcription factors, such as collagen type IV, were reduced in knockout mice. In summary, our results show that lack of PACAP leads to disturbed signaling in spermatogenesis, which could be a factor responsible for reduced fertility in PACAP knockout mice, and further support the role of PACAP in reproduction.

Okadaic acid-induced inhibition of protein phosphatase 2A enhances chondrogenesis in chicken limb bud micromass cell cultures.

The role of major cellular serine/threonine-specific protein phosphatases, protein phosphatase 1 and 2A, was investigated during chicken cartilage differentiation under in vitro conditions. Activity of protein phosphatase 2A decreased parallel to differentiation of chondrogenic cells, whereas activity of protein phosphatase 1 remained unchanged as assayed in the supernatants of the homogenised chicken limb bud micromass cell cultures. When okadaic acid, a potent inhibitor of protein phosphatase 1 and 2A was applied in 20 nM concentration for 4 h during the second and third culturing days, it significantly increased the size of metachromatic cartilage areas measured in 6-day-old colonies. Following okadaic acid treatments, a significant inhibition in the activity of protein phosphatase 2A was found, while the activity of protein phosphatase 1 was unaffected as measured an days 2 and 3. TRITC-phalloidin labelling demonstrated that okadaic acid disorganised actin filaments and induced rounding of chondrogenic cells. This deterioration of actin filaments was reversible. Electron microscopy and biochemical analysis of colonies revealed that the ultrastructure and major components of cartilage matrix remained unchanged under the effect of okadaic acid. Okadaic acid-treatment applied to cultures containing predominantly differentiated chondrocytes (after day 4) did not influence the cartilage formation. 3H-thymidine and bromodeoxyuridine incorporation-assays demonstrated enhanced cell proliferation in the okadaic acid-treated colonies compared to that of the untreated ones. Our results indicate, for the first time, that protein phosphatase 2A is involved in the regulation of chondrogenesis. Inhibition of protein phosphatase 2A with okadaic acid may result in increased chondrogenesis via modulation of proliferation and cytoskeletal organisation, as well as via alteration of protein kinase A-signaling pathway of the chondrogenic cells.

Decreased protein phosphatase 2A activity in hippocampal long-term potentiation.

Using autophosphorylated Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) as substrate, we now find that long-term potentian (LTP) induction and maintenance are also associated with a significant decrease in calyculin A-sensitive protein phosphatase (protein phosphatase 2A) activity, without changes in Mg2+-dependent protein phosphatase (protein phosphatase 2C) activity. This decrease in protein phosphatase 2A activity was prevented when LTP induction was inhibited by treatment with calmidazolium or D-2-amino-5-phosphonopentanoic acid. In addition, the application of high-frequency stimulation to 32P-labeled hippocampal slices resulted in increases in the phosphorylation of a 55-kDa protein immunoprecipitated with anti-phosphatase 2A antibodies. Use of a specific antibody revealed that the 55-kDa protein is the B'alpha subunit of protein phosphatase 2A. Following purification of brain protein phosphatase 2A, the B'alpha subunit was phosphorylated by CaM kinase II, an event that led to the reduction of protein phosphatase 2A activity. These results suggest that the decreased activity in protein phosphatase 2A following LTP induction contributes to the maintenance of constitutively active CaM kinase II and to the long-lasting increase in phosphorylation of synaptic components implicated in LTP.

High complexity in the expression of the B' subunit of protein phosphatase 2A0. Evidence for the existence of at least seven novel isoforms.

Association of the catalytic subunit (C2) with a variety of regulatory subunits is believed to modulate the activity and specificity of protein phosphatase 2A (PP2A). In this study we report the cloning and expression of a new family of B-subunit, the B', associated with the PP2A0 form. Polymerase chain reactions and cDNA library screening have identified at least seven cDNA isotypes, designated alpha, beta 1, beta 2, beta 3, beta 4, gamma, and delta. The different beta subtypes appear to be generated by alternative splicing. The deduced amino acid sequences of the alpha, beta 2, beta 3, beta 4 and gamma isoforms predict molecular weights of 57,600, 56,500, 60,900, 52,500, and 68,000, respectively. The proteins are 60-80% identical and differ mostly at their termini. Two of the isoforms, B' beta 3 and B' gamma, contain a bipartite nuclear localization signal in their COOH terminus. No homology was found with other B- or B- related subunits. Northern analyses indicate a tissue-specific expression of the isoforms. Expression of B' alpha protein in Escherichia coli generated a polypeptide of approximately 53 kDa, similar to the size of the B' subunit present in the purified PP2A0. The recombinant protein was recognized by antibody raised against native B' and interacted with the dimeric PP2A (A.C2) to generate a trimeric phosphatase. The deduced amino acid sequences of the B' isoforms show significant homology to mammalian, fungal, and plant nucleotide sequences of unknown function present in the data bases. Notably, a high degree of homology (55-66%) was found with a yeast gene, RTS1, encoding a multicopy suppressor of a rox3 mutant. Our data indicate that at least seven B' subunit isoforms may participate in the generation of a large number of PP2A0 holoenzymes that may be spatially and/or functionally targeted to different cellular processes.

Isolation and characterization of the catalytic subunit of protein phosphatase 2A from Neurospora crassa.

The catalytic subunit of protein phosphatase 2A (PP2Ac) was purified from Neurospora crassa extract by (NH4)2SO4-ethanol precipitation followed by DEAE-Sephacel, heparin-Sepharose, and MonoQ chromatography steps about 900-fold to a specific activity of 1200 U/g with a 2% yield. The apparent M(r) of PP2Ac was estimated to be 35 kDa by gel filtration and 33 kDa by SDS polyacrylamide gel electrophoresis. Half maximal inhibition of PP2Ac was achieved at 0.3 nM okadaic acid, 0.1 nM microcystin-LR, 56 nM cantharidin and 280 nM endothall concentrations. The preparation was completely inhibited by 20 mM NaF, was insensitive to rabbit muscle inhibitor-2, and was specific for the alpha-subunit of rabbit muscle phosphorylase kinase. According to its biochemical properties, N. crassa PP2Ac is very similar to its mammalian counterparts. Antipeptide antibodies raised against the N-terminal and C-terminal ends of human PP2Ac did not cross-react with N. crassa PP2Ac, indicating sequence differences outside the catalytic core of the enzyme.

Quantitation of protein phosphatase 1 and 2A in extracts of the budding yeast and fission yeast.

Serine/threonine protein phosphatases are also involved in the control of cell division. The aim of the present study was to compare the activity of protein phosphatase 1 (PP1) and 2A (PP2A) in cell extracts of the budding and fission yeast, made at different phases of growth. The activities of PP1 and PP2A toward phosphorylase were similar in extracts of S. cerevisiae. In S. pombe extracts, PP1 was responsible for more than 80% of the phosphorylase phosphatase activity. Ammonium sulfate-ethanol treatment increased the specific activity of the phosphatases and the percentage of PP2A in S. cerevisiae extracts. No increase in the proportion of PP2A was observed upon the same treatment of S. pombe extracts. The above results were confirmed by fractionation of PP1 and PP2A activities on a heparin-Sepharose column. The proportion of PP1 and PP2A activities did not change significantly during exponential cell growth but cells from stationary phase exhibited lower phosphatase activities. These results may indicate a lower level of expression of the PP2A genes in S. pombe and/or differences in the structure of the holoenzymes or their regulators in the two genera.

Purification and partial characterization of protein phosphatases from rat thymus.

Protein phosphatases assayed with phosphorylase alpha are present in the soluble and particulate fractions of rat thymocytes. Phosphorylase phosphatase activity in the cytosol fraction was resolved by heparin-Sepharose chromatography into type-1 and type-2A enzymes. Similarities between thymocyte and muscle or liver protein phosphatase-1 included preferential dephosphorylation of the beta subunit of phosphorylase kinase, inhibition by inhibitor-2 and retention by heparin-Sepharose. Similarities between thymocyte and muscle or liver protein phosphatase-2A included specificity for the alpha subunit of phosphorylase kinase, insensitivity to the action of inhibitor-2, lack of retention by heparin-Sepharose and stimulation by polycationic macromolecules such as polybrene, protamine and histone H1. Protein phosphatase-1 from the cytosol fraction of thymocytes had an apparent molecular mass of 120 kDa as determined by gel filtration. The phosphatase-2A separated from the cytosol of thymocytes may correspond to phosphatase-2A0, since it was completely inactive (latent) in the absence of polycation and had activity only in the presence of polycations. The apparent molecular mass of phosphatase-2A0 from thymocytes was 240 kDa as determined by gel filtration. The catalytic subunit of thymocyte type-1 protein phosphatase was purified with heparin-Sepharose chromatography followed by gel filtration and fast protein liquid chromatography on Mono Q column. The purified type-1 catalytic subunit exhibited a specific activity of 8.2 U/mg and consisted of a single protein of 35 kDa as judged by SDS-gel electrophoresis. The catalytic subunit of type-2A phosphatase from thymocytes appearing in the heparin-Sepharose flow-through fraction was further purified on protamine-Sepharose, followed by gel filtration. The specific activity of the type-2A catalytic subunit was 2.1 U/mg and consisted of a major protein of 34.5 kDa, as revealed by SDS-gel electrophoresis.

Autophosphorylation of phosphorylase kinase and its regulatory function in the dephosphorylation of phosphorylase A.

Autophosphorylation of phosphorylase kinase was measured under conditions that favoured autoactivation. Heparin and troponin C stimulated the autophosphorylation of phosphorylase kinase at pH 6.8 in a Ca2+-dependent manner. The concentration required for the half-maximal stimulation of autophosphorylation for calcium ions was 2 microM in the absence of effectors, whereas 0.7 microM and 0.1 microM in the presence of troponin C and heparin, respectively. Calmodulin increased the rate of autophosphorylation of the alpha subunit only, resulting in a slight increase in the rate of autoactivation of phosphorylase kinase. Troponin C, heparin and polybrene enhanced the rate of autophosphorylation of both alpha and beta subunits. The increased autophosphorylation coincided with an enhancement of kinase activity. Neither of these stimulatory macromolecules had significant influence on the total number of phosphate groups incorporated into the alpha or beta subunits by autophosphorylation. Thio-autophosphorylated form of phosphorylase kinase behaved as an inhibitor in the dephosphorylation of phosphorylase a by the catalytic subunits of phosphatase-1 or phosphatase-2A and by the latent form of phosphatase-2A. Concentration of phosphorylase kinase needed to 50% inhibition was in the range of 0.05-0.08 microM.