Nasopharyngeal carcinoma (NPC) manifests beneath the nasopharyngeal mucosa or within the pharyngeal recess, known as the Fossa of Rosenmüller [1, 2]. NPC is responsible for more than 100,000 new cases and 72,987 deaths in 2018 . Deeper understanding of the molecular mechanisms of NPC has led to testing of targeted therapies, immunotherapies and combination of these therapies with chemotherapeutic drugs.
Sensitivity of cancer cells to potential therapeutic agents are first evaluated in monolayer culture. Monolayer culture is economical, high-throughput and provides first-hand information on sensitivity of cells to drugs tested . However, the model does not mimic the behaviour and microenvironment of tumour cells in vivo [4, 5]. The spheroid model recapitulates the properties of tumors in vivo such as cellular heterogeneity, microenvironment, cell-cell interactions, cell-extracellular matrix (ECM) interactions, growth kinetics, gene expression and drug resistance mechanisms [4, 6, 7]. Thus, the spheroid model provides a more physiological platform for drug screening [7, 8, 9].
Thus far, we have conducted spheroid assays in 24-well plates as described by Abdul Rahman et al . This method described in Abdul Rahman et al, was a modification of the method described in Smalley et al . In order for spheroids to proliferate and invade, the 24-well plates are coated with collagen matrix. The main ingredient of the collagen matrix is bovine collagen I. The collagen type I is the major extra-cellular protein found in human organs. Given that the collagen type I is available in abundance in the bovine collagen I, it is preferred in our experiments . However, spheroid assays conducted in 24-well plates require high volume of collagen matrix. Hence, high volume of bovine collagen I is needed which is costly. Moreover, the set-up of experiments is laborious and time-consuming. We employed the 3D cell culture chip (hereafter will be referred to as ‘3D chip’) to conduct spheroid drug sensitivity assays in order to minimize the cost and time involved in using 24-well plates. The 3D chip requires 10 times less bovine collagen I to prepare the collagen matrix and the experiment set-up takes less than an hour.
In this pilot study, prior to conducting drug sensitivity assays, growth and invasion of HK-1 spheroids (spheroids generated from NPC cell line HK-1) embedded in the 3D chip and the 24-well plate were first compared. In order to ensure that the findings of drug sensitivity assays conducted in the 24-well plate is comparable to the findings in the 3D chip, HK-1 spheroids were treated with combination of cisplatin and paynantheine (a mitragyna alkaloid compound which was isolated and purified from kratom leaves - a local medicinal plant found in Malaysia)  in the 3D chip and the 24-well plate, simultaneously. Snapshots of HK-1 spheroids were taken every 24 hours to monitor the effect of the drug combination on spheroid growth and invasion.