Induction of solid tumor differentiation by the peroxisome proliferator-activated receptor-gamma ligand troglitazone in patients with liposarcoma

Abstract

Agonist ligands for the nuclear receptor peroxisome proliferator-activated receptor-gamma have been shown to induce terminal differentiation of normal preadipocytes and human liposarcoma cells in vitro. Because the differentiation status of liposarcoma is predictive of clinical outcomes, modulation of the differentiation status of a tumor may favorably impact clinical behavior. We have conducted a clinical trial for treatment of patients with advanced liposarcoma by using the peroxisome proliferator-activated receptor-gamma ligand troglitazone, in which extensive correlative laboratory studies of tumor differentiation were performed. We report here the results of three patients with intermediate to high-grade liposarcomas in whom troglitazone administration induced histologic and biochemical differentiation in vivo. Biopsies of tumors from each of these patients while on troglitazone demonstrated histologic evidence of extensive lipid accumulation by tumor cells and substantial increases in NMR-detectable tumor triglycerides compared with pretreatment biopsies. In addition, expression of several mRNA transcripts characteristic of differentiation in the adipocyte lineage was induced. There was also a marked reduction in immunohistochemical expression of Ki-67, a marker of cell proliferation. Together, these data indicate that terminal adipocytic differentiation was induced in these malignant tumors by troglitazone. These results indicate that lineage-appropriate differentiation can be induced pharmacologically in a human solid tumor.

Figure 1

Histologic changes in liposarcoma tumor tissue with accumulation of intracellular lipid in three separate patients (I, II, III). Shown are hematoxylin and eosin-stained biopsies of liposarcoma tissue obtained (A) immediately before study entry and (B) after 6 weeks of daily dosing with troglitazone. Magnification: ×400.

Figure 2

Nuclear expression of PPARγ protein in liposarcoma tissue. Immunohistochemical staining of a biopsy sample of liposarcoma tissue from patient 2 obtained immediately before study entry. Comparative hematoxylin and eosin staining of tissue is noted in Fig. 1IIA. Magnification: ×400.

Figure 3

Decreases in Ki-67 proliferation-associated antigen expression after 6 weeks of troglitazone treatment. The percentage of cells with strong nuclear staining for Ki-67 was quantified by immunohistochemical staining with the MIB-1 mAb, as described in Patients and Methods.

Figure 4

Troglitazone-associated increases in expression of genes linked to adipocytic terminal differentiation. mRNA was prepared from serial biopsies of liposarcoma tissue from patients 1 and 2 (A and B, respectively) and subjected to Northern analysis as described in Patients and Methods. The levels of mRNA for aP2, adipsin, and PPARγ were quantified and normalized against levels of mRNA for β–actin. Levels of gene expression then were scaled against normal fat, which was set as 100% expression for these adipocytic-lineage genes.

Figure 5

Representative quantitative one-dimensional MAS ¹H-NMR spectra acquired from the tumor tissue of patient 1 (A) before therapy and (B) after 6 weeks of troglitazone therapy, showing increases in triglycerides standardized to the TSP peak at the right. (Insets) Where the vertical scale of the same spectra in the 3.2–3.3 ppm region was increased to allow visualization of nontriglyceride metabolites.

Figure 6

Serial MRI images of pelvic liposarcoma in patient 3 (A) before and (B) after 6 weeks of troglitazone administration. Note the subtle change in the fat density signal (whitish stranding) within the tumor (low T1/high T2 signal characteristics) after troglitazone exposure.