ABSTRACT
Background: BRCA1 and BRCA2 (BRCA1/2)-deficient tumors display impaired homologous recombination repair (HRR) and enhanced sensitivity to DNA damaging agents or to poly(ADP-ribose) polymerase (PARP) inhibitors (PARPi). Their efficacy in germline BRCA1/2 (gBRCA1/2)-mutated metastatic breast cancers has been recently confirmed in clinical trials. Numerous mechanisms of PARPi resistance have been described, whose clinical relevance in gBRCA-mutated breast cancer is unknown. This highlights the need to identify functional biomarkers to better predict PARPi sensitivity. Patients and methods: We investigated the in vivo mechanisms of PARPi resistance in gBRCA1 patient-derived tumor xenografts (PDXs) exhibiting differential response to PARPi. Analysis included exome sequencing and immunostaining of DNA damage response proteins to functionally evaluate HRR. Findings were validated in a retrospective sample set from gBRCA1/2-cancer patients treated with PARPi. Results: RAD51 nuclear foci, a surrogate marker of HRR functionality, were the only common feature in PDX and patient samples with primary or acquired PARPi resistance. Consistently, low RAD51 was associated with objective response to PARPi. Evaluation of the RAD51 biomarker in untreated tumors was feasible due to endogenous DNA damage. In PARPi-resistant gBRCA1 PDXs, genetic analysis found no in-frame secondary mutations, but BRCA1 hypomorphic proteins in 60% of the models, TP53BP1-loss in 20% and RAD51-amplification in one sample, none mutually exclusive. Conversely, one of three PARPi-resistant gBRCA2 tumors displayed BRCA2 restoration by exome sequencing. In PDXs, PARPi resistance could be reverted upon combination of a PARPi with an ataxia-telangiectasia mutated (ATM) inhibitor. Conclusion: Detection of RAD51 foci in gBRCA tumors correlates with PARPi resistance regardless of the underlying mechanism restoring HRR function. This is a promising biomarker to be used in the clinic to better select patients for PARPi therapy. Our study also supports the clinical development of PARPi combinations such as those with ATM inhibitors.
Subject(s)
Biomarkers, Tumor/genetics , Breast Neoplasms/drug therapy , Drug Resistance, Neoplasm/genetics , Poly(ADP-ribose) Polymerase Inhibitors/pharmacology , Rad51 Recombinase/genetics , Animals , BRCA1 Protein/genetics , BRCA2 Protein/genetics , Breast/pathology , Breast Neoplasms/genetics , Breast Neoplasms/pathology , Drug Resistance, Neoplasm/drug effects , Female , Germ-Line Mutation , Humans , Mice , Mice, Nude , Poly(ADP-ribose) Polymerase Inhibitors/therapeutic use , Recombinational DNA Repair/drug effects , Recombinational DNA Repair/genetics , Retrospective Studies , Treatment Outcome , Xenograft Model Antitumor AssaysABSTRACT
We tested in vitro 49 isolates of Chlamydia pneumoniae obtained from 35 children with community-acquired pneumonia against clarithromycin and erythromycin. The children were part of a treatment study comparing the two drugs. Clarithromycin was 2- to 10-fold more active than erythromycin, with a MIC for 90% of strains tested and minimal chlamydiacidal concentration for 90% of strains tested of 0.031 microgram/ml compared with 0.125 microgram/ml for erythromycin. Eight of these children, two of whom were treated with erythromycin and six of whom received clarithromycin, remained culture positive after treatment. We were able to test 21 isolates from these children. All were susceptible to both drugs, and the MICs did not change after therapy.
Subject(s)
Chlamydia Infections/microbiology , Chlamydophila pneumoniae/drug effects , Clarithromycin/pharmacology , Erythromycin/pharmacology , Pneumonia, Bacterial/microbiology , Child , Child, Preschool , Chlamydia Infections/drug therapy , Chlamydophila pneumoniae/isolation & purification , Clarithromycin/therapeutic use , Erythromycin/therapeutic use , Humans , Microbial Sensitivity Tests , Pneumonia, Bacterial/drug therapyABSTRACT
The in vitro susceptibilities of 12 strains of Chlamydia pneumonia to a new quinolone, OPC-17116; ofloxacin; and sparfloxacin were determined. OPC-17116 was slightly less active than sparfloxacin but more active than ofloxacin, with a MIC for 90% of strains tested and a minimal chlamydiacidal concentration for 90% of strains tested of 0.5 micrograms/ml.
Subject(s)
Anti-Infective Agents/pharmacology , Chlamydophila pneumoniae/drug effects , Fluoroquinolones , Ofloxacin/pharmacology , Piperazines/pharmacology , Quinolones/pharmacology , Microbial Sensitivity TestsABSTRACT
We evaluated the performance of three commercially available monoclonal antibodies for confirmation of the presence of Chlamydia pneumoniae in cell culture by examining their abilities to stain inclusions of eight strains of C. pneumoniae. The antibodies tested were two unconjugated C. pneumoniae-specific monoclonal reagents and one conjugated genus-specific reagent. All three produced similar intensities of staining of C. pneumoniae, with some strain-to-strain variation. Methanol appeared to be a better choice of fixative than acetone, which greatly reduced the intensity of fluorescence with one of the species-specific antibodies.
