Provided herein are therapeutic nanoparticles having a diameter of between 10 nm to 30 nm, and containing a polymer coating, and a nucleic acid containing a sequence complementary to a sequence within a micro-RNA identified as having a role in cancer cell metastasis or anti-apoptotic activity in a cancer cell (e.g., miR-10b) or a sequence within an mRNA encoding a pro-apoptotic protein that is covalently linked to the nanoparticle. Also provided are pharmaceutical compositions containing these therapeutic nanoparticles. Also provided herein are methods of decreasing cancer cell invasion or metastasis in a subject having a cancer and methods of treating a metastatic cancer in a lymph node in a subject that require the administration of these therapeutic nanoparticles to a subject.