Tissue response after implantation of pure titanium and bioresorbable screws in scapula with postoperative irradiation: an experimental study on rats.

OBJECTIVE: The study focuses on the comparison of tissue reaction to titanium and bioresorbable implants with and without postoperative irradiation on an animal model. MATERIALS AND METHODS: Thirty-nine LEW/W rats were randomly assigned to experimental or control groups. One titanium and one bioresorbable screw (poly-L-lactide [PLLA] and L- and D-lactide poly-L/D-lactide [PDLLA]) were implanted into the left scapulas of 24 rats. Half of them received 30 Gy to the operation site and the other half received 42 Gy. In the control groups, 3 rats received 30 Gy, and 6 rats received 42 Gy to the scapula area without operation; and 6 rats had implants inserted as in the experimental group, but received no postoperative irradiation. The scapulas were removed 14 or 30 days after irradiation and a histologic analysis was performed. RESULTS: The host tissue reaction to titanium and PLLA-PDLLA screws without postoperative irradiation was of similar intensity. In irradiated animals, the inflammatory tissue reaction was more evident around the titanium screws than around the bioresorbable screws, irrespective of the radiation dose and of the time that elapsed from the irradiation. The reaction was more evident on the 14th day than on the 30th day after the last radiation dose (70 and 86 days after surgery, respectively). The intensity of the inflammatory tissue reaction, irrespective of the implant type, was more intense in the group irradiated with 42 Gy. CONCLUSIONS: PLLA-PDLLA implants appear to cause less tissue reaction after irradiation and could be safer reconstructive devices than titanium implants for patients undergoing surgery and adjuvant radiotherapy for cancer.

Chronic mild stress facilitates melanoma tumor growth in mouse lines selected for high and low stress-induced analgesia.

Both chronic stress conditions and hyperergic reaction to environmental stress are known to enhance cancer susceptibility. We described two mouse lines that displayed high (HA) and low (LA) swim stress-induced analgesia (SSIA) to investigate the relationship between inherited differences in sensitivity to stress and proneness to an increased growth rate of subcutaneously inoculated melanoma. These lines display several genetic and physiological differences, among which distinct sensitivity to mutagens and susceptibility to cancer are especially noticeable. High analgesic mice display high proneness both to stress and a rapid local spread of B16F0 melanoma. However, stress-resistant LA mice do not develop melanoma tumors after inoculation, or if so, tumors regress spontaneously. We found that the chronic mild stress (CMS) procedure leads to enhanced interlinear differences in melanoma susceptibility. Tumors developed faster in stress conditions in both lines. However, LA mice still displayed a tendency for spontaneous regression, and 50% of LA mice did not develop a tumor, even under stressed conditions. Moreover, we showed that chronic stress, but not tumor progression, induces depressive behavior, which may be an important clue in cancer therapy. Our results clearly indicate how the interaction between genetic susceptibility to stress and environmental stress determine the risk and progression of melanoma. To our knowledge, HA/LA mouse lines are the first animal models of distinct melanoma progression mediated by inherited differences in stress reactivity.

Distinct susceptibility to inoculated melanoma and sensitivity to cancer pain in mouse lines with high and low sensitivity to stress.

Approximately 30 years ago, we developed 2 mouse lines with enhanced and decreased opioid system activity using bidirectional selection for high (high analgesia [HA] line) and low (low analgesia [LA] line) swim stress-induced analgesia. These mouse lines differ substantially in pain sensitivity, measured as hind paw withdrawal latency in a hot plate test. Moreover, compared with the LA mice, the HA mice exhibited reduced energy expenditure under stress and different depression-like behavior as well as higher sensitivity to mutagens and the high frequency of spontaneous and carcinogen-induced tumors. In the current study, we observed distinct differences in the growth rate of orthotopically implanted melanoma and the onset of cancer pain. Whereas the HA line was prone to tumors and carcinogenesis was rapid in all specimens, the LA mice either did not develop tumors (70%) or developed tumors that often regressed spontaneously (30%). Animals from both lines developed robust thermal hypersensitivity in the tumor-bearing paw compared with animals that were injected with saline. However, we found that hyperalgesia in tumor-bearing mice persists for a much shorter time in the HA than in LA mice. Naltrexone, given subcutaneously, restored hyperalgesia in the HA mice, whereas it was ineffective in the LA mice. The results suggest that activity of the opioid system may influence carcinogenesis and the intensity of cancer pain and indicates that HA and LA mice are good models for such studies.

Susceptibility loci and chromosomal abnormalities in radiation induced hematopoietic neoplasms in mice.

Genetics of susceptibility to radiation-induced hematopoietic neoplasms and somatic chromosomal aberrations were analyzed in 305 backcross (CcS-17xCcS-2)xCcS-2 mice of two CcS/Dem recombinant congenic strains. Irradiated CcS-2 mice were previously shown to exhibit high frequency of myeloid neoplasms whereas irradiated CcS-17 mice were susceptible to T-cell lymphomas. Mice were exposed to four whole-body irradiation doses of 1.7 Gy at one week intervals, which resulted in 139 hematopoietic neoplasms. The hematopoietic neoplasms were classified according to the Bethesda proposals for classification of lymphoid and nonlymphoid hematopoietic neoplasms in mice. Genotyping of mice with 24 microsatellite markers and subsequent statistical analysis indicated linkage of the radiation induced T-lymphomas to two loci on chromosome 10 (D10Mit134) and chromosome 12 (D12Mit52). T-lymphoma susceptibility appeared to be linked to D10Mit134 in a sex dependent way. In contrast, the myeloid-granulocytic leukemias susceptibility is linked to combined effects of chromosome 5 (D5Mit179) and 16 (D16Mit34). Cytogenetic analysis was performed according to the standard G-bands procedure and confirmed using FISH method. We found non-random numerical and structural chromosomal changes in lymphoid neoplasms. Cytogenetic analysis indicated chromosomal aberrations presumably associated with lymphomagenesis, no specific cancer-related rearrangements were observed.

[Genetically engineered mice: mouse models for cancer research]. / Genetycznie zmodyfi kowane myszy jako modele do badan w onkologii

Genetically engineered mice (GEM) have been extensively used to model human cancer. Mouse models mimic the morphology, histopathology, phenotype, and genotype of the corresponding cancer in humans. GEM mice are created by random integration of a transgene into the genome, which results in gene overexpression (transgenic mice); gene deletion (knock-out mice); or targeted insertion of the transgene in a selected locus (knock-in mice). Knock-out may be constitutive, i.e. total inactivation of the gene of interest in any cell, or conditional, i.e. tissue-specific inactivation of the gene. Gene knock-down (RNAi) and humanization of the mouse are more sophisticated models of GEM mice. RNA interference (RNAi) is a mechanism in which double-stranded RNAs inhibits the respective gene expression by inducing degradation of its mRNA. Humanization is based on replacing a mouse gene by its human counterpart. The alterations in genes in GEM have to be heritable. The opportunities provided by employing GEM cancer models are: analysis of the role of specific cancer genes and modifier genes, evaluation of conventional cancer therapies and new drugs, identification of cancer markers of tumor growth, analysis of the influence of the tumor's microenvironment on tumor formation, and the definition of the pre-clinical, discrete steps of tumorigenesis. The validation of mouse models of human cancer is the task of the MMHCC (Mouse Models of Human Cancer Consortium). The GEM models of breast, pancreatic, intestinal and colon, and prostate cancer are the most actively explored. In contrast, the models of brain tumors and ovary, cervical, and skin cancer are in the early stage of investigation.