KB-V1

Identification of Compounds that can Overcome MDR through High-Throughput Screening

Multidrug resistance (MDR) in cancer cells, driven by overexpression of ABC transporters such as P-glycoprotein (Pgp), limits the efficacy of chemotherapy. In order to identify compounds with the ability to overcome Pgp-mediated MDR, Zahra et al. screened 1,127 inhibitors (Selleckchem library) in KB-3-1 cells and their Pgp-overexpressing multidrug-resistant derivative KB-V1 cells (Fig. 1A). The majority of compounds were more potent in KB-3-1 cells compared to KB-V1 cells. They retested 118 of the top hit compounds from the primary screen in two pairs of parental and resistant cell lines (KB-3-1/KB-V1 and A2780/A2780-Pac-Res) at 1 μM in a 3-day SRB proliferation assay (Fig. 1A, 1B). Fifteen compounds (out of 118) retained similar potency in sensitive and resistant cells at 1 μM (Fig. 2A, 2B), and are thus able to overcome Pgp-mediated MDR. Paclitaxel was used as a resistance control in Pgp-overexpressing cell lines (Fig. 2C).

Fig. 1. Screening for compounds with the ability to overcome Pgp-mediated MDR (Zahra R, Furqan M, et al. 2020).

Fig. 2. Secondary screening with 118 compounds in both pairs of parental and resistant cell lines (Zahra R, Furqan M, et al. 2020).

Highly Cytotoxic Cryptophycin Derivatives with Modification in Unit D for Conjugation

Cryptophycins are highly potent cyclodepsipeptides, making them ideal candidates for drug conjugates for tumor therapy. Functionalization for conjugation of this class of compounds often comes at the cost of a toxicity penalty. Using a modular and scalable synthetic methodology, Dessin et al. have modified unit D of cryptophycins to diversify this class, and introduce a number of new analogues with functional groups amenable to conjugation.

All synthesized cryptophycins were assayed for cytotoxicity in KB-3-1, a human cervix carcinoma cell line, and the most active were further tested in the MDR subclone KB-V144 (Fig. 3A). The Dap-derived cryptophycins 33a (Dap), 33b (Dap(Me)) and 34a (Dap(Me2)) had the highest activity and picomolar cytotoxicity with the 34a having the lowest IC₅₀ of 2.91 pM. The Dab-derived analogues 33c (Dab), 33d (Dab(Me)) and 34c (Dab(Me2)) were significantly less active but maintained the same trend: increased cytotoxicity with methylation of the amine and 34c having the highest toxicity (38.3 pM). The diethylated amine 34b and the allylmethylamine 33k had picomolar activity. Most of the amines had resistance factors (FR) in the range 103–104 against KB-V1 cells, but 33k had a low FR of 40.4 and triple-digit picomolar activity against KB-V1 cells.

Fig. 3. Cytotoxic profile of synthesized cryptophycins (Dessin C, Schachtsiek T, et al., 2024).