Background Osteosarcoma is the most common primary bone tumor and has a peak incidence in adolescence. The prognosis for recurrent and metastatic disease is poor and over one-third of patients with localized disease at presentation will recur after treatment with metastases. LOFU produces non-lethal, transient mechanical and thermal stress to cause protein misfolding, endoplasmic reticulum stress, and induction of the heat shock response (refs). Trabectedin is directly tumoricidal through inhibiting transcription and DNA repair, modulates the tumor microenvironment by selectively depleting M2 macrophages, and inhibits the transcription factor heat shock factor 1 (HSF1) (refs). We hypothesized that combination therapy would synergistically intensify the unfolded protein response and heat shock response to facilitate antigen presenting cell activation and efficient presentation to cytotoxic T cells. To examine this, experiments are being conducted to investigate the effect of LOFU in combination with trabectedin and/or radiation therapy (RT) in a murine model of osteosarcoma.

Methods Palpable (<5 mm) subcutaneous K7M2 murine osteosarcoma tumors in BALB/c mice were treated with a) LOFU, b) trabectedin (intravenous (IV) or intratumoral (IT)), c) LOFU + trabectedin, and d) radiation. Tumor growth (ANOVA (Kruskal-Wallis) with Dunn’s test for multiple comparisons), pulmonary metastases (Fisher’s exact test) and survival (Kaplan-Meier) were measured and analyzed in GraphPad Prism.

Results Mean tumor volume in the combination therapy group (428 mm³) was less than nontreated controls (887 mm³), LOFU alone (670 mm³), trabectedin alone (1218 mm³, p=0.0386). Radiation therapy resulted in complete ablation of the tumors. None of the combination therapy mice had grossly detectable lung metastases at time of death but metastases were present in the trabectedin only (20%), LOFU only (50%), and control (50%) groups (not statistically significant).

Conclusions Combination therapy with trabectedin and LOFU yielded smaller tumor size and fewer pulmonary metastases compared to individual therapies alone.