CSF1 Antisense Treatment Suppresses Growth of Human Embryonic and Colon Carcinoma Xenografts in Mice

3.1.1. Human Embryonic Cancer Cells Upregulate Host CSF-1 Production

Human embryonic cancer cells (CRL-2073) show no detectable mRNA or protein for human CSF-1 or CSF-1R in vitro. When these cells are xenografted into the testis of SCID mice, however, mouse tissue CSF-1 gene and protein expression increases significantly compared to untreated mice. Associated with increasing CSF-1 tissue expression is an enhanced infiltration of macrophages within and surrounding the tumor. These findings indicate that human embryonic cancer cells stimulate increased host tissue expression of CSF-1. Correlated with these results, increased mouse CSF-1R expression is seen in tumor lysates (40).

3.1.2. CSF-1 Oligodeoxyribonucleotide Treatment Suppresses CSF-1 Expression and the Growth of Embryonic Tumor Xenografts

Severe combined immunodeficient (SCID) mice bearing established human embryonic tumors were treated systemically with CSF-1 antisense oligodeoxyri-bonucleotides (ODNs), scrambled ODN or Ringer's solution. Antisense ODN treatment was well tolerated. Local inflammatory reactions were not observed and no significant changes in the complete blood count (CBC) of treated mice were seen. Treatment with CSF-1 antisense ODN significantly downregulated tissue CSF-1 mRNA and protein levels and suppressed the growth of embryonic tumors to dormant levels. Marked differences were found in the testicular weight between SCID mice with embryonic tumors treated with CSF-1 ODN for 2 wk

(89 ± 32 mg tumor weight) and those treated with Ringer's solution (285 ± 31 mg) or scrambled ODN (278 ± 27 mg) (40).

3.1.3. CSF-1 Antisense ODN Decreases Angiogenic Activity and MMP-2 Expression in Embryonic Tumor Xenografts

In human embryonic cancer cell xenografts, both intravital video microscopy and histomorphometry of embryonic tumors showed a significantly increased density of vascular sprouts in controls compared to untreated mice that returned to baseline levels after CSF-1 antisense ODN treatment in mouse testis. Similarly, VEGF-A, KDR/flk-1 and Ang-1 mRNA levels were significantly reduced in CSF-1 antisense ODN-treated mice. Protein expression of MMP-2, a key molecule in mediating tumor metastasis and angiogenesis, increased significantly in controls compared to untreated animals. Treatment with CSF-1 antisense ODN but not scrambled ODN, significantly downregulated MMP-2 protein expression in testicular tissue. Positive MMP-2 antigen staining was primarily observed in the intertubular interstitium, the capsule of testicular tubules and less frequently in the walls of vessels in untreated and ODN-treated mice, whereas in control mice, MMP-2 expression was primarily intratubular (40).

3.1.4. CSF-1 Antisense Treatment Suppresses the Growth of a Human Colon Carcinoma Xenografts and Increases Survival in Mice

The promising results with CSF-1 antisense treatment in the mouse model of human embryonic tumorogenicity encouraged us to test CSF-1 antisense treatment in other human tumor models. We chose colon carcinoma because of its poor prognosis, short median survival, and high incidence, and utilized SW-620 human colon carcinoma cells that lack expression of CSF-1 or CSF-1R. Using an established flank model in nude mice, we showed that host CSF-1 tissue mRNA and protein levels increase with tumor progression. After 2 wk of CSF-1 antisense ODN treatment at 5 mg/kg/d, CSF-1 mRNA and protein expression was significantly downregulated compared to controls. Tumor growth was markedly retarded in mice following CSF-1 blockade and tumor weights were significantly decreased compared to controls. Similar to mice bearing embryonic tumors, CSF-1 treatment was well tolerated in nude mice bearing colon carcinoma and the CBC was not significantly influenced by the treatment. MMP-2 protein expression in tumor lysates markedly increased with tumor progression and declined significantly following CSF-1 inhibition. CSF-1 ODN, but not scrambled ODN treatment, resulted in downregulation of mRNA levels of Ang-1 and the VEGF-A receptors Flt-1 and KDR/flk-1 associated with decreased angiogenesis. Long-term (6 mo) survival was observed in 8 of 14 mice following CSF-1 blockade, whereas all mice were dead after 65 d in the control groups. At sacrifice 6 mo after therapy, no metastases were detected. At

65 d (atwhich time the last animal in the control groups died), 85.7% of CSF-1 antisense-treated mice were still alive.

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