Background: Evidence suggests that activation of the PI3K/AKT/mTOR pathway by paclitaxel may play a role in the development of taxane resistance. Conversely, PI3K inhibitors have been shown to sensitize tumors to the effects of paclitaxel. Therefore, the link between taxane resistance and activation of the PI3K/AKT/mTOR signaling pathway suggests inhibition of this pathway in combination with antimitotic drugs like paclitaxel may improve treatment outcomes in many malignancies. To further investigate this hypothesis we combined the TORC 1/2 inhibitor sapanisertib (TAK-228), the PI3Kα isoform inhibitor serabelisib (TAK-117), and paclitaxel in a phase I trial of heavily pretreated patients to determine the safety, efficacy, and RP2D. Methods: This is an open label, cohort study of sapanisertib (TAK-228) and serabelisib (TAK-117) given on days 2-4, 9-11, 16-18, and 23-25 with paclitaxel on days 1, 8, and 15 of a 28-day cycle. A traditional 3+3 dose escalation design with a maximum of 5 dosing cohorts was used. All 5 cohorts plus an expansion cohort are presented. Results: Enrollment has been completed and the overall results are summarized. Nineteen patients were enrolled; the majority were heavily pretreated with the average number of prior regimens exceeding 4. Based upon ITT, the ORR is 37%. The ORR is 47% in patients that completed at least 3 cycles. The clinical benefit rate is 73% and the PFS currently stands at approximately 11 months. Two patients with endometrioid endometrial adenocarcinoma achieved a complete response. All patients received comprehensive genomic profiling and 7 patients received prior mTOR inhibitor. Overall, the combination was well tolerated, except by patients in cohort 5. One DLT occurred in the last patient enrolled. The most common non-laboratory AEs were nausea (6%), fatigue (5%), and mucositis (5%). There were 45 (9%) grade 3 or 4 events, and the most common were decreased WBC and non-febrile neutropenia. Hyperglycemia was common in patients with a history of diabetes mellitus. Conclusions: Overall, the combination of sapanisertib, serabelisib, and paclitaxel was safe and efficacious throughout the first 4 cohorts. There were few serious adverse events, and most side effects were managed with routine supportive care interventions. Preliminary clinical results appear very promising, especially for patients with PI3K/AKT/mTOR pathway mutations. The positive effects of the combination were routinely seen in the lowest dosing cohorts and clinical benefit was even seen in patients that had previously failed everolimus or temsirolimus. All patients were either resistant or refractory to paclitaxel at time of enrollment, so further exploration of this combination to elucidate the mechanism of benefit is warranted. Clinical trial information: NCT03154294