Hyperthermic response of a mouse fibrosarcoma as modified by phenothiazine drugs

Prochlorperazine enhances radiosensitivity of non-small cell lung carcinoma by stabilizing GDP-bound mutant KRAS conformation

Lung cancer is considered as leading cancer with the highest mortality. The KRAS-oncogenic mutations are dominant in lung carcinoma leading to poor prognosis and radioresistance, which is a major impediment to radiotherapy. Thus, KRAS mutant inhibitors that synergistically sensitize tumours to radiation are urgently needed. In pursuance of the search for a novel radiosensitizer, high-throughput screening of FDA-approved drugs was performed at active site of K-Ras. Prochlorperazine (PCZ), an antipsychotic drug, showed good binding affinity with KRAS-mutant proteins. PCZ binds to the GTP-binding pocket of KRAS-mutant protein and inhibits its constitutive activation by stabilizing the GDP-bound conformation of K-Ras mutants by 9 kcal/mol compared to WT. PCZ alongwith radiation decreased the clonogenic survival of KRAS-mutant NSCLC but not KRAS-WT cells. The combination treatment activates p-ATM, p53, and p21 proteins, leading to cell cycle arrest. PCZ with increasing radiation caused a linear increase in γH2AX foci, suggesting enhanced DSBs-associated apoptosis in radioresistant A549 cells. Pharmacokinetics study showed C_max = 526 ng/ml at 30min, 4.6h half-life in plasma, and highest accumulation in tumours. PCZ and 10Gy irradiation synergistically radiosensitize mice xenografts via downregulation of Ras/Raf/MEK/ERK pathway. Our efforts have led to the discovery of PCZ as a lead compound. In preclinical analyses, treatment with PCZ alone and in combination with radiation led to regression of KRAS^-G12S tumours.

Exploitation of hypoxia for radiation therapy: a lesson from phenothiazines

In experimental radiation therapy of tumours, phenothiazines are known to sensitize hypoxic cancer cells while offering protection to the normal surrounding tissue. It is hypothesized that the differential radiosensitization of tumour cells and radioprotection of normal cells by phenothiazines is related to the presence of Fe2+ and Fe3+ ion concentration respectively. As a result of changed biochemical environment such as pH, hypoxia and accumulation of ferritin, the Fe2+ ion concentration in tumours, especially in the hypoxic cells, is expected to be higher (and to be further enhanced by irradiation) than in the well-oxygenated normal cells. In normal cells, iron would predominantly be in the Fe3+ form, which might increase the protective effect of phenothiazines. A many-fold increase in radiation effect has been shown by us in vivo as well as in vitro systems in the combined presence of phenothiazines and Fe2+ ions. Our findings suggest that the hypoxic condition can be exploited for radiation therapy by employing suitable metal-based chemomodulation.

Studies on indomethacin as a potentiator for hyperthermic and radiation responses in a mouse fibrosarcoma

Indomethacin, a non-steroidal anti-inflammatory drug which is also a calcium antagonist and an inhibitor of prostaglandin synthesis was observed to have a chemotherapeutic effect in a mouse fibrosarcoma. More significantly, administration of the drug before exposure to either radiation or hyperthermia, enhanced their effects. Apart from tumor growth delay, tumor cures were also observed in all the three modalities tested. The data suggests a potential anti-cancer role for indomethacin in combination modalities.