A 3D biomimetic model of tissue stiffness interface for cancer drug testing.

Contrary to oversimplified preclinical drug screens that derive treatment responses of cancer cells grown on plastic cell culturing surfaces, the actual in vivo scenario for cancer cell invasion is confronted with a diversity of tissue stiffness. After all, the packing of organs and tissues in the body translates to the abundant presence of tissue stiffness interfaces. The invasive dissemination of cancer cells in vivo might be encouraged by favorable tissue stiffness gradients, likely explaining the preferential spread of cancer cells which is subjective to the cancer type and origin of the primary site. Yet these critical tumor microenvironmental influences cannot be recapitulated in 2D preclinical drug screens, hence omitting potentially invaluable in vivo patterns of drug responses that may support safer clinical dosage implementation of cancer drugs. Current attempts to study stiffness implications on cancer cells are largely confined to 2D surfaces of tunable stiffness. While these studies collectively show that cancer cells migrate better on a stiffer matrix, the generation of a biomimetic 3D tissue stiffness interface for cancer cell migration would clearly give a more definitive understanding on the probable push and pull influences of the 3D ECM. Herein, we developed a biomimetic platform which enables the precise placement of spheroids at tissue stiffness interfaces constructed with natural ECM collagen type I. This enables a standardized comparison of spheroid invasion under a 3D stiffness gradient influence. We found that cancer cells in 3D infiltrated more extensively into a softer matrix of 300 Pa while showing significantly reduced invasion into stiffer matrix of 1200 and 6000 Pa. These biomimetic spheroid cultures postinvasion were suitably subjected to paclitaxel treatment and subsequent daily live quantification of apoptotic cells to evaluate the implications of tissue stiffness on chemotherapeutic treatment. We importantly found that cancer cells which more extensively infiltrated the 300 Pa matrix also succumbed to paclitaxel induced apoptosis earlier than cells in stiffer matrices of 1200 and 6000 Pa respectively. This suggests that reduced invasion of cancer cells attributed to increased tissue stiffness barriers may favor their reduced apoptotic susceptibility to chemotherapeutic treatment.