Acquired Resistance to Poly (ADP-ribose) Polymerase Inhibitor Olaparib in BRCA2-Associated Prostate Cancer Resulting From Biallelic BRCA2 Reversion Mutations Restores Both Germline and Somatic Loss-of-Function Mutations.

PARP1/2 inhibitors are effective against BRCA2-deficient tumors. The PARP inhibitor (PARPi) olaparib received FDA breakthrough designation for treatment of metastatic castration-resistant prostate cancers (CRPC) carrying mutations in BRCA1/2 or ATM genes. Emergent resistance to PARPi has been associated with tumor-specific BRCA2 mutations that revert the normal open reading frame rescuing homologous recombination. We describe a case of metastatic CRPC with germline BRCA2 mutation with acquired resistance to olaparib related to biallelic BRCA2 reversion mutations of both the germline and somatic loss of function alleles detected by circulating tumor DNA testing. We also summarize a retrospective analysis of 1,534 prostate cancer cases with ctDNA analysis showing a 1.6% incidence of germline BRCA2 mutations. Within the germline BRCA2-positive cases exposed to platinum chemotherapy or PARP inhibition, the prevalence of reversion mutations was 40%. This report documents the frequency of reversion mutations in a large cohort of prostate cancer patients carrying of BRCA mutations. It also shows the potential utility of ctDNA analyses for early detection of reversion mutation driving tumor resistance.

Polyclonal RB1 mutations and acquired resistance to CDK 4/6 inhibitors in patients with metastatic breast cancer.

Background: While deregulation of the cyclin D1-CDK4/6-retinoblastoma pathway is common in hormone receptor positive (HR+) breast cancer, Rb is usually intact in HR+ breast cancer, and targeted CDK 4/6 inhibitors that act upstream of Rb, are routinely being utilized in clinical practice. However, factors that can lead to clinical resistance to CDK 4/6 inhibitors are not known. Patients and methods: We identified patients who had pre- and post-genotyping in tissue and peripheral blood samples after receiving CDK 4/6 inhibitors. Genotyping was carried out in tumor tissue or blood collected before start of CDK 4/6 inhibitor and after disease progression on CDK 4/6 inhibitor, covering more than 90% of the coding region in RB1. Results: We identified detectable acquired RB1 mutations in circulating tumor DNA (ctDNA) after exposure to CDK4/6 inhibitor (palbociclib, palbociclib, ribociclib) for 5, 8, and 13 months, respectively, in three patients. The RB1 mutations included substitution in donor splicing site of exon 8 of the RB1 gene in patient #1; substitution in donor splicing site of exon 22 of RB1 gene, exon 19 deletion, exon 3 insertion in patient #2; and RB1 exon 16 H483Y mutation in patient #3. None of these RB1 mutations were present in the pre-CDK 4/6 specimen highlighting these molecular alterations, which lead to functional loss of Rb1, likely emerged under selective pressure from the CDK4/6 inhibitor potentially confering therapeutic resistance. Conclusion: This is the first clinical report to describe the emergence of somatic RB1 mutations after exposure to palbociclib or ribociclib, in patients with metastatic breast cancer. Further research is needed to validate these findings, identify how these mutations temporally emerge under selective pressure of CDK 4/6 inhibitor, and develop rational therapeutic strategies.

The effects of a single course of a calculus-softening scaling and root planing gel. A scanning electron microscopic study.

The effect of a calculus scaling gel was evaluated as an adjunct to instrumentation in a double blind, split-mouth, clinical study. Fifteen comparable periodontally involved teeth from 5 patients were instrumented on the mesio-buccal root surface with the aid of either the test gel, placebo gel, or no gel until smoothness was achieved. Test or placebo gel was applied subgingivally for 10 minutes. Instrumentation time, ease, number of strokes, and gingival/tooth surfaces changes were recorded. Scanning electronic microscopic (SEM) evaluation of root surface topography was evaluated. The results demonstrated effective calculus removal in all treatment groups with no differences found between them. Instrumentation time, ease, and number of strokes were similar for all treatment groups. There were no harmful effects to soft or hard tissues. The results of this study do not support the use of calculus scaling gel as an adjunct to root instrumentation.

Comparison of postoperative bupivacaine with lidocaine on pain and analgesic use following periodontal surgery.

The purpose of this study was to compare postoperative administration of bupivacaine, a long-acting local anesthetic, with lidocaine, a short-acting local anesthetic, on pain perception and analgesic use following periodontal surgery. Ten male subjects were selected on the basis of having similar bilateral mandibular quadrants with moderate to severe periodontal disease requiring osseous surgery. The study was a matched-pair, double-blind design. Carpules of 2% xylocaine with 1:100,000 epinephrine and 0.5% bupivacaine with 1:200,000 epinephrine were wrapped in opaque tape and placed in separate coded envelopes. At the time of suturing, the quadrant was injected with one Carpule from one envelope. The Carpules from the second envelope were saved for the second surgery, which took place approximately one month later. Subjects were given standardized postoperative instructions and prescriptions for Peridex and Tylenol #3. They were told not to take the analgesic unless pain or discomfort occurred. They were given a self-administered questionnaire and asked to assess pain and/or discomfort 2, 4, 6, 8, 10, and 12 hours after the procedure, the amount of analgesic taken, and time when complete sensation returned. Results showed that the quadrants which received lidocaine maintained postoperative anesthesia an average of 2.47 hours while the Marcaine quadrants had a significantly longer duration of 5.62 hours. A large intra- and intersubject variability was noted in the amount of analgesic taken. The lidocaine group reported an average of 3.70 tablets versus a significantly smaller amount for the bupivacaine group of 1.60 tablets. Throughout all time intervals, the bupivacaine group reported significantly less pain than the lidocaine group. When used at the end of a mandibular periodontal surgical procedure, bupivacaine provides a significantly greater duration of anesthesia, decreased postoperative pain, and a reduction of anesthesia, decreased postoperative pain, and a reduction in the amount of analgesics taken.

Brain glucose uptake and unawareness of hypoglycemia in patients with insulin-dependent diabetes mellitus.

BACKGROUND: In patients with insulin-dependent diabetes mellitus (IDDM) whose treatment results in nearly normal mean plasma glucose concentrations, an unawareness of hypoglycemia can develop, and such patients are at increased risk for seizures and coma. We tested the hypothesis that during hypoglycemia, these patients would have normal glucose uptake in the brain and that consequently no sympathoadrenal activation would begin, resulting in an unawareness of hypoglycemia. METHODS: We measured glucose uptake in the brain at plasma glucose concentrations of 105 and 54 mg per deciliter (5.8 and 3.0 mmol per liter) in 24 patients with IDDM, stratified into three groups according to their glycosylated hemoglobin values (mean [+/- SD] values, 7.2 +/- 0.5, 8.5 +/- 0.4, and 10.2 +/- 1.3 percent) and compared the values for brain glucose uptake with those measured in 15 normal subjects at plasma glucose concentrations of 85 and 55 mg per deciliter (4.2 and 3.1 mmol per liter). We also recorded the subjects' hypoglycemic-symptom scores and measured their plasma concentrations of counterregulatory hormones. RESULTS: There was no significant change in the uptake of glucose in the brain (calculated as the uptake during hypoglycemia minus the uptake during normoglycemia) among the patients with IDDM who had the lowest glycosylated hemoglobin values (+0.6 +/- 2.0 mg [3.3 +/- 11.1 mumol] per 100 g of brain tissue per minute, P = 0.39). Conversely, glucose uptake in the brain fell in both the group with intermediate values (a decrease of 1.3 +/- 1.0 mg [7.2 +/- 5.6 mumol] per 100 g per minute, P = 0.009) and the group with the highest values (a decrease of 1.8 +/- 1.6 mg [10.0 +/- 9.0 mumol] per 100 g per minute, P = 0.01), as it did in the normal subjects (a decrease of 1.6 +/- 1.8 mg [9.0 +/- 10.1 mumol] per 100 g per minute, P = 0.003). The responses of plasma epinephrine and pancreatic polypeptide and the frequency of symptoms of hypoglycemia were lowest in the group with the lowest glycosylated hemoglobin values. CONCLUSIONS: During hypoglycemia, patients with IDDM who have nearly normal glycosylated hemoglobin values have normal glucose uptake in the brain, which preserves cerebral metabolism, reduces the responses of counterregulatory hormones, and causes an unawareness of hypoglycemia.

Adaptation in brain glucose uptake following recurrent hypoglycemia.

Brain glucose metabolism is impaired during hypoglycemia, but, if sustained, brain metabolism reverts to normal in animal models--data in man are lacking. We tested the hypothesis that adaptations occur to allow maintenance of normal rates of brain glucose uptake (BGU) following recurrent hypoglycemia in man. Twelve normal humans were studied over 4 days. On the initial day, arterial plasma glucose concentrations were decreased from 4.72 to 2.50 mmol/liter in five 0.56 mmol/liter steps. Cerebral blood flow, brain arteriovenous glucose difference, BGU, and cognitive function were quantitated at each step. BGU was initially impaired at the 3.61 mmol/liter glucose step (P = 0.04) and was antedated by increments in epinephrine that began at 4.16 mmol/liter (P = 0.03). The onset of hypoglycemic symptoms occurred during the 3.61 mmol/liter glucose step (P = 0.02), whereas tests of cognitive function generally deteriorated at the 3.05 mmol/liter step (P < 0.05). During the next 56 hr, mean glucose concentrations were kept at 2.9 +/- 0.1 mmol/liter and reached normal only during meals. The stepped clamp protocol was repeated beginning at 4.16 mmol/liter on the last day. No decrement in BGU was observed at any step; cognitive function was preserved until significantly lower glucose concentrations on the final day relative to the first (P = 0.04). Subjects remained asymptomatic of hypoglycemia until they reached a glucose concentration of 2.50 mmol/liter (P < 0.001 vs. day 1), while initial increments in all counterregulatory hormones were forestalled to lower glucose steps than on day 1. Therefore, adaptations occur that allow normal BGU and cerebral function to be maintained during recurrent systemic hypoglycemia. Counterregulatory events that should result in symptoms of hypoglycemia and increments in endogenous glucose production are prevented until extremely subnormal glucose concentrations.

Diminished brain glucose metabolism is a significant determinant for falling rates of systemic glucose utilization during sleep in normal humans.

Systemic glucose utilization declines during sleep in man. We tested the hypothesis that this decline in utilization is largely accounted for by reduced brain glucose metabolism. 10 normal subjects underwent internal jugular and radial artery cannulation to determine cerebral blood flow by N2O equilibrium technique and to quantitate cross-brain glucose and oxygen differences before and every 3 h during sleep. Sleep stage was graded by continuous electroencephalogram, and systemic glucose turnover was estimated by isotope dilution. Brain glucose metabolism fell from 33.6 +/- 2.2 mumol/100 g per min (mean +/- SE) before sleep (2300 h) to a mean nadir of 24.3 +/- 1.1 mumol/100 g per min at 0300 h during sleep (P = 0.001). Corresponding rates of systemic glucose utilization fell from 13.2 +/- 0.8 to 11.0 +/- 0.5 mumol/kg per min (P = 0.003). Diminished brain glucose metabolism was the product of a reduced arteriovenous glucose difference, 0.643 +/- 0.024 to 0.546 +/- 0.020 mmol/liter (P = 0.002), and cerebral blood flow, 50.3 +/- 2.8 to 44.6 +/- 1.4 cc/100 g per min (P = 0.021). Brain oxygen metabolism fell commensurately from 153.4 +/- 11.8 to 128.0 +/- 8.4 mumol/100 g per min (P = 0.045). The observed reduction in brain metabolism occurred independent of stage of central nervous system electrical activity (electroencephalographic data), and was more closely linked to duration of sleep. We conclude that a decline in brain glucose metabolism is a significant determinant of falling rates of systemic glucose utilization during sleep.

Octreotide reverses hyperinsulinemia and prevents hypoglycemia induced by sulfonylurea overdoses.

Emergency therapy of sulfonylurea overdoses with glucose is often unsatisfactory because glucose stimulates insulin release and initiates a need for escalating quantities of hypertonic glucose to maintain normoglycemia. We tested the hypothesis that octreotide, an analog of somatostatin, would reverse hyperinsulinemia induced by a sulfonylurea overdose. Eight normal subjects received glipizide (1.45 mg/kg) on three occasions. Within 3 h, all subjects became hypoglycemic (< 50 mg/dL) and were initially treated with 50% dextrose followed by 1) dextrose infusion, 2) octreotide (30 ng/kg.min, iv), or 3) diazoxide (300 mg, iv, every 4 h). Euglycemia (85 mg/dL) was maintained with supplementary dextrose in treatment limbs 2 and 3. Insulin concentrations were 4-5 times greater with dextrose alone or in combination with diazoxide than with octreotide (P < 0.01). Dextrose requirements during diazoxide or dextrose alone were not different, but were both greater than those during octreotide treatment (P < 0.0001). All therapies were stopped at 13 h. Glucose levels remained above 3.6 mmol/L (65 mg/dL) in six of eight subjects receiving octreotide for the remaining 4 h. Glucose fell to below 3.6 mmol/L within 1.5 h of stopping either dextrose or diazoxide in each subject. Overall, octreotide reduced and in four of eight subjects entirely eliminated the need for exogenous glucose after a large overdose of glipizide. We conclude that octreotide is safe and effective and should be strongly considered as a logical therapeutic alternative for this metabolic emergency.

The effectiveness of scaling and root planing with curets designed for deep pockets.

This study evaluates the effectiveness of subgingival scaling and root planing with longer shank, thinner blade, rigid curets compared to the standard rigid Gracey curet. A total of 35 non-molar teeth from 7 patients provided 140 root surfaces for evaluation; 52 root surfaces were instrumented with the rigid longer shank curets; 52 with the standard rigid Gracey curets; and 36 provided untreated controls. A bilateral matched design was utilized where contralateral teeth in the same arch were instrumented. Instrumentation was standardized at 15 minutes per tooth. Both scaled and unscaled teeth were extracted immediately after the experimental procedures. They were viewed under a stereomicroscope with a 0.10 mm grid to assess the percent of surface covered by calculus and unaltered cementum. The curet efficiency was also evaluated. The results indicated a significant treatment effect compared to the controls in relation to the percentage of residual calculus and curet efficiency. However, there was no significant difference between the rigid longer shank and standard rigid Gracey curets. There was a difference noted when tooth surfaces were evaluated. Mesial tooth surfaces had the least remaining calculus and demonstrated the best curet efficiency.