Biological features of tissue and bone sarcomas investigated using an in vitro model of clonal selection

Abstract

The malignancy progression is an evolutionary process in which tumor clones are selected and competed for the duration of the disease. Intratumor heterogeneity is one of the key problems in the development of treatment methods for cancer patients. In this study we obtained metastatic soft tissue and bone sarcomas (STBSs) cultures from 54 patients, performed in vitro cloning and randomly selected 83 clones. Cloning was successful in 22 cases (40.7%). STBSs cultures with a high clonogenic potential (CP) were characterized by greater proliferative activity and increased Aldehyde dehydrogenase (ALDH) expression. We studied the transcription activity of the following cancer-testis genes (CTG): MAGE, NY-ESO-1, PRAME, GAGE, SSX1, HAGE1, PASD1, SCP1, SEMG1, SLLP1 and SPANXA1. The SEMG1 expression wasn't registered in any studied case. CTG activity wasn't observed in 10 cases out of 52 (19,2%) STBS cultures. We observed CTG activation and increased transcription activity in 82 STBSs clones. Clustering by the gene profile has revealed three different patterns: 1 st - with low expression CTG, 2nd - with co-expression GAGE1, PASD1 and PRAME, 3d - with co-expression SLLP1 and GAGE1. The last two clusters included most cloned cell lines and their clones. CP of STBSs cell lines was associated with the parameters of patients overall survival (OS) at comparable progression-free survival (PFS). Among patients with STBSs with the high CP, median OS was 7.6 months (min 0.7 - max 11.0 months). In the group with the low CP, OS did not reach the median value by the end of the five-year observation period. PFS was 5.6 months (min 0.2 - max 19.2 months) in the first group and 3.2 months (min 0.3- max 71.3 months) in the second group. Resistance to therapeutic doses of chemotherapy drugs was correlated with CP cultures STBSs. We suggest that chemotherapy-resistant clones are pre-existing in the tumor rather than being formed under the influence of chemotherapy. Highly aggressive metastatic sarcomas may be a promising candidate for immunotherapy against cancer-testis antigens (CTAs).

Keywords: cancer stem cells markers; cancer-testis genes; chemoresistance and proliferative activity of tumor cells; clonogenic; intratumor heterogeneity; metastatic soft tissue and bone sarcoma; potential; tumor biology; tumor cell culture.