Pembrolizumab monotherapy for previously treated metastatic triple-negative breast cancer: cohort A of the phase II KEYNOTE-086 study.

BACKGROUND: Treatment options for previously treated metastatic triple-negative breast cancer (mTNBC) are limited. In cohort A of the phase II KEYNOTE-086 study, we evaluated pembrolizumab as second or later line of treatment for patients with mTNBC. PATIENTS AND METHODS: Eligible patients had centrally confirmed mTNBC, ≥1 systemic therapy for metastatic disease, prior treatment with anthracycline and taxane in any disease setting, and progression on or after the most recent therapy. Patients received pembrolizumab 200 mg intravenously every 3 weeks for up to 2 years. Primary end points were objective response rate in the total and PD-L1-positive populations, and safety. Secondary end points included duration of response, disease control rate (percentage of patients with complete or partial response or stable disease for ≥24 weeks), progression-free survival, and overall survival. RESULTS: All enrolled patients (N = 170) were women, 61.8% had PD-L1-positive tumors, and 43.5% had received ≥3 previous lines of therapy for metastatic disease. ORR (95% CI) was 5.3% (2.7-9.9) in the total and 5.7% (2.4-12.2) in the PD-L1-positive populations. Disease control rate (95% CI) was 7.6% (4.4-12.7) and 9.5% (5.1-16.8), respectively. Median duration of response was not reached in the total (range, 1.2+-21.5+) and in the PD-L1-positive (range, 6.3-21.5+) populations. Median PFS was 2.0 months (95% CI, 1.9-2.0), and the 6-month rate was 14.9%. Median OS was 9.0 months (95% CI, 7.6-11.2), and the 6-month rate was 69.1%. Treatment-related adverse events occurred in 103 (60.6%) patients, including 22 (12.9%) with grade 3 or 4 AEs. There were no deaths due to AEs. CONCLUSIONS: Pembrolizumab monotherapy demonstrated durable antitumor activity in a subset of patients with previously treated mTNBC and had a manageable safety profile. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov, NCT02447003.

Geranylgeranyltransferase I of Candida albicans: null mutants or enzyme inhibitors produce unexpected phenotypes.

Geranylgeranyltransferase I (GGTase I) catalyzes the transfer of a prenyl group from geranylgeranyl diphosphate to the carboxy-terminal cysteine of proteins with a motif referred to as a CaaX box (C, cysteine; a, usually aliphatic amino acid; X, usually L). The alpha and beta subunits of GGTase I from Saccharomyces cerevisiae are encoded by RAM2 and CDC43, respectively, and each is essential for viability. We are evaluating GGTase I as a potential target for antimycotic therapy of the related yeast, Candida albicans, which is the major human pathogen for disseminated fungal infections. Recently we cloned CaCDC43, the C. albicans homolog of S. cerevisiae CDC43. To study its role in C. albicans, both alleles were sequentially disrupted in strain CAI4. Null Cacdc43 mutants were viable despite the lack of detectable GGTase I activity but were morphologically abnormal. The subcellular distribution of two GGTase I substrates, Rho1p and Cdc42p, was shifted from the membranous fraction to the cytosolic fraction in the cdc43 mutants, and levels of these two proteins were elevated compared to those in the parent strain. Two compounds that are potent GGTase I inhibitors in vitro but that have poor antifungal activity, J-109,390 and L-269,289, caused similar changes in the distribution and quantity of the substrate. The lethality of an S. cerevisiae cdc43 mutant can be suppressed by simultaneous overexpression of RHO1 and CDC42 on high-copy-number plasmids (Y. Ohya et al., Mol. Biol. Cell 4:1017, 1991; C. A. Trueblood, Y. Ohya, and J. Rine, Mol. Cell. Biol. 13:4260, 1993). Prenylation presumably occurs by farnesyltransferase (FTase). We hypothesize that Cdc42p and Rho1p of C. albicans can be prenylated by FTase when GGTase I is absent or limiting and that elevation of these two substrates enables them to compete with FTase substrates for prenylation and thus allows sustained growth.

In vitro induction of swine peripheral blood monocyte proliferation by the fibroblast-derived murine hematopoietic growth factor CSF-1.

The addition of conditioned medium from murine L929 fibroblasts (MGF) to cultures of swine peripheral blood mononuclear cells (MNL) resulted in growth of cells of macrophage/monocyte lineage (MO). Glass-adherent swine MNL, shown to be greater than 95% phagocytic MO, grew in the presence of MGF, whereas swine blood granulocytes and lymphocytes were not MGF-responsive. Primary and secondary MO growth were directly dependent on MGF presence and concentration. MGF-stimulated MO synthesized DNA, as measured by cellular incorporation of tritium-labeled thymidine (3H-TdR). This mitogenic response was maximal by 5 to 6 days in primary MO cultures and declined thereafter to a lower magnitude in secondary MO cultures. In the presence of MGF, viable MO numbers increased with an approximate population doubling time of 5 to 7 days in primary culture. This growth rate was prolonged, to about 10 to 12 days, for MGF-stimulated MO in secondary cultures. MGF removal from primary and secondary MO cultures resulted in rapid growth cessation and cell death. MGF-stimulated MO could not be sustained in secondary culture beyond 7 weeks. MGF-cultured MO were positive for latex phagocytosis, non-specific esterase, Fc-receptor expression, and could mediate antibody-dependent cell-mediated cytotoxicity. The MO-mitogenic principle of MGF was identified as the murine, macrophage-specific colony-stimulating factor, CSF-1 (M-CSF). The swine MO-proliferative response to MGF was inhibited by addition of monospecific goat antisera to M-CSF. Purified M-CSF stimulated the growth of swine MO from cultures of MNL and primary glass-adherent MO.

Metabolism of acetylcholine receptors in skeletal muscle.

The acetylcholine receptor in skeletal muscle is an integral plasma membrane glycoprotein. Its biosynthesis and incorporation into plasma membrane and its degradation are being studied with the use of biochemical, biophysical, and microscopic techniques. In this report, previously published data are combined with new information to yield a consistent and fairly detailed description ofthe mechanisms involved in receptor metabolism. It is proposed that the biosynthesis, transport, and incorporation of the receptor into plasma membranes involve a mechanism similar, or identical, to that used by the cell for production and secretion of secretory proteins. The receptor is degraded by a random-hit process, which involves internalization, transport to secondary lysosomes, and hydrolysis. Sites of regulation of receptor metabolism are discussed in the context of regulation of the number and distribution of receptors in plasma membranes, particularly with respect to the formation and stability of neuromuscular junctions.