Upfront Osimertinib Alone vs. Osimertinib and Radiotherapy for the Treatment of EGFR-Positive NSCLC Brain Metastases: A Multi-Institutional Series

PURPOSE/OBJECTIVE(S)

Given the increased brain penetrance of osimertinib, the role of upfront radiotherapy (RT) has been questioned for the management of patients with EGFR+ NSCLC brain metastases (BM). We conducted a multi-institutional review of patients with EGFR+ NSCLC treated with upfront osimertinib or osimertinib in combination with RT for new or progressing BM.

MATERIALS/METHODS

Our multi-institutional analysis included 128 patients with 714 BM treated between 2013 and 2022. Two BM treatment groups were evaluated: (1) upfront osimertinib alone (n = 66) and (2) osimertinib + RT [whole brain radiation therapy or stereotactic/fractionated radiosurgery (SRS/FSRT)] prior or concurrently with osimertinib (n = 62)]; both groups began treatment within 2 months of BM diagnosis. Time-to-event analysis was conducted with the Kaplan-Meier (KM) method, and outcomes included intracranial control (IC) [both local and distant], intracranial progression free survival (IPFS), and overall survival (OS). A Cox proportional hazards model was utilized for multivariate analysis (MVA).

RESULTS

Median follow-up from BM diagnosis was 33.9 months (0.13-76.2 months). No differences in age (p = 0.46), sex (p = 0.72), DS-GPA (p = 0.08), KPS (p = 0.57), number of BM (p = 0.19) or volume of BM (p = 0.45), RT dose (p = 0.45), number of systemic metastases (p = 0.88), and patients symptomatic at presentation (p = 1.0) were noted. Prior treatment of BM was more common in the osimertinib + RT group (50% osimertinib + RT and 27% osimertinib; p = 0.01). The 12-month KM rates for osimertinib vs osimertinib + RT groups for IC were 72% vs 73% (p = 0.33); IPFS 53% vs 66% (p = 0.007); and OS 65% vs 80% (p = 0.025). On MVA, higher KPS (p = 0.002) was associated with increased OS and no extracranial metastasis with increased OS (p = 0.01) and IPFS (p = 0.001). MVA showed no association between osimertinib vs osimertinib + RT for IC, IPFS, or OS. Of the 66 patients treated with upfront osimertinib, 18 patients (27%) with 31 lesions eventually required RT for intracranial progression with the majority 72% being treated with SRS/FSRT at median of 13.5 months (1-22 months) following the start of osimertinib.

CONCLUSION

This study suggests that upfront osimertinib alone may provide sufficient intracranial control to allow RT to be deferred until further intracranial progression in select patients. Prospective trials are warranted to further guide treatment.

Diel periodicity and influence of age and mating on sex pheromone titer in gypsy moth,Lymantria dispar (L.)

The diel periodicity of sex pheromone titer from pheromone glands of femaleLymantria dispar is described. On the day of emergence (day 0), pheromone titer was generally low; means ranged from 1 to 4 ngcis- 7,8-epoxy-2-methyloctadecane during photophase and gradually increased to 8.4 ng over the course of scotophase. For day-1, -2, and -3 females, the diel fluctuations of titer were more pronounced. Lowest titers (5-9 ng) occurred 0-4 hr after lights-on, and peak titers (19-32 ng) were found 0-4 hr before lights-off. Comparison of the average daily titer among the different age groups (data pooled over six time points at 4-hr intervals) indicated that significantly less pheromone was extracted from glands of day-0 (4.5 ng) than day-1 (12.4 ng), day-2 (15.4 ng), or day-3 females (13.5 ng). No significant differences were found among the three older ages. Femalesin copula exhibited a rapid reduction in titer within the first 0.5 hr of mating initiation (7.6 ng vs. 19.5 ng from virgin females of similar age). After the second 0.5 hr, the reduction in titer was not nearly as marked, falling only to 4.5 ng. Twenty-four hours after mating, titer fell below the limits of detection (0.5 ng). All extracts from pheromone glands of virgin or mated females contained < 1.0 ng of the putative pheromone precursor, 2-methyl-cis-7-octadecene.

Regulation of pheromone biosynthesis by a brain hormone in two moth species

Experiments were performed to characterize the action of a brain hormone on pheromone biosynthesis in female redbanded leafroller and cabbage looper moths. Results showed that the two species differed in their respective control mechanisms. In the cabbage looper, pheromone titer from decapitated females that received either saline or brain extract injections was not significantly different from control females, suggesting that pheromone biosynthesis was not dependent on the presence of the brain hormone. In contrast, with redbanded leafroller females, studies using radiolabeled acetate incorporation as well as incorporation of deuterium-labeled hexadecanoic acid showed that (i) the brain hormone was required for pheromone biosynthesis, (ii) the brain hormone regulated pheromone biosynthesis by activating synthesis of octadecanoyl and hexadecanoyl intermediates, and (iii) the brain hormone did not control other enzymes in the pathway. Regulation of fatty acid synthetase was unlikely since assays of the enzyme from decapitated and normal females showed no differences in the amount or distribution of the 18- and 16-carbon acyl end products. These results in conjunction with those from organ cultures of the pheromone gland suggest that the brain hormone acts by increasing the substrate supply for fatty acid synthesis.

Toxicity of Bacillus thuringiensis Spore and Crystal Protein to Resistant Diamondback Moth (Plutella xylostella)

A colony of Plutella xylostella from crucifer fields in Florida was used in mortality bioassays with HD-1 spore, CryIA(a), CryIA(b), CryIA(c), CryIB, CryIC, CryID, CryIE, or CryIIA. The data revealed high levels of field-evolved resistance to HD-1 spore and all CryIA protoxins and no resistance to CryIB, CryIC, or CryID. CryIE and CryIIA were essentially not toxic. When HD-1 spore was combined 1:1 with protoxin and fed to susceptible larvae, spore synergized the activity of CryIA and CryIC 5- to 8-fold and 1.7-fold, respectively, and did not synergize the mortality of CryIIA. When fed to Florida larvae, spore failed to synergize the activity of all three CryIA protoxins, synergized the activity of CryIC 5.3-fold, and did not synergize the mortality for CryIIA. Binding studies with CryIA(b), CryIB, and CryIC were performed to determine possible mechanisms of resistance. The two techniques used were (i) binding of biotinylated toxin to tissue sections of larval midguts and (ii) binding of biotinylated toxin to brush border membrane vesicles prepared from whole larvae. Both showed dramatically reduced binding of CryIA(b) in resistant larvae compared with that in susceptible larvae but no differences in binding of CryIB or CryIC.

Sensitive and rapid detection of Clonorchis sinensis infection in fish by loop-mediated isothermal amplification (LAMP)

The fish-borne clonorchiasis caused by the oriental liver fluke Clonorchis sinensis is endemic in a number of countries with over 35 million people being infected globally. Rapid and accurate detection of C. sinensis in its intermediate host fish is important for the control and prevention of clonorchiasis in areas where the disease is endemic. In the present study, we established a loop-mediated isothermal amplification (LAMP) approach for the sensitive and rapid detection of C. sinensis metacercariae in fish. The specificity and sensitivity of primers designed from the C. sinensis cathepsins B3 gene were evaluated, and specific amplification products were obtained with C. sinensis, while no amplification products were detected with DNA of related trematodes, demonstrating the specificity of the assay. The LAMP assay was proved to be 100 times more sensitive than a conventional polymerase chain reaction for detection of C. sinensis. The established LAMP assay provides a useful tool for the rapid and sensitive detection of C. sinensis in fish, which has important implications for the effective control of human clonorchiasis.

Greenhouse tests on resistance management of Bt transgenic plants using refuge strategies

Experimental evaluation of the effectiveness of resistance management tactics is vital to help provide guidelines for the deployment of transgenic insecticidal crops. Transgenic broccoli expressing a Cry1Ac gene of Bacillus thuringiensis (Bt) and the diamondback moth, Plutella xylostella (L.), were used in greenhouse tests to evaluate the influence of size and placement of nontransgenic refuge plants on changes in resistance allele frequency and pest population growth. In the first test with an initial Cry1Ac-resistance (R) allele frequency of 0.007, P. xylostella were introduced into cages with the following treatments: 0, 3.3, 10, 20, and 100% refuge plants. Results after four generations showed that resistance could be delayed by increasing the proportion of refuge plants in the cage. Population growth was also influenced by refuge size with the highest populations occurring in treatments that had either no refuge plants or all refuge plants. In the second test, we evaluated the effect of refuge placement by comparing 20% separate and 20% mixed refuges. P. xylostella with an initial frequency of resistant alleles at 0.0125 were introduced into cages and allowed to cycle; later generations were evaluated for resistance and population growth. Separating the refuge had a pronounced effect on delaying resistance and slowing establishment of resistant larvae on Bt plants. Combining information from both trials, we found a strong negative correlation between the number of larvae on Bt plants and the mortality of the population in leaf dip bioassays. Results from larval movement studies showed that separate refuges delayed resistance better than mixed refuges because they conserved relatively more susceptible alleles than R alleles and did not increase the effective dominance of resistance.

Development and characterization of diamondback moth resistance to transgenic broccoli expressing high levels of Cry1C

A field-collected colony of the diamondback moth, Plutella xylostella, had 31-fold resistance to Cry1C protoxin of Bacillus thuringiensis. After 24 generations of selection with Cry1C protoxin and transgenic broccoli expressing a Cry1C protein, the resistance that developed was high enough that neonates of the resistant strain could complete their entire life cycle on transgenic broccoli expressing high levels of Cry1C. After 26 generations of selection, the resistance ratios of this strain to Cry1C protoxin were 12,400- and 63,100-fold, respectively, for the neonates and second instars by a leaf dip assay. The resistance remained stable until generation 38 (G38) under continuous selection but decreased to 235-fold at G38 when selection ceased at G28. The Cry1C resistance in this strain was seen to be inherited as an autosomal and incompletely recessive factor or factors when evaluated using a leaf dip assay and recessive when evaluated using Cry1C transgenic broccoli. Saturable binding of (125)I-Cry1C was found with brush border membrane vesicles (BBMV) from both susceptible and Cry1C-resistant strains. Significant differences in Cry1C binding to BBMV from the two strains were detected. BBMV from the resistant strain had about sevenfold-lower affinity for Cry1C and threefold-higher binding site concentration than BBMV from the susceptible strain. The overall Cry1C binding affinity was just 2.5-fold higher for BBMV from the susceptible strain than it was for BBMV from the resistant strain. These results suggest that reduced binding is not the major mechanism of resistance to Cry1C.

Assessment of insecticide resistance after the outbreak of diamondback moth (Lepidoptera: Plutellidae) in California in 1997

During an outbreak of the diamondback moth, Plutella xylostella (L.), in California in 1997, nine populations were collected from the major broccoli areas throughout the state. Populations were assayed for their susceptibility to currently used materials (Bacillus thuringiensis subsp. kurstaki, permethrin, and methomyl) and to newer materials that had not yet been commercially used in California (spinosad, emamectin benzoate, and chlorfenapyr). For the currently used insecticides, elevated levels of resistance were seen only with permethrin and seven of the nine populations had tolerance ratios (TR) of > 100. With the newer chemistries, TR values were all < 15. To compare potential cross-tolerance, TR values of the currently used insecticides were compared with TR values of the newer insecticides. There were significant relationships found between: methomyl and emamectin benzoate, methomyl and spinosad, and permethrin and spinosad. Further biochemical studies are needed to confirm the actual mechanisms that lead to these relationships and field tests are needed to determine what impact, if any, such TR levels would have on control in the field. These data indicate that resistance to at least one of the commonly used insecticides (permethrin) may have played a role in the outbreak during 1997. However, other factors may have been at least equally important. The winter of 1996-1997 was warmer than normal, and during the period from February through August of 1997 the amount of rainfall was < 50% of normal. Hot and dry conditions are known to be conducive to outbreaks of P. xylostella. These data add to an overall knowledge about the geographic variation of resistance in P. xylostella populations within the United States. They also serve as a baseline for monitoring changes in susceptibility to these newer insecticides and can also help explain the occurrence of outbreaks caused by factors other than insecticide resistance.

Field tests on managing resistance to Bt-engineered plants

Several important crops have been engineered to express toxins of Bacillus thuringiensis (Bt) for insect control. In 1999, US farmers planted nearly 8 million hectares (nearly 20 million acres) of transgenic Bt crops approved by the EPA. Bt-transgenic plants can greatly reduce the use of broader spectrum insecticides, but insect resistance may hinder this technology. Present resistance management strategies rely on a "refuge" composed of non-Bt plants to conserve susceptible alleles. We have used Bt-transgenic broccoli plants and the diamondback moth as a model system to examine resistance management strategies. The higher number of larvae on refuge plants in our field tests indicate that a "separate refuge" will be more effective at conserving susceptible larvae than a "mixed refuge" and would thereby reduce the number of homozygous resistant (RR) offspring. Our field tests also examined the strategy of spraying the refuge to prevent economic loss to the crop while maintaining susceptible alleles in the population. Results indicate that great care must be taken to ensure that refuges, particularly those sprayed with efficacious insecticides, produce adequate numbers of susceptible alleles. Each insect/Bt crop system may have unique management requirements because of the biology of the insect, but our studies validate the need for a refuge. As we learn more about how to refine our present resistance management strategies, it is important to also develop the next generation of technology and implementation strategies.