CIGB-552 has antitumor effects in vitro and in vivo
The studies of anticancer activity of CIGB-552 were performed usingin vitro culture systems as well as clinically relevant in vivo models, as is shown in figure 2. We began with the demonstration of a selective antiproliferative activity in several cancer cell lines. We demonstrated that CIGB-552 has powerful antiproliferative and cytotoxic effects compared to its precursor peptide L-2. In this assays, we evaluated the effect of the peptide on non-tumor cell lines where the IC50 was higher respect to tumor cells. These differences suggest the selectivity of this peptide to malignant cells. The IC50 values observed in tumor cell lines suggest a tumor type-dependent pattern of sensitivity (Fernandez Masso et al., 2013).
Since apoptosis often occurs as a consequence of a cell cycle blockade, we checked whether the cytotoxicity of L-2 was mediated by an alteration of the cell division cycle. Analyses by flow cytometry of tumor cells treated with L-2, showed the absence of the G2/M peak and the accumulation of cells in S phase. Recently, we demonstrated that this difference is caused by the internalization mechanism of the peptide (Vallespi et al., 2010).
The in vivo therapy on solid tumors was a subsequent phase in the proof of concept of CIGB-552 as an anticancer drug (Figure 2). In our institute, we developed a murine model of tumor CT-26. This model was used to study the administration route and the dosage regimen for the treatment. Firstly, we demonstrated that the subcutaneous administration of CIGB-552 led to a significant reduction of tumor growth compared to the group treated with saline solution. After two week of treatment, the tumor volume was decreased and this behavior was observed until the end of the study (Vallespi et al., 2014). Therefore, this in vivo study demonstrated that subcutaneous administration of CIGB-552 was able to inhibit the 50% of tumor growth injecting the peptide once a week, during 2 weeks. In collaboration with an EPO-Berlin institute, we further evaluated the effect of a subcutaneous administration of CIGB-552 in a xenograft model of human colon cancer HT-29. In this mouse model, we analyzed the body weight as an indicator of tolerability. As occurs in the syngeneic CT26 model, the peptide showed a significant reduction of tumor volume compared with the control group. All mice of groups treated with CIGB-552 keep the body weight during the study, indicating safety and tolerability. This study included a group treated with Oxaliplatin, a standard drug in the therapy of colorectal cancer. Oxaliplatin induced a significant inhibition of tumor growth, but this effect was accompanied by a severe loss of body weight and two deaths probably due to its high toxicity (Vallespi et al., 2014).
The mechanisms involved in the reduction of tumor growth in response to CIGB-552 were evaluated in both murine syngeneic and human xenograft models. In vivo , the groups treated with CIGB-552 exhibit induction of apoptosis in the tumor and a decrease of microvessels density (Vallespi et al., 2014). The resistance to programed cell death and the sustained angiogenesis are included in a group of properties called hallmarks of cancer, a set of functional capabilities acquired during the multistep development of human tumors. Thus, the antitumor mechanism of the peptide CIGB-552 is associated with proteins and signaling pathways that trigger apoptosis inhibit the proliferation and induce the reduction of blood vessels formation.
Monolayers of tumor cells cultivated in vitro and mouse xenografts implanted with those cells, have been the standard toolkit to cancer biologists for decades. However, the need for better and more clinically predictive models of human cancer is imminent. Spontaneous cancer in pet dogs is considered an attractive model to study the efficacy of drug candidates to cancer therapy (Rowell, McCarthy, & Alvarez, 2011). Cancers in affective animals such as pet dogs are characterized by histological features similar to human cancer, tumor growth over long periods, inter-individual and intra-tumor heterogeneity, the development of recurrent or resistant diseases, and metastasis to relevant distal sites (Hawai et al., 2013). Based on that, we evaluated the safety, tolerability and antineoplastic effect of CIGB-552 in tumor-bearing dogs. In this study, our group keeps the same dosage regimen used by subcutaneous route in mouse models. The treatment with CIGB-552 had not any negative effect on total leukocytes, do not affect the levels of liver transaminases or hemoglobin during the study (Vallespi et al., 2017). Interesting, the white blood count return to normal levels after completing the study, which suggest that treatment with the peptide do not induce leucopenia, a common issue in chemotherapy regimens. The dogs enrolled into the study showed a tumor regression (> 50 %), demonstrating a stabilization of the disease (Vallespi et al., 2017).
Altogether, these preclinical results validate the peptide CIGB-552 as a potent antiproliferative and antitumor drug which mechanism is related with the inhibition of various hallmarks of cancer. In addition, the subcutaneous administration of CIGB-552 is safe and successful as an anticancer treatment at least, at preclinical level.