Since the problem of transporter-mediated multidrug resistance of tumor cells is becoming increasingly important in cancer therapy, it is necessary to modulate the activity of efflux transporters of the ABC family, among which P-glycoprotein is the best known. We consider the nucleotide binding domain, a universal fragment of these transporters, as a target for the rational design of small molecule compounds capable of preventing ATP-dependent drug efflux. Using various ATP mimetics, we showed that they suppress the efflux of fluorescent substrates and paclitaxel from the cells due to suppressing the ATPase activity of the transporters. The combined use of paclitaxel and ATP mimetics significantly increases its antitumor efficacy, including in cells with the multidrug resistance phenotype. The considered compounds are promising agents for the development of therapeutic efflux modulators, since they are not toxic at the given concentrations and do not induce the transporter overexpression. Moreover, the compounds overcome not only P-gp-mediated but also BCRP-mediated resistance of tumor cells.