2469 - Inhibition of mTOR signaling enhances Trabectedin activity in Soft Tissue Sarcoma

Background

Soft-tissue sarcomas (STS) are life-threatening diseases, for which more efficient therapeutic options are necessary. Trabectedin (T) is an anti-tumor drug approved for the treatment of advanced STS. Synergistic drug combinations could improve T results in STS patients. Rapamycin (R) is an mTOR pathway inhibitor. Synergy with T has been described in ovary clear cell carcinoma. Of note, R suppresses DNA double-strand breaks repair, thus generating the perfect set-up for T activity. Altogether, we hypothesize that T+R combination (T+R) is synergistic in STS, and that mTOR inhibition enhances T activity.

Methods

Human STS cell lines (n = 9) were treated with increasing doses of T (1x10^-7M to 1x10^-11M) and/ or R (1x10^-9 to 1x10^-11) to determine IC50 and combination index (CI) values. Cells were initially exposed to R, 2 hours later T was added, under the assumption that R pre-treatment favors T cytotoxicity. Cell viability, at 72 h, was measured by MTS assay. Apoptosis was determined by Western Blot for PARP and Caspase 3 cleavage. In vivo experiments were performed in immunocompetent 3-methylcolanthrene fibrosarcoma mice: T was administrated via IV (0.15 mg/kg; q7dx1) and R via IP (0.50 mg/kg; q7dx2). Body weight and tumor volume were measured every 2 days for 15 days of treatment. Tumors were collected for analysis (snap frozen and paraffin embedding).

Results

T+R was synergistic in all STS cell lines: CP0024 primary leiomyosarcoma and 93T449 liposarcoma cell lines showed strong synergism with CI at the ED50 of 0.129 and 0.027, respectively. This synergy was followed by an increase of PARP and Caspase 3 cleavage. The synergism was confirmed in vivo: mice treated with R+T showed tumor growth delay in comparison to the drugs alone (p < 0.05). Stable disease was achieved in 7 out of 7 mice.

Conclusions

R+T is synergic in STS and deserves exploration in clinical setting. Further research will reveal the mechanisms underlying this synergy.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

Javier Martín Broto.

Funding

PharmaMar.

Disclosure

D.S. Moura: Research grant / Funding (institution): PharmaMar; Research grant / Funding (institution): Eisai; Research grant / Funding (institution): Novartis; Travel / Accommodation / Expenses: PharmaMar; Travel / Accommodation / Expenses: Eisai. M. Lopez-Alvarez: Travel / Accommodation / Expenses: Eisai. N. Hindi: Travel / Accommodation / Expenses: PharmaMar; Research grant / Funding (institution): Eisai; Research grant / Funding (institution): Novartis; Research grant / Funding (institution): PharmaMar; Honoraria (self): PharmaMar. J. Martin-Broto: Research grant / Funding (institution): PharmaMar; Research grant / Funding (institution): Eisai; Research grant / Funding (institution): Novartis; Honoraria (self): PharmaMar; Honoraria (self): Lilly; Honoraria (self): Novartis; Speaker Bureau / Expert testimony: PharmaMar. All other authors have declared no conflicts of interest.