Clinical efficacy of sequential treatments in KRASG12C-mutant metastatic colorectal cancer: findings from a real-life multicenter Italian study (CRC-KR GOIM).

BACKGROUND: The presence of KRASG12C mutation in metastatic colorectal cancer (mCRC) correlates with poor outcome. Although different selective inhibitors are under clinical development, the optimal treatment remains uncertain. Thus, we conducted a retrospective analysis in a large cohort of patients with KRASG12C mCRC treated in 12 Italian oncology units. PATIENTS AND METHODS: Patients with unresectable mCRC harboring KRASG12C mutation receiving a first-line chemotherapy doublet or triplet between 2011 and 2021 were included in the study. Evaluation of overall response rate (ORR), progression-free survival (PFS) and overall survival (OS) analysis was carried out. RESULTS: A total of 256/6952 (3.7%) patients with mCRC displayed KRASG12C mutation; of these, 111 met the inclusion criteria. The ORR of first-line therapy was 38.7% (43/111). Median PFS (mPFS) was 9 months [95% confidence interval (CI) 7.5-10.5 months]. After progression, only 62% and 36% of the patients are fit to receive second or third lines of treatment, with limited clinical benefit. Median OS (mOS) was 21 months (95% CI 17.4-24.6 months). In patients receiving first-line triplet chemotherapy, ORR was 56.3% (9/16), mPFS was 13 months (95% CI 10.3-15.7 months) and mOS was 32 months (95% CI 7.7-56.3 months). For irinotecan-based doublets, ORR was 34.5 (10/29), mPFS was 9 months (95% CI 6.4-11.6 months) and mOS was 22 months (95% CI 16.0-28.0 months). With oxaliplatin-based doublets ORR was 36.4% (24/62), mPFS was 7 months (95% CI 4.6-9.4 months) and mOS was 18 months (95% CI, 13.6-22.4 months). CONCLUSION: Patients with KRASG12C-mutant mCRC had a disappointing response to standard treatments. Within the limitations of a retrospective study, these results suggest that first-line chemotherapy intensification with FOLFOXIRI is a valid option in fit patients.

Morphological maturation of thalamic neurons as studied in fetal neural transplants.

This study attempts to determine whether fetal thalamic neuroblasts from rat embryos (embryonic age 15 days) labeled with horseradish peroxidase (HRP) can differentiate into their normal dendritic phenotype when transplanted as a cell suspension into a lesioned site in the adult somatosensory thalamus. The HRP labeling provided a Golgi-like staining of numerous neurons up to 12-14 days after transplantation. There were three main results. 1) As early as 2 days after transplantation three morphologic cell types were observed: Two were bipolar and the third multipolar. These cellular profiles are characteristic of adult ventroposterolateral, reticular, and ventroposteromedial neurons and suggest that transplanted neurons can take shape in the absence of specific arrangements of afferent fibers. 2) The initial stage of dendritic growth was characterized by numerous growing specializations and consisted of a rapid, arborizing growth that appeared to proceed at an accelerated rate relative to normal development. During the later stage, which was characterized by the great reduction of growing specializations, dendritic remodeling resulted in a simpler morphology, and the transplanted neurons did not achieve an adult morphology. 3) Putative axons exhibiting growth cones were present in impressive densities in the transplants, and a number of them grew into the neuron-depleted host thalamus. A very small number of axons grew into host gray matter outside the lesioned area, indicating that neurodegenerative areas provide a better substrate for neurite outgrowth than intact tissue. In rare instances axons were visible in the internal capsule, indicating that the biochemical inhibition provided by mature myelin and oligodendrocytes may not be an absolute obstacle to axonal growth.

Neuroplasticity as a basis for therapeutics in spinal cord injuries and diseases.

The concept of neuroplasticity in the adult is now well accepted. Amongst the most striking neuroplastic phenomena are those that systematically follow a lesion in the neural system itself. The work reported in this symposium emphatically illustrates the plasticity of neurons participating in spinal cord networks in various conditions that involve axonal lesions and neuronal degeneration. The purpose of this paper is to evaluate the potential for post-lesion neuroplastic changes to serve as a basis for future therapeutics with specific emphasis on two important pathologies observed in humans: spinal cord injuries and degenerative motoneuronal diseases. Spontaneous attempts at axonal regeneration and growth of axotomized neurons can be seen after a spinal trauma although the number of neurons involved is often low and variable from one population to another. In any case, axons fail to cross the scar tissue, most probably due to specific neurono-glial interactions. Successful recovery of neural systems (and therefore possible functional recovery) that can be expected as a result of these spontaneous attempts at regeneration of axotomized axons is, overall, very poor. Innumerable attempts have been made to provide severed axons in the spinal cord with a suitable substrate. Altogether, the results obtained when regeneration is facilitated in the adult through a series of different ways point to several remarkable conclusions: (i) adult neurons are indeed able to grow an axon; (ii) the failure to grow an axon after axotomy which is normally observed depends, at least in part, on an unsuitable substrate; (iii) growth ability seems to be much more restricted for neurons with large myelinated axons than for neurons with unmyelinated ones. Several therapeutic avenues can be considered that can be grouped in three different endeavors: to fill in the gap, and to change the nature of the gap, to protect fibers that have not been directly injured. An additional possibility is that compensation of lost inputs by transplants of monoaminergic neurons below the level of the lesion can be of therapeutic value. Experimental models of spinal neurodegeneration have been less intensely studied than those of spinal cord injuries. Data suggesting the existence of spontaneous neuronal plasticity in the aftermath of motoneuronal loss are, however, available. Two types of neuronal attempts at regeneration can be considered: sprouting of surviving motoneurons leading to the reoccupation of vacant motor endplates and possible attempts to grow by afferents that have been deprived of their postsynaptic target cells. These attempts may be facilitated experimentally by the use of growth factors and fetal neural transplants. The use of growth factors may be of therapeutic value and preliminary studies are presently in progress. The therapeutic value of neural transplants to replace lost motoneurons in amyotrophic lateral sclerosis or spinal muscular atrophies is not easily determined. It seems excluded that transplanted motoneurons replace lost neurons at all levels of the neuraxis. In contrast, neural transplantation may be interesting to replace a specific set of motoneurons, namely those controlling respiratory muscles.

Effects of MPTP on the fine structure of neurons in substantia nigra of dogs.

This study evaluates fine structural changes in neurons from pars compacta of substantia nigra in dogs 1 and 4 days after administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. The toxin induced a disruption and high amplitude swelling of mitochondria, and dispersion of rough endoplasmic reticulum at 4 days. Mitochondria in dendrites were less damaged than those in the soma. Swelling of myelinated axons in the nigrostriatal pathway was evident at 1 and 4 days after injection. Similar morphologic changes are produced by axotomy and inhibitors of mitochondrial function.

Asymmetric and symmetric synaptic junctions in the dorsal lateral geniculate nucleus of cat and monkey.

We have investigated the applicability of traditional classifications of synaptic junctions in the dorsal lateral geniculate nucleus (DLGN) of the cat and monkey. Our principal sample is restricted to synapses made by the retinal terminal (round vesicles) in DLGN and to synapses made by flattened vesicle processes that were postsynaptic to the retinal terminal. We inspected consecutive thin sections through 250 synaptic junctions that showed clear synaptic clefts in every section. The thickness of the membrane and postsynaptic density (PSD) was measured on each section and an average thickness was computed for each synaptic junction. In both species the frequency distribution for these measurements forms an uninterrupted progression from the absence of a continuous PSD through the presence of a heavy density with most synaptic contacts falling in the midrange. Twenty-two of the round vesicle profiles and 40 of the flat vesicle profiles we studied had very modest densities (13-16 nm) and exhibited a continuous PSD on some sections, but only small puffs or a complete lack of density on others. We concluded that this group which constituted 25% of the synaptic contacts we studied could not be classified as asymmetric or symmetric. As a group the round vesicle synaptic junctions exhibited a heavier PSD than the flat vesicle contacts. The difference between the mean thickness in both species was statistically significant. However, we hesitate to describe the round vesicle synapses as asymmetric and the flat vesicle contacts as symmetric because such a large proportion of the former made synaptic contacts with a PSD thickness within the range of the latter.

Synaptology of retinal terminals in the dorsal lateral geniculate nucleus of the cat.

We have made a fine structural investigation of the synaptic patterns made by axon terminals of retinal ganglion cells in the dorsal lateral geniculate nucleus of the cat. We compared the retinal input to dendritic processes that bear clusters of large appendages with the retinal input to relatively smooth dendritic segments that have only a few isolated spines. The study was restricted to the portion of laminae A and A1 that receive central visual field input. We were able to completely reconstruct 33 individual terminal boutons from long series of consecutive thin sections. Retinal terminals that were presynaptic to dendritic appendages tended to occupy the central position in the complex synaptic zones of geniculate fine structure called glomeruli. These terminals were surrounded by significantly more profiles than retinal terminals that were presynaptic to dendritic stems and averaged twice as many synaptic contacts per terminal bouton. The retinal input to dentritic appendages was heavily involved in a specific synaptic pattern called the triadic arrangement while retinal input to dendritic stems was only lightly involved in triads. Dendritic appendages in triads received greater synaptic input from profiles with flattened vesicles than did the dendritic stems that were found in triads.

Quantitative analysis of the optic nerve of the North American opossum (Didelphis virginiana): an electron microscopic study.

On the basis of an electron microscopic examination of the optic nerve of the North American opossum it was estimated that the nerve has approximately 100,000 axons, of which 98% are myelinated. The myelinated axons ranged from 0.3 to 6.7 micrometers in diamter (mean 1.6 micrometers), while unmyelinated axons were 0.2 to 1.6 micrometers in diameter (mean 0.6 micrometers). Axoplasm and axon (axoplasm plus myelin) diameter spectrums were unimodal and positively skewed. The mean of the ratio of axoplasm to axon diameter was 0.69. However, this ratio varied widely across axons and was nonlinearly distributed, decreasing with axon diameter. An inverse relationship between axon density and a high proportion of large-caliber axons was located dorsally in a cross section obtained near the eye. However, in sections obtained near the optic chiasm, regions having the highest proportion of large-diameter axons were in the ventral periphery of the nerve. It is suggested that within the 40-mm length of the nerve, there may be a change from a retinotopic organization of axons according to their diameter and central targets.

Evidence against the smooth endoplasmic reticulum as a continuous channel for the retrograde axonal transport of horseradish peroxidase.

The involvement of the axonal smooth endoplasmic reticulum as a channel for the retrograde axonal transport of horseradish peroxidase (HRP) has been tested by analysing serial sections of 52 HRP-positive organelles in chick optic nerves. The enzyme marker was injected in the posterior, contralateral optic tectum 10 h before fixation of young chicks. The two optic nerves, retinas and optic tecta were incubated for electron microscopic demonstration of HRP. Thin sections of the retinas and tecta and serial thin sections of the optic nerves were studied in some cases with the aid of a goniometer. Of the 52 organelles, 42% had a tubular shape, 46% were oval and 12% were multivesicular bodies. None of the organelles was found to have continuities with other membranous structures, including tubules or cisternae of the smooth endoplasmic reticulum. In 10 cases, the smooth endoplasmic reticulum was followed in serial sections over a length of up to 4 micrometer. In every case, the reticulum appeared to form a continuous system although some tubular extensions apparently ended blindly near other organelles. In neither the 10 series of serial sections nor in any other individual micrographs did any recognizable profile of the smooth endoplasmic reticulum contain HRP. Measurements of the thickness of the membranes of HRP-containing organelles, of the smooth endoplasmic reticulum and of plasmalemma were made, since these membranes have been distinguished on the basis of their thickness in other cells. The plasmalemma in the axons was about 20% thicker than that of the smooth endoplasmic reticulum, and about 9% thicker than that of HRP-labeled organelles. The membrane of the smooth endoplasmic reticulum and HRP-organelles could also be distinguished by this means. It is concluded that in chick retinal ganglion cell axons, HRP is not transported in a retrograde direction via a continuous channel of smooth endoplasmic reticulum.

Ontogenesis of receptive field characteristics in the dorsal lateral geniculate nucleus of the rabbit.

The responses of rabbit dorsal lateral geniculate neurons to light or optic nerve shock were tested for 415 units in 43 rabbit pups 2--20 days of age. Units were driven by optic nerve shock at the youngest ages tested, but could not be driven by light until postnatal day six. Examples of each of the three prominent categories of receptive fields found in the adult were first observed at 8 days of age. Cells with receptive field properties not characteristic of the dorsal lateral geniculate nucleus of the adult were encountered until 17 days of age. The percentage of neurons with uniform and motion sensitive receptive fields approached adult levels soon after eye opening (11--12 days) but the percentage of cells with concentric receptive fields showed a steady increase throughout the neonatal period studied. The relevance of our data to the development of the visual response in the dorsal lateral geniculate nucleus and striate cortex is discussed.