The multidrug efflux transporter ABCB1 is clinically important for drug absorption and distribution and can be a determinant of chemotherapy failure. Recent structure data shows that three glutamines donate hydrogen bonds to co-ordinate taxol in the drug binding pocket. This is consistent with earlier drug structure-activity relationships that implicated the importance of hydrogen bonds in drug recognition by ABCB1. By replacing the glutamines with alanines we have tested whether any or all of Q347, Q725 and Q990 are important for the transport of three different drug classes. Flow cytometric transport assays show that Q347A and Q990A act synergistically to reduce transport of Calcein-AM, BODIPY-verapamil and OREGON GREEN-taxol bisacetate but the magnitude of the effect was dependent on the test drug and no combination of mutations completely abrogated function. Surprisingly, Q725A mutants generally improved transport of Calcein-AM and BODIPY-verapamil, suggesting that engagement of the wild-type Q725 in a hydrogen bond is inhibitory for the transport mechanism. To test transport of unmodified taxol, stable expression of Q347/725A and the triple mutant was engineered and shown to confer equivalent resistance to the drug as the wild-type transporter, further indicating that none of these potential hydrogen bonds between transporter and transport substrate are critical for function of ABCB1. The implications of the data for plasticity of the drug binding pocket are discussed.

(1) Background: Retroareolar breast tumors are common, but they rarely progress to malignancy. This report presents a case of a 41-years-old woman with a superficial breast tumor, emphasizing the significance of considering a wide range of options when evaluating breast lumps. (2) Methods: The patient presented with a steadily growing, ulcerating superficial tumor in her left breast. To determine the nature of the tumor, a diagnostic assessment was conducted, which included a positron emission tomography (PET) scan and histological analysis. (3) Results: The diagnostic assessment confirmed the presence of a malignant Grade II superficial infiltrating ductal carcinoma. Following the diagnosis, the patient underwent a modified radical mastectomy under general anesthesia. Subsequently, she received four cycles of adjuvant chemotherapy, followed by taxol administrations. (5) Conclusions: This case report underscores the importance of conducting a thorough examination and maintaining a high index of suspicion for breast tumors. By documenting this case, the report contributes to the existing knowledge on various manifestations of breast cancer and highlights the necessity of early identification and aggressive treatment. This knowledge can be applied to identify and manage similar cases in the future, leading to improved patient outcomes.